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Sedimentary uranium (U) and thorium (Th) isotopes are invaluable proxies to assess bottom water redox conditions, site‐specific sediment focusing and vertical rain rates. We investigate if authigenic uranium (aU) can serve as a proxy for bottom water ventilation at International Ocean Discovery Program Site U1537 in the Scotia Sea and we provide Th‐normalized vertical rain rates and focusing factors. The presented data set is complemented by bulk sediment δ234U, porewater U concentrations and biogenic barium. Furthermore, we introduce a method to check temporal variations in the detrital factor for the calculation of aU by comparing measured and modeled δ234U. We observed partial uranium remobilization in the core for sections older than 70 ka, identified by δ234U anomalies and porewater U concentrations. During interglacials, the accumulation of aU in the sediment is regulated by the decomposition of substantial quantities of organic matter, ultimately controlled by high export productivity and associated high particulate organic carbon fluxes. Conversely, during glacial times, low export productivity coincides with low aU concentrations, suggesting well‐oxygenated bottom waters. However, during the Last Glacial Maximum, a rise in aU likely indicates reduced ventilation, suggesting an absence of Weddell Sea Deep Water and/or enhanced water column stratification between 23 and 17.5 ka.

The circulation of Antarctic Intermediate Water is thought to make an important contribution to the global ocean–climate system, but the details of this interaction are not fully understood. Furthermore, the behaviour of Antarctic Intermediate Water under glacial and interglacial conditions is not well constrained. Here we present a 25,000-year-long record of neodymium isotopic variations—a tracer of water-mass mixing—from the middle depths of the tropical Atlantic Ocean. Our data reveal abruptly enhanced northward advection of Antarctic Intermediate Water during periods of reduced North Atlantic overturning circulation during the last deglaciation. These events coincide with an increase in the formation of Antarctic Intermediate Water and warming in the southwest Pacific Ocean, which suggests a tight link with Southern Hemisphere climate. In contrast, the initial incursion of southern source water into the North Atlantic ∼19,000 years ago coincided with weak Antarctic Intermediate Water formation in the Pacific and reduced overturning in the North Atlantic. We conclude that reduced competition at intermediate water depth at this time allowed expansion of Antarctic Intermediate Water into the North Atlantic. This early incursion of Antarctic Intermediate Water may have contributed to freshening of the North Atlantic, perhaps spurring the subsequent collapse of North Atlantic deep convection. The formation and circulation of Antarctic Intermediate Water has varied over glacial–interglacial timescales. A neodymium record from the Atlantic Ocean basin suggests that changes in circulation may have been driven by changes both in Antarctic Intermediate Water formation in the Southern Ocean and in the strength of North Atlantic meridional overturning.

A major obstacle in understanding the evolution of Cenozoic climate has been the lack of well dated terrestrial evidence from high-latitude, glaciated regions. Here, we report the discovery of exceptionally well preserved fossils of lacustrine and terrestrial organisms from the McMurdo Dry Valleys sector of the Transantarctic Mountains for which we have established a precise radiometric chronology. The fossils, which include diatoms, palynomorphs, mosses, ostracodes, and insects, represent the last vestige of a tundra community that inhabited the mountains before stepped cooling that first brought a full polar climate to Antarctica. Paleoecological analyses, ⁴⁰Ar/³⁹Ar analyses of associated ash fall, and climate inferences from glaciological modeling together suggest that mean summer temperatures in the region cooled by at least 8°C between 14.07 ± 0.05 Ma and 13.85 ± 0.03 Ma. These results provide novel constraints for the timing and amplitude of middle-Miocene cooling in Antarctica and reveal the ecological legacy of this global climate transition.

