The region offshore Cape Blanc, NW Africa, is one of the most productive zones in the world’s oceans due to the occurrence of an eastern boundary upwelling system and dust input from the Sahara. It is also a well-known site for benthic foraminiferal research, where vertical zonation of the living foraminifera was first described in detail. However, earlier studies are based only on >150μm or >250μm specimens collected along one transect. Therefore, the relative proportion of the smaller, phytodetritus-related species (e.g., Alabaminella, Epistominella) is likely underestimated. This region was also the focus of foraminiferal stable carbon isotope (δ¹³C) studies.

However, previous area works concentrated either on the sea surface or on the deep-water signals and their oceanographic meaning. Thus, there is a lack of data linking these two realms.

Here we investigated foraminiferal assemblages, δ¹³C determinants, patterns, and shifts from the continental shelf to the abyssal plain. We analyzed ca. 360 samples from 12 multicore split in two parallel depth transects from ca. 100 to 3400 m water depth. The topmost 10 cm of each multicore was sampled in 1 cm intervals. We analyzed the δ¹³C composition of benthic species Cibicidoides wuellerstorfi (epifauna) and Uvigerina peregrina (infauna), as well as planktonic species Globigerinoides ruber white (>150 μm).  Benthic and planktonic foraminiferal assemblages (>63 μm) were also determined.

The δ¹³C difference between the sea-surface and the ocean-floor values (∆δ¹³C_{G. ruber white - C. wuellerstorfi}) do not show notable changes along the two studied transects. However, the δ¹³C difference between the epifaunal and the infaunal species (∆δ¹³C_{C. wuellerstorfi - U. peregrina}) shows a major increase from the continental shelf to the abyssal plain. Moreover, the benthic and planktonic foraminiferal assemblages present vertical and horizontal zonation related to the environmental parameters (e.g., oxygen, temperature, nutrients) and this is in accordance with the changes observed in geochemical signals showcasing a faunal and δ¹³C shift from the shore to the abyssal plain.

Our findings argue for different determinants of δ¹³C off Cape Blanc. In the nearshore (ca.100-1500 m water depth) the main control is mineral-rich dust input from the Sahara, while below this depth and further away from the continental shelf lateral advection plays the dominant role.

How to cite: Botond-Árpád, L., Cristiano Mazur, C., Stefano, C., Karin, Z., and Lóránd, S.: Determinants on foraminiferal stable carbon isotopes offshore Cape Blanc, NW Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20351, https://doi.org/10.5194/egusphere-egu24-20351, 2024.

The Last Glacial Maximum (23,000 – 19,000 years ago; LGM) is the most recent time when Earth’s climate was fundamentally different from today. The LGM hence remains an important target to evaluate climate models under boundary conditions different from today. Evaluation of paleoclimate simulations is mostly done using proxy-based reconstructions. However, such reconstructions are indirect and associated with marked uncertainty, which often renders model-data comparison equivocal. Here we take a different approach and use macro-ecological patterns preserved in fossil marine zooplankton to evaluate simulations of LGM near-surface ocean temperature.

We utilise the distance-decay pattern in planktonic foraminifera to evaluate modelled temperature gradients. Distance decay emerges because of differences in habitat preferences among species that cause the compositional similarity between assemblages to decrease the further apart they are from each other in environmental space. Distance decay is a fundamental concept in ecology and is observed in many different taxa and ecosystems, including planktonic foraminifera that show a monotonous decrease in similarity with increasing difference in temperature. Because the ecological niches of planktonic foraminifera are unlikely to have changed since the LGM, the distance-decay relationship based on simulated LGM temperatures and LGM assemblages should in principle be identical to the modern distance decay pattern. Thus we can use fossil planktonic foraminifera species assemblages to evaluate climate model simulations based on ecological principles.

Our analysis is based on an extended new LGM planktonic foraminifera database (2,085 assemblages from 647 unique sites) and a suite of 10 simulations from state-of-the-art climate models (PMIP3 and 4). We find markedly different planktonic foraminifera distributions during the LGM, primarily due to the equatorward expansion of polar assemblages at the expense of transitional assemblages. The distance-decay pattern that emerges when the LGM assemblages are combined with simulated ocean temperatures is different from the modern pattern. All simulations suggest large thermal gradients between regions where the planktonic foraminifera indicate no, or only weak, gradients. This pattern arises from the pronounced shift to polar species assemblages in the North Atlantic where the simulations predict only moderate cooling. In general, the models predict spatially rather uniform cooling, whereas the microfossil evidence suggests more pronounced regional differences in the temperature change. The difference between reconstructions and the simulations reaches up to 10 K in the North Atlantic.

Importantly, simulations with a reduced AMOC and hence lower North Atlantic near sea surface temperatures, yield a distance-decay pattern that is much more similar to the modern pattern. The planktonic foraminifera assemblages thus question the view of the LGM ocean as an equilibrium response to external forcing. Our method opens up new avenues to evaluate climate model simulations in other settings using fundamental ecological patterns.

How to cite: Jonkers, L., Laepple, T., Rillo, M., Dolman, A., Shi, X., Lohmann, G., Paul, A., Mix, A., and Kucera, M.: Climate model evaluation based on ecological principles: using fossil plankton biodiversity patterns to probe simulated thermal gradients in the ice age North Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19366, https://doi.org/10.5194/egusphere-egu24-19366, 2024.

