Over the past two centuries, fossil fuel burning and other anthropogenic activities have caused the atmospheric CO₂ concentration to rise from 280 ppm to 419 ppm. Over the same time interval, the surface oceans have absorbed more than 500 billion tons of carbon dioxide from the atmosphere, or approximately 30 % of the total anthropogenic carbon dioxide emissions. This absorption of CO₂ from the atmosphere has benefitted human mankind significantly by reducing the greenhouse gas levels in the atmosphere. When anthropogenic CO₂ is absorbed by seawater, chemical reactions occur that reduce seawater pH, concentrations of carbonate ions, and the saturation states of the biominerals aragonite and calcite in a process commonly referred to as ocean acidification. When the pH and carbonate saturation drop in seawater, carbonate biominerals in shells and skeletons may begin to dissolve, and the water become corrosive for this reason.

Atmospheric CO₂, pH and carbonate saturation have fluctuated significantly over the Phanerozoic history in the oceans. This research presentation focuses on the on the abundance, biodiversity and biogeography of larger benthic symbiont-bearing foraminifera during the Phanerozoic. Benthic and planktic foraminifera produce approximately 20 % of the overall carbonate in modern oceans and as such they are major components of the carbonate budget. How did larger benthic foraminifera react to changes in the oceans over the course of the Phanerozoic history? How did high CO₂ and low pH levels impact this important group and what lesson can we learn from the fossil record for future developments?

This presentation illustrates the reaction of modern and fossil larger benthic symbiont-bearing foraminifera (LBF) to major perturbations in the ocean systems. Larger symbiont-bearing foraminifera have an excellent fossil record, are ubiquitous components of tropical and subtropical biotas and contribute significantly to the carbonate produced in the tropical world's oceans. The fossil record of larger symbiont-bearing foraminifera provides a unique archive to assess the impact of decreasing pH and calcite saturation on environments in future oceans.

How to cite: Langer, M. R.: The fossil record of larger symbiont-bearing foraminifera: A unique archive to assess the impact of decreasing pH and calcite saturation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16549, https://doi.org/10.5194/egusphere-egu23-16549, 2023.

The Late Permian was a time interval characterized by extreme environmental perturbations, culminating with the Siberian Traps-related gas emissions and the subsequent global warming and ocean acidification, which produced the most severe mass extinction of the Phanerozoic (Dal Corso et al., 2022). Evidence of these perturbations are recorded in fossil archives, as pristine brachiopod shells (Garbelli et al., 2017). Here, we show shell microstructural variations and stable isotopes profiles recorded by specimens of Araxilevis intermedius (Abich, 1878), a large-sized and thick-shelled brachiopod species abundant in the Upper Permian of Iran. Nine specimens of A. intermedius were selected from several Wuchiapingian beds of the Hambast Formation in the Abadeh Section and of the Julfa Formation in the Ali Bashi Mountains Main Valley section (Iran), following the correlation by Viaretti et al. (2021). Prior to the isotope analysis different screening tests were performed on the brachiopod shells from both sections: Scanning Electron Microscope microstructural analysis, cathodoluminescence (CL) and trace elements analyses. Specimens of A. intermedius are characterized by a three-layered shell, comprising a secondary layer of cross-bladed laminae and a tertiary columnar layer; the primary layer is not preserved. The specimens from the Hambast Formation of Abadeh show a partially altered shell, whereas those from the Julfa Formation of the Ali Bashi Mountains show a well-preserved microstructure, despite CL analysis indicating that all the specimens were non-luminescent, both the microstructurally well-preserved and the altered ones. After having checked the shell preservation, 12 to 29 powder samples were collected from the longitudinal shell section of each pristine specimen of A. intermedius using a sclerochronological approach. This method allowed to investigate the seasonal environmental changes recorded by the brachiopod shells of A. intermedius from Iran and to test if this species of the Class Strophomenata, abundant in this time interval also outside Iran, can be considered a good archive for paleoclimatic and paleoenvironmental reconstructions in the Late Permian.

