A five-year program of physical and biological measurements is proposed to study the seasonal and interannual variability of the Alaska Coastal Current (ACC). The dynamics of the ACC govern stratification and circulation over the inner portion of the Alaskan shelf, a region that plays a critical role in the early life history of several commercially important fish species, including juvenile salmon. The system responds strongly to large seasonal and interannual changes in freshwater discharge and wind-forcing. Moreover, seasonal shifts in dynamics likely exert strong influences on the temporal and spatial structure of stratification, on the spring phytoplankton bloom and on the advective transport of zooplankton and fish. Seasonal cycles in dynamics may also play a key role in explaining how nutrients are replenished in this downwelling-favorable system that is inundated by nutrient-deplete freshwater discharge. Thus, variability in wind-forcing and freshwater discharge produce significant changes in ACC dynamics which can influence the recruitment success of zooplankton and fish through a number of different pathways. This study will focus on understanding:
Seasonal and interannual variability in ACC freshwater content and transport.
The ACC's role in governing springtime mixed layer evolution over the shelf.
Processes controlling temporal and spatial variability in the spring bloom.
Processes that may produce onshore nutrient flux.
These processes are inherently three-dimensional and exhibit a wide range of temporal scales. To address these sampling requirements, this program will exploit the capabilities of a new, autonomous, telemetering vehicle (Seaglider) to make continuous, high-resolution sections of the ACC. Seaglider measures temperature, conductivity, pressure, chlorophyll fluorescence, dissolved oxygen and volume scattering function, profiles from the surface to within 10 m of the bottom and provides 2 km horizontal resolution. The vehicle will operate year-round, repeating a sampling pattern designed to provide 5 sections across the ACC every 20 days. The sampling strategy was designed in coordination with other Long Term Observation Program (LTOP) investigators to augment exisiting and proposed LTOP components. The temporal and spatial resolution provided by Seaglider surveys will resolve processes such as springtime restratification and phytoplankton blooms, while the multi-year extent of these observations will explore the system's response to long timescale perturbations in forcing.