The session presents applications of paleontology and paleoecology to evolutionary theory, environmental and paleoenvironmental reconstruction, biostratigraphy, paleoclimate, paleoceanography, sea-level change, and population dynamics, as well as modern experimental approaches and culture studies centered on the same fields. The diverse session program will stimulate discussions and the exchange of ideas which will lay the foundations for future paleontological research, particularly as a tool to understand the ongoing change of the global ecosystem.

Public information:
Three main themes: Episodes in the History of Life, Recent Impacts on Ecosystems, Macroevolution

Co-organized by CL2
Convener: Stefano Dominici | Co-conveners: Heather BirchECSECS, Flavia Fiorini, Sofie Lindström, Bas van de Schootbrugge, Silvia Danise, Michael Kaminski, Daniele Scarponi
| Attendance Wed, 06 May, 08:30–12:30 (CEST)

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Session materials Session summary Download all presentations (125MB)

Chat time: Wednesday, 6 May 2020, 08:30–10:15

D949 |
Melanie Tietje, William J. Baker, Rafaël Govaerts, Stephen A. Smith, Miao Sun, and Wolf L. Eiserhardt

Spatial patterns of plant diversity follow the well-known global latitudinal biodiversity gradient, however there is little consensus about the underlying causes for this pattern. Here we present a spatial analysis of a complete checklist of the world’s seed plants, integrated with a comprehensive plant Tree of Life. This combination allows insights into the evolutionary drivers of plant species richness patterns, specifically current plant biodiversity patterns, and the diversification processes that shaped them. Our study provides a comprehensive global species richness map and relates the observed species richness pattern to speciation rates derived from phylogeny, and with environmental variables, which are hypothesized to impact speciation rates. Initial results show that tropical rain forest regions, although being areas that contain among the highest numbers of species, are regions with comparatively low speciation rates, contradicting the widespread notion that rainforests are “cradles” of biodiversity. This finding seems further supported by contrasting association of environmental variables, like precipitation and temperature, with speciation rates and species richness.

How to cite: Tietje, M., Baker, W. J., Govaerts, R., Smith, S. A., Sun, M., and Eiserhardt, W. L.: Global patterns of plant diversity and their evolutionary drivers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9733, https://doi.org/10.5194/egusphere-egu2020-9733, 2020.

D950 |
CO2 driven changes in leaf biochemistry may have influenced fire behaviour at the Triassic-Jurassic boundary
Sarah Baker, Rebecca Dewhirst, Jennifer McElwain, Matthew Haworth, and Claire Belcher
D951 |
Major palaeoenvironmental upheavals in both marine and terrestrial realms during the Toarcian oceanic anoxic event: a multi-proxy approach
Francesca Galasso, Susanne Feist­Burkhardt, Annette Schmid- Röhl, Stefano Benasconi, and Elke Schneebeli-Hermann
D952 |
| Highlight
Monika Doubrawa, Peter Stassen, Marci M. Robinson, Tali L. Babila, James C. Zachos, and Robert P. Speijer

During the early Paleogene, a long-term warming trend of Earth’s climate was punctuated by a major global warming event, known as the Paleocene-Eocene Thermal Maximum (PETM) and marked by a carbon isotope excursion (CIE) and an acidification episode. The associated worldwide environmental perturbations are best studied in open marine settings, and resulted in a major extinction event in deep-sea benthic foraminifera, followed by migration and diversification. Yet, the evolutionary impact on shelf foraminiferal faunas is still poorly constrained due the inherent stratigraphic complexities in these environments. In order to understand the prelude and aftermath of peak warming during the PETM, we study the South Dover Bridge core (SDB), drilled in the US Atlantic Coastal Plain in Maryland. Here, the Paleocene-Eocene transition is stratigraphically well constrained by calcareous nannoplankton and stable isotope records. Additionally, the PETM is regionally characterized by the appearance of fine-grained sediments, known as the Marlboro Clay, contrasting with the late Paleocene glauconitic sands. Our newly generated high-resolution foraminiferal stable isotope, biotic and grain size data enable an assessment of the stratigraphic completeness of this site, and the disentanglement of the successive recovery-phases, by correlation across the paleoshelf.

The mid-shelf benthic foraminiferal assemblage we recorded in the upper Paleocene indicates well-oxygenated, continuously oligo- to mesotrophic bottom water conditions. These conditions were temporarily interrupted during a pre-PETM CIE, which initiated minor, but prominent, changes in foraminiferal assemblage. The relationship with the PETM is still unclear, but it may indicate that the latest Paleocene climate was not as stable as previously assumed and instead exhibited a more gradual change towards the PETM. At the onset of the PETM diversity decreases, as more stress-resistant benthic taxa become predominant and planktic abundances increase. This probably points to periodically dysoxic bottom waters due to river-induced stratification, resulting from enhanced regional river outflow, as well as to a shift to episodic food fluxes to the sea floor.

The studied expanded SDB sequence also presents an excellent and nearly complete record of the PETM isotope recovery phase. Throughout this recovery phase a third, more diverse foraminiferal assemblage starts to prevail, indicating a gradual return to sustained high food levels and increasing oxygen levels, related to a decrease of river influence. Species, dominant during the core phase of the PETM, like Anomalinoides acutus or Pseudouvigerina wilcoxensis, show strongly declining numbers in the recovery phase. Other taxa, like Cibicidoides alleni, returned to the shelf ecosystem, after disappearing nearly completely from the sediments during the initial PETM CIE interval. This coincides with reduced planktic foraminiferal abundances and a tendency towards more silty and less clayey sediments, linked to renewed bottom current activities and winnowing.

The lack of severe benthic extinction among shelf-dwelling benthic foraminifera and the observed lateral variability in environmental conditions, demonstrate how foraminiferal shelf communities can adapt to massive global carbon perturbations. As more regional data will become available, these will enable more constraints on environmental parameters and variations along the Atlantic Coastal Plain prior and during the PETM.

How to cite: Doubrawa, M., Stassen, P., Robinson, M. M., Babila, T. L., Zachos, J. C., and Speijer, R. P.: Perturbation and recovery of shelf ecosystems during the PETM, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15431, https://doi.org/10.5194/egusphere-egu2020-15431, 2020.

D953 |
Laura Cotton, David Evans, and Daniela Schmidt

The Eocene-Oligocene transition (EOT) is one of the most dramatic climate shifts of the Cenozoic with severe consequences for reef ecosystems. The onset of continental Antarctic glaciation is associated with widespread environmental change, resulting in a global peak in biotic turnover. Whilst numerous studies of the biotic response to the changes at the EOT have been carried out, most high-resolution studies consist of open ocean records of marine plankton and predominantly single groups of organisms. However, this is not representative of the ocean system as a whole and does not provide a holistic view of mechanism of restructuring of the marine ecosystems. The shelf seas and reefs are some of the most diverse and fundamentally important ecosystems of the oceans. Long-term diversity loss across the EOT has been shown in several macrofossil studies, but mainly at low resolution, and recovery is not well understood.  Many shelf species are ecosystem engineers whose loss and recovery have profound implications for the entire ecosystem. Understanding these interactions will provide insights into shallow marine ecosystems and their response to major climate perturbations.

The Tanzanian Drilling Project EOT record (TDP 11, 12, 17) is recognised globally for its completeness and exceptionally preserved calcareous microfossils. It is most importantly, though, a rare record of both shallow water organisms and open ocean plankton. The latter are fundamentally important for reconstructions of the environment and a globally calibrated timescale. Here we draw together a unique dataset of high-resolution mollusc, Dasycladaceae, bryozoan, larger benthic foraminifers, coral, smaller benthic foraminifera, trace element and isotope records from the EOT. The response and recovery of these species is compared with known, modern physiology of each group to provide a complete picture of the shallow marine ecosystem response.

Following rapid extinctions within the larger foraminifera during the transition, molluscs, Dasycladaceae and bryozoans all show increases in abundance, indicating a major shift in shelf ecosystem composition. These assemblage changes are coincident with a period of more positive values in d13C of both benthic and planktonic foraminifera and changes in trace element values. Comparison with the open ocean record of planktonic foraminiferal, pteropod, and nannofossils confirm these assemblage changes are a biological, rather than sedimentological response and additionally support a that a transition to more eutrophic conditions took place. an environmental framework of traditional and novel geochemistry, indicate that increased nutrient fluxes played a pivotal role in restructuring shelf ecosystem dynamics and therefore offers new insight into mechanisms of reorganisation under ecosystem loss and environmental change.

How to cite: Cotton, L., Evans, D., and Schmidt, D.: Shelf ecosystem response to the Eocene-Oligocene Transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1053, https://doi.org/10.5194/egusphere-egu2020-1053, 2020.

D954 |
| Highlight
Anna Losiak, Claire Belcher, and Elmar Buchner

Impact craters are formed when an asteroid strikes the surface with the hyper-velocity (usually higher than ~1km/s). The kinetic energy of the impactor is released as an explosion, a crater is formed, and target material is deposited outside, forming a proximal and later distal ejecta blanket. This consists of rocks, the surface soil layer and numerous plants remains (Cassidy et al. 1965, Khryanina 1981, Herd et al. 2008), including remains of trees directly killed by the asteroid (Losiak et al. 2016, Losiak et. Al. 2020). We have found a number of charcoals that we suggest are related to the formation of the following confirmed impact craters: Kaali Main, Kaali 2/8 (Estonia, Losiak et al. 2016), Morasko (Poland, Szokaluk et al. 2019), Whitecourt (Canada, Herd et al. 2008) and Ries crater (Buchner and Schmieder 2009). Three of these locations represent small (30-100 m in diameter) impact craters developed primarily in unconsolidated materials such as glacial tills and fluvioglacial sands. Whereas, Ries is a much larger and older crater: it is 24 km in diameter and 14.5 Ma old.

