The ~1800–800 Ma period is known as the 'Boring Billion (BB)' because of the relative stasis of the carbon isotope record during this time. However, geochemical data from the Paleo-Mesoproterozoic strata deposited in different areas indicate heterogeneity and complexity of the oxygen contents in the oceans, which hampers paleoenvironmental reconstructions from this period. In addition, very little research has been carried out on the Palaeoproterozoic strata of the North China Craton (NCC). In this study, we report analyses of U-Pb isotopes, elemental abundances, Fe speciation, and molecular markers from the Huangqikou formation in the northwestern part of the Ordos Basin (OB), NCC. The Huangqikou formation was deposited in the rift valley at about 1736 Ma. Our new data, combined with previous analyses, suggest that the warm and humid depositional environment of the Huangqikou formation in the Helanshan area evolved from a marine foreshore setting to a marine backshore setting, with increasing degree of seawater hypoxia. But a relatively oxygenated environment corresponded to the lower part. On the other hand, the Huangqikou formation in the Zhuozishan area evolved from a terrestrial deltaic environment to a marine foreshore environment, with cumulatively reducing conditions. This study points out that the late Paleoproterozoic strata deposited in the western part of the NCC might mainly formed in reduced seawater. But some degree of oxidation had occurred in the surface water during this period, which proves the oxygenation of the surface environment during the early period of Earth evolution.

How to cite: Ma, Q., Zhou, Y., and Zerkle, A.: Sea water chemistry in the late Paleoproterozoic: Insight from the Huangqikou formation, western part of the North China Craton, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5965, https://doi.org/10.5194/egusphere-egu23-5965, 2023.

The Permian–Triassic time interval is associated with major perturbations in the biogeochemical cycling of several redox-sensitive elements. In particular, sulphur isotope ratios (δ³⁴S) reveal substantial perturbations in sedimentary sulphates. Despite this, few studies utilise this δ³⁴S variability for long-term high-resolution correlation. Through the sulphur isotope analysis of sedimentary evaporites of the Staithes S-20 borehole (northeast England), we have generated the most stratigraphically complete evaporite sulphur isotope (δ³⁴S_evap) curve from a single stratigraphic section for the late Permian to Late Triassic. The Staithes S-20 record and its comparison with the global δ³⁴S_evap curve demonstrate the utility of sulphur isotope data for stratigraphic correlation and dating, especially evaporite bearing sequences. The δ³⁴S_evap data for the late Permian to Late Triassic were incorporated into a biogeochemical box model to yield estimates for the pyrite burial flux with time. We propose three significant pyrite burial events (i.e. PBEs) throughout the Triassic. Our model outputs predict a major increase in pyrite burial over the Permian/Triassic boundary, possibly driven by Siberian Traps volcanism. After ~10 million years, the pyrite burial flux achieves relative stability until the latest Triassic.  

How to cite: Salisbury, J., Gröcke, D., Cheung, H. D. R. A., Kump, L., McKie, T., and Ruffell, A.: Sulphur isotopes in Permian–Triassic evaporites: an 80‐million‐year record of pyrite burial, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12950, https://doi.org/10.5194/egusphere-egu23-12950, 2023.

