Understanding past Earth system processes is an essential component of placing current climate changes in context and testing climate model output. In this context, reconstructing patterns in marine or terrestrial temperatures is as important as understanding the mode of the hydrological cycle. However, there is only limited research on past hydrological systems, as the interplay between evapotranspiration, precipitation and runoff makes comprehensive reconstructions challenging. To overcome this issue, the spatiotemporal distribution of precipitation and riverine runoff can be estimated by reconstructing the dynamics of enhanced fresh water input into marginal sea.

Here, we focus on the hydrological conditions of shallow marine areas around the southern paleo-North Sea during the Eocene, including the Paris, Hampshire and Belgium Basins.  We utilised fossil bivalve shells (Venericor planicosta and Crassatella ponderosa) as archives as they can be used to reconstruct both long-term climate changes due to their widespread abundance and temporal continuity in the geological record as well as short-term variability via the time-distinct (sub-seasonal) layering of their shells. We reconstruct fresh water flux to these basins at different spatiotemporal resolutions, ranging from regional differences across millions of years to (sub-)seasonally resolved local variations. Depending on the targeted spatiotemporal resolution, different proxy systems were used. For the reconstruction of large scale changes in the input of terrigenous material by riverine runoff, Ba/Ca and ⁸⁷Sr/⁸⁶Sr are employed. In addition, δ¹⁸O and Δ₄₇+Δ₄₈ measurementswere conductedto detect sub-annual changes in the isotopic composition of the sea water by isotopically lighter fresh-water influx.

Result exhibit regionally specific Ba/Ca and ⁸⁷Sr/⁸⁶Sr values for each of the examined basins, generally reflecting the hinterland geology. However, these values show time dependent variations throughout the Eocene, suggesting variable degrees of terrigenous input by varying riverine runoff. The detected changes in riverine runoff are generally congruent to the depositional evolution of the basins, as derived from the sedimentary record, revealing less terrigenous input signal with increasing open marine conditions and vice versa.  A specimen of V. planicosta from the Paris Basin, showing a distinct riverine signal in Ba/Ca and ⁸⁷Sr/⁸⁶Sr, was used for combined δ¹⁸O and Δ₄₇+Δ₄₈ measurements to identify seasonal variations in the oxygen isotopic composition of the sea water (δ¹⁸O_SW). The resulting δ¹⁸O_SW values show a minimum seasonal variability of 0.9‰ and an enhanced fresh water input during the summer.

These results shed new light on the hydrological conditions in Western Europe during the Eocene and show how different proxy systems can be interlinked to reconstruct basin hydrology on different spatiotemporal scales.

How to cite: Kniest, J. F., Davies, A. J., Evans, D., Fiebig, J., Gerdes, A., Müller, W., Todd, J. A., Sigwart, J. D., Vellekoop, J., Voigt, S., and Raddatz, J.: Reconstructing regional to local scale patterns of fresh water input into the Eocene North Sea Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15713, https://doi.org/10.5194/egusphere-egu24-15713, 2024.

El Niño-Southern Oscillation (ENSO) is the strongest signal of global interannual climate anomaly and reconstructing past ENSO variations using high-resolution paleoclimate archives can improve our understanding of ENSO variability, as well as improve our ability to predict future climate changes. Here, a daily resolution standardized growth index (SGI) was established using a giant clam (Tridacna spp.) shell specimen MD2 (life span: AD 1994-2013), collected from the Yongshu Reef, southern South China Sea (SCS). The cross-spectral and correlation analysis indicated that the SGI variation of MD2 was strongly influenced by ENSO variability on an interannual timescale. Tridacna spp. is in symbiosis with zooxanthellae, and its growth index is usually modulated by the photosynthetic efficiency of zooxanthellae. During the El Niño (La Niña) period, the convective anomalies stimulated in western Pacific would increase (decrease) the effective solar radiation on Yongshu Reef, and in turn influence the photosynthesis rate of zooxanthellae and enzyme activity for the calcification site and thus the SGI of giant clam MD2. The SGI can explain 54.7% of ENSO variance, demonstrating the potential for Tridacna SGI in ENSO reconstruction. Compared with conventional ENSO reconstruction using high-resolution geochemical proxies, the method of giant clam SGI is rapid and economical.

