Dissolved Fe Supply to the Central Gulf of Alaska Is Inferred to Be Derived From Alaskan Glacial Dust That Is Not Resolved by Dust Transport Models

Re-examination of previously published dissolved iron time-series data from Ocean Station Papa in the central Gulf of Alaska (GoA) reveals 33%-70% increases in the dissolved iron inventories occurring between September and February of successive years, implying a source of Fe to this region during autumn or early winter. Because I can virtually rule out many possible iron sources at this time of year, I suggest Alaskan glacial dust is the likely iron source. Large plumes of such dust are known to be generated regularly in the autumn by anomalous offshore winds and channeled through mountain gaps, simultaneously from several locations spanning similar to 1,000 km of the northern Gulf of Alaska coastline. Large dust flux events occur when below-freezing, low-humidity air temperatures persist for many days during the autumn. I suggest that existing state-of-the-art global dust models fail to reproduce this Alaskan dust flux because the model spatial resolution is too coarse to resolve the high winds through the narrow mountain gaps that generate the dust. Future work that could help to confirm this Fe source to the central GoA includes time-series profiles of iron concentrations, and ancillary information from sensor-equipped profiling floats. If this mechanism of Fe supply to the central GoA were confirmed, it would imply this Alaskan dust is transported >= 1,100 km from the coast, more than twice as far as has been visually documented from satellite observations. Plain Language Summary While it is well known that availability of the essential micronutrient iron limits biological productivity in large regions of the ocean, we lack a quantitative understanding of the processes that supply the iron to these regions. This is at least in part because observations that could infer seasonally variable sources remain rare. Here I re-examine an exceptional seasonally resolved timeseries of previously published dissolved iron profiles from the central Gulf of Alaska, and note that dissolved iron inventories (amount of iron per square meter) increase between September and February of successive years, implying a source of iron to the region over that time interval. Because I can virtually rule out other plausible sources, I infer that this iron is supplied from large dust plumes generated from glacierized riverbed sediments of the southern Alaska coastal region, which are known to occur in the autumn. Existing models of dust supply fail to simulate dust from these sources because they lack the horizontal spatial resolution needed to resolve the winds from these narrow mountain valleys. This result could have implications for dust sources from narrow mountain valleys from other parts of the globe.

Automated summary

Re-examination of dissolved iron time-series data in the central Gulf of Alaska reveals an increase in iron inventories between September and February, suggesting a potential source of iron from Alaskan glacial dust. The existing global dust models fail to replicate this dust flux due to inadequate spatial resolution to capture the high winds generating the dust. Confirmation of this iron source could have implications for understanding dust sources from narrow mountain valleys globally.