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Keep up on What’s Happening on the Alaska Fisheries Science Center
Arctic Cruise in August


Throughout the month of August, Jessica Randall, part of the Fisheries Oceanography Coordinated Investigations (FOCI) program with the Alaska Fisheries Science Center, will be sending dispatches from the NOAA ship Ron Brown. The ship is conducting surveys in the U.S. Chukchi and Beaufort Seas to obtain baseline oceanographic data. Sampling is also being conducted at hotspots for productivity and biodiversity, known as Distributed Biological Observatory (DBO) sites (for more information see:

This survey, in its fifth year of operations, is part of a multi-institutional effort to improve our understanding of arctic ecosystems.

August 14, 2015 - Gear Profile: CTD (conductivity, temperature, and depth)

Survey tech Mark Bradley and Chief Scientist Nancy Kachel moving the CTD on deck in preparation for deployment during evening snow flurries near Barrow Canyon.

Arguably one of the most important instruments in an oceanographer’s toolbox is a CTD. Although the acronym CTD stands for conductivity, temperature, and depth, other sensors are often attached to gather more data such as pH levels and fluorescence (measure of primary production or algae life). For oceanographic cruises, this device is mounted in a large metal cage, usually housing 8-36 bottles used to collect water samples at different depths.

In a standard deployment, the ship hovers on station as the instrument is lowered to within a few meters of the ocean floor while a cable connecting the instrument to the vessel provides real-time data to create a profile of the water column. This is known as the ‘downcast’. This signature then allows a researcher to select where to collect water samples – either at fixed depths or at those of particular interest (such as a chlorophyll maximum).

From the water collected, a variety of samples can be collected depending on the size of the bottle to help inform oceanographers about the chemical make-up of the water column. For our work, nutrients, chlorophylls, and salinity samples are collected. These profiles are also used to help identify currents, different water masses, and study ocean acidification.

Fun fact: CTD’s have a water intake tube that allows them to create the water column profiles. Sometimes jellyfish tentacles get sucked up. When this happens there is often a sudden change in salinity values that, to the trained eye, is the telltale mark of a jellyfish.

More information on CTD’s can be found at:


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