Tropical cyclones (TC) are one of the most destructive weather phenomena on Earth. However, the short duration of instrumental weather records means that little is known of the frequency of TCs through geological time. Here we analyse a Tridacna squamosa shell with a life span about 6 years (from 12 May 2013 to 18 December 2018) from the northern South China Sea. Studies of daily growth rate variations (DGRV) were correlated with coeval environmental changes to develop a proxy for TC. Results reveal that the frequency and variation of extreme DGRV were conspicuously different between the typhoon-affected season (July to October) and the relatively stable growth season (March to June). During the typhoon-affected season, the frequency of sudden onset of decreased sea surface temperature, attenuated solar radiation and heavy precipitation can result in more days for extreme decreases of DGRV. On interannual timescale, the frequency of extreme DGRV was significantly correlated with TC influence days. Our findings indicate that the frequency of extreme DGRV profile in Tridacna squamosa shells has potential to be a novel recorder for past TC activity. We conclude that fossil shells in different geological eras offer the potential to extend modern instrumental datasets and provide opportunities for investigating TC activity in response to past and future global change.

How to cite: Zhao, N., Yan, H., Luo, F., Yang, Y., Liu, S., Zhou, P., Liu, C., and Dodson, J.: Daily growth rate variation in Tridacna shells as a record of tropical cyclones in the South China Sea: Palaeoecological implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2804, https://doi.org/10.5194/egusphere-egu24-2804, 2024.

The annual temperature cycle is an important component of the Earth’s climate system. Here, the multiple snapshots sea surface temperature (SST) seasonality during past ~1600 years of northern South China Sea were reconstructed using monthly resolved δ¹⁸O and Sr/Ca profiles of fossil Tridacna and  coral skeletons. The results showed SST seasonality in northern SCS was contrary to temperature of China mainland and West Pacific Warm Pool, with a large seasonality during cold period (Little Ice Age, Dark Ages Cold period) and a small seasonality during warm period (Medieval Climate Anomaly). During Little Ice Age and Dark Ages Cold periods, strong East Asia Winter Monsoon (EAWM) and La Niña-like state of tropical Pacific Ocean promote a cold winter, and thus induce a large SST seasonality of northern SCS. During the Medieval Climate Anomaly, weak East Asia Winter Monsoon (EAWM) and El Niño-like state of tropical Pacific Ocean promote a warm winter, and thus induce a small SST seasonality of northern SCS.

How to cite: Liu, C., Yan, H., Zhou, P., Wang, G., Zhao, N., and Han, T.: Seasonality in northern South China Sea during the late Holocene, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2805, https://doi.org/10.5194/egusphere-egu24-2805, 2024.

Earth’s climate history serves as a natural laboratory for testing the effect of (very) warm climates on the biosphere. The Cretaceous period featured prolonged intervals of greenhouse climates characterized by high atmospheric CO₂ concentrations and mostly ice-free poles (O’Brien et al., 2017; Ladant and Donnadieu, 2016). In such a climate, shallow seas in low latitudes likely became very hot, especially during the summer (Jones et al., 2022; de Winter et al., 2021). At the same time, life seems to have thrived there in reef-like ecosystems built by rudists, an extinct group of bivalve mollusks (Gili and Götz, 2018). The summer temperatures documented for these ecosystems exceed the maximum tolerable temperatures of any marine mollusk alive today, which raises the question how these animals adapted to more extreme temperatures.

Studying the growth of these ancient organisms and the extreme climate conditions they faced can yield valuable insight into the resilience of marine ecosystems to climate change. To tackle this climate resilience conundrum, we present a detailed sclerochronological (incrementally sampled) dataset of daily to seasonal scale variability in shell chemistry from fossil mollusks from a Campanian (75-million-year-old) low-latitude shallow marine ecosystem. With it, we investigate the extreme climate conditions these animals lived through and how this affected their growth or even the paleo-weather patterns they experienced. The goal of this study is to demonstrate how high-resolution geochemical records through fossil mollusk shells can shed light on the variability in past warm ecosystems and open the discussion about the limits of life in the shallow marine realm during a greenhouse climate.