How to cite: Geng, J., Yan, H., Liu, C., Han, T., Liu, S., Zhao, N., Wen, H., Yang, H., Zhou, P., Wang, G., and Dodson, J.: Reconstruction of ENSO variability using the standardized growth index of a Tridacna shell from Yongshu Reef, South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21421, https://doi.org/10.5194/egusphere-egu24-21421, 2024.

The El Niño Southern Oscillation (ENSO) is a worldwide climate phenomenon impacting temperatures and precipitation regimes in Australia, Southeast Asia, and America. Previous studies have shown this climate phenomenon and the Indo–Australian monsoon to have a strong influence on Malaysian Borneo’s hydroclimate. In a context of climate change and increasingly strong extreme ENSO events, understanding the influence of ENSO on this region, as well as its evolution through time, is essential to better constrain the possible future impacts it will have on the Maritime Continent’s hydroclimate. To compensate for the limited availability of dependable instrumental data in the first half of the 20^th century, we used coupled δ¹⁸O and Sr/Ca records from massive corals’ carbonate calcium skeletons to build a proxy for past hydroclimate: δ¹⁸O_seawater (δ¹⁸O_sw). We first assessed our two 90 and 60-year-long δ¹⁸O_sw records’ quality as proxies for hydroclimate by correlating them with different instrumental datasets before performing moving windowed correlations with the NINO3.4 index, an indicator of ENSO state. Results show variable agreement with local instrumental data depending on the distance from the river mouth, monsoon season, and instrumental dataset used. When correlated against the NINO3.4 index, our δ¹⁸O_sw records showed a nonstationary increasing influence of ENSO from the 1980s and onwards on the local hydroclimate with correlation coefficients r > 0.8 using month groups towards the end of the year. Our findings highlight the differences in results depending on the chosen dataset, time scale, or period of the year, as well as the usefulness of these geochemical archives to better understand the impacts of climate phenomena across periods predating reliable instrumental data.

How to cite: Naciri, W., Boom, A., Watanabe, T. K., Garbe-Schönberg, D., Hathorne, E., Browne, N., Evans, N. J., Nagarajan, R., and Zinke, J.: Paired coral Sr/Ca and δ18O records reveal increasing ENSO influence on Malaysian Borneo’s hydroclimate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6241, https://doi.org/10.5194/egusphere-egu24-6241, 2024.

Weather-scale precipitation have a significant impact on ecosystems and human activities. Reconstructing weather-scale precipitation events is critical to improving our understanding of precipitation event mechanisms. Currently, the snail shells ultra-high resolution δ¹⁸O records obtained by secondary ion mass spectroscopy (SIMS) is the main methods of reconstruction the terrestrial weather-scale precipitation events. However, research in this field is limited due to the rarity and costliness of SIMS instrumentation, as well as the complexity of sample preparation. In this study, we collected three modern land snails (Cathaica fasciola) from the Shizuishan area in Northwest China in June, September, and December 2021. The shells of these snails were sampled continuously with a spatial resolution of ~700μm and tested using gas-source mass spectrometry (GSMS) to obtain high-resolution δ¹⁸O records. The results showed that the δ¹⁸O of snails shell (δ¹⁸O_shell) of different snails grown at the same time period were well reproducible. We obtained the growth rate of Cathaica fasciola is 546μm/day from June to September. This growth rate is obviously faster than Xingyang (181μm/day from June to September) and Xi'an (56μm/day from April to September). The observed disparity in growth rates may be attributed to the snail survival strategy changes, which appear to be more efficient in water usage in the monsoon margin zone. More importantly, the δ¹⁸O_shell exhibited sensitivity to precipitation, as evidenced by three negative fluctuations in δ¹⁸O_shell record that corresponded to three precipitation events during the period. These findings indicate that δ¹⁸O_shell records obtained by GSMS could effectively capture weather-scale precipitation information in the monsoon margin region. GSMS is widely used, less costly for testing, and relatively simple for sample preparation. This greatly improves the feasibility and applicability in reconstruct weather-scale precipitation events under different climatic conditions using δ¹⁸O_shell record, and deepens our understanding of the mechanisms such events. Meanwhile, this finding holds significance in unraveling the intricate nature of weather-scale precipitation events. 