Extreme and rapid climatic and environmental perturbations have punctuated Earth history. The causes and consequences of these past global-change events are relatively well constrained, but how the system can naturally recover through feedbacks remain largely unconstrained. The Toarcian in the Early Jurassic is an ideal time interval to understand the response of Earth system to rapid climate change. Indeed, it was marked by one of the most extreme hyperthermal events of the Phanerozoic accompanied by major environmental changes, named the Toarcian Oceanic Anoxic Event (T-OAE, ca. 183 Ma). Most studies have focused on the triggering mechanisms and the palaeoenvironmental response, whereas the recovery phase has been less studied. Increased chemical weathering of silicate rocks and burial of organic carbon are the two primary natural mechanisms generally proposed as negative feedbacks controlling the recovery. However, to date, the response of these feedbacks, their efficiency, and their timing are still uncertain, hampering an accurate view of the carbon cycle-climate dynamics. This study aims to tackle this lack of empirical data by providing a multi-proxy dataset combining sedimentological observations, mineralogical and geochemical analyses. Four worldwide distributed sites have been selected for this study: Fontaneilles in France (Grand Causses Basin), Vilyui in Siberia (Siberian Basin), Agua de la Falda in Chile (Andean Basin), and Ait Athmane in Morocco (High Atlas Basin). Our high-resolution carbon isotope records allow us to correlate the studied sites to trace the global carbon cycle dynamics in the aftermath of the Toarcian event. Lithium isotope ratios are used to trace global weathering rates and to understand processes that control the long-term carbon cycle. Our results indicate that higher silicate weathering rates during the Toarcian hyperthermal likely helped the climate system recover and return to cooler climatic conditions. High mercury and tellurium concentrations recorded after the T-OAE interval suggest that protracted Karoo-Ferrar volcanic activity may have played a role in the recovery.

How to cite: Fantasia, A., Adatte, T., Spangenberg, J. E., Mattioli, E., Regelous, M., Salazar, C., Millot, R., Bodin, S., Letulle, T., Rogov, M., and Suan, G.: Multiproxy constraints on recovery processes during the hyperthermal Toarcian Oceanic Anoxic Event, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14596, https://doi.org/10.5194/egusphere-egu23-14596, 2023.

The Cretaceous-Paleogene (K-Pg) boundary experienced major environmental perturbations due to volcanism and bolide impact, as well as the most famous mass extinction in geologic history. However, the response of the climate system to these drivers at different timescales, and thus their relationship to the mass extinction is highly debated. In particular, the role of climate change in biodiversity patterns immediately preceding the boundary is poorly understood. 

Lipids from fossil peats (coals) provide an opportunity to reconstruct terrestrial temperatures across the Cretaceous–Paleogene boundary at a millennial-scale resolution. Here we present mean annual air temperature records spanning ~70 ka over the K-Pg boundary, from sites across North America (palaeolatitudes 45–55 degrees N). Our data show that temperatures ranged from 16–29 degrees C, more than 10 degrees C higher modern temperatures at equivalent latitudes in North America.

Using 5-ka temporal bins, our data show that MAATs peaked at ~26 degrees C in the last millennia of the Cretaceous, following 35 ka of warming from ~23 degrees C. Peak warmth was followed by ~5 degrees C cooling over the following 30 ka. We observe no “impact winter” nor a spike in temperature immediately following the boundary. If such phenomena occurred, their duration was below the resolution of our record: ~1 ka. Our record also shows a previously unrecognised brief interval of cooling from 10 to 5 ka pre-boundary.

Our study places new bounds on millennial-scale trends in MAAT change in the terrestrial realm and demonstrates large and rapid temperature swings across the K-Pg interval. These data allow for improved understanding of the role of climate in the decline of Cretaceous flora and fauna and may help elucidate the relative influence of volcanism and bolide impact on terrestrial temperatures.

How to cite: O'Connor, L., Jerrett, R., Price, G., van Dongen, B., Crampton-Flood, E., and Lengger, S.: A millennial-scale record of mean annual air temperatures spanning 70 ka over the Cretaceous-Paleogene boundary, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17389, https://doi.org/10.5194/egusphere-egu23-17389, 2023.

