Mapping Si and N Isotopes in Southern Ocean Surface Waters in Relation to Fe and Nutrient Concentrations and Diatom Valve Morphology

• Applicants: Dr. Peter Leslie Croot; Dr. Christina de la Rocha
• Subject Area: Oceanography
• Term: from 2007 to 2009
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 44315390

The silicon (Si) and nitrogen (N) stable isotopic composition of diatoms are the two main proxies for reconstructing patterns of nutrient utilization in past Southern Ocean surface waters, interesting because the growth of Southern Ocean phytoplankton influences atmospheric carbon dioxide levels and thus global climate. We will produce the first dataset on the isotopic composition of dissolved Si and N in surface waters. We will sample along a transect from Punta Arenas (Chile) to Neumayer Station (Antarctica), east to the Kerguelen Plateau, and then up to Cape Town (South Africa). We will also measure dissolved iron, nutrient, and chlorophyll concentrations and the size of the diatom, Fragilariopsis kerguelensis. These data will improve our understanding of the nutrient use proxies by revealing the spatial scale over which variations in the isotopic composition of nutrients occur and how isotopic variations relate to environmental factors such as the iron limitation of phytoplankton growth. Observed changes in diatom morphology will aid development of a new proxy, one potentially for iron availability or productivity regime.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1158: Infrastructure area - Antarctic Research with Comparative Investigations in Arctic Sea Ice Areas
• Participating Person: Dr. Rainer Gersonde