Gili, E. and Götz, S.: Treatise Online no. 103: Part N, Volume 2, Chapter 26B: Paleoecology of rudists, 1, https://doi.org/10.17161/to.v0i0.7183, 2018.

Jones, M. M., Petersen, S. V., and Curley, A. N.: A tropically hot mid-Cretaceous North American Western Interior Seaway, Geology, 50, 954–958, https://doi.org/10.1130/G49998.1, 2022.

Ladant, J.-B. and Donnadieu, Y.: Palaeogeographic regulation of glacial events during the Cretaceous supergreenhouse, Nat Commun, 7, 12771, https://doi.org/10.1038/ncomms12771, 2016.

O’Brien, C. L., Robinson, S. A., Pancost, R. D., Sinninghe Damsté, J. S., Schouten, S., Lunt, D. J., Alsenz, H., Bornemann, A., Bottini, C., Brassell, S. C., Farnsworth, A., Forster, A., Huber, B. T., Inglis, G. N., Jenkyns, H. C., Linnert, C., Littler, K., Markwick, P., McAnena, A., Mutterlose, J., Naafs, B. D. A., Püttmann, W., Sluijs, A., van Helmond, N. A. G. M., Vellekoop, J., Wagner, T., and Wrobel, N. E.: Cretaceous sea-surface temperature evolution: Constraints from TEX 86 and planktonic foraminiferal oxygen isotopes, Earth-Science Reviews, 172, 224–247, https://doi.org/10.1016/j.earscirev.2017.07.012, 2017.

de Winter, N. J., Müller, I. A., Kocken, I. J., Thibault, N., Ullmann, C. V., Farnsworth, A., Lunt, D. J., Claeys, P., and Ziegler, M.: Absolute seasonal temperature estimates from clumped isotopes in bivalve shells suggest warm and variable greenhouse climate, Commun Earth Environ, 2, 1–8, https://doi.org/10.1038/s43247-021-00193-9, 2021.

How to cite: de Winter, N., Arndt, I., Claeys, P., Fraaije, R., al Fudhaili, N., Goderis, S., Jagt, J., López Correa, M., Munnecke, A., Stolarski, J., Vanhaecke, F., and Ziegler, M.: Living on the edge: How did shallow-marine ecosystems thrive during hothouse climates?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7323, https://doi.org/10.5194/egusphere-egu24-7323, 2024.

Because our modern world is characterized by climate change, it is useful to study climate conditions of past greenhouse worlds in order to obtain a better understanding of what a similar world would entail. An example of such a past greenhouse climate is represented by the Late Maastrichtian Warming Event (LMWE), a global temperature increase of approximately 2.5-5°C that occurred 300-100 kyr prior to the Cretaceous-Paleogene boundary meteorite impact and the ensuing mass extinction. This warming event has traditionally been linked to a major pulse of Deccan Traps volcanism. Previous research has also recorded the LMWE in the Maastrichtian type region (SE Netherlands, NE Belgium), where this event is marked by characteristic blooms of the dinoflagellate Palynodinium grallator and a sudden appearance of hermatypic corals. A recent study using clumped-isotope analyses on fossil bivalves has shown that the LMWE was characterized by a 5 degrees warming in average annual sea water temperatures in this region (40° paleolatitude). However, little is known about changes in seasonality across this warming event, as high-resolution paleoseasonality reconstructions have not been previously attempted. Here, we present a seasonal, stable-isotope record through the LMWE for the Maastrichtian type area (SE Netherlands, NE Belgium), using stratigraphically well-constrained oyster specimens. This new record contributes to our understanding of the effects of a global warming event on seasonality in a mid-latitude shelf sea. Consistent with previous results, we have found a decreasing trend in δ¹⁸O values in the interval corresponding to the peak of the warming event, followed by an increase during the cooling-down period. Our results show that the LMWE also had profound effects on the seasonality in the Maastrichtian type area. The δ¹⁸O seasonality temporarily decreased at the onset of the event, suggesting that winter temperatures warmed disproportionately. Possibly, this could have allowed the previously recorded establishment of hermatypic corals in the region. Subsequently, seasonality increased again through the warming event, with the highest seasonality recorded in the later part of the event. Over the coming months, additional oyster specimens will be assessed for both stable and clumped isotopes to obtain a more complete record of seasonality throughout the LMWE.