Preliminary examination of the biomarker composition of Paleocene to Campanian (~63-74 Ma) organic-rich sediments recovered from the Transkei Basin (Hole U1581B; 35° 41’S, 29° 39’E), offshore South Africa, during IODP Expedition 392 reveals suites of alkenones and alkyl alkenoates derived from haptophyte algae. This discovery augments evidence for the temporal continuity of their occurrence since the early Aptian and expands their paleogeographic range to high southern latitudes (~60°S) during the Cretaceous and Paleocene. In addition, the similarity of alkenone distributions between Maastrichtian and Danian samples suggests a conformity in the biosynthetic pathways for their production across the K/Pg boundary likely attesting to the survival of their source haptophytes and recovery after the extinction event. Alkenone distributions in the Transkei Basin sediments are dominated by series of C₃₇ to C₄₀ diunsaturated components and remain broadly consistent throughout the Cretaceous to Paleocene stratigraphic  succession. The presence of both the C₃₈ alkadien-2-one and C₃₉ alkadien-3-one represents the earliest recognition of these compounds thereby extending the advent for biosynthesis of both methyl and ethyl alkenones to the Campanian (~74 Ma). These sediments also contain C₃₇ methyl and both C₃₈ and C₄₀ ethyl alkadienoates. No C₃₇, C₃₈ or C₃₉ triunsaturated alkenones were detected in the Paleocene through Campanian succession but minor amounts of a C₄₀ alkatrien-3-one were confirmed in Cretaceous samples based on its elution time and diagnostic mass spectrum. This finding raises the question why only the C₄₀ triunsaturated component is observed, coupled with pervasive evidence that C₃₇ to C₃₉ triunsaturated alkenones emerge after the Early Eocene Climatic Optimum (EECO). Among extant haptophytes, C₄₀ alkenones occur in species within phylogenic Group II, notably Isochrysis, but are absent in extant marine species comprising phylogenic Group III. These observed distributions of alkenones in the marine realm can be best explained as evidence for contributions from both Isochrysidaceae and Noelaerhabdaceae following their divergence in the early Cretaceous.  

How to cite: Doiron, K., Brassell, S., Bijl, P., Wager, T., Herrle, J., Uenzelmann-Neben, G., Bohaty, S., and Childress, L. and the Expedition 392 Science Party: Alkenones confirmed in sediments from high southern latitudes during the Cretaceous and Paleocene: results from the Transkei Basin (IODP Site U1581), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10010, https://doi.org/10.5194/egusphere-egu23-10010, 2023.

The nature of Cretaceous-Eocene boundary is one of the outstanding questions of Crimea Geology. The new data are presented to show that the Cretaceous-Eocene boundary can be established in the Central Crimea very accurately by using the method of quantitative genetic analyses including the Isotope Geochemistry. Integrated lithostratigraphic investigations and Isotope composition of Carbon/Oxygen were conducted on the Cretaceous -Eocene section of the western slope of Ak-Kaya mount (Belogorsk, Crimea). Four layers of different types of rocks were investigated, where the layer 1 and 2 belong to the Maastrichtian, 3 and 4 to the Eocene.

The top of the Maastrichtian layer is characterized by a differently oriented fracture system, including large paleoseismic dislocations or a seismogenic trench. The fracture networks are connected and filled with material similar to the Eocene basal horizon including fragments of various sizes of Maastrichtian rocks.

Five microfacial types of the collected rock samples were distinguished as a result of microscopic examination. Also X-ray phase analysis, δ¹³С and δ¹⁸О isotopic analysis and X-ray fluorescence analysis were made to specify and compare the mineral composition of Maastrichtian and Eocene rocks. These analyzes allowed to specify paleogeographic conditions. In addition, measurements of fractures in the Cretaceous–Eocene boundary deposits were made to determine the stages of deformation of the whole structure.

As a result of the research, it was obtained:

1) throughout the entire studied geological interval, sedimentation occurred in a shallow sea of normal salinity. However, conditions were probably more humid in the Eocene, based on lower salinity values.

2) Three major stages of deformation were identified: pre-Eocene, Eocene, and post-Eocene.

3) The average temperature of the formation of Maastrichtian rocks is 19-22°C, and Eocene rocks is 24-27°C. The increase in temperature up to 38°C during the formation of the Eocene basal horizon may be associated with the global climatic event EECO (Early Eocene Climate Optimum). The synchronicity of the formation of steep submeridional fractures and the basal horizon of the Eocene has been proved. It is shown that the Eocene deformation stage corresponds to the formation of paleoseismic dislocations during the main phase of tectonic activity in the Pontids (Eastern Turkey).

