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The bottom water conditions in the Central South Pacific (CSP) and associated changes in the Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW) under warmer-than-present conditions need to be better understood. These water masses transfer their properties to the major ocean basins. We analyzed Late Miocene to Early Pliocene (5.6–3.6 Ma) marine sediment core sections from the CSP for benthic foraminifera, ice rafted debris (IRD), Ostracoda, planktic foraminifera Orbulina universa abundance, and organic geochemical proxies to assess the bottom water characteristics under warmer-than-present day conditions. A significant increase in IRD abundance between 5.3 and 4.9 Ma marks the Early Pliocene warm phase. The benthic foraminiferal assemblages indicate shifts in bottom water conditions over time in the CSP region. Between 5.6 and 5.3 Ma, predominantly oxygenated bottom water with moderate organic matter flux prevailed. This shifted to suboxic conditions with increased organic matter flux from 5.3 to 4.9 Ma. Subsequently, between 4.9 and 4.4 Ma, bottom water conditions alternated frequently between oxic and suboxic states. Enhanced bottom water formation and inflow of LCDW and AABW in the CSP during 4.4–4.0 Ma promoted oxygenated conditions, accompanied by low organic export flux. However, sluggish bottom water circulation from 4.0 to 3.6 Ma reverted to suboxic conditions, associated with increased carbon burial. Notably, productivity peaked intermittently between 5.3 and 3.6 Ma, as indicated by the occurrence of suboxic species assemblages and increase in the abundance of Orbulina universa, benthic microfauna (ostracods), and other paleoproductivity indicators.

The Antarctic Circumpolar Current (ACC) represents the world’s largest ocean-current system and affects global ocean circulation, climate and Antarctic ice-sheet stability1–3. Today, ACC dynamics are controlled by atmospheric forcing, oceanic density gradients and eddy activity4. Whereas palaeoceanographic reconstructions exhibit regional heterogeneity in ACC position and strength over Pleistocene glacial–interglacial cycles5–8, the long-term evolution of the ACC is poorly known. Here we document changes in ACC strength from sediment cores in the Pacific Southern Ocean. We find no linear long-term trend in ACC flow since 5.3 million years ago (Ma), in contrast to global cooling9 and increasing global ice volume10. Instead, we observe a reversal on a million-year timescale, from increasing ACC strength during Pliocene global cooling to a subsequent decrease with further Early Pleistocene cooling. This shift in the ACC regime coincided with a Southern Ocean reconfiguration that altered the sensitivity of the ACC to atmospheric and oceanic forcings11–13. We find ACC strength changes to be closely linked to 400,000-year eccentricity cycles, probably originating from modulation of precessional changes in the South Pacific jet stream linked to tropical Pacific temperature variability14. A persistent link between weaker ACC flow, equatorward-shifted opal deposition and reduced atmospheric CO2 during glacial periods first emerged during the Mid-Pleistocene Transition (MPT). The strongest ACC flow occurred during warmer-than-present intervals of the Plio-Pleistocene, providing evidence of potentially increasing ACC flow with future climate warming.

One of Earth’s most fundamental climate shifts – the greenhouse-icehouse transition 34 Ma ago – initiated Antarctic ice-sheet build-up, influencing global climate until today. However, the extent of the ice sheet during the Early Oligocene Glacial Maximum (~33.7–33.2 Ma) that immediately followed this transition, a critical knowledge gap for assessing feedbacks between permanently glaciated areas and early Cenozoic global climate reorganization, is uncertain. Here, we present shallow-marine drilling data constraining earliest Oligocene environmental conditions on West Antarctica’s Pacific margin – a key region for understanding Antarctic ice sheet-evolution. These data indicate a cool-temperate environment, with mild ocean and air temperatures preventing West Antarctic Ice Sheet formation. Climate-ice sheet modeling corroborates a highly asymmetric Antarctic ice sheet, thereby revealing its differential regional response to past and future climatic change.

One of Earth’s most fundamental climate shifts – the greenhouse-icehouse transition 34 Ma ago – initiated Antarctic ice-sheet build-up, influencing global climate until today. However, the extent of the ice sheet during the Early Oligocene Glacial Maximum (~33.7–33.2 Ma) that immediately followed this transition, a critical knowledge gap for assessing feedbacks between permanently glaciated areas and early Cenozoic global climate reorganization, is uncertain. Here, we present shallow-marine drilling data constraining earliest Oligocene environmental conditions on West Antarctica’s Pacific margin – a key region for understanding Antarctic ice sheet-evolution. These data indicate a cool-temperate environment, with mild ocean and air temperatures preventing West Antarctic Ice Sheet formation. Climate-ice sheet modeling corroborates a highly asymmetric Antarctic ice sheet, thereby revealing its differential regional response to past and future climatic change.