Nearshore coastal areas are subject to harsh conditions, being shaped by continuous wave action and exposed to turbulence, erosion, and dynamic processes of sediment reworking. Situated at the interface between land and water, the environmental signatures preserved in microfossil assemblages from coastal environments are often prone to taphonomic alterations, which potentially bias the fossil record and compromise accurate reconstructions. The preservation and composition of microfossil assemblages, however, is of highest importance for paleoenvironmental and paleoclimatic reconstructions.

We have analyzed benthic foraminiferal assemblages from a suite of extremely shallow-water habitats along the Dhofar coastline (Oman) to assess their value for paleoenvironmental reconstructions and inferences. Foraminiferal assemblages from these extremely shallow and turbulent water habitats face hostile conditions to their existence and preservation, where the formation of dead assemblages is the result of postmortem processes, among which out-of-habitat transport and the destruction and disintegration of tests are most significant. We examined habitat-specific samples from extreme shallow-water areas to: (1) illustrate and document the species richness and preservation status of foraminiferal assemblages, (2) assess whether the foraminiferal biotas preserve sufficient environmental information to be useful for paleoenvironmental inferences, and (3) provide novel insight into the diversity and composition of benthic foraminifera along the varied habitats of the southern Oman coast. Our analyses show that extremely shallow foraminiferal assemblages from the southern coast of Oman retain the environmental signatures of their habitats despite intense environmental processes, making them useful for paleoenvironmental studies. Features of these signatures are recorded in the structural composition, species richness, dominance, and diversity indices of foraminiferal communities, in addition to numerical abundances of shell preservation groups.

How to cite: Langer, M. R., Trubin, I. S., and Kamoun, M.: Environmental Signatures Preserved In Extremely Shallow-Water Benthic Foraminifera From Oman, Arabian Sea , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2889, https://doi.org/10.5194/egusphere-egu24-2889, 2024.

The eastern north Atlantic hosts a volumetrically important oxygen minimum zone (OMZ) influenced by the subtropical ocean circulation in the area and the upwelling off NW Africa. Ocean warming related to the increase in greenhouse gases and coastal eutrophication due to anthropogenic activity, leads to ocean deoxygenation and OMZs expansion. This makes relevant to study of the north Atlantic middle depth variability analogs in past climate change scenarios, to understand the future of the north Atlantic OMZ. During this study, we used benthic foraminifera from site GeoB9512-5 (793 m water depth) off NW Africa to reconstruct the bottom water oxygen concentration changes in the north Atlantic OMZ during the last 27,000 years. This high-resolution record registered an enhanced OMZ during the Bølling–Allerød (B-A) and Holocene that declined during the Heinrich Stadial 1 (HS1) and Younger Dryas (YD). These shifts are related to changes in bottom water ventilation and organic matter concentrations during the last deglaciation. Low benthic foraminifera diversity is synchronous with the oxygen decline of the B-A and Holocene, and benthic foraminifera assemblages show relevant changes consistent with these oxygenation shifts seen in our site. We provide new evidence of potential north Atlantic OMZ expansion in times of reduced bottom water ventilation during the B-A and Holocene times. This changes were driven by the shifts in the subtropical circulation during the last deglaciation registered in previous studies, and are relevant for understanding the future of OMZs in a climate change scenario and its possible consequences for marine biodiversity.

How to cite: Barragán Montilla, S. and Reyes Macaya, D. A.: Deglacial North Eastern Atlantic Oxygen Minimum Zone changes registered by Benthic foraminifera, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3023, https://doi.org/10.5194/egusphere-egu24-3023, 2024.

The marine nitrogen cycle is being altered on a global scale by increasing anthropogenic production and use of chemical fertilizers. Nitrate (NO₃⁻) is an important macronutrient that is limiting in some marine environments. Modelling studies have predicted increased NO₃⁻ concentrations during glacial periods due to reduced water column denitrification as compared to interglacials. The aim of our study is to provide a widespread, quantitative reconstruction of bottom-water NO₃⁻ concentrations ([NO₃^-]_BW) in the intermediate Pacific covering the last deglaciation. Downcore samples taken from the Eastern Tropical South Pacific in the Gulf of Guayaquil (M77/2-059-1), and Eastern Tropical North Pacific from the Mexican Margin (MAZ-1E-04), Sea of Okhotsk (MDO1-2415), and Gulf of California (DSDP-480) were utilized. We have utilized the pore density of the denitrifying benthic foraminifera Bolivina spissa and Bolivina subadvena as proxy for deglacial [NO₃⁻] concentrations. These shallow infaunal foraminifera species are abundant in oxygen-depleted environments all around the Pacific. They can denitrify and most likely take up NO₃^- as an electron acceptor through the pores, making their pore density an empirical proxy for NO₃^- concentrations. We found that the [NO₃^-]_BW in the Gulf of Guayaquil, Gulf of California, and Mexican Margin were higher during the glacial period than the Holocene. The Gulf of Guayaquil showed a pronounced decrease in [NO₃^-]_BW during the Heinrich Stadial, while the Mexican Margin showed a peak in [NO₃^-]_BW during the entire Younger Dryas. The Sea of Okhotsk core covers only from the Younger Dryas until the middle Holocene, and [NO₃^-]_BW was found to increase from the Younger Dryas to the Holocene. In all cores studied, we also compared past and present [NO₃^-]_BW. Our data shows that both the Gulf of Guayaquil and the Gulf of California had higher [NO₃^-]_BW in the past than today. In contrast, the Mexican Margin and the Sea of Okhotsk had lower [NO₃^-]_BW in the past than today. We speculate that a site-specific balance between reduced water column denitrification, sea-ice retreat, increased nutrient input from continental shelves as a result of sea-level changes, changes in water mass ventilation, a decrease in upwelling productivity, or thermal contrast between land and sea may account for changes in nitrate concentrations during cold-warm periods at the studied sites. A comprehensive understanding about past nutrient cycling under rapidly changing climatic conditions is one prerequisite to predict future changes in marine nutrient budgets in the Eastern Equatorial Pacific.