How to cite: Zhang, Q., Yan, H., Dong, J., Wang, G., Jia, Y., and Li, X.: Daily-weekly scale precipitation events in the monsoon marginal zone recorded by high-resolution δ18O of land snail shells, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8312, https://doi.org/10.5194/egusphere-egu24-8312, 2024.

Stream water oxygen isotopes are a powerful natural tracer of watershed functions (e.g., water collection, storage, mixing, and release). However, instrumental δ¹⁸O_water records have limited spatial coverage and rarely span over more than a decade. Long-lived (> 200 years) freshwater pearl mussels (Margaritifera margaritifera) are a promising natural archive for complementing these δ¹⁸O chronicles because their shells faithfully capture the isotope composition of the water in which the mussel lived. The reconstruction of reliable shell-based δ¹⁸O_water chronologies relies on several steps: (i) identifying which layer of the shell biomineralizes in thermodynamic equilibrium with the ambient water, (ii) determining the seasonal timing and rate of shell growth to assign each isotope sample to a precise calendar date, and (iii) employing a temperature record or temperature reconstruction to resolve the thermodynamic relationship between δ¹⁸O_shell and δ¹⁸O_water. First, we assessed the oxygen isotope fractionation between the ambient water and both sublayers of the outer shell layer, i.e., the outer prismatic and inner nacreous portion. We found that reconstructions based on δ¹⁸O_shell of the prismatic sublayer provided excellent δ¹⁸O_water data, whereas the nacreous portions showed evidence of growth rate-induced (kinetic) effects. Second, we carried out tank experiments to quantify temperature controls on biomineralization rates, constrain the seasonal timing and rate of shell formation, and construct a monthly resolved seasonal growth model. Third, we assessed the temperature sensitivity of shell ultrastructural properties and observed a poor relationship between water temperature and the nacre table thickness, strongly masked by pH fluctuations in stream water. Based on these findings, we have reconstructed sub-seasonal δ¹⁸O_water records of streams in Luxembourg, Germany and Sweden extending back to the early 19^th century. These unprecedented reconstructions of stream water δ¹⁸O chronicles will open new vistas on multidecadal to centennial dynamics in the continental water cycle (e.g., for the assessment of watershed sensitivity to global change).

How to cite: Gey, C. J., Pfister, L., Türk, G., Thielen, F., Leonard, L., and Schöne, B. R.: Reconstructing stream water oxygen isotopes using freshwater pearl mussels (Margaritifera margaritifera): Toward an exploration of sub-seasonal watershed dynamics over the past 200 years, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1862, https://doi.org/10.5194/egusphere-egu24-1862, 2024.

The Mg/Ca ratio of foraminiferal tests is widely used to reconstruct seawater temperature in past climates. With traditional methods (i.e. Inductively Coupled Plasma Optical Emission Spectrometry or ICP-OES), multiple tests have to be clustered together to attain enough material for analysis. The need for high amounts of carbonate can be problematic for shelf sediments if suitable foraminifera are scarce. As a consequence, grouping of different taxa into one bulk value or ‘sample grouping’ is applied, losing information on interspecific and intra-specimen geochemical variability. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) solves this problem by targeting extremely small surfaces, e.g., single foraminifer tests or even single chambers.

Nevertheless, understanding LA-ICP-MS-generated foraminiferal Mg/Ca records requires in-depth knowledge on the growth and reproductive cycle of extinct foraminiferal taxa, such as Cibicidoides sp. and Anomalinoides acutus from the Paleocene-Eocene transition and early Eocene. These species are commonly used for environmental reconstruction because they are thought to have incorporated the ocean water chemistry in equilibrium with their tests, yet not much is known about their life or precipitation cycle.

