Why measure the ocean?

The ocean is essential to everyday life for many who reside in Southeast Alaska. It supports a variety of fishing operations (subsistence, recreational, and commercial), tourism, and is one of the pillars of the local ecosystem. Despite this importance to so many domains, many of the Southeast Alaskan waterways are very rarely directly measured. This makes it challenging to assess what role the ocean has in changes to the health of the local ecosystem.

This program aims to fill this observational gap and take regular measurements of temperature and salinity (how salty the ocean is) at a number of key sites across Southeast Alaska. Over time, we will establish a baseline of the oceanic conditions. Changes from this baseline will provide important environmental context to a variety of topics, such as the fish stock assessments, health of other marine organisms, and even the receding glaciers.

How do we measure the ocean?

Personnel from the Alaska Trollers Association (ATA) are provided with small instruments called CTDs (for Conductivity-Temperature-Depth). These instruments have sensors that measure ocean temperature and salinity, and can be sent down to depths of over 1000 feet. About once per month, the ATA personnel will go to several core sites scattered across Southeast Alaska (see map below) and put the CTD in the water to perform a vertical profile. The CTD measures ocean temperature and salinity continuously over the whole profile, and when it is recovered we can see how temperature and salinity change from top to bottom (see example below).

A map of stations across Southeast Alaska where ATA vessels collect observations

An RBR CTD about to placed in the water to collect a vertical profile.

An example of temperature profiles collected at S6 in Sitka Sound. Warm colors indicate late-summer profiles, and cold colors are winter profiles. Temperature near the surface (0 meters) is very seasonally variable, while it is more consistent at depth.

Who else is involved?

This work also involves personnel from Alaska Sea Grant and the University of Alaska Fairbanks (UAF), who help coordinate field logistics and analyze the data collected by the ATA.

This program was made possible with generous support from Alaska Sea Grant and the Alaska Ocean Observing System (AOOS).