Here we present the results from a set of experiments that reproduce the process of formation of charcoals within the proximal ejecta blankets of small impacts. Firstly, charring experiments were achieved using the iCone Calorimeter that recreated a range of heating possibilities that might results from small impact cratering processes. The iCone allows samples to be heated, with or without ignition at a range of radiant heat fluxes for given durations; these heat fluxes can be static or transient, both of which may be relevant to different impact formation mechanisms. Secondly, we buried leaves and fragments of different woods in heated sand over a range of temperatures durations and cooling regimes to assess the potential for relatively cool ejecta to cause transformations of organic material to char in situ. All the chars created in the experiments were analysed via reflectance microscopy and compared with the charcoal that have been produced by modern wildfires. Our aim being to better understand the environmental effects of differently sized impact craters, but also to study the mode of preservation of plants killed during such extraterrestrial impact events.

Buchner & Schmieder 2009. MAPS44:1051–1060.

Cassidy et al. 1965. Science149:1055-1064.

Herd et al. 2008. Geology36:955–958.

Hudspith et al. 2010. PPP291:40–51.

Khryanina 1981Int. Geology Rev.23:1-10.

Losiak et al. 2016. MAPS51:681–695.

Losiak et al. 2020. MAPSaccepted.

Scott 2010 PPP291:11–39.

Sztokaluk et al. MAPS54:1478-1494. 

How to cite: Losiak, A., Belcher, C., and Buchner, E.: Fossil plant remains preserved as charcoal within proximal ejecta blankets of impact craters reveal the influence of asteroid collisions with the Earth’s surface , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11609, https://doi.org/10.5194/egusphere-egu2020-11609, 2020.

D955 |
Chelsea Korpanty, Leon Hoffman, Jürgen Titschack, Claudia Wienberg, and Dierk Hebbeln

Cold-water corals (CWC) act as ecosystem engineers and thus contribute to biodiversity on continental margins worldwide. CWC mounds – built over geologic time by the interplay of biological, sedimentological, and oceanographic processes – create ecological niches for a variety of macrobenthic marine taxa (e.g. molluscs, sponges, bryozoans). The growth of CWC mounds is discontinuous over time due to changes in environmental and ecological conditions, such as food supply, water temperature, and dissolved oxygen concentration. While surficial distribution patterns of living and recently-dead mound macrobenthic communities have been described, their temporal ecological relationship with coral growth and mound formation is yet largely unexplored. Therefore, this project aims to determine what effects stagnations in CWC growth (i.e. repeated periods of ecosystem “turn off”) have on the local biodiversity and community structure of other CWC mound taxa, and thus what influences CWC mound development may have on regional biodiversity and biogeography in the deep sea over geologic time. Focusing on a single taxonomic group with high preservation potential, this study 1) quantitatively assesses temporal ecological trends of coral mound molluscan assemblages (bivalves and gastropods), and 2) statistically correlates those data with coral growth and palaeoceanographic records. Preliminary results from two CWC mound gravity cores through Brittlestar Ridge I in the Alboran Sea, western Mediterranean (~13.2 – 2.9 ka) indicate that throughout both cores the molluscan assemblages are typically quantitatively dominated by sessile benthic filter-feeding bivalves, particularly Heteranomia squamula and Hiatella arctica. Although bivalves are more abundant and diverse than gastropods in both cores, these taxonomic groups yield generally similar downcore dynamics in abundance and diversity. Comparisons of total molluscan assemblages (bivalves and gastropods combined) suggest that the older assemblages – those associated with the Bølling-Allerød interstadial (13.5-12.8 ka) and Early Holocene (11.3-9.8 ka) – are more similar to one another than to younger assemblages in the cores. Rotational vector fitting analyses indicate that these older assemblages are significantly related to higher productivity and different hydrodynamics (and sediment input), which are factors that have also been linked to CWC growth in the region. Altogether, our paleoecological reconstructions so far reaffirms the connectivity of benthic communities with local oceanographic conditions and adjacent taxa. Additional ecological assessments will further refine our understanding of the relationships between CWC growth and benthic communities, and in turn the temporal drivers and dynamics of CWC mound biodiversity.

How to cite: Korpanty, C., Hoffman, L., Titschack, J., Wienberg, C., and Hebbeln, D.: Quaternary molluscan assemblages of cold-water coral mounds: a new perspective on deep-sea ecosystem dynamics in the western Mediterranean , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8566, https://doi.org/10.5194/egusphere-egu2020-8566, 2020.

D956 |
Anne Strack, Lukas Jonkers, Marina C. Rillo, Helmut Hillebrand, and Michal Kucera

Understanding the response of marine ecosystems to climate change requires knowledge of processes that operate over long time scales. Over the last decades, abundant data have been generated on the change in the composition of marine microplankton assemblages across the last deglaciation. These data were used to reconstruct various aspects of the ocean and climate system during this climatic upheaval; however, their potential to evaluate biotic response to climatic forcing has been rarely explored. Here, we compiled records of plankton response to the last deglaciation covering the entire North Atlantic Ocean. The records comprise assemblage composition data of marine zooplankton (planktonic foraminifera) and phytoplankton (coccolithophores, diatoms and dinoflagellates) covering the last 24 ka with a resolution of at least 1 ka. The comparability of the data is ensured by using either published age models or a combination of radiocarbon ages and correlated oxygen isotope data. We use these records to first determine the shape of the major compositional change in each record by principle components analyses and quantification of compositional turnover. The mean global response of the plankton to the deglaciation was then evaluated by an Empirical Orthogonal Function analysis of the main biotic trends across all sites. A preliminary analysis was run solely on the zooplankton data set as the phytoplankton data set is still work in progress. We find that the dominant response of the zooplankton consists of synchronous unidirectional shifts initiated between 16-17 ka BP, and progressing into the Holocene. When regressed on the global ocean temperature and CO2 trends, we can see a proportionate response to the forcing during the last glacial maximum, the deglaciation and the early Holocene. In contrast, the late Holocene is characterised by continued compositional change, which does not appear related to environmental forcing. We speculate that this decoupling indicates the existence of a multi-millennial delay in community change following the climatic forcing, likely due to biotic interactions acting on communities that have been newly assembled or geographically displaced due to abiotic forcing. We will present a similar analysis for marine phytoplankton and discuss the consequences of the observations for the understanding of community variability on millennial time scales.

How to cite: Strack, A., Jonkers, L., Rillo, M. C., Hillebrand, H., and Kucera, M.: Multi-millennial legacy of climate change in marine plankton communities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20597, https://doi.org/10.5194/egusphere-egu2020-20597, 2020.

D957 |
Nisan Sariaslan, Olugbenga T. Fajemila, and Martin Langer

The Lagos Lagoon is among Africa’s largest estuarine ecosystems. It is bordered by one of the fastest growing megacities in the world (Lagos) and the ultimate repository of contaminants carried in industrial, municipal and agricultural wastes. The high levels of pollutants have progressively deteriorated the water quality, adversely affected marine ecosystems, impacted the livelihood of the coastal population and pose serious risks to human health. Benthic foraminifera are excellent proxies and sensitive bioindicators of environmental disturbances but comprehensive studies on the structure, distribution, diversity and impact of pollution upon foraminiferal communities have not yet been conducted. In order to demonstrate the potential of foraminifera as proxies of environmental perturbations, benthic foraminifera were investigated on a lagoon-wide basis.

Lagos Lagoon has areas that range from low levels of direct impact to severely affected by various forms of anthropogenic disturbance. The goal of this study was to elucidate foraminiferal community structure, to analyze patterns of distribution and species richness and to identify taxa that track documented records of pollution in Lagos Lagoon sediments. The sediments were analyzed for a range of physicochemical properties via a multi-parameter sensor probe-device including temperature, pH, depth and total dissolved solids (TDS) measurements. Quantitative analysis of 24 sediment samples yielded a total 3872 individuals of benthic foraminifera that belong to 42 species and 25 genera. They comprise 10 porcelaneous, 22 hyaline perforate and 10 agglutinated species. Ammobaculites aff. A. exiguus, Ammotium salsum, Ammonia tepida, Ammonia parkinsoniana and Trochammina sp. have been found to be the most abundant species.

Heat maps were generated from abundance records for selected species to illustrate environmental preferences and relative resistance levels to individual forms of anthropogenic disturbance. The features recorded allow to delineate the spatial effects of hydrocarbon and heavy metal pollutants, urban sewages, and sand dredging activities. The data generated may ultimately form the basis to assess the progressive deterioration of Lagos Lagoon environments from cores by using benthic foraminifera as bioindicators of environmental perturbation.

How to cite: Sariaslan, N., Fajemila, O. T., and Langer, M.: Benthic foraminifera as tracers in one of Africa's most polluted water bodies: The Lagos Lagoon (Nigeria), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8053, https://doi.org/10.5194/egusphere-egu2020-8053, 2020.

D958 |
Irina Polovodova Asteman, Thorbjørn Joest Andersen, Torsten Linders, Kjell Nordberg, and Nicolas Van Nieuwenhove

The Koster Trench is the deepest part of the Kosterfjord (Skagerrak, North Sea), which stretches southward along the west coast of Sweden. Since 2009 Kosterfjord has been included in the Marine Protected Area Kosterhavet National Park due to the presence of cold-water coral reefs. In this study we present multiproxy data from the sediment core KSK12-01D taken in the southern part of the Koster Trench. The core has been dated by 137Cs and was subject to bulk geochemistry (TOC, C/N and heavy metals: Ni, Cu, Zn, As, Cd and Pb) and micropaleontological (benthic foraminifera, dinocysts and selected palynomorphs) analyses. Results show that the core is an archive for the environmental changes that took place between ~1988 and 2012. Both TOC and heavy metals indicate high/good to moderate ecological quality status, as defined by the Swedish Environmental Protection Agency. Dinocysts suggest a major change occurring in the upper water column around 2002. The cysts of Pentapharsodinium dalei peak around 1992 and shows overall slightly higher relative abundances between 1988 and 2002. Increased abundance of cysts produced by Protoceratium reticulatum (i.e. Operculodinium centrocarpum sensu Wall and Dale 1966), cysts produced by Biecheleria baltica and heterotrophic dinoflagellates, oligotrichids, pollen and spores characterise the upper core part deposited from 2002 to 2012. Furthermore, there is a clear increase of calcareous Alexandrium cysts in the top of the core (~2008-2012). Benthic foraminifera show a major faunal change reflected in a drastic increase of agglutinated species (mainly Textularia earlandi) from 2007 towards present day, while the lower part of the core (1988-2007) is dominated by calcareous species (Stainforthia fusiformis, Epistominella exigua, Cassidulina laevigata, Bulimina marginata andHyalinea balthica). Overall, the changes in the dataset suggest an increased freshwater input or a higher river/land runoff, as supported by a local climate and hydrography data showing increasing precipitation and particulate organic carbon in the surface waters over the time period covered by our record.