The reproductive cycle of modern benthic foraminifera ranges from a few weeks to a year, depending on species and size, requiring about a single day to precipitate a new chamber. This implies a potential change in geochemistry from chamber to chamber. Hence, LA-ICP-MS hypothetically allows for an extremely high-resolution, in situ Mg/Ca record across a year, or a precipitation season, if sufficient snapshots of chamber calcification moments are incorporated. As a result, a comparison of cyclic temperature changes on both annual (seasonal variations across individual specimens of a sample) and sub-millennial (variations across closely spaced samples) scale could be feasible. However, the complex growth of the foraminiferal test (e.g. layering due to overgrowth of older chambers) likely also results in geochemical variability within chambers.

Here we investigate the inter- and intra-chamber variability in Mg/Ca composition of extinct benthic foraminifera using LA-ICP-MS. We evaluate the resulting potential and risks stemming from inhomogeneous trace-element distribution in the tests. We utilize foraminiferal tests from shelves from the western North Atlantic and the North Sea Basin, covering a paleodepth transect (<150 m) during the early Eocene. The foraminiferal tests record not only the long-term global warming trend of the early Paleogene but also short temperature spikes during hyperthermals such as the Paleocene-Eocene Thermal Maximum.

How to cite: Doubrawa, M., Stassen, P., Robinson, M. M., Speijer, R. P., and Vellekoop, J.: Inter- and intra-chamber variability of trace elements in benthic foraminifera – potential and risks of LA-ICP-MS analyses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3059, https://doi.org/10.5194/egusphere-egu24-3059, 2024.

Greenland is particularly vulnerable to ongoing anthropogenic climate change and observational data document recent rapid mass loss of many of the Greenland Ice Sheet (GIS) glaciers. Mass loss of the GIS represents a major contributor to global sea level rise, but uncertainties in future projections are large. A recent acceleration in mass loss has been observed, with 2012 and 2018/19 record years documented by direct observations. However, estimates of melt variability and glacier runoff remain uncertain before the satellite era and the influence on surface ocean waters is unclear. In general, available observational records from high latitudes are sparse and short. Models require high-resolution data of past variability to resolve how fast the GIS reacts to warming.

Past climate can be reconstructed from natural proxy archives. In high latitudes, however, most proxy time series utilised to date come from indirect land-based proxies. Calcified coralline algae are important shallow-marine calcifiers that grow attached to the seafloor and have emerged as subannual-resolution climate recorders for the extratropics. By analyzing long-lived coralline algae from Disko Bay, West-Greenland, in close proximity to Jakobshavn Glacier, we address this data gap. Jakobshavn Glacier is one of the largest glaciers in Greenland and the single largest source of mass loss from the GIS over the last 20 years. Sclerochronological analysis and ultra-high-resolution laser ablation ICP-MS data from calcified coralline algae (Clathromorphum compactum) provide seasonally-resolved records that capture the impact of surface temperature warming and glacier runoff on coastal Arctic environments. Algal Ba/Ca ratios track past glacier-derived meltwater input to the ocean surface layer and we report an unprecedented nonlinear increase in Jakobshavn glacier runoff into Disko Bay in the last 20 years. Our chronology from southern Disko Bay sites shows a distinct increasing trend from the early 2000s, recording the acceleration of GIS glacier mass loss and matching recent years of record amounts of ice loss in satellite data. The rate of increase in Ba/Ca (a runoff proxy) is unprecedented over at least the last 100 years, highlighting the rising influence of global warming on Arctic coastal ecosystems. The new algal chronology provides a long-term perspective on high-resolution variability in Jakobshavn Glacier runoff into Disko Bay, extending before observations, and confirming model data.