How to cite: Chizhova, E., Lygina, E. A., Pravikova, N. V., Tveritinova, T. Yu., and Krasnova, E. A.: Eocene seismicity and paleogeography of the Central Crimea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-551, https://doi.org/10.5194/egusphere-egu23-551, 2023.

The North Atlantic Igneous Province (NAIP), a large igneous province (LIP), was emplaced between ~62 and 50 million years ago (Ma), with a voluminous burst of volcanic activity centred around 56-54 Ma. Global paleoclimate reconstructions from this Paleocene and Early Eocene interval indicate progressively warmer conditions, with several superimposed warming events or ‘hyperthermals’, such as the Paleocene–Eocene Thermal Maximum (PETM; 56 Ma). These hyperthermals represent transient massive perturbations to the carbon cycle, marked by substantial global warming, ocean acidification and negative stable carbon isotope excursions. International Ocean Discovery Program Expedition 396 to the Mid-Norwegian continental margin recovered a suite of Paleocene–Eocene sedimentary and igneous materials. This notably includes a unique and extremely expanded succession comprising of up to ~80m of PETM (ash-rich) sediments and volcanic ash layers infilling a hydrothermal vent crater. The craters on the Mid-Norwegian margin and similar structures associated with other LIPs were previously identified as surface expressions of a potent carbon release mechanism: the venting of thermogenic carbon generated in the thermal aureoles around volcanic dikes and sills intruded into the underlying sedimentary basins.

In recent years, much progress has been made towards understanding the role of deep earth processes and particularly LIP volcanism on paleoclimate through the application and refinement of proxies as sedimentary mercury (Hg) content. Large scale and especially LIP volcanism are considered important Hg emitters that may result in increased sedimentary Hg content. Here, we present high-resolution bulk sedimentary Hg content data from the sedimentary strata within the hydrothermal crater, spanning the PETM. We use our new data with biostratigraphic, stable carbon isotope, and lithological constraints, to shed light on the timing of hydrothermal crater formation, duration and re-activation of hydrothermal activity within the crater after formation. Finally, these new findings are placed in a global Hg and carbon cycle framework to assess the timing, characteristics, and impact of NAIP activity during the PETM.

How to cite: Frieling, J., Mather, T., Jones, M., Fendley, I., Xu, W., Berndt, C., Planke, S., and Alvarez Zarikian, C. and the IODP Expedition 396 scientists: Exploring links between the North Atlantic Igneous Province and Paleocene–Eocene climate change using sedimentary mercury, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2714, https://doi.org/10.5194/egusphere-egu23-2714, 2023.

Numerous hyperthermal events have been documented through the Paleocene-Eocene transition. The best known hyperthermal event is the Paleocene-Eocene Thermal Maximum (PETM; around 56Ma), a period that led to surface and bottom water warming of about 5°C within a few millennia at tropical latitudes. It is therefore considered as one of the best analogues of current global warming. The PETM is also characterized by an abrupt 3-4 per mil negative δ¹³C excursion in deep marine core sediments and by a thin clay-rich layer associated with the PETM onset, most often interpreted as carbonate dissolution due to the shoaling of the CCD. The duration represented by these clays and carbonates is of peculiar interest to constrain the exported carbonate production dynamics of surface ocean and its dissolution throughout the water column. This is key to produce realistic carbon budgets across hyperthermal events.

