The South Atlantic Transect (SAT) is a multidisciplinary scientific ocean drilling experiment designed to investigate the evolution of the ocean crust and overlying sediments across the western flank of the Mid-Atlantic Ridge (Coggon et al., 2024). The SAT comprises International Ocean Discovery Program (IODP) Expeditions 390 and 393, built on engineering preparations during Expeditions 390C and 395E. It targeted six sites on 7, 15, 31, 49, and 61 Ma ocean crust to sample intact in situ crust regarding crustal age, spreading rate, and sediment thickness and to investigate the hydrothermal interactions within the aging ocean crust.An integrated petrological, geochemical and microstructural study unravels the conditions of host rock alteration and the formation conditions of mineralization within hydrothermally formed veins and voids.This contribution focuses on the internal microstructure of hydrothermal veins in drill cores sampled during IODP Expeditions 390 and 393. Microstructures, preferably in calcite, were analyzed using Electron Backscatter Diffraction (EBSD). Here, data on the density and misorientation of calcite sub-grains potentially allow the assessment of intraplate stresses and stress variations with depth and distance from the Mid-Atlantic Ridge, related to the increasing density of crust with cooling and age.Microstructures in vein calcite are characterized by the formation of sub-grains, indicating that calcite deformation is mainly characterized by dislocation glide. Mechanical twinning is very subordinate and does not substantially contribute to internal deformation. The evaluated misorientation axes between the calcite sub-grains indicate that basal and prism planes are the main intracrystalline gliding planes. The activation of these slip planes requires relatively high differential stresses, which are far above the critical stresses for twinning. Analysis of average calcite sub-grain sizes shows a general trend characterized by a continuous decrease in sub-grain size with decreasing distance from the mid-ocean ridge.Oxygen stable isotope data from vein calcite indicate low precipitation temperatures in the range of 2° to 10 °C, without a correlation between precipitation temperature and the age of the oceanic host rock, and with a very minor influence of magmatic fluids. Therefore, we assume that vein calcite precipitated from seawater.The microstructural and stable isotope data imply that several calcite veins formed in situ at the drilled sites. The microstructures, particularly the calcite sub-grain sizes, seem to indicate that the related differential stresses decrease with increasing distance from the Mid-Atlantic Ridge. This can be related to the higher cooling rates of the oceanic host rocks situated closer to the Mid-Atlantic Ridge; higher cooling rates presumably generate higher internal stresses due to higher rates of density increase and volume loss with cooling. Alternatively, it may also be related to the fact that the ridge-push forces, and therefore the related intraplate stresses, decrease with increasing distance to the Mid-Atlantic Ridge.References:Coggon, R.M. et al., 2024. South Atlantic Transect. Proceedings of the International Ocean Discovery Program, 390/393: College Station, TX (International Ocean Discovery Program). https://doi.org/10.14379/iodp.proc.390393.101.2024

Recent studies have demonstrated that contourites from the Agulhas Plateau (AP) are unique archives for reconstructing the global thermohaline circulation. Nonetheless, the strength of the current regime influencing the AP and a significant proportion of reworked sediments may influence the interpretation of proxies and sedimentation rates, among other factors. Recently, many studies have focused on shallow contouritic systems, emphasising shallow carbonate drifts, for which the bulk composition of detrital components has been well characterized. In contrast, research on deep contourites is less frequent and particularly sparse in the context of deep carbonate contouritic deposits. To identify potential proxies for current intensity in deep carbonate contourites, we conducted a high-resolution study based on bulk elemental geochemical and grain size data, as well as cyclostratigraphy and statistical analysis. Here, we present an age model for the International Ocean Discovery Program (IODP) Site U1475 (Indian Ocean - South Atlantic Ocean) on a precessional time scale spanning the Miocene-Pliocene transition and identify the potential use of the ln (Ca/Sr) ratio for reconstructing changes in the vigor of near-bottom current at this site. The potential application of this geochemical ratio is based on the unusual opposing trend between calcium and strontium, despite both being associated with carbonates. Intense bottom currents likely enhance the winnowing of fine carbonates (Sr-enriched calcareous nannofossils), concentrating relatively coarser carbonates (Ca-enriched foraminifera) in sediments. Spectral analyses reveal that obliquity (41 kyr), with a prominent ∼173 kyr amplitude modulation, is the primary orbital forcing driving deep circulation from 6.1 to ∼5.6 Myr, whereas short eccentricity (100 kyr) and modulation of obliquity (∼173 kyr) show stronger influence it from ∼5.6 Myr. At 5.45 Myr, the influence of short eccentricity is strong enough to favor high flow speeds at Site U1475, which is coeval with the earliest Northern Hemisphere glaciation. Moreover, these high current intensity occur in phase with maximum obliquity during the cold periods (e.g., TG14, TG12), while low current intensity occur concurrently with minimum obliquity. Based on the integrated data utilized, we propose that ln (Ca/Sr) serves as a reliable proxy for reconstructing near-bottom current speed variability at specific depths within carbonate systems, such as the Agulhas Plateau.

