Welcome to GEOTRACES
GEOTRACES is an international programme which aims to improve the understanding of biogeochemical cycles and large-scale distribution of trace elements and their isotopes in the marine environment. Scientists from approximately 35 nations have been involved in the programme, which is designed to study all major ocean basins over the next decade.
GEOTRACES Sections. For more information please click here. In red: Planned Sections. In yellow: Completed Sections. In black: Sections completed as GEOTRACES contribution to the IPY. Download the map.
Overview of the dissolved iron, manganese and aluminium distributions along the North Atlantic GEOTRACES GA03 section
- Published on Monday, 22 September 2014 09:45
Three trace elements distributions (iron, manganese and aluminium) help to constrain the sources of chemical elements in the North Atlantic Ocean. Atmospheric, Mediterranean Sea and margin inputs are confirmed while the importance of the hydrothermal venting is revealed.
Hatta, Measures and co-workers (2014, see references below) established an overview of dissolved iron, manganese and aluminium (dFe, dMn and dAl respectively) distributions (see figures below) along the North Atlantic GA03 GEOTRACES section. Elevated dFe concentrations correlate with elevated dAl ones in the surface waters of the subtropical gyre, confirming a substantial atmospheric source for both tracers. But this is not the case for dMn. Sedimentary inputs from margins concern the three tracers but are mostly revealed from elevated dMn signals in the eastern basin, particularly near the African coast and in the western basin, along the advective flow path of the Upper Labrador Sea Water.
The most striking results are found in the neutrally buoyant hydrothermal plume sampled over the Mid-Atlantic Ridge. There the largest dFe anomaly (~68 nM), a dMn anomaly (up to ~33 nM) and large amount of Al (up to 40nM) are detected, with signals visible for ~500 km to the west of the ridge.
Figure. Distribution of dissolved iron (upper), aluminiun (middle) and manganese (lower) along the North Atlantic GA03 GEOTRACES section. Warm colours (red, orange, etc.) indicate high concentrations. Click here to view the figure larger.
Organic copper complexation may stabilise seawater stable copper isotopic composition
- Published on Monday, 22 September 2014 10:52
Three deep-sea profiles were produced for the analysis of copper (Cu) concentration, along a transect covering very different biogeochemical regions: the oligotrophic North Tasman Sea (30ºS), the Tasman Front (40°S) and the productive waters of the Southern Ocean in the south (46°S).
Despite these differences, the Cu isotope composition of all three profiles was relatively homogenous. This homogeneity is attributed to the fact that more than 99% of the Cu is organically complexed, measured as part of the same study (Thompson et al, 2014; see references below). It is therefore argued that organic complexation stabilises heavy values of seawater stable copper isotopic composition (δ65Cu).
The authors also propose that decomposition of organic Cu complexes in environments such as anoxic basins may provide an isotopically heavy source of Cu for further scavenging and/or removal to the sediments. Such mechanism would help to balance the oceanic budget of δ65Cu, discussed in Little et al, 2014 (see reference below, and GEOTRACES science highlight).
Figure: Three dissolved copper concentration profiles versus depth (left panel) along with the isotope composition for dissolved copper (right panel). Samples were collected from three stations (P1, P2 and P3) occupied in the Tasman Sea region.
Field data allow constraining total mercury budget
- Published on Monday, 08 September 2014 10:11
Thanks to recent measurements during several oceanographic expeditions, among them GEOTRACES cruises, estimates of the total amount and spatial distribution of anthropogenic mercury in the global ocean were substantially improved.
Global budgets of total mercury suggest that there has been a tripling of the surface water mercury content and a ~150% increase in the amount of mercury in thermocline waters.
This study has been recently published in Nature Journal (1).
Figure: GEOTRACES researchers led by Carl Lamborg found that antropogenic mercury (primarily atmospheric emissions produced by coal burning and cement production, as well as gold mining) have caused ocean waters down to 100 meters depth being enriched in the toxic element up to 3.5 times the background level resulting from the natural breakdown, or weathering, of rocks on land. Once in the ocean, mercury adheres to organic particles and sinks or is consumed by progressively larger marine animals. One result is that intermediate levels of the ocean (between 100 and 1,000 meters depth) are also enriched in mercury up to 2.5 times the natural background rate. Even the deepest parts of the ocean have not escaped unscathed. Researchers found signs of pollution-derived mercury in the North Atlantic at depths below 1,000 meters, but those levels decreased as sampling efforts moved away from the North Atlantic basin. This is likely because pollution mercury has not yet moved with deep ocean currents throughout the global ocean, a process that can take as long as 1,000 years (extracted from WHOI's press release). Artwork: Jack Cook, WHOI. Click here to view the figure larger.
A new model of the oceanic aluminium distribution
- Published on Tuesday, 26 August 2014 14:23
Taking into account most of the parameters that govern any trace element's oceanic behaviour is a challenge, given their number and complexity.
Marco van Hulten and co-workers (2014, see reference below) propose here the most complete model ever written for the oceanic aluminium (Al) distribution. In addition to atmospheric input -which was the only term constraining the Al distribution in a preceding model, see van Hulten et al., 2013-, circulation, sediment re-suspension and biological incorporation by diatoms are considered in this new scheme.
These new sources and sinks are significantly improving the simulated distribution, more specifically a sediment source of Al in the bottom waters of the Northern Atlantic and the velocity fields.
Figure: The dissolved aluminium concentration (nM) of a global model simulation of aluminium. The circles are the observations. The sources in the model comprise the release of Al from dust and from resuspended deep-ocean sediments, the latter depending on the bottom Si concentration. Al is removed by reversible scavenging by biogenic silica. (This figure may be reused, changed and redistributed according to Creative Commons BY-SA. Click here to view the figure larger.)
- GEOTRACES recommends reading...
- Impact of volcanic ash on marine algae and the global carbon cycle
- A geochemical-physical coupled approach to study phytoplankton plume dynamics off the Crozet Islands (Southern Ocean)
- The distribution of dissolved iron in the West Atlantic Ocean
- Successful completion of French GEOVIDE cruise in the North Atlantic Ocean