Last week we sailed on the R/V Acadiana to C6C to de-winterize the SONDE attachments only to be stymied by a jack-up rig and increasingly bad sea state. We sailed for three hours, and when we arrived, the water was calm enough to dive, so we suited up. With the first team of divers literally standing on the transom to jump in, a jack-up rig radioed for us to wait so they could post up near our dive site. We waited for two hours on station (incidentally, we could have completed everything we needed to do in that time), with 10-15 kt wind on the water for the duration, and when the first team finally splashed, the sea state was trash. Dive Safety Officer Lora Pride called it all off. These things happen. But there were some good photos, and a video of the scene out there at C6C before we got stopped, so I thought I’d post them. We’ll be out again soon.
Here you’ll see some video of one of the many service helicopters that land on the rig and some of us getting ready on the back of the Acadiana. The sea state is relatively calm at this point, so it would have been perfect timing to dive.
Nancy Rabalais’s team has been able to process some of the data and issued a press release on this year’s bottom water hypoxia. As I mentioned in the last post, the zone of hypoxia was actually two zones, which you can see below. The total estimated square mileage of bottom water at or below 2 mg/L dissolved oxygen was 5,052 square miles/14,785 square kilometers, which is almost three times larger than the goal proposed by the Mississippi River Gulf of Mexico Watershed Nutrient Task Force in 2001 