SSP2.1

The study of astronomical climate forcing and the application of cyclostratigraphy experienced a spectacular growth over the last decades. In 2018, the first Cyclostratigraphy Intercomparison Project (CIP) workshop constituted the first attempt to compare different methodological approaches and unite the global community around standard, uniform and reliable procedures. Two major conclusions were: [1] There is a need for further organization of the cyclostratigraphic community (e.g. to streamline different methodologies); [2] Cyclostratigraphy is a trainable skill, but currently many universities lack specific resources for training and education. Today, a regular newsletter, a dedicated free open-access journal “Cyclostratigraphy and Rhythmic Climate Change (CRCC)”, a scientific podcast titled CycloPod, and an educational website “www.cyclostratigraphy.org” connect the cyclostratigraphy community. The newly created CycloNet (Research Foundation Flanders FWO Funding) expands this effort into a real and sustainable scientific research network with partners from all around Europe, and open to the global community. At the same time, CycloNet creates a platform for streamlining and integrating new multi-disciplinary approaches. The main scientific targets for CycloNet in the next five years are: [1] Set up a diverse and sustainable community structure, relying on exchange, interaction and training, [2] Boost research by novel methodological approaches applying advanced signal processing techniques, [3] Organize a second Cyclostratigraphic Intercomparison Project. With this poster, we reach out to the broader community to exchange ideas on concepts and activities that CycloNet can help to develop further towards the future.

How to cite: Claeys, P., Sinnesael, M., De Vleeschouwer, D., and Zeeden, C.: CycloNet: European Cyclostratigraphy Network, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6334, https://doi.org/10.5194/egusphere-egu22-6334, 2022.

The Cambrian Explosion is a fundamental turning point in the evolution of life that occurred during the Cambrian Period (~541 to ~485 million years ago), which involved the origination and explosive radiation of all major animal phyla. The bursts of evolution characterizing this period appear concurrently with major modifications to the physico-chemical conditions of the world’s oceans, and are recorded in critical fossil localities where soft-tissues are exceptionally well preserved, including Lagerstätten such as the Burgess Shale and Chengjiang Biota. As a result of the severe lack of biostratigraphically-correlatable fossils (due to widespread endemism during the Cambrian) and sparse high-precision radioisotopic dates, the Cambrian time scale remains among the least defined stage of all the Phanerozoic Eon, with a minimum uncertainty of ±2 million years at its stage boundaries. The absence of a high-resolution geological time scale for the Cambrian Explosion hampers our ability to robustly address widely debated questions concerning the origins and rates of the evolutionary and ecological events, their relationship with paleoceanographic conditions, their responses to astronomically-forced climate change, including from Milankovitch “grand” cycles, and whether these events were globally synchronous.

Using an integrated set of geophysical/chemical proxies with advanced time series techniques on selected stratigraphic sections, this project aims at (1) Generate sets of high- resolution geophysical and geochemical stratigraphic proxies enabling to capture Milankovitch forcing within the selected sedimentary records, (2) Building a high-resolution time scale to improve our knowledges on the timing of major Cambrian evolutionary milestones and geochemical changes and (3) Determine the relationships between Cambrian evolutionary and ecological events with the paleoceanographic changes and Milankovitch cycles.

How to cite: Pas, D., Jamart, V., and Daley, A.: Generating a highly resolved astronomical time scale for the evolutionary and ecological events during the Cambrian Explosion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12868, https://doi.org/10.5194/egusphere-egu22-12868, 2022.

Lithuania is located in the eastern part of the Silurian Baltic Basin which was located near the equator during the Silurian. Kurtuvėnai -161 borehole is located in the Northwest Lithuania. The Silurian geological section of investigated interval is composed of siliciclastic and carbonate deposits and represents deep marine environments.

Samples for stable carbon isotope analysis were collected from 1441 – 1316 m depth interval. The sampling intervals range from 0.2 up to 1m. The stable carbon isotope values from carbonates were measured using Thermo Gasbench II coupled with a Thermo Delta V isotope ratio mass spectrometer.

In the investigated interval 10 graptolites biozones were distinguished: Lapworthi Biozone is distinguished in the lowest part of the section and linked to the Adavere Regional Stage (uppermost Telychian); the centrifugus - belophorus biozones mark the Jaani Regional Stage; perneri - lundgreni biozones correspond to the Jaagarahu; and parvus - nassa biozones marks the Gėluva Regional Stage of the Wenlock.

According to the δ¹³C_carb isotope analysis results, a positive excursion was detected in the lower part of the studied interval from 1422.8 m up to 1390.8 m depth. There, the δ¹³C_carb maximum value is 3.87 ‰. This positive δ¹³C_carb anomaly can be linked to the Ireveken positive stable carbon isotopes excursion and the centrifugus – belophorus biozones interval of the lower Wenlock. We can also observe a positive δ¹³C_carb excusion in the upper part of Homerian (from 1327 m depth) which potentially can be the lower part of the Mulde positive stable carbon isotopic event.

In summary, the δ¹³C_carb values varied from -1.35 ‰ up to 3.92 ‰ in studied interval of Kurtuvėnai-161 borehole. A more detailed biostratigraphic and lithological study is needed for a better understanding of the integrated stratigraphy of the Silurian geological section in the Kurtuvėnai-161 borehole in the future.

How to cite: Želvys, T., Spiridonov, A., Cichon-Pupienis, A., Garbaras, A., and Radzevicius, S.: Preliminary report on δ13Ccarb isotope excursion through the Silurian of Kurtuvėnai - 161 borehole, Northwest Lithuania, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2950, https://doi.org/10.5194/egusphere-egu22-2950, 2022.

The Hangenberg Crisis, at the Devonian-Carboniferous Boundary, severely affected the marine realm. The crisis is characterised by several events associated with change in the sedimentation and biotic extinctions and turnovers. The Hangenberg Black Shale event that recorded the extinction peak in the pelagic realm corresponds to a widespread development of oceanic anoxia and/or dysoxia. The Hangenberg Sandstone event is associated with an extinction of neritic fauna in shallow-water settings, including the final demise of several classical Devonian faunas (stromatoporoids, quasiendothyrid foraminifers, placoderms, etc.). The succession of these events is nowadays explained by a combination of sea level fluctuations (third order transgressive sequence, out-of-sequence regression) and global climatic changes. Through the identification of Milankovitch cycles in the Chanxhe record, we aim at getting a better understanding of the timing and orbital forcing of the different events of the Hangenberg Crisis in shallow-water settings.