We installed the new Isotopx ATONA Faraday cup detector amplifiers on an Isotopx NGX mass spectrometer at Lamont-Doherty Earth Observatory in early 2018. The ATONA is a capacitive transimpedance amplifier, which differs from the traditional resistive transimpedance amplifier used on most Faraday detectors for mass spectrometry. Instead of a high-gain resistor, a capacitor is used to accumulate and measure charge. The advantages of this architecture are a very low noise floor, rapid response time, stable baselines, and very high dynamic range. We show baseline noise measurements and measurements of argon from air and cocktail gas standards to demonstrate the capabilities of these amplifiers. The ATONA exhibits a noise floor better than a traditional 1013 Ω amplifier in normal noble gas mass spectrometer usage, superior gain and baseline stability, and an unrivaled dynamic range that makes it practical to measure beams ranging in size from below 10−16 to above 10−9 A using a single amplifier.

Evidence from high-sedimentation-rate South Atlantic deep-sea cores indicates that global and Southern Ocean carbon budget shifts preceded thermohaline circulation changes during the last ice age initiation and termination and that these were preceded by ice-sheet growth and retreat, respectively. No consistent lead-lag relationships are observed during abrupt millennial warming events during the last ice age, allowing for the possibility that ocean circulation triggered some millenial climate changes. At the major glacial-interglacial transitions, the global carbon budget and thermohaline ocean circulation responded sequentially to the climate changes that forced the growth and decline of continental ice sheets.

Mono Lake in eastern California has the highest natural boron concentrations measured in a natural water body. Inputs to Mono Lake are from creeks that drain from the Sierra Nevada, accounting for over 80% of the total water input, and springs account for most of the rest of the water budget. We measured boron concentrations and isotope compositions of water sources in the lake and lake water collected over several seasons. The δ11B offset of at least +2.5‰ between Mono Lake water compared to its inputs suggests that, like seawater, the boron isotopic composition of the lake is influenced by the removal of light boron by coprecipitation and/or sorption of borate. Given the alkalinity of the lake, boron fractionation likely occurs before or as the water sources enter the lake. The famous tufa towers around the lake are a physical representation of a ‘chemical delta’ that alters the boron isotopic composition of the source fluids as they enter the lake. Based on different combinations of the measured end members, the residence time of boron in Mono Lake is estimated to be within the range of 5~80 ka.

The crystalline basement and Caledonian orogenic belt of East Greenland between 70 and 78° N are divided into five source regions on the basis of heavy mineral assemblages, mineral geochemistry, and isotopic age data from 42 modern moraine/outwash samples. The sand types generated by the five source regions can be recognized in the Mesozoic sedimentary rocks of Mid-Norway, and are named, from south to north, MN7 (Gåseland), MN4i (Milne Land–Renland), MN2ii (Hinks Land–Suess Land), MN2iii (Payer Land–Dronning Louise Land), and MN6 (Germania Land). These provide a framework for interpreting the provenance of Greenland–Norway rift sedimentary deposits. The provenance characteristics of Liverpool Land have also been defined, but whether this relatively small region merits a separate provenance status is unclear. Provenance links can be made by comparing the source region sand types with the composition of onshore and offshore sediments from previous studies. Triassic sandstones of the Nordland Ridge and the far south of the Møre Basin, along with Jurassic sandstones of the Heidrun Field in the Haltenbanken area, were derived from the MN4i source region. The provenance of Cretaceous sandstones in East Greenland can be linked to the MN2ii source region. The source of Turonian sandstones on Traill Ø can be pinpointed by zircon U–Pb ages to the Neoproterozoic Lyell Land Group of the Franz Josef Allochthon. Cretaceous sandstones in the Vøring and Møre basins were derived from the MN2iii and MN4i source regions. In addition, some of the Cenomanian–Campanian sedimentary rocks of East Greenland and Mid-Norway contain Permian–Cretaceous-aged zircon grains that are absent from the moraine/outwash samples. The most likely source of these zircon grains is the circum-Arctic region, implying the existence of a long-lived axial drainage system that entered the Greenland–Norway rift from the north.

