SUBPROJECT - A6
Influence of centennial to millennial scale climate change on low-latitude oxygen minimum conditions
The reconstruction of the factors controlling the intensity and the spatial extent of the oxygen minimum zone (OMZ) off Peru since the last glacial maximum 20,000 years ago will remain the focus of the investigations in A6. Particular emphasis will be dedicated to a quantitative reconstruction of the lower boundaries and horizontal margins of the OMZ, i.e. the oxic to suboxic transitions. These transition zones have been most sensitive to past changes and will allow to study past analogues of potential future transitions from high to low oxygen areas and expansions into real OMZs. In combination with the previous findings obtained within SFB 754, information on past oxygen levels will be obtained by application of sedimentary stable Mo isotopes, a well-established geochemical tool to reconstruct past global, as well as local oxygen levels and redox conditions of bottom waters. This information will be combined with existing and new Fe isotope data of the solid phase as well as with the determination of accumulation rates of redox sensitive metals, such as Mo itself, as well as U, V, Cd, Mn, Fe, and others, which vary as a function of redox- potential and oxygenation levels of the sediment pore waters driven by external forcing, such as productivity and climate. Over the last decade, environmental changes appear to have driven the exceptionally productive Peruvian Upwelling ecosystem close to a tipping point and an expanding OMZ. As a consequence, more frequent alternations of anoxic vs. suboxic conditions, often causing sulfidic plumes in shelf waters occurred. A second part of the efforts in A6 will thus be devoted to reconstructing the occurrence of sulfidic events using redox sensitive metals at highest temporal resolution for selected time windows of periods with a strong OMZ. The investigations of A6 will provide a data basis for the modelling of the paleo-ocean circulation in the southeastern tropical Pacific in A1 but the modelling results of A1 will also be an integral part of the A6 synthesis, which will combine all available proxy data evidence and will lead to a coherent reconstruction of the strength and the spatial extent of the OMZ off Peru since the last glacial maximum.
References
Ehlert, C., P. Grasse, D. Gutiérrez, R. Salvatteci and M. Frank (2014) Nutrient utilisation and weathering inputs in the Peruvian upwelling region since the Little Ice Age. Clim. Past, doi: 10.5194/cp-11-187-2015
Ehlert, C., P. Grasse and M. Frank (2013) Changes in silicate utilisation and upwelling intensity off Peru since the Last Glacial Maximum – insights from silicon and neodymium isotopes. Quaternary Sci. Rev., 72, 18-35, doi: 10.1016/j.quascirev.2013.04.013
Ehlert, C., P. Grasse, E. Mollier-Vogel, T. Böschen, J. Franz, G.F. de Souza, B.C. Reynolds, L. Stramma and M. Frank (2012) Factors controlling the silicon isotope distribution in waters and surface sediments of the Peruvian coastal upwelling. Geochim. Cosmochim. Acta, 99, 128-145, doi: 10.1016/j.gca.2012.09.038
Grasse, P., C. Ehlert and M. Frank (2013) The influence of water mass mixing on the dissolved silicon isotope composition of the eastern Equatorial Pacific. Earth Planet. Sc. Lett., 380, 60-71, doi: 10.1016/j.epsl.2013.07.033
Leduc, G., C.T. Herbert, T. Blanz, P. Martinez and R.R. Schneider (2010) Contrasting evolution of sea surface temperature in the Benguela upwelling system under natural and anthropogenic climate forcings. Geophys. Res. Lett., 70, doi: 10.1029/2010GL044353
Mollier-Vogel, E., G. Leduc, T. Böschen, P. Martinez and R.R. Schneider (2013) Rainfall response to orbital and millennial forcing in northern Peru over the last 18 ka. Quarternary Sci. Rev., 76, 29-38, doi: 10.1016/j.quascirev.2013.06.021
Mollier-Vogel, E., E. Ryabenko, P. Martinez, D. Wallace, M.A. Altabet and R.R. Schneider (2012) Nitrogen isotope gradients off Peru and Ecuador related to upwelling, productivity, nutrient uptake and oxygen deficiency. Deep-Sea Res. Pt. I 70, 14-25, doi: 10.1016/j.dsr.2012.06.003
Reynolds, B.C., M. Frank and A.N. Halliday (2008) Evidence for a major change in silicon cycling in the subarctic North Pacific at 2.73 Ma. Paleoceanography 23, PA4219, doi: 10.1029/2007PA001563
Robinson, R.S., J. Etourneau, P. Martinez and R.R. Schneider (2014) Expansion of pelagic denitrification during early Pleistocene cooling. Earth Planet. Sc. Lett., 389, 52-61, doi: 10.1016/j.epsl.2013.12.022
Salvatteci, R., D. Gutierrez, A. Sifeddine, L. Ortlieb, E. Druffel, M. Boussafir and R. Schneider (2016) Centennial to millennial-scale changes in oxygenation and productivity in the Eastern Tropical South Pacific during the last 25,000 years. Quaternary Science Reviews, 131, 102-117
Scholz, F., J. McManus, A.C. Mix, C. Hensen and R.R. Schneider (2014) The impact of ocean deoxygenation on iron release from continental margin sediments. Nat. Geosci., doi: 10.1038/NGEO2162
Contact:
Prof. Ralph Schneider Prof. Martin Frank
Tel.: +49 431 880 1457 Tel.: +49 431 600 2218
schneider(a)gpi.uni-kiel.de mfrank(a)geomar.de