To this end, we generated a new 4 Ma (57.5-53.5) record of extraterrestrial ³He-derived sedimentation rates from pelagic sediments recording at least 10 hyperthermal events at ODP Site 1209 (North Pacific). Our main results indicate that carbonate sedimentation dropped drastically during the PETM onset (minimum of 0.02 cm/ka) and recovered rapidly during the recovery phase of the event (around 0.7 cm/ka). Surprisingly, the sedimentation rate is low (0.3 cm/ka) after the recovery until the Eocene Thermal Maximum 2 (ETM2; around 54Ma). After this major event, the sedimentation rate increased abruptly (0.7 cm/ka) over the last 500 ka of the studied interval due to the overabundance of Zygrhablithus bijugatus a large rod-shaped nannofossil whose ecology is poorly understood yet.

Comparisons between the new record of extraterrestrial ³He-derived sedimentation rate and dissolution proxies from this and previous studies lead us to challenge the widely accepted model previously proposed for hyperthermal events, which assumes that the CaCO₃ accumulation is mainly controlled by dissolution.

How to cite: Pige, N., Suan, G., Blard, P. H., and Mattioli, E.: Extraterrestrial 3He-based reconstruction of sedimentation rates across the Paleocene-Eocene transition at ODP Site 1209 (North Pacific), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8719, https://doi.org/10.5194/egusphere-egu23-8719, 2023.

The distribution of the bryozoans in the shallow-marine-estuarine sediments of the late Early–Late Eocene La Meseta Formation, Seymour Island shows a sharp decline in bryozoan biodiversity between the lower, basal transgressive facies of Telm1 and upper part of the formation (Telm6-7) at the end of Eocene (Hara 2001). In the lowermost part of LMF (Telm1) the cheilostome bryozoans, preserved as internal moulds systematically belonging to buguloids and catenicelloideans, at the present day are widely distributed in the tropical-warm temperate latitudes and deposited in the shallow-water settings (Hara 2015). Within a 2 meters thick interval of the basal transgressive facies of Telm1 unit, the most common are multilamellar colonies, showing a great variety of shapes dominated by celleporiforms and cerioporids.

The middle part of (LMF, Telm4-5) reveal a presence of the microporoideans and disc-shaped lunulitiform - warm-loving, free-living bryozoans. Environmentally, Recent, lunulitids are known to occur in warm, shallow-shelf conditions, at temperatures of 10-29˚C, on coarse, sandy to muddy bottom, what suggest the shallow-water setting for the middle part of the LMF.

10 million years older, the Cape Melville Formation on King George Island dated as Early Miocene is dominated by the infaunal bivalves, which provide a unique fossil record in the Antarctic Peninsula region during the latest Oligocene to earliest Miocene interglacial to glacial transition. Only one bryozoan was described identified as Aspidostoma melvillensis (Hara and Crame, 2004).

The shallow-marine, pectinid-rich biofacies of the Pecten Conglomerate of CIF, Cockburn Island, taxonomically shows the mosaic pattern in occurrence of bryozoan taxa, which are known from the Middle and Late Cretaceous, another originated in the Paleogene, as well as those which are solely common in the Neogene. Exclusively encrusting colony growth-form of the Pliocene biota suggests sedimentation in the shallow-water environment and indicates an interglacial palaeoenvironment of the CIF Formation (Hara & Crame, in revision).

The cold-water geographical distribution of the Recent bryozoans with dominant Neocheilostomatina of Buguloidea and the ascophoran lepraliomorphs of Smittinoidea and Schizoporelloidea, shows a dynamic history of this highly endemic fauna, which evolved over long period of time.

Hara, U. 2001. Bryozoa from the Eocene of Seymour Island, Antarctic Peninsula. Palaeontologia Polonica, In: Palaeontological Results of the Polish Antarctic Expeditions, Part III, 60, 33-156.

Hara U., 2015. Bryozoan internal moulds from the La Meseta Formation (Eocene) of Seymour Island, Antarctic Peninsula. Polish Polar Research, 36: 25-49.

• Hara and J. A. Crame 2004. A new aspidostomatid bryozoan from the Cape Melville Formation (lower Miocene) of King George Island, West Antarctica. Antarctic Sciences, 16, 319-327.