Dal Corso J., Song H., Callegaro S., Chu D., Sun Y., Hilton J., Grasby S.E., Joachimski M.M. & Wignall P.B. 2022. Environmental crises at the Permian–Triassic mass extinction. Nat. Rev. Earth Environ, 3, 197-214.

Garbelli C., Angiolini L. & Shen S.Z. 2017. Biomineralization and global change: A new perspective for understanding the end-Permian extinction. Geology, 45(1), 19-22.

Viaretti M., Crippa G., Posenato R., Shen, S.Z. & Angiolini L. 2021. Lopingian brachiopods from the Abadeh section (Central Iran) and their biostratigraphic implications. Boll. Soc. Paleont. It., 60(3), 213-254.

How to cite: Viaretti, M., Crippa, G., and Angiolini, L.: Selecting the best brachiopod biomineral archive of the Wuchiapingian climate change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4839, https://doi.org/10.5194/egusphere-egu23-4839, 2023.

Calcareous nannofossil Watznaueria barnesiae is a resistant and tolerant species and previous morphometric studies have evidenced minor (Erba et al., 2010; Lubke et al.2016) or no size changes during Oceanic Anoxic Events (OAEs) (Bornemann et al. 2006; and Faucher et al. 2017b) as well as during the Cenomanian to Maastrichtian (Linnert et al. 2014). Here, we present the morphometric record from the western Tethys (Cismon core from the Belluno Basin; Piobbico core and the Monte Petrano section from Umbria-Marche Basin, Italy) across the latest Barremian- late Cenomanian which represents a relatively long-time interval (ca. 26 Myrs) marked by interludes of profound changes in the ocean and climatic conditions named (OAE 1a, 1b and 1d). Our study shows that indeed W. barnesiae experienced coccolith and central unit variations during the studied interval. Specifically, smaller coccoliths with also smaller central unit marked the early Aptian to early Albian. The middle Albian to the early Cenomanian was characterized by larger and rounded coccoliths without significant changes in the central unit dimension. Short-term size changes are detected in correspondence of OAE 1a and OAE 1b marked by W. barnesiae size decrease. Particularly, OAE 1a was characterized by the smallest and most elliptical specimens of the studied interval. During the OAE 1b W. barnesiae coccoliths were characterized by a moderate decrease in the mean size, because specimens were already smaller before the event. The morphometric data were correlated with calcareous nannofossil temperature and nutrient indices calculated on the same samples investigated for morphometry. Long-term size changes do not show a clear correspondence with temperature and nutrient variations. W. barnesiae size changes across the early Aptian to early Albian may be related to large igneous province activity. Short-term size variations during OAE 1a and OAE 1b were influenced by the combination of large CO₂ emissions, temperature and fertility increase. In conclusion, although W. barnesiae is a resistant and tolerant species it shows morphometric changes both in short- and long-term, probably in response to partially different causes.

How to cite: Bettoni, C., Bottini, C., Castiglione, S., Erba, E., and Raia, P.: Short and long-term size changes of calcareous nannofossil Watznaueria barnesiae across the latest Barremian- late Cenomanian interval (Cretaceous) in the western Tethys., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7095, https://doi.org/10.5194/egusphere-egu23-7095, 2023.

