Biogenic opal isotopes - new tool for evaluation of past nutrient cycling and hydrographic structure in the Pacific Southern Ocean in relation to climate and Antarctic cryosphere evolution

• Applicant: Dr. Edith Maier
• Subject Area: Atmospheric Science ; Palaeontology
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257126812

Atmospheric CO2 concentrations present a repetitive pattern of gradual decline and rapid increase during the past climate cycles, closely related to temperature and global ice volume history. It has been recognized that the Southern Ocean (SO) represents a key area governing past and present CO2 change. However, the sensitivity of this carbon modulator to climate-change induced reorganizations in wind patterns, ocean circulation, stratification, sea ice extent and biological production remains under debate. Data on past SO hydrography and productivity are mainly from the Atlantic sector. To obtain a more comprehensive picture of SO processes it remains to be tested to what extent Atlantic processes can be translated to the yet little studied Pacific sector. This sector is not only the largest part of the Southern Ocean, but it also represents the main drainage area of the marine-based West Antarctic Ice Sheet (WAIS). The proposed study aims to generate paleo-data sets from two sediment core transects across the Pacific SO using a newly-established method, which comprises combined oxygen and silicon isotope measurements of purified diatoms and radiolarians. The selected sediment intervals and sites will allow to describe for the first time the evolution in physical and nutrient properties at surface and subsurface water depth during different climate conditions, from colder than present (e.g. Last Glacial Maximum) to warmer than present (e.g. Marine Isotope Stage 5.5), and from different environmental settings in the eastern and western polar Pacific SO. The study will allow to test hypotheses concerning the SO´s role in the climate system by evaluation of (1) the sensitivity of the Pacific SO ecosystems to dust-borne micronutrient deposition (iron fertilization) and related Si-uptake rates, (2) the formation and extent of surface water stratification and (3) the 'silicic-acid leakage' hypothesis, postulating high-low latitude nutrient exchange critical for understanding productivity and carbon sequestration in the ocean. The new proxies will also provide information on the timing of surface ocean salinity anomalies resulting from meltwater shedding to gain information on WAIS stability and to test the assumption of a total WAIS draw down during MIS 5.5. Obtained paleo-records will be compared with simulations with an atmosphere-ocean general circulation model combined with a biogeochemical model including Si isotopes from an ongoing SPP1158-DFG project (CAU Kiel, PI B. Schneider). This should allow for better separation and statistically supported analysis of the individual impacts of ocean circulation and biological production on the air-sea CO2 exchange. Basic information on dust and biogenic deposition rates, physical ocean parameters (e.g. sea ice, sea surface temperature) and the generation of appropriate age models will be available in close cooperation with ongoing research in the frame of other national and international projects.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1158: Infrastructure area - Antarctic Research with Comparative Investigations in Arctic Sea Ice Areas
• Participating Persons: Dr. Andrea Abelmann; Dr. Rainer Gersonde; Professorin Dr. Birgit Schneider