Abstract
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 2.5 nM) due to low aerosol deposition and removal by biogenic particles (i.e. phytoplankton cells). However, surface water dAl concentrations were enhanced on the Iberian and Greenland shelves (up to 30.9 nM) due to continental inputs (rivers, glacial flour, and ice melt). Dissolved Al in surface waters scaled negatively with chlorophyll a and biogenic silica (opal) concentrations. The abundance of diatoms exerted a significant (p<0.01) control on the surface particulate Al (pAl) to dAl ratios by decreasing dAl levels and increasing pAl levels. Dissolved Al concentrations generally increased with depth and correlated strongly with silicic acid (R2>0.76) west of the Iberian Basin, suggesting net release of dAl at depth during remineralization of sinking opal-containing particles. Enrichment of dAl at near-bottom depths was observed due to the resuspension of sediments. The highest dAl concentrations (up to 38.7 nM) were observed in Mediterranean Outflow 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 distributions of dAl in the North Atlantic differ when compared to other regions of the Atlantic and global oceans. Responsible for these large inter- and intra-basin differences are the large spatial variabilities in the main Al source, atmospheric deposition, and the main Al sink, particle scavenging by biogenic particles.
Highlights
Aluminium (Al) in the oceans has been used as a tracer for mineral dust deposition (Han et al, 2008; Measures and Vink, 2000; Measures and Brown, 1996) and water masses (Measures and Edmond, 1990)
Average surface dissolved aluminium (dAl) concentrations decreased from 3.3 ± 1.7 nM (n = 5) in the IB to 3.2 ± 0.8 nM (n = 4) in the ENAB, and 2.8 ± 1.2 nM (n = 5) in the IcB to 1.7 ± 0.7 nM (n = 4) and 1.7 ± 0.6 nM (n = 3) in the IrB and LB, respectively
Our low surface dAl values agreed with literature values for the ENAB (Barrett et al, 2015; Kramer et al, 2004; Measures et al, 2008; Ussher et al, 2013) and IrB (Middag et al, 2015b), and coincided with low particulate Al (pAl) concentrations (Gourain et al, 2018) except over the Greenland shelf
Summary
Aluminium (Al) in the oceans has been used as a tracer for mineral dust deposition (Han et al, 2008; Measures and Vink, 2000; Measures and Brown, 1996) and water masses (Measures and Edmond, 1990). Menzel Barraqueta et al.: Aluminium in the North Atlantic Ocean and the Labrador Sea and Bruland, 1985), especially in association with siliconrich particles (Moran and Moore, 1988a). A major source of Al to the surface ocean is dry atmospheric deposition of terrigenous material (Kramer et al, 2004; Measures et al, 2005; Orians and Bruland, 1986), which can be carried thousands of kilometres in the atmosphere before deposition into the ocean (Duce et al, 1991; Prospero and Carlson, 1972). Wet atmospheric deposition (rain, fog, and snow) plays an important role in supplying Al to both the North Atlantic (Schlosser et al, 2014; Shelley et al, 2017) and the global ocean (Guerzoni et al, 1997; Vink and Measures, 2001). Hydrothermal vents (Measures et al, 2015; Resing et al, 2015) were noted as Al sources to the deep Atlantic and Pacific oceans, with plumes extending at depth over 3000 km in the Pacific Ocean
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