Northwest Fisheries Science Center

The Main Deck

Acoustic and trawl adventures in the Northeast Pacific

This portal tracks the research and sea-going activities of the Fisheries Engineering and Acoustic Technologies (FEAT) Team from NOAA¿s Northwest Fisheries Science Center.  Follow us as we use acoustics, trawling, and oceanographic sampling to learn about the Northeast Pacific Ocean.

Back deck of Bell M. Shimada
Acoustic echogram of hake
trawl catch

Salinity and variability

By Sandy Parker-Stetter, NWFSC
January 24, 2017

While hiding from the weather, we did a calibration of our echosounders near Sausalito, CA (which isn’t far from the Golden Gate Bridge). Before and after the calibration, we did casts with the Conductivity-Temperature-Depth (CTD) rosette, and the data were very different than from the open ocean a few days earlier.

Salinity at depth

“Saltwater” is typically defined as water with salinities (i.e. dissolved salt) of ~30 to 35. Data from the Pacific Ocean near Bodega Bay (north of San Francisco) are shown as an example. The rightmost line (dark gold) is from an offshore station with a bottom depth of 150 m. Here, the water has a uniform salinity of 32 down to 20 m below the surface. The next line in (light gold) is from a station that was closer to shore with a bottom depth of 60 m. At this site, water within 12 m of the surface is slightly fresher than the water below.

Our anchorage outside of Sausalito was “brackish,” often defined as having salinity levels between 0.5 and ~29. The two casts from near Sausalito are shown in blue. The large differences between the surface and 20 m (differences of 20 and 15) indicate that the surface waters are fresher than the water below, likely due to river and/or stormwater runoff. Another interesting note is that the two casts are quite different from one another, likely influenced by tidal cycles.

Many lakes and rivers are “freshwater” and have salinity values <0.5. As an example, I’ve shown data from Lake Washington in the figure (leftmost, in red). Salinity levels are <0.1 from the surface down to 20 m.

Now that the weather has dropped, we’re heading out of brackish and back into saltwater!

Tagged: Hake, Acoustics, Winter hake research, FEAT, FRAM, Oceanography, Ecosystem, California Current Large Marine Ecosystem, CCLME, El Niño, La Niña, Climate

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