PS-18-05 Daily Log
May 30, 2018 (Day 1)*
*Note: these will be posted on a one-day delay, i.e., this report is for yesterday’s activities.
We made it offshore!
Thankfully Subtropical Storm Alberto moved quickly through the northern Gulf of Mexico, so we were able to load the vessel yesterday and depart at 0120 this morning. We set a course for offshore waters south of Louisiana to start our search for Sargassum. Conditions were close to ideal; relatively calm seas, clear skies, and an eager science team. While steaming towards our hopeful sampling location, everyone busied themselves with sampling preparations, and started to acquaint themselves with life at sea.
Today was relatively uneventful; however, it was a great opportunity to test equipment and shake off the rust. Here is a short synopsis of some of the day’s activities.
During our transit, we encountered an oil sheen on the water’s surface. We stopped at a location within the slick to collect reflectance data for Dr. Hu’s lab; these data can help determine whether there is an elevated SWIR (short-wave infrared) signal for the detection of oil emulsions. The source of the sheen is unknown. It could have been from natural seeps, of which there are many in the Gulf of Mexico. Another possibility is leakage from unplugged wells of a platform toppled by Hurricane Ivan in 2004, which was in the vicinity of our sampling area. After a brief stop to collect reflectance data, we resumed our course.
Much of the day was spent heading south and west in search of “blue” water, which we encountered at approximately 1600, along with a few sea turtles and whales, and finally–Sargassum! While happy to find Sargassum at last, there were no large mats or weedlines, but rather scattered clumps and pieces spread throughout convergence “slicks”. We decided to not collect Sargassum here, as there were no features large enough to sample, and continued further south to approximately 28° N, 89° W where we decided to sample an “open water” station. Reflectance measures were taken, as well as water samples and a CTD cast. We were admittedly a bit rusty, having not sampled in a year, so our first neuston attempt had to be repeated. The second attempt went very well.
Then came the big test, trying out the frame trawl sampler for the first time. The net and frame went in the water smoothly, and we trawled just under the surface of the water at approximately 3.5 knots for about 20 minutes. Some clumps of Sargassum were collected, along with a large juvenile Jack (Carangid species), along with a number of eel leptocephalus larvae, and other larval fishes and invertebrates. This was a great first attempt, and we’re excited to use this gear for the remainder of the trip.
All in all, not a bad day on the water. We did not sample a full day and large Sargassum mats, but we are confident we are in the Sargassum neighborhood, and hope for better success tomorrow.