University of Alaska
University of Alaska

Maintained by Tom Weingartner, Seth Danielson and David Leech of the Institute of Marine Science at UAF's School of Fisheries and Ocean Science

Bear Glacier, seen looking northwest from station GAK1

Located at the mouth of Resurrection Bay near Seward, Alaska, temperature and salinity versus depth profiles have been taken at oceanographic station GAK1 since December, 1970. This multi-decade time series is one of the longest running oceanographic time series in the North Pacific. Long-term means of temperature and density at selected depths show the annual cycle of these two water properties. Monthly mean profiles at the standard depths are shown here, of temperature and salinity. Anomalies show interannual variation in the thermohaline structure at GAK1. Salinity, not temperature, is the primary variable that drives the density here in the northern Gulf of Alaska. The annual cycle of salinity closely follows that of density at all depths. GAK1 is the station closest to shore on the Seward Line transect of hydrographic stations, which extends approximately 230 km to the southeast of GAK1. For reference, we provide Gulf of Alaska a large-scale look at the surface current field, annual precipitation rates, and a view of the topographic/bathymetric relief.

For the first 20 years, sampling was accomplished by ships-of-opportunity, primarily research vessels as they left or entered the port, thus the time interval varied from several times per month to several times per year. Since September 1990 the sampling has been accomplished monthly, usually as a single CTD (conductivity-temperature-depth) profile to within 10m of the bottom, 263m. The location is 59° 50.7' N, 149° 28.0' W and is located within the Alaska Coastal Current, so it is well "connected" with the shelf circulation. The platform is the R/V Little Dipper, a 26' vessel. Samples taken between September 1990 and 1996 were sponsored by NOAA's Office of Global Programs (Office of Ocean and Earth Sciences, Ocean Observing Division, Observing Networks Branch) and since that time by the Exxon Valdez Oil Spill Trustees Council.

The first column of the CTD DATA FILE is the platform abbreviation and cruise number. The second column is the consecutive station number of the GAK1 cast (a unique identifing number within the ensemble of all casts for the cruise). The time is in decimal years beginning on 1 January. Depth in meters is next followed by temperature (°C), salinity (psu), sigma-t (kg/m3) and dynamic height (dynamic meters).

View of Rugged Island, to the east of station GAK1. Until about 1975, the profiling was accomplished with discrete samples using Nansen bottles. Since that time STDs (salinity-temperature-depth) or CTDs have been used. The accuracies of the temperature and salinity are plus/minus 0.02 in °C and PSU. Since parts of the record were discrete samples, we have only used the values at the standard oceanographic depths for this time series, though the other values are available. A summary of the seasonal cycle in these data was published in Xiong and Royer (1984) and the interannual variability was discussed in Royer (1989 and 1993). These data have been used in attempts to explain changes in biological populations of the region (Parker, et al., 1993 and Muter, et al., 1993). It would be helpful to others if you find the data useful and publish using them to notify us to add your reference to those below. We also are interested in knowing non-published uses for the dataset: such feedback helps us maintain the continued support for this long-term dataset.

EVOS HomepageThe sampling has been enhanced by the Exxon Valdez Oil Spill Trustee Council with the addition of a subsurface mooring with temperature and conductivity sensors placed at six depths through the water column. Mooring data is available starting in December, 1997. The EVOS webpage has description of the Gulf Ecosystem Monitoring (GEM) program, online annual reports and other literature employing the use of GAK1 data. Sampling has also been supplemented by the Northeast Pacific GLOBEC program and the North Pacific Reseach Board.

 

Access Data: These data are available for all interested users. If you use the data in your work, please let us know so that we can better demonstrate the utility of this dataset when it comes time to renew funding support.

GAK1 mooring timeseriesGAK1 mooring anomaly timeseries

GAK1 Time Series

GAK1 Anomalies

Note: Anomalies are computed with respect to the mooring data period of record (2000-2012).

Data Plots:

Mooring Time Series by deployment:

CTD Time Series:

camera

Current and ongoing research utilizing the GAK1 time series includes evaluation of the Gulf of Alaska fresh water and heat budgets. We find that GAK1 can serve to nowcast and hindcast the baroclinic volume transport andthe fresh water content within coastal current (Weingartner et. al., 2005).

Gulf of Alaska Coastal Discharge: Now updated through the end of 2011.. The Discharge Data File contains monthly estimates of the Alaskan Southeast and South Coast runoff, along with the total estimate new Seward and the monthly anomalies. Plots include visualisation of the smoothed discharge, the discharge anomaly and estimates of the discharge plus major Canadian rivers and galacial ablation. For more information on freshwater discharge, the Alaska Coastal Current, and measurements taken in the Northern Gulf of Alaska near station GAK1, see our Cape Fairfield Line homepage. The Pacific Fisheries Environmental Laboratory presents compiled data of the upwelling index for 15 stations along the northern and eastern Pacific Ocean coasts. See also NPRB funded project #734

View of Cape Aialik, to the soutwest of GAK1.


Publications employing data from the GAK1 Time Series:

If you find the GAK1 time series useful, please let us know!


Contacts:

Thomas C. Royer
Eminent Professor of Oceanography, retired
Samuel L. and Fay M. Slover Chair in Oceanography
Center for Coastal Physical Oceanography
Old Dominion University,
Crittenton Hall,
768 West 52nd Street,
Norfolk, VA 23529
royer@ccpo.odu.edu

Thomas J. Weingartner
Professor
Institute of Marine Science
School of Fisheries and Ocean Sciences
Room 115 O'Neill Building
University of Alaska Fairbanks
Fairbanks, AK 99775-7220
Phone: (907) 474-7993
weingart@ims.alaska.edu

 

 

Seth L. Danielson
Research Assistant Professor
Institute of Marine Science
School of Fisheries and Ocean Sciences
Room 112 O'Neill Building
University of Alaska Fairbanks
Fairbanks, AK 99775-7220
Phone: (907) 474-7834
sldanielson@alaska.edu

 

 


Photos taken at station GAK1 by Seth Danielson, August 2001.