9 research outputs found
Dissolved Pb and Pb isotopes in the North Atlantic from the GEOVIDE transect (GEOTRACES GA-01) and their decadal evolution
During the 2014 GEOVIDE transect, seawater samples were collected for
dissolved Pb and Pb isotope analysis. These samples provide a high-resolution
snapshot of the source regions for the present Pb distribution in the
North Atlantic Ocean. Some of these stations were previously occupied for Pb
from as early as 1981, and we compare the 2014 data with these older data,
some of which are reported here for the first time. Lead concentrations were
highest in subsurface Mediterranean Water (MW) near the coast of Portugal,
which agrees well with other recent observations by the US GEOTRACES program
(Noble et al., 2015). The recently formed Labrador Sea Water (LSW) between
Greenland and Nova Scotia is much lower in Pb concentration than the older
LSW found in the West European Basin due to decreases in Pb
emissions into the atmosphere during the past 20Â years. Comparison of North
Atlantic data from 1989 to 2014 shows decreasing Pb concentrations consistent
with decreased anthropogenic inputs, active scavenging, and
advection/convection. Although the isotopic composition of northern North
Atlantic seawater appears more homogenous compared to previous decades, a
clear spatiotemporal trend in isotope ratios is evident over the past
15Â years and implies that small changes to atmospheric Pb emissions continue.
Emissions data indicate that the relative proportions of US and European Pb
sources to the ocean have been relatively uniform during the past 2 decades,
while aerosol data may suggest a greater relative proportion of natural
mineral Pb. Using our measurements in conjunction with emissions inventories,
we support the findings of previous atmospheric analyses that a significant
portion of the Pb deposited to the ocean in 2014 was natural, although it is
obscured by the much greater solubility of anthropogenic aerosols over
natural ones.</p
Mercury distribution and transport in the North Atlantic Ocean along the GEOTRACES-GA01 transect
We report here the results of total mercury (HgT) determinations along the 2014 Geotraces Geovide cruise (GA01 transect) in the North Atlantic Ocean (NA) from Lisbon (Portugal) to the coast of Labrador (Canada). HgT concentrations in unfiltered samples (HgTUNF) were log-normally distributed and ranged between 0.16 and 1.54âŻpmolâŻLâ1, with a geometric mean of 0.51âŻpmolâŻLâ1 for the 535 samples analysed. The dissolved fraction (<âŻ0.45âŻÂ”m) of HgT (HgTF), determined on 141 samples, averaged 78âŻ% of the HgTUNF for the entire data set, 84âŻ% for open seawaters (below 100âŻm) and 91âŻ% if the Labrador Sea data are excluded, where the primary production was high (with a winter convection down to 1400âŻm). HgTUNF concentrations increased eastwards and with depth from Greenland to Europe and from subsurface to bottom waters. The HgTUNF concentrations were similarly low in the subpolar gyre waters (ââŒââŻ0.45âŻpmolâŻLâ1), whereas they exceeded 0.60âŻpmolâŻLâ1 in the subtropical gyre waters. The HgTUNF distribution mirrored that of dissolved oxygen concentration, with highest concentration levels associated with oxygen-depleted zones. The relationship between HgTF and the apparent oxygen utilization confirms the nutrient-like behaviour of Hg in the NA. An extended optimum multiparameter analysis allowed us to characterize HgTUNF concentrations in the different source water types (SWTs) present along the transect. The distribution pattern of HgTUNF, modelled by the mixing of SWTs, show Hg enrichment in Mediterranean waters and North East Atlantic Deep Water and low concentrations in young waters formed in the subpolar gyre and Nordic seas. The change in anthropogenic Hg concentrations in the Labrador Sea Water during its eastward journey suggests a continuous decrease in Hg content in this water mass over the last decades. Calculation of the water transport driven by the Atlantic Meridional Overturning Circulation across the PortugalâGreenland transect indicates northward Hg transport within the upper limb and southward Hg transport within the lower limb, with resulting net northward transport of about 97.2âŻkmolâŻyrâ1
Introduction to the French GEOTRACES North Atlantic Transect (GA01): GEOVIDE cruise
The GEOVIDE cruise, a collaborative project within the framework of the international GEOTRACES programme, was conducted along the French-led section in the North Atlantic Ocean (Section GA01), between 15 May and 30 June 2014. In this special issue (https://www.biogeosciences.net/special_issue900.html), results from GEOVIDE, including physical oceanography and trace element and isotope cyclings, are presented among 18 articles. Here, the scientific context, project objectives, and scientific strategy of GEOVIDE are provided, along with an overview of the main results from the articles published in the special issue