How to cite: Willems, A., Jagt, J. W. M., and Vellekoop, J.: High-resolution paleoseasonality records across the Late Maastrichtian Warming Event (Late Cretaceous) as revealed by oyster shells from the Maastrichtian type area (SE Netherlands, NE Belgium), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7846, https://doi.org/10.5194/egusphere-egu24-7846, 2024.

Whales are critical organisms in the ocean ecosystems, but direct and indirect human impact has decimated their populations. Because whales have long lifespans and migrate over large areas, there is no ecological baseline to evaluate their population dynamics. However, such information is available in fossil whale remains. Geoscientific expertise can aid conservation by interpreting proxy values from the most chemically stable tissue: their teeth. In this project we focus on North Atlantic toothed whales from the late Pleistocene on, with the aim to reconstruct their migrations and ecologies.

Whale teeth contain information about both the individual and its environmental conditions, depending on the proxy that is evaluated. An integrative methodology was developed to be applied on modern and fossil specimens. This includes oxygen isotope analysis to reconstruct migration and bathymetric niches, Sr/Ca and Ba/Ca ratios to assess trophic position and dietary patterns, and Raman spectroscopy for elemental composition and crystallography. Additionally, Scanning Electron Microscopy (SEM) enables growth analysis and measurements of chemical composition through EDX. However, fossil teeth in a marine environment might be altered by diagenesis, making their proxy values unrealistic and not comparable with modern values. By quantifying these changes we can identify and correct for altered proxy values: thus allowing reconstruction of ecologies.

In this initial phase of the project the modern teeth have been analysed using Raman spectroscopy and SEM. Notably, Raman has shown that both the enamel and cementum can be used to produce reliable spectra, while the dentine does not allow this. Chemical composition from the EDX can be assessed over growth layers and correlated with the Raman results. We provide an interdisciplinary framework to assess multiple proxies found in fossil and modern teeth, using geochemical methods to answer biological questions. In addition, we utilize physiological data obtained from stranded individuals whose teeth were sampled, along with historical records of whale populations. There is a large emphasis on anthropogenic impact, by evaluating specimens along a timeline for impact of fishing, whaling, climate change and pollution.

How to cite: Luiten, B., Jarochowska, E., IJsseldijk, L., and King, H.: Whale teeth as witnesses: assessing anthropogenic impact on whale ecology through a multi-proxy analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8293, https://doi.org/10.5194/egusphere-egu24-8293, 2024.

Quantitative reconstructions of past precipitation and temperature variations at the seasonal scale are essential for understanding East Asian Monsoon (EAM) dynamics. However, archives capable of capturing seasonal climate signals on land are limited. Here, we present high-resolution stable oxygen isotope (δ¹⁸O_shell) and carbonate clumped isotope (Δ₄₇) data from modern and fossil land snail shells collected from the eastern (Lingbao, LB) and western (Yuanbao, YB) edge of the Chinese Loess Plateau (CLP).

The δ¹⁸O_shell of modern snails similarly reflect the seasonal variation in precipitation oxygen isotopic signals at both locations. The Δ₄₇-derived temperatures for the same snails indicate that the seasonal temperature difference (summer vs. winter) is larger at YB than LB, aligning with modern observations from the western edge of the CLP, where a higher elevation results in a larger seasonality. The averaged whole shell Δ₄₇-derived temperatures (T₄₇) from modern Cathaica pulveritrix shells at LB and their related Cathaica richthofeni snails at YB resemble growing season temperatures. Interestingly, the T₄₇ of shells of three smaller snail species, Pupilla muscorum, Kaliella lamprocystis, and Vallonia sp. are substantially (up to 10 ºC) lower than those of C. richthofeni from the same site. The temperature difference between snail species and among specimens suggests that optimal living conditions and micro-environments likely play a key role in the temperature signal recorded in the snail shells.