How to cite: Hara, U.: Cenozoic bryozoan biota: their palaeoecology and climatic environmental significance  in Antarctic ecosystems , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14043, https://doi.org/10.5194/egusphere-egu23-14043, 2023.

When a permanent ice cap developed on Antarctica during the Eocene–Oligocene transition (EOT; ~34.44 to 33.65 million years ago (Ma)), Earth witnessed a transition from a greenhouse towards a glacially driven climate. Evidence of high-latitude cooling and increased latitudinal temperature gradients across the EOT has been found in both marine and terrestrial environments. However, the timing and magnitude of temperature change in the North Atlantic remains poorly constrained.

Here, we used two independent organic geochemical palaeothermometers derived from (i) alkenones and (ii) Glycerol Dialkyl Glycerol Tetraether (GDGT) lipids, to reconstruct sea surface temperature (SST) evolution across the EOT from the southern Labrador Sea (Sites: ODP 647 and DSDP 112). In the Labrador Sea alkenones do not appear until the earliest Oligocene (both sites) while GDGT lipids (analysed in Site 647 only) provides a well-constrained temperature record across the EOT.  

Our SST records provide the most detailed record for the northern North Atlantic through the 1 Myr leading up to the EOT onset, and reveals a distinctive cooling step of ~3 ºC (from 27 to 24 ºC), between 34.9 and 34.3 Ma, ~500 kyr prior to Antarctic glaciation. This cooling step, when compared visually to other SST records, is asynchronous across North and South Atlantic sites. This illustrates a considerable spatiotemporal variability in SST evolution in the northern sector of the North Atlantic and the Norwegian-Greenland Sea. Overall, the cooling step fits within a phase of general SST cooling recorded across sites in the North Atlantic in the 5 Myr interval bracketing the EOT.

We used a modelling study (GFDL CM2.1) to try and reconcile the observation of pre-EOT cooling with the hypothesis that Atlantic Meridional Overturning Circulation (AMOC) switched on or intensified on the lead up to the EOT, which would be expected to have warmed the North Atlantic region. Results suggest that a reduction in atmospheric CO₂ from 800 to 400 ppm may be sufficient to counter warming from an AMOC start-up. In the model, the AMOC start-up is initiated during closure of the Arctic–Atlantic gateway.

While the model simulations applied here are not yet in full equilibrium, and the experiments are idealized, the results, together with the proxy data, highlight the heterogeneity of basin-scale surface ocean responses to the EOT thermohaline changes, with sharp temperature contrasts expected across the northern North Atlantic as positions of the subtropical and subpolar gyre systems shift in response to climatic and oceanic adjustments.

How to cite: Sliwinska, K. K., Hutchinson, D. K., Varma, D., Weitkamp, T., Sheldon, E., Liebrand, D., Coxall, H. K., de Boer, A. M., and Schouten, S.: Sea surface temperature evolution of the North Atlantic Ocean across the Eocene-Oligocene Transition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8831, https://doi.org/10.5194/egusphere-egu23-8831, 2023.

Long-term and abrupt changes in precipitation (P) patterns remain ambiguous in a warmer climate. Modern studies project that a warmer climate will cause intensification of the hydrological cycle. However, paleoclimate evidence from the warm period, i.e., the Medieval Climate Anomaly (MCA; 800-1400 AD), contradicts this because, during MCA, some regions were humid (wet), while others had arid (dry) climates. Here, we investigated the P response to variations in the temperature (T) and Atlantic Meridional Overturning Circulation (AMOC) variation throughout the Northern Hemisphere (NH) using 75 for P, 17 for the AMOC, and 48 records for T from NOAA and PAGES paleoclimate databases.

