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.
Impact of volcanic ash on marine algae and the global carbon cycle
- Published on Thursday, 24 July 2014 08:38
Volcanic ash fertilization of iron-limited phytoplankton in remote marine waters has been suggested to perturb global biogeochemical cycles and climate. For example, ash from the Pinatubo (Philippines) eruption in 1991 was suggested to have fertilized vast areas of the iron-limited Southern Ocean - potentially causing the drawdown in atmospheric carbon dioxide observed subsequently. However, until recently the impact of volcanic ash on phytoplankton communities in the Southern Ocean had never been directly tested.
Browning and co-authors conducted over 20 experiments in the South Atlantic and Southern Ocean where they added small quantities of volcanic ash to natural phytoplankton communities incubated in bottles. The responses they observed led to two important findings: (i) they conclusively demonstrated for the first time that volcanic ash deposition events strongly stimulated phytoplankton in the Southern Ocean; and (ii) at several experimental locations phytoplankton responded significantly to supply of volcanic ash, but not to iron only. This latter finding could be particularly important as it suggests phytoplankton at these sites may have been limited by another micronutrient other than iron. Manganese concentrations at these sites were amongst some of the lowest ever recorded in seawater and Browning and co-authors therefore suggested that the enhanced response to ash may have likely been a result of relieving manganese (co)limitation.
Both of these findings could both have important implications for our understanding of marine biogeochemistry in the Southern Ocean. Firstly, the Southern Atlantic and Drake Passage, where the experiments were conducted, are areas highly prone to ash deposition from explosive volcanic eruptions in South America - suggesting that ash-driven fertilization and potential carbon export from these waters could be an important control on the biogeochemistry of the region. Secondly, if manganese is (co)limiting marine algae in these waters, addition of this element alongside iron might be critical for stimulating phytoplankton blooms in the region.
Figure: Maps showing the sites where experiments were conducted, highlighting the nutrient concentrations measured in seawater (warmer colors represent higher nutrient concentrations) and the response of phytoplankton to iron and ash additions (warmer colors represent larger phytoplankton responses). For (d-e) sites where the phytoplankton response was statistically significant (relative to bottles where no treatment was made) are shown with black outlines. Please click here to view the figure larger.
A geochemical-physical coupled approach to study phytoplankton plume dynamics off the Crozet Islands (Southern Ocean)
- Published on Wednesday, 23 July 2014 12:06
Interaction of the currents with the sediments deposited on the margins of the Crozet Islands (Southern Ocean) contributes to the supply of iron and other micronutrients to marine waters. This natural fertilization feeds a phytoplankton bloom that was object of study of the KEOPS 2 GEOTRACES process study.
Sanial and co-authors (2014, see reference below) combined three independent methods - including geochemical and physical methods. This allowed them to assess the origin of the natural iron fertilization and the rates and times scale of the offshore transport in the phytoplankton bloom of Crozet. Shelf-water contact ages were determined using radium isotopes and were compared to in situ drifter data and modeling data based on altimetry.
This work highlights the key role played by the horizontal transport in the natural iron fertilization and provides constraints on the transit time of surface waters between the shelf and offshore waters.
Figure: Ages of surface waters derived from a Lagrangian model based on altimetry data. The drifter launched offshore Crozet Islands followed the numerical plume deduced from the model. White circles show the location of radium samples. Please click here to view the figure larger.
The distribution of dissolved iron in the West Atlantic Ocean
- Published on Wednesday, 09 July 2014 13:16
Iron (Fe) is an essential trace element for marine life. Extremely low Fe concentrations limit primary production and nitrogen fixation in large parts of the oceans and consequently influence ocean ecosystem functioning. In a publication published on 30 June in Plos ONE, Rijkenberg and co-authors present dissolved Fe (DFe) values measured at an unprecedented high intensity (1407 samples) along the longest full ocean depth transect (17500 kilometers) covering the entire western Atlantic Ocean.
DFe measurements along this transect revealed details about the supply and cycling of Fe. External sources of Fe identified included off-shelf and river supply, hydrothermal vents and aeolian dust. Nevertheless, vertical processes, such as the recycling of Fe resulting from the remineralization of sinking organic matter and the removal of Fe by scavenging, dominated the distribution of DFe. Iron recycling and lateral transport of DFe from the eastern tropical North Atlantic Oxygen Minimum Zone (OMZ) were important sources of DFe to the northern West Atlantic Ocean.
Finally, this study showed that the North Atlantic Deep Water (NADW), the major driver of the so-called oceanic conveyor belt, contains excess DFe relative to phosphate after full biological utilization and is therefore an important source of Fe for biological production in the global ocean.
Figure: The distribution of DFe along the 17500 km long full depth transect in the western Atlantic Ocean. Click here to view the figure larger.
Successful completion of French GEOVIDE cruise in the North Atlantic Ocean
- Published on Tuesday, 08 July 2014 20:28
The GEOVIDE cruise (GA01) has been successfully completed on 30 June, after 47 days of sailing in the North Atlantic from Lisbon (Portugal) to St John's (Newfoundland, Canada).
The North Atlantic is a key region for Earth climate and oceanic circulation, being a major area of the Merdional Overturning Circulation (MOC), which characteristics and variability have been studied since 2002 in the framework of the OVIDE project. Moreover, the Trace Element and Isotope (TEI) cycles are largely unknown in this zone and present very contrasted sources.
GEOVIDE is an international collaborative project that aims to better constrain (i) the uncertainties on water and heat fluxes, notably by adding new tracers and information on export and circulation of deep waters, and (ii) the biogeochemical fluxes and processes.
Forty scientists from 15 laboratories from 7 different countries successfully occupied 78 stations, with a total of 163 classical rosette casts and 53 clean rosette ones. In-situ pumps were deployed 25 times, representing more than 140 hours of pumping. In addition, a mono-corer was deployed 11 times, and 9 plankton nets traits were realized. 60 XBTs were dropped, and 17 floats were deployed. Finally, 140 clean underway surface samples were collected as well as 18 aerosol and 10 rainwater samples.
Figure: R/V Pourquoi pas? during GEOVIDE cruise - © IFREMER
Chief scientists : Géraldine Sarthou (LEMAR-IUEM, Brest, France) and Pascale Lherminier (LPO-IUEM, Brest, France).
- Dissolved iron sources in the North Atlantic Ocean quantified
- AGU Fall 2014 - GEOTRACES Special Sessions
- Undocumented cadmium, zinc and copper sink in oxygen minimum zones
- Successful GEOTRACES Intermediate Data Product presentation at Goldschmidt 2014
- The impact of the different sources of iron on the ability of the ocean to absorb atmospheric carbon dioxide: reversing the paradigm?