During latest Miocene times the Mediterranean Sea main connection with the global ocean was through the Atlantic, just as it is today. This configuration could have likely resulted in a pronounced longitudinal environmental gradient, with warm and highly oligotrophic waters in the east, and cooler, less oligotrophic conditions in the west (a scenario resembling modern conditions). This setting provides a natural laboratory to test the effectiveness of quantitative microfacies analysis in tracking palaeoenvironmental gradients. Two approaches were compared: the presence/absence of carbonate producers assessed on the basis of literature data and a quantitative skeletal assemblage analysis of reef sites spanning the Western, Central, and Eastern Mediterranean. While the presence/absence approach only offers a broad environmental overview, the quantitative analysis better differentiates between the eastern and western settings. The eastern sector displays a higher relevance of symbiont-bearing foraminifera, suggesting warmer conditions. In contrast, the western sector is comparatively richer in heterotrophic organisms, likely reflecting a higher nutrient availability and cooler water. These results support the reliability of quantitative microfacies analysis and provide a framework for comparing reef-bearing, carbonate systems across the Mediterranean within climatic homogeneous time intervals. Both approaches suggest that these carbonate factories represent subtropical, modern-like, biotic assemblages adapted to the cooler, oligotrophic, and likely semi-restricted conditions that were prevalent prior to the Messinian Salinity Crisis.

Abstract. Understanding how the Earth’s system behaves under climate forcing conditions is critical for predicting how future climate change scenarios may affect the planet. In this regard, the Miocene, with an atmospheric temperature ~4 °C higher than modern and a near-modern ocean configuration, stands out as a potential analogue for future climate projections. Our current understanding of the Miocene derives principally from the Atlantic and Pacific Oceans, whereas the Indian Ocean remains understudied. Nevertheless, different studies performed in the equatorial Indian Ocean have revealed that the multiple climate shifts that occurred during the Miocene modified both the atmospheric and oceanic processes in this basin (e.g., changes in westerlies position, nutrient flux and productivity). In the present study, we investigate how changes in the climate conditions affected the surface ocean system at Ocean Drilling Program (ODP) Site 752, located in the southeastern Indian Ocean, across the Middle to Late Miocene. For this purpose, we present a new quantitative dataset of calcareous nannofossil assemblages, in conjunction with already existing multi-proxy data. Our results indicate that the warm atmospheric conditions reached during the Miocene Climatic Optimum (MCO), starting at ~16.9 Ma, caused an intensification of the seasonal signal at ODP Site 752 that lasted until 15.32 Ma. After this period, we detected a shift in the calcareous nannofossil assemblage towards species characteristic of low-nutrient and warm-water conditions (e.g., Reticulofenestra pseudoumbilicus, Reticulofenestra haqii). Nevertheless, with the progression towards the Late Miocene Cooling, which started at ~7 Ma, and the increased influence of the cooler and more productive Southern Ocean waters, the calcareous nannofossil assemblage evolved into a community characterised by relatively high-nutrient and cold-water taxa (e.g., Coccolithus pelagicus, Calcidiscus leptoporus). By 10.67 Ma, we recorded a reversion in the nannoplankton assemblage to species typical of low-nutrient and warm-water conditions that lasted until 9.88 Ma. The comparison with available eNd(t) records for Site 752 and 707 (located in the equatorial Indian Ocean) revealed that this change in the assemblage composition responded to a strengthening of the Pacific Ocean water influx occurring at this time. High-nutrient and cold-water conditions were reestablished after 9.88 Ma, lasting until the end of the studied record at ~7.34 Ma. Our evaluation of the primary producer community from a multi-proxy-based perspective revealed a progressive evolution of the surface ocean conditions in the southeastern Indian Ocean region across the Middle to Late Miocene for the first time. Furthermore, the strong correlation with existing proxy data for global climate records suggests that large-scale climate events are the main factors driving the changes in the primary producer community and surface ocean conditions at the Broken Ridge during the Middle to Late Miocene. However, certain regional processes (e.g., strengthening of the Pacific Ocean influx) may also occasionally influence surface ocean conditions. Moreover, this multi-proxy approach allowed us to better understand the Indian Ocean–Southern Ocean interaction, and more specifically, the nutrient transport efficiency between these two ocean basins during a climate change scenario. Specifically, our multi-proxy-based dataset revealed that the Antarctic divergence region experienced a northward migration after the MCO, leading to a deep reorganisation of nutrient transport across the surface southeastern Indian Ocean.