Aluminium in the North Atlantic Ocean and the Labrador Sea (GEOTRACES GA01 section): roles of continental inputs and biogenic particle removal
The distribution of dissolved aluminium (dAl) in the water column of the North Atlantic and Labrador Sea was studied along GEOTRACES section GA01 to unravel the sources and sinks of this element. Surface water dAl concentrations were low (median of 2.5ânM) due to low aerosol deposition and removal by phytoplankton. However, surface water dAl concentrations were enhanced on the Iberian and Greenland shelves (up to 30.9ânM) due to continental inputs (rivers, glacial flour and ice melt). A negative correlation was observed between dAl in surface waters and primary production, phytoplankton community structure and biogenic opal production. The abundance of diatoms exerted a significant (pââ0.76) west of the Iberian Basin, suggesting net release of dAl at depth during remineralization of sinking biogenic opal containing particles. Enrichment of dAl at near-bottom depths was observed due to resuspension of sediments near the sediment-water interface. The highest dAl (up to 38.7ânM) concentrations were observed in Mediterranean Overflow Waters which act as a major source of dAl to mid depth waters of the eastern North Atlantic. This study clearly shows that the vertical and lateral distribution of dAl in the North Atlantic differs when compared to other regions of the North Atlantic and global ocean due to the large spatial differences both in the main source of Al, atmospheric deposition, and the main sink for Al, particle scavenging, between different oceanic regions
Aluminium in the North Atlantic Ocean and the Labrador Sea (GEOTRACES GA01 section): roles of continental inputs and biogenic particle removal
Abstract. The distribution of dissolved aluminium (dAl) in the water column of the North Atlantic and Labrador Sea was studied along GEOTRACES section GA01 to unravel the sources and sinks of this element. Surface water dAl concentrations were low (median of 2.5ânM) due to low aerosol deposition and removal by phytoplankton. However, surface water dAl concentrations were enhanced on the Iberian and Greenland shelves (up to 30.9ânM) due to continental inputs (rivers, glacial flour and ice melt). A negative correlation was observed between dAl in surface waters and primary production, phytoplankton community structure and biogenic opal production. The abundance of diatoms exerted a significant (pââ0.76) west of the Iberian Basin, suggesting net release of dAl at depth during remineralization of sinking biogenic opal containing particles. Enrichment of dAl at near-bottom depths was observed due to resuspension of sediments near the sediment-water interface. The highest dAl (up to 38.7ânM) concentrations were observed in Mediterranean Overflow Waters which act as a major source of dAl to mid depth waters of the eastern North Atlantic. This study clearly shows that the vertical and lateral distribution of dAl in the North Atlantic differs when compared to other regions of the North Atlantic and global ocean due to the large spatial differences both in the main source of Al, atmospheric deposition, and the main sink for Al, particle scavenging, between different oceanic regions. </jats:p
TSLRF: Two-Stage Algorithm Based on Least Angle Regression and Random Forest in genome-wide association studies
Introduction to the French GEOTRACES North Atlantic Transect (GA01): GEOVIDE cruise
The GEOVIDE cruise, a collaborative project within the framework of the international GEOTRACES programme, was conducted along the French-led section in the North Atlantic Ocean (Section GA01), between 15 May and 30 June 2014. In this Special Issue, results from GEOVIDE, including physical oceanography and trace element and isotope cyclings, are presented among seventeen articles. Here, the scientific context, project objectives and scientific strategy of GEOVIDE are provided, along with an overview of the main results from the articles published in the special issue
Introduction to the French GEOTRACES North Atlantic Transect (GA01): GEOVIDE cruise
The GEOVIDE cruise, a collaborative project within the framework of the international GEOTRACES programme, was conducted along the French-led section in the North Atlantic Ocean (Section GA01), between 15 May and 30 June 2014. In this Special Issue, results from GEOVIDE, including physical oceanography and trace element and isotope cyclings, are presented among seventeen articles. Here, the scientific context, project objectives and scientific strategy of GEOVIDE are provided, along with an overview of the main results from the articles published in the special issue