The Cenomanian-Turonian boundary interval is characterized by environmental perturbations related to the Oceanic Anoxic Event 2 (OAE 2), affecting marine biota, including benthic and planktonic foraminifera. This study shows a continuous record of benthic foraminifera that, together with published planktonic foraminiferal and geochemical data, allow to interpret the paleoceanographic changes in surface and bottom waters across the OAE 2 interval in the Clot Chevalier section (Vocontian Basin, SE France). The Clot Chevalier section is located at an outer shelf-upper bathyal environment according to benthic foraminifera, and their composition and abundance changes allow the identification of seven distinct faunal intervals. Below the OAE 2 (middle Cenomanian), the seafloor shows moderately oxic conditions and oligotrophic regimes suggested by high species diversity and abundance of infaunal and epifaunal taxa. Within the OAE 2 (upper Cenomanian), characterized by the highest values of Total Organic Carbon (TOC), the benthic calcareous taxa (Gavelinella sp., Gyroidinoides sp., Praebulimina elata, Tappanina laciniosa) are abundant and radiolaria dominate the microfossil assemblages (> 50%) suggesting eutrophy and suboxic conditions at the seafloor. The lowest part of the OAE 2 shows high abundance of the benthic agglutinated taxa Ammobaculites sp., Ammodiscus cretaceus, Gaudryina sp., Textulariopsis bettenstaedti that gradually disappear close to the top of OAE 2. Moreover, at ~1 m above the onset of the OAE 2, and simultaneously to the Plenus Cold Event (PCE), a repopulation event and ventilation at the seafloor is documented by the occurrence of the oxic benthic foraminiferal taxa Frondicularia sp. and Ramulina aculeata. Above the OAE 2 (lowermost Turonian), calcareous and agglutinated taxa re-occur with high species diversity and abundance, identifying moderately oxic conditions and mesotrophic regimes. In conclusion, oxygen and organic carbon variations at the seafloor associated to the OAE 2 can be inferred by the benthic foraminiferal composition and distribution.

How to cite: Amaglio, G., Petrizzo, M. R., Holbourn, A., Kuhnt, W., and Wolfgring, E.: Benthic foraminiferal response to the paleoenvironmental changes during the Late Cretaceous Oceanic Anoxic Event 2 at Clot Chevalier (Vocontian Basin, SE France), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6659, https://doi.org/10.5194/egusphere-egu23-6659, 2023.

Oceanic Anoxic Event (OAE)2 (latest Cenomanian, ca. 94 Ma) represents a major palaeoceanographic phenomenon that took place during an interval of extreme global warmth. High-resolution climate records reveal considerable changes in temperature, carbon cycling, and ocean chemistry during this climatic perturbation. In particular, a transient fall in temperature has been detected in the English Chalk on the basis of invasion of boreal faunas and bulk oxygen-isotope excursions: it was called Plenus Cold Event (PCE) characterized by two cooler water intervals punctuated by an intervening warmer episode.

Being calcareous nannoplankton sensitive to changes in surface water conditions, the nannofossil record is ideal to implement our understanding of the paleoceanographic perturbations occurring during OAE 2, and specifically the climatic variability. Previous studies documented how some calcareous nannofossil species, in particular B. constans, underwent size reduction during OAE 2 in response to increased pCO₂ and trace metal concentrations with a temporary size recovery in correspondence of the PCE.

Here, we integrate the nannofossil morphometric datum by reconstructing calcareous nannofossil abundance and assemblage composition in the same three sections (Eastbourne, UK; Clot Chevalier, France; Novara di Sicilia, Italy) previously studied for morphometries. In addition, we performed morphometrics of B. constans and nannofossil quantitative analyses on Tarfaya (Morocco) section. Correlation between the four studied sites is achieved by biostratigraphy and carbon-isotope stratigraphy (δ¹³C_carb and δ¹³C_org).

Nannofossil temperature and nutrient index are calculated to detect if variations in temperature and/or nutrients a) are coeval and similar in the four sections; b) depend on the latitude and/or the paleoceanographic context; c) during the PCE are registered in all studied sections; d) correlate with the nannofossil size changes.

Results highlight some similarities in the fluctuations of the relative abundance of the cold-water species E. floralis in Eastbourne and Clot Chevalier around the PCE interval not mirrored at lower latitudinal sites possibly suggesting that the inflow of cooler waters did not reach the lower latitudes.

How to cite: Bottini, C. and Erba, E.: Calcareous nannoplankton response to the latest Cenomanian Oceanic Anoxic Event 2, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10956, https://doi.org/10.5194/egusphere-egu23-10956, 2023.