Fossil snails from LB show a larger variability in δ¹⁸O_shell  during the Last Glacial Maximum (LGM, 19–18 ka), with wet season values approximately 3‰ more depleted than modern shells. In contrast, the seasonal temperature difference in fossil snails is smaller than in their modern counterparts, and growing season temperatures are ~10 °C lower than the present at LB. Fossil shells from YB also have a more negative δ¹⁸O_shell during the last deglaciation (14‒13 ka) than their modern counterparts. Similar to LB snails, the whole shell T₄₇ of fossil snail shells at YB indicates that growing season temperatures were ~10 °C lower than recorded by their modern counterparts, and the temperature variability on a seasonal scale is smaller than in modern snails. The relatively large variability, negative δ¹⁸O_shell values and low T₄₇ values in fossil shells suggests weaker evaporation or longer water vapor transportation under glacial conditions. While snail shells can capture high-resolution climate signals, variations in living conditions and micro-environments among snail species and specimens should be considered in future Δ₄₇-based temperature studies and their applications.

How to cite: Guo, J., Zong, X., Yang, W., Dong, J., de Winter, N., Yan, H., Song, Y., Sun, Y., Peterse, F., and Ziegler, M.: Seasonal scale records of hydroclimate and temperature derived from clumped isotopes of land snail shells from the Chinese Loess Plateau , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8416, https://doi.org/10.5194/egusphere-egu24-8416, 2024.

Conservation paleobiology (CP) is a relatively new, synthetic field of research that combines paleontology theories and analytical methods to address current issues related to conserving and managing biodiversity and understanding long-term present-day ecosystem dynamics.  

This research focuses on the latter aspect of CP and investigates how macrobenthic communities have responded to climate change in the past in the Pleistocene marine setting of Montalbano Jonico (Bradanic Trough, southern Italy). Specifically, being a SABS, the Montalbano Jonico Ideale Section presented a significant opportunity to explore past macrobenthic environmental dynamics of shelf marine environments in a data-rich and well-known environmental and stratigraphic framework.

We quantified responses of shelf macrobenthic assemblages to long-term climate changes using 29 samples (∼ 3,975 fossil remains) retrieved along the SABS, deposited between MIS 20 and MIS 18. Previously established paleo-bathymetric reconstructions indicate shelf environments during cold periods (glacials and stadials), which alternated with deeper settings (outer shelf/slope) during warmer phases (interstadials), reflecting the orbitally-driven climate shifts registered by stable oxygen isotopes.

Shelf macrobenthic assemblages naturally alternated between two states over observed long-term climate oscillations. Cold climate faunas were characterized by lower species richness and negligible abundance of species exclusive to the Mediterranean-to-Lusitanian regions compared to warm interstadial assemblages. The high similarity between cold climate assemblages and the distinct composition and abundances of interstadial faunas suggests that, over millennial timescales, shelf benthic assemblages have been primarily structured by environmental forcing, proving either remarkable resilience or persistence in the face of significant environmental and climatic perturbations.

In addition, being the interglacial MIS 19 a climate analog for future climate change, paleobiologic features (e.g., standardized richness or amount of most abundant taxa) might serve as an ecological baseline for the near future.

While biomonitoring, ecological data, and strategies are the main avenues for conservation and ecosystem management, conservation paleobiological approaches can provide unique insights from the recent past into biodiversity dynamics and ecosystem structure of present-day ecosystems that would have otherwise gone unnoticed.

How to cite: Scarponi, D., Cervellieri, M., Crippa, G., La Perna, R., Girone, A., Maiorano, P., and Marino, M.: Conservation paleobiology of the Montalbano Jonico succession (southern Italy): A Standard Auxiliary Boundary Stratotype (SABS) for the Middle Pleistocene of the Quaternary System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9658, https://doi.org/10.5194/egusphere-egu24-9658, 2024.

