The worlds’ oceans play a key role in the earth climate system. Oceans take up large amounts of atmospheric CO2 through physical and biological processes, and thereby buffer climate change. The supply of macro-nutrients, including phosphorus, nitrogen and silicic acid controls the productivity of phytoplankton in the ocean and consequently the ocean CO2 uptake by biological processes. In recent years it has become clear that a low supply of iron can limit productivity in about 40% of the worlds’ oceans. Furthermore, important roles in controlling ocean productivity for cobalt, manganese and zinc have recently been demonstrated. These trace elements are essential for phytoplankton in various biochemical roles and thus serve as micronutrients.
The International GEOTRACES was initiated in the mid 2000s and has as aim to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes (TEIs) in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions.
As part of GEOTRACES a host of research cruises has been conducted in ocean basins along zonal sections to determine in detail the distributions, sources and sinks of TEIs in the water column. Our team has been leading a range of GEOTRACES activities, where we combine the use of TEIs as tracers for flux processes (e.g. helium isotopes for hydrothermal inputs, aluminium for atmospheric inputs, manganese and radium isotopes for benthic supply) to investigate the biogeochemical cycling of TEIs, and their interactions with surface ocean productivity and the carbon and nitrogen cycles (incl. diazotrophy). This presentation will report on our findings in the worlds’ oceans, with a focus on the Pacific Ocean, and highlight the critical roles of TEIs in the present and future oceans. The role of scavenging and release of trace elements by particles in the ocean will be highlighted using trace element additions and removal along large scale water mass transport routes. In addition, the role of TEI additions along ocean boundaries (rivers, atomosphere, shelf sediments, hydrothermal vents) will be assessed in a mechanistic and quantitative manner.

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