Oceanic Anoxic Event 2 (OAE 2), spanning the Cenomanian/Turonian boundary (93.9 Ma) was an episode of major perturbations in the global carbon cycle with a δ¹³C excursion of 2-3‰ documented worldwide. To investigate the response of biota to OAE 2 at high latitudes, we present data from Integrated Ocean Discovery Program (IODP) Sites U1513 and U1516 drilled in the Mentelle Basin (Indian Ocean, offshore SW Australia; paleolatitude of 59°-60° S in the mid-Cretaceous).

The distribution and variations in abundance of planktonic and benthic foraminifera, radiolaria, and calcipheres and their paleoecological preferences permit interpretation of their response to the dynamics of the water mass stratification during the OAE 2.

The lower OAE 2 interval is characterized by the abundance of the opportunistic Microhedbergella that alternates with common eutrophic radiolaria in the surface waters. The concomitant high abundance of benthic foraminifera, especially gavelinellids, might suggest episodes of enhanced oxygenation at the sea floor. The eutrophic feature of the water masses seems more pronounced at Site U1513 because of the rarity of the intermediate dwelling planispiral taxa and the consistent occurrences of the opportunistic and eutrophic calcispheres. In this interval biota indicate a reduced water mass stratification with alternating episodes of enhanced surface water productivity and variations of the thickness of the mixed layer.

Lithologies in the middle OAE 2 interval are characterized by a very low CaCO₃ content and are marked by the near absence of calcareous foraminifera. Radiolaria are the sole microfossils present except for a couple of isolated samples that contain three benthic foraminifera at Site U1516 and calcispheres at Site U1513.The high abundance of radiolaria and the rarity of calcareous microfossils indicate very high fertility conditions and, possibly, shoaling of the CCD which resulted from the emission of volcanogenic CO₂ from the Kerguelen Plateau Large Igneous Province making waters more corrosive.

Conditions moderate after this extreme perturbation as reflected by the sudden increase in abundance of foraminifera and return of carbonate deposition presumably after deepening of the CCD. At Site U1513 the dominance of Microhedbergella over the other planktonic foraminiferal genera, the presence of lower mixed layer planispiral and scattered keeled taxa, and the radiolaria distributions and abundances might suggest the presence of a thick mixed layer with significant thermal differences between surface and thermocline waters. Benthic agglutinated taxa, the epifaunal Gavelinella and Stensioeina and the opportunist Praebulimina show a significant increase in abundance that suggests the presence of oxic-dysoxic bottom waters. On the contrary at Site U1516 Microhedbergella is progressively replaced in abundance by Muricohedbergella to indicate a relatively stable water column with a thick mixed layer and a thin thermocline and frequent episodes of eutrophy toward the top.

At both sites the termination of OAE 2 does not correspond to modifications in the microfossils assemblages; rather, they maintain the same features observed in the underlying interval.

Finally, this study provides a complete record of the microfossil response to the palaeonvironmental perturbation associated to the OAE 2 at southern high latitudes.

How to cite: Petrizzo, M. R., Amaglio, G., Wolfgring, E., Watkins, D. K., MacLeod, K. G., Huber, B. T., and Hasegawa, T.: Response of microfossils to the Late Cretaceous Oceanic Anoxic Event 2 at southern high latitudes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7874, https://doi.org/10.5194/egusphere-egu23-7874, 2023.