One of Earth’s most fundamental climate shifts, the greenhouse-icehouse transition 34 million years ago, initiated Antarctic ice sheet buildup, influencing global climate until today. However, the extent of the ice sheet during the Early Oligocene Glacial Maximum (~33.7 to 33.2 million years ago) that immediately followed this transition—a critical knowledge gap for assessing feedbacks between permanently glaciated areas and early Cenozoic global climate reorganization—is uncertain. In this work, we present shallow-marine drilling data constraining earliest Oligocene environmental conditions on West Antarctica’s Pacific margin—a key region for understanding Antarctic ice sheet evolution. These data indicate a cool-temperate environment with mild ocean and air temperatures that prevented West Antarctic Ice Sheet formation. Climate–ice sheet modeling corroborates a highly asymmetric Antarctic ice sheet, thereby revealing its differential regional response to past and future climatic change. Editor’s summary Earth’s climate underwent a dramatic transition around 34 million years ago, when the Antarctic Ice Sheet first began to form, but the regional evolution of that ice sheet remains poorly defined. Klages et al . present data from marine sediments near West Antarctica showing that conditions there during the beginning of the Oligocene were mild and unfavorable to the growth of a permanent ice sheet. Model results based on those data suggest that the ice sheet in West Antarctica did not begin to form until 7 or 8 million years after the process began in East Antarctica.

The Antarctic Circumpolar Current (ACC), the world’s strongest zonal current system, connects all three major ocean basins of the global ocean and therefore integrates and responds to global climate variability. Its flow is largely driven by strong westerly winds and is constricted to its narrowest extent in the Drake Passage. Fresh and cold Pacific surface and intermediate water flowing through the Drake Passage (cold-water route) and warm Indian Ocean water masses flowing through the Agulhas region (warm-water route) are critical for the South Atlantic contribution to Meridional Overturning Circulation changes. Furthermore, physical and biological processes associated with the ACC affect the strength of the ocean carbon pump and therefore are critical to feedbacks linking atmospheric CO2 concentrations, ocean circulation, and climate/cryosphere on a global scale. In contrast to the Atlantic and Indian sectors of the ACC, and with the exception of drill cores from the Antarctic continental margin and off New Zealand, there are no deep-sea drilling paleoceanographic records from the Pacific sector of the ACC. To advance our understanding of Miocene to Holocene atmosphere-ocean-cryosphere dynamics in the Pacific and their implications for regional and global climate and atmospheric CO2, International Ocean Discovery Program Expedition 383 recovered sedimentary sequences at (1) three sites in the central South Pacific (CSP) (U1539, U1540, and U1541), (2) two sites at the Chilean margin (U1542 and U1544), and (3) one site from the pelagic eastern South Pacific (U1543) close to the entrance to the Drake Passage. Because of persistently stormy conditions and the resulting bad weather avoidance, we were not successful in recovering the originally planned Proposed Site CSP-3A in the Polar Frontal Zone of the CSP. The drilled sediments at Sites U1541 and U1543 reach back to the late Miocene, and those at Site U1540 reach back to the early Pliocene. High sedimentation rate s

Semiautomated methods for microscopic image acquisition, image analysis, and taxonomic identification have repeatedly received attention in diatom analysis. Less well studied is the question whether and how such methods might prove useful for clarifying the delimitation of species that are difficult to separate for human taxonomists. To try to answer this question, three very similar Fragilariopsis species endemic to the Southern Ocean were targeted in this study: F. obliquecostata, F. ritscheri, and F. sublinearis. A set of 501 extended focus depth specimen images were obtained using a standardized, semiautomated microscopic procedure. Twelve diatomists independently identified these specimen images in order to reconcile taxonomic opinions and agree upon a taxonomic gold standard. Using image analyses, we then extracted morphometric features representing taxonomic characters of the target taxa. The discriminating ability of individual morphometric features was tested visually and statistically, and multivariate classification experiments were performed to test the agreement of the quantitatively defined taxa assignments with expert consensus opinion. Beyond an updated differential diagnosis of the studied taxa, our study also shows that automated imaging and image analysis procedures for diatoms are coming close to reaching a broad applicability for routine use.

