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Project OC3

High- and low-latitude atmosphere-ocean interactions

F. Lamy, T. Felis, R. Gersonde, A. Abelmann
H. Fischer, S. Kasemann, G. Lohmann, U. Merkel, G. Mollenhauer, M. Rutgers van der Loeff,
M. Schulz, R. Tiedemann

We provide new insights into dust-iron induced impacts on global climate and into high-low latitude climate links at orbital-to-interannual timescales, thereby helping to estimate the potential of geoengineering visions for mitigating future climate change and deciphering the operation of climate links at human generation timescales beyond the instrumental record.

Cruise Ant26-2
South Pacific locations of sediment cores recovered during R/V Polarstern Cruise Ant26-2 (Gersonde et al., 2011). Cores are located beneath the modern pathway of dust originating from Australia.

Atmosphere-ocean interactions at high latitudes are thought to play a key role in past atmospheric CO2 variability by controlling the sea-ice field, upper ocean physical parameters and stratification, nutrient utilization and biological export, deep-water exposure rates, and high-low latitude exchange of nutrients and heat. Low-latitude atmosphere-ocean interactions (e.g. ENSO) have severe impacts on global climate at society-relevant timescales, affecting the Asian monsoon and European winter climate (Kumar et al. 1999, Brönnimann et al. 2007). We study Pleistocene-Pliocene atmosphere-ocean processes in the mid- and highlatitude South Pacific using an exceptional set of new sediment cores. In addition, tropical-subtropical climate variability and teleconnections to high latitudes are quantified at monthly resolution for Holocene and last interglacial key intervals based on coral cores in combination with data from observational climatologies, ice-core records, and Earth system models.

Key Hypotheses

  • The long-term cooling since the mid-Pliocene (Martinez-Garcia et al. 2010) was caused by dust-iron induced changes in Southern Ocean productivity regimes, carbon export and burial.
  • Glacial dust deposition in the Southern Ocean is not restricted to the Atlantic sector as previously postulated (Maher et al. 2010) but also occurred in the South Pacific from Australian/New Zealand sources (as proposed by Thiede 1979) and thus could have enhanced the Southern Ocean role in regulating past atmospheric CO2 variability.
  • Westerly winds impact the upwelling of deep water masses in the Southern Ocean and control the return flow of intermediate waters to the tropics.
  • Extreme seasonal to interannual events and regime shifts (droughts, floods, cyclones) were characterized by frequencies, amplitudes and durations not observed in the short instrumental record, and were controlled by characteristic interactions between high (AO/NAO) and low latitude (ENSO) climate modes during different mean states.
Sampling positions
Locations where modern and fossil corals have been recovered for sub-seasonally resolved reconstructions of sea surface temperature and salinity variability throughout time intervals of the last centuries, the Holocene, the last deglaciation, the Last Glacial Maximum, and the Last Interglacial period. (Map: NASA)

Specific Methods

  • Quantification and localization of dust flux and sources based on sediment composition analyses, including 230Thexc flux, Nd determination and biomarkers (n-alkanes, BIT, MBT/CBT)
  • Estimation of past ocean physical (SST, sea ice, ventilation) and biological (paleoproductivity, nutrient utilization) variability based on foraminiferal (δ18O, δ13C) and opal isotopic composition (δ18O, δ30Si), alkenones, dioles, and diatom counts
  • Earth-system modeling, including simulations with an interactive mineral dust module
  • SST and salinity reconstructions at monthly resolutions from corals (Sr/Ca, U/Ca, δ18O), including physical mechanisms for proxy-based climate reconstructions (climate data analysis, Earth-system modeling).