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

Glacierized coastal catchments of the Gulf of Alaska (GoA) 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 and particulate 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 drive the seasonal runoff patterns. The ?O-18 signature and specific conductance show distinctive seasonal variations in stream water sources between the 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, however, the hydroclimate is the primary driver of the timing of dissolved and suspended yields. We show the yields of dissolved organic carbon is higher and that the d(13)C(POC) is enriched in the Southeast streams illustrating contrasts in organic carbon export across the GoA. Finally, we illustrate how future yields of solutes and sediments to the GoA may change as watersheds evolve from glacial influenced to precipitation dominated. This integrated analysis provides insights into how watershed characteristics beyond glacier coverage control properties of freshwater inputs to the GoA and the importance of expanding study regions to multiple hydroclimate regimes.

Automated summary

Glacialized coastal catchments of the Gulf of Alaska are experiencing rapid hydrologic fluctuations due to climate change. These catchments play a significant role in delivering dissolved and suspended inorganic and organic matter to the nearby marine environments, but little is known about the total solute and particulate fluxes to the ocean. This study presents data collected from 10 streams in two regions of Alaska, revealing the seasonal runoff patterns driven by glaciers and distinctive variations in stream water sources between regions. The study also highlights the differences in organic carbon export across the Gulf of Alaska and explores how future solutes and sediments may change as watersheds transition from glacial influenced to precipitation dominated.