The sedimentary record of the interval of interest at Chanxhe is composed of 16 m of alternating decimetre-thick carbonate beds with shaly siltstones, which displays a clear cyclicity. The carbonate-siliciclastic alternations (~0.8 m) are bundled into larger cycles (~5 m) which are separated by intervals dominated by the shaly facies. This is followed by 11 m of carbonate dominated lithology with thin shale layers displaying a less clear cyclicity with ~3 m thick cycles. Then the equivalent of the Hangenberg dark shales is recorded as two dark shaly intervals separated by a carbonate bed. After the Hangenberg dark shales, the section displays carbonates, with the Devonian Carboniferous boundary in massive carbonates 7 m above the top of the black shales.

Samples have been collected along the record every 10 cm which were measured by the portable X-Ray Fluorescence device (Tracer 5, Bruker), allowing to provide elemental data throughout the record. Spectral analysis is applied on Ca and Al, to identify the main cyclicity in the record. The 0.8 meter-thick limestone/shale alternations is clearly recorded in the Ca and Al records and are associated with precession cycles (18 kyr), while the 5 m-cycles are associated with short eccentricity (100 kyr). Prior to the Hangenberg anoxic events, the 100-kyr cycles became less clear and shorter (~ 3 m) which is interpreted as a minimum eccentricity. During the Hangenberg, the cyclicity returns. However, after the Hangenberg and near the Devonian Carboniferous boundary, the facies become very homogeneous, consisting of massively bedded carbonates with no observable cyclicity,  which is also  other contemporaneous sedimentary successions (e.g. China, Poland).   

How to cite: Da Silva, A.-C., Franck, L., Arts, M., and Denayer, J.: Timing and pacing of the Hangenberg Crisis (Devonian-Carboniferous Boundary) in the Chanxhe sections, Belgium, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9471, https://doi.org/10.5194/egusphere-egu22-9471, 2022.

The Nordkapp Basin is located in the southwest Barents Sea. It was formed by rifting in the late Palaeozoic. As the area containing the basin moved north from the equator the climate changed from warm and arid to temperate and humid. Initially a large carbonate platform developed in the Barents Sea in the Carboniferous and Permian. The change in climate due to northward drift caused the platform to shift from a carbonate to clastic platform at the end of the Permian. The sea level changed several times during the Mesozoic due to a combination of eustatic changes and salt diapirism. The depositional environment in the area had been interpreted from multiple cores to vary from onshore coastal plain and delta plain to shelf environment due to the large scale sea level changes. In this work, the cores have been revisited to study smaller scale changes within the environments that had been recognised but not described extensively. The nature of small scale changes is different in different environments and can be seen in different aspects like the bioturbation intensity and clay and sand content. This work will compare the smaller scale sea level changes across the different environments encountered in the cores.

How to cite: Sandvold, M. and Felix, M.: Small scale changes superimposed on larger scale sea level-induced changes in cores from the Nordkapp Basin., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2502, https://doi.org/10.5194/egusphere-egu22-2502, 2022.

The Permian time is characterized by various geodynamic and biotic events. The rifting of Gondwana and the formation of the super-continent Pangea are the most important events. The cessation of major Gondwana rifting and thermal cooling has subsequently resulted in the development of marine Tethyan settings at the margin of the northwestern Indian Plate. Based on detailed outcrop-based lithostratigraphical investigations, a total of three formations have been distinguished. The presence of diagnostic foraminifer’s species able to assign Wordian, Capitanian-Wuchiapingian, and Late Wuchiapingian to Changhsingian ages to these rock units respectively. The detailed biostratigraphic and sedimentological analyses of the upper Permian units of northern Pakistan divulged three phases of the carbonate platform development. Initially, the early Permian pure clastic Gondwana deposits were replaced by the Tethyan setting during the middle Permian (Wordian) time whereby the wave-dominated delta was established as the sea-level rises. However, such deltaic deposits were gradually evolved into a pure carbonate system during the Capitanian time in response to gradual transgression. The Capitanian and Wuchiapingian times show the development of a diverse shallow carbonate platform along the northwestern Indian Plate. The late Permian global regression has significantly disturbed the carbonate factory and subsequently developed river-dominated deltaic deposits of carbonate and clastic mixed system. Such a mixed system was again evolved in a carbonate platform during the Early Triassic.

How to cite: Wadood, B., Li, H., and Khan, S.: Evolution of the Permian carbonate platform on Gondwana shelf, Pakistan: sedimentological and biostratigraphic approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-227, https://doi.org/10.5194/egusphere-egu22-227, 2022.

The Toarcian oceanic anoxic event (T-OAE), dated as early Toarcian is considered one of the most extreme paleoenvironmental perturbations in Earth’s history. It is characterized by global warming, accelerated weathering, sea level rise, oceanic anoxia and acidification and extensive accumulation of organic matter. In Jurassic times, calcareous nannoplankton was already a most efficient rock-forming group and therefore pelagic sedimentary successions preserve invaluable data to track changes across the T-OAE. In this work, we focus on Schizosphaerella across the T-OAE recovered in the uppermost Pliensbachian–lower Toarcian Sogno Core that consists of a fully pelagic, continuous, well-dated record from a deep plateau (~1500 m water depth) in the Lombardy Basin (northern Italy). The objective of this investigation is the quantification of changes in size and abundance of the micrite-forming schizosphaerellids to derive their biocalcification tempo and mode in response to the T-OAE perturbations, to assess the implications of Schizosphaerella biocalcification changes, in terms of abundance and size, for the pelagic carbonate sedimentation. Absolute abundances and morphometric changes obtained for “small Schizosphaerella punctulata” (valve width < 7 μm),  S. punctulata (valve width > 7 μm) and “encrusted S. punctulata” (all specimens characterized by a crust surrounding the valve) revealed large fluctuations in the investigated interval. We identify an abundance fall caused by the failure of S. punctulata and “encrusted S. punctulata” during the core of the T-OAE, that along with the increased abundance of small specimens produced the reduction of average dimensions. Thus, the average size decline is not the result of a general valve reduction, but rather derives from the increase in abundance of small specimens (< 7 μm). This is substantiated by absolute abundances of individual S. punctulata morphogroups that unambiguously demonstrate that such a pattern is not an artefact of relative abundances (closed sum problem).

We hypothesize that the concomitant drop in abundance and shrinkage of valve size is related to hyperthermal conditions associated with excess CO₂ and ocean acidification.

Finally, the co-occurrence in the same samples of S. punctulata specimens (> 7 mm) with and without a crust, is indicative of species-specific diagenetic effects. Based on the S. punctulata ultrastructure we conclude that specimens without diagenetic crusts belongs to S. astrea while encrusted specimens are attributable to S. punctulata and we infer that the presence of the diagenetic crust could be taxonomically diagnostic to distinguish S. punctulata from S. astrea.

How to cite: Faucher, G., Visentin, S., Gambacorta, G., and Erba, E.: Size and abundance variations of Schizosphaerella across the Toarcian Oceanic Anoxic Event, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11752, https://doi.org/10.5194/egusphere-egu22-11752, 2022.

