Search

The Borkewehr section near Balve at the southeastern end of the Remscheid-Altena Anticline is currently the best and most complete Devonian/Carboniferous Boundary (DCB) succession of the Rhenish Massif, Germany. Based on a multidisciplinary approach, focusing on refined conodont and ammonoid biostratigraphy, microfacies analyses, sequence stratigraphy, carbon isotopes (Corg and Ccarb), trace element geochemistry, including REE data, and cyclostratigraphy, the section is proposed as a candidate for the new basal Carboniferous GSSP. The succession represents a pelagic “seamount” setting. It spans the upper Famennian to lower Viséan, with a condensed development of most Rhenish lithostratigraphic units and sedimentary sequences. It is the type-section of the oxic and strongly cyclic, fossiliferous Wocklum Limestone and of important uppermost Famennian and basal Carboniferous index species. The First Appearance Datum (FAD) of Protognathodus kockeli s.str., in a phylogenetic succession from the ancestral Pr. semikockeli n. sp., is proposed as future GSSP level. This FAD is sandwiched between many other marker levels for global correlation. Below are, from base to top, the transgressive base of the at least partly anoxic Hangenberg Black Shale (base Lower Hangenberg Crisis Interval), the Hangenberg Regression (onset of siltstones of the basal Middle Crisis Interval), the level of maximum regression, indicated by maximum Zr/Al values, and the initial transgression of the basal Upper Crisis Interval, marked by the re-onset of carbonate deposition. Above follow the locally cryptogenic FAD of Siphonodella (Eosiphonodella) sulcata s.l. at the base of the post-Crisis Interval (Hangenberg Limestone), associated with a conodont biofacies shift, the FAD of Si. (Eo.) bransoni, and, much higher, the sharp Lower Alum Shale Event at the base of the classical middle Tournaisian. The significance of the section is greatly enlarged by its precise correlation with numerous other Rhenish DCB sections that provide important additional data on faunas, geochemistry, geochronological ages, and magnetic susceptibility. The new Borkewehr data suggest changes of weathering intensity, based on Rb/K and K/Al trends, and Milankovitch cyclicity associated with the climate changes of the Hangenberg Crisis. The local conodont extinction rate at the top of the Wocklum Limestone lies at 57 % while there are no survivors in ammonoids, trilobites, or deep-water corals. Positive carbon isotopic shifts of carbonate in the Upper Crisis Interval and of Corg in the Middle Crisis Interval are decoupled, which suggests complex underlying processes that are not yet understood.

The Late Devonian oceans were susceptible to the development of anoxic conditions, as evidenced by repeated widespread organic-rich shale deposition. Understanding how these anoxic facies were deposited will provide insight into Devonian climatic modes. To this end, we constructed a high-resolution cyclostratigraphic model based on portable XRF-generated elemental ratio records from a Frasnian-Famennian (~372 Ma) black shale section. These black shales are associated with the Kellwasser Crisis, one of the largest mass extinctions of the Phanerozoic, which is not fully understood to this day. The studied section at Winsenberg is located in the Rhenish Massif in Germany and represents a basinal setting at southern low paleolatitudes. Spectral analysis was carried out on the Si/Ca ratios generated by XRF, which is interpreted as the detrital (distal) vs carbonaceous (local) input. The resulting astrochronology suggests a duration of ca. 1 Myr from the base of the Lower Kellwasser to the F-F boundary at the top of the Upper Kellwasser level. This corresponds to an average sedimentation rate of 0.9 cm/kyr. Both the Lower and Upper Kellwasser shales occur at the onset of a 405 kyr eccentricity cycle. We further interpret the Ti/Al record as a riverine runoff signal, as Ti is associated with the coarse-grained fraction, and K/Al as a chemical weathering signal, as K is leached easier than Al. Both tuned records exhibit eccentricity-modulated precession cycles. On precession and short eccentricity timescales, Ti/Al and K/Al are positively correlated, suggesting an orbitally forced wet/dry monsoonal climate in the region where the section was deposited. On longer timescales, the weathering signal becomes decoupled from the riverine runoff signal, highlighting that K/Al (chemical weathering) decreased even during wetter periods. This decoupling is linked to soil maturation in the hinterland, as potassium leaching from mature soils became increasingly limited. Soil build-up and maturation forms a potential mechanism for nutrient storage and subsequent release into the ocean, potentially triggering eutrophication and anoxia.

Earth’s climate during the Neogene period changed in several steps from a planet with unipolar ice sheets to today’s bipolar configuration. Yet, time-continuous and well-preserved sedimentary archives from this time interval are scarce. This is especially true for those records that can be used for tracing the role of astronomical climate forcing. Ocean Drilling Program (ODP) Site 752 was drilled on Broken Ridge (Indian Ocean) and provides a time-continuous sedimentation history since the early Miocene in its upper portion. To date, no astronomical-scale paleoclimate research has been conducted on this legacy ODP site. Here, we use X-ray fluorescence (XRF) core scanning data and benthic foraminifera (BF) taxonomic and quantitative analyses to reconstruct the paleoceanographic changes in the Indian Ocean since 23 Ma. Productivity-related elements from the XRF dataset, show higher productivity during the early Miocene and late Pliocene/early Pleistocene. Moreover, we found strong 405-kyr and ~110-kyr eccentricity imprints in the spectral analysis result of this XRF-derived paleoproductivity proxy. Although the precession signal is also quite remarkable in the spectral analysis results, the 4-cm resolution may not be adequate to further test the precession contribution. Bottom water oxygenation reconstructed using BF, suggest no oxygen minimum zone conditions for the late Miocene on site 752. Dissolved oxygen concentrations (DOC) indicate low oxic conditions (⁓ 2 ml/L) during this time, and relatively low stress species distribution (< 32%) along with abundant oxic species like H. boueana, C. mundulus, L. pauperata and Gyroidinoides spp. suggest predominantly high oxic conditions during the late Miocene (DOC > 2 ml/L). Meanwhile, the grain size (> 425µm) record shows an increasing trend at ~5 Ma, which indicates more current winnowing. Therefore, we argue that the drop in Mn is the result of the increase in the current winnowing, instead of the OMZ expansion. On the other hand, high-amplitude changes in Fe content from the lower Miocene to the middle Miocene, cannot be explained by eolian input, suggesting the source might be the neighbor-distanced Amsterdam-St. Paul hot spot. The source of Fe might be the neighbor-distanced Amsterdam-St. Paul hot spot. We conclude that the legacy ODP Site 752 constitutes an excellent paleoceanographic archive that allows us to reconstruct Indian Ocean dynamics since the early Miocene. New drillings on Broken Ridge with state-of-the-art scientific ocean drilling techniques will provide more detailed information and be highly beneficial for paleoclimatic and paleoceanographic research.