The Cretaceous-Paleogene (K-Pg) boundary 66 Ma coincides with the most recent of the ‘Big Five’ Phanerozoic mass extinctions. The extinction was driven by rapid and extreme environmental changes, which included global cooling, surface ocean acidification, and productivity decline, following an extra-terrestrial impact at Chicxulub in the Gulf of Mexico. The excellent global fossil record of the K-Pg extinction and recovery allows examination into how severe environmental perturbations affect calcifying organisms across different oceanographic settings. Combining samples from the expanded shelf section on Seymour Island, Antarctica, and IODP sites 690 and 1135 (paleolatitude 65°S), we present new quantitative morphometric and μ-computed tomography data from large collections of well-preserved macro- and microfossil taxa (benthic molluscs, planktonic and benthic foraminifera) across the K-Pg boundary in the southern high latitudes. Planktonic foraminifera show large extinctions and a size decrease in survivors at the K-Pg boundary itself, but the magnitude of size change is smaller than at lower latitude localities. Surviving shallow marine bivalves from Seymour Island show increased variability of body size and volume at the K-Pg boundary persisting for ~300 kyrs into the Paleogene. Surviving deep-sea benthic foraminifera from Site 690 in the same ocean basin and at the same paleolatitude, respond to both events at the boundary itself and the initial re-stabilisation of the global carbon cycle some 300 kyrs after the K-Pg, with shifts in size, growth rate, and surface:volume ratio. These data reveal the importance of morphological plasticity for promoting resilience and survival in calcifiers across this mass extinction event. They also suggest that trait changes across the K-Pg event occur at different times in different environmental settings and groups, supporting the hypothesis that environmental heterogeneity plays an important role in modulating resilience.

How to cite: Witts, J., Birch, H., Flower, A., MacFie, C., and Schmidt, D.: Morphological plasticity and environmental heterogeneity drove resilience of high latitude marine calcifying taxa across the Cretaceous-Paleogene mass extinction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6982, https://doi.org/10.5194/egusphere-egu23-6982, 2023.

Modern studies on marine ecosystems are limited in time so the evaluation of their stability under the ongoing CO₂ emissions and global warming remains uncertain and necessarily requires a long-term perspective. The dynamic early Paleogene climate offers the crucial opportunity to detect relationships among calcareous plankton, past carbon cycle perturbations and climate. Specifically, the EECO (~53-49 Ma) represents a key interval to investigate the planktic foraminiferal resilience on a long-term perspective as it records the peak temperature and pCO₂ of the entire Cenozoic. We investigated the Pacific Sites 1209-1210 and eastern Indian Ocean Site 762 following the evidence that the EECO marked impacted planktic foraminiferal assemblages at the Atlantic Oceans. Abrupt and permanent abundance decline (more than one-third) of the symbiont-bearing genus Morozovella occurred at the EECO beginning (J event, ~53 Ma) at sites 1209-1210, whereas Acarinina concomitantly increased, as from the Atlantic sites. Site 762 recorded the southern high-latitude migration of the warm Acarinina species coupled with the decline of the ‘cold’ subbotininds. Another major change documented at the Pacific and Indian Oceans revealed to be similar to the Atlantic record and involved the coiling direction (ability to add chambers clock- or counter-clockwise) of the genus Morozovella. Indeed, the morozovellid coiling direction is dominantly dextral below the EECO but became sinistral within the EECO, although this change is registered ~ 200 kyr later at the Pacific Ocean and ~ 200 kyr before at Site 762 where it occurred at the K/X event (~52.8 Ma). Therefore, the morozovellids crisis observed in the Atlantic and Pacific Oceans can be mainly read as the dextral forms decline. Searching for the driving causes of the observed modifications, we performed stable isotope analysis on sinistral and dextral morozovellids morphotypes (possibly cryptic species) from sites 1209-1210 and 762. Results show that the sinistral forms generally record lower d¹³C values, once again as recorded for the Atlantic Ocean. This evidence suggests a reduced symbiosis relationship and/or a slightly deeper habitat, probably a strategy to sustain the stressors induced by the EECO. Our record advises on a causal relationship to chemical-physical modifications in the surface waters, such as the temperature increase. The increased temperature of at least 1°C [Mg/Ca (LA)-ICP-MS] recorded by sinistral morozovellids within the EECO may have acted in the reduced photosymbiotic activity. Conversely, acarininids do not show preferential coiling nor below neither within the EECO and they reveal d¹³C values that imply major ecological flexibility, possibly enabling them to proliferate. The EECO also induced the virtual disappearance of the genus Chiloguembelina after the K/X event at all the Atlantic, Pacific and Indian sites investigated. This disappearance appears to be related to thermocline warming and Oxygen Minimum Zone enhanced oxygenation. Our records demonstrate the wide geographic and possibly global character of the striking modifications occurred in the planktic foraminiferal assemblages during the first ~800 kyr of the EECO. Our derived paleobiology gives new insights into planktic foraminiferal strategies adopted under long-term global warming.