How to cite: Polovodova Asteman, I., Andersen, T. J., Linders, T., Nordberg, K., and Van Nieuwenhove, N.: Recent environmental change in a marine protected area as reflected by sediment proxy data. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8249, https://doi.org/10.5194/egusphere-egu2020-8249, 2020.

D959 |
| Highlight
Rayanne Vitali, Claire Belcher, Jed Kaplan, Stephen Sitch, and Andrew Watson

Oxygen has varied in its abundance in the atmosphere throughout Earth’s long –term evolutionary history. Laboratory experiments have shown that fire responds rapidly to oxygen changes. Therefore it has been suggested that increases and decreases in atmospheric oxygen levels have influenced fire frequency, fire behaviour and plant evolutionary adaptations to fire.

Recent research has indicated that periods with high atmospheric oxygen, such as the Cretaceous period, which also saw the evolution of new plant groups had the coupled effect of altering fire behaviour. Such modelled fire behaviour has been able to estimate that fires during this period would have been more intense and spread more rapidly which likely fed back to changes in ecosystem dominance. However, we are lacking understanding of how oxygen driven changes in fire might feedback to influence the dominance and distribution of land-surface vegetation cover across Earth’s surface throughout Earth history.

Here I will present, a series of oxygen-fire-land cover simulations using the LPJ-LMfire Dynamic Global Vegetation Model that considers how oxygen-mediated changes in fire frequency and behaviour lead to changes in dominance of selected plant functional types within Earth’s biomes and influence the total land area covered by forest.

Our aim being to explore the coupled influence of oxygen and a climate on vegetation distributions mediated by fire throughout Earth’s past such that we can work towards understanding the balance of natural fire feedbacks to the Earth system versus human interrupted fire feedbacks in our modern day.

How to cite: Vitali, R., Belcher, C., Kaplan, J., Sitch, S., and Watson, A.: Oxygen-fire-vegetation feedbacks and the distribution of Earth’s biomes , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9500, https://doi.org/10.5194/egusphere-egu2020-9500, 2020.

D960 |
Eugene Bergh, John Compton, and Matthias Zabel

The Meridional Overturning Circulation is crucial in regulating Earth‘s climate and is composed of various ocean currents, playing an important role in heat exchange and the distribution of water masses. The transfer of water masses also affects regional carbon storage, nutrient contents, temperature, evaporation and precipitation balances in the oceans. The advancement in our understanding of the interaction between these water masses can contribute to our current knowledge on the state of the oceans. The use of foraminiferal isotope geochemistry and faunal analyses has greatly contributed to understanding the changes our oceans have undergone in the Quaternary. The purposes of this study are to determine what the timescales were at which the bottom water masses were changing and to determine at which periods the influence of these water masses were the strongest. A combination of neodymium and δ13C isotopes, as well as faunal abundance records in this study, were derived from foraminifera in cores recovered at 3522 m and 3631 m water depths along the western margin of South Africa to investigate deep water mass variability in the southeast Atlantic Ocean during the last two glacial terminations. The neodymium isotope composition (143Nd/144Nd), expressed as εNd, were measured in planktic foraminifera from the western continental slope of South Africa. This isotopic tracer is useful in tracking deep water masses on the sub-millennial scale owing to the short residence time of Nd in seawater. Foraminifera (single-celled protists) microfossils acquire the bottom water Nd signature upon burial that can be useful in providing insight into the variability of deep water masses. In addition to the εNd records, the foraminiferal δ¹³C results also support the results of the neodymium isotopes. These records in this study are largely correlative with the abundances of benthic species Cibicidoides wuellerstorfi, reflecting shifts between the southern-sourced Antarctic Bottom Water (AABW) and the northern-sourced North Atlantic Deep Water (NADW) during the last two glacial terminations at ~130 ka and ~18 ka. The εNd, δ¹³C results and C. wuellerstorfi relative abundances indicate an intensified inflow of southern-sourced water masses and weakened NADW inflow along the margin during peak glacial periods MIS 6 and MIS 2. The terminations of these peak glacials were more beneficial to stronger penetration of NADW into the southeast Atlantic.

How to cite: Bergh, E., Compton, J., and Zabel, M.: A combined approach in determining late Quaternary fluctuations in deep water masses derived from neodymium isotopes, faunal variations and d13C in foraminifera along the western continental slope of South Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-85, https://doi.org/10.5194/egusphere-egu2020-85, 2020.

D961 |
| Highlight
Martin Zuschin, Alexandra Haselmair, Ivo Gallmetzer, Anna Wieser, and Adam Tomasovych

We studied the origin and collapse of Holocene benthic baseline communities in the northern Adriatic Sea from sediment cores and surface grab samples at eight widely spaced sites. They cover areas with sedimentation rates spanning two orders of magnitude, with different nutrient input and with different degrees of time-averaging, ranging from decadal to millennial temporal resolution. Data from sediment cores indicate that during the transgressive phase and maximum flooding, sea-level and establishment of the modern circulation pattern determined the development of benthic communities in shallow-water, vegetated habitats with epifaunal biostromes and, in deeper waters, with bryozoan meadows. After sea-level stabilization, the composition of these baseline communities remained relatively uniform and started to change markedly only with the intensification of human impacts in the late highstand, leading to a dominance of infauna and a decline of epifauna at all sites. This profound ecological change reduced species richness, increased the abundance of infaunal suspension feeders, and led to a decline of grazers and deposit feeders. Live-dead data from grab samples give deeper insight into the degree of anthropogenic impact in historical times. At all sites the living assemblages differ strongly from the death assemblages. At some sites from oligotrophic settings with low sedimentation rates, a total overturn in the community composition is obvious: formerly abundant species have disappeared completely, while the living assemblage is numerically dominated by species that were not present before. Even at sites, which are characterized by physically stressful conditions (i.e., high sedimentation rates in the Po delta), some species that were abundant in the death assemblage have totally disappeared from the living assemblage. Comparison with the dataset from sediment cores documents the recent establishment of an impoverished community, which has no analogue in the Holocene history of the northern Adriatic Sea.

How to cite: Zuschin, M., Haselmair, A., Gallmetzer, I., Wieser, A., and Tomasovych, A.: Basin-wide homogenization of soft-bottom benthic communities in the wake of anthropogenic habitat degradation in the northern Adriatic Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2668, https://doi.org/10.5194/egusphere-egu2020-2668, 2020.

D962 |
| Highlight
Paolo G. Albano, Jan Steger, Marija Bošnjak, Beata Dunne, Zara Guifarro, Elina Turapova, Bella Galil, Gil Rilov, and Martin Zuschin

We quantify a large-scale extirpation of native species from the Israeli Mediterranean shelf, a region strongly affected by rapidly changing environmental conditions and the introduction of non-indigenous species, based on an extensive sampling programme of mollusks on intertidal to subtidal soft and hard substrata. We reconstruct historical species richness from shelly death assemblages, quantify the time range they cover with radiocarbon dating, and compare their richness with today’s living assemblage diversity. The median native richness is 50% of the historical richness for the intertidal, but only 8% for the subtidal down to 40 m. Samples from the mesophotic zone show a much higher median of 42%, which is likely an underestimation due to sampling constraints. In contrast, non-indigenous species show assemblages matching the historical richness. Seasonality is very strong: autumn samples, after the summer heat peak, are highly impoverished in native species but enriched in non-indigenous ones. Additionally, a comparison between today’s and historical native species maximum size shows that shallow subtidal native populations are mostly non-reproductive. In contrast, non-indigenous species reach reproductive size. These results suggest that a recent large-scale change in environmental conditions is strongly favoring non-indigenous species and is the main cause behind the shallow subtidal native species decline. Such an environmental factor is likely seawater temperature that plays a greater role in the shallow subtidal than in the cooler mesophotic zone, and affects subtidal species more than intertidal ones, pre-adapted to a climatically extreme environment.

How to cite: Albano, P. G., Steger, J., Bošnjak, M., Dunne, B., Guifarro, Z., Turapova, E., Galil, B., Rilov, G., and Zuschin, M.: Climate change driven massive extirpation of native species from the Israeli Mediterranean shelf , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13783, https://doi.org/10.5194/egusphere-egu2020-13783, 2020.

D963 |
| Highlight
Karin Moelling

The recent discovery of exoplanets with putative habitable zones which may be as frequent as 1025 stimulate the interest in the origin of life on the exoplanets but also on the Earl Earth (EE). Meteorites and missions to Mars or Moon teach us about their composition, and make us think about the origin of life in general. Prebiotic molecules such as amino acids, nucleosides, and fullerenes arrived from extraterrestric space and cyanobacteria and archaea are inhabitants of the EE. They exhibit properties such as protein synthesis, which requires advanced machineries adapted to our Earth. What could be early precursors of such mechanisms. What kind of life can we envision in its simplest form? Molecules which can replicate, mutate, and evolve are signatures of life.

The simplest such biomolecules on Earth may be non-protein-coding (nc)RNA catalytic RNA, the ribozymes and viroids, which can fulfill many protein functions, including replication, evolution, and are a prerequisite for peptide synthesis. Ribozymes/viroids can evolve to higher complexity. Archaea and bacteria resemble giant viruses suggesting a continuous transition from dead to living matter. Archaea are extremophiles which revolutionalized our view on what life can be like in respect to environmental conditions and specialized metabolic pathways. Some exotic spots on Earth can teach us about other habitable zones. Meteorites help to understand chemical compositions on other planets and the consequences for life. During evolution loss and gain of of genetic information are important evolutionary driving forces. Viroids  are discussed as models for potentially other forms of life. Simulators of Mars environment are under study to determine possible effects on biological sepcimens.