Time series analysis of palaeoclimate data is used to identify quasi-periodic changes attributable to astronomical forcing of insolation by Earth’s axial obliquity and precession, and orbital eccentricity, i.e., Milankovitch cycles. Hays et al. (1976) applied time series analysis – including spectral analysis, filtering, tuning and hypothesis testing – on palaeoclimatic data from the most recent 500 Ka of Earth history to demonstrate forcing from these astronomical parameters. The CENOGRID “splice” (Westerhold et al., 2000) has since extended this evidence to 66 Ma. Investigators have also recognised the imprint of Milankovitch cycles in palaeoclimatic records reaching back into the Precambrian. Palaeoclimate time series present unique challenges: sample spacing is generally not constant; measured data represent combinations of palaeoenvironmental factors; most problematic of all, palaeoclimate time scales are almost never known with adequate certainty. Important time constraints are provided by geochronology from volcanic ash layers, geomagnetic reversals and selected chemostratigraphic events, but only at isolated, widely spaced points along geologic time, and only extremely rarely do they provide a precision sufficient to determine the time-periodicity of palaeoclimate variations at Milankovitch scales. Investigators must also grapple with uncertainties in celestial mechanics, and in the theory of climate change, sedimentation and alteration. From this collective information, one may choose to investigate mechanisms of climate or environmental change (climate modelling); estimate the chronology and duration of stratigraphic series of palaeoclimate data (cyclostratigraphy); and constrain the celestial mechanics of Earth’s distant past. In principle, all of these objectives can be obtained through application of a hierarchical Bayesian model: astronomical forcing -> climate -> environment -> sedimentation -> alteration -> observation. Bayesian theory allows us to reverse all of the arrows and to update information about sedimentation, the environment, climate, and astronomical forcing. However, in Bayesian statistics, expressing a likelihood function is a fundamental step and requires parameterising stochastic quantities. One needs to be clear and explicit about errors. We present an example that considers an explicit-likelihood route for Quaternary data (Carson et al., 2019). In the more distant geologic past, uncertainties about climate and sedimentation are increasingly challenging. Strategies tend to be based on pattern identification by the investigator, with or without numerical techniques. Examples include recognising orbital eccentricity bundling in paleoclimatic data sequences that exhibit precession cycling, and studying the relationships between frequency and amplitudes (Meyers and Malinverno, 2018). We review examples illustrating the relationship between frequency and amplitude together with the supporting theory. References: Carson et al., Proc. R. Soc. A (2019), 475, 20180854; Hays et al., Sci. (1976), 194(4270), 1121-1132; Meyers, S.R., Malinverno, A., Proc. Natl. Acad. Sci. U.S.A. (2018), 115(25), 6363-6368; Westerhold et al., Sci. (2020), 369, 1383-1387.

The last 30 million years (Myr) of Cenozoic climate change broadly charted the transformation from a world with solitary Antarctic ice sheets through to a bipolar glaciated Earth. Highly resolved records of carbonate content (%CaCO3) provide insight into regional impacts of ever shifting climate, cryosphere and carbon cycle interactions. Here, we use X-ray fluorescence (XRF) ln(Ca/Fe) data collected at Ocean Drilling Program Site 1264 (Angola Basin side of Walvis Ridge, SE Atlantic Ocean) to generate the first SE Atlantic %CaCO3 record spanning 30-0 Myr ago (Ma). Minimal changes in terrigenous-derived XRF data supports that the %CaCO3 reflects the balance between productivity and dissolution in this region. This XRF data also helped to formulate a comprehensive and continuous depth and age model for the entirety of Site 1264 (~316 m; 30-0 Ma). These verified depth and age models constitute a key framework for future palaeoceanographic studies at this location.We identify three phases with distinctly different orbital imprints of CaCO3 deposition in the SE Atlantic. The shifts between these phases broadly occur across major developments in climate, the cryosphere and/or the carbon cycle: 1) strong ~110 kyr eccentricity pacing prevails during Oligo-Miocene global warmth (~30-13 Ma); 2) eccentricity-modulated precession imprints more strongly after the mid Miocene Climate Transition (mMCT) (~14-8 Ma); 3) strong obliquity pacing prevails in the late Miocene (~7.7-3.3 Ma) following widespread cooling and the increasing influence of high-latitude processes.The lowest %CaCO3 (92-94%) occur between 18.5-14.5 Ma, potentially reflecting increased dissolution or decreased productivity driven by widespread early Miocene warmth. Deposition recovered after the mMCT (~14 Ma), likely associated with changes in regional surface and/or deep-water circulation following Antarctic reglaciation. The highest Site 1264 %CaCO3 and MARs indicate the late Miocene Biogenic Bloom (LMBB) occurs between ~7.8-3.3 Ma. The LMBB’s onset (~7.8 Ma) and peak productivity (~7 Ma) at 1264 are contemporaneous with the LMBB in the equatorial Pacific Ocean; however the termination is ~1 Myr later in the Atlantic compared to the Pacific. Globally synchronous patterns in the LMBB, including the onset and peak, may be driven by an increased nutrient input into the global ocean, for instance from enhanced aeolian dust and/or weathering fluxes. Regional diachrony and variability in the LMBB’s expression may be driven by regional differences in cooling, continental aridification and/or changes in ocean circulation during the latest Miocene.

Cyclostratigraphy and astrochronology are now at the forefront of geologic timekeeping. While this technique heavily relies on the accuracy of astronomical calculations, solar system chaos limits how far back astronomical calculations can be performed with confidence. High-resolution paleoclimate records with Milankovitch imprints now allow reversing the traditional cyclostratigraphic approach: Middle Eocene drift sediments from Newfoundland Ridge are well-suited for this purpose, due to high sedimentation rates and distinct lithological cycles. Per contra, the stratigraphies of Integrated Ocean Drilling Program Sites U1408-U1410 are highly complex with several hiatuses. Here, we built a two-site composite and constructed a conservative age-depth model to provide a reliable chronology for this rhythmic, highly resolved (

International audience; Mio-Pliocene sedimentary archives of the East Asian summer monsoon (EASM) in NE Tibet record a monotonic response to orbital forcing, dominated by eccentricity. By contrast, Pleistocene archives display a more stochastic response that varies regionally and temporally. When and why this response changed is poorly understood. Here, we present a new high-resolution Rb/Sr ratio data set of EASM intensity from the Sanmenxia Basin, North China, that spans the Plio-Pleistocene transition. Our results indicate decreased monsoonal rainfall in the late Pliocene, dated at 2.75–2.6 Ma, associated with an intensified response to obliquity and enhanced climate stochasticity. This transition is attributed to the increase of Northern Hemisphere ice volume. Quaternary monsoons display a sensitivity unique to the modern icehouse with large bipolar ice sheets, while pre-Quaternary monsoons were solely impacted by Antarctic ice sheet dynamics on orbital time-scales.

The Pliocene sedimentary record provides a window into Earth's climate dynamics under warmer-than-present boundary conditions. However, the Pliocene cannot be considered a stable warm climate that constitutes a solid baseline for middle-of-the-road future climate projections. The increasing availability of time-continuous sedimentary archives (e.g., marine sediment cores) reveals complex temporal and spatial patterns of Pliocene ocean and climate variability on astronomical timescales. The Perth Basin is particularly interesting in that respect because it remains unclear if and how the Leeuwin Current sustained the comparably wet Pliocene climate in Western Australia, as well as how it influenced Southern Hemisphere paleoclimate variability. To constrain Leeuwin Current dynamics in time and space, this project obtained eight clumped-isotope Δ47 paleotemperatures and constructed a new orbitally resolved planktonic foraminifera (Trilobatus sacculifer) stable isotope record (δ18O) for the Plio-Pleistocene (4–2 Ma) interval of International Ocean Discovery Program (IODP) Site U1459. These new data complement an existing TEX86 record from the same site and similar planktonic isotope records from the Northern Carnarvon Basin (Ocean Drilling Program (ODP) Site 763 and IODP Site U1463). The comparison of TEX86 and Δ47 paleothermometers reveals that TEX86 likely reflects sea surface temperatures (SSTs) with a seasonal warm bias (23.8–28.9 ∘C), whereas T. sacculifer Δ47 calcification temperatures probably echo mixed-layer temperatures at the studied Site U1459 (18.9–23.2 ∘C). The isotopic δ18O gradient along a 19–29∘ S latitudinal transect, between 3.9 and 2.2 Ma, displays large variability, ranging between 0.5 ‰ and 2.0 ‰. We use the latitudinal δ18O gradient as a proxy for Leeuwin Current strength, with an inverse relationship between both. The new results challenge the interpretation that suggested a tectonic event in the Indonesian Throughflow as the cause for the rapid steepening of the isotopic gradient (0.9 ‰ to 1.5 ‰) around 3.7 Ma. The tectonic interpretation appears obsolete as it is now clear that the 3.7 Ma steepening of the isotopic gradient is intermittent, with flat latitudinal gradients (∼0.5 ‰) restored in the latest Pliocene (2.9–2.6 Ma). Still, the new analysis affirms that a combination of astronomical forcing of wind patterns and eustatic sea level controlled Leeuwin Current intensity. On secular timescales, a period of relatively weak Leeuwin Current is observed between 3.7 and 3.1 Ma. Notably, this interval is marked by cooler conditions throughout the Southern Hemisphere. In conclusion, the intensity of the Leeuwin Current and the latitudinal position of the subtropical front are both long-range effects of the same forcing: heat transport through the Indonesian Throughflow (ITF) valve and its propagation through Indian Ocean poleward heat transport. The common ITF forcing explains the observed coherence of Southern Hemisphere ocean and climate records.

