Monitoring Transport in the Alaska Coastal Current: A Feasibility Study
Investigator
University of Alaska Fairbanks
Synopsis
Fishermen have long known that the abundance of commercially important fish species can vary from year to year. Scientists know that different ocean conditions favor different species, and that conditions vary over time. But scientists do not fully understand how these changes in ocean conditions occur, nor are they able to predict them. In this study, scientists will develop a plan to monitor currents that flow along the coast of the Gulf of Alaska. The goal is to quantify and understand changes in the marine environment that occur year-to-year and decade-to-decade. This is regarded as an essential step toward helping fishery managers understand and predict variations in fisheries. Such information also could help fishermen prepare for changes in fish abundance and species composition.
Results
What researchers learned
We investigated the possibility of using Seward sea level data to monitor transport in the ACC. We used historical data from Seward along with data collected from a single mooring with instruments at 5 different depths to assess the feasibility of this approach. Our results are inconclusive on this specific issue because we concluded that a single mooring does not provide an adequate measure of the transport through the ACC. We reviewed possible reasons for this failure and found that the current structure changes seasonally and on synoptic time scales so that the mooring is not always located in the main axis of the current.
Instead, we examined the relationship between vertically integrated salinity anomalies at hydrographic station GAK 1 and the (geostrophic) baroclinic transport through the 40-km-wide ACC. Our main finding is that there is a statistically significant relationship between these two variables (r = 0.65, P < 0.05, N = 40). The results suggest that about 40% of the baroclinic transport variance in the ACC can be explained by the GAK 1 data.
Using recently collected data from the GLOBEC program, we find that Seward sea level is significantly correlated with salinity and the dynamic height at station GAK 1. (GAK 1 is a hydrographic station located at the mouth of Resurrection Bay. The station lies on the inshore edge of the ACC.) These results suggest that Seward sea level is potentially useful to monitor the baroclinic component of transport in this coastal current.
We were unable to demonstrate the feasibility of using Seward sea level to assess transport variability as given by a single mooring in the ACC. However, we believe that the above results coupled with known theoretical results suggests that this approach is feasible and should be tested. An adequate test requires deploying a carefully designed mooring program that captures the total transport in the ACC.