How to cite: Govindankutty Menon, A., Davis, C. V., Nürnberg, D., Schmiedl, G., and Glock, N.: A quantitative, deglacial reconstruction of bottom-water nitrate in the intermediate Pacific using the pore density of the denitrifying benthic foraminifera , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3095, https://doi.org/10.5194/egusphere-egu24-3095, 2024.

The mid-Brunhes dissolution interval (~533–191 ka) is characterized by various paleoclimatic/paleoceanographic events in the world that occurred mainly at ~400 ka during Marine Isotope Stage (MIS) 11. The duration of MIS 15–12 is important to understand a succession of various paleoclimatic/paleoceanographic events at the onset of the mid-Brunhes dissolution interval (e.g., Birth et al., 2018). For example, MIS 13 was marked by asymmetrical temperature and precipitation between the hemispheres, northward displacement of InterTropical Convergence Zone (ITCZ), and global carbon cycle changes (Ao et al., 2020). We investigated fossil deep-sea benthic foraminifera and sediment geochemistry (11 major elements by XRF analysis) during ~670–440 ka (MIS 16–12) at ODP Site 758 and core GPC03 (2925 m and 3650 m water depth, respectively) in the northeast tropical Indian Ocean (~5°N, ~90°E).

Two multidimensional scaling (MDS) axes were recognized in the benthic foraminiferal faunas. MDS axis 1 is related to the specific depth habitats of benthic foraminiferal faunas possibly with trophic level, whereas MDS axis 2 may be related to the low food supply with episodic food pulses/relatively stable low food flux. The difference of MDS axis 1 between ODP Site 758 and core GPC03 was smaller during ~610–560 ka (MIS 15), whereas it was larger during ~560–480 ka (MIS 14–13). MDS axis 2 showed generally similar stratigraphic variations between the two cores during ~610–560 ka, whereas it was different during ~560–480 ka. The proportion of lithogenic matter to biogenic carbonate was also relatively low during ~610–530 ka under the highstand. Thus, both the lithogenic supply and the depth gradient of benthic foraminiferal faunas between the two cores were changed across MIS 15/14 (~570–540 ka).

At ODP Site 758, the decrease of Globigerina bulloides across MIS 15/14 implies the long-term weakening of wind-driven mixing of the surface water (Chen and Farrell, 1992). It may be caused by the weakening of the Indian summer monsoon at that time, possibly with the northward displacement of the ITCZ (e.g., Ao et al., 2020). In our study area, the depth gradient of the benthic foraminiferal faunas may be controlled by the linkage between the surface and deep oceans that was altered transiently but significantly across MIS 15/14, possibly through the particulate organic matter ballasting by calcareous plankton skeletons and/or lithogenic matter.

How to cite: Takata, H., Ikehara, M., Seto, K., Asahi, H., Lim, H. S., Hyun, S., and Khim, B.-K.: Biotic response of deep-sea benthic foraminifera in the northeast tropical Indian Ocean at the onset of the mid-Brunhes dissolution interval, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4897, https://doi.org/10.5194/egusphere-egu24-4897, 2024.

The Early-Middle Pleistocene Transition (EMPT; 1.4-0.4 Myrs) stands out as one of the most studied intervals in Earth’s recent climate history. Specifically, during the EMPT an increase in the amplitude of climatic fluctuations is registered without proportional changes in the orbital cycles. Nevertheless, the mechanisms and the climatic components responsible for the onset of the EMPT are still under debate.

As high-resolution studies on equatorial to mid-latitude microfossil assemblages during the EMPT are still limited, we performed a detailed benthic foraminifera assemblage work on samples from Site U1460 (eastern Indian Ocean, 27°S, 112°E, 214.5 m water depth), cored during IODP Expedition 356 on the SW sector of the Australian shelf. This site is interested by the presence of warm, calcium carbonate-supersaturated waters, and thus is strongly affected by early-marine diagenesis. Moreover, the studied cores are under the influence of the Leeuwin Current (LC), which, in turn, represents a warm and oligotrophic surface water mass, flowing poleward along the Australian coastline.

Preliminary data record a polyspecific benthic foraminiferal assemblage with high diversity. The first part of the record (MIS 27-23) is dominated by Cibicidoides spp., Heterolepa spp., Trifarina spp., and nodosarids, whereas the most recent cores (MIS 22-16) recorded abundant agglutinated tests (e.g., Gaudryina spp., Spiroplectinella spp., Textularia spp., Spirotextularia spp.), Cibicidoides spp., Siphogenerina spp., Uvigerina spp., and bolivinids. Other common taxa detected throughout the whole record are Lenticulina spp. and lagenids.