Stable isotope sclerochemistry of mollusks and otoliths is key in reconstructing temperature and seasonality in past greenhouse climates. It is therefore crucial to understand the paleoecology and –environment of these organisms, and how these factors influence intra-and inter-taxon isotope variability and variation. To gain more insights in these factors, we measured seasonal changes in δ¹⁸O and ^δ13C compositions in multiple specimens of two carditid bivalve species, a turritelline gastropod species, and two species of otoliths from demersal fish, from two successive early Eocene (latest Ypresian, 49.2 Ma) coquinas in the inner neritic Aalter Sand Formation, located in the Belgian part of the southern North Sea Basin (paleolatitude ~41°N). Results demonstrate variability among taxa in average, amplitude and shape of intra-annual δ¹⁸O and δ¹³C values. This intertaxon variability is at least partly caused by growth cessation during winters in turritellines and otoliths, leading to an incomplete representation of the seasonal cycle in their growth increments, compared to carditid bivalves. Other contributing factors to isotopic variability include sedimentary transport, mobility, and the lifespan of the specimens. Specifically, ophidiid fish otolith isotope records appear to reflect environmental conditions over a wider range of habitats and environments, due to sedimentary transport and postmortem transport by free-swimming predatory fish. Our study therefore highlights the variability between different taxa and environments in the shallow marine realm, which has implications for seasonality reconstructions. Studying multiple taxa and specimens in a death assemblage provides a more complete spectrum of isotope variation and variability.

How to cite: Vellekoop, J., Vanhove, D., Jelu, I., Claeys, P., Ivany, L. C., de Winter, N. J., Speijer, R. P., and Steurbaut, E.: A comparison of bivalve, gastropod and fish otolith stable isotope profiles from the Aalter Sands, early Eocene southern North Sea Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9755, https://doi.org/10.5194/egusphere-egu24-9755, 2024.

The consequences of prolonged human stressors on populations of marine benthic species are generally difficult to assess due to the paucity of long-term monitoring data. The youngest fossil record, preserved in sediment cores and grab samples, provides a rich historical archive that allows tracking ecological responses to natural environmental changes and reconstructing the state of populations prior to the onset of anthropogenic impacts. However, most studies using these paleoecological records focus on microfossil- or mollusc assemblages, and only limited knowledge is available on the responses of other key components of marine ecosystems, such as echinoids. This study presents a novel record of well-preserved tests of the infaunal clypeasteroid Echinocyamus pusillus from Holocene marine sediment cores, which provide new insights into the long-term population dynamics and ecological responses of the widely distributed echinoid. We investigated trends in test size and abundance of E. pusillus and relate them to sedimentological conditions during the last ~11,000 years in the shallow northern Adriatic Sea, where coastal marine habitats have been under prolonged anthropogenic pressure. We combined these data with radiocarbon dating of multiple specimens to extract ecological signals from time averaged assemblages. The sediment cores and grab samples collected from four stations, which cover different benthic habitats, document environmental changes during the post-glacial transgression and the Holocene-Anthropocene transition, as evidenced by shifts in molluscan assemblages and geochemical proxy records. The data suggest significant fluctuations in E. pusillus abundance, but remarkably stable test sizes over the past millennia and across sampling stations. Moreover, the age-dating results indicate a paucity of dead tests originating from the late 19^th and 20^th centuries in the surface mixed layer. This points to a strong decline in test production and thus population densities over the past ~200 years. This pattern can be linked to pronounced environmental changes during the onset of the Anthropocene, including siltation, eutrophication, and increased frequency of hypoxic events. Rapid decline of populations during that time combined with temporal mixing of fossil assemblages may thus explain the overall lack of body size shifts observed in sediment cores. Our results provide a fundamental baseline for evaluating temporal and spatial changes in body size and abundance of E. pusillus in the northern Adriatic Sea. They can be compared with recent monitoring and fossil data from other areas and serve to disentangle natural population variability from responses to recent intensification of human impacts.

How to cite: Bachmann, B., Nawrot, R., and Zuschin, M.: Impact of Holocene environmental change on northern Adriatic populations of Echinocyamus pusillus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11757, https://doi.org/10.5194/egusphere-egu24-11757, 2024.