Lower and Middle Jurassic sedimentary deposits in southern Germany have accumulated in a shallow-marine shelf environment and are typically dominated by clayey lithologies with minor occurrences of sandstones and limestones. The sedimentary evolution and paleoclimatic significance of these poorly exposed deposits often remain largely unexplored. Here we present a suite of high-resolution x-ray fluorescence (XRF) core scanning data from southern Germany covering the Upper Toarcian and Aalenian stages. The overall objective of this study is to identify Transgressive-Regressive cycles based on the analysis of three cores obtained during scientific drilling campaigns in 2019-2021. Cores have been analyzed with an Avaatech XRF Core Scanner at a 10 mm sampling interval, an energy of 10 keV and a current of 500 µA to measure element intensities ranging from aluminium through iron. Resulting trends in elemental ratios indicative for subtle grain-size variations such as Si/Al are used to reconstruct shoreline trajectories and establish a sequence stratigraphic framework (see Thöle et al. 2020). Particularly the thick and largely homogenous Opalinuston Formation appears suitable in that respect, likely resulting from extraordinarily high sedimentation rates during the lower Aalenian in southern Germany, thus providing a complete but unexplored archive of paleoclimatic signals.

References:

Thöle, H., Bornemann, A., Heimhofer, U., Luppold, F. W., Blumenberg, M., Dohrmann, R., & Erbacher, J. (2020). Using high‐resolution XRF analyses as a sequence stratigraphic tool in a mudstone‐dominated succession (Early Cretaceous, Lower Saxony Basin, Northern Germany). The Depositional Record, 6(1), 236-258.

How to cite: Mann, T., Bornemann, A., and Erbacher, J.: A sequence-stratigraphic framework for the Toarcian – Aalenian from southern Germany based on x-ray fluorescence core scanning data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4877, https://doi.org/10.5194/egusphere-egu22-4877, 2022.

Sedimentary successions capture the history of geological features and events observable on present-day earth surface as well as those exposed earlier but currently buried or lost to erosion. The Mesozoic rocks in the Kutch Basin (western India) deposited between Middle Jurassic and Early Cretaceous reveal interesting provenance information on lost orogens and buried basins. The southwesterly sediment transport direction indicates north and northwest of the Indian subcontinent as the source area. Detrital zircon and monazite U-Th-Pb geochronology identify dominant sediment input from source rocks equivalent to the late Neoproterozoic Pan-African orogeny (500–650 Ma) along with substantial input from those equivalent to the Cambro-Ordovician Bhimphedian (aka Kurgiakh) (400–500 Ma) orogeny. All other contributing source rocks (ranging from 700 Ma to 3300 Ma) are traceable to the source area following the sediment transport direction. However, outcrops of crystalline rocks with zircon and monazite ages corresponding to the dominant age components are virtually lacking. Rocks equivalent to the Pan-African orogeny are found only as sparse isolated outcrops in the source area. In contrast, this orogeny is well reported from the southern granulite terrain (India), Madagascar, Seychelles and Eastern Africa. Therefore, considering the position of continents during the Mesozoic and the predominance of a 500–650 Ma sediment source in the Kutch Basin, the Pan-African orogenic belt possibly extends to north and north-western India. The current dearth of these outcrops suggests extensive erosion during the Mesozoic greenhouse climate and/or burial under the Deccan Flood Basalts. The other dominant source (400–500 Ma), equivalent to the Bhimphedian orogeny, currently reported as isolated outcrops in the Himalayan-fold-thrust belt (northern India) might have been disturbed and buried by thrusting during the Cenozoic Himalayan orogeny. This study also reveals a large gap of nearly 280 Ma between the youngest detrital zircon (458 Ma) and the depositional age (~170 Ma). This gap may be explained by (i) input of recycled sediment from an older basin, and/or (ii) absence of younger metamorphic events in the source area. The evidences of sediment recycling from thin-section petrography and ultra-stable heavy mineral assemblages (dominated by zircon, rutile and tourmaline) suggest the possibility of a so far unknown (buried or completely eroded) sedimentary basin older than the Kutch Basin. The on-going study of detrital rutile grains in these sediments may provide an alternative explanation for the 280 Ma gap by revealing lower temperature metamorphic events that are not recorded by U-Th-Pb ages of zircon and monazite.

How to cite: Chaudhuri, A., Dunkl, I., Schönig, J., von Eynatten, H., and Das, K.: Geochronology of sediments as a tool to identify lost geological features - a case study from the Mesozoic sedimentary succession of the Kutch Basin, western India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8915, https://doi.org/10.5194/egusphere-egu22-8915, 2022.

High-amplitude shifts in sedimentary δ¹³C characterize the Cretaceous system and have been proven to be of great use for supraregional chemostratigraphic correlation. Here we present an upper Berriasian to lower Coniacian (c. 142 – 88 Ma) composite carbon isotope record based on 14 drill cores, two outcrops and almost 5000 samples. The total record comprises a composite thickness of about 1500 m. All cores and successions are located in the larger Hanover area, which represents the depocenter of the North German Lower Saxony Basin (LSB) in early to mid-Cretaceous times.

Boreal Lower Cretaceous sediments are predominantly represented by CaCO₃-poor mud- and siltstones of up to 2000 m thickness in northern Germany, which become more carbonate-rich during the Albian-Cenomanian transition and even chalkier in the upper Cenomanian to Coniacian interval. A number of global carbon isotope key events including the Valanginian Weissert Event, the OAEs 1a, b and d (Aptian-Albian) as well as for the early Late Cretaceous the Mid-Cenomanian Event (MCE), the OAE 2 (Cenomanian-Turonian Boundary Event) and the Navigation Event, among others, have been identified allowing for a detailed comparison with Tethyan and other Boreal records. Thus, this new detailed chemostratigraphy provides a unique opportunity to potentially overcome many still existing Boreal–Tethyan correlation issues. The presented record can be considered to be almost complete, albeit a small gap in the early Albian cannot be ruled.

How to cite: Bornemann, A., Erbacher, J., Blumenberg, M., and Voigt, S.: A new Berriasian to Coniacian composite carbon isotope record from the Boreal Realm, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2200, https://doi.org/10.5194/egusphere-egu22-2200, 2022.