Ref: Broecker and Moelling Geosciences (2019), Annals NY Acad Sci. (2019), Frontiers Microbiol (2019). Book: Moelling:Viruses more friends than foes World Scientific Press ( 2017)



How to cite: Moelling, K.: Forms of life on Early Earth as model for Exoplanets?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2095, https://doi.org/10.5194/egusphere-egu2020-2095, 2020.

D964 |
David Bond and Charlotte Stephenson

The Devonian was one of the most dynamic periods in Earth history, with major changes on land and in the oceans that experienced at least two of the ten most severe biotic crises of the Phanerozoic. The Period saw the first extensive global floral record; prior to the Devonian, plant assemblages were low in diversity and abundance, and were restricted to areas close to water sources with little competition from co-existing taxa. By the end, plants were geographically widespread in diverse environments. Their colonisation of the land surface has been implicated in the Frasnian/Famennian marine crisis, but little is known of the effects of plants on the global biosphere during the rest of the Devonian. Synthesis of 389 publications reporting 294 Devonian plant genera has resulted in a database that we analyse at generic and stage level for trends in Devonian plant evolution and extinction. Our analysis reveals several key events within this dynamic phase of terrestrialisation: 1) an early Euramerican presence for all plant groups, suggesting this region may have been the site of origination for several higher taxa; 2) the origination of lycopsids in equatorial settings was followed by latitudinal migration northward and southward; 3) a major turnover in plants between the Late Givetian and Middle Frasnian, when significant diversity losses occurred in every palaeo-region in every extant plant group – this may be a hitherto unidentified terrestrial extinction event that coincided with one or both of the Taghanic and Frasne minor marine crises; 4) several Devonian marine black shale events coincide with major steps in terrestrialisation suggestive of a causal link and supporting the notion that plant evolution played a significant role in the Frasnian/Famennian mass extinction nexus.

How to cite: Bond, D. and Stephenson, C.: The Devonian plant revolution and its role in multiple marine extinction crises, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2558, https://doi.org/10.5194/egusphere-egu2020-2558, 2020.

D965 |
Katie Collins, Stewart Edie, and David Jablonski

Of all the macrofossil groups, bivalves (clams, scallops, oysters and mussels) have perhaps the best global record. Known from the Cambrian, bivalves have survived every mass extinction and climate perturbation the planet has suffered. Many of the ~90 living families of bivalves with a fossil record have roots that stretch back to the Paleozoic.

This lineage longevity makes bivalves an ideal model group for studying biodiversity responses to changing climate – families have been separate for a long time, and their varied ecological roles and habitats means that the effects of climate on different biogeographic regions and ways of making a living can be teased apart. The abundance of bivalves in marine and freshwater deposits provides large specimen-level datasets for analysing survivorship across climate-event boundaries, such as the Paleocene-Eocene Thermal Maximum, a major warming event, or the end-Pliocene cooling. Bivalves have been shown to be a good proxy for much of marine benthic biodiversity, and they can give us insights into questions such as: is biodiversity response to climate perturbation predictable? What species and lineages are at risk, and can we identify them?

Not only can bivalves help us track effects of climate changes of the past thanks to their rich fossil record; they may also be a major player in human efforts towards our own future climate resilience. Bivalves today provide food for many millions of people worldwide, both in artisanal and commercial fisheries, and perform vital ecosystems services, such as water filtration, sequestration of carbon, and as both food and habitat for many other animals of all sizes. Increased aquaculture of molluscs has been postulated as a way to take more of the burden of feeding the world’s population off the terrestrial realm, and without the adverse effects of finfish farming.

This talk will discuss patterns and fluctuations of bivalve diversity through time, focusing on predictive models for survivorship across major climate transitions in the Cenozoic, and using the past behaviour of species and clades to look ahead to potential marine diversity responses to projected climate scenarios.

How to cite: Collins, K., Edie, S., and Jablonski, D.: The clams before the storms: the fate of bivalve diversity during times of crisis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8044, https://doi.org/10.5194/egusphere-egu2020-8044, 2020.

D966 |
| Jean Baptiste Lamarck Medal Lecture
Michael Benton

Feathers are a diagnostic character of birds, and yet new fossils show they likely originated more than 100 million years before the first birds. In fact, feathers probably occurred in all dinosaur groups, and in their cousins, the pterosaurs, as we showed in 2019. This finding confirms current knowledge of the genomic regulation of feather development. Our work stems from ten years of collaboration with Chinese colleagues, during which we set ourselves the taks of understanding fossil feathers. Our first discovery was to answer the question, ‘Will we ever know the colour of dinosaurs?’. In 2010, we were able to announce the first objective evidence for colour in a dinosaur. Using ultrastructural studies of fossil feathers, we identified melanosomes for the first time in dinosaur feathers, and these demonstrated that Sinosauropteryx had ginger and white rings down its tail. Studies of other dinosaurs identified patterns of black, white, grey, brown, and ginger. This is part of a new wave in palaeobiology where we apply objective approaches to provide testable hypotheses, once thought impossible in the historical sciences.

How to cite: Benton, M.: The early origin of feathers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1318, https://doi.org/10.5194/egusphere-egu2020-1318, 2020.

D967 |
Tomaso Bontognali, Franziska Blattmann, Zulfa Al Disi, Hamad Al Saad Al Kuwari, Zach DiLoreto, Maria Dittrich, Jean-Luc Josset, Nikolaus Kuhn, Judith McKenzie, Fadhil Sadooni, and Kenneth Williford

The study of early life on Earth and the search for life on Mars often includes investigations of modern analogues: natural environments that share similarities to what we hypothesize may have existed on the early Earth and early Mars. The study of modern analogues provides key information on how biosignatures are formed and preserved, which is essential for interpreting the geological record. Research conducted in recent years in various modern sabkhas located along the coast of Qatar have demonstrated that these extreme evaporitic environments represent an inspirational gold mine for the field of geobiology and astrobiology.

The intertidal zones of the Qatari sabkhas are typically colonized by microbial mats. Their presence leads to the formation of Microbially Influenced Sedimentary Structures (MISS). Examples of studied MISS include polygonal, domical, blistered, tufted and crinkled microbial mats. We discuss biological vs. physiochemical factors responsible for their formation, as well as their fossilization potential. These MISS often occur in a precise sequence along a transect from the lower to the upper intertidal zone. We propose that a MISS sequence represents a stronger morphological biosignature than a single MISS. The community composition of some of the studied mats revealed an uppermost layer dominated by anoxygenic phototrophs. We propose that such mats represent a particularly good analogue for studying life in the Early Archean, a time when the cyanobacteria that usually dominate the uppermost photo-oxic layer of most modern mats probably did not exist.

Besides influencing sediment morphology, the extracellular polymeric substances (EPS) constituting the mats serve as nucleation sites for the precipitation of authigenic minerals. Among these possible precipitates, our research focused on microbially influenced Mg-rich carbonates and Mg-rich silicates. Linking these minerals to a microbial process is of particular interest in view of the forthcoming rover missions to Mars (i.e., ExoMars and Mars 2020). Indeed, orbital spectral analyses revealed the presence of Mg-rich clays and Mg-rich carbonates in the surroundings of the proposed landing sites. It will be exciting to test the hypothesis that, on Mars, some of these minerals may have formed at low temperatures from liquid water and may, therefore, represent a target phase for the investigation of biosignatures.

How to cite: Bontognali, T., Blattmann, F., Al Disi, Z., Al Saad Al Kuwari, H., DiLoreto, Z., Dittrich, M., Josset, J.-L., Kuhn, N., McKenzie, J., Sadooni, F., and Williford, K.: The sabkhas of Qatar: modern analogues for studying early life on Earth and on Mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21629, https://doi.org/10.5194/egusphere-egu2020-21629, 2020.

Chat time: Wednesday, 6 May 2020, 10:45–12:30

D968 |
Anna Tikhonova and Sofia Merenkova

We present the initial data on the distribution of benthic foraminifera (BF) on East Siberian Sea shelf. Previous researchers analyzed BF in the sediment cores from the continental slope and basin areas of the East Siberian Sea (Wollenburg et al., 2000; Mackensen et al, 2014; Barrientos et al, 2018) but not from central shelf. Last year we received boxcorer samples of bottom sediments from the shelf of the East Siberian Sea and the Laptev Sea during the 78th cruise of research vessel Akademik Mstislav Keldysh (September-October 2019). We examined the species composition of BF assemblages of Rose Bengal-stained surface samples from 2 stations in the East Siberian Sea and 7 stations in the Laptev Sea, and compared this data set with an existing data set along the East Siberian Sea and the Laptev Sea.

Recent studies (Shakhova et al, 2007, 2009, 2015; Nicolsky et al, 2009) state that the East Siberian Sea is one of the largest sources of methane emission into the atmosphere due to degradation of permafrost, ice complex retreat and decaying gas hydrates deposits. Perhaps this has an impact on the species composition of the BF assemblages and the morphological changes and defects of their shells, which we have identified. Samples from active methane seeps of the Laptev Sea have been studied to identify the relationship between methane emission and the reaction of benthic foraminifera. This data have been compared with “background” (i.e. non-venting, without any methane seeps activity) stations of the Laptev Sea and the East Siberian Sea.

The identified features require further detailed study.

How to cite: Tikhonova, A. and Merenkova, S.: The modern assemblages of benthic foraminifers of the East Siberian Sea initial and active methane seeps zones of the Laptev Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1337, https://doi.org/10.5194/egusphere-egu2020-1337, 2020.

D969 |
Heather Birch, Daniela N. Schmidt, Chloe Jones, Marci M. Robinson, and Andy Fraass

Within the marine fossil record, size is a fundamental trait providing information on both assemblages and individual species. Changes in size within an assemblage are largely driven by species composition typically related to environmental conditions. Changes in size of an individual species can be an indicator of health and whether optimal growth conditions (i.e. temperature, salinity and food availability) prevail. Over evolutionary timescales, individuals tend to increase in size (Cope’s rule) also altering the average size of the population.

