University of Alaska
University of Alaska

Maintained by Dr. Tom Weingartner of the Institute of Marine Science at UAF's School of Fisheries and Ocean Science

GAK1 BREAKING NEWS: April 4, 2008 > See our new Real-Time Surface Buoy ... this buoy is presently deployed in a "Test Mode" off the end of the Seward Marine Center Dock. Our eventual goal is to get it out at station GAK1.

May 2007 observations show we had an anomalous spring and summer... the temperatures and salinites lie outside of the long-term month of May standard deviations and from March-October 2007, the deep waters are on average colder than any year since the early 1970s. See below for additional plots. Profiles from September and October 2007 indicate that the anomaly has not advected away from and the temperatures remain low near the bottom. Analysis of this event was presented at the 2008 Ocean Sciences meeting in Orlando, Florida and at the 2008 Alaska Marine Science Symposium in Anchorage.

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 of temperature and salinity 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 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 either from the NODC data archives or Data Management at Institute of Marine Science, c/o Rob Cermak, University of Alaska, Fairbanks, Alaska 99775-7220. 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 might 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.

 

Data Plots:

Mooring Time Series:

GAK1 Long Term Time Series:

>> May 2007 observations show we have had an anomalous spring and summer... the temperatures and salinites lie outside of the long-term month of May standard deviations and from March-October 2007, the deep waters are on average colder than any year since the early 1970s. See below for additional plots. Profiles from September and October 2007 indicate that the anomaly has not advected away from and the temperatures remain low near the bottom.

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).

Related data and plots: We present Sitka air temperature anomalies with a 5 year butterworth filter and fresh water discharge into the Gulf of Alaska, monthly discharge anomalies, and monthly discharge means. 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.

View of Cape Aialik, to the soutwest of GAK1.

Publications Employing the GAK1 Time Series:

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

Contacts:

 

Thomas C. Royer
Eminent Professor of Oceanography
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

 

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

Last update 2 July, 2007