Global warming is leading to more persistent boreal summers in the Northern Hemisphere, characterised by a longer season with more extreme heat waves. These seasonal changes have already led to many ecological and socio-economic implications. Statistical significance between summer weather persistence and its potential drivers is weak due to the short instrumental period, in turn preventing skilful predictions. In this study, we develop a new proxy for seasonal weather persistence based on varve thickness measurements to extend observations further back in time. We used two lakes, Nautajärvi in Finland and Diss Mere in England, which provide i) a continuous, seasonally resolved varved records that cover most of the Holocene Epoch; ii) a detailed understanding of the annual depositional varve model supported by lake monitoring, demonstrating that the seasonal sedimentation responds to summer and winter-type weather conditions; and iii) a consistent varve structure over the entire study period, so data are comparable through time. In both lakes, the varve model is made of two seasonal layers, representing the limnological summer and winter. The thickness of the seasonal layers indicate either the length of the season (i.e. longer period of sedimentation) and/or occurrence of extreme events (e.g. intensification of the sedimentological process). This agrees with the definition of seasonal weather persistence, which refers to either stationarity or recurrence of characteristic surface weather or atmospheric circulation of a season. In order to estimate the relative persistence of the summer and winter season over a year, we calculate the percentage of the winter and summer layers contributing to the varve (annual) thickness in the two lakes. Our results show that the early and late Holocene annual mean climate was controlled by winter weather variability, while the mid-Holocene has a predominant summer component. The Holocene winter-summer-winter weather pattern in Europe follows the evolution of the regional latitudinal temperature gradient (LTG) supporting current hypothesis that a weakening of the LTG in response to Global Warming is the origin of more persistent summers today.

How to cite: Martin-Puertas, C., Boyall, L., Hernandez, A., Ojala, A., Abrook, A., Kosonen, E., Lincoln, P., and Swingedouw, D.: Estimation of seasonal weather persistence during the Holocene from varved records, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12809, https://doi.org/10.5194/egusphere-egu24-12809, 2024.

Otoliths, the calcified biominerals in the inner ear of teleost fishes, provide a unique opportunity to investigate changes in growth parameters in historical fish populations as they are preserved in large numbers in marine sediments. They exhibit species-specific morphology and serve as life history archives, as they grow continuously in a concentric fashion by the accretion of alternating mineral- and protein-rich layers around a core, making them valuable for ecological and palaeontological studies. We employ sclerochronological analyses on otoliths from fish sampled alive as well as on radiocarbon-dated fossil otoliths derived from a sediment core off the coast of Piran, Slovenia. We want to verify the accuracy of historical growth patterns, which is fundamental to reconstructing reliable long-term chronologies and drawing meaningful conclusions about past fish growth dynamics. We focus here on the non-commercial but very common demersal species, the black goby (Gobius niger Linnaeus, 1758) which inhabits the Adriatic shelf regions in large numbers today and in the Holocene. We aim to test the hypothesis that growth rates and subsequently body sizes of these non-commercial fishes have undergone changes during the late Holocene and Anthropocene in the northern Adriatic Sea due to climate-induced environmental perturbations.

Before applying growth modeling to the fossil otoliths, it is crucial to ensure the preservation and reliability of the incremental record. Accordingly, we employ a comprehensive approach by comparing modern and Holocene gobiid otoliths using visual, structural and microchemical techniques. Our coupled approach includes light microscopy (LM), backscatter electron (BSE) imaging, electron backscatter diffraction (EBSD), and electron probe microanalysis (EPMA). We analyse macro- and micro-optical features, crystallographic structures, and chemical variations within the otolith incremental record. We use a novel technique to determine the geological ages of the fossil specimens in which we cut the otoliths in half, allowing sclerochronological analysis and radiocarbon dating on the same specimen.

Our visual and microchemical analyses revealed that key microincremental features are well preserved in the Holocene otoliths, enabling a direct comparison with modern counterparts. Despite occasional diagenetic alterations that potentially hinder incremental analysis in some of the Holocene specimens, bipartite incremental features, which are essential for growth analysis, are well preserved in both sets of otoliths. Additionally, visual and microchemical patterns indicate that modern otoliths exhibit partially vateritic structures.