How to cite: Hetzinger, S., Halfar, J., and Tsay, A.: Nonlinear 21st century increase of Greenland Ice Sheet runoff into Disko Bay surface water recorded by long-lived coralline algae, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5846, https://doi.org/10.5194/egusphere-egu24-5846, 2024.

Over the past century, the Indian Ocean stands out as the fastest warming ocean in the world. Yet, the southwestern Indian Ocean (SWIO) faces challenges in acquiring in-situ observational data, both spatially and temporally. The limited availability of long term continuous high-resolution instrumental data in the SWIO hinders a comprehensive understanding of sea surface temperature (SST) variability and its intricate relationship with large-scale atmospheric and oceanic modes. This scarcity further hinders efforts to disentangle natural variability from anthropogenic influences. To address these limitations, we present a 335 yr continuous coral record of monthly SST reconstruction in the Indian Ocean based on proxy Sr/Ca, obtained from Ambodivahibe Bay, northeast of Madagascar.

Sampled from a strategic region under the control of the NW monsoon during austral summer and trade winds for the rest of the year, this unique long record provides insights into coral resilience in a coastal upwelling zone amidst the rapid pace of ocean warming, as well as long-term trade wind variability, which significantly impacts the temperature signature of the South Equatorial Current and the downstream Northeast Madagascar current (NEMC), subsequently influencing moisture delivery to the East African and Asian Monsoon regions.Our SST reconstruction uncovers annual to multidecadal variations in the tropical SWIO spanning from 1672 to 2007, highlighting the dynamic interplay between local and remote climate processes, each dominating at different time scales. Furthermore, this new record extends the existing coral Sr/Ca-SST monthly reconstructions in the SWIO back to the 17^th century and underscores the enhanced capacity to reconstruct regional climate variability using proxy records from multiple sites. Particularly noteworthy is its ability to capture SST variations under the alternating influence of monsoon and trade winds. This new coral Sr/Ca record provides valuable initial SST reconstruction along the route of the NEMC, serving as an indicator of the long-term NEMC strength variability.

How to cite: Zhang, M., Zinke, J., Boom, A., Garbe-Schönberg, D., Watanabe, T., and Frick, D.: A 335-year Coral-Based Reconstruction of Sea Surface Temperature along the Route of the Northeast Madagascar Current in the Tropical Southwestern Indian Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6200, https://doi.org/10.5194/egusphere-egu24-6200, 2024.

Ocean’s oxygen (O₂) is essential to most marine life forms and represent a fundamental component of the biogeochemical cycling of nitrogen and carbon. Its inventory is declining in response to global warming. Contrasting predictions about the future of the tropical oxygen deficient zones (ODZs) in numerical simulations and palaeoceanographic evidence for contracted ODZs during Cenozoic’s warmest periods, make long-term predictions about the future of ocean O₂ challenging. We present new evidence for tropical ocean oxygenation during the Paleocene-Eocene Thermal Maximum (PETM), a rapid warming event that serves as a geologic analogue to ongoing warming. Foraminifera-bound nitrogen isotopes indicate that the tropical North Pacific ODZ contracted during the PETM, implying higher O₂. Metabolic modelling of aquatic ectotherms shows that a concomitant increase in planktic foraminifera size implies that seawater oxygen partial pressure (pO₂) rose in the shallow subsurface throughout the tropical North Pacific, beyond the spatial extent of the ODZs. These findings call for an oceanographic mechanism capable of both enhancing subsurface oxygenation and operating beyond the regional scale of the North Pacific ODZs, on millennial timescales. These divergent changes are consistent with Ocean General Circulation Models under SSP5-8.5 scenario for 2300, in which a decline in biological productivity allows tropical subsurface oxygen to rise even as global ocean oxygen declines. The tropical upper ocean oxygen increase may have relieved physiological stress, helping to avoid a mass extinction in planktic organisms during the PETM, in spite of the largest benthic extinction of the Cenozoic.