The Albian-Santonian interval (113-83 Ma) is considered as a transitional period between the Early Cretaceous times, marked by a succession of short climatic variations associated with volcanism episodes and the Late Cretaceous times, marked by a progressive decrease of temperatures. This 30 Myr-longed interval is characterized by a gradual increase of temperature in oceanic domain, which culminates during the Cretaceous thermal Maximum, at the end of the Turonian (~ 90 Ma). Although the evolutions of continental weathering and climatic conditions are well documented in oceanic domain of low to middle latitudes, especially in Atlantic and Tethyan oceans, their record are less well known in high latitudes, especially in the proto-Indian Ocean. Thanks to the Exp IODP 369, two new boreholes, U1512 and U1513, drilled respectively in the Bight Basin (Southern Australia) and in the Mentelle Basin (Southwestern Australia), provide the opportunity to study the Albian to Santonian deposits at high latitudes (~60°S). Cores of the site U1513 recovered a sedimentary sequence from Albian to Santonian whereas the site U1512 record a continuous sequence from Turonian to Santonian. An integrated study, coupling mineralogical determination (XRD analyse and SEM observation) and isotopic analyses of neodymium on clay fraction was done on both sites in order to determine climatic and weathering conditions in these southern high latitude zone.

Our study reveals that the clay fraction are dominated by smectites (>85% in average) with lower proportions of kaolinites (< 25%) and traces of illites (<5%) associated with opal-CT and clinoptilolites. SEM observations have demonstrated a negligible impact of both burial diagenesis and authigenesis on clay assemblage. They are thus interpreted as the products of the alteration of rocks and pedogenic blankets from adjacent landmasses. At Site U1513, the Albian clay fraction contains noticeable proportions of kaolinites (5 to 25%), which progressively decrease during the Cenomanian and disappear at the Cenomanian-Turonian boundary (~94 Ma). Turonian to Coniacian deposits are almost exclusively composed of smectites. The decrease in kaolinite proportions is coeval with a decrease in ε_Nd values, which indicates a probable diminution in the erosion of Australian Archean rocks. At Site U1512, clay mineral assemblages, show slight variations along the borehole, which reflects stable weathering conditions during the 10 Myr of the Turonian-Santonian interval.

The dominance of smectites and to a lesser extent of kaolinites seem to indicate a warm to temperate and humid climate for high latitude zone during the Albian-Santonian interval. The decrease in kaolinite proportions from Albian to early Turonian in U1513 reflect probably a decrease of hydrolysis conditions associated with increasing temperatures and sea-level rise in southwestern Australian margins. The absence of noticeable variations from the Turonian to the Santonian in both sites would be the result of a stable continental climate for several million years after the Cretaceous thermal maximum (~ 90 Ma). The persistent presence of kaolinites in U1512 (southern Australia) could be due to the proximity of the Bight Basin with Australian Western Highlands.

How to cite: Munier, T., Riquier, L., Baudin, F., Metgalchi, A., Revillon, S., and Boudouma, O.: Continental weathering and climate conditions in southern high latitudes during the Albian-Santonian interval (U1512 and U1513 sites, Exp IODP 369, SW Australia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10544, https://doi.org/10.5194/egusphere-egu22-10544, 2022.

The late Cenomanian-Turonian interval is characterized by major changes in the global carbon cycle, identified by stable carbon isotope excursions with associated climatic variations (e.g., OAE2, Late Turonian Events). These changes are linked to significant paleoceanographic modifications that impacted the biota, especially primary producers (e.g., calcareous plankton), forcing extinctions and evolutionary radiations. A reliable biostratigraphy is an essential tool to correlate both environmental and biotic changes worldwide.

Calcareous nannofossils and planktic foraminifera are well recognized as useful markers for biostratigraphy and paleoecological studies. However, the Cenomanian-Turonian calcareous nannofossil biohorizons are still poorly constrained because the nannofossil assemblages suffer from marked provincialism and taxonomic uncertainty that can blur their biochronological potential.

In order to improve the calcareous nannofossil biostratigraphic scheme of the late Cenomanian-Turonian interval, we present new data from the Breonio section (northeastern Italy), in the southwestern part of the Trento Plateau, and from the Quero section (northeastern Italy), located in the western Belluno Basin (central-western Tethys).

The analyses of calcareous nannofossil and planktic foraminiferal assemblages were integrated with the δ¹³C, δ¹⁸O and CaCO₃ curves. The δ¹³C values highlight several positive, global, stable carbon isotope shifts in both sections. The CaCO₃ signal of the Quero section suggests that the isotopic signal is pristine because the CaCO₃ values are not coupled with δ¹³C isotope shifts. On the contrary CaCO₃ curve seems generally to reflect the lithological signal. On the basis of biostratigraphic data the detected positive shifts have been correlated with the late Cenomanian-Turonian events, specifically, the Oceanic Anoxic Event 2, Holywell, Round down, Pewsey, and Late Turonian Events 1, 2, 3. The stratigraphic position of biohorizons with respect to the globally recognized δ¹³C excursions can provide a valuable mean to evaluate their potential synchronism/diachronism.

Our preliminary data show a good correspondence with the recent calcareous nannofossil-planktic foraminiferal integrated scheme (Geologic Time scale 2020; Gale et al. 2020) for the late Cenomanian-Turonian interval, although some calcareous nannofossil markers were not recorded. Interestingly, some «standard» and additional calcareous nannofossil events are promising proxies for the Late Turonian Events 1 and 2.

References

Gale A.S., Mutterlose J. & Batenburg S. (2020). The Cretaceous Period, in Gradstein F.M. et al., eds., Geologic Time Scale 2020: Boston, Elsevier, pp. 1023-1086.

How to cite: Simonato, M., Gardin, S., Giusberti, L., Luciani, V., Preto, N., Roghi, G., Barbieri, S., Xausa, F., and Fornaciari, E.: Integrated calcareous plankton biostratigraphy and stable isotopes stratigraphy of Cenomanian-Turonian interval of Breonio and Quero sections (central-western Tethys), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11890, https://doi.org/10.5194/egusphere-egu22-11890, 2022.

Oceanic Anoxic Event 2 (ca. 94 Ma; OAE2) was one of the largest Mesozoic carbon cycle perturbations, but associated carbon emissions, primarily from the Caribbean large igneous province (LIP) and marine burial fluxes, are poorly constrained. Here, we use the carbon cycle box model LOSCAR-P to quantify the role of LIP volcanism and enhanced marine organic carbon (C_org) burial as constrained by the magnitude and shape of the positive stable carbon isotope (δ¹³C) excursion (CIE) in the exogenic carbon pool and atmospheric pCO₂ reconstructions. In our best fit scenario, two pulses of volcanic carbon input—0.065 Pg C yr^–1 over 170 k.y. and 0.075 Pg C yr^–1 over 40 k.y., separated by an 80 k.y. interval with an input of 0.02 Pg C yr^–1—are required to simulate observed changes in δ¹³C and pCO₂. Reduced LIP activity and C_org burial lead to pronounced pCO₂ reductions at the termination of both volcanic pulses, consistent with widespread evidence for cooling and a temporal negative trend in the global exogenic δ¹³C record. Finally, we show that observed leads and lags between such features in the records and simulations are explained by differences in the response time of components of the carbon cycle to volcanic forcing. 