The Benguela Upwelling System (BUS), situated in the Southeastern Atlantic Ocean, is known as the most productive wind-driven coastal system on Earth. The BUS is boarded to the north and to the south by the Angola Benguela Front (ABF) and the Agulhas retroflection region, respectively. The ABF is a permanent thermal frontal feature located at around 16°S, which separates the cool Benguela Ocean Current (BOC) from the northernmost Angola warm water masses (e.g., the South Atlantic Central Waters; SACW). The Agulhas retroflection region, instead, represents an area, in the southernmost sector of the BUS, where the Agulhas current (AgC) retroflects towards the Indian Ocean, due to westerlies' stress curl. However, eddies of the warm and saline Agulhas waters can access the southern Atlantic Ocean and subsequently mix within the Benguela current. In this work, statistical analyses (cluster and PCA analyses, Globorotalia truncatulinoides coiling ratio, and the Agulhas Leakage Efficiency Index) were applied to the planktonic foraminifera assemblages in 94 samples from Holes U1575A and U1576A, collected during International Ocean Discovery Program (IODP) Expedition 391. Precisely, the sites were drilled along the Tristan-Gough-Walvis Ridge (TGW) seamount track, in the northernmost sector of the BUS, at increasing distance from the Namibian continental margin. The investigated record corresponds to the Early to Late Pleistocene, which comprises the Early-Middle Pleistocene Transition (EMPT). The EMPT is an interval in the Earth history spanning from 1.40 to 0.40 Myrs and characterized by prominent glacial to interglacial sea surface temperature (SST) variations. Our results provide new understandings on the regional paleoceanographic changes occurring within the northern part of the BUS, based upon the ecology and distribution of the planktonic foraminiferal assemblages. Specifically, changes in the assemblage composition during the Pleistocene permitted the characterization of the different water masses (BOC, SACW; AgC) and their interplay, as well as the reconstruction of the local variations of the thermocline in the BUS. The interaction between the water masses mentioned above, produces changes in the BUS such as the fluctuations of the ABF and the influx of the AgC waters from the Agulhas retroflection area. Moreover, we further examined the possible correlations between the paleoceanographic variability and climatic events (e.g., Benguela Niño/Niña-like states and deglaciations phases), which occurred since the onset of the EMPT.

In modern oceans, upwelling processes are responsible for high biological productivity and low sea surface temperatures at coastal zones. Upwelling may have intensified during the late Neogene in the eastern South Pacific due to the strengthening of the Humboldt Current System. Records of Neogene coastal upwelling are preserved in outcrops along the coast of north-central Chile (~ 26°S to 28°S) as diatomaceous mudstone deposits of the Neogene Bahía Inglesa Formation. To place such records in a broader paleoceanographic context, however, their stratigraphic assessment still needs refinements. Our work presents a multiproxy dataset to provide a stratigraphic framework for the Bahía Inglesa Formation at Quebrada Tiburón (27°42' S, 70°59' W), one of the southernmost outcrops of diatomaceous mudstone. Our approach is based on tephrochronometry, strontium isotope chronology (mollusk shells 87Sr/86Sr), and calcareous nannoplankton, diatom, and planktonic foraminifera biostratigraphy. Zircon crystals separated from a volcanic ash layer at the base of the sequence were analyzed by laser ablation ICP-MS for U-Pb dating. The youngest cluster of five concordant zircon crystallization ages indicates a tephra deposition after 8.68 ± 0.15 Ma. The 87Sr/86Sr analyses were performed on an oyster and a pectinid from sandstones underlying the diatomaceous mudstone using high-precision MC-ICP-MS measurements. The corrected and adjusted 87Sr/86Sr ratios resulted in 8.12 ± 0.40 Ma and 6.10 ± 0.25 Ma ages. The microfossil biostratigraphy was based on First (FAD) and Last Appearance (LAD) datums of biostratigraphic markers from the diatomaceous mudstone. The presence of mainly Miocene diatoms (e.g., Actinocyclus ingens, Cavitatus joseanus, and Nitzschia fossilis) and the planktonic foraminifera Neogloboquadrina acostaensis (sinistral) indicate a Tortonian age for the base of the diatomaceous mudstone. The Messinian-Zanclean boundary was identified in the middle interval of the mudstone by the disappearance of the calcareous nannoplankton species Calcidiscus pataecus and the appearance of Helicosphaera sellii and Umbilicosphaera sibogae. This interpretation is supported by the continuity and limit of the diatoms Actinocyclus ellipticus, Azpeitia nodulifer, and Coscinodiscus plicatus overlapping with Hemidiscus cuneiformis. A Zanclean age was attributed to the upper part of the mudstone sequence due to the co-occurrence of the calcareous nannoplankton species Reticulofenestra pseudoumbilicus and Sphenolithus moriformis, the diatoms Actinocyclus ellipticus, the co-occurrence of the diatoms Nitzschia fossilis and Shionodiscus oestrupii, and the planktonic foraminifera Globoconella miotumida and Sphaeroidinellopsis seminulina. The following sandstones contain Pliocene mollusks. Although inconsistencies between biostratigraphic data of taxa from different microfossil groups were observed (likely due to the lack of a local biozonation appropriate for the upwelling context), our dataset suggests a late Tortonian to Zanclean (8.68 to 3.5 Ma) age constraint for the succession and late Messinian to Zanclean (6.09 to 3.5 Ma) age for the diatomaceous mudstone. Further studies will apply our stratigraphic constraints for paleoenvironmental reconstructions. This research is part of the CRC 1211 “Earth-Evolution at the dry limit” project, funded by the German Research Foundation (DFG).

