HypoxiaIn the Northern Gulf of Mexico
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Daily LogsDay One17 July 1600 Load ship, calibrate SeaBird CTD for oxygen, depart dock at midnight 0900 Collect series of salinities from 23 to as low as possible, 3 psu, for nutrient gradient 1130 Arrive station A’1, strong oxycline near bottom at 8 m, 0.5 mg/L 1230 Depart for next series of A’ transects 1600 Depart from end of A’ line to head to A7, southern end of A trans 1800 Jenn and Sam see a shark Very low oxygen across most of the trans A, mostly less than 0.5 mg/L 2100 Blue crabs, Callinectes similis, both ovigerous females and males swimming at surface of the water avoiding low oxyen near the bottom 0.1 – 0.2 mg/L 2300 Nearshore station mixed; depart trans A to trans B, inshore end Day Two19 July 0100 New day, new transect, low oxygen Several jellyfish, Quinquecira quenqueloculina (?) in subsurface water Some blue crabs, C. similis, at the surface 0200 A bit farther SE on trans B. Lots of sea nettles in the water. Smaller portunid crab at the surface. Low oxygen below. Small shark at B4; paired unidentifiable fish. 0400 Large needlefish at surface, B6. 0700 Low oxygen out to B9, almost 40 m Thunderstorms as cold front approaches 0730 Out to B10, 50 m, just on edge of low oxygen, 1.92 mg/L Close it off at 57 m 0800 Start on SE end of trans C, working towards shore Hypoxia not as extensive in deeper waters on trans C. 1500 Within 25 m contour, hypoxia on trans C, 0.9 at C7 1600 *Station C6C* and successful box coring at C6B, Jenn for foraminiferans and Ling for diatoms 1900 Station C4 with close to anoxia. Successful box coring Jenn has samples for foraminiferans at a station not normally this low in dissolved oxygen Crew change for scientists 2100 Nearshore, north end of trans C in 5 m, normal oxygen. Headed to D’1 2300 End of day, low oxygen Day 3
20 July 0000 Happy Birthday Melissa, wish you were here! Headed offshore on trans D’ 0200 Severely low oxygen on many trans D’ stations, 0.2 mg/L from 15 m to 30 m. Benthic eel, portunid crabs, and penaeid shrimp swimming at surface 0300 Still headed south, hypoxia now deeper than 30 m 0400 Out of hypoxia in 45 m water, headed west to trans D 0700 Station D5 on south end of trans D barely above 2 mg/L 0900 Arrival of Canadian Broadcast Corporation, Jackie Corkery, producer, documentary series, film and sound crew, for the coastal ocean portion of a 4-part series on the ocean. Landed at D3 via the R/V Acadiana 0930 Just in time to film box coring All other stations on trans D until beach station below 0.5 mg/L, several with hydrogen sulfide in the bottom water 1500 Close off trans D in 5 m with 4.6 mg/L Headed to E1 off Marsh Island 1800 Start nearshore on trans E 1900 Canadian Broadcast Corporation crew departs on the R/V Acadiana 2100 Little hypoxia so far on trans E, box coring on trans E, repeat E2A from 2008 2335 No hypoxia on trans E but consistent with SEAMAP contours from couple weeks earlier Day 4
21 July 0000 Headed west to offshore end of trans F, normal bimonthly transect 0100 Looking similar to trans D, well-mixed down to 12 to 15 m Could this year be similar to 1998 when persistent winds from the SW pushed low oxygen mass to east in deeper water? 0250 Continuing trans F with bottom oxygen levels of approx. 4.5 mg/L Marine forecast was wrong, sustained winds to 20 kn, seas up to 4 to 5 ft 0400 Continue with no low oxygen and high winds and seas 0600 Very thin lens of low oxygen at F2 and F1 off the Atchafalaya area 0800 F0 just near the Atchafalaya Bay/Gulf intersection [N.B. hypoxia in Atchafalaya Bay earlier: 16 July 2009: Dr. Brian Roberts, LUMCON, reported extremely low oxygen concentrations within Atchafalaya Bay below 1 mg/L, including F0. Several supersaturated surface waters.] 1030 Begin trans G through day to G6. Calms down for day crew. Only one station below 2 mg/L 1800 Head west to offshore end of trans H in 30 m 2000 Begin trans H on offshore end in 35 m. 2200 Seas rough up for night crew, 17 kn from south, 4 to 5 ft Day 5
22 July 0130 End trans H on inshore end in 8 m, no hypoxia, as low as 2.4 mg/L
Depart trans H and head to inshore end of trans I, still rough, mixing shallower waters
0300 Trans I seems to be well-mixed as well. No wonder, persistent 17-20 kn winds with 6 ft swells. Again, a gift from the sea goddess for the night crew.
0700 Well mixed nearer shore, but thin layer of hypoxia begins in 20 m out to 30 m
1245 Into deeper water on trans I (31 m) and out of hypoxic zone
Transit to offshore end of trans J
1500 Offshore end of trans J in 3 mg/L
1830 No low oxygen so far on trans J, seas calm down for night shift, finally!
2100 Sta J4, no low oxygen, box coring for forams and diatoms, 3 for 3, plus one to grow on.
2400 Finished with trans J, no hypoxia, headed west to trans K, inshore end Day 623 July 0130 Begin inshore end of trans K in 6 m depth off Cameron LA 0330 Midway on trans K, no low oxygen.
0730 End of trans K, no low oxygen
0800 Head to trans off Sabine, TX/LA border to finish out grid and look for any remnants of hypoxia from earlier in month and late June
0900 Offshore end of trans M, no low oxygen
1700 Inshore end of trans S northeast of Galveston, no low oxygen; finish off grid and look for any remnants of hypoxia from earlier in month and late June
2130 End of trans S, no low oxygen
2200 Heading to port, Cocodrie, numbers being calculated and explained and compared.
P.S. This is the end of our SILVER ANNIVERSARY cruise. The first shelfwide cruise was in 1985. Three participants from that cruise are on board for this cruise, Nancy Rabalais, LUMCON; Jim Lee, LSU; Sam LeBouef, LUMCON. Gene Turner from LSU was also present on the summer 1985 cruise.
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