Maurice Ewing Bank – Georgia Basin Depth Transect: A Southern Ocean Perspective on Paleogene Climate Evolution (IODP 862-Pre)

Gabriele.Uenzelmann-Neben [ at ]


Twenty-first century atmospheric pCO2 concentrations will rise to levels that the Earth has not experienced for more than 30 Myr (>500 ppm). Geological records from the Paleogene (66 to 23 million years ago, Ma) provide the means to decipher the operation of the Earth System under high pCO2 conditions, but tackling this scientifically and societally important problem requires precise integration of climate datasets across latitudes and ocean basins. Currently we lack the continuous high- resolution archives from the southern high latitudes that we need to provide comprehensive information on (sub)polar climate evolution and test competing hypothesized mechanisms of Paleogene climate change, such as the influence of atmospheric pCO2 change versus the opening of Southern Ocean tectonic gateways to deep-water circulation. Here we present the new International Ocean Discovery Program (IODP) pre-proposal 862-Pre (SW Atlantic Paleogene Climate) designed to drill a depth transect of Paleogene sites in the subantarctic South Atlantic Ocean on the easternmost tip of the Falkland Plateau (Maurice Ewing Bank and Georgia Basin). In the modern ocean, this is a critical area for deep-water mixing and communication between the Pacific and Atlantic oceans across the Drake Passage, with local bathymetry controlling the dispersal and propagation of deep- and bottom-waters throughout the Atlantic. The plan is to recover a composite of Paleogene sections spanning an extensive range of paleo-water depths (~500-4500 m) to determine the timing and variability of shallow- and deep-water connectivity across the Drake Passage and to test whether the onset of a proto-Antarctic Circumpolar Current (ACC) circulation had a direct impact on high-latitude and global climate evolution. These drillcores will thus provide crucial insight on the long-standing question of the relative influence of atmospheric pCO2 drawdown vs. Southern Ocean gateways in driving Paleogene climate evolution. The target sites are also ideally positioned to assess the relationships between local tectonic subsidence of deep-water barriers, high-latitude climate change, and the onset of bottom-water production in the Weddell Sea and northward propagation into to the deep western Atlantic - a process that, along with ACC circulation, fundamentally altered Cenozoic circulation in the Atlantic. Multi-proxy datasets from expanded hemipelagic sections will shed new light on climate change, biotic shifts, and deep-sea chemistry during the Paleogene, allowing evaluation of: (i) the magnitude of temperature change and response of high-latitude plankton groups across transient 'greenhouse' events, (ii) the initiation of southern high latitude cooling and onset of Antarctic Peninsula glaciation during the middle Eocene - early Oligocene 'greenhouse' to 'icehouse' transition, and (iii) variation in the Calcite Compensation Depth in the South Atlantic and its relation to changes in global carbon cycling. Following the positive recommendation by the Science Evaluation Panel (SEP) for IODP 862-Pre two companion seismic reflection survey and piston coring operations in the eastern Falkland Plateau region of the subantarctic southwest Atlantic Ocean have been developed. One Site Survey Investigation (SSI) cruise led by Uenzelmann-Neben (AWI, Bremerhaven) and Westerhold (MARUM, Bremen) is proposed to survey the Maurice Ewing Bank extending southward across the Falkland Trough. The complementary SSI led by Bohaty (Univ. Southampton, UK) is proposed to survey the eastern half of the region across the Georgia Basin and Northeast Georgia Rise. The collaboration between German and UK groups will feasibly provide the extensive data coverage needed to survey the entire east–west transect of drillsites to meet the scientific objectives of 862-Pre. This transect is a fundamental requirement to allow reconstruction of deep-water properties across a range of palaeo-water depths and surface- water conditions across several modern frontal boundaries.

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Conference (Poster)
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IODP/ICDP Kolloquium, 02 Mar 2015 - 04 Mar 2015, Bonn, Germany.
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Westerhold, T. , Bohaty, S. M. and Uenzelmann-Neben, G. (2015): Maurice Ewing Bank – Georgia Basin Depth Transect: A Southern Ocean Perspective on Paleogene Climate Evolution (IODP 862-Pre) , IODP/ICDP Kolloquium, Bonn, Germany, 2 March 2015 - 4 March 2015 .

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