A multibarrel seabed drill rig was used for the first time to drill unconsolidated sediments and consolidated sedimentary rocks from an Antarctic shelf with core recoveries between 7% and 76%. We deployed the MARUM-MeBo70 drill device at nine drill sites in the Amundsen Sea Embayment. Three sites were located on the inner shelf of Pine Island Bay from which soft sediments, presumably deposited at high sedimentation rates in isolated small basins, were recovered from drill depths of up to 36 m below seafloor. Six sites were located on the middle shelf of the eastern and western embayment. Drilling at five of these sites recovered consolidated sediments and sedimentary rocks from dipping strata spanning ages from Cretaceous to Miocene. This report describes the initial coring results, the challenges posed by drifting icebergs and sea ice, and technical issues related to deployment of the MeBo70. We also present recommendations for similar future drilling campaigns on polar continental shelves.

Precisely dated Antarctic continental margin and Southern Ocean geological records show that the early Pleistocene interglacial Marine Isotope Stage 31 (MIS-31) was characterized by warmer than present surface waters with reduced sea-ice and enhanced high latitude marine carbonate production. Micropaleontologic, isotopic, and paleomagnetic evidence from drill cores at 77°S (Cape Roberts Project-1) and 53°S (ODP Site 1094) indicate circumantarctic changes in sea surface temperature and water mass stratification that are in phase with high southern latitude insolation changes during MIS-31. These changes imply a significant, though as yet unquantifiable reduction in Antarctic ice volume. This study supports the hypothesis that the interhemispheric antiphased relationship of the precession cycle attenuates a potentially significant Antarctic ice volume signal in the deep sea oxygen isotope record. The implications are that Antarctic marine ice sheets may be more susceptible to warming and high insolation driven retreat than has been widely recognized.

Alternative production methods compatible with the environment and selective winning are discussed, especially selective surface blasting of dolomite, vertical ripping with hydraulic excavators and a new limestone quarry in the north Eifel., Alternative production methods compatible with the environment and selective winning are discussed, especially selective surface blasting of dolomite, vertical ripping with hydraulic excavators and a new limestone quarry in the north Eifel.

In the last decades it has become apparent that climatic change is greatly influenced by changes in the global ocean circulation. One of the most important current systems is the thermohalinc circulation of the Atlantic Ocean, responsible for the interhemispheric heat exchange. This current system transports cold, higher saline deep water from the northern Atlantic Ocean to the southern hemisphere and in return warmer waters of the South Atlantic Ocean to the north, positively influencing the northern continental climate. To understand the fluctuations in the heat transport thraugh glacial/interglacial cycles in the Late Quaternary, it is necessary to study several key areas. One of such areas is the south-eastern South Atlantic Ocean, where warmer Indian Ocean (sub)surface water is carried around the cape of South Africa via the Agulhas Current into the Atlantic Ocean.

In the last decades it has become apparent that climatic change is greatly influenced by changes in the global ocean circulation. One of the most important current systems is the thermohalinc circulation of the Atlantic Ocean, responsible for the interhemispheric heat exchange. This current system transports cold, higher saline deep water from the northern Atlantic Ocean to the southern hemisphere and in return warmer waters of the South Atlantic Ocean to the north, positively influencing the northern continental climate. To understand the fluctuations in the heat transport thraugh glacial/interglacial cycles in the Late Quaternary, it is necessary to study several key areas. One of such areas is the south-eastern South Atlantic Ocean, where warmer Indian Ocean (sub)surface water is carried around the cape of South Africa via the Agulhas Current into the Atlantic Ocean.

In the last decades it has become apparent that climatic change is greatly influenced by changes in the global ocean circulation. One of the most important current systems is the thermohalinc circulation of the Atlantic Ocean, responsible for the interhemispheric heat exchange. This current system transports cold, higher saline deep water from the northern Atlantic Ocean to the southern hemisphere and in return warmer waters of the South Atlantic Ocean to the north, positively influencing the northern continental climate. To understand the fluctuations in the heat transport thraugh glacial/interglacial cycles in the Late Quaternary, it is necessary to study several key areas. One of such areas is the south-eastern South Atlantic Ocean, where warmer Indian Ocean (sub)surface water is carried around the cape of South Africa via the Agulhas Current into the Atlantic Ocean.

In the last decades it has become apparent that climatic change is greatly influenced by changes in the global ocean circulation. One of the most important current systems is the thermohalinc circulation of the Atlantic Ocean, responsible for the interhemispheric heat exchange. This current system transports cold, higher saline deep water from the northern Atlantic Ocean to the southern hemisphere and in return warmer waters of the South Atlantic Ocean to the north, positively influencing the northern continental climate. To understand the fluctuations in the heat transport thraugh glacial/interglacial cycles in the Late Quaternary, it is necessary to study several key areas. One of such areas is the south-eastern South Atlantic Ocean, where warmer Indian Ocean (sub)surface water is carried around the cape of South Africa via the Agulhas Current into the Atlantic Ocean.