Hydroclimate Drives Seasonal Riverine Export Across a Gradient of Glacierized High-Latitude Coastal Catchments

Abstract

Glacierized coastal catchments of the Gulf of Alaska are undergoing rapid hydrologic fluctuations in response to climate change. These catchments deliver dissolved and suspended inorganic and organic matter to nearshore marine environments, however, these glacierized coastal catchments are relatively understudied and little is known about total solute fluxes to the ocean. We present hydrologic, physical, and geochemical data collected during April-October 2019-2021 from 10 streams along gradients of glacial fed to non-glacial (i.e., precipitation) fed, in one Southcentral and one Southeast Alaska region. Hydrologic data reveal that glaciers have a dominating influence on seasonal runoff patterns. The ẟ18O signature and specific conductance show distinctive seasonal variations in stream water sources between the two study regions apparently due to the large amounts of rain in Southeast Alaska. Total dissolved solids concentrations and yields were elevated in the Southcentral region, due to lithologic influence on dissolved loads. Hydroclimate is the primary driver of the timing of dissolved and suspended yields in both regions of the Gulf of Alaska. We show the yields of dissolved organic carbon is higher and that the δ13CPOC is enriched in the Southeast streams illustrating contrasts in organic carbon export across the Gulf of Alaska. Furthermore, we illustrate how future yields of solutes and sediments to the Gulf of Alaska may change as watersheds evolve from glacial influenced to precipitation dominated. This integrated analysis provides insights into how watershed characteristics beyond glacier coverage control the properties of freshwater inputs to the Gulf of Alaska and the importance of expanding study regions to multiple hydroclimate regimes.