Paleobiogeochemistry of marine sediments

The sediments on the sea floor are natural archives of past climate and ocean variability. I propose to unravel the information preserved in these records by determining the contents of various organic remains and mineral and chemical properties, so- called proxies. The key to my novel contributions to paleo-oceanographic research is a multi-proxy approach, using a wide range of proxies, which enables my group to differentiate between local and global climate signals, and to establish phasing (i.e. causal) relationships between different components of the climate system. Research in my group has two primary long-term goals: to understand more fully the importance of the tropical Pacific Ocean in past global climate change, and to establish a thorough understanding of nitrogenisotope evidence for past changes in the oceanic nitrogen inventory. The equatorial Pacific is fundamental toEarth's climate system, and has been purported to be instigator, amplifier and mediator of past global climatechange on inter-annual to multi-millennial time-scales. For example, the El Niño Southern Oscillation (ENSO)dominates the inter-annual variability of the tropical Pacific today, with tele-connections affecting climateworldwide, and it has thus been proposed that past global climate change could have been modulated by"ENSO-like" variations in the mean state of the tropical Pacific. My cross-disciplinary research into thesystematics of nitrogen isotope evidence for past changes in the oceanic N cycling and inventory will shed light on the over-arching question whether or not biogeochemical changes, such as nitrate cycling are the primary cause for changes in the oceanic sequestration of atmospheric CO2 on multi-millennial time-scales. This kind of multi-proxy reconstruction of the full range of the spatial and temporal variability of the ocean and atmosphere and the interrelation between various components of Earth's climate system is required for validating current climate models and for establishing a 'background' state against which potential anthropogenic influences will have to be measured.