Our study bridges the temporal gaps by directly comparing modern and fossil otoliths from the same species and study area. This approach reveals the hidden details in their microstructures and helps to establish a potential growth baseline for fish living in pre-industrial times. By examining historical fish size and growth patterns in populations living before significant human-induced environmental changes, we are providing insights into the effects of climate change on fish populations, which is important for fisheries management and conservation.

How to cite: Leonhard, I., Jarochowska, E., Nawrot, R., Lipej, L., Agiadi, K., and Zuschin, M.: Unveiling past and present fish growth patterns using an integrated structural, microchemical and geochronological analysis of modern and fossil otoliths , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15553, https://doi.org/10.5194/egusphere-egu24-15553, 2024.

Anthropogenic disturbances such as pollution, eutrophication and increased frequency of hypoxia led to profound changes in the abundances of marine species and overall community structure. They also led to changes in the population size structure of some species, a phenomenon still little understood. In this project, we use data from sediment cores to document long-term changes in population size structure of two common mollusc species of soft bottom communities of the northern Adriatic Sea (NAS): the bivalve Varicorbula gibba (Olivi, 1792) and the gastropod Turritellinella tricarinata (Brocchi, 1814) (= Turritella communis Risso, 1826). They are similar in their habitat preferences, but V. gibba is an opportunistic species with a higher tolerance of natural and anthropogenic disturbances. Ecological monitoring and analyses of sediment cores have shown that T. tricarinata was replaced by V. gibba as the dominant species of soft bottom communities in the NAS during the 20^th century, probably due to increased eutrophication and a higher frequency of hypoxia. It has also been shown that V. gibba did increase in average size.

We test whether size changes have also occurred in T. tricarinata using material from sediment cores from the area off the Po delta in the western-, and Panzano and Koper Bays in the eastern NAS. The cores capture the last 150 to 7,000 years depending on the location. Measurements of shell length and width are used to analyze population size structure. Changes in sediment composition and geochemical proxies of pollution and eutrophication are studied as possible drivers of size changes and are placed in a chronological framework based on radiocarbon-dated shells.

Our preliminary results indicate that although abundance of T. tricarinata decreased throughout the region in the second half of the 20th century, shell length increased in some stations during that time. This pattern contrasts with the results of previous studies, which suggested that larger specimens of molluscs are more vulnerable to hypoxia. Our results may reflect complex interactions between nutrient enrichment and oxygen availability in controlling population dynamics of this species. However, more data are necessary to document long-term trends in population size structure driven by natural environmental change and to establish a baseline for size variability in T. tricarinata and V. gibba in the NAS prior to increased anthropogenic impact. Our study will provide a better understanding of how population size structure of marine benthic species changes in response to anthropogenic disturbances.

How to cite: Schweigl, L., Nawrot, R., Tomašových, A., and Zuschin, M.: Effect of Holocene environmental change on the size structure of mollusc indicator species of the northern Adriatic Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17629, https://doi.org/10.5194/egusphere-egu24-17629, 2024.

The northern Adriatic Sea is one of the most degraded marine ecosystems worldwide and has been under anthropogenic influence for many centuries. Reconstructing pre-human impact benthic communities is vital to establish baseline conditions, allowing a better understanding of how anthropogenic activities and climate warming have influenced and altered marine ecosystems over time. This historical context helps to assess the extent of anthropogenic influence, guiding future conservation efforts and management strategies.

Our primary goal is to uncover the composition of pre-human impact benthic communities on the shallow shelf along the Slovenian coast (Gulf of Trieste) and to reconstruct the natural state of these habitats.

This investigation involved systematic grab sampling of subtidal soft substrates across three distinct areas, encompassing eight stations in the Bay of Koper and Bay of Piran, at water depths ranging from seven to ten meters. We focus on analyzing the composition of mollusc death assemblages, time-averaged accumulations of empty shells present in the uppermost mixed layer of seafloor sediments. Due to high durability of these skeletal remains and generally low sedimentation rates in shelf environments, death assemblages integrate shells over time spans of decades to millennia, making them valuable natural archives of past community states. Our results show that samples collected near the major port of Koper are strongly dominated by the opportunistic and stress-tolerant bivalve Varicorbula gibba, and show significantly lower species richness compared to stations located further away from this potential source of environmental disturbance. Moreover, assemblages from the protected area of the Debeli rtič are compositionally distinct from those of other areas. These patterns likely reflect the combined effects of differential levels of anthropocentric impacts, as well as differences in substrate characteristics and the magnitude of time averaging of the death assemblages among sampling stations.