How to cite: Papadomanolaki, N. M., van Helmond, N. A. G. M., Paelike, H., Sluijs, A., and Slomp, C. P.: Quantifying volcanism and organic carbon burial across Oceanic Anoxic Event 2, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4796, https://doi.org/10.5194/egusphere-egu22-4796, 2022.

The late Cretaceous climate is represented by an 8-10 °C decline of global mean temperatures that terminated global warmth of mid-Cretaceous times. Causal mechanisms of the cooling are still not well constrained and discussed in the interplay of reduced volcanic greenhouse gas emission and intensified silicate weathering as a global carbon cycle feedback. The lithium isotopic composition (δ⁷Li) of marine carbonates is a proxy for the chemical weathering intensity of silicate rocks, and thus provides information about the role of silicate weathering as thermostat and sink for atmospheric CO₂.

Here, we present the first detailed chalk-derived Late Cretaceous δ⁷Li record (91-66 Ma) of the boreal white chalk in Northern Germany (Lägerdorf-Kronsmoor-Hemmoor) and from sections in southern England as archive for the seawater lithium isotopic composition. In the course of this study, we will also analyze the archives of skeletal calcite from brachiopods, belemnites and rudists, which should enable us to identify systematic offsets among different calcifiers related to vital effects by the direct comparison of fossilized shells and their surrounding sediments.

To handle the potential impact of clay contamination in bulk carbonates, we applied a pre-leaching and leaching procedure with 1 M ammonium acetate and 0.05 M nitric acid. The method was tested for a 1.85 Ma old sample of coccolith ooze from the Manihiki Plateau (equatorial West Pacific Ocean), which has consistent δ⁷Li values and shows a systematic negative 3-4 ‰ offset to modern seawater. In addition, the degree of potentially leached silicates is monitored by the analysis of E/Ca ratios, like Al/Ca.

In total, our late Cretaceous lithium isotope record shows a trend of rising δ⁷Li values between +16 and +25 ‰. Superimposed, the curve displays a rise in the Santonian, a local maximum in the early Campanian followed by a drop to a local minimum in the late Campanian. Subsequently, the δ⁷Li values rise again towards elevated values in the Maastrichtian. Overall, the shape of the δ⁷Li curve strongly resembles the evolution of deep-sea temperatures based on benthic oxygen isotopes suggesting a close link between climate and weathering. Thereby, more positive δ⁷Li values correspond to cooling periods and the late Campanian lowering of δ⁷Li values parallels the intermittent deep-sea warming. Such a pattern points towards a strong relationship between the congruency of silicate weathering and climate on a multi-million year time scale.

How to cite: Huber, S. J., Schlidt, V., Lenk, L., Seitz, H.-M., Raddatz, J., and Voigt, S.: Insights from the first detailed record of Late Cretaceous seawater lithium isotopic composition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5761, https://doi.org/10.5194/egusphere-egu22-5761, 2022.

This study investigates the Paleogene deep-water depositional system of the Gosau Group at Gams, Styria (Austria). The examined sections of Danian to Ypresian age (NP1-NP12) comprise sediments of the Nierental and Zwieselalm formations. Four deep-water clastics facies assemblages were encountered, (1) carbonate-poor turbidites, (2) carbonate-rich turbidites, (3) marl-bearing turbidites and (4) a marl-dominated facies. Slump beds and mass flow deposits are common in all facies.

The examined sections predominantly consist of sandy and silty graded beds, including fine breccia layers at the base, to silty shales or claystones on top. Normal grading, lamination, amalgamation of sandy beds and bioturbation are characteristic for all sections. The thickness of sandstone beds varies strongly from only centimeters to several meters, but in general, sandy beds get thicker at sections dated at late Selandian age or younger. Within thinner beds Bouma T_bcd intervals are present. Thus, most sections contain sequences of thin to medium-bedded, fine-grained turbidites.

Based on heavy mineral, thin section, microprobe, and paleoflow analyses, provenance was from the surrounding Northern Calcareous Alps (NCA) rocks and exhuming metamorphic Upper Austroalpine units to the south. Provenance indexes based on heavy mineral assemblages indicate the dominance of an upper greenschist to lower amphibolite facies source of the investigated sediments. In addition, biogenic-calcareous material was delivered by adjacent contemporaneous shelf zones.

The sedimentary depocenter was situated at the slope of the incipient Alpine orogenic wedge, in frontal parts of the NCA, facing the subducting Penninic Ocean/Alpine Tethys. The evolution of the Gams Basin was connected to the eoalpine and mesoalpine orogeny, and the adjunctive transpressional setting. The Gams slope basin provided a fairly small depositional area and accommodation space on the incipient alpine orogenic wedge, and the pervasive tectonic deformation of the NCA destroyed and obscured important features of the formerly confined source-to-sink system. However, the Gams deep-water depositional system is interpreted as an aggrading or prograding submarine fan, deposited into a small confined slope basin, positioned along an active continental margin, bound and influenced by (strike-slip) faults, related to crustal shortening. The development of the Gams slope basin and its infilling sequences was mainly dominated by tectonism and sediment supply, rather than by eustatic sea-level fluctuations. General greenhouse conditions, with enhanced chemical weathering under seasonal conditions are assumed for the entire Gosau Group of Gams (Upper Cretaceous to Eocene), which enhanced erosion and facilitated a greater terrestrial sediment supply. Particularly an increased input of siliciclastics around the PETM is noticeable, including significant numbers of sandy turbidites. The basin was cut off during the Eocene due to renewed orogeny. A Quaternary analogue for the Paleogene basin setting of the Gams area is represented by the Santa Monica Basin in the California Continental Borderland.

How to cite: Koukal, V. and Wagreich, M.: The Paleogene Gosau Group of Gams slope basin of the incipient Eastern Alpine orogenic wedge (Austria), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4589, https://doi.org/10.5194/egusphere-egu22-4589, 2022.

The Eocene, as the warmest epoch during the Cenozoic, has received much attention as it can inform us about the features of global warmth, highly relevant to a “high-CO₂” future. However, there is still a lack of knowledge regarding some key features of global warm climates, such as how higher global temperatures might have affected the duration and intensity of seasonality.  Furthermore, recognizing seasonal cycles is essential when interpreting proxy data and reconstructing paleo climate, e.g. in order to understand inter-annual bias between proxies. 

In the current study the seasonal variations in sea surface temperature (SST) and fresh water input into the Anglo-Paris Basin (subjacent areas of the Paleo-North Sea) was investigated. Marginal seas, like the Paleo North Sea, are an important intersection between the continental and marine realm, and are especially sensitive to short-term climate variations.