Non-destructive, high-resolution measurement of sediment cores are useful to reveal sediment feature which reflect climatic or oceanographic changes. Such non-destructive measurement (e.g. XRF core scanner measurement) could be reveal sediment feature in finer scale than discrete sample measurement. Although elemental mapping is also useful to reveal 2-dimentional structure of half split core surface, elemental mapping of large materials such as archive half core sections were usually difficult. In this study, we utilize recently released micro-XRF (M6 JETSTREAM provided by Bruker Corporation) which could measure archive half core directly and could make high-resolution element maps. The fine scale sediment feature which reflecting exact timings of drastic climate changes were revealed by micro-XRF using sediments obtained by following two Sites. Using the Neogene sediments obtained from DSDP Site 266, located at the high-latitude of Indian ocean close to the Antarctica, the distinctive chemical markers of IRD were observed in specific sections of Site 266. IRD is primarily distinguished by its characteristic iron-rich signature, and the identified fragments measure between 4.2 and 6.4 millimeters in length along their longest axis. Traditionally, these individual particles could only be discerned through destructive analysis. The large-scale micro-XRF capabilities of the JETSTREAM now enable us to non-destructively quantify and fingerprint IRD. The drastic changes of primary producer from the calcareous plankton to the siliceous plankton was also suggested from elemental mapping results. The sediments obtained from ODP Site 752, located on an isolated ridge in the Indian Ocean contained concretion at Paleogene age when hiatus or lower sedimentation rate was suggested by age model. We measured the concretion and the surrounding sediments together using specialized method of JETSTREAM, and revealed high-resolution elemental maps of concretion and surroundings sediments. The maps clearly shows that each element (Ca, Fe, Mn) is concentrated on different part on and around the concretion. The Ca concentration is higher at an interval above a concretion, which may suggest high calcareous productivity during the sedimentation period. In this study, we used legacy cores (archive halves) stored at Kochi Core Center (KCC), as the member of ReCoRD program (ReC23-01). Our measurement clearly shows reanalysis of previously obtained core materials by new technics reveals new feature of sediments which is useful to reconstruct past climate changes.

In 2023, the ReCoRD program was initiated by a joint venture of the Kochi Core Center (KCC), Kochi University and the Japan Drilling Earth Science Consortium (J-DESC) as a new workshop type, providing access to IODP cores archived at the KCC in Kochi, Japan. The first ReCoRD workshop, ReC23-01, ”Tracing Intermediate Water Current Changes and Sea Ice Expansion in the Indian Ocean”, was held between the 27th of August and the 5th of September 2023 at the KCC in Kochi. The goals of ReC23-01 were to gather new data to test the hypothesis that the expansion of sea ice around Antarctica impacted water circulation in the Indian Ocean through changes in intermediate water formation and the northward expansion of the Antarctic polar front through the Middle to Late Miocene following the Middle Miocene Climatic Transition (< 13.8 Ma). During ReC23-01, we targeted a latitudinal transect from the high southern latitudes to the tropical Indian Ocean consisting of 1 DSDP and 2 ODP sites. DSDP Site 266 represents the high-latitude target site located just south of the present-day location of the polar front. Data gathered for Site 266 during ReC23-01 is a new tracer location for ice-rafted debris (IRD) accumulation and changes in the Southern Hemisphere frontal system for the Neogene in the Indian Ocean. ODP Site 752 on the Broken Ridge provides a unique record of mid-latitude intermediate water paths, including SAMW and AAIW originating from the high latitudes and the Tasman Leakage. ODP Site 707 represents a critical end member of the south equatorial current and related Indonesian Intermediate Waters in the tropical Indian Ocean. The ReC23-01 workshop within the ReCoRD program allowed international research collaborators to fully benefit from the legacy of over 50 years of International Ocean Drilling Research from the Deep Sea Drilling Program (DSDP), Ocean Drilling Program (ODP), and International Ocean Discovery Program (IODP). Combining in-tandem sedimentological core descriptions with existing and new core data provides a unique opportunity to re-investigate and evaluate archived (legacy) core material. In particular, the availability of computer tomography (CT) core images provided critical information in assessing sedimentology and drilling disturbance in older DSDP and ODP core material to gather new data from over 50-year-old cores. ReC23-01 illustrates how ReCoRD-style workshops can offer a new way to explore research questions that could not be easily addressed by single sea-going expeditions. These workshops provide additional and powerful research opportunities based on legacy core material beyond individual sample and data requests, with large-scale community benefits. For instance, ReC23-01 provided an excellent training opportunity for early career researchers in a shipboard-like setting.