Our results show a continuous weakening trend in AMOC from the 9^th to 13^th centuries. The weakened AMOC has probably altered the atmospheric heat and water vapor distribution, and consequently the hydroclimate around the NH. The hydroclimate over the eastern North America and the Western Europe looks more vulnerable to weak AMOC as it shifted from warm-humid to cold-arid climates. Weak AMOC induces motion in Inter-Tropical Convergence Zone (ITCZ) southwards. Our results show signals of an ITCZ shift over equatorial Africa and southern Asia with the warm and humid response. Although warm (cold) climates are not always associated with increased (decreased) P, they may also lead to arid (humid) climates. Overall, we found that when T is higher than their average, the hydrological conditions are arid, but when T is similar or close to the average level, the conditions are humid. However, these hydroclimate responses may vary according to the regionally available water resources. Therefore, an improved understanding of long-term T variability and AMOC trend changes, specifically during warmer periods, could provide relevant insights into the present and future climates.

How to cite: Pratap, S., Markonis, Y., and R. Blöcher, J.: Understanding Atlantic Meridional Overturning Circulation and linked variations in precipitation and temperature distribution during the warmer climate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-129, https://doi.org/10.5194/egusphere-egu23-129, 2023.

It has been hypothesized that lower atmospheric CO₂ concentrations and lower temperatures during glacial times caused the enrichment of carbon isotopes of particulate organic material (δ¹³C_org-POM) produced in the surface ocean. Some downcore measurements of organic carbon isotopes of bulk sediments show such a trend, however, others do not. The lack of a coherent picture could be due to issues relating to the bulk sediments, including diagenetic alteration, the nature of the organic material, input of allochthonous material, and sediment redistribution.

Recent work by Hoogakker et al. (2022) shows that planktonic foraminifera-bound organic carbon δ¹³C values (δ¹³C_FBOM) are remarkably similar to those of δ¹³C_org-POM. Here we present the first down-core organic carbon isotope record of planktonic foraminifera-bound organic carbon (δ¹³C_FBOM) from the Southern Ocean (ODP Site 1088), to test for a glacial enrichment in δ¹³C_org-POM. The samples (Globigerina bulloides, Globorotalia truncatulinoides, and G. inflata) cover the last 20,000 years.

Our δ¹³C_FBOM results show a slight positive trend toward the Last Glacial Maximum (LGM), in accordance with the hypothesized δ¹³C_org-POM trend, but not to the extent as shown in some bulk sediments from more tropical latitudes. We discuss our results in the context of predicted past δ¹³C_org-POM using ice core atmospheric pCO₂ concentrations, G. bulloides calcification DIC (from inorganic carbon isotopes), and temperature (using Mg/Ca). 

How to cite: Paoloni, T., Hoogakker, B., Grant, H., Keenan, P., and Hamilton, H.: Planktonic Foraminiferal δ13Corg as a novel proxy for Carbon Cycling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5657, https://doi.org/10.5194/egusphere-egu23-5657, 2023.

Neodymium (Nd) isotopes have been applied for decades now to trace ocean circulation both in the present and past oceans. Their tracer utility stems from the characteristic Nd isotope signature of different rocks and their imprint on seawater as well as the biological inactivity of Nd and its appropriate residence time in the ocean, allowing for the determination of water mass provenance and flow paths. However, the application of this tracer, especially for the reconstruction of past ocean circulation changes, has been challenged based on uncertainties e. g. in the magnitude of the benthic flux of Nd to deep waters, Nd isotope exchange and input at ocean margins, and diagenetic alterations of the original bottom water Nd isotope signature in sediments.

Based on recent studies of dissolved Nd isotope distributions in surface to deep waters we show the power of Nd isotopes for tracing the provenance of currents and water masses particularly within restricted geographic regions. Using additional trace metal and isotope data from marine sediments analyzed alongside authigenic Nd isotopes, we explore the validity and limits of Nd isotopes as tracer of past ocean circulation changes.

How to cite: Pahnke, K., Struve, T., Sutorius, M., Waltemathe, H., and Zander, M.: Tracing ocean circulation using neodymium isotopes – promises and limitations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17352, https://doi.org/10.5194/egusphere-egu23-17352, 2023.