Integrating oceanographic surveys and stream runoff observations to estimate seasonal variation in freshwater content within a high latitude glacier fed estuary

Abstract:

Freshwater discharge from coastal watersheds delivers key nutrients to nearshore habitats and drives coastal currents. Forecasted climate changes over the next century will modify the timing and volume of freshwater delivered to the Gulf of Alaska (GOA) region. Limited high spatial and temporal resolution discharge data inhibits the investigation of potential changes to freshwater flux and the resulting impacts on coastal ecosystems and ocean current dynamics. This study combines monthly conductivity, temperature, depth (CTD) ocean survey data, observed and modeled freshwater discharge, and ocean drifter data collected within Kachemak Bay, an arm of the Cook Inlet in south-central Alaska, with the objective of determining the interaction of freshwater and sea water within the Bay. During late fall and winter the salinity and temperature are homogeneous throughout much of the water column. A temperature and salinity gradient forms within the top ~20 meters during the spring freshet and summer melt season. Sea surface salinity decreases during the spring and summer seasons, increases in late summer and fall and in the winter months mixes vertically in response to mixing driven by wind. Sea surface temperature increases in the spring and summer and decreases in the fall and winter. Until recently, constraints on modeled and field-based discharge observations limited the linkage between freshwater flux and sea surface salinity and temperature. Utilizing the existing CTD, drifter, and freshwater discharge data, we will quantify freshwater discharge into Kachemak Bay and estimate seasonal freshwater content changes within the Bay. This approach will begin to inform how future changes in freshwater flux may change the circulation dynamics and nutrients supplied to nearshore ecosystems within Kachemak Bay and the GOA.