How to cite: Moretti, S., Auderset, A., Deutsch, C., Schmitz, R., Gerber, L., Thomas, E., Luciani, V., Petrizzo, M. R., Schiebel, R., Tripati, A., Sexton, P., Norris, R., d'Onofrio, R., Zachos, J., Sigman, D., Haug, G., and Martínez-García, A.: Foraminifera nitrogen isotopes and body size reveal an oxygen rise in the tropical upper ocean during the Paleocene-Eocene Thermal Maximum (PETM), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11373, https://doi.org/10.5194/egusphere-egu24-11373, 2024.

Climate change is one of the main drivers for the wave of species extinctions predicted for this century. IPCC extinction risk assessments are based in part on predicted climate-driven reductions in the geographic ranges of focal species (range loss). This builds on the well-established IUCN (2022) Red List criterion, in which a species is considered critically endangered (>50% extinction risk) if it loses ≥80% of its geographic range. However, while there is clear evidence that extinction risk is related to the absolute geographic range of a species, the empirical relationship between range loss and extinction risk is not well understood. Using fossil evidence of true extinctions over the past 23 million years, with 2600 range change observations of 1215 marine genera, this study implements a Bayesian hierarchical weighted generalized additive model to investigate how extinction risk changes with the percentage decrease in geographic range of a genus. Results clearly indicate how extinction risk increases non-linearly with range loss. Taxon dependent differences in the relationship between extinction risk and range loss indicate great potential for adapting its application in extinction risk predictions and the IUCN criteria.

How to cite: Straube, E., Steinbauer, M., Finnegan, S., and Mathes, G.: Predicting extinction risk by range loss: Evidence from the fossil record, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-413, https://doi.org/10.5194/egusphere-egu24-413, 2024.

Species diversity increases with time averaging according to the species-timespan relation. This scaling effect can exaggerate geographic or temporal variability in diversity because the time averaging of fossil assemblages can vary by several orders of magnitude owing to variability in sedimentation, mixing and/or disintegration, and thus can affect analyses focusing on the detection of baseline and novel community states in the Holocene stratigraphic record or in live-dead comparisons. However, the relation between abundance and sample size-independent diversity can be used to detect the fingerprints of time averaging. A decrease in sediment accumulation rate should lead to higher abundance and diversity, and the relation is thus expected to be positive. Consistently with this hypothesis, we find that sedimentation rates in the Holocene record of the northern Adriatic correlate negatively with abundance and diversity. Moreover, as sedimentation rates decrease, correlation between abundance and diversity becomes increasingly positive. This scaling-induced relation differs from a negative abundance-diversity relationship observed in living (non-averaged) communities. We suggest that the positive abundance-diversity relation will be a diagnostic of scenarios where variability in fossil abundance and diversity is determined by temporal scaling controlled by variability in sediment accumulation rate rather than by variability in natural or anthropogenic processes.

How to cite: Tomašových, A., Kowalewski, M., Nawrot, R., Scarponi, D., and Zuschin, M.: Assessing abundance-diversity relationship in the context of time-averaging: implications for evaluating baseline and novel states in conservation paleobiology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13312, https://doi.org/10.5194/egusphere-egu24-13312, 2024.

Predation can play an important role in shaping marine ecosystems, but we often lack long-term baseline data that would allow for tracking how predator-prey interactions have responded to increasing anthropogenic impact. Here, we assess temporal changes in benthic community composition and interactions between drilling predatory gastropods and their molluscan prey using the Holocene fossil record of the northern Adriatic Sea (NAS), a shallow shelf characterized by a long history of human transformation of coastal and deltaic ecosystems. Molluscan assemblages differ between the Isonzo and Po prodeltas but both regions show consistent temporal trends in the abundance of dominant species. Samples of mollusc prey collected at high stratigraphic resolution indicate that drilling frequencies have drastically declined in the prodelta of the Po River since the mid-20th century, while a weaker trend in more condensed sediments of the Isonzo delta is not statistically significant. The decrease in drilling predation intensity and the community turnover is related to the loss of predatory gastropods, decreased abundance of preferred and increased abundance of less-preferred prey organisms, and a rapidly progressing infaunalization observed in the northern Adriatic basin during the most recent decades. Our results align with data showing the substantial depletion of marine resources at higher trophic levels in the NAS and indicate that the strong simplification of the food web since the late 19^th century accelerated since the mid-20th century.