The Pliocene provides an excellent opportunity to look at environmental drivers and ecological responses to a warmer world, at high resolution and with extant species. A short glaciation phase, during marine isotope stage (MIS) M2, interrupted the Pliocene global warming between ~ 3.31 – 3.26 Ma. This event provides the ideal framework to quantify how biota, already adapted to warming conditions, respond to a short, but substantial cooling event. 

We analysed the size and species composition of samples collected as part of the Pliocene Research, Interpretation and Synoptic Mapping (PRISM) Project from a variety of locations around the globe. The samples cover the Atlantic, Indian and Pacific oceans at a range of latitudes (e.g. DSDP Site 521, 586, 607 and ODP Site 716, 754, 887). We measured the maximum diameter of planktonic foraminifera tests with a fully automated light microscope, enabling high resolution sampling at a multitude of sites, before, during and after the MIS M2 glaciation event. On average 2000 specimens were measured per sample, resulting in over a million analyses in total. Changes in planktonic foraminiferal assemblage composition were characterised by quantifying relative species abundances and augmented by determining the largest species.

Planktonic foraminiferal assemblage size shows a general increase during the Pliocene likely related to warming temperatures. What is unclear is if this change is driven by changes in diversity due to extinction and origination, responses to environmental change or a general increase in size of species found through the record. Here we discuss reactions of species and (or) ecological groups to environmental change and determine the individual drivers of size change across the world’s oceans.

How to cite: Birch, H., Schmidt, D. N., Jones, C., Robinson, M. M., and Fraass, A.: Environment, diversity, evolution and Cope's Rule: Drivers of size in planktonic foraminifera., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2977, https://doi.org/10.5194/egusphere-egu2020-2977, 2020.

D970 |
Haiyan Long and Ziye Li

Salt-marsh foraminifera are routinely used as sea-level indicators since their vertical distribution is closely linked with elevation relative to the tidal frame. In this study, 106 surface sediment samples were collected across separate intertidal transects established at five micro-tidal salt-marsh situated along the coasts of the Jiaozhou Bay, western margin of the Yellow Sea, dead and live foraminifera were identified respectively. The dead population contains the mixture of both subtidal species and salt-marsh species, and all the live assemblages consist of salt-marsh species which can provide exact information of salt-marsh foraminiferal distribution. The agglutinated species present in the five marshes including Trochammina inflata, Miliammina fusca and Jadammina macrecens are all cosmopolitan species, however, the calcareous species contain numbers of endemic species, overall, dominant calcareous species included Cribrononion porisuturalis, Pseudononionella variabilis, Elphidiella kiangsuensis and Pseudogyroidina sinensis. Vertical foraminifera zonations have been recognized in Daguhe and Hongshiya marsh samples with some species occupying strict latitude range, which primarily related to elevation, however, no obvious assemblages zonations can be recognized in Nvgukou, Shanjiaodi and Yanghe marsh. We hypothesize that salt-marsh foraminifera in Jiaozhou Bay possesses potential in paleoenvironmental studies as the key indicators for monitoring Holocene sea-level and environmental changes.

How to cite: Long, H. and Li, Z.: Distribution of Salt-marsh foraminifera in Jiaozhou Bay: Implications for sea-level reconstructions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10354, https://doi.org/10.5194/egusphere-egu2020-10354, 2020.

D971 |
Michael Kaminski, Abduljamiu Amao, Lamidi Babalola, Thomas Garrison, Fabrizio Frontalini, and Bassam Tawabini

In recent years the popular press has asked the question whether the sea surface temperatures in the Arabian Gulf are becoming too hot to sustain animal life. According to a climate modal published by Pal and Eltahir (2016), the hottest temperatures in the Arabian Gulf are likely to be seen in the area between Doha (Qatar) and Dhahran (Saudi Arabia). In order address this question, we are gathering baseline annual temperature data at several nearshore locations in Bahrain and Saudi Arabia. We measured seawater temperatures and substrate temperatures in the intertidal zone during the hottest time of the year at a lagoon in Askar, Bahrain. For the purpose of this study, we concentrated our attention on an exposed tidal flat that has a southward-facing slope. We additionally observed the distribution and behavior of marine benthic organisms in the intertidal zone. We repeated our observations every two weeks during the 2019 summer-autumn season.

The intertidal mudflat in Murray’s Pool south of Askar (Bahrain) experiences summer temperatures in excess of 52°C at low tide on a hot summer afternoon. A “kill zone” with regard to meiofauna is observed on the mudflat where sediment temperature rises above ca. 40°C. In summer, a community of living foraminifera, gastropods, ostracods and diverse worms is only present in the tidal channels that contain water at low tide. Living foraminifera in the tidal channel mainly consist of the genera Ammonia, Peneroplis, and smaller miliolids. In the summer-autumn season of 2019, “summer” conditions persisted until the end of October. Temperatures below 40° were finally observed on the mudflat the first week of November. At this time, living juvenile Peneroplis specimens were observed on the surface of the mudflat. The site is currently being monitored on a bi-weekly basis to determine the length of the growing season.

We conclude that the intertidal faunas in Murray’s Pool are thermally stressed, and the higher intertidal areas are already too hot to sustain benthic marine life during the summer-autumn season. This finding is in line with predictions of climate models, which foresee that portions of the Arabian Gulf will become too hot to sustain animal life in the next decades.

How to cite: Kaminski, M., Amao, A., Babalola, L., Garrison, T., Frontalini, F., and Tawabini, B.: Substrate temperature as a primary control on meiofaunal populations in the intertidal zone of the Arabian Gulf: a persistent kill zone linked to elevated temperature, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10598, https://doi.org/10.5194/egusphere-egu2020-10598, 2020.

D972 |
Flavia Fiorini, Stephen W. Lokier, Yuzhu Ge, Chelsea L. Pederson, and Adrian Immenhauser

Live and dead benthic foraminifera assemblages were studied from 50 samples collected in a lagoon located between Yas Island and Ras al Gurhab Island (UAE) in a system dominated by carbonate sedimentation.

Living and dead foraminifera tests are present at all of the sampled locations. The foraminifera assemblage is dominated by a high diversity of miliolidae together with epiphytic larger benthic foraminifera belonging to the genera Peneroplis, Spirolina and Sorites. Hyaline foraminifera, such as Ammonia and Elphidium, are commonly found at all the locations while agglutinated foraminifera are uncommon and have a scattered occurrence.

The abundance and diversity of benthic foraminifera were calculated for each sample. Four benthic foraminifera ecological indices were applied to the studied samples. For each of the samples we calculated: the total foraminiferal number (number of foraminifera in 1 g of sediment >125 μm); the percentages of agglutinated, porcellaneous and hyaline foraminifera tests; the ratio between living and dead benthic foraminifera; the ratio between larger benthic foraminifera with normal and abnormal test growth. The above-mentioned data have been applied to construct a foraminiferal assemblage database that facilitates the discrimination between inner and outer lagoonal environments.

How to cite: Fiorini, F., Lokier, S. W., Ge, Y., Pederson, C. L., and Immenhauser, A.: Benthic foraminifera distribution and diversity in inner and outer lagoonal sediments of the UAE (United Arab Emirates), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12381, https://doi.org/10.5194/egusphere-egu2020-12381, 2020.

D973 |
Julia Wukovits, Jutta Wollenburg, Gernot Nehrke, Nicolaas Glock, Petra Heinz, and Alexandra-Sophie Roy

This study aims to emphasize the ecological importance of foraminifera contained within the > 1000 µm sediment fraction. Stones and gravel offer a habitat for diverse and rich epilithic foraminiferal communities. However, gravel-rich sediments > 1000 µm are usually not the subject of quantitative benthic foraminifera studies, because most foraminifera species used as proxies or bioindicators are sediment-dwelling and found within smaller sediment size fractions. Therefore, there is a current lack of knowledge about the biology and ecology of epilithic foraminifera, specifically about agglutinated species.

During a cruise at the Gullmarfjord/Sweden in September 2018, we retrieved a core at a station at 7 m water depth, which contained organic-rich material and a relatively large portion of gravel and shell fragments, which were densely populated by monothalamus, agglutinated foraminifera.

A faunal analysis of foraminifera in the > 1000 µm sediment fraction showed, that the most abundant species (> 85 %, 54 ind. 10 cm-3) in > 1000 µm consisted of Tholosina vesicularis, an unicellular agglutinated species that can reach up to 4 mm diameter. SEM-analysis revealed, that large quantities of partially decomposed diatom frustules were embedded within the protoplasm of T. vesicularis individuals, which were supposedly the remains of the foraminiferal diet. The sediment fraction of 125 - 1000 µm was dominated by Ammonia species (58 %, 190 ind. 10 cm-3), a genus known for its fast turnover of diatom-derived carbon and as key-players in benthic nutrient fluxes. Preliminary biovolume analysis of the two genera (T. vesicularis: n = 74, Ammonia spp.: n = 110) resulted in far higher values for T. vesicularis (853 ± 944 µm-3 10 cm-3, med. = 506 µm-3 10 cm-3), than for Ammonia spp. (117 ± 56 µm-3 10 cm-3, med. = 96 µm-3 10 cm-3), within the uppermost sediment layer of 0 - 1 cm. Therefore, T. vesicularis could be a main driver of benthic carbon turnover in gravel-dominated sediments. We hypothesize, that the epilithic fauna, when present is at least as relevant as sediment-dwelling species.

Additionally, biodiversity indices (species diversity, Shannon-Index, Evenness), show a slightly higher diversity and a more even distribution within the softer substrate, compared to the stones.

This is most likely due to the motility of the free-living forms of the smaller size fraction, which allows them a flexible response to spacial competition. However, niche separation between hard and soft-substrate allows the co-existence of the opportunistic species T. vesicularis and Ammonia spp..

In conclusion, this study shows, that if present, the > 1000 µm fraction can contain important information for the interpretation of ecological studies on the communities of live foraminifera and their role in marine ecosystems.