Widespread marine anoxia triggered by the runoff and recycling of nutrients was a key phenomenon associated with the Frasnian–Famennian (FF) mass extinction. However, the relative importance of global-scale processes versus local influences on site-specific environmental change remains poorly understood. Here, nitrogen-isotope (δ15N) trends are combined with organic-biomarker, phosphorus, and Rock-Eval data in FF sites from the USA (H-32 core, Iowa), Poland (Kowala Quarry), and Belgium (Sinsin). Up-to-date cyclostratigraphic age models for all three sites allow the nature and timing of changes to be precisely compared across the globe. Negative δ15N excursions across the FF interval from the H-32 core and Kowala correlate with geochemical evidence for euxinic, phosphorus-rich, water columns, and possible cyanobacterial activity, suggestive of increased diazotrophic N fixation, potentially coupled with ammonium assimilation at the latter site. By contrast, previously studied sites from Western Canada and South China document enhanced water-column denitrification around the onset of the Upper Kellwasser (UKW) Event, re-emphasizing the geographical heterogeneity in environmental perturbations at that time. Moreover, environmental degradation began >100 kyr earlier in Poland, coeval with a major increase in bioavailable phosphorus supply, than in Iowa, where no such influx is recorded. These regional differences in both the timing and nature of marine perturbations during the FF interval likely resulted from the variable influx of terrigenous nutrients to different marine basins at that time, highlighting the importance of local processes such as terrestrial runoff in driving environmental degradation during times of climate cooling such as the UKW Event.

The Silurian (443.8-419.2 million years ago) is a period of important biodiversity changes, dynamic climate change, including strong sea level fluctuations and the development of low-oxygen conditions in the ocean1-2-3. To date the Silurian lacks in (cyclostratigraphic) age constraints and in understanding in the way astronomical cycles modulate the Silurian climate, which hinders our understanding of Silurian climate dynamics. To assess the role of astronomical cycles in the pacing of the Silurian climate, we study the imprint of astronomical cycles on the record of the Sommerode-1 core from Bornholm, Denmark (53.65-118.66m).The core contains a near continuous Telychian record including the SOCIE and Valgu carbon isotope excursions/events4-5-6. The core was scanned at University of Bremen/ MARUM (November 2021) using the Bruker M4 Tornado µXRF scanner, enabling for a high-resolution cyclostratigraphic and chemostratigraphic study of the Telychian.XRF core measurements provided semi-quantitative element data, spaced at 0.5 mm, were converted into element concentrations (ppm) using a set of reference standards. A Principal Component Analysis simplified the variability in our dataset into 3 components. PC1 has high loadings for Al, Si, K, Ti, Fe and Co, and is interpreted as a detrital component. PC2 has high loadings for Ca and Mn, and is interpreted as an indicator of oxygenation conditions. PC3 has high loadings for S, indicative for the sulphides/dysoxic/anoxic conditions-8-9.Peaks for Mn at 69-85m and S at 85-104m, indicate that part of the core (69-85 m) was deposited under oxic conditions while another part of the core (85-104 m) was deposited under anoxic/dysoxic conditions. We note that the transition to oxic conditions at 90 m coincides with the Valgu isotopic event4 while the SOCIE4 (80-70 m) event occurs during oxic conditions. Spectral analysis (wavelet, MTM and Evolutive Harmonic Analysis (EHA)) on the 3 components reveals the imprints of long and short eccentricity, obliquity and precession. An EHA spectra of the detrital component was used to trace the long eccentricity in the depth domain which was used to infer changes in sedimentation rates. The sedimentation rates are used to convert the record from the depth to time domain. Astronomical cycles filtered from the record in the time domain show that astronomical cycles exert a great control on the depositional record. Indicating the astronomical cycles modulated the Telychian climate which in term paced oxygenation conditions at the sea-floor.1.Melchin et al. (2005) The Silurian Period 525–558 –2. Bond & Grasby (2017) Palaeogeogr., Palaeoclim., Palaeoecol. 478, 3–29. –3. Saltzman (2005) Geology, 33, 7, 573-576. –4. Hammarlund et al. (2019) Palaeogeogr., Palaeoclim., Palaeoecol. 526, 126–135. –5. Schovsbo, et al. (2015). Geological Survey of Denmark and Greenland Bulletin, 33, 9–12.6. Loydell, D. K., et al. (2017). Bulletin of the Geological Society of Denmark, 65, 135–160.7. Algeo, T. J., & Maynard, J. B. (2004). Chemical Geology, 206(3–4), 289–318.8. Ferriday, T., & Montenari, M. (2016). Stratigraphy & Timescales (Vol. 1).9. Rothwell, R. G., & Croudace, I. W. (2015). Tracking Environmental Change Using Lake Sediments. (Vol. 2)

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.

The Indonesian Throughflow (ITF) controls the oceanic flux of heat and salt between the Pacific and Indian Oceans and therewith plays an important role in modulating the meridional overturning circulation and low latitude hydrological cycle. Here, we report new sea surface temperature and aridity records from the west coast of Australia (IODP Site U1460), which allow us to assess the sensitivity of the eastern Indian Ocean to the major reorganization of Earth’s climate that occurred during the Mid-Pleistocene Transition. Our records indicate glacial coolings at 1.55 and 0.65 million years ago that are best explained by a weakening of the ITF as a consequence of global sea level and tectonic changes. These coincide with the development of pronounced gradients in the carbon isotope composition of the different ocean basins and with substantial changes in regional aridity, suggesting that the restrictions of the ITF influenced both the evolution of global ocean circulation and the development of the modern hydrological cycle in Western Australia., Scientific Reports, 9 (1), ISSN:2045-2322