Foraminiferal tests resulted to be severely encrusted and their preservation strongly varies between glacial and interglacial intervals. Specifically, benthic specimens show poor to moderate preservation during glacials whereas their preservation increases during interglacial stages.

In addition, planktonic foraminifera were also picked to record the variations of the plankton/benthos (P/B) ratio during the studied time interval. This ratio reflects the eustatic fluctuations of the sea level in the region. Particularly, highstand and lowstand stages correspond to higher and lower values of the P/B ratio, respectively. Furthermore, constraining sea-level variability at Site U1460 will allow detailed reconstructions of LC current behavior during the EMPT. The abovementioned data, together with the evaluation of the benthic assemblage, will permit the determination of the paleobathymetry, as well as of the bottom water conditions at the studied site. The environmental reconstruction based on the benthic foraminifera assemblage during the glacial/interglacial phases will be used to assess the local climatic variations during the EMPT.

How to cite: Arrigoni, A., Piller, W. E., and Auer, G.: The Early-Middle Pleistocene Transition in the eastern Indian Ocean: foraminiferal assemblage, sea-level fluctuations and climate variability on the SW Australian shelf , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16223, https://doi.org/10.5194/egusphere-egu24-16223, 2024.

The exchange of water between the Pacific and Indian Oceans is important in regulating planetary climate. North of Australia, this exchange plays a key role in regulating the Indo-Pacific Warm Pool with far-reaching effects via Indonesian Throughflow (ITF). The exchange south of Australia is far less understood, and much of the exchange occurs at intermediate depths through Tasman Leakage (TL). Here, we investigate Ocean Drilling Program (ODP) Site 752 which was drilled on Broken Ridge. The Site is located within the path of TL, and thus, can provide a paleoceanographic history of TL. Benthic foraminiferal (BF) assemblage is a useful tool to reconstruct paleoceanographic patterns. At ODP Site 752, BF assemblages vary over time but at no point exhibit evidence of extreme stress or oxygen deficiency. Benthic foraminiferal diversity measured with the Fischer Alpha diversity index remains between 5 and 10, indicating moderate diversity throughout the last 9 million years. Furthermore, the high abundance of epiphytic species Cibicidoides wuellerstorfi and Lobatula lobatula likely reflects a high current energy environment over Broken Ridge during this time. Based on our comprehensive benthic foraminiferal assemblage study, we suggest that the driving factor behind the benthic ecological changes on Broken Ridge since the Late Miocene has been TL intensity, distinguished by its kinetic energy. In addition, we present a ~13 Myr neodymium (Nd) isotopic record, suggesting that TL onset likely occurred sometime in the late Middle Miocene, advecting isotopically older Pacific-sourced waters into the Indian Ocean. The latter findings challenge the previously presumed onset of TL at ~7 Ma and indicate a much earlier initiation of TL between 14 – 10 Ma, that intensified during the Late Miocene when the modern-like TL was established.

How to cite: Lyu, J., Barragán Montilla, S., Bialik, O., Christensen, B., Auer, G., Sarr, A.-C., and De Vleeschouwer, D.: Early Initiation of Tasman Leakage and the formation of modern Indian Ocean circulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7569, https://doi.org/10.5194/egusphere-egu24-7569, 2024.

The Eocene sediments of the London and Hampshire basins, which include the Isle of Wight, have long been a challenge for those interested in foraminifera and biostratigraphy. Despite many attempts at creating a viable zonation, this has proven impossible with Bowen (1954) stating that: “it is evident that no zonal scheme can be advanced for the [London Clay] formation base upon foraminifera”.

          Here we present a zonation for the London Clay Formation based on smaller benthic foraminifera (SBF) and, in addition, indicate that the Early Eocene Climatic Optimum (EECO) event may have generated a glacio-eustatic signal. In the same way, using SBF and larger benthic foraminifera (LBF), the Late Lutetian Thermal Event (LLTE) and the Middle Eocene Climatic optimum (MECO) can also be identified, confirming the suggestion of Dawber et al. (2011). The LLTE and MECO events record the most northerly occurrence of numulitids in the UK, with the LLTE event particularly characterised by the northward limit of alveolinids and other LBF. Offshore Selsey Bill, which is east of the Isle of Wight, there is a distinctive carbonate-rich rock that is almost entirely formed of alveolinids and other bioclastic debris. Known since the 19^th century it was, at one time, quarried as a building stone for local use. In the marine area around the Channel Islands, and on the Cotentin Peninsula, there are further occurrences of alveolinids, probably generated by a distinct glacio-eustatic event at this level in the succession. These Early and mid-Eocene glacio-eustatic events clearly pre-date the first, significant, glacio-eustatic event (Oi1) at the Eocene/Oligocene boundary (Westerhold et al., 2020).

Bowen, R.N.C. 1954. Foraminifera from the London Clay. Proceedings of the Geologists’ Association, 65(2), 125–174. https://doi.org/10.1016/S0016-7878(54)80004-6

Dawber, C.F., Tripati, A.K., Gale, A.S., MacNiocaill, C., Hesselbo, S.P., 2011. Glacioeustacy during the Middle Eocene? Insights from the stratigraphy of the Hampshire Basin, UK. Palaeogeography, Palaeoclimatology, Palaeoecology, 300, 84–100.