How to cite: Wukovits, J., Wollenburg, J., Nehrke, G., Glock, N., Heinz, P., and Roy, A.-S.: The relevance of epilithic foraminifera in ecological studies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17668, https://doi.org/10.5194/egusphere-egu2020-17668, 2020.

D974 |
Fabio Francescangeli, Yvonne Milker, Eric Armynot du Châtelet, and Gerhard Schmiedl

Estuaries are transitional ecotones influenced by both marine and terrestrial (fresh) waters. For the past 200 years, estuarine environments experienced intense and rapid environmental degradations due to anthropogenic action (e.g., urban sewage, industry, aquaculture, and agricultural runoff). The distribution of benthic foraminifera in estuarine areas is the result of complex interactions between a large number of biotic and abiotic parameters. The natural stress (such as variation in salinity, sediment size, organic load) may be associated to anthropogenic stresses, enhancing the high natural variability of these areas. The objectives of the present work are to describe the specific composition of benthic foraminifera and to investigate their ecological interactions upstream of the Elbe Estuary (Germany). In this important estuarine area, there is a lack of a comprehensive investigation in terms of benthic foraminifera. So far, the ecology of living benthic foraminifera has not been studied in greater detail and it is largely unknown which species occur in this transitional area. For this purpose, a surface sampling was carried out from 24 stations along the salinity gradient of the Elbe Estuary. Living and dead foraminiferal assemblages were analyzed and the relative correlation with environmental parameters (such as salinity, pH, temperature, sediment size, organic matter) was investigated. Living assemblages are characterized by very low densities and largely dominated by “Ammonia” group. Dead assemblages are more diverse and dominated by estuarine taxa (Ammonia aomoriensis, Haynesina germanica, and Cribroelphidium selseyense). Upstream of the estuarine area, the low salinity prevents the development of living benthic foraminifera while downstream, sediment grain size seems to be a major key-factor, influencing foraminiferal distributions. This work sheds new light on benthic foraminiferal ecology and biodiversity of this important estuarine area of Northern Europe.

How to cite: Francescangeli, F., Milker, Y., Armynot du Châtelet, E., and Schmiedl, G.: Distribution of benthic foraminifera upstream of the Elbe Estuary (Northern Europe): ecological interactions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18244, https://doi.org/10.5194/egusphere-egu2020-18244, 2020.

D975 |
Abduljamiu O. Amao and Michael Kaminski

The study explored an end-to-end application of a ResNet convolutional neural network (transfer learning) to classify benthic foraminifera images using the FastAI library. 201 SEM images of 13 benthic foraminifera including Ammonia convexa, Ammonia tepida, Asterorotalia gaimardi,  Asterorotalia indica, Bulimina biserialis, Bulimina marginatta, Elphidium advenum, Elphidium hispidium, Elphidium jenseni, Elphidium neosimplex , Perenoplis arianus , Perenoplis pertusus and Quinqueloculina sp. The images were separated into two groups in a 80 -20 split for training and validation dataset respectively. We successfully trained a state-of-the-art image classifier for a very small dataset, achieving 96.5% accuracy in just a handful of lines of code on a very small dataset i.e. accurately predicting the binomial nomenclature of species. The fastai AI/Machine learning library we used offers interesting prospects in taxonomy where it can be used for multilabel image classification. Fastai’s recent research breakthroughs are embedded in the library, resulting in significantly improved accuracy and speed over other deep learning libraries, whilst requiring dramatically less code. The library sits on top of PyTorch and provides a single consistent API to the most important deep learning applications and data types. It also offers an opportunity to a novice user, new to data science to apply state of the art deep learning to practical problems quickly and reliably. It has several advantages over other known libraries is its flexibility to import data of various kind and from various sources. It is fast, has a large and friendly community backing and its immune to several limitation of other libraries.

How to cite: Amao, A. O. and Kaminski, M.: Multi-labelled taxonomic prediction using a small benthic foraminifera dataset trained on a FastAi library, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21465, https://doi.org/10.5194/egusphere-egu2020-21465, 2020.

D976 |
Valeria Luciani, Roberta D'Onofrio, Wade Bridget S., and Dickens Jerry R.

Coiling direction is a basic characteristic of trochospiral planktic foraminifera. However, although modifications in the coiling direction within ancient planktic foraminiferal populations may reflect important changes in evolution or environment, they remain scarcely discussed. Here we present data on fluctuations in the coiling direction within morphologically defined Morozovella species from successions that span the interval of peak Cenozoic warmth, the Early Eocene Climatic Optimum (EECO; ~53-49 Ma). We selected three widely separated Ocean Drilling Program (ODP) sites in the Atlantic Ocean: the subtropical Site 1051, the equatorial Site 1258 and the temperate south Atlantic Site 1263. The surface-dwelling genus Morozovella is of particular interest because it dominated tropical-subtropical early Paleogene assemblages and  suffered an abrupt and permanent decline in abundance and taxonomic diversity at the start of the EECO. At all ODP sites investigated, morozovellids display a dominant dextral coiling preference during the interval preceding the EECO. However, all species became at all sites prevailing sinistral within the EECO. Specifically, the switch from dominant dextral to sinistral coiling occurred at all sites ~ 300 Kyr after the K/X event (~52.8 Ma). The coiling switch occurred ~550 kyr to ~650 kyr after a distinct drop in abundance. We provide therefore evidence of a coiling variation during the warmest interval of the early Paleogene. Our records highlight that the recorded coiling variations might provide a biostratigraphic tool for correlation of early Eocene marine strata. In order to establish whether this coiling switch was related to changes in morozovellid ecological niche we estimated stable carbon isotopes on dextral and sinistral species from samples located below and above the recorded coiling change. Results suggest that sinistral species moved higher in the mixed-layer after the coiling switch. It is thus possible that only species sinistrally coiled were able to keep the optimal environmental conditions for their survivorship. We need however more effort to understand the meaning of these modifications, such to verify whether variations in sea surface temperature or other parameters directly corresponded to the coiling change. Coiling switches can relate to ecophenotypic adaption (when a single species changes morphology in response to variation in environmental parameters, such as temperature) or genetic variance (when two almost identical morphotypes have different genetic signatures so they represent ‘cryptic’ species from a morphological point of view). Previous interpretations of coiling flips in planktic foraminifera in the early Eocene, especially including morozovellids, have favoured a genetic explanation rather than an ecological response. Our present data cannot validate or disprove this idea, but should stimulate renewed thought on the matter.

How to cite: Luciani, V., D'Onofrio, R., Bridget S., W., and Jerry R., D.: Dominant dextral to sinistral coiling change in planktic foraminifera Morozovella during the Early Eocene Climatic Optimum in the Atlantic Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21576, https://doi.org/10.5194/egusphere-egu2020-21576, 2020.

D977 |
Arianna Valentina Del Gaudio, Werner E. Piller, Gerald Auer, Patrick Grunert, and Walter Kurz

The Mariana forearc system represents the only known currently active serpentine mud volcanism in a convergent margin setting. Here, International Ocean Discovery Program (IODP) Expedition 366 recovered material from three serpentinite mud volcanoes at increasing distances from the Mariana trench subduction zone along a south-to-north transect: Yinazao (Blue Moon), Fantangisña (Celestial), and Asùt Tesoru (Big Blue). Cores contain serpentinite mud with lithic clasts from the subducting Pacific Plate, forearc crust and mantle. Furthermore, at almost all drilled sites, a thin cover of pelagic sediment containing planktic and benthic foraminifera, calcareous nannofossils, radiolaria and sponge spicules was recovered, constraining the most recent mud volcano activity. The base of the seamounts overlies pelagic sediment and volcanic ash/tephra layers which establish a maximum age for the mud activity. Additionally, separate serpentinite mud flows are intercalated by distinct sedimentary layers.

Integrated biostratigraphy, based on planktonic foraminifera and calcareous nannofossils, is used to assess the minimum and maximum age of mud flow activity and of the distinct sedimentary layers and serpentinite mud flow layers. Biostratigraphic information will also provide time indications on lower plate dehydration and serpentinization of the forearc wedge. Preliminary results from Fantangisña seamount (Site U1497 and U1498) reveal the existence of biostratigraphic marker species for both planktonic foraminifera and calcareous nannofossils. Specifically, the presence of Globigerinella calida, Globorotalia flexuosa, Globorotalia truncatulinoides, Globorotalia tumida, Sphaeroidinella dehiscens (amongst planktic foraminifera) and Gephyrocapsa spp., Pseudoemiliania lacunosa, Reticulofenestra asanoi, Discoaster deflandrei, Discoaster variabilis (amongst calcareous nannofossils) allow a possible age assessment from Late Pleistocene to Late Miocene.

Planktonic assemblages are dominated by (sub)tropical Globigerinoides forms such as G. conglobatus, G. ruber, G. elongatus, G. sacculifer, G. trilobus. Other common (sub)tropical species detected are G. menardii, and O. universa, whereas G. siphonifera, N. dutertrei, S. dehiscens and P. obliquiloculata are less common.

Benthic foraminifera are less abundant but show high diversity. Forms of Lagena, Cibicidoides, Fissurina, Ehrenbergina, Gyroidina, Melonis, Pullenia, Osangularia, Favulina, Reophax, Rhabdammina, Saccorhiza, and Hormosinella are present. To the best of our knowledge, the occurrence of benthic forms in such environments is highly unusual and has not been recorded in detail so far.

Quantitative and statistical analyses on foraminifera assemblages will provide information on water column and bottom water conditions. Moreover, a detailed comparison between assemblages pre- and post-volcanism may reflect possible changes in the ecological conditions.

Collected data will not only allow to constrain in time the evolution of submarine volcanoes in the Mariana convergent system but also to investigate foraminifera ecology in such an extreme environment.


How to cite: Del Gaudio, A. V., Piller, W. E., Auer, G., Grunert, P., and Kurz, W.: Micropaleontological proxies as tool to date serpentinite mud volcanisms and seamount subduction and to reconstruct paleoenvironmental conditions in the Mariana convergent margin system (IODP Expedition 366), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7139, https://doi.org/10.5194/egusphere-egu2020-7139, 2020.