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

International Ocean Discovery Program (IODP) Expedition 366 recovered cores from three serpentinite mud volcanoes that also contain clasts that originate from the subduction-channel along the Philippine Sea Plate – Pacific Plate boundary. The drilled and sampled mud volcanoes (Yinazao, Fantangisña, and Asùt Tesoru) are located at distances of 55 to 72 km from the Mariana Trench.In general the recovered cores comprise serpentinite mud with lithic clasts from the underlying forearc lithosphere and from the subducting Pacific plate. This aloows the reconstruction of mass transport processes and geochemical cycling within the forearc, the spatial variability of slab-related fluids within the forearc, and water-rock-reactions in subduction and supra-subduction zone settings, the metamorphic and tectonic history of the subduction channel, and the timing and rates of these processes.Mafic rock clasts, embedded within a serpentine mud matrix, from the flanks and summits of both Asùt Tesoru and Fantangisña Seamounts were analyzed for reconstruction of their metamorphic and deformational overprint in order to reveal the tectono-metamorphic conditions at the metamorphic peak within the subduction channel and the subsequent low-grade overprint during exhumation.Several seamounts comprise clasts of lower plate metabasites with different metamorphic overprint (from low-grade greenschist facies to lower blueschist facies). The metabasites are also associated with clasts of fossiliferous carbonates and cherts with different degrees of metamorphic and deformational overprint, that also originated from the Pacific lower Plate. This implies that these rocks were exhumed from different depths within the subduction channel before being regurgated within a serpentinite mud matrix. The blueschist facies metamorphic rocks, being affected by metamorphic pressures in the range of 11 to 13.8 kbar at minimum, were very likely exhumed from greater depth within the subduction channel before being captured by uprising, localized serpentine mud flows, indicating evidence that corner flow is actually taking place along the Mariana convergent margin, and, to our knowledge, this is the first direct evidence of exhumation of high-pressure rocks by corner flow in an active subduction zone. Final exhumation, however, is related to the embedding of the rocks within a serpentinite mud matrix and the buoyant ascent of serpentinite mudflows along forearc fracture zones extending from the plate boundary to the upper plate sea floor.Biostratigraphic analyses of calcareous nannofossils and planktonic foraminifera from serpentinite mud flows, and intercalated pelagic sediments immediately above the metabasites analysed in this study give an age record of ~ 6.10 Ma (late Miocene, Messinian) to 4.20 Ma (early Pliocene, Zanclean), indicating that the final exhumation of the metabasites occurred during late Miocene times, slightly before 6.10 Ma.

The Late Miocene and Early Pliocene were characterized by widespread oxygen depletion in the Pacific and Indian Oceans, coinciding with the “Late Miocene–Early Pliocene Biogenic Bloom” (LMBB). In the Indian Ocean, this oxygen depletion has been linked to enhanced productivity in the northern basins, leading to Oxygen Minimum Zone (OMZ) expansion. A longstanding hypothesis proposes that the OMZ extended south of Broken Ridge (∼31°S). We test this hypothesis using benthic foraminiferal assemblages from ODP Site 752 (∼1086 m water depth) spanning the last 9 Myr. We apply a semi-quantitative reconstruction of bottom water oxygenation using the Enhanced Benthic Foraminiferal Oxygen Index (EBFOI), benchmarked against the present-day core-top assemblage. Our results indicate persistently oxic bottom water conditions (3.2–5.2 mL/L) throughout the study interval. Although significant faunal changes occur, particularly between 5.5 and 2.2 Ma, these do not align with LMBB timing. Instead, we interpret assemblage shifts as responses to the intensification of Tasman Leakage, which brought oxygen-rich intermediate waters into the southern Indian Ocean. Our results challenge previous interpretations of OMZ expansion to Broken Ridge and highlight the role of southward water mass sourcing in shaping intermediate-depth oxygenation. This study provides a new mechanistic framework and emphasizes the importance of integrating faunal, sedimentological, and geochemical data to reassess regional OMZ histories.

The Indian Ocean Dipole (IOD) is a distinct east-west temperature gradient in the Indian Ocean, similar to the El Niño Southern Oscillation in the Pacific. Here, positive IOD (+IOD) events bring warm eastern and cool western sea surface temperatures, and vice versa for negative IOD (-IOD). This temperature seesaw brings increased seasonal rainfall to northeastern Africa while western Australia faces severe droughts during +IOD events. Conversely, -IOD states result in more droughts in Africa and increased precipitation in Australia. In addition to these immediate climatic impacts, possible IOD-driven teleconnections may impact the Australasian Monsoon system, as they (appear to) modulate summer monsoon precipitation over India, Southeast Asia, and possibly Australia.However, despite its nature as a key climate driver in the Indian Ocean today, little data exists on changes in large-scale IOD patterns in the geologic past, especially in our past understanding of its role in ENSO dynamics. For instance, on glacial-interglacial timescales, sea level-driven exposure of the West Australian Shelf affects Pacific heat transport into the western region of the IOD. These changes were further exacerbated by the ongoing restriction and reorganization of the Indonesian Gateway since 5 Ma ago and the related changes in Pliocene to recent ENSO dynamics.To disentangle the impact of IOD patterns in the Plio-Pleistocene climatic patterns in the Indo-Pacific region, we present new X-ray fluorescence core scanning data from Ocean Drilling Project (ODP) Site 763 between 2 – 5 Ma ago. These data provide new insights into Australian climate dynamics, which we could then relate to Indo-Pacific Warm Pool (IPWP) changes and the establishment of Late Pliocene to Pleistocene pIOD mean states. Changes in IOD and IPWP sea surface temperature patterns were constructed using a selected set of latitudinal temperature gradients through the equatorial Indo-Pacific. Temperature gradients were calculated using published SST reconstructions based on mixed layer planktonic foraminifer (Trilobatus sacculifer) Mg/Ca records from ODP Site 806 (West Pacific Warm Pool), ODP Site 763 (eastern Indian Ocean) and ODP Site 709 (western Indian Ocean).Comparison of these data for the first time, reveals the close interconnectivity of tropical climate and oceanographic changes over the study interval. These include Plio-Pleistocene Australian and African hydroclimate trajectories and the contemporary monsoonal precipitation over Southeast Asia. We further pinpoint shifts in the Indian Ocean climate system corresponding to the tectonic restriction of the Indonesian Gateway (3.6 Ma), the Pliocene M2 glacial event (3.3 Ma), and the intensification of Northern Hemisphere glaciation (2.9- 2.7 Ma).Our results provide insight into the importance of permanent shifts in the Indian Ocean Walker Circulation mean states for near-future climate scenarios. Our recorded IOD mean state shifts highlight the need for further detailed studies to better understand past IOD changes and their associated paleoclimatic impact in the region.

