2018 Shelfwide Cruise: July 23 - July 30
The 2018 shelf-wide cruise to determine the extent of low oxygen bottom waters on the Louisiana-Texas continental shelf is dedicated to the memory of Dr. Wesley J. Tunnell, Jr. who passed away on Saturday, July 14, 2018, after a long successful and not successful battle with cancer.
- July 23
- Departed Cocodrie dock at 00:01, July 23, with a prediction for “West winds 20 to 25 knots. Seas 5 to 7 feet with occasional seas to 8 feet.” The trip to Southwest Pass of the Mississippi River was fairly smooth with a following sea. Inside the river, it was relatively calm. We were able to obtain a gradient of salinities up the river to about the location of the Pilot House, then re-entered the Louisiana Bight to commence sampling at A’1 and the beginning of hypoxia mapping. This is where we encountered our first 5- to 7-ft seas. Not enough time to get our sea legs on.
We got our “occasional” 8-ft seas along most of trans A’1. Mid-way was a series of thunder storms that chased us around and kept us inside the skin of the ship. At one station we were in near “white-out), right under the lightening, and hail. Finally made our way to the end of trans A’ and west to offshore end of trans A to work our way in on Jul 24. Seas still not helpful to work and getting a good set of DO measures to run Winklers against. Delaying the correction of bottom data. One station on trans A below 2 mg/l.
- July 24
- Jul 24, inshore end of trans B severely hypoxic with hypoxic water well up into the water column. Continued through 20 m depth. These data and next few transects indicate that the strong winds from the west and northwest a few days ahead of the cruise and during the first two days were pushing the hypoxic water mass towards shore and piling it up. Shift over to end of trans C. Finally starting to get calmer seas, but sea legs taking longer to settle down. From 25 m from offshore end of trans C onto the beach fairly severe hypoxia. Trans D’ also hypoxic out to 20 m.
- July 25
- Jul 25, trans D, as with those to the east confines hypoxia to within 16 m from offshore almost up to barrier islands. Calming down. Hypoxic conditions on trans E and F in mid-water depths from 8 to 16 m mid transect. Beginning to see mixed waters in shallower nearshore waters.
- July 26
- Jul 26, moving right along in much calmer seas, almost flat, but no hypoxia on trans G.
Flora and faunal notes: not much, too busy to lounge around. Black flies and green-head flies nearshore, some mosquitos, squid at mid transects in surface waters at night. Most of trans F bottom water chlorophyll filters indicated Cocsinodiscus diatoms in the not-quite hypoxic bottom waters. Trans G surface waters with high abundance of Trichodesmium, but becoming almost crystal clear. Secchi disk depths up to 18.5 m. Late night and early morning of trans F and G, the invasion of the body-snatching dragon flies. H4 a shark follows the Secchi disk down to 15 m, then hangs out under the ship. Or, was it a mahi mahi?, get the fishing pole out to verify!
- The final dissolved oxygen data will be corrected, as necessary, from linear regression with the Winkler titrations over a range of 0.22 to 8.43 mg/L. Initial observations indicate correction, but the f-factor for the Winkler standard remains to be verified. Any corrected data will be reflected in other derived measurements.
- Salinity data not yet verified with PortaSal samples.
- CTD data remain to be post-processed with ALIGN CTD to be applied.
- Instrumentation was calibrated pre- and post-cruise according to manufacturer's specifications and standard method procedures were applied for several variables, not yet calculated, according to several LUMCON EPA-approved Quality Assurance Project Plans.
- Data collected as part of process studies remain to be analyzed and synthesized.
- Final QA/QC'd data will be submitted to NOAA NODC within two years of collection.