D978 |
Suryendu Dutta

Palaeogegraphic model suggests that the Indian plate was separated from Gondwana during Late Jurassic and started moving towards the northern hemisphere during the Early Cretaceous and remained as an island continent during the entire Cretaceous until it collided with Asia in Early Eocene at ca. 50 Ma.  It is believed that many vertebrate groups may have originated in India or other Gondwanan land masses and were carried on the rafting Indian plate and finally dispersed ‘out of India’ following the collision between India and Asia. However, the evolution of plants on the rafting continent is poorly documented.


A brief outline on evolution of plant terpenoids from Permian to Eocene on the Indian continent will be discussed during the presentation. The Permian coals are characterized by tricyclic and teracyclic diterpenoids. The possible source of these compounds is extinct seed ferns.

The molecular composition of Jurassic and early Cretaceous coals and sediments suggests that the vegetation was contributed by conifers (e.g. Arucariaceace, Podocarpaceae) during the period. Aromatic triterpenoids derived from angiosperms are detected in the sediments of Late Maastrichtian age. Drastic reduction of coniferous vegetation and proliferation of angiosperms in early Palaeogene are observed in the present study. The terpenoid signatures of early Palaeogene lignites suggest that the western India was covered by widespread thick closed rain forests dominated by family Dipterocarpaceae thriving under the influence of tropical climate.

How to cite: Dutta, S.: Evolution of plant terpenoids on a ‘biotic ferry’, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7365, https://doi.org/10.5194/egusphere-egu2020-7365, 2020.

D979 |
Anuradha Tewari, Kevin Lepot, Suryendu Dutta, Borja Cascales-Miñana, and Armelle Riboulleau

The Lower Devonian Rhynie chert of Scotland is an iconic geological formation that preserves the earliest known terrestrial ecosystem. This assemblage contains key evidence of earliest lineages of land plants, e.g., protracheophytes and paratracheophytes (former Rhyniaceae), together with animals, fungi, algae, and bacteria (Edwards et al., 2017). The exquisite preservation of this early biota provides an ideal scenario to explore the basal evolution of the land biosphere.

The Rhynie chert has been vastly studied from multiple viewpoints, however, the biomolecular composition, i.e., “molecular signature”, of the Rhynie flora, including the early detection of fossil lignin, remains clearly unresolved. Lignin biosynthesis has been considered as one of the crucial influences behind the survival and proliferation of land plants in terrestrial ecosystems. Here, we characterize the molecular fossils to help decipher the botanical affinities of the Rhynie flora.

Kerogens were isolated by the standard HF/HCl extraction procedure, and bitumens were extracted from the kerogens using organic solvents. The bitumens were studied with GC-MS, and the kerogens were analysed using Py-GC-MS and Py-GC×GC–TOFMS in the presence of TMAH reagent. The bitumens are characterized mainly by some aliphatic compounds such as a series of n-alkanes, pristane, phytane, and a series of diterpanes in very low abundance, as well as a set of aromatic compounds such as naphthalene and methylnaphthalenes, phenanthrene and methylphenanthrenes and retene. The pyrolysates, obtained using Py-GC-MS are dominated by benzene and methyl benzenes, phenol and methylphenols, Polycyclic Aromatic Hydrocarbons (PAHs) like naphthalene and methylnaphthalenes, phenanthrene and methylphenanthrenes, anthracene and methylanthracene, fluoranthene, pyrene, etc. Series of fatty acid methyl esters (FAME) and of n-alkane/alkene doublets were also detected. The thermochemolysates acquired from Py-GC×GC–TOFMS include the same compounds; additional methoxybenzene derivatives, methoxy toluene, methoxy benzaldehydes, and benzoic acid methyl esters, generated by reaction with TMAH, were also identified. Phenols and methoxybenzenes in the pyrolysates and thermochemolysates originate from lignin, and this is the first time that lignin monomers are formally identified from Rhynie chert samples.


Edwards, D., Kenrick, P., Dolan, L., 2017. History and contemporary significance of the Rhynie cherts—our earliest preserved terrestrial ecosystem. Philosophical Transactions B Royal Society 373: 20160489.

How to cite: Tewari, A., Lepot, K., Dutta, S., Cascales-Miñana, B., and Riboulleau, A.: Molecular signatures of kerogens and bitumens from the Lower Devonian Rhynie chert: Insights into the botanical affinity of the earliest land plants, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18997, https://doi.org/10.5194/egusphere-egu2020-18997, 2020.

D980 |
Sofie Lindström, Hans Peter Nytoft, Gunver K. Pedersen, Grzegorz Niedzwiedzki, Karen Dybkjær, Leif Johansson, Henrik I. Petersen, Hamed Sanei, Christian Tegner, and Rikke Weibel

The end-Triassic mass extinction is considered to have been caused by voluminous and repeated emissions of CO2 and/or methane and other gases from magmatic activity in the Central Atlantic Magmatic Province. Despite improved geochronological dating and correlation between the magmatic activity and the extinctions, exactly how the biotic crisis commenced remains poorly understood. Here, we compile palynological and palaeobotanical data, bulk organic δ13C, biomarkers, mercury and other geochemical proxies, charcoal, and sedimentology, from a Rhaetian terrestrial succession in southern Sweden. Our results provide an insight into the climatic, environmental and ecosystem changes that took place at the onset of the mass extinction event.

How to cite: Lindström, S., Nytoft, H. P., Pedersen, G. K., Niedzwiedzki, G., Dybkjær, K., Johansson, L., Petersen, H. I., Sanei, H., Tegner, C., and Weibel, R.: Land plants and terrestrial environmental changes during the onset of the end-Triassic event, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20732, https://doi.org/10.5194/egusphere-egu2020-20732, 2020.

D981 |
Achim Bechtel, Marek Widera, and Michal Woszczyk

Samples of detrital lignite have been collected for organic geochemical and carbon isotope analyses from the First Lusatian lignite seam at the Adamów, Jóźwin IIB and TomisÅ‚awice opencast mines, deposited after the last peak of the Mid-Miocene Climatic Optimum. The aim of the study is to improve the chemotaxonomic value of biomarkers by relating the results to existing paleobotanical data, and to gain information about the influencing factors on δ13C of lignite and lipids. Furthermore, biomarker and isotopic proxies are tested for their applicability in paleoclimate studies.

The relative abundances of mid-chain (C23, C25) n-alkanes and their 1–2‰ higher δ13C values compared to long-chain n-alkanes (C29, C31) argue for a minor contribution of macrophytes (graminoids, etc.) to peat formation, enhanced during periods of raised water level. The presence of ferruginol and dehydroferruginol testifies the contribution of taxodioid Cupressaceae. The abundances of pimarane-type diterpenoids and the presence of non-aromatic abietane-derivatives argue for the contribution of Pinaceae. Based on the presence of lupeol and lupane-type triterpenoids, an input of Betulaceae can be concluded. The contribution of further angiosperms cannot be specified based on the composition of pentacyclic triterpenoids. However, the results indicate mixed vegetation, and are in agreement with paleobotanical data highlighting abundant conifers of the Cupressaceae and Pinaceae families, as well as angiosperms of various families (e.g., Nyssa, Quercus, Fagus), including Betulaceae (e.g., Alnus, Betula, Corylus). Based on the relationship between the carbon preference index of n-alkanes and mean annual air temperatures, obtained from a global database of peatlands, an average temperature of 24.5 °C is obtained. This value is significantly higher as estimated from paleobotanical data (15.7–19.7 °C), probably due to the influence of changes in vegetation on carbon preference index.

The relative abundances of diterpenoids versus di- plus angiosperm-derived triterpenoids in detrital lignite samples revealed variable contributions of gymnosperms and angiosperms during the middle Miocene. Consistent with these results, a positive relationship exists between the di-/(di- + tri-) terpenoid biomarker ratios and δ13C of lignite samples, indicating the dominating role of varying gymnosperm/angiosperm contributions on the carbon isotopic composition of lignite. The C-isotope data of long-chain n-alkanes, diterpenoids, and angiosperm-derived triterpenoids co-vary within the profiles, arguing for an overall control of changes in δ13C of atmospheric CO2 on δ13C of plant lipids. Fluctuations in δ13C of individual compounds may also be related to changes in carbon cycling within the peat, humidity and air temperature.

How to cite: Bechtel, A., Widera, M., and Woszczyk, M.: Composition of lipids from the First Lusatian lignite seam of the Konin Basin (Poland): relations to vegetation, climate and carbon cycling during the mid-Miocene Climatic Optimum, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15, https://doi.org/10.5194/egusphere-egu2020-15, 2020.

D982 |
Emilia Jarochowska, Madleen Grohganz, Niklas Hohmann, Axel Munnecke, and Theresa Nohl

The Silurian is characterized by several extinction events, among them the late Ludfordian Lau event, which mainly affected conodont and graptolite communities. This event was followed by the strongest global positive δ13C excursion of the Phanerozoic. This event has been first recognized in the classical succession in Gotland, Sweden, where a continuous increase in δ13C values of up to nearly 9 ‰ from the upper När Formation to the Eke Formation is observed. It has been attributed to large scale carbon cycle perturbations. This time period is also characterized by a regression and associated changes in sedimentation and deposition rates. This raises the question to what extent these factors contribute to the observed changes in faunal diversity and geochemical proxies.

A mechanism linking changes in seawater chemistry and the faunal turnover has been proposed based on a high abundance of malformed acritarchs observed during the onset phase of some Phanerozoic isotope excursions including the Lau isotope excursion. Malformations during the late Silurian Pridoli event coincide with a significant increase in trace metal content measured in fossils and host rock, which suggests the teratology to be caused by metal pollution. However, also in the case on an increase in the trace metal content the contribution of changing depositional rates has not been quantified.  