The Middle to Late Miocene represents an important time interval in the Indian Ocean (IO), due to the reorganization of land masses, the establishment of monsoonal wind system and climatic changes. However, variations in intermediate and surface water dynamics through the IO still remain poorly understood. In this regard, Ocean Drilling Program (ODP) Site 752, located in the western flank of Broken Ridge (30° 53.475ˈS/93° 34.652ˈE), constitutes a key location to understand how the above-mentioned dynamics may have affected the path of oceanic currents within the eastern sector of the IO during the studied Miocene interval. A first biostratigraphic framework for ODP Site 752 was established during ODP Leg 121. However, the poor preservation of the material for the Middle to Late Miocene sediment interval resulted in only limited biostratigraphic data and consequently low-resolution age-depth model. In this regard, our study presents a newly updated high-resolution biostratigraphic age-depth model for this time period (from ~8 to ~15 Myrs) at Hole 752A, based on fully quantitative nannofossil assemblage analyses. Furthermore, a recently published astronomically tuned age-depth model (Lyu et al., 2023; DOI: 10.1029/2023PA004761), tied to the shipboard biostratigraphic age model, was used in order to validate our new quantitative nannofossil record. The comparison showed a high consistency for the whole record, with the exception of the interval between ~12-13 Myrs, where the age difference between the two respective models is high. We link these discrepancies to the potential variance in age of the recorded bioevents for this interval between basins, as well as the error associated with the mathematical approach of the tuned age model. Based on our quantitative nannofossil data, we further evaluated overall changes in the nannofossils assemblages at ODP Site 752. The assemblage is dominated by reticulofenestrids (e.g., Reticulofenestra minuta, Reticulofenestra pseudoumbilicus). Other species with a contribution >1%, are Calcidiscus tropicus, Calcidiscus pataecus, Coccolithus pelagicus, Coronocyclus nitescens, Discoaster spp., Helicosphaera spp., Sphenolithus moriformis and Umbilicosphaera jafari. Statistical analyses will be performed on the assemblage to define variations on the nutrient availability of the Broken Ridge surface waters and will be presented afterwards.

The Miocene Climatic Optimum (MCO) represents a climate period characterized by lower ice volumes and temperatures that were 3-4°C warmer than today. Indian Ocean Sub-Antarctic Mode Water (SAMW) is primarily formed south of 30°S and is the main return path for deep waters to the surface, migrating and intermixing northwards at Intermediate Water (IW) depths. The modern SAMW transports nutrients into the lower latitudes, strongly impacting mid- and low latitude productivity. During warmer climates, decreasing sea ice may increase nutrient trapping in the Southern Ocean, reducing the nutrient flux through SAMW into the lower latitudes. To better understand trajectories of nutrient fluxes in future climate change scenarios studies in past warm climate analogues of the near future – such as the MCO – are necessary. Thus, we use Ocean Drilling Project (ODP) Site 752, located on Broken Ridge in the southeastern Indian Ocean at a water depth of 1086.3 m, as a key location for understanding changes in IW conditions. This study aims to reconstruct paleoenvironmental conditions and bottom-water oxygenation at ODP Site 752 during the Middle to Late Miocene (15-8 Ma) using benthic foraminifera assemblages as a proxy for bottom-water-oxygenation and the enhanced Benthic Foraminifera Oxygen Index (eBFOI) for calculating dissolved oxygen content. We combine these assemblage data with Mg/Ca ratios of Cibicidoides wuellerstorfi and Cibicidoides mundulus as a proxy for bottom water temperatures (BWT). For reconstructing sea surface temperatures (SST), and temperatures from the open ocean thermocline, the Mg/Ca data were additionally gathered on the foraminifera species Globigerina bulloides (SST) and Globorotalia menardii (thermocline). We aim to analyze temperature variability through the water column to investigate influxes from cooler water bodies by increasing SAMW intensity and compare our new temperature data with our benthic foraminiferal assemblages. Therefore, we provide novel insights into Late Miocene IW circulation changes and deep water mass variation with the progressive northward shift of the Subantarctic Tropical Front (SAF).We present a high-resolution record of benthic foraminifera, tracing paleoenvironmental changes in deep water masses in addition to IW variation in the southeastern Indian Ocean. After the MCO, benthic foraminifera assemblages, and respectively the eBFOI indicate a relatively high oxic environment. Starting around 11 Ma, we first detect an increase of dysoxic conditions and deep infaunal foraminifera, e.g. the genus Bolivina spp., with minimal variation in the dissolved oxygen content of the bottom water. Such an assemblage shift is contemporary with increased current winnowing following the northward migration of the SAF. Furthermore, the higher abundance of epiphytic species Cibicidoides wuellerstorfi and Lobatula lobatula, and also Vulvulina pennatula as an elevated epifauna, support an increase in bottom current energy at Broken Ridge from 15 to 11 Ma. Combined, our assemblages and Mg/Ca paleotemperature data suggest that the strengthening of the SAMW and Antarctic Intermediate Water formation in the Late Miocene, since about 11 Ma, resulted in notable changes in bottom water conditions at Broken Ridge, including the increase of current winnowing.