How to cite: Zuschin, M., Nawrot, R., Dengg, M., Gallmetzer, I., Haselmair, A., Kowalewski, M., Scarponi, D., Wurzer, S., and Tomašových, A.: Anthropocene breakdown of predator-prey interactions in the northern Adriatic Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14914, https://doi.org/10.5194/egusphere-egu24-14914, 2024.

Changes in life history of marine species in response to harvesting and human-induced environmental changes are frequently observed in modern ecosystems, but the true magnitude of these shifts is difficult to evaluate without robust information on the pre-impact state of the affected populations. The edible bivalve Noah’s Ark shell (Arca noae L.) is commercially exploited in the eastern Adriatic Sea, where its fishery rapidly expanded during the first half of the 20th century until a mass mortality in the late 1940s caused a population collapse. In spite of partial recovery, the lack of data on growth parameters of this species prior to that event complicates establishing sustainable levels of harvesting. To provide a baseline for assessment of the current state of populations of A. noae we compared modern and fossil (middle to late Holocene) specimens from the northern Adriatic Sea using samples from benthic surveys and sediment cores. Estimates of growth and longevity were based on annual shell growth lines visible in acetate peel replicas of the umbo and outer prismatic shell layer. The maximum lifespan observed in our modern samples was 35 years – a full decade longer than previously documented for this species. However, this estimate was still much shorter than the lifespan of multiple fossil specimens, among which the ontogenetically oldest one reached the age at least 85 years. Our results indicate that modern individuals of A. noae grow faster and have shorter lifespan compared to their Holocene counterparts, suggesting that harvesting pressure combined with increasing water temperatures and eutrophication of the northern Adriatic Sea had a significant impact on the population dynamics of this species.

How to cite: Nawrot, R., Peharda, M., Macharia, S., Uvanović, H., Tomašových, A., and Zuschin, M.: Changes in growth and longevity of the exploited bivalve Arca noae in the northern Adriatic Sea: a conservation paleobiology perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17776, https://doi.org/10.5194/egusphere-egu24-17776, 2024.

Mollusks and benthic foraminifera are reliable tools to paleo-environmental reconstructions because they commonly occur in most marine habitats and are sensitive to major and short-lived changes of environmental drivers, induced by both natural and anthropogenic events. Their community structure provides useful information about the characteristics of their habitat and some species are sensitive to specific environmental controls. Features such as changes in species composition and community, or variation in test morphology provide evidence of fluctuation of several environmental factors. Therefore, both mollusks and benthic foraminifera can be used as an efficient method for identifying the history and ecological trajectory of marine ecosystems.

This study focuses on the macro- (mollusks) and micropaleontological (benthic foraminifera) study of a 3 m long sediment core collected in the former military arsenal of the La Maddalena harbor (N Sardinia, Italy), at a depth of 15 m. The core site is located on the S-E coast of La Maddalena island, that underwent a complex history of human occupation along with natural environmental evolution and human-derived pressures. We aimed to reconstruct the main environmental changes recorded in the fossil benthic communities along the core, and to propose the most likely factors that caused these changes. Both mollusks and benthic foraminifera have been picked from the core, identified at genus/species level and counted. Ecological indications for each species have been extracted from literature. Univariate and multivariate statistics have been applied to highlight the community dynamics.