The obtained community data will be cross-checked with live assemblage data based on the systematic benthic monitoring efforts conducted over the last 15 years (2005–2020) to ascertain changes in the mollusc community. The examination of modern and historic data will provide a robust long-term baseline that is essential for understanding and quantifying the impacts of significant human-induced modern stressors on the northern Adriatic marine ecosystem.

How to cite: Pavlović, M., Nawrot, R., Steger, J., Mavrič, B., and Zuschin, M.: Establishing ecological baselines for benthic communities in the southern Gulf of Trieste (northern Adriatic Sea) using molluscan death assemblages, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22064, https://doi.org/10.5194/egusphere-egu24-22064, 2024.

Parasites play an essential role in maintaining healthy ecosystems. However, as human activities continue to degrade the environment and contribute to climate change, it is essential to understand if and how parasite-host interactions has been affected. In this study, we examined the relationship between the bivalve species Chamelea gallina and trematodes. Trematodes are a group of parasites with no significant body fossil record. We analyzed the dynamics of the trematode population, including its diversity, prevalence, pit size, and pit aggregation, by studying 193 infested valves and 838 pits retrieved in fossil and dead assemblages of C. gallina from Adriatic Sea Basin (Italy). The samples were collected from Late Holocene marine succession (~3 ky cal B.P. with sub-centennial error) and thanatocoenosis from the modern seabed. Our analysis based on Gaussian finite mixture modeling shows no decrease in the number of trematode taxa infesting C. gallina over the past 3000 years. However, the prevalence of trematode infestation decreased significantly over time (one order of magnitude), along with the average number of pits, median size, and parasite pit aggregation. These changes suggest a severe decline (or collapse) of the trematode-C. gallina interaction in the Adriatic Sea during a time of increasing human influence on this land-locked basin.

How to cite: Huntley, J., Fitzgerald, E., Delaney, R., and Scarponi, D.: Conservation paleobiology: Reconstructing the baseline of parasitic-host interaction for Chamelea gallina in the Northern Adriatic., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22193, https://doi.org/10.5194/egusphere-egu24-22193, 2024.

The late Neogene was a time of climate transition in North-African waters, as shown by early Messinian ostracod assemblages recorded both in the Southern Mediterranean (Gulf of Gabès, Tunisia) and in Atlantic (Northwestern Morocco) sites. A cooling trend since the Burdigalian-Langhian Miocene Climate Optimum culminated in the late Miocene, approximately coinciding with the the progressive closure of the connections between Atlantic and Proto-Mediterranean that induced the Messinian Salinity Crisis. During this event all the marine taxa disappeared from the Mediterranean. Some late Miocene ostracods, presently living in shallow tropical western African waters, and not occurring in modern temperate-subtropical environments, re-entered from the Atlantic in the early Pliocene, when the Mediterranean returned to be a fully marine sea. In this number are included the genera Carinovalva and Ruggieria, that became extinct in the Mediterranean during the late Pliocene or in the Pleistocene, possibly coinciding with major cooling phases. Conversely, the genus Chrysocythere was not able to recolonize the Mediterranean waters, probably due to the Pliocene shallow water subtropical-temperate temperatures in the area of the Strait of Gibraltar. Several Miocene endemic Proto-Mediterranean tropical species and a number genera, (e.g.: Syrtica, Okadaleberis, Dallonella), went completely extinct due to the Messinian Salinity Crisis.

How to cite: Mazzini, I., Parisi, R., Aiello, G., Barra, D., and Padma Vitolo, J.: Late Neogene cooling and the disappearance of tropical ostracod taxa in the Mediterranean-Atlantic Region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22498, https://doi.org/10.5194/egusphere-egu24-22498, 2024.