Storms and strong currents end Slope Sea operations

The Slope Sea portion of this cruise ended a little early due to storms and strong currents, but will provide important information on this poorly understood region of the ocean.  We did not complete our entire planned cruise track for the Slope Sea, but we did complete 84 stations in the northeast for a total of 133 bongo and CTD tows and 13 water casts.  The bongos will be used for our plankton analyses, including our hunt for bluefin tuna larvae.

Plankton sampling continued to catch scombrid larvae, including a few more potential bluefin larvae. We never hit a large enough patch to justify releasing drifters. We will save the drifters for another cruise that leaves in two weeks for the Slope Sea.  The water samples from the water casts will be sent off for dissolved inorganic carbon (DIC) and total alkalinity analyses. Both DIC and total alkalinity are used by chemical oceanographers to estimate pH of the water, and examine current ocean acidification conditions of the ecosystem. The basic hydrographic data collected (temperature and salinity by depth) will be used to define ocean features in the Slope Sea and to help ground truth satellite data.

little tunny larvae.jpg

Picture of a recently caught 8-mm long little tunny (Euthynnus alletteratus) larvae.  Larval scombrids eat other larval fish, as seen by the larvae in the stomach of the little tunny / bonito.  Photo credit: Ciara Willis, Dalhousie University

washing down bongo nets

Ciara (front) and Chris (middle) wash down the bongo nets as ENS Fuller (back) prepares for a water cast.  Photo credit: Harvey Walsh, NOAA/NEFSC.

Weather and sea conditions required an adjustment to our planned cruise track, moving inshore one evening when winds and seas along the Gulf Stream made bongo sampling difficult.  We normally send the bongo down to 200 meters deep ( about 660 feet), and use about 280 to 300-meters of wire, and still could not get the net to that depth.  On the final tow of the evening, we deployed over 400 meters of wire and still could not get the net below a depth of 150 meters ( about 480 feet).

Like flying a kite on a breezy day, the current was pushing the net up with too much force or lift to overcome with our standard weight.  The ship’s bridge and crew were safely able to deploy and tow the gear, but the sea conditions wouldn’t allow for us to collect samples that we could compare to all the others we had collected. After we moved inshore to escape the strong current, we continued to see a highly diverse plankton community in the waters just offshore of our standard sampling locations during EcoMon.

plankton in bogo sample

Plankton collected in a bongo sample about 30 miles north of Cape Hatteras, North Carolina.  The sample had squid paralarvae and fish larvae including: common dolphinfish (Coryphaena hippurus), shoal / dusky flounder (Syacium spp.), and unidentified gobies (Gobiidae).  Photo credit: Ciara Willis, Dalhousie University

Even though we moved inshore, we could not escape the thunderstorms that were moving through the area. We had suspended operations at a station just north of Cape Hatteras due to lightning in the area. Have you ever wondered if lightning strikes the ocean? A few minutes after we arrived at the inshore station there was a very close strike, or the ship was struck by lightning ( it depends on who you ask).  Everyone on board was safe, but we lost gyros and some other electronics.  We steamed on to the next station, the second to last scheduled for the northeast part of the cruise, as the ship’s Electronics Technician (ET) began repairing systems.  We discovered that the CTD would not talk to the computer when we resumed operations at the next station. Wherever the lightning hit, our science gear did not escape the damage.

We decided to move down to the southeast shelf, south of Cape Hatteras, North Carolina, to escape the marginal weather, and the unknown amount of time it would take to diagnose and fix the CTD problem.  Thankfully, the CTD was repaired on the transit south thanks to the persistence and skill of Betsy Broughton (NEFSC scientist) and Kirk Andreopoulos (ET on the Gordon Gunter).  We will continue to explore poorly understood parts of the western Atlantic during the second half of this cruise, this time in the waters off the southeast United States coast.

Check back on to read about what and why we are studying the ocean south of Cape Hatteras, North Carolina.

Harvey Walsh
Chief Scientist
NOAA Ship Gordon Gunter  GU 1702

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