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.
Sinking organic matter: a major driver of the oceanic zinc cycle?
- Published on Thursday, 17 April 2014 08:22
Zinc (Zn) is a marine micronutrient, important for phytoplankton and involved in biogeochemical cycling throughout the oceans. Despite the importance of this element, the processes that control the oceanic Zn cycle are still poorly understood. As with other trace elements, this lack of knowledge is being addressed by high-resolution sampling as part of the GEOTRACES program.
A new study by John and Conway, presenting the first high-resolution coupled profiles of both dissolved Zn and cadmium (Cd) concentration and isotope ratios from the GEOTRACES North Atlantic (GA03) section, suggests that scavenging of isotopically heavy Zn onto organic matter plays an important role in the surface marine cycling of Zn, and may be important for understanding why Zn, like silicon (Si), has a deeper regeneration in the oceans than nitrogen (N), phosphorus (P) and Cd. The new GEOTRACES data is supported by modeling and culture experiments, which show that whilst Cd and major nutrients are quickly released as phytoplankton degrade, a significant portion of the Zn is instead scavenged back onto organic matter.
Figure: Zn and Cd concentration and stable isotope profiles along the North Atlantic GA03 section.
Click here to view the figure larger.
New data on oceanic rare earth elements concentrations and neodymium isotopic compositions
- Published on Tuesday, 25 March 2014 09:24
Early 2014 was favourable to the publication of new data of rare earth elements (REE) concentrations and neodymium (Nd) isotopic compositions in extreme areas of the ocean: the Southern Atlantic, the North East Corner of the Pacific and the remote South Pacific. Three works of three different groups (Garcia-Solsona et al.; Haley et al.; Molina-Kescher et al.), all published in Geochimica Cosmochimica Acta.
These three works confirm the conservativity of Nd isotopic composition far from main biogeochemical disturbances, as lithogenic inputs or significant biological activity. But more importantly, they reveal features in the behaviors of the REE that might need to be considered more closely. These features rely on particle/dissolved exchanges that are not understood yet but they also yield unexpected decoupling along the REE array... Read more to discover the fascinating world of REE and Nd isotopic composition!
When atmospheric dynamic controls the nutrient distributions in the ocean
- Published on Wednesday, 02 April 2014 09:55
Rainfall detection with satellites together with high-resolution data (~0.3°) for dissolved iron (DFe), aluminium (DAl), and inorganic phosphorus (DIP), confirm the existence of a sharp north–south biogeochemical boundary in the surface nutrient concentrations of the (sub)tropical Atlantic Ocean.
Wet deposition in the region of the intertropical convergence zone (ITCZ) acts as the major dissolved iron (DFe) source to surface waters. These variations of higher Fe inputs tied to the ITCZ movements drive a shift in the latitudinal distribution of N2 fixation and subsequent phosphate depletion in surface waters.
Thus, atmospheric dynamic is driving surface nutrient concentrations and microbial (diazotrophic) activity, which divide the (sub)tropical Atlantic into a high-phosphate, low-iron system in the south, and a low-phosphate, high-iron system in the north.
Figure: From the top to the bottom: Data from the AMT-17 (red) and D361 (green) cruises for satellite derived rainfall, surface DFe, surface DIP, and depth integrated N2 fixation (filled circles) and Trichodesmium spp. abundance (filled stars). Click here to view the figure larger.
First full depth profiles of zinc isotopes in the ocean, thanks to IPY/GEOTRACES cruise (GIPY5)
- Published on Wednesday, 02 April 2014 14:37
Three major and original features are deduced from the 3 first full depth profiles measured by Zhao and co-workers in the Southern Ocean:
- below 1000 m, the comparison of the results with North Atlantic and Pacific data reveals that the oceanic zinc (Zn) isotopic composition appears to be homogeneous (δ66Zn = +0.53 ± 0.14 per mil (2SE = 0.03, n = 21)).
- oceanic Zn isotopic composition is more variable in the upper 1000 m (δ66Zn values are more variable); these new Zn isotope data are consistent with a scenario whereby Zn removal from the surface ocean occurs via two processes: a dominant one that does not involve an isotopic fractionation (incorporation of Zn into organic matter associated with only diatom frustules, a type of phytoplankton) and a lesser one that preferentially removes the light isotope (metabolic uptake into the cells of all phytoplankton).
- a mass balance calculation is proposed to explain the homogeneous Zn isotopic composition of the deep ocean. δ66Zn value is slightly heavier that all the possible external sources (~+0,35 per mil). Thus, an isotopically light sink is required but not identified yet. The author's working hypothesis is that the burial of isotopically light Zn in cellular organic matter could represent the light sink from the oceanic dissolved pool.
Figure: Zinc (Zn) isotopic data for IPY GEOTRACES samples from the Southern Ocean (green), plotted with data from the same laboratory for the GEOTRACES BATS intercalibration site in the Atlantic (blue, Boyle et al., 2012) and for the SAFe sample at 1000m in the Pacific (red). There is variability in Zn isotopes at depths shallower than about 500m, and a sample from the sediment-water interface in one depth profile at 67°S is anomalous, but in between all seawater samples yet published have a mean δ66Zn of 0.53 per mil, with a spread of only 0.06 per mil (± 2 standard errors of the mean).
- Second GEOTRACES-India cruise in the Indian Ocean left port
- First results from platinum reference samples published
- The potential of anthropogenic 236-Uranium as a new and transient oceanographic tracer demonstrated in the North Atlantic
- GEOTRACES Taiwanese cruise is sailing in the Western Pacific
- Successful release of GEOTRACES Intermediate Data Product 2014