Glacial to Holocene atmosphere-ocean interactions between high and low latitudes
F. Lamy, H. Fischer, M. Schulz, R. Tiedemann
A. Abelmann, T. Bickert, L. Dupont, R. Gersonde, J. Groeneveld, U. Merkel, S. Mulitza, A. Paul, M. Prange, J.-B. Stuut, A. Wegner
OC3 investigates atmosphere-ocean interactions between the high and low latitudes in controlling global climate variability on orbital, millennial, and up to decadal time scales focusing on the climate variability during the Holocene, the last glacial termination and the later part of the last glacial. This work is primarily based on new material and data, which were recently collected during expeditions with RV Polarstern (ANT-XXVI/2) and RV Sonne (SO-213) to the Pacific Sector of the Southern Ocean (Fig. 1) and with RV Sonne (SO-202) to the subpolar North Pacific and the Bering Sea (Fig. 2).
Both the North and South Pacific research cruises were extremely successful with core recoveries of more than 2300 m in total. Among these sediment records a number of sediment cores provide very high sedimentation rates suitable for analyzing orbital and sub-orbital scale variability in the high latitude Pacific Ocean. Two PhD projects within Marum OC3 work on this new sediment material. The first project concerns the mapping of the development of sea surface temperature, sea ice and productivity regimes around the last glacial/interglacial transition (past 30- 40 kyr) in the Pacific Southern Ocean using diatom assemblages. The study will generate data to decipher the response of the Pacific SO to the deposition of glacial dust, Southern Ocean basin-basin contrast, high-low latitude tele-connections in the Pacific and the relationship between Pacific SO and Antarctic ice core climate records. In the second project, laminated sediment sequences from the Bering Sea are investigated to provide insight in polar North Pacific climate evolution during the past glacial/interglacial transition at seasonal-decadal time resolution (Fig. 3). The multi-proxy approach generates data on the timing and the mechanisms of the establishment of an oxygen minimum zone in the Bering Sea. The comparison with Greenland ice core records will enhance the understanding of climate transfer mechanisms in northern high-latitudes.
Further support for OC3 comes from two Cluster of Excellence projects now integrated in OC3, which provide information on tropical thermocline variability and dust records from ice-cores. The “Impact of Atlantic meridional overturning circulation on thermocline dynamics” sub-project builds on the hypothesis that changes in the strength of Atlantic Meridional Overturning Circulation (AMOC) can trigger changes in tropical thermocline depth as suggested by theoretical considerations and coupled climate models. The relevance of this mechanism is evaluated by combining proxy data and model results. “The role of mineral dust in abrupt climate changes” sub-project deals with improving our understanding of the high resolution variability of dust input to the Greenland ice sheet at selected time slices that are analysed in sub-annual resolution. Several ice core sections from the NGRIP ice core (75.1°N 42.3°W) are available for this study. The NGRIP ice core is layer counted until 60 kyr B.P. and therewith best applicable for high-resolution studies. The ice core analyses are flanked by comprehensive coupled climate model simulations.
Figure 1: Location of sediment cores recovered during expeditions ANT-XXVI/2 and SO213 in the Pacific Southern Ocean and selected cores from the Atlantic and Indian Southern Ocean sectors studied in the frame of the OC3 Project (stars indicate ODP 177 sites).
Figure 2: Location of sediment cores recovered during SO202 expedition to the North Pacific and Bering Sea. Cores from Bering Sea sites are in the focus of OC3 studies.
Figure 3: Example of laminated sediment section recovered at the northern Bering Sea Slope (SO202-18-3) from the last glacial/interglacial transition. Core photography compared with computer tomography of sediment section. Light layers represent laminae with high biogenic opal (diatom) content.
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