The Early-Middle Pleistocene Transition (EMPT; 1.4-0.4 Myrs) stands out as one of the most studied intervals in Earth’s recent climate history. Specifically, during the EMPT an increase in the amplitude of climatic fluctuations is registered without proportional changes in the orbital cycles. Nevertheless, the mechanisms and the climatic components responsible for the onset of the EMPT are still under debate. As high-resolution studies on equatorial to mid-latitude microfossil assemblages during the EMPT are still limited, we performed a detailed benthic foraminifera assemblage work on samples from Site U1460 (eastern Indian Ocean, 27°S, 112°E, 214.5 m water depth), cored during IODP Expedition 356 on the SW sector of the Australian shelf. This site is interested by the presence of warm, calcium carbonate-supersaturated waters, and thus is strongly affected by early-marine diagenesis. Moreover, the studied cores are under the influence of the Leeuwin Current (LC), which, in turn, represents a warm and oligotrophic surface water mass, flowing poleward along the Australian coastline. Preliminary data record a polyspecific benthic foraminiferal assemblage with high diversity. The first part of the record (MIS 27-23) is dominated by Cibicidoides spp., Heterolepa spp., Trifarina spp., and nodosarids, whereas the most recent cores (MIS 22-16) recorded abundant agglutinated tests (e.g., Gaudryina spp., Spiroplectinella spp., Textularia spp., Spirotextularia spp.), Cibicidoides spp., Siphogenerina spp., Uvigerina spp., and bolivinids. Other common taxa detected throughout the whole record are Lenticulina spp. and lagenids. Foraminiferal tests resulted to be severely encrusted and their preservation strongly varies between glacial and interglacial intervals. Specifically, benthic specimens show poor to moderate preservation during glacials whereas their preservation increases during interglacial stages. In addition, planktonic foraminifera were also picked to record the variations of the plankton/benthos (P/B) ratio during the studied time interval. This ratio reflects the eustatic fluctuations of the sea level in the region. Particularly, highstand and lowstand stages correspond to higher and lower values of the P/B ratio, respectively. Furthermore, constraining sea-level variability at Site U1460 will allow detailed reconstructions of LC current behavior during the EMPT. The abovementioned data, together with the evaluation of the benthic assemblage, will permit the determination of the paleobathymetry, as well as of the bottom water conditions at the studied site. The environmental reconstruction based on the benthic foraminifera assemblage during the glacial/interglacial phases will be used to assess the local climatic variations during the EMPT.

Data on marine microfossil assemblage composition have multiple applications. Initially, they were primarily used for (chrono)stratigraphy and palaeoecology, but these data are now also widely used to study evolutionary and ecological processes, such as past biodiversity and its links with environmental dynamics, or to provide a basis for conservation efforts and biomonitoring. The large range of potential applications renders microfossil abundance data ideal for reuse. However, the complexity inherent in taxonomic data, which encompass extant and extinct species, coupled with the inherent intricacies of information on biological communities extracted from sedimentary archives, poses considerable hurdles in reusing marine microfossil data, even when they are publicly available. Here, we present guidelines derived from an online survey conducted within the marine micropalaeontological community, aimed at improving the reusability of microfossil assemblage data. These guidelines advocate for clarity and transparency in the documentation of the methods and the outcome, and we outline the data attributes required for effective reuse of micropalaeontological data. These guidelines are intended for researchers who generate microfossil abundance datasets and for reviewers, editors, and data curators at repositories. A total of 113 researchers evaluated the relevance of about 50 data attributes that might be needed to enable and maximise the reuse of marine microfossil abundance datasets. Each property is ranked based on the survey results. All information is, in principle, considered “desired”. Information that improves the reusability is ranked as “recommended”, and information that is required for reuse is ranked as “essential”. Analysis of a selection of datasets available online reveals a rather large gap between data properties deemed essential by survey participants and what is actually contained in publicly available microfossil assemblage datasets. While the survey indicates that the micropalaeontological community values good data stewardship, improving data reusability still requires new efforts to incorporate all the essential information. The guidelines presented here are intended as a step in that direction. Determining the optimal forms and formats for data sharing are obvious next steps the community needs to take.

