Environmental Drivers Overview

Gulf of Alaska Mooring (GAK1)

Researchers take samples and change instruments at the GAK1 mooring site. Photo courtesy of Seth Danielson.

Who We Are

seth_danielson

Seth Danielson, University of Alaska Fairbanks

 Tom Weingartner, 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 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 force changes in oceanographic conditions.

Where are we sampling?

The mooring is located at the mouth of Resurrection Bay in the Gulf of Alaska and is the first station of the Seward line oceanographic survey sites transect.  The location is 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.

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 on an opportunistic basis by “ships of opportunity,” which were primarily research vessels as they left of 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 monthly basis from locally-operated vessels , a 26’ vessel usually a single CTD (conductivity, temperature, depth) cast to profile the water column from the surface to within 10 meters of the ocean bottom.

What are we finding?

The 45-year record at GAK1 shows great variability in Gulf of Alaska shelf temperatures and salinities, which hides longer term trends. In the 1970s, ocean temperatures were cold and salinities high, but from the 1980s through the early 2000s temperatures warmed and salinities decreased. Between 2008 and 2012 temperatures cooled, but this trend ceased beginning in 2013 and, based on 2014 data, appears to be reversing. Over the 44-year record, temperatures in the upper 100 m of the ocean have increased by ~0.8 °C and salinities have decreased by ~0.2. In deeper waters, between 100 and 200 m, temperatures have increased by ~0.8 °C and salinities have increased by ~0.1. The upper ocean changes coincide with warmer and wetter winters and increased precipitation, glacial melting and evaporation, and coastal freshwater discharge.

The measurements taken at GAK1 may have implications for the animals and plants living within the shelf ecosystem. Increased runoff implies a decrease in essential nutrients for phytoplankton, leading to reduced ability for plankton to grow. Since phytoplankton are one of the greatest consumers of carbon dioxide, factors that affect their growth will also reduce the overall global use of carbon dioxide and lead to greater ocean acidity. The increase in water column stratification implies that vertical mixing may be limited, also reducing plankton growth. The trend toward warmer and wetter winters suggests that the spring plankton bloom on the shelf may be occurring earlier than in the past. The combination of these changes may alter species composition and the efficiency by which carbon is passed up the food chain .

THIS FIGURE SHOWS THE TIME SERIES OF MONTHLY TEMPERATURE (IN CELSIUS), SALINITY (PRACTICAL SALINITY UNITS [PSU]), AND DENSITY (SIGMA-T IS A MEASURE OF THE DENSITY OF SEAWATER AT A GIVEN TEMPERATURE) ANOMALIES (DEVIATIONS FROM THE TIME-SERIES MEAN) FROM 1970 TO CURRENT. MORE INFORMATION CAN BE FOUND AT: http://www.ims.uaf.edu/GAK 1/.