In order to resolve seasonal and perennial changes in SST and freshwater balance, we measured Ba/Ca, δ¹⁸O, and the clumped isotopic composition (∆₄₇) of exceptionally well-preserved fossil molluscs. Although δ¹⁸O is commonly used for the reconstruction of temperature, its calculation often assumes a constant δ¹⁸O value of seawater, which might not be true on seasonal scales and/or within swallow marine basins. In this context, ∆₄₇ was employed to determine the average temperature amplitude, due to its independence from δ¹⁸O_seawater. Additionally, Ba/Ca was used to account for periods with enhanced fresh water input, because barium mostly enters the oceans via fluvial systems and could therefor indicate seasonally enhanced and isotopic lighter fresh water input.            

The bivalve species Venericor planicosta was employed as proxy archive, due to its long life span (10-20 years) and its wide distribution in the Anglo-Paris Basin during the Eocene. The pristinely preserved, aragonitic bivalve shells were sampled by micro-milling (δ¹⁸O, ∆₄₇), as well as, laser ablation (Ba/Ca), to generate proxy records with high temporal resolution.

The isotopic data reveal well pronounced seasonal oscillation with a sinusoidal shape and a maximum difference of 2‰, from -3,5‰ to -5,5‰. On average, the inter-annual variation of the δ¹⁸O record is around 1‰. The Ba/Ca record, on the other hand, shows a flat background with recurring large and sharp peaks. While the baseline Ba/Ca values are around 20 µmol/mol, the peaks can reach up to 300 µmol/mol. The peaks largely fall together with periods of depleted δ¹⁸O values. These results hint to a possible seasonal bias of temperature records in the Anglo-Paris basin based purely on δ¹⁸O, due to variable δ¹⁸O of seawater. This is further implied by the back-calculation of δ¹⁸O_seawater from ∆₄₇ measurements, revealing a range from 2‰ to -4‰. 

How to cite: Kniest, J. F., Davies, A., Todd, J. A., Sigwart, J. D., Evans, D., Fiebig, J., Voigt, S., and Raddatz, J.: Eocene seasonality resolved by coupled Ba/Ca and stable oxygen isotope ratios in bivalve shells, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4815, https://doi.org/10.5194/egusphere-egu22-4815, 2022.

Carbon dioxide (CO₂) emissions are rapidly rising leading to warmer oceans, surface ocean acidification, and complex changes in marine biogeochemical cycling. Calcareous nannoplankton: single-celled marine haptophytes, are likely particularly susceptible to such environmental changes, because they form microscopic plates made out of calcium carbonate (calcite). As these organisms lie at the base of the marine food web, it is critical that we understand how they respond to climate change over longer (millennial) timescales so that we can better predict the long-term effects of current and future environmental change on marine communities.

The high CO₂ world of the early Eocene (~56 to 48 Ma) is characterized by multiple transient warming events (‘hyperthermals’), and is generally considered to be one of the best geologic analogues for future climate change. Here, we present preliminary, low-resolution calcareous nannoplankton assemblage data from the early Eocene of recently-drilled IODP Site U1553 (Campbell Plateau) in the South Pacific Ocean. Sediment cores recovered from Holes C and D at Site U1553 provide arguably one of the most complete and expanded early Eocene records yet from this relatively understudied region, including many of the previously recognized hyperthermals. This coupled with the high calcium carbonate content of the sediments, makes it an ideal case study for exploring millennial-scale changes in calcareous nannoplankton community composition and morphometry during transient warming events.

Within this presentation, we predominantly focus on the Paleocene-Eocene Thermal Maximum (PETM): the largest and best-studied of the early Eocene hyperthermals. Our results suggest that the turnover in nannoplankton species during this warming event was very similar to that observed at other southern high latitude sites such as Maud Rise. More minor ecological ‘jostling’ appears to have occurred prior to the onset of the PETM and following the event; however, the significance of these smaller changes in community composition have yet to be statistically analyzed at the time of writing. It is our aim to combine our assemblage counts with morphometric data to determine whether calcareous nannoplankton acted as a source or sink of carbon dioxide during the early Eocene hyperthermal events. We will also extend our dataset to include several of the smaller hyperthermals that succeeded the PETM, to elucidate whether calcareous nannoplankton exhibit a scaled or threshold response to warming.

How to cite: Jones, H., Niederbockstruck, B., and Röhl, U. and the IODP Expedition 378 Scientists: Calcareous nannoplankton community composition across multiple early Eocene hyperthermal events at International Ocean Discovery Program (IODP) Site U1553 (Campbell Plateau, SW Pacific), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9745, https://doi.org/10.5194/egusphere-egu22-9745, 2022.

The late Miocene-early Pliocene Biogenic Bloom was a significant event defined by the anomalously high marine biological productivity documented in the Indian, Pacific, and Atlantic Oceans; but its causes and consequences at different paleogeographical settings are not yet fully understood. Previous records from Ocean Drilling Program (ODP) Site 1085 (Cape Basin, Southeast Atlantic Ocean) indicate enhanced biological productivity between 7 and 4 Ma, as supported by increased linear sedimentation rates, benthic foraminiferal accumulation rates, and increased total organic carbon mass accumulation rates (Diester-Haass et al., 2002; 2004). To look into the paleoenvironmental consequences of the Biogenic Bloom, we investigated the benthic foraminiferal turnover at this site. Results were integrated with an age model based on a bio-astrocyclostratigraphic tuning and low-resolution carbon and oxygen stable isotope records on benthic foraminifera (i.e. Cibicidoides mundulus) across an interval spanning from the Tortonian (late Miocene) to the Zanclean (early Pliocene). Quantitative analyses of the assemblages and statistical analyses point to increased food supply to the seafloor. The proliferation of phytodetritus exploiting taxa such as Alabamina weddellensis and Epistominella exigua point to an episodic nutrient supply related to seasonal phytoplankton blooms during the Biogenic Bloom.

Reference

Diester-Haass, L., Meyers, P. A., & Vidal, L. (2002). The late Miocene onset of high productivity in the Benguela Current upwelling system as part of a global pattern. Marine Geology, 180(1-4), 87-103.

Diester-Haass, L., Meyers, P. A., & Bickert, T. (2004). Carbonate crash and biogenic bloom in the late Miocene: Evidence from ODP Sites 1085, 1086, and 1087 in the Cape Basin, southeast Atlantic Ocean. Paleoceanography, 19(1).

Acknowledgements

University of Padova DOR grant, CARIPARO Foundation Ph.D. scholarship.

Spanish Ministry of Economy and Competitiveness and FEDER funds (PID2019-105537RB-I00).

How to cite: Gastaldello, M. E., Agnini, C., Westerhold, T., Dallanave, E., and Alegret, L.: The response of benthic foraminifera to the late Miocene-early Pliocene Biogenic Bloom: the record from Southeast Atlantic Ocean (ODP Site 1085), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2260, https://doi.org/10.5194/egusphere-egu22-2260, 2022.