More than 90 species of benthic foraminifera have been identified, and 101 mollusk species (846 specimens). The foraminifera diversity indices show a general reduction from the first 50 cm downcore. This slight decline is accompanied by changes in foraminiferal assemblages. The results concerning changes in foraminiferal species composition, their abundance and biodiversity, supported by statistical analyses (cluster analysis), allowed identification of three major foraminiferal associations corresponding to different marine coastal settings. The same results have been obtained by using mollusks and their ecological significance in the framework of benthic marine bionomics. Species are related to infralittoral vegetated bottom such as Posidonia meadows (HP) or photophilous algae through the core, but with variation in percentage of abundance, and HP species decreases from the bottom to the top, whereas species related to muddy bottom follow the opposite trend (coastal detritic mud, deep mud). This testifies that the area underwent a progressive reduction of Posidonia meadows and light-loving algae with a shift toward muddy bottoms, possibly related to the effect of the intensive renovation works of the harbor area. Moreover, radiocarbon dating obtained from Cerithium specimens indicated that the sedimentation rate increases in the upper portion of the core, according to the ecological signal reconstructed by the analysis of the mollusk assemblage.

How to cite: Basso, D., Dessi, R., Racis, R., Demuro, S., Buosi, C., Preda, A., and Bracchi, V. A.: Recent environmental changes in the area of La Maddalena Harbour (Sardinia, Italy): data from mollusks and benthic foraminifera, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18785, https://doi.org/10.5194/egusphere-egu24-18785, 2024.

Predatory fishes are expected to regulate the abundances and body sizes of prey fishes on coral reefs, which may, in turn, have cascading effects across the food web. However, such top-down processes have been challenging to test, especially on Caribbean reefs where predator communities have been altered by centuries of selective harvesting, and therefore potentially function differently. To address this shifting baseline problem, we used Holocene fossil, archeological and modern fish remains (5758 otoliths and 807 shark denticles) to track changes in the relative abundances and body sizes of fishes of different functional and trophic modes on Caribbean reefs in Panama and the Dominican Republic over millennia. Piscivorous fish declined in relative abundance by 50-70% and became smaller since major human exploitation, which would have resulted in a decline in predation intensity since prehistoric times. In contrast, prey fishes like anchovy and damselfish became more abundant and larger over the same time period, consistent with a release from predation. Cryptobenthic fishes showed no change in body size or abundance over time, most likely because they are protected from predation and are controlled to a greater extent by habitat and food availability than predation. Our data support the hypothesis that predator loss has precipitated a release from predation for certain prey fish species, and yet despite this, some important facets of reef function have remained resilient over time.

How to cite: O'Dea, A., De Gracia, B., García-Méndez, K., Cybulski, J., Lueders-Dumont, J., and Dillon, E.: Fossil otoliths reveal changing predator-prey dynamics and partial resilience in reef fishes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13217, https://doi.org/10.5194/egusphere-egu24-13217, 2024.

Woodlands in the British landscape have been reduced to fragments and continue to decline in species diversity. In the heavily human-modified landscape of the English Midlands, Ancient Semi-Natural Woodland sites have undergone various human disturbance, including extensive modification such as clear-felling in the 20th century. Through the integration of information from the fossil pollen record, place-name evidence of past vegetation cover, archaeological records and recent botanical surveys, we examine the patterns of past resilience of woodlands to environmental disturbances, to understand more about their current status and future concerns to ensure the persistence of these now rare, socially and ecologically important habitats. 
 
By adopting an interdisciplinary approach, we examine multiple sites across the English counties of Leicestershire and Rutland as case studies, integrating the different spatiotemporal datasets to provide new insights. The methodology aims to identify regions that have maintained long-term, stable woodland cover and to elucidate how ecosystems have changed and recovered after natural environmental or anthropogenic disturbances over the past 8,000 years and including more recent changes in the Anthropocene. Environmental change including deforestation and reforestation events have been identified with further details about the anthropogenic influence being provided by the historical (place-name evidence) and archaeological records. Our analysis is targeted at developing a replicable, spatiotemporal framework to identify future resilient woodland ecosystems in a time of Anthropocene environmental change, and to inform local policy and conservation efforts.

How to cite: Sellers, H., Berrio, J. C., Williams, M., Jones, R., De Sabbata, S., Evans, A., Neilson, A., and Burns, M.: An interdisciplinary approach to understanding British resilient woodlands in an Anthropocene landscape, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9773, https://doi.org/10.5194/egusphere-egu24-9773, 2024.