How to cite: Filippi, G., Sigismondi, S., D'Onofrio, R., Tiepolo, M., Cannaò, E., Dickens, G., Wade, B., Westerhold, T., and Luciani, V.: Planktic foraminiferal changes and the Early Eocene Climatic Optimum (EECO, ~ 53-49 Ma): crisis or resilience strategy to global warming?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7934, https://doi.org/10.5194/egusphere-egu23-7934, 2023.

Preserving adaptive capacities of coastal ecosystems in the Anthropocene requires an understanding of their natural variability prior to modern times. We quantified responses of nearshore molluscs assemblages to past environmental changes using 101 samples (~57300 specimens) retrieved from the subsurface Holocene succession and present-day seabed of the Po-Adriatic System (Italy). Present-day assemblages shifted in their faunal composition with respect to their mid-late Holocene counterparts. Major differences are observed in lower nearshore settings, where present-day samples show higher heterogeneity, reduced standardised richness, reduced relative abundance of Lentidium mediterraneum, and increased relative abundance of Varicorbula gibba, scavengers (genus Tritia), and deposit feeders (nuculid bivalves). A dominance of infaunal opportunistic species and shifts towards detritus-feeding and scavenging are often associated with disturbed benthic habitats. Our results suggest that the ongoing anthropogenic stressors (mainly bottom trawling and non-native species) are currently shifting benthic communities into novel states outside the range of natural variability archived in the fossil record.

How to cite: Scarponi, D., Rojas, A., Nawrot, R., Cheli, A., and Kowalewski, M.: Assessing biotic response to anthropogenic forcing using mollusc assemblages from the Po-Adriatic System (Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5721, https://doi.org/10.5194/egusphere-egu23-5721, 2023.

Summer temperatures in excess of 60°C, have been measured in surficial substrates in the exposed areas of intertidal mudflats along the coast of the Arabian Gulf in Bahrain and Saudi Arabia. The incoming flood tide in coastal lagoons may have a temperature as high as 42°C. As a result, large swaths of the intertidal zone in the western Arabian Gulf are barren of living meiofauna (e.g., foraminifera, ostracods, gastropods, and worms) during the hottest months of the year. Samples collected from the intertidal zone in summer yield only dead assemblages of foraminiferal, ostracod, and gastropod shells. Dead assemblages of the foraminifer Peneroplis collected from the upper reaches of the intertidal zone consist largely of juvenile specimens, implying that the living populations, when present, do not reach maturity. In summer, the full range of living meiofaunal organisms is only observed in tidal channels that remain submerged during low tide.

Our laboratory experiments have determined the upper temperature limit for the survival of gastropods and ostracods collected from coastal lagoons of the Western Arabian Gulf is in the range of 47 to 48.5 degrees C. At 50°C total mortality is observed. In Saudi Arabia, substrate temperatures exceeding the lethal temperature for these organisms are already observed in late April, and persist until late October.

The presence of a summer dead zone for intertidal calcifying organisms is consistent with predictions of climate models, which suggested that by 2050 portions of the Arabian Gulf may become too hot to support animal life. On the western coast of the Arabian Gulf, these predictions have already become a fact. 

How to cite: Kaminski, M., Prayudi, S. D., Korin, A., and Tawabini, B. S.: Intertidal lagoons in the western Arabian Gulf are summer dead zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7210, https://doi.org/10.5194/egusphere-egu23-7210, 2023.