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Project OC2

Land-ocean interaction and climate variability in low latitudes

E. Schefuß, M. Prange, M. Mohtadi, K. Zonneveld, L. Dupont
K.-H. Baumann, T. Bickert, J. Burrows, S. Kasemann, H. Kuhnert, S. Mulitza, J. Pätzold, U. Röhl

Combined paleoenvironmental and climate-model studies covering the late Holocene, the late Quaternary and the late Neogene provide insights into the interactions of land-ocean processes and into climate feedback mechanisms affecting low latitude areas.

Xie and Arkin
Areas for field work and sediment core sampling (red). Blue shades indicate high annual rainfall.

Latitudinal and longitudinal gradients in ocean hydrography are considered major drivers of climate over adjacent land masses, in particular, the intensity and position of the tropical rainbelt. Our study areas along the East African coast and in the Indonesian Throughflow region frame much of the Indian Ocean, allowing the reconstruction of the temporal and spatial evolution of its hydrography and interaction with regional and global climate. Samples from the South American continental margin, the Amazon and its tributaries provide unparalleled information on the synchronicity of changes in continental rainfall distribution with changes in the Atlantic Meridional Overturning Circulation.

The study of proxy records using high-resolution marine terrestrial archives  is flanked by numerical climate modeling with dynamic vegetation and water isotopes to test hypotheses on the oceanic control of tropical rain-belt variability derived from previous work.

Key Hypotheses

  • Basin-wide changes in SST gradients control meridional and zonal shifts of the tropical rain belt on centennial to millennial timescales, and reductions in the strength of the AMOC affect the tropical rain belt synchronously at a global scale.
  • SST control on tropical hydrology is independent of glacial or interglacial boundary conditions.
  • Anthropogenic changes in regional hydrology through land use (e.g. deforestation) have surpassed natural variability during the Holocene.
  • Cryosphere expansion during the Neogene is as important as changes in orography for the evolution of the tropical rain belt.

Specific Methods

  • Compound-specific isotope analyses on sedimentary plant lipids combined with numerical climate models, including water isotopes to analyze changes in continental hydrology.
  • Non-traditional stable isotope (lithium, boron and calcium) analyses to trace erosion processes, eroded sources, and to quantify weathering conditions and anthropogenic land use.
  • Paired measurements of oxygen isotopes and Mg/Ca ratios on planktonic foraminifera to reconstruct seawater temperature and salinity.