Westerhold, T., and 23 others, 2020. An astronomically dated record of Earth’s climate and its predictability over the last 66 million years. Science, 369(6509), doi: 10.1126/science.aba6853.

How to cite: Hart, M. and Smart, C.: EECO, LLTE and MECO events in the Eocene succession of the Isle of Wight and adjacent areas., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3605, https://doi.org/10.5194/egusphere-egu24-3605, 2024.

The tremendous biodiversity of tropical reef ecosystems fascinates ecologists and evolutionary biologists alike, yet it is threatened by increasing natural and anthropogenic disturbances worldwide. Meiobenthic biotas on coral reefs, especially ostracods, are poorly understood in terms of their diversity and compositional patterns. This study represents the first large-scale assessment of shallow-marine ostracods from three islands of the Zanzibar Archipelago (Zanzibar, Pemba, Mafia, Tanzania), where the reef ecosystem is highly diverse and productive. We characterized four ecologically distinct ostracod faunas each associated with different benthic habitats, that were deep fore reefs, shallow fringing reefs, degraded fringing reefs and intertidal algae. We identified typical ostracod taxa that showed affinities to hard corals or algae on the reef platforms, respectively. We concluded that water depth and habitat type are likely the most important environmental factors determining the diversity and faunal structure of reefal ostracod assemblages in the tropical, shallow-marine setting. Highest diversity was found on shallow fringing reefs where reefal and algal taxa exhibited maximum overlap of their distributional ranges, while the sand flats, mangrove and marginal reefs within the intertidal zone had much lower diversity with high dominance of euryhaline taxa. Furthermore, the detriment of human activities to overall reef health is evident as shown by the diversity loss and compositional changes of ostracod faunas near Zanzibar Town, where the coastal development has been the most intense during past decades. This study therefore highlights the ecological significance of reefal ostracods and indicates the usefulness of ostracods as a model proxy for environmental assessment. 

How to cite: Tian, S. Y., Langer, M. R., Yasuhara, M., and Wei, C.-L.: Composition and diversity of reefal ostracod assemblages from the Zanzibar Archipelago (Tanzania): Proxies for paleoenvironmental reconstructions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3885, https://doi.org/10.5194/egusphere-egu24-3885, 2024.

Climate variability impacts key characteristics of marine phytoplankton communities, including community composition, size structure, and biodiversity. As each phytoplankton species has specific ecological and biogeochemical traits, changes in phytoplankton community composition can have consequences for ecosystem processes. The calcareous nannoplankton, a marine phytoplankton group that includes coccolithophores, play a unique role in marine biogeochemical cycles though the production and export of both organic and inorganic carbon (biomass and calcite, respectively). However, it is challenging to investigate if differences in calcareous nannoplankton community composition have consequences for community biogeochemical traits (size, biomass, calcite) because the diversity of cellular calcification traits across calcareous nannoplankton species is poorly quantified. Here, we transform the morphological trait data preserved in the fossil record of Paleogene calcareous nannoplankton assemblages to reconstruct past community cell size structure and its associated biomass and calcite traits through the Oligocene ‘coolhouse’ in the Pacific Ocean. Community composition at the low and mid-latitude sites that we investigated (ODP Site 130-804, ODP Site 143-869, ODP Site 198-1211) was distinctly different to composition at the high latitude site studied (IODP Site 378-U1553). The dominant warm water-affinity taxa at lower latitude sites (Syracosphaera, Discoaster) and temperate-cool water-affinity taxa at the high latitude site (Cyclicargolithus, Reticulofenestra, Chiasmolithus) have distinctly different morphological traits, leading to latitudinal differences in total community biomass and calcite and how biomass and calcite is partitioned across size classes. Within each site, community composition through the Oligocene instead tends to fluctuate between species with substantial degrees of biogeochemical trait overlap, largely moderating the degree of biogeochemical impact resulting from shifts in community composition through time. Our results suggest that the impacts of climate-driven biotic reorganisation on community biogeochemical traits can be minimised when replacement species have similar size and calcification traits (higher levels of trait redundancy). Conversely, the biogeochemical implications of even relatively small changes in community composition can be amplified by strongly dissimilar calcification traits within an assemblage. Physiological and ecological traits that influence production rates of biomass and calcite will also factor into the biogeochemical impact of community composition shifts but are difficult to quantify using existing methods. Our research highlights the importance of considering calcification and size diversity when exploring the wider consequences of calcareous nannoplankton responses to climate change in both past and present-day communities.

How to cite: Sheward, R. M. and Herrle, J. O.: Calcification diversity is key to understanding if the biotic responses of calcareous nannoplankton communities to climate change have biogeochemical consequences , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16996, https://doi.org/10.5194/egusphere-egu24-16996, 2024.

The Middle to Late Miocene represents an important time interval in the Indian Ocean (IO), due to the reorganization of land masses, the establishment of monsoonal wind system and climatic changes. However, variations in intermediate and surface water dynamics through the IO still remain poorly understood. In this regard, Ocean Drilling Program (ODP) Site 752, located in the western flank of Broken Ridge (30° 53.475ˈS/93° 34.652ˈE), constitutes a key location to understand how the above-mentioned dynamics may have affected the path of oceanic currents within the eastern sector of the IO during the studied Miocene interval.