During the Messinian Salinity Crisis (5.97-5.33 Ma), evaporite deposition throughout the Mediterranean basin records a
series of dramatic environmental changes as flow through the Strait of Gibraltar was restricted. In the first stage of
evaporite deposition, cycles of gypsum appear in shallow basins on the margins of the Mediterranean. The complex
environmental history giving rise to these cycles has been investigated for decades but remains somewhat mysterious.
Notably, whether the evaporites are connected to significant changes in Mediterranean sea level is an open question.
In one proposed model, competition between tectonic uplift and erosion at the Strait of Gibraltar gives rise to self-sustaining
sea-level oscillations, or limit cycles, which trigger evaporite deposition. I show that limit cycles
are not a robust result of the proposed model and discuss how any oscillations produced by this model depend on
an unrealistic formulation of a key model equation. A more realistic formulation would render sea-level limit cycles improbable,
if not impossible, in the proposed model.

How to cite: Baum, M.: Limit Cycle Model of Messinian Salinity Crisis Incorrect and Irreproducible, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1042, https://doi.org/10.5194/egusphere-egu22-1042, 2022.

The Miocene-Pliocene transition (MPT) in the Mediterranean area represents one of the unresolved geological riddles of the Neogene. The MPT coincides with the end of the Messinian salinity crisis (MSC, Hsü et al., 1977), an event that led to the deposition of massive volume of evaporite on the Mediterranean seafloor. The final stage of the MSC started at ~5.53 Ma and its uppermost part corresponds to the “Lago-Mare” phase, characterized by the occurrence of brackish shallow water ostracods of Parathethyan origin. The “Lago-Mare” deposits are sharply overlain by Zanclean (earliest Pliocene) marine sediments, astrocronologically dated to start at 5.33 Ma (Van Couvering et al. 2000).

The interpretation of this abrupt environmental change is strongly debated. One scenario assumes a catastrophic flooding of all Mediterranean sub-basins that were previously disconnected from the Atlantic Ocean and from each other (Caruso et al., 2020). An alternative scenario invokes a gradual refilling started during the Lago-Mare phase and continued during the basal Pliocene (early Zanclean) (Roveri et al., 2008; Stoica et al., 2016; Merzeraud et al., 2018).

To investigate the paleoenvironmental conditions across the MP transition, we investigated six sections along a west to east transect of the Apennines foredeep, using an integrated approach that merge the traditional stratigraphic, palaeontological, geochemical, and petrographic data with the analysis of molecular fossils (lipid biomarkers).

The top of the Messinian sediments is marked by a bioturbated dark layer in all six studied sections. The presence of glauconite at the top of the dark layer and of firm ground burrows of the Glossifungites icnofacies filled with Zanclean sediments suggest starved sedimentary conditions and the partial lithification of the sea floor during the earliest Zanclean. In addition, the benthic foraminifera indicate an increase of bottom oxygen content and a deepening of the basin across the MPT. Preliminary results of over 40 samples indicate excellently preserved molecular fossils both in the “Lago-Mare” sediments and in the Zanclean open marine deposits with a predominance of terrestrially-derived higher-plants long chain n-alkanes (LC_alk) and of glycerol dialkyl glycerol tetraethers (GDGTs) of both marine and terrestrial origin. Future analyses will focus on the compound specific carbon and hydrogen isotopes of LC_alk to further constrain precipitation and vegetation changes associated to the MPT. Changes in seawater (via isoprenoidal GDGTs) and land temperatures (via branched GDGTs) will be also reconstructed.

How to cite: Pilade, F., Dela Pierre, F., Natalicchio, M., Vasiliev, I., Birgel, D., Mancini, A., Lozar, F., and Gennari, R.: THE END OF THE MESSINIAN SALINITY CRISIS IN THE MEDITERRANEAN: new data on the Miocene-Pliocene boundary., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2053, https://doi.org/10.5194/egusphere-egu22-2053, 2022.

The Western Pacific Warm Pool (WPWP) significantly affects the heat budget and associated climate over the Indian Ocean region. The reduction in the WPWP is manifested in the form of reduced Indonesian Throughflow (ITF) and may be well represented by the census count and oxygen isotope records of planktic foraminifera.

The present study is an attempt to reconstruct the episodes of reduction in the WPWP during the Quaternary, on the basis of extremely low relative abundance of planktic foraminifera Pulleniatina (Pu.) obliquiloculata from the ODP Hole 769B in the Sulu Sea. This species is a thermocline dweller, that thrives in tropical to warm subtropical latitudes. It is considered to be an indicator of Kuroshio Current and shows a direct correlation with the expansion of the WPWP.

In the ODP Hole 769B, Pu. obliquiloculata shows a low relative abundance during the Quaternary, except a few instances of significant increase, so much so that it comprises almost 50% of the entire faunal assemblage. The rising trend is characteristic of high SST and an expansion in WPWP. We have identified seven distinct events of sharp decline in the relative abundance of Pu. obliquiloculata (<5%) and named these events as Pulleniatina Minimum Events (PMEs). These events are: PME-1- (2.21-2.08 Ma); PME- 2 (1.8-1.36 Ma); PME- 3 (0.9-0.87 Ma); PME-4 (0.79-0.65 Ma), PME-5 (0.48-0.44 Ma), PME-6 (0.16-0.13 Ma) and PME-7 (0.04-0.02 Ma) in descending stratigraphic order. We interpret these events to mark be the result of the reduction in the WPWP. We have also found the occurrence of temperate fauna during the stratigraphically younger last five PMEs (PME7 to PME3), which indicate reduction in the Western Pacific Warm Pool (WPWP) probably caused by glaciations. The glacial events probably enhanced the Oyashio Current, which caused the influx of cool fertile waters in the Sulu Sea. The evidence of the increased fertility in the Sulu Sea is marked by the increased relative abundance of Neogloboquadrina dutertrei, a fertility indicator species, during the PME7 to PME3. The PME2 and PME1 show no presence of temperate fauna. These events of reduction in the WPWP may be attributed to the development of El Niño like conditions.

The PMEs were also correlated with the five PL events recorded by Sinha et al (2006) from ODP Hole 763A in the Eastern Indian Ocean. These PL events: PL-1- (2.22 Ma); PL-2 (1.83 Ma); PL-3 (0.68 Ma), PL-4 (0.45 Ma) and PL-5 (0.04 Ma), represented reduced strength of ITF either due to the glacial events (PL-3 to PL-5 events) or due to ENSO induced changes (reduction) in the WPWP (PL-1-and PL-2 events).

The PMEs show striking correlation with the PL events, giving testimony to episodes of reduction in the WPWP during Quaternary.

