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.
Why is the deep ocean zinc isotopic signature so heavy?
- Published on Friday, 14 November 2014 09:54
The oceanic balance of the micronutrient zinc (Zn) is getting more puzzling –although better documented- while the Zn isotope data set increases. Presenting the first high resolution section of seawater dissolved Zn concentration and Zn isotope ratios (δ66Zn) from the North Atlantic, Conway and John (2014, see reference below) confirm that the deep ocean is fairly homogeneous for δ66Zn, close to +0.5‰, except near local North Atlantic sources of Zn (margins, the Mediterranean Sea, hydrothermal vents) where it is isotopically lighter.
Balancing the Zn isotopic budget raises questions. Indeed, the known inputs of this element (continental, riverine, and aerosol) display δ66Zn ranging between 0 and +0.3‰ while the known outputs (carbonates, ferromanganese nodules, and ferromanganese crusts) are isotopically heavier (+0.9 to +1‰). As previously suggested by Little et al. (2014, see also highlight about it), an isotopically light sink is therefore missing. The authors suggest that burial of biogenic Zn in sediments might be this important sink. They also suggest a potential role for zinc sulfide (ZnS) precipitation in low-oxygen open-ocean waters as a possible light sink, analogous to recent studies on Cd (Janssen et al., 2014, see also highlight about it).
Figure. Distribution of dissolved stable Zn isotope ratios (δ66Zn) for the US GEOTRACES North Atlantic GA03 and GA03_e sections. δ66Zn is expressed relative to JMC Lyon standard. Station numbers are shown for 2010 (USGT10, red) and 2011 (USGT11, blue). The black vertical line denotes the crossover between the cruises at USGT10-12 and USGT11-24. Click here to view the figure larger.
Present day neodymium isotopic composition of the Caribbean Sea deep waters questions the paleo-application of this tracer in restricted basins
- Published on Friday, 07 November 2014 13:41
The first profiles of neodymium (Nd) concentration and isotopic composition in the Carribbean Sea have been published. They show that surface and intermediate waters flow through the Caribbean with essentially unchanged Nd isotopes ratios (εNd), whereas deep waters are strongly modified. Indeed, they likely receive radiogenic Nd released from the local sediments, of volcanic origin. Osborne and co-authors (2014, see reference below) suggest that this important shift is facilitated by the long residence time of these deep waters (150 years). This finding has general implications for paleoceanographic studies in restricted basins, where the composition of seawater is sensitive to its residence time within the basin.
Figure. Schematic cross-section of the Caribbean and Gulf of Mexico basins, showing the Nd isotopic composition and concentration of inflowing Atlantic water and how it changes to more radiogenic compositions and higher concentrations within the deep Caribbean. Interaction of seawater with radiogenic Nd from the margins of the Caribbean may be responsible for this change, aided by the slow replenishment rate and long residence time of deep waters in the Caribbean and Gulf of Mexico. Click here to view the figure larger.
UK GEOTRACES Process Study in the Celtic Sea
- Published on Friday, 07 November 2014 16:07
The UK research vessel Discovery will depart on November 9th from Falmouth to examine the off shelf transport of iron in the Celtic Sea. The cruise, led by Prof. Jonathan Sharples, will return to Southampton on December 3rd.
This is the first of three research cruises examining the off shelf transport of iron which are part of a large NERC funded Shelf Sea Biogeochemistry programme (http://www.nerc.ac.uk/research/funded/programmes/shelfsea/). The other two cruises will be held next year in spring (1-30 April 2015, chief scientist Dr. Richard Sanders) and summer (10 July – 2 August 2015, chief scientist Dr. Mark Moore).
The Shelf Sea Biogeochemistry research programme aims to reduce the uncertainty in our understanding of nutrient and carbon cycling within the shelf seas, and their role in global biogeochemical cycles.
Contact : Maeve Lohan, University of Plymouth, UK.
The sources of the water soluble organic matter contained in the aerosols over the Atlantic ocean decoded
- Published on Friday, 07 November 2014 10:58
Organic matter is an important component of aerosols, which can absorb (or scatter) light, contributing a warming (or cooling) effect to the atmospheric radiative budget. However, this impact is tightly linked to the molecular characteristics of aerosol organic matter. It is, therefore, of prime importance to establish the organic matter molecular details of aerosols from different sources.
This characterization is the aim of Wozniak et al. paper (2014, see reference below). Based on aerosols samples collected in the framework of the North Atlantic US GEOTRACES GA03 cruise, the authors analyzed their water soluble organic matter (WSOM) molecular characteristics using an ultrahigh-resolution analytical method*. Multivariate statistics allowed the identification of five sources with very different distinguishing WSOM characteristics, enlightening the origin of these different aerosol components.
*electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry.
Figure. Three dimensional plots showing the principal component analysis a) scores for samples from the five aerosol emission sources and the b) molecular formula loadings that distinguish each source from the others. Click here to view the image larger.
- Overview of the dissolved iron, manganese and aluminium distributions along the North Atlantic GEOTRACES GA03 section
- Organic copper complexation may stabilise seawater stable copper isotopic composition
- Field data allow constraining total mercury budget
- A new model of the oceanic aluminium distribution
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