The Pliocene sedimentary record provides a window into Earth’s climate dynamics under warmer-than-present boundary conditions. However, the Pliocene cannot be considered a stable warm climate that constitutes a solid baseline for middle-road future climate projections. Indeed, the increasing availability of time-continuous sedimentary archives (e.g., marine sediment cores) reveals complex temporal and spatial patterns of Pliocene ocean and climate variability on astronomical timescales. The Perth Basin is particularly interesting in that respect because it remains unclear if and how the Leeuwin Current sustained the comparably wet Pliocene climate in West-Australia, as well as how it influenced Southern Hemisphere paleoclimate variability. To constrain Leeuwin Current dynamics in time and space, this project constructed a new orbitally-resolved planktonic foraminifera (Trilobatus sacculifer) stable isotope record (δ18O and clumped isotopes Δ47) for the Plio-Pleistocene (4–2 Ma) interval of International Ocean Discovery Program (IODP) Site U1459. It complements an existing TEX86 record from the same site and similar planktonic isotope records from the Northern Carnarvon Basin (ODP Site 763 and IODP Site U1463). The comparison of TEX86 and Δ47 paleothermometers reveals that TEX86 likely reflects sea surface temperatures (SST, 23.8–28.9 °C), whereas T. sacculifer Δ47 calcification temperatures probably echo the state of the lower mixed layer and upper thermocline at the studied Site U1459 (18.2–20.8 °C). The isotopic δ18O gradient along a 19° S–29° S latitudinal transect, between 3.9–2.2 Ma, displays large variability, ranging between 0.5 and 2.0 ‰, whereby a low latitudinal gradient is indicative of a strong Leeuwin Current and vice versa. These results challenge the interpretation that suggested a tectonic event in the Indonesian Throughflow as the cause for the rapid steepening of the isotopic gradient (0.9 to 1.5 ‰) around 3.7 Ma. The tectonic interpretation appears obsolete as it is now clear that the 3.7 Ma steepening of the isotopic gradient is intermittent, with flat latitudinal gradients (~0.5 ‰) restored in the latest Pliocene (2.9–2.6 Ma). Still, the new analysis affirms that a combination of astronomical forcing of wind patterns and eustatic sea level controlled Leeuwin Current intensity. A period of relatively weak Leeuwin Current between 3.7 and 3.1 Ma is advocated; a time interval also marked by cooler conditions throughout the Southern Hemisphere. In conclusion, the intensity of the Leeuwin Current and the latitudinal position of the subtropical front are rooted in the same forcing: Heat transport through the Indonesian Throughflow (ITF) valve propagated to the temperate zone through Indian Ocean poleward heat transport. The common ITF forcing explains the observed coherence of Southern Hemisphere ocean and climate records.

An unusually short glaciation interrupted the warm Pliocene around 3.3 Ma (Marine Isotope Stage (MIS) M2). Different hypotheses exist to explain why this glaciation event was so pronounced, and why the global climate system returned to warm Pliocene conditions relatively quickly afterwards. One of these proposed mechanisms is a reduced equator-to-pole heat transfer, in response to a tectonically reduced Indonesian Throughflow (ITF). The ITF is a critical part of the global thermohaline ocean circulation, transporting heat from the Indo-Pacific Warm Pool to the Indian Ocean. When ITF connectivity is reduced, the water and heat supply for the Leeuwin Current, flowing poleward along Australia's west coast, is also diminished. To assess the possible relationship between mid-Pliocene glaciations and latitudinal heat transport through the Indonesian Throughflow, we constructed a multi-proxy orbital-scale record for the 3.7–2.8 Ma interval from International Ocean Discovery Program (IODP) Site U1463, off northwest Australia. The comparison of the Site U1463 record with paleoclimate records from nearby Site 763 and West Pacific Warm Pool Site 806 allows for a detailed regional reconstruction of Pliocene paleoceanography and thus for testing the proposed hypothesis. An astronomically-paced decrease in potassium content characterizes the late Pliocene interval of U1463. This record documents the increasing aridity of northwest Australia, periodically alleviated by reinforced summer monsoon precipitation under summer insolation maxima. The δ 18 O record of the planktonic foraminifer Globigerinoides sacculifer correlates exceptionally well with the sea surface temperature (SST) record from Site 806 in the West Pacific Warm Pool, even during MIS M2. Hence, Site U1463 preserves an uninterrupted ITF signal even during Pliocene glaciations. However, the U1463 δ 18 O G.sacculifer record exhibits a 0.5‰ offset with the nearby Site 763A record around MIS M2. This implies that Site 763A, about 500 km west of U1463, more closely tracks Indian Ocean SST records across MIS M2. The U1463 data reveal that heat-transport through the Indonesian Throughflow did not shut down completely during MIS M2, but rather its intensity decreased prior to and during MIS M2, causing Site 763A to temporarily reflect an Indian Ocean, rather than an ITF signal. We conclude that ITF variability significantly influenced latitudinal heat transport by means of the Leeuwin Current and hence contributed to the relative intensity of MIS M2. We propose the ITF valve between the Pacific and Indian Ocean as a positive feedback mechanism, in which an initial sea level lowering reduces ITF heat transport, in turn amplifying global cooling by advancing the thermal isolation of Antarctica.

The late Miocene to early Pliocene was a time of global cooling, albeit in a warmer-than present climate state. Increased marine primary productivity characterizes this interval, often referred to as the late Miocene-early Pliocene biogenic bloom (~9-3.5 Ma). To explain its manifestation, paleoceanographers often involve ocean gateway or monsoon-related mechanisms, formulating hypotheses of increased or redistributed nutrients in the ocean. However, the exact cause-and-effect chains remain obscure, since important diachronicity is observed across ocean basins for the main phase and the termination of this event. Here, we compile proxy data for late Miocene to Pliocene paleoproductivity from all major ocean basins, including calcareous and siliceous plankton groups. By systematically evaluating the age-depth model accuracies of previously published records we demonstrate that a globally synchronous and long-sustained reduction in primary productivity was initiated with a sharp decline between 4.6 and 4.4 Ma. Our compilation supports that relatively rapid processes (~200 kyr) influenced nutrient availability towards the end of the biogenic bloom. By evaluating different mechanisms influencing the ocean nutrient budget on such time scales, we propose orbital forcing as an important candidate to have tipped the balance towards a less productive ocean. We show that this decline in productivity coincided with a prolonged period of low orbital eccentricity and a shift towards lower-amplitude obliquity. This specific astronomical configuration prevents the development of extreme seasonal contrasts which could lead to reduced nutrient supply to the ocean due to decreased riverine influx.

Carbonate-rich middle Eocene sedimentary sequences are relatively scarce, hampering the reconstruction of paleoclimate dynamics within this high-CO2 world. Nevertheless, the Newfoundland Ridge (North-Atlantic Ocean) hosts a unique sedimentary archive of middle Eocene paleoceanographic change at astronomical 104-year resolution. International Ocean Discovery Program (IODP) Sites U1408 and U1410 exhibit well-defined lithologic alternations between calcareous ooze and clay-rich intervals, occurring at the obliquity beat and associated with changing intensities of Northern Component Water (NCW) formation (Vahlenkamp et al., 2018). These lithological variations are captured by the calcium-iron ratio (Ca/Fe) proxy as a measure of carbonate content. Yet, the asymmetric shape of the Ca/Fe cycles immediately reflects a strong non-linear response to the sinusoidal obliquity forcing. To explore the causes of this non-linearity, we built a simple physically-motivated and time-dependent model that simulates the sedimentary response at IODP Sites U1408 and U1410 between 46 and 42 million years ago. dy/dt = 1/T (bx – y) The orbital input x constitutes of an insolation gradient during boreal winter (more specifically at winter solstice), as NCW formation is a high northern latitude winter process that depends on the Atlantic interhemispheric temperature gradient (Karas et al., 2017; Vahlenkamp et al., 2018). The latitudes between which the insolation gradient x is calculated is not user-prescribed but part of the parametrization of the model. Two further parameters define the model. The characteristic time constant T accelerates (T < 1) or slows the response to the forcing (T > 1), whereas the base of the exponential-response term b determines the degree of non-linearity in the system. We explored this four-space first with a coarse and then with a finer mesh, and found that the optimum model lies in the neighbourhood of the following values: latitudinal gradient between 63°N and 31°S, T = 4.94 kyr, b = 2.13. The corresponding system reproduces the asymmetric shape of the Ca/Fe cycles, while also exhibiting precession-obliquity interference patterns that occur in the proxy series. These kind of simple modelling efforts hold the potential to refine our mechanistic understanding of the Earth System response to astronomical forcing in the deep and warmer-than-present geologic past. Karas et al. (2017) Pliocene oceanic seaways and global climate. Scientific Reports 7: 39842 Vahlenkamp et al. (2018) Astronomically paced changes in deep-water circulation in the western North Atlantic during the middle Eocene. Earth and Planetary Science Letter 484: 329 – 340.

