Flocculated meltwater particles control Arctic land-sea fluxes of labile iron

Abstract

Glacial meltwater systems supply the Arctic coastal ocean with large volumes of sediment and potentially bioavailable forms of iron, nitrogen and carbon. The particulate fraction of this supply is significant but estuarine losses have been thought to limit the iron supply from land. Here, our results reveal how flocculation (particle aggregation) involving labile iron may increase horizontal transport rather than enhance deposition close to the source. This is shown by combining field observations in Disko Fjord, West Greenland, and laboratory experiments. Our data show how labile iron affects floc sizes, shapes and densities and consequently yields low settling velocities and extended sediment plumes. We highlight the importance of understanding the flocculation mechanisms when examining fluxes of meltwater transported iron in polar regions today and in the future, and we underline the influence of terrestrial hotspots on the nutrient and solute cycles in Arctic coastal waters.

The heterogeneous nature of Fe delivery from melting icebergs

“…As has been demonstrated in this study and elsewhere (e.g., Markussen et al, 2016), surface waters in stratified, glaciated fjords can exhibit extremely high TdFe concentrations due to the presence of glacially derived particle plumes. TdFe concentrations in surface waters of Kongsfjorden (mean 8.1 µM, median 3.7 µM) exceeded those in icebergs (3.6 µM and 144 nM, respectively).…”

Assessing the Role of High‐Frequency Winds and Sea Ice Loss on Arctic Phytoplankton Blooms in an Ice‐Ocean‐Biogeochemical Model

“…In the Barents Sea, the model also underestimates by 0.16 mmol/m 3 (Mignot et al, 2018) Labrador Sea spring 600 800 (Mignot et al, 2018) Labrador Sea and Baffin Bay autumn 300 298 (Harrison & Cota, 1991) Baffin Bay autumn 230 227 (Harrison et al, 1982) Hudson Bay autumn 250 200 (Lapoussière et al, 2013) Beaufort Sea/Darnley Bay autumn 30 20-310 (Mundy et al, 2007) relative to WOA13. DIM underestimations in both regions are likely related to the high influence of runoff and/or glacial melt water containing DIM (Bhatia et al, 2013;Holmes et al, 2012;Markussen et al, 2016). Meanwhile, these land DIM sources are absent in our simulation.…”

Reactive Iron and Iron‐Bound Organic Carbon in Surface Sediments of the River‐Dominated Bohai Sea (China) Versus the Southern Yellow Sea

“…On the other hand, flocculation of Fe colloids does not necessarily mean their rapid settlement from the water column to the sediment because the filterability of estuarine colloids does not equate to the tendency of sediments (Mayer, 1982). Rather, much of larger Fe-rich flocs may remain suspended in estuarine water and be transported several kilometers outward without settling more than 1 m due to low settling velocities (Markussen et al, 2016), which are determined by floc size, shape and density (Herzog et al, 2017;Mayer, 1982). A recent study indicates that increasing availability of labile Fe enhances flocculation kinetics of Fe but decreases the sphericity and density of Fe flocs, which favors floc suspension in water (Markussen et al, 2016).…”

“…Rather, much of larger Fe-rich flocs may remain suspended in estuarine water and be transported several kilometers outward without settling more than 1 m due to low settling velocities (Markussen et al, 2016), which are determined by floc size, shape and density (Herzog et al, 2017;Mayer, 1982). A recent study indicates that increasing availability of labile Fe enhances flocculation kinetics of Fe but decreases the sphericity and density of Fe flocs, which favors floc suspension in water (Markussen et al, 2016). As a result, flocs may be flushed off the estuaries into shelf waters and then be removed to shelf sediments by gravitational and/or planktic biodepositional mechanisms (Mayer, 1982).…”