Who We Are
Seth Danielson, University of Alaska Fairbanks
Tom Weingartner, University of Alaska Fairbanks
Continuously
measures oscillations here
Season. Year. Decade.
Why are we sampling?
Temperature and salinity profiles in relation to depth have been taken at the oceanographic station GAK1 beginning in December, 1970. This multi-decade time series of oceanographic profile data is one of the longest in the North Pacific for any location. Averages of temperature and density (which is related to salinity) at selected depths show the annual cycle of changes in these two important environmental parameters over the long-term and help scientists understand climatic changes and how these translate into changes in oceanographic conditions.
Where are we sampling?
The station is located at the mouth of Resurrection Bay in the Gulf of Alaska and is the station closest to shore of the Seward Line ecological survey monitoring transect. The site is at 59° 50.7’ N, 149°28.0’W and is located within the Alaska Coastal Current, so the waters it monitors are well “connected” with water shelf circulating over the continental shelf in the Gulf of Alaska.
DEPLOYMENT OF THE CTD INSTRUMENT TO COLLECT SALINITY AND TEMPERATURE DATA CONTINUOUSLY ALONG ITS VERTICAL DESCENT TO THE OCEAN FLOOR, 263 M BELOW THE VESSEL.
How are we sampling?
For the first 20 years that sampling at the GAK1 station occurred, it was accomplished by “ships of opportunity,” comprised primarily of research vessels as they left or entered the port. The frequency of sampling thus varied from several times per month to several times per year. Since September 1990, the sampling has been accomplished on a nominally monthly basis from locally-operated vessels. Today, the primary survey vessel is the 40’ R/V Nanuq, from which a single CTD (conductivity, temperature, depth) cast profiles the water column from the surface to within 10 meters of the ocean bottom. The CTD cast also collects water samples for analysis of nutrients and phytoplankton. A net towed through the upper 100 m of the water column collects zooplankton.
What are we finding?
Data from the 2017-2018 GAK1 mooring is shown below. In the record-length anomaly timeseries for GAK1, the data show that the surface waters warm faster than waters near the seafloor. In addition, the surface is freshening and the waters near the seafloor have an opposite trend, but the latter is just barely significantly different from zero at the 95% confidence level. These trends show that the water column is progressively stratifying over time: a result that carries potentially important ramifications for the productivity of the Gulf of Alaska ecosystem. With only a brief period of waters cooler than average, positive temperature anomalies that began during the marine heatwave starting winter 2013/2014 in the Gulf of Alaska have persisted into 2018 throughout the GAK1 water column at GAK1.
TIME SERIES OF THE 2017-2018 GAK1 MOORING RECORDS. COLORS DENOTE THE NOMINAL DEPTH OF EACH INSTRUMENT FROM SHALLOW (CYAN, 20 M) TO DEEP (MAGENTA, 250 M).
GAK-1 MONTHLY ANOMALY TIME SERIES FOR THE 1970-2019 PERIOD OF RECORD. TEMPERATURE (UPPER TWO PANELS) AND SALINITY (LOWER TWO PANELS) ANOMALIES REPRESENT DEVIATIONS FROM THE SEASONAL AVERAGES OVER THE UPPERMOST AND LOWERMOST 50 M OF THE WATER COLUMN. THE DATA EXHIBIT A LONG-TERM TREND IN WARMING PUNCTUATED BY SIGNALS ASSOCIATED WITH CYCLES OF EL NINO AND OTHER PHENOMENA. BLACK LINES SHOW THE PERIOD OF RECORD TREND. TEXT PROVIDES TREND STATISTICS (BEST FIT LEAST SQUARES LINEAR) OVER THE RECORD LENGTH.
STATISTICS OF THE NEAR SURFACE (0-50M) AND NEAR SEAFLOOR (200-250M) SALINITY AND TEMPERATURE TRENDS OVER THE PERIOD OF RECORD. PARAMETERS INCLUDE THE DATE RANGE, DEPTH RANGE, NUMBER OF DATA POINTS (N), TREND SLOPE (PER DECADE) AND CONFIDENCE INTERVAL, AND THE CORRELATION SQUARED R2 AND P-VALUE FOR THE BEST FIT LINEAR TREND.