Trace metal distributions within a Sitka eddy in the northern Gulf of Alaska

Abstract

In the northern Gulf of Alaska, mesoscale, anticyclonic eddies have been implicated as a mechanism of the cross-shelf exchange of iron (Fe)-replete coastal waters with Fe-deplete subarctic Alaskan gyre waters. Based on existing hydrography and macronutrient distributions, a Sitka eddy sampled during August 2007 is divided into a surface eddy core, a shallow subsurface eddy core, and a deeper subsurface eddy core. The distributions of aluminum (Al), manganese (Mn), and Fe in the eddy are examined and compared to distributions at shelf stations similar to where the eddy formed as well as basin stations representative of the Fe-limited subarctic Alaskan gyre. Relative to basin stations, dissolved and particulate Al and dissolved Mn were elevated in eddy core waters. Reactive Fe concentrations within the shallow subsurface eddy core were nearly seven times greater than reactive Fe concentrations at similar densities at the basin stations. This shallow subsurface eddy core is likely mixed into the euphotic zone during storm-induced mixing as well as mixing during isopycnal relaxation as an eddy dies out.

Estuarine removal of glacial iron and implications for iron fluxes to the ocean

“…Most importantly, from a flux standpoint, these data clearly highlight the importance and dominance of particulate glacial flour in providing soluble meltwater‐derived iron to the ocean, as the observed total dissolvable concentration of the iron that makes it through the estuary is 3 orders of magnitude greater than the dissolved fraction, and there is fundamentally less removal of this portion of the riverine iron load in the estuary (Figures c and d). This is a critical point, as once glacial flour enters the ocean, it can be transported well off shore to Fe‐limited phytoplankton populations based on a variety of transport mechanisms which have been shown to drive offshore phytoplankton nutrient dynamics (i.e., sediment resuspension and coastal eddies) [ Brown et al , ; Lam and Bishop , ; Lippiatt et al , ].…”

Dissolved Fe in the Deep and Upper Arctic Ocean With a Focus on Fe Limitation in the Nansen Basin

“…According to literature (Lam et al, 2006;Brown et al, 2012) lateral transport from the coast, shelves and land-fast-glaciers, with or without further transport by mesoscale eddies, is feeding the blooms over nearby Canadian Basin. In the present study the major driver of such lateral transport is the TPD (Gordienko and Laktionov, 1969;Gregor et al, 1998;Macdonald et al, 2005).…”

Seasonal and spatial variabilities in northern Gulf of Alaska surface water iron concentrations driven by shelf sediment resuspension, glacial meltwater, a Yakutat eddy, and dust

“…Another key mechanism of offshore Fe transport in the GoA is eddies, as they often form in Fe-rich coastal regions and transport coastally derived Fe offshore. While a number of other physical processes that could transport Fe offshore have been documented [e.g., Stabeno et al, 2004;Siedlecki et al, 2012], only a few such studies have actually included Fe observations [Johnson et al, 2005;Cullen et al, 2009;Wu et al, 2009;Lippiatt et al, 2011;Brown et al, 2012;Xiu et al, 2011;Aguilar-Islas et al, 2016].…”