Background

The development and application of trace-element "clean" techniques a quarter century ago revealed for the first time "oceanographically-consistent" distributions of many trace elements in the ocean

• Last major program of marine chemistry (GEOSECS) dates from the 1970s.
• Improved ability to sample the ocean without contamination
• Increased sensitivity of analytical instrumentation
• Thanks to advances in modeling: rates and fluxes derived from distributions

Objectives:

• To determine full water column distributions of selected Trace Elements and Isotopes (TEIs), including their concentration, chemical speciation, and physical form, along a sufficient number of sections in each ocean basin to establish the relationships between these distributions and more traditional hydrographic parameters; and
• To evaluate the sources, sinks, and internal cycling of these TEIs and thereby characterize more completely the physical, chemical and biological processes regulating their distributions, and their sensitivity to global change

Research fields:

Trace elements and isotopes (TEIs) play a major role in the following research fields:

• TEIs as micronutrients in ocean biogeochemistry and their role in relation to carbon cycle
• Tracers of present biogeochemical processes and circulation - mixing, inputs, transport and fate of pollutants
• Proxies to reconstruct past ocean conditions, and the ocean’s response to global change

GEOTRACES at AWI

GEOTRACES offers the framework to study a wide range of tracers in parallel. At AWI Geochemistry we concentrate on the study of natural radionuclides. These yield information on the rate of transport processes in the ocean. When measured along with other TEIs, we can derive the pathways and rates of transport and biogeochemical cycling of such trace elements using inverse modeling. An example is the study of the sources of iron in the Southern Ocean.

Pilot studies: Two Polarstern expeditions have been carried out with the aim to align the sampling and analytical procedures. During ANT XXIII/1 (Bremerhaven-Cape Town, Oct/Nov 2005) we studied the distribution of a wide range of TEI in surface waters of the eastern Atlantic under influence of upwelling and Sahara dust inputs. In cooperation with a range of geochemists from labs in Germany, France, England, Sweden, Monaco we tested clean techniques to sample large volume surface waters without contamination from the ship. During a subsequent expedition (Drake Passage, ANT XXIII/3, Jan/Feb 2006) we sampled radionuclides in parallel with rare earth elements and their isotopes in coordination with the LEGOS lab in Toulouse.

Expedition program: During the International Polar Year GEOTRACES studies have been carried out with Polarstern in the Arctic (2007) and Antarctic (2008). Our group has investigated the distribution of short-lived radionuclides (²³⁴Th, ²¹⁰Po, ²¹⁰Pb, ²²⁸Ra), again in coordination with studies of TEIs on Polarstern and on other ships.

In 2010 we have been involved in a METEOR expedition to the tropical Atlantic (M81/1) and RV PELAGIA expeditions (64PE319 and 64PE321) to the northwestern Atlantic to study the tracer field along the pathway of North Atlantic Deep Water.