A fully cored sequence of Hesse Clay, Port Campbell Limestone and uppermost Gellibrand Marl in the onshore Otway Basin, southeastern Australia, offers new insight into the evolution of the middle Miocene Port Campbell Limestone. The Port Campbell Limestone comprises grey unconsolidated to semi-consolidated and rarely lithified bioclastic muddy carbonate sands in a stack of thin repetitive cycles within cycles of predominantly shoaling-upward character. A glauconitic band with a distinctive mollusc–echinoderm–bryozoan fauna provides a distinctive marker interval in the sequence. In mineralogy, the Port Campbell Limestone is predominantly calcite with traces of remnant aragonite in muddier low-permeability sands, and with dolomitic zones in permeable intervals. The small non-carbonate component of the Port Campbell Limestone is between 3 and 15 wt% and comprises quartz silt with minor clay, feldspar and mica. Dissolution overprints are prominent throughout the carbonate sequence. Three distinct geochemical signatures of provenance are evident in the Port Campbell Limestone sequence, including possible volcanogenic contributions with felsic sources. Foraminifera are common and generally well preserved. Foraminiferal data suggest a depositional transition from outer shelf conditions in the Gellibrand Marl at ca 15 Ma to middle shelf environments in the lower part of the Port Campbell Limestone during the Middle Miocene Climatic Optimum (MMCO) at ca 14.24 Ma. Shallowing after 14 Ma indicates variable paleodepths of ca 13.2 Ma when the sequence was emergent for a brief but undetermined period, corresponding with sharp changes in geochemical ratios. Observed cyclicity in these mid-shelfal, cold-water carbonates is strongly correlated with orbital forcings—eccentricity and obliquity. Sedimentation rates determined from cyclostratigraphic analysis indicate 4–6 cm/kyr at the end of the MMCO, diminishing to 1.5–3 cm/kyr during the MMCT and the subsequent accumulation of the Port Campbell Limestone.KEY POINTSThe Port Campbell Limestone is a stack of thin repetitive depositional cycles within cycles. The cyclicity is strongly correlated with orbital forcings—eccentricity and obliquity—and this is reflected in the geochemistry.Foraminiferal data suggest a depositional transition from outer shelf conditions in the Gellibrand Marl at ca 15 Ma to middle shelf environments in the lower part of the Port Campbell Limestone during the Middle Miocene Climatic Optimum (MMCO) at ca 14.24 Ma.The sequence was emergent for a brief but undetermined period at ca 13.2 Ma, corresponding with sharp changes in geochemical ratios.Three distinct geochemical signatures of provenance are evident in the Port Campbell Limestone sequence, including possible volcanogenic contributions with felsic sources. The Port Campbell Limestone is a stack of thin repetitive depositional cycles within cycles. The cyclicity is strongly correlated with orbital forcings—eccentricity and obliquity—and this is reflected in the geochemistry. Foraminiferal data suggest a depositional transition from outer shelf conditions in the Gellibrand Marl at ca 15 Ma to middle shelf environments in the lower part of the Port Campbell Limestone during the Middle Miocene Climatic Optimum (MMCO) at ca 14.24 Ma. The sequence was emergent for a brief but undetermined period at ca 13.2 Ma, corresponding with sharp changes in geochemical ratios. Three distinct geochemical signatures of provenance are evident in the Port Campbell Limestone sequence, including possible volcanogenic contributions with felsic sources.

The International Ocean Discovery Programme (IODP) and its predecessors generated a treasure trove of Cenozoic climate and carbon cycle dynamics. Yet, it remains unclear how climate and carbon cycle interacted under changing geologic boundary conditions. Here, we present the carbon isotope (δ13C) megasplice, documenting deep-ocean δ13C evolution since 35 million years ago (Ma). We juxtapose the δ13C megasplice with its δ18O counterpart and determine their phase-difference on ~100-kyr eccentricity timescales. This analysis reveals that 2.4-Myr eccentricity cycles modulate the δ13C-δ18O phase relationship throughout the Oligo-Miocene (34-6 Ma), potentially through changes in continental weathering. At 6 Ma, a striking switch from in-phase to anti-phase behaviour occurs, signalling a reorganization of the climate-carbon cycle system. We hypothesize that this transition is consistent with Arctic cooling: Prior to 6 Ma, low-latitude continental carbon reservoirs expanded during astronomically-forced cool spells. After 6 Ma, however, continental carbon reservoirs contract rather than expand during cold periods due to competing effects between Arctic biomes (ice, tundra, taiga). We conclude that, on geologic timescales, System Earth experienced state-dependent modes of climate–carbon cycle interaction., Climate and carbon cycle interactions during major Earth system changes through the Cenozoic remain unclear. Here, the authors present a combined δ13C-δ18O megasplice for the last 35 Ma which allows them to identify three marked intervals of distinct climate–carbon cycle interactions.

Ocean gateways facilitate circulation between ocean basins, thereby impacting global climate. The Indonesian Gateway transports water from the Pacific to the Indian Ocean via the Indonesian Throughflow (ITF) and drives the strength and intensity of the modern Leeuwin Current, which carries warm equatorial waters along the western coast of Australia to higher latitudes. Therefore, ITF dynamics are a vital component of global thermohaline circulation. Plio‐Pleistocene changes in ITF behavior and Leeuwin Current intensity remain poorly constrained due to a lack of sedimentary records from regions under its influence. Here, organic geochemical proxies are used to reconstruct sea surface temperatures on the northwest Australian shelf at IODP Site U1463, downstream of the ITF outlet and under the influence of the Leeuwin Current. Our records, based on TEX86 and the long‐chain diol index, provide insight into past ITF variability (3.5–1.5 Ma) and confirm that sea surface temperature exerted a control on Australian continental hydroclimate. A significant TEX86 cooling of ~5°C occurs within the mid‐Pliocene Warm Period (3.3–3.1 Ma) suggesting that this interval was characterized by SST fluctuations at Site U1463. A major feature of both the TEX86 and long‐chain diol index records is a strong cooling from ~1.7 to 1.5 Ma. We suggest that this event reflects a reduction in Leeuwin Current intensity due to a major step in ongoing ITF constriction, accompanied by a switch from South to North Pacific source waters entering the ITF inlet. Our new data suggest that an additional ITF constriction event may have occurred in the Pleistocene.