A first biostratigraphic framework for ODP Site 752 was established during ODP Leg 121. However, the poor preservation of the material for the Middle to Late Miocene sediment interval resulted in only limited biostratigraphic data and consequently low-resolution age-depth model. In this regard, our study presents a newly updated high-resolution biostratigraphic age-depth model for this time period (from ~8 to ~15 Myrs) at Hole 752A, based on fully quantitative nannofossil assemblage analyses. Furthermore, a recently published astronomically tuned age-depth model (Lyu et al., 2023; DOI: 10.1029/2023PA004761), tied to the shipboard biostratigraphic age model, was used in order to validate our new quantitative nannofossil record. The comparison showed a high consistency for the whole record, with the exception of the interval between ~12-13 Myrs, where the age difference between the two respective models is high. We link these discrepancies to the potential variance in age of the recorded bioevents for this interval between basins, as well as the error associated with the mathematical approach of the tuned age model.

Based on our quantitative nannofossil data, we further evaluated overall changes in the nannofossils assemblages at ODP Site 752. The assemblage is dominated by reticulofenestrids (e.g., Reticulofenestra minuta, Reticulofenestra pseudoumbilicus). Other species with a contribution >1%, are Calcidiscus tropicus, Calcidiscus pataecus, Coccolithus pelagicus, Coronocyclus nitescens, Discoaster spp., Helicosphaera spp., Sphenolithus moriformis and Umbilicosphaera jafari. Statistical analyses will be performed on the assemblage to define variations on the nutrient availability of the Broken Ridge surface waters and will be presented afterwards.

How to cite: Puentes Jorge, X., Piller, W. E., Hechemer, T., Lyu, J., De Vleeschouwer, D., and Auer, G.: Biostratigraphy and paleoecology of calcareous nannoplankton at Broken Ridge, eastern Indian Ocean, during the Middle to Late Miocene (ODP Site 752), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16594, https://doi.org/10.5194/egusphere-egu24-16594, 2024.

During the Early Miocene a global cooler interval was followed by warmer paleoclimate conditions. At the end of the Burdigalian, the Miocene Climatic Optimum (MCO) occurred and brought about global warming and resulting changes in paleoecology and paleoceanography. The Qom Basin (Iran) was situated between the Mediterranean Sea and Indian Ocean and is considered as part of the main Tethyan Seaway, established from Oligocene to Miocene times. In this study, two calcareous nannofossil biozones are recognized in the e-member of the Qom Formation (Burdigalian), the NN3 (zone Sphenolithus belemnos) and NN4 (zone Helicosphaera amplipareta) zones, respective. The modifications in paleoecology and climatic conditions played a vital function in the assemblage structure and the frequency of the calcareous nannofossils during the Burdigalian. From the early to the middle Burdigalian, paleoecologic conditions in the Qom Basin changed from oligotrophic with a warm climate to eutrophic, accompanied by an increase in productivity in the basin, coincided with a cooler climate and inferred upwelling conditions. In contrast, in the late Burdigalian, mesotrophic to oligotrophic conditions were dominant in the basin, affected by the predominance of the MCO and global warming. Warming impacted nutrient availability and salinity, and changes in circulation patterns in the Tethyan Seaway because of the stepwise tectonic closure of the Qom Basin. The paleoceanography and tectonic activity thanks to alteration in the connectivity between the Tethyan Seaway and other basins influenced the calcareous nannofossils assemblages.

Keywords: Miocene Climatic Optimum, Calcareous nannofossils, Qom Formation, Paleoecology, Burdigalian

How to cite: Sharifi-Yazdi, M., Wagreich, M., and Granero Ordoñez, P.: Calcareous nannofossils biostratigraphy and paleoecology of the Miocene Qom Formation (Burdigalian, Central Iran) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3669, https://doi.org/10.5194/egusphere-egu24-3669, 2024.

The Campanian-Maastrichtian boundary (CMB) as defined by the GSSP at Tercis-de-Landes, France, is currently in investigation by the newly installed Maastrichtian Working Group. Although the base of the Maastrichtian was set at a mean of marker bioevents, it was actually defined near the guide event of the first occurrence (FO) of the ammonite Pachydiscus neubergicus, ca. 35 ka younger than the GSSP level. The main calcareous nannofossil marker is the last occurrence (LO) of Uniplanarius trifidus (Quadrum trifidum), estimated at ca. 750 ka younger. Paleogeographically, Tercis was situated in the Tethys-Atlantic transition to the cooler northern temperate realm.

A largely similar paleogeographic position at the northern Tethyan-European margin is provided by the Upper Cretaceous sedimentary successions cropping out in the western Fore-Balkan Mountains area in Bulgaria. One of the most representative section comprising the Upper Campanian-Lower Maastrichtian interval is the Oslen-Krivodol section, situated in the western part of the Central Balkan–Fore-Balkan Tectonic Zone, that forming the northern (marginal) segment of the Balkan Orogen in Bulgaria.