How to cite: Singh, V., Singh, A., and Sinha, D.: Pulleniatina Minimum Events from the Sulu Sea as evidence for Reduction in the Western Pacific Warm Pool during Quaternary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12, https://doi.org/10.5194/egusphere-egu22-12, 2022.

The deep water formation in the Labrador and Nordic Seas is crucial for the global thermohaline circulation nowadays and it remains debated whether changing boundary conditions in terms of global warming may influence the deep convecting activity. Deep convection leads to the formation of Iceland Scotland Overflow Water (ISOW), which is an essential part of the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). However, surface conditions in the Nordic Seas were unlikely always favorable for the formation of deep water in the past.

During Marine Isotope Stage (MIS) 11, a strong and active AMOC [e.g. 1] was reconstructed, which also contributed to the mass loss of the Greenland Ice Sheet [2]. However, cold and fresh surface conditions prevailed in the central Nordic Seas [3], which have been ascribed to freshwater input from the higher latitudes [4]. Thus, the question arises, whether and where deep water formation took place in the Nordic Seas.

Here, we reconstruct authigenic neodymium isotopes extracted from deep sea sediment from the Gardar Drift from 470 to 374 ka. IODP Site U1304 is located directly in the modern flow path of ISOW and should therefore sensitively track changes of this water mass in the past. Today, it is characterized by a strongly radiogenic neodymium isotopic composition, which markedly differs from other North Atlantic water masses.

Starting right at the onset and for the full length of the interglacial MIS 11c, a radiogenic Nd isotopic composition is switched on and prevailed indicating the presence of ISOW at the core site. More unradiogenic conditions indicate the return to glacial like conditions during a short event in MIS 11b. However, during MIS 11a the radiogenic values point again to a persistent presence of ISOW.

Thus, although the boundary conditions in terms of freshwater fluxes and sea level were significantly differing in the central Nordic Seas, the deep water formation presumably happened in the southern part of the Nordic Seas. This led to the active formation of ISOW, which in turn helped drive the active and strong AMOC during MIS 11.

[1] Dickson et al. (2009), Nat. Geosci. 2: 428-433.

[2] Rachmayani et al. (2017), Paleoceanography 32: 1089-1101.

[3] Kandiano et al. (2016), GRL 43: 10929-10937.

[4] Doherty and Thibodeau (2018), Front. Mar. Sci. 5: 251.

How to cite: Link, J. M. and Frank, N.: Persistent ISOW formation during MIS 11, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10018, https://doi.org/10.5194/egusphere-egu22-10018, 2022.

The mean cooling of the global ocean during the Last Glacial Maximum (LGM) was recently estimated to 2.6°C using noble gases trapped in ice cores (1). The ocean, however, is highly heterogeneous with respect to its internal temperature varying both in latitude and water depth. While temperature changes in the deep ocean are small at about 2 - 3 °C (1,2), the upper ocean is more dynamic. Regional temperature anomalies of up to 7°C are predicted during the LGM compared to modern interior ocean temperature by global ocean circulation models (3). Due to the temperature drop to near freezing conditions and the global increase in salinity from ice sheet growth, the oceans’ deep interior became strongly haline stratified (2). Temperatures of the glacial ocean thermocline are, however, less well constrained.

Here, thermocline temperature reconstructions since the last glacial based on the Li/Mg ratio in cold-water coral skeletons are presented. The coral samples, collected from 300 - 1200 m water depths from different sites in the Atlantic (43°N to 25°S), reveal synchronous 5 - 7°C cooling during the last glacial period compared to today, as well as a dramatic shoaling of the thermocline. At the end of the LGM, warming of the upper thermocline ocean occurred early in the southern hemisphere followed by a fluctuating warming and thermocline deepening in the northern Hemisphere. This supports the oceanic climate seesaw proposed by Stocker and Johnson in 2003 (4). We thus propose dramatic changes in the export of polar waters towards the Equator and an enhanced subsurface ocean stratification leading to a mostly polar Atlantic with a shallow permanent thermocline during the glacial.

References:

1) Bereiter et al., Nature 553, 39-44 (2018).
2) Adkins et al., Science 298, 1769-1773 (2002).
3) Ballarotta et al., Clim. Past 9, 2669-2686 (2013).
4) Stocker and Johnsen, Paleoceanography 18, 1087 (2003).

How to cite: Lausecker, M., Hemsing, F., Krengel, T., Förstel, J., Schröder-Ritzrau, A., Border, E. C., Orejas, C., Titschak, J., Wienberg, C., Hebbeln, D., Wefing, A.-M., Montagna, P., Douville, E., Matos, L., Raddatz, J., and Frank, N.: Severe cooling of the Atlantic thermocline during the last glacial, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9308, https://doi.org/10.5194/egusphere-egu22-9308, 2022.

Over the last decades, significant increases in temperature and in the incidence of extreme climatic events have been registered in the Iberian Peninsula. Environmental changes  are easily recorded in high mountain lakes, due to their sensitivity and isolated location. Since paleolimnological information can be very useful for planning and modelling future climate change scenarios, it is necessary to find suitable lakes and test their sensitivity to current and past climatic shifts in order to adequately fulfill these tasks.

In order to test the suitability of the Bassa Nera pond as an indicator of global climatic change, this study aims to examine the variations of different  paleoindicators over the last 15,000 years. The variations of paleoenvironmental data can be then compared with the changes of different biological indicators (chironomids, diatoms, pollen), to find likely correlations that can be used to figure out future climatic scenarios and to provide information for environmental management.

For this study, a core of approximately 1,100 cm was extracted (PATAM 12-A-14) and dated with radiometric techniques. Sedimentological analysis was performed by applying conventional stratigraphic techniques and X-ray fluorescence methods. The variability of the sedimentary sequence allowed us to reconstruct the different climatic events. The pond recorded a long sedimentary sequence encompassing the last 15,000 years. The sedimentological analysis allowed us to establish 5 different stratigraphic units which we have separated in two principal sections. The first section is formed by organic rich facies while the remains of the core is composed mainly of clays and silts facies with some sand layers.

These data will be very useful to establish which and how past climatic events have affected this high mountain basin, when reconstructing the evolution of main paleolimnological indicators of environmental change. And in conjunction with subsequent studies, it will establish whether or not the suitability of the Bassa Nera as a sentinel of climatic global change. This in turn will allow the  establishment of a network of sentinel lakes in the Iberian Peninsula.

How to cite: Blasco, A., Calero, M. A., Rull, V., Cañellas-Boltà, N., Garcés, S., Montoya, E., and Vegas-Vilarrúbia, T.: The Bassa Nera pond (Central Pyrenees), a potential sentinel of climatic changes over the last 15,000 years., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6605, https://doi.org/10.5194/egusphere-egu22-6605, 2022.