The Eocene-Miocene successions recovered at DSDP sites on the Jan Mayen Ridge (NE Atlantic) and on the adjacent East Greenland margin provide a sedimentary record of the rifting and separation of the Jan Mayen Microcontinent from East Greenland. A combination of palynology, conventional heavy mineral analysis, single-grain major and trace element geochemistry and radiometric dating of amphibole and zircon has revealed a major change in sediment provenance took place at the Early/Late Oligocene boundary corresponding to a prominent seismic reflector termed JA. During the Eocene and Early Oligocene, lateral variations in provenance character indicate multiple, small-scale transport systems. Site 349 and Kap Brewster were predominantly supplied from magmatic sources (Kap Brewster having a stronger subalkaline signature compared with Site 349), whereas Site 346 received almost exclusively metasedimentary detritus. By contrast, Late Oligocene provenance characteristics are closely comparable at the two Jan Mayen sites, the most distinctive feature being the abundance of reworked Carboniferous, Jurassic, Cretaceous and Eocene palynomorphs. The Site 349 succession documents an evolution in the nature of the magmatic provenance component. Supply from evolved alkaline magmatic rocks, such as syenites, was important in the Middle Eocene and lower part of the Early Oligocene, but was superseded in the later Early Oligocene by mafic magmatic sources. In the latest Early Oligocene, the presence of evolved clinopyroxenes provides evidence for prolonged magmatic fractionation. Initial low degrees of partial melting led to generation of alkaline (syenitic) magmas. The extent of partial melting increased during the Early Oligocene, generating basaltic rocks with both subalkaline and alkaline compositions. Towards the end of the Early Oligocene, the amount of partial melting and magma supply rates decreased. In the Late Oligocene, there is no evidence for contemporaneous igneous activity, with scarce magmatic indicator minerals. The provenance change suggests that the hiatus at the Early/Late Oligocene boundary represents the initiation of the proto-Kolbeinsey Ridge and separation of the Jan Mayen Microcontinent from East Greenland.

The global circulation of the oceans and the atmosphere transports heat around the Earth. Broecker and Denton 1 suggested that changes in the global ocean circulation might have triggered or enhanced the glacial–interglacial cycles. But proxy data for past circulation taken from sediment cores in the South Atlantic Ocean have yielded conflicting interpretations of ocean circulation in glacial times—δ 13 C variations in benthic foraminifera 2 , 3 , 4 , 5 , 6 support the idea of a glacial weakening or shutdown of North Atlantic Deep Water production, whereas other proxies, such as Cd/Ca, Ba/Ca and 231 Pa/ 230 Th ratios, show little change from the Last Glacial Maximum to the Holocene epoch 7 , 8 , 9 . Here we report neodymium isotope ratios from the dispersed Fe–Mn oxide component of two southeast Atlantic sediment cores. Both cores show variations that tend towards North Atlantic signatures during the warm marine isotope stages 1 and 3, whereas for the full glacial stages 2 and 4 they are closer to Pacific Ocean signatures. We conclude that the export of North Atlantic Deep Water to the Southern Ocean has resembled present-day conditions during the warm climate intervals, but was reduced during the cold stages. An increase in biological productivity may explain the various proxy data during the times of reduced North Atlantic Deep Water export.

Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 173.The ocean's meridional overturning circulation (MOC) is a key factor in climate change. The Atlantic MOC, in particular, is believed to play an active role in the regional and global climate variability. It is associated with the recent debate on rapid climate change, the Atlantic Multi-Decadal Oscillation (AMO), global warming, and Atlantic hurricanes. This is the first book to deal with all aspects of the ocean's large-scale meridional overturning circulation, and is a coherent presentation, from a mechanistic point of view, of our current understanding of paleo, present-day, and future variability and change. It presents the current state of the science by bringing together the world's leading experts in physical, chemical, and biological oceanography, marine geology, geochemistry, paleoceanography, and climate modeling. A mix of overview and research papers makes this volume suitable not only for experts in the field, but also for students and anyone interested in climate change and the oceans.