Pre-Quaternary paleoclimate studies in Australia mainly focus on terrestrial records from the southeastern part of the continent. IODP Expedition 356 drilled on the northwestern Australian shelf, yielding Miocene-Pleistocene paleoclimate records in an area where climate archives are scarce. Postexpedition research revealed a dry-to-humid transition across the latest Miocene and early Pliocene (start of the "Humid Interval"). However, the complex tectonic history of the area makes these interpretations challenging. In this study, we investigate late Miocene to early Pliocene sediment cores from two sites that are only 100 km apart but situated in two adjacent basins (Northern Carnarvon and Roebuck Basins). Combining lithofacies study, time series analysis of potassium content (K wt%), and calcareous nannofossil abundance counts (N/g), this work disentangles the complex interplay between basin evolution and climate change between 6.1 and 4 Ma. Overall, the investigated proxies show high correlation between both sites, except during 6.1-5.7 Ma. During this interval, Site U1463 records a gradual increase in K wt%, correlated with basin deepening, whereas Site U1464 records an abrupt rise in K wt% at similar to 6 Ma. We explain this diachronicity by differential basin subsidence. The tectonic interplay with our paleorecords makes it difficult to pinpoint the exact onset of the "Humid Interval," but we conclude that K wt% and coccolith abundances at Site U1464 indicate that a fluvial deposition system was already established since at least 6 Ma. This age is consistent with data supporting a southward movement of the Intertropical Convergence Zone rain belt at similar to 7 Ma.

Fifty-one years of scientific ocean drilling through the International Ocean Discovery Program (IODP) and its predecessors generated a treasure trove of Cenozoic climate and carbon cycle dynamics. Yet, it remains unclear how climate system and carbon cycle interacted under changing geologic boundary conditions. Here, we present the carbon isotope (d13C) megasplice, documenting deep-ocean d13C evolution since 35 million years ago (Ma). We juxtapose the d13C megasplice with its d18O counterpart and determine their phase-difference on ~100-kyr eccentricity time-scales. This analysis uncovers that 2.4-Myr eccentricity modulates the in-phase relationship between d13C and d18O during the Oligo-Miocene (34-6 Ma), potentially related to changes in continental weathering. At 6 Ma, a striking switch from in-phase to anti-phase behaviour occurs, signalling a threshold in the climate system. We hypothesize that Arctic glaciation and the emergence of bipolar ice sheets enabled eccentricity to exert a major influence on the size of continental carbon reservoirs. Our results suggest that a reverse change in climate - carbon cycle interaction should be anticipated if CO2 levels rise further and we return to a world of unipolar ice sheets.

A recent biostratigraphic re-evaluation of Ocean Drilling Program (ODP) Site 722 (Bialik et al., accepted, Paleoceanogr. and Paleocl.) provides new insights into the history of monsoon driven upwelling in the Arabian Sea between 15 and 8.5 Ma. They suggest the modern monsoon was only established after tectonic preconditioning, linked to the uplift of the Himalayas, closure of the Tethyan Seaway, and the inception of Indonesian Throughflow restriction. But the requisite topography for the Indian monsoon was already in place by at least the late early Miocene which suggests another driver. However, as northern hemisphere latitudinal heat gradients continued to be shallower than modern throughout the Miocene, steepening southern hemisphere gradients during the middle Miocene glaciation of Antarctica ~14.8 Ma (Pound et al., 2012, Earth-Sci. Rev., 112) may have played an important role in pacing the monsoon system during the middle to late Miocene.Here we further explore these findings by using recently acquired X-ray fluorescence (XRF) core scanning data from two additional ODP sites located in the central (Site 707) and southern (Site 752) Indian Ocean. We trace the timing and pacing of these environmental changes along a cross hemispheric transect within key areas of the larger Indian Ocean-Atmospheric system: (1) the monsoonal upwelling regions along the Oman Margin (Site 722); (2) the Somali/Findlater jets (Site 707); and (3) the high-pressure zone in the southern horse latitudes (Site 752).Using updated age constraints at all sites, we show that the intensification of upwelling at Site 722 is tightly linked to climatic and oceanographic changes in the southern high latitudes (e.g., Groeneveld et al., 2017; Sci. Adv.). This close co-evolution of southern hemisphere climatic shifts and monsoon dynamics hints at a strong contribution of increasing southern hemisphere thermal gradients on the middle to late Miocene evolution of the Indian Ocean circulation system and Indian monsoon dynamics. Our findings thus re-emphasize the Indian summer monsoon as the result of a complex cross-hemispheric ocean-atmospheric system spanning the Indo-Pacific (e.g., Gadgil, 2018, J. Earth Syst. Sci., 127). We postulate that the Indian Ocean-Atmospheric system experienced a gradual intensification that began after the Middle Miocene Climatic Optimum with Antarctic Ice Sheet expansion. These changes then culminated in a synchronous shift ~11 Ma during the Ser4/Tor1 sea level lowstand (Haq et al., 1987; Science, 235). Future chrono-, chemo- and cyclostratigraphic work at ODP Sites 707 and 752 will further help to constrain the timing of these events, and fully place them in the context of the global climatic evolution during the Miocene.

International audience; The geologic time scale for the Cenozoic Era has been notably improved over the last decades by virtue of integrated stratigraphy, combining high-resolution astrochronologies, biostratigraphy and magnetostratigraphy with high-precision radioisotopic dates. However, the middle Eocene remains a weak link. The so-called “Eocene time scale gap” reflects the scarcity of suitable study sections with clear astronomically-forced variations in carbonate content, primarily because large parts of the oceans were starved of carbonate during the Eocene greenhouse. International Ocean Discovery Program (IODP) Expedition 369 cored a carbonate-rich sedimentary sequence of Eocene age in the Mentelle Basin (Site U1514, offshore southwest Australia). The sequence consists of nannofossil chalk and exhibits rhythmic clay content variability. Here, we show that IODP Site U1514 allows for the extraction of an astronomical signal and the construction of an Eocene astrochronology, using 3-cm resolution X-Ray fluorescence (XRF) core scans. The XRF-derived ratio between calcium and iron content (Ca/Fe) tracks the lithologic variability and serves as the basis for our U1514 astrochronology. We present a 16 million-year-long (40-56 Ma) nearly continuous history of Eocene sedimentation with variations paced by eccentricity and obliquity. We supplement the high-resolution XRF data with low-resolution bulk carbon and oxygen isotopes, recording the long-term cooling trend from the Paleocene-Eocene Thermal Maximum (PETM – ca. 56 Ma) into the middle Eocene (ca. 40 Ma). Our early Eocene astrochronology corroborates existing chronologies based on deep-sea sites and Italian land sections. For the middle Eocene, the sedimentological record at U1514 provides a single-site geochemical backbone and thus offers a further step towards a fully integrated Cenozoic geologic time scale at orbital resolution.

Much of our understanding of Earth's past climate comes from the measurement of oxygen and carbon isotope variations in deep-sea benthic foraminifera. Yet, long intervals in existing records lack the temporal resolution and age control needed to thoroughly categorize climate states of the Cenozoic era and to study their dynamics. Here, we present a new, highly resolved, astronomically dated, continuous composite of benthic foraminifer isotope records developed in our laboratories. Four climate states-Hothouse, Warmhouse, Coolhouse, Icehouse-are identified on the basis of their distinctive response to astronomical forcing depending on greenhouse gas concentrations and polar ice sheet volume. Statistical analysis of the nonlinear behavior encoded in our record reveals the key role that polar ice volume plays in the predictability of Cenozoic climate dynamics.