Models developed in the field of stratigraphic paleobiology have demonstrated that changing deposition rates have a substantial influence on the stratigraphic distribution of fossils. In the same sense, element concentrations can be altered by changing deposition rates, which may dilute or condense the primary element signal. For this study, concentrations of different trace elements were measured across a profile in an outcrop Bodudd (Gotland) which exposes the Lau isotope excursion from the upper När to the Eke Formation. Using a newly developed statistical method, the effects of changing deposition rates were quantified and the measured element signal corrected for these effects. This method uses a deposition model to transform the measured element signal, which is a function of the stratigraphic height in the outcrop, back into a temporal rate. The temporal rate reflects the primary element signal and is defined as a function of time instead of stratigraphic height. Thus, the effect of changing deposition rates is accounted for. Approximate deposition models were created based on Th concentrations measured across the profile, which act as a proxy for the rate of terrestrial input, and based on the chitinozoan yield, which reflects deposition rates. Pre- and post-transformation element patterns were compared for different deposition models and evaluated with respect to their ability to preserve element peaks.

How to cite: Jarochowska, E., Grohganz, M., Hohmann, N., Munnecke, A., and Nohl, T.: Testing for the effects of depositional rates in multiproxy models of environmental and faunal change: the Silurian Lau δ13C excursion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7615, https://doi.org/10.5194/egusphere-egu2020-7615, 2020.

D983 |
Adam Tomašových, Martin Zuschin, Ivo Gallmetzer, and Alexandra Haselmair

The northeastern Adriatic seafloor is formed by warm-temperate bioclastic carbonates with coralline algae, bryozoans and mollusks. These sediments represent a mixture of past and present-day production owing to low sedimentation rates and bioturbation. Although low sedimentation rates do not allow resolution of ecological history at centennial or even millennial scales on the basis of raw stratigraphic data, age unmixing based on radiocarbon-calibrated amino acid racemization shows that one of the major molluscan sediment producers – the infaunal suspension-feeder Timoclea ovata  – markedly peaked in production ~5,000 years during the maximum flooding and earliest highstand phase and significantly diminished in abundance during the late highstand phase at Brijuni, with a large proportion of dead shells now present in surface sediments representing shells that are several centuries old. This species still occurs in living assemblages but our analyses indicate that its former production was by several orders of magnitude higher. In contrast, stratigraphic trends in absolute and proportional abundance of this species in ~1.5 m-thick sediment cores show a gradual or a very mild upcore decline, indicating that raw stratigraphic data do not efficiently detect millennial-scale ecological dynamic. The temporal decline in production of Timoclea ovata is associated with an increase in water depth and an increase in sediment-accumulation rate, and led to a transition from molluscan oyster-scallop shell bed to late highstand bryomol sediments.

How to cite: Tomašových, A., Zuschin, M., Gallmetzer, I., and Haselmair, A.: Time averaging and stratigraphic unmixing: reconstructing ecological decline in molluscan production (Holocene, Brijuni, NE Adriatic), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11698, https://doi.org/10.5194/egusphere-egu2020-11698, 2020.

D984 |
Michele Azzarone, Daniele Scarponi, Giulia Barbieri, Veronica Rossi, Claudio Pellegrini, Fabiano Gamberi, and Fabio Trincardi

Direct observations from the geologic record are commonly used in conjunction with indirect seismo-stratigraphic inferences to detail environmental settings and stratal architecture of sedimentary successions. However, examples of integration between seismic facies and macrobenthic insights are scarce and limited to the use of such a group as auxiliary to other proxies. This case study investigated mollusc and ostracod dynamics along an onshore-offshore profile that intersects the C2 clinothem (15.6 – 14.4 ky BP) of the Po River Lowstand Wedge (PRLW) and the overlying transgressive deposits formed in the central Adriatic Sea. Multivariate analyses were applied to benthic data to assess to what extent mollusc and ostracod assemblages can improve the resolution of seismic-derived depositional environments and stratigraphic architecture of cored succession. Along the profile of the C2 clinothem, seismic reflection facies correspond with three sedimentary environments. Specifically, i) High Amplitude Continuous reflections (HAC) are interpreted as delta plain/subaqueous shelf; ii) High Amplitude Continuous Wavy Dipping reflections (HACWDip) characterize prodelta deposits, and iii) Low Amplitude Continuous reflections (LAC) are associated with distal basin settings. The integration of quantitative palaeoecologic trends with the seismic-derived depositional environments allowed the subdivision of the HAC facies into a proximal (core LSD-26) and a distal (cores LSD-27 and -28) area. In particular, the proximal area with HAC seismic facies encompasses semi-barred lower delta plain with vegetated substrates that evolves to more open, nearshore settings. Conversely, the distal area with HAC seismic facies is distinguished by clusters reminiscent of ecological mixing due to strong bioturbation and gravity flows in offshore transition/inner shelf settings. The paucity of benthic fauna for the units with HACWDip (core LSD-05) and LAC (core LSD-04) seismic facies, hampered a complete reconstruction of the palaeoenvironmental dynamics. However, both benthic groups investigated support the seismic-derived interpretation of shelf and basinal settings respectively, both subjected to high sedimentation rates. Moreover, the integration of mollusc and ostracod multivariate-derived trends with grain-size data across the study profile reveals distinctive stratal stacking patterns useful in constraining the position of key stratigraphic surfaces such as the Maximum Regressive Surface that marks the initial phase of the abandonment of the PRLW.

How to cite: Azzarone, M., Scarponi, D., Barbieri, G., Rossi, V., Pellegrini, C., Gamberi, F., and Trincardi, F.: Linking macrobenthic fauna and seismic facies to improve stratigraphic reconstructions: the case of the Mid Adriatic Depression since the late glacial period (Central Adriatic Sea), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7320, https://doi.org/10.5194/egusphere-egu2020-7320, 2020.

D985 |
Michaela Berensmeier, Adam Tomašových, and Zuschin Martin

Sediments of the NW Adriatic Sea preserve important information about environmental changes during the Holocene and due to recent anthropogenic impact. This study is based on new data of a 3-m-long gravity core taken from 31 m water depth. Large environmental and ecological shifts are indicated by changes in geochemistry (XRF core scanning data, geochemical bulk analyses) and molluscan composition, particularly in the uppermost decimeters.

Sedimentologically, the record can be divided into 4 facies types: (1) laminated silty sediments with some sands, terrestrial plant remains, and scarce mollusc shells (at 175-300 cm sediment depth), (2) bioturbated silty, fine-sandy sediments with terrestrial plant remains, scarce mollusc shells, and calcirhizomes (70-175 cm), (3) strongly bioturbated, clayey silt with increasing abundance in mollusc shells (20-70 cm), and (4) clayey silt with a peak in molluscan shell abundances and diversity, with abundant bivalves (Corbula gibba) and gastropods (Turritellinella tricarinata, 0-20 cm).

Corbula gibba valves were used for C14-calibrated amino acid racemization (AAR) analyses of valves. The resulting shell ages show a bisection in the record: (1) an uppermost, surface-mixed layer with very young shells (median age = 50 years) and (2) an age-homogeneous composition down to 30 cm sediment depth (median age = 3000 years). This downcore shift in age distributions probably indicates that the 20th century shells of Corbula gibba are not mixed beyond 10 cm. This pattern implies decreasing bioturbation and increasing sedimentation in the study area in the 20th century.

How to cite: Berensmeier, M., Tomašových, A., and Martin, Z.: Major environmental and ecological shifts in late Holocene marine sediments of the NW Adriatic Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7572, https://doi.org/10.5194/egusphere-egu2020-7572, 2020.

D986 |
Rafał Nawrot, Daniele Scarponi, Adam Tomašových, and Michał Kowalewski

Late Quaternary fossil record offers a window into ecosystem dynamics during episodes of abrupt climate warming and sea-level rise following the Last Glacial Maximum, but in marine settings ecological inferences might be hindered by high time-averaging affecting transgressive deposits. However, the signature of temporal shifts in local skeletal production rates may be preserved in the age-frequency distributions (AFDs) of death assemblages. We use carbonate-target radiocarbon ages of 191 shells to examined variation in AFDs among four bivalves species collected from a 2.3-meter-long core recording the post-glacial transgression on the northern Adriatic shelf over the last the last ~14,500 yr.

The scale of time-averaging within species (interquartile age range) varied from 200 to 7,400 yrs, while the between-species age offsets (differences between the median ages of species) ranged from ~2 to 6,400 yrs within 5-cm-thick core intervals. Although the median ages of Varicorbula, Timoclea and Parvicardium increased with increasing burial depth, shells of Lentidium appeared age-homogeneous throughout the core. Age unmixing revealed a single massive peaks in the abundance of this opportunistic, shoreface species around 14 cal ka BP, coincident with the initial marine flooding of this shelf area during the melt-water pulse 1A. Moreover, a prominent gap in the AFDs between 11 and 12.5 cal ka BP corresponds to a minor sea-level fall associated with the Younger Dryas cold spell. Importantly, the reconstructed onsets and durations of shell production pulses across the four species are consistent with independently-derived relative sea-level history at the site. The species gradually replaced each other through time as the dominant component of the assemblage in accordance with their bathymetric preferences estimated from surveys of the modern Adriatic benthic fauna.

The diachronous production histories of four bivalve species coupled with subsequent exhumation of old shells and burial of younger shells through bioturbation and sediment reworking resulted in the ecologically mixed fossil assemblages. These assemblages are thus characterized by multi-modal age distribution and millennial-scale age offsets between species co-occurring in the same stratigraphic increments. Although this stratigraphic homogenization and disorder greatly limits the resolution of the raw stratigraphic record, our results demonstrate the power of AFDs to capture shifts in abundance of benthic species during recent episodes of rapid sea-level rise. Fossil assemblages from transgressive deposits preserved on continental shelves represent a rich and underutilized source of data on long-term biotic responses to global climate change and associated shifts in sea level.

How to cite: Nawrot, R., Scarponi, D., Tomašových, A., and Kowalewski, M.: Response of benthic species to post-glacial sea-level rise on the northern Adriatic shelf revealed by stratigraphic unmixing of fossil assemblages, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17636, https://doi.org/10.5194/egusphere-egu2020-17636, 2020.