The ecological upheavals produced by the Cretaceous-Paleogene mass extinction event (K-Pg, -66 Ma) have been mostly studied at large scale with emphasis on clades' diversity dynamics. How this event affected the structure of paleocommunities is comparatively less investigated, especially within large vertebrate clades like fish. Here, we quantified changes in the contribution of elasmobranchs (sharks, skates, rays) and actinopterygians (ray-finned fishes) to the fish community across the K-Pg extinction by analyzing ichthyolith (fossil teeth and denticles) abundance through time. Based on extensive sampling of 20 horizons from two outcrops spanning the K-Pg event in Austria (>4 tons of rock, >9,000 ichthyoliths), we show that the K-Pg event fostered elasmobranch abundance while reducing actinopterygian density in the Tethys Ocean. Elasmobranch ichthyolith dominance in postextinction communities is not driven by estimated local environmental change (paleobathymetry, bottom-water oxygenation) and may relate to the greater independence of this clade from lower trophic levels in their ecology and early life stages than actinopterygians. We further measured the size structure of ichthyolith assemblages and found that the K-Pg event initiated an increase in the range of ecological niche space occupied by elasmobranchs simultaneously to the demise of actinopterygians in postextinction communities. Finally, using the fine taxonomic resolution of the elasmobranch fossil record, we demonstrate that local environmental fluctuations controlled elasmobranch community structure and richness, which are decoupled from global-scale upheavals. Our results challenge previous hypotheses and provide insights into global and regional environmental forcing over the structure of fish communities across a mass extinction event.

The Late Miocene Cooling (LMC) has been recognized as a global event in the climate record and posited as the start of modern ecosystems. Whereas climate shifts in modern tropical terrestrial ecosystems around 7.0–5.4 Ma are known, little is known about the impact of the LMC on coral reefs, where few good proxy records exist. During the Pliocene, a stratigraphic interval is present in the Central Indo-Pacific, where reefs that were present at the start of the Messinian disappeared by the Early Pliocene. This “Pliocene Reef Gap” has often been ascribed to non-climatic factors. However, a lack of proxy data prevents an understanding of climatic changes during this time. Here, we present a TEX86H-based sea surface temperature (SST) record for the Coral Sea, suggesting that the LMC is present across the Central Indo-Pacific. During the LMC, SST at ODP Site 811 declined by about 2 °C, while cooling lasted from 7.0 to 5.4 Ma. This cooling has also been seen in other parts of the Central Indo-Pacific. The LMC caused many changes in the Central Indo-Pacific, including a southwest shift in the monsoon belt, changes in terrestrial inputs, and changes in the strength of ocean currents. All of these factors can be stressors affecting coral reef growth. This suggests the overall impact of the LMC was to increase the stress on reef systems, which could have provided a driver for the collapse of individual reefs and therefore a potential cause for the Pliocene Reef Gap. The change in SST and other stressors associated with the cooling caused coral reef systems to collapse across the Central Indo-Pacific.

Concerning climatic conditions during the Miocene Climate Optimum (MCO), global temperatures were about 3-4°C warmer than modern, and characterized by globally lower ice volume. Indian Ocean Sub-Antarctic Mode Water (SAMW) is primarily formed south of 30°S and is the primary return path for deep waters to the surface, migrating and intermixing northwards at Intermediate Water (IW) depths. Today, the SAMW carries access nutrients into the lower latitudes, strongly impacting latitude productivity. During warmer climates, decreasing sea ice may increase nutrient trapping in the Southern Ocean, reducing the nutrient flux through SAMW into the lower latitudes. Thus, the MCO may indicate future climate, nutrient transport, and SAMW formation by exploring differences between cooler (modern) and warmer (MCO) climates. Ocean Drilling Project (ODP) Site 752, located on Broken Ridge in the southeastern Indian Ocean at a water depth of 1086.3 m, is a key location for investigating changes in IW conditions in the Indian Ocean after the MCO and the Middle Miocene Climatic Transition (MMCT). In particular, the reactions to global warming and the reorganization of oceanic and atmospheric circulation following the MCO and MMCT can be detected. This also includes the analysis of SAMW, Antarctic Intermediate Water (AAIW), and Tasman Leakage (TL). The present study aims to reconstruct paleoenvironmental conditions and bottom-water oxygenation at Site 752 during the Middle to Late Miocene (15-8 Myrs). To achieve this, we apply benthic foraminifera assemblages as proxies for bottom water oxygenation, for example, enhanced Benthic Foraminifera Oxygen Index (eBFOI), paleoproductivity, and stable carbon and oxygen isotopes. Initial results in the Middle to Late Miocene show an occurrence of oxic benthic foraminifera at a relatively constant abundance, especially in the early Late Miocene. In addition, in a relatively high oxic environment, an increase of dysoxic conditions occurred during the early Late Miocene, with peaks of abundance in dysoxic and deep infaunal benthic foraminifera. A co-occurrence of infaunal dysoxic and epifaunal oxygen-rich species is accompanied by enhanced current winnowing and an increase of nutrient flux during the Late Miocene (Lyu et al., 2023; DOI: 10.1029/2023PA004761). These data indicate that during the Late Miocene, since approximately 10 Ma, the strengthening of SAMW and AAIW formation resulted in notable changes in bottom-water conditions at Broken Ridge, such as increased current winnowing. The observed changes in IW are potentially linked to the shift of the southern hemisphere westerlies towards the north and the subsequent northward migration of the frontal system in the southern hemisphere around Antarctica after 12 Ma.