At the section of Oslen-Krivodol, a several meter-thick succession of glauconitic limestones, clayey to nodular limestones and chalky sediments is exposed that includes inoceramids and belemnites. The lower part of the over 7 m thick Oslen-Krivodol succession is composed of green to greenish glauconitic limestones of the Darmantsi Formation. The succeeding Kunino Formation is represented by thin- to medium bedded limestones, clayey and nodular limestones. Belemnite rostra occur in the entire section, whereas inoceramid bivalves were collected only from two levels in the upper part of the Kunino Formation. A complete nannofossil zonal succession could be established, from the uppermost Campanian to the lowermost Maastrichtian. The following subzones could be distinguished: UC15c^TP, UC15de^TP, UC16a^TP (uppermost Campanian), and UC16b^TP (basal Maastrichtian). The nannofossil bioevent for the base of the Maastrichtian, the LO of U. trifidus, is at 3.25m in the section. Strontium isotope stratigraphy indicates the CMB interval around values of 0.707728 ±0.000004. Additional nannofossil bioevents in the CMB interval include the FO and LO of Microrhabdulinus ambiguus below those two CMB levels, and the sudden decrease of warm-water nannofossil indicators like Watznaueria spp. which seems to indicate a threshold crossing for global cooling along the Campanian-Maastrichtian boundary isotope event. Higher in the section, Arkhangelskiella maastrichtiensis s.str. occurs.

Two dinocyst zones have been recognized in the section: the upper Campanian Areoligera coronata and the lower Maastrichtian Cerodinium diebelii Zone. Their boundary is marked by the last occurrence of typical Campanian taxa (Odontochitina, C. robusta, C.horridum, A. fenestra) and the appearance of characteristic Maastrichtian forms (C. diebelii, M. carpentierae, Glaphyrocysta).

Only one level from the upper part of the Kunino Formation have yielded abundant, but badly preserved (as internal moulds) inoceramid bivalves. The inoceramids are represented mainly by the genus Cataceramus, but Endocostea is also present: Endocostea typica Whitfield, 1880; Cataceramus pallisieri (Douglas, 1942); Cataceramus subcircularis (Meek, 1876) and Cataceramus barabini (Morton, 1834). Based on the presence of E. typica we can indicate the eponymous inoceramid zone at the base of the Maastrichtian. 

How to cite: Wagreich, M., Pavlishina, P., Dochev, D., Eder, L., and Koukal, V.: The Campanian-Maastrichtian boundary interval at the Oslen-Krivodol reference section, Bulgaria: nannofossils, dinoflagellate cysts, inoceramids and strontium isotope stratigraphy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4668, https://doi.org/10.5194/egusphere-egu24-4668, 2024.

The late Aptian-early late Albian transition has been characterized by changes in surface water temperature and fertility recognized in several successions at low- and mid-latitudes. Less is known about paleoenvironmental conditions at higher latitudes. In this work we focused on the southern South Atlantic which is a key region to explore the Early Cretaceous oceanography and climate. We studied calcareous nannofossils in the Deep Sea Drilling Project (DSDP) Site 511, drilled on the Falkland Plateau, which yields one of the few sedimentary sequences at southern high-latitudes that records a relatively continuous upper Aptian–Albian sequence. Calcareous nannofossils were investigated to refine the biostratigraphy, reconstruct size variations of Watznaueria barnesiae and Biscutum constans and obtain relative abundances.

The data collected indicate that responded to temperature and fertility fluctuations throughout the studied interval. Specifically, the temperature and nutrient index are suggestive of multiple variations in surface water conditions related either to global perturbations and local changes in the paleoceanography. Relatively lower temperature and fertility characterized the late Aptian. A brief warming phase is associated with the Aptian/Albian boundary followed by a moderate change in the assemblage composition in the early and early late Albian, with abundant cold-water species Repagulum parvidentatum and more abundant surface-water fertility species. Morphometric analyses indicate changes in W. barnesiae and B. constans average size which mostly follow the size patterns identified in the Tethys across the same stratigraphic interval suggestive to reflect a global response to paleoenvironmental changes occurred during this peculiar phase. W. barnesiae size variations are of less amplitude compared to B. constans and occur at different stratigraphic levels. Both species show smaller specimens in the late Aptian compared to the middle-late Aptian. Largest B. constansare identified in the early late Albian. A difference in the total average size of both species is also identified, with average larger specimens occurring in the Falkland compared to the Tethys.

How to cite: Bottini, C., Bettoni, C., Erba, E., and Herrle, J.: Response of calcareous nannoplankton to paleoenvironmental changes across the Aptian-Albian transition of the southern South Atlantic (Falkland Plateau, DSDP Site 511), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8209, https://doi.org/10.5194/egusphere-egu24-8209, 2024.

Rapid climatic changes at the end of glacial cycles have shaped landscapes and biodiversity globally, yet their influence on the landscapes of the islands of Macaronesia remains poorly understood. Here we discuss how three microfossil records from the islands of Tenerife, Gran Canaria and La Gomera can shed light on landscape transformations linked to climatic changes after the Late Glacial Maximum. Phytoliths as proxy data from vegetation change and microalgae (diatoms and chrysophytes) as proxies of hydrological dynamics are analysed alongside sedimentological and geochemical data to understand the multiple aspects of landscape change linked to climatic variability. Our data show the occurrence of significant vegetation changes linked to deglaciation, after 16,000 cal yr BP in Gran Canaria and Tenerife based on increases in palm (Phoenix canariensis) phytolith and shifts in grassland composition. Records from Tenerife and La Gomera show a decrease in palms and changes in microalgae communities after the end of the African Humid Period linked to the aridization of the Sahara (c. 5000 cal yr BP-present day). Multi-proxy and inter-island record comparison reveals significant variability dependent on mesoclimates and local vegetation dynamics, showing the complexity of understanding the influence of climatic changes in the landscapes of this archipelago.

