Alaskan Glacial Dust Is an Important Iron Source to Surface Waters of the Gulf of Alaska.

This work evaluates glacial dust as a source of sediment, and associated iron (Fe), to the Fe‐limited Gulf of Alaska (GoA). A reanalysis of GoA sediment data, using rare earth elements and thorium as provenance tracers, suggests a flux to the ocean surface of Copper River (AK) glacial dust, and associated Fe, that is comparable to the flux of dust from Asia, at least 1,000 km from the narrow mountain valley glacial dust source area. This work suggests dust from Asia may not be the largest source of Fe to the GoA. Dust models fail to accurately simulate this glacial dust transport because their coarse resolution underestimates wind speeds, and the dust flux. This work suggests that glacial dust fluxes may have been important in the geologic past (e.g., the last glacial maximum) from locations where there was more extensive coverage by glaciers than at present. Plain Language Summary: The growth of phytoplankton, the base of the marine food web, is known to be limited by availability of the micronutrient iron in the Gulf of Alaska. We evaluated the importance of glacial dust in this region as a source of iron, and other trace metals, by using concentrations of the rare earth elements and thorium in particles as tracers of their geographic origin. We analyzed for these elements in glacial dust samples from the Copper River valley (Alaska), the largest source of glacier‐derived dust. Together with previously published concentrations for dust from Asia and volcanic material, we estimated the inputs of each source material to the sediments of the Gulf of Alaska. This information, together with published sediment mass accumulation rates, suggests an important contribution of Alaskan glacial dust and associated iron, to surface waters of the Gulf of Alaska, at least 1,000 km from the source. Dust models fail to accurately simulate this dust transport because their coarse spatial resolution substantially underestimates wind speeds. Glacial dust fluxes may have been important sources of iron in the geologic past (e.g., the Last Glacial Maximum) from New Zealand and South America, when there was more extensive glacial coverage. Key Points: Copper River glacial dust contributes substantially to Gulf of Alaska sediments, and associated iron to surface watersDust models lack sufficient spatial resolution to accurately simulate the winds that drive the flux of glacial dust from narrow valleysGlacial dust‐associated iron may have been important in the geologic past in times and locations with more extensive glacial coverage [ABSTRACT FROM AUTHOR]