First Looks: Winter Oceanography

Dr. Ned Cokelet, a BEST-BSIERP scientist at NOAA's Pacific Marine Environmental Laboratory, has equipped the fishing vessel Aldebaran with oceanographic instruments to measure basic ecosystem conditions, such as water temperature, salinity and phytoplankton abundance.

These measurements, taken simultaneously while fish are being caught, will help scientists to unravel the complex relationships between climatic conditions and fish in the Bering Sea.

How is this done?

The photo at right shows the instrument package (click for larger image). Seawater is pumped from beneath the ship to:

a vortex debubbler that removes bubbles that could throw off the measurements,
a chlorophyll fluorometer that measures the amount of phytoplankton,
a flow meter that monitors the flow rate and detect fouling, and
a thermosalinograph that measures the water temperature and salinity.

Signals are fed to the electronics control box and up to the ship's wheelhouse where a computer records the data.

A first look at temperature and salinity

Bering Sea Temperature, January - March 2008

This map shows the sea surface temperature along the vessel's track. The colder water (less than 2 deg. C) wrapping around the Alaska Peninsula is due to the Alaska Coastal Current (ACC) that enters the Bering Sea through Unimak Pass. The ACC forms along the Pacific coast of British Columbia and Alaska, where it picks up cold, fresh glacial water on its way to the Bering Sea.

We also see warmer water (>2.8 deg. C) north and west of Unimak Pass. That water flowed in from the west along the north side of the Aleutian Islands. It originated farther south in the Pacific Ocean and entered the Bering through passes between the islands. The water is cooler along the northern fringe of the diagram, where it is cooled by wind and sea ice from the north. See a larger version of this map.

Bering Sea Salinity, January - March 2008

This map shows the sea surface salinity along the ship track of F/V Aldebaran. As it wraps around the Alaska Peninsula, the ACC also delivers fresher (salinity <31.5 psu) water as can be seen here east of Unimak Pass. Saltier water (>32.5 psu) northwest of Dutch Harbor has flowed in from the west. The intermediate salinity water between these two extremes results from a mixture between the two water types and also from fresher water from the north on the continental shelf (water depth <200 m). See a larger version of this map.