How to cite: Castilla-Beltrán, A., Martín Ramos, M. P., Davtian, N., Fernández-Palacios, E., Criado Hernández, C., Nogué, S., Villanueva, J., Fernández-Palacios, J. M., and de Nascimento, L.: Phytolith and microalgae records of Late Pleistocene and Holocene climate-driven landscape shifts in the Canary Islands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13058, https://doi.org/10.5194/egusphere-egu24-13058, 2024.

Oxygen isotope (δ¹⁸O) and carbon isotope (δ¹³C) data obtained from marine carbonate shells allow the understanding of paleoclimatic conditions. The mass difference between the isotopes of an element leads to a change in the ratio of heavy and light isotopes within the structure of an organism due to certain events. In this study, we present the paleoclimatic findings from the analysis of fossils obtained from sediment cores of a lagoon on the Marmara coast, located in the coastal region of Kumlubent on the Gelibolu peninsula, Çanakkale.

In the Kumlubent lagoon, two sediment cores were taken from depths of 3.40 m and 2.78 m respectively. The cores were mainly composed of gray sand material intercalating with distinct intervals of silt-size materials, sapropels, and layers of pebbles suggesting event-type sedimentations.   Morphological identification of the fossil shells in the sediment cores was examined by using light microscopy as well as a Scanning Electron Microscope (SEM). Oxygen and carbon isotope measurements in the carbonate shells were measured by Inductively Coupled Mass Spectrometry (ICP-MS) analyses.  The values obtained were converted to δ¹⁸O-δ¹³C values based on the ratio "¹⁸O:¹⁶O seawater-¹³C:¹²C" to track depletion and enrichment. Our results show that the marine fossil community in Kumlubent lagoon includes 35 different species and 25 genera. The abundance of species in the sediment cores varied significantly indicating possible intervals of high primary production. The most commonly found genus in the cores were Bittium species — in particular Bittium latreillii, Bittium reticulatum, and Bittium sp.— - which were selected for the oxygen and carbon isotope analyses. Using the isotopic behavior diagram constructed from the collected data, we investigated the relationship between the behavior of the δ¹⁸O isotope ratio and the dry periods of the environment in which the Bittium species, as observed in the recovered sediment cores. δ¹⁸O data in the ranged from -2.63‰ to -0.94‰, and δ¹³C values ranged from 0.25‰ to 1.98‰. Paleotemperature calculations for Kumlubent carbonate shells indicated seawater temperatures between 24.8°C and 32.0°C during the formation of the shell material. δ¹⁸O and δ¹³C values showed opposite increase-decrease patterns reflecting varying precipitation-evaporation and varying freshwater input in the Kumlubent region in the Sea of Marmara.

How to cite: Tülümen, E. B., Tarı, U., Olgun Kıyak, N., and Kapan Ürün, S.: Paleoclimatic study of Kumlubent Lagoon based on Oxygen-18 and Carbon-13 isotope data from sequenced mollusc shells on the western coast of the Sea of Marmara, NW Türkiye, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8682, https://doi.org/10.5194/egusphere-egu24-8682, 2024.

Current climate change is causing profound environmental changes in coastal ecosystems, such as rising temperatures, increased precipitations and extreme weather events, including flooding. The stratigraphic record of the salt marshes of northern Spain constitutes a unique archive for exploring natural and anthropogenic processes and dynamics. While salt marshes located along the northeastern margin of Spain have received considerable attention in the scientific literature, those located in the northwestern sector have not been extensively studied, thus creating a fundamental gap in our knowledge.

This research aims to investigate recent environmental changes recorded in a salt marsh setting from the Nalón estuary (Asturias, N Spain). A comprehensive multidisciplinary approach (benthic foraminifera, pollen content, grain size, TOC, TN, trace metals and magnetic susceptibility), coupled with a robust chronology (²¹⁰Pb, ¹³⁷Cs, ^239+240Pu), has been applied to a short sediment core drilled in the Junquera salt marsh, located in the middle estuary.

This sedimentary record, which spans to the last ~150 years, reveals the dominance of fluvial processes in the Nalón estuary, with the occurrence of a strong flood in the mid-20^th century. This extreme natural event, which disturbed previous environmental dynamics, can be stratigraphically constrained with distinctive micropaleontological and geochemical signatures. Subsequently, trace metals, magnetic susceptibility and pollen content show variable patterns consistent with the extensive mining activities and land-use modifications developed upstream.

How to cite: Gardoqui, J., Cearreta, A., García-Artola, A., Irabien, M. J., Gómez-Arozamena, J., Villasante-Marcos, V., Galaz-Samaniego, C., and Peñalba, C.: The sedimentary record of the Junquera salt marsh (Nalón estuary, N Spain): a tale about contemporary fluvial processes, mining pollution and land-use changes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1881, https://doi.org/10.5194/egusphere-egu24-1881, 2024.