MARUM, University of Bremen, Germany (1); Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Germany (2); University of Tübingen, Germany Precise future predictions of Mediterranean sea surface temperature (SST) variability as one of the most sensitive regions to climate change are hampered by insufficient knowledge of accurate SST reconstructions in resolution relevant for human time-scales from warmer-than-present periods. The Last Interglacial (LIG; ~130,000 to 116,000 years ago) is the most recent period with warmer-than-present climate; however, continuous subdecadal records of LIG SST are unavailable due to a small number of undisturbed sedimentary records and sample-size limitations of conventional methodologies. We circumvent these issues by applying Mass Spectrometry Imaging on finely laminated sapropel S5 sediment deposited in the Eastern Mediterranean; the result is an alkenone-based SST time-series in 1-4 year resolution. These data reveal prominent and rapid decadal SST oscillations in the Eastern Mediterranean with a ~60 years cyclicity that is persistent throughout most of the record, suggesting similar LIG decadal climate oscillations as in the Holocene. We also compare the reconstructed rate of SST change during the LIG to the present-day observational record, and find that LIG temperature change often exceeded the present-day rate of change. On the other hand, comparison of the LIG multidecadal SST to the projected increase in Mediterranean SST until 2100 AD suggests SST increase at the end of the 21st century to be unprecedented in magnitude and duration. We thus conclude that future warming of the Mediterranean could cause an unrivalled change in the Mediterranean planktonic ecosystems and their biological responses.

A high-resolution potassium content record of sediments from Integrated Ocean Drilling Program (IODP) Site U1422 drilled in the northern Sea of Japan was employed to yield an astronomical timescale for this ∼205 m thick sedimentary archive. The K content was quantified using the natural gamma radiation (NGR) data routinely measured on DV JOIDES Resolution. The U1422 K (wt.%) series shows an increasing trend with time, which parallels the growth of North Hemisphere ice sheets since ∼4 Ma, as revealed by the global benthic foraminifer's oxygen isotope stack (LR04). We propose that K content variations reflect changes in the relative contributions of Asian eolian dust and volcanic weathering products, in response to changes in global ice volume. Using the shipboard age model, constrained by palaeomagnetism and nanofossils datums, we tuned the U1422 K content variations to the LR04 stack. Our tuned age model for site U1422 goes back to 3.9 Ma. The studied record indicates that Asian dust generation is enhanced during periods of global cooling. The synchronous variations between the U1422 K record and the LR04 stack also suggest that global cooling played a dominant role in promoting the central Asian aridification since ∼3.9 Ma, while the uplift of Tibetan Plateau plays a secondary role, considering many disagreements still exists between the timing and amplitude of the Qinghai-Tibetan uplift and the evolution of central Asian aridity since the early Pliocene.

North Atlantic Deep Water (NADW) currently redistributes heat and salt between Earth's ocean basins, and plays a vital role in the ocean-atmosphere CO2 exchange. Despite its crucial role in today's climate system, vigorous debate remains as to when deep-water formation in the North Atlantic started. Here, we present datasets from carbonate-rich middle Eocene sediments from the Newfoundland Ridge, revealing a unique archive of paleoceanographic change from the progressively cooling climate of the middle Eocene. Well-defined lithologic alternations between calcareous ooze and clay-rich intervals occur at the ∼41-kyr beat of axial obliquity. Hence, we identify obliquity as the driver of middle Eocene (43.5–46 Ma) Northern Component Water (NCW, the predecessor of modern NADW) variability. High-resolution benthic foraminiferal δ 18 O and δ 13 C suggest that obliquity minima correspond to cold, nutrient-depleted, western North Atlantic deep waters. We thus link stronger NCW formation with obliquity minima. In contrast, during obliquity maxima, Deep Western Boundary Currents were weaker and warmer, while abyssal nutrients were more abundant. These aspects reflect a more sluggish NCW formation. This obliquity-paced paleoceanographic regime is in excellent agreement with results from an Earth system model, in which obliquity minima configurations enhance NCW formation.

The Middle Pleistocene Transition (MPT) represents a major change in Earth's climate state, exemplified by the switch from obliquity-dominated to ∼100-kyr glacial/interglacial cycles. To date, the causes of this significant change in Earth's climatic response to orbital forcing are not fully understood. Nonetheless, this transition represents an intrinsic shift in Earth's response to orbital forcing, without fundamental changes in the astronomical rhythms. This study presents new high-resolution records of International Ocean Discovery Program (IODP) Site U1460 (eastern Indian Ocean, 27°S), including shallow marine productivity and organic matter flux reconstructions. The proxy series covers the interval between 1.1 and 0.6 Ma and provides insights into Pleistocene Leeuwin Current dynamics along the West Australian shelf. The large >45 m global sea level drop during the marine isotope stage (MIS) 22–24 is marked in our data, suggesting that the MPT led to large-scale changes in Indian Ocean circulation patterns and surface water conditions. We consider shelf exposure (and thus the “Sahul-Indian Ocean Bjerknes mechanism”) as a possible key process to increase the upwelling of nutrient-rich sub-Antarctic Mode waters through the Leeuwin Undercurrent along the Australian shelf. We conclude that the shoaling of nutrient-rich lower-thermocline waters enhanced mid-latitude productivity patterns in the eastern Indian Ocean across the 900-ka event.

During International Ocean Discovery Program (IODP) expeditions, shipboard-generated data provide the first insights into the cored sequences. The natural gamma radiation (NGR) of the recovered material, for example, is routinely measured on the ocean drilling research vessel DV JOIDES Resolution. At present, only total NGR counts are readily available as shipboard data, although full NGR spectra (counts as a function of gamma-ray energy level) are produced and archived. These spectra contain unexploited information, as one can estimate the sedimentary contents of potassium (K), thorium (Th), and uranium (U) from the characteristic gamma-ray energies of isotopes in the ^(40)K, ^(232)Th, and ^(238)U radioactive decay series. Dunlea et al. [2013] quantified K, Th and U contents in sediment from the South Pacific Gyre by integrating counts over specific energy levels of the NGR spectrum. However, the algorithm used in their study is unavailable to the wider scientific community due to commercial proprietary reasons. Here, we present a new MATLAB algorithm for the quantification of NGR spectra that is transparent and accessible to future NGR users. We demonstrate the algorithm's performance by comparing its results to shore-based inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma-emission spectrometry (ICP-ES), and quantitative wavelength-dispersive X-ray fluorescence (XRF) analyses. Samples for these comparisons come from eleven sites (U1341, U1343, U1366-U1369, U1414, U1428-U1430, U1463) cored in two oceans during five expeditions. In short, our algorithm rapidly produces detailed high-quality information on sediment properties during IODP expeditions at no extra cost.

Cyclostratigraphy is an important tool for understanding astronomical climate forcing and reading geological time in sedimentary sequences, provided that an imprint of insolation from Earth’s orbital eccentricity, obliquity and/or precession is preserved (Milankovitch forcing). Numerous stratigraphic and paleoclimate studies have applied cyclostratigraphy, but the robustness of the methodology and dependence on the investigator have not been systematically evaluated. Here, we present an experimental design of three artificial cases with known input parameters. Each case is designed to address specific challenges that are relevant to cyclostratigraphy. Case 1 simulates the situation of a scientist onboard a research vessel: for his/her analysis, nothing more than a drill-core photograph and the approximate position of a stage boundary is available. Case 2 is a proxy record with clear nonlinear cyclical patterns, which interpretation is complicated by the presence of a stratigraphic gap. Case 3 represents a modeled Late Devonian proxy record, with a low signal-to-noise ratio and no specific astronomical solution available for this age. Each case was analyzed by 17 to 20 participants as part of the Cyclostratigraphy Intercomparison Project (CIP). The test group was heterogeneous in terms of experience and dedicated time and self-reflected on the results during a meeting in Brussels, Belgium. The analyses demonstrate that not every participant came to the correct solution. However, the median solution of all submitted analyses accurately approached the correct solution in all three cases and some participants obtained the exact correct answers. This experiment demonstrates that cyclostratigraphy is a powerful tool for deciphering time in sedimentary successions, and importantly, it is a trainable skill. Systematically better performances were obtained for cases that were closer in type and stratigraphic age to the experience of individual participants. Finally, we emphasize the importance of an integrated stratigraphic approach and provide a set of guidelines on what good practices in cyclostratigraphy should include. With the CIP, we cannot provide a quantitative measure of reliability and uncertainty of cyclostratigraphy. Instead, our case studies provide valuable insight in current common practices in cyclostratigraphy, their merits and pitfalls. Therewith, CIP is a starting point for further discussions on how to move this maturing field forward.

The Pliocene was characterized by a gradual shift of global climate toward cooler and drier conditions. This shift fundamentally reorganized Earth's climate from the Miocene state toward conditions similar to the present. During the Pliocene, the progressive restriction of the Indonesian Throughflow (ITF) is suggested to have enhanced this shift toward stronger meridional thermal gradients. Reduced ITF, caused by the northward movement of Australia and uplift of Indonesia, impeded global thermohaline circulation, also contributing to late Pliocene Northern Hemisphere cooling via atmospheric and oceanographic teleconnections. Here we present an orbitally tuned high-resolution sediment geochemistry, calcareous nannofossil, and X-ray fluorescence record between 3.65 and 2.97 Ma from the northwest shelf of Australia within the Leeuwin Current. International Ocean Discovery Program Site U1463 provides a record of local surface water conditions and Australian climate in relation to changing ITF connectivity. Modern analogue-based interpretations of nannofossil assemblages indicate that ITF configuration culminated similar to 3.54 Ma. A decrease in warm, oligotrophic taxa such as Umbilicosphaera sibogae, with a shift from Gephyrocapsa sp. to Reticulofenestra sp., and an increase of mesotrophic taxa (e.g., Umbilicosphaera jafari and Helicosphaera spp.) suggest that tropical Pacific ITF sources were replaced by cooler, fresher, northern Pacific waters. This initial tectonic reorganization enhanced the Indian Oceans sensitivity to orbitally forced cooling in the southern high latitudes culminating in the M2 glacial event (similar to 3.3 Ma). After 3.3 Ma the restructured ITF established the boundary conditions for the inception of the Sahul-Indian Ocean Bjerknes mechanism and increased the response to glacio-eustatic variability.

A Correction to this paper has been published: https://doi.org/10.1038/s41467-021-21827-8

In this paper we formulate answers to three important questions related to Givetian carbonate records and their use for reconstructing million-year-scale past palaeoenvironmental changes. First, we provide detailed illustrations of the fascinating diversity that shaped a significant shallow reefal platform during early to late Givetian time in the Rhenohercynian Ocean; secondly we improve the sedimentological model of the extensive Givetian carbonate platform in the Dinant Basin; and thirdly we evaluate the application of magnetic susceptibility as a tool for long-term trend correlations and palaeoenvironmental reconstructions. These goals are reached by making a sedimentological, geophysical and geochemical study of the La Thure section. Through the early–late Givetian interval we discerned 18 microfacies ranging from a homoclinal ramp to a discontinuously rimmed shelf and then a drowning shelf. The comparison of these sedimentological results with those published for the south of the Dinant Syncline allowed us to provide an up to date model of the vertical and lateral environmental development of one of the largest Givetian carbonate platforms in Europe. This comparison also increased the knowledge on the distribution of facies belts in the Dinant Basin and allowed us to highlight the Taghanic Event. Palaeoredox proxies reveal a substantial change in the oxygenation level, from oxygen-depleted to more oxic conditions, between middle and late Givetian time. We demonstrated the relationship between variation in magnetic susceptibility values and proxies for siliciclastic input (such as Si, Al). The La Thure section is considered a key section for the understanding of internal shelf settings bordering Laurussia9s southeastern margin.

The Late Devonian mass extinction was the second of five global mass extinctions that shaped life on Earth during the Phanerozoic Eon, and occurred at the Frasnian– Famennian boundary (FFB, 372 Ma). Here, we focus on this time interval at the famous Steinbruch Schmidt section in Germany. This section includes the well exposed Kellwasser black shale intervals, the FFB, and a U-Pb dated ash layer. In this study, we sampled an interval of 5.3 m around the FFB, with an average sampling interval of 3 cm, leading to a collection of about 200 samples. On every sample, we measured carbon and oxygen stable isotopes, magnetic susceptibility and micro XRF elemental geochemistry. Magnetic susceptibility (MS) and detrital-input-related elements such as Ti and Al are higher during the Kellwasser, and there is a good correlation between Al, K, Ti, Fe and MS. 􀀀13C values are high at and around the Kellwasser levels. We selected the MS, Ti/Al and 􀀀13C signals for spectral analysis, as we expect these proxies to contain the best-preserved astronomical signal. We applied the technique developed by Meyers (2015) on the evaluation of eccentricity-related amplitude modulation independently to the 3 signals. Obtained results for the 3 signals are exactly in the same range, with a sedimentation rate of 0.47 cm/kyr and it allows the transformation of the signal from the distance domain (5.3 m) into the time domain (about a 1100 kyr). If we filter precession from signal and look at its envelope, we can see a clear modulation by 100 kyr cycle, including 5 to 6 precession cycles, as expected for the Devonian. These results are in agreement with the timing proposed by De Vleeschouwer et al. (2017). Furthermore, as in De Vleeschouwer et al. (2007), we have identified a strong obliquity Power at the FFB, which is associated at Steinbruch Schmidt with a low eccentricity power. This would correspond to a period with low seasonality and could have influenced the development of anoxia. This time frame combined with the dating of the ash layer below the FFB boundary (Percival et al., 2018) provides an anchor point for this cyclostratigraphic framework. De Vleeschouwer, D., Da Silva, A.-C., Sinnesael, M., Chen, D., Day, J.E., Whalen, M.T., Guo, Z., Claeys, P., 2017. Timing and pacing of the Late Devonian mass extinction event regulated by eccentricity and obliquity. Nature Communications 8, 2268. Meyers, S.R., 2015. The evaluation of eccentricity-related amplitude modulation and bundling in paleoclimate data: An inverse approach for astrochronologic testing and time scale optimization. Paleoceanography 30, 1625–1640.

A detailed paleoenvironment reconstruction from the Mozambique Channel, western Indian Ocean, based on the calcareous nannoplankton assemblages was conducted for the interval between 2.85 and 1.85 Myr. This study covers the period during which the successive extinction of the last five species of discoasters occurred. New productivity data obtained from the abundances of the Discoaster species (Discoaster brouweri, D. triradiatus, D. pentaradiatus, D. surculus, and D. tamalis) and other indicative calcareous nannoplankton taxa showed abundance variations, which were at paced with the 100, 41, and 23 kyr astronomical periodicities. A shift in the productivity and water-column stratification proxies occurred at ~2.4 Ma, after the onset of the Northern Hemisphere glaciation. Here we propose that the variability recorded at International Ocean Discovery Program Site U1476 reflects the interplay between forcing associated with warm tropical Pacific and cold southern ocean influences. The former is shown by consistent occurrence of warm water taxa (Calcidiscus leptoporus, Oolithotus spp., Rhabdosphaera clavigera, Syracosphaera spp., Umbellosphaera spp.), typical of Indonesian Throughflow surface waters. On the other hand, the occurrence of Coccolithus pelagicus indicates the influence of cold, nutrient-rich sub-Antarctic surface waters. A more mixed water column initiated at ~2.4 Ma, and a consequent productivity increase led to the gradual reduction of the Discoaster species, until their extinction at 1.91 Ma. This period was characterized by the low values of the Florisphaera profunda index and high abundances of upper photic zone flora, indicative of nutrient-rich surface water conditions. High productivity at the location during this period could have also been amplified by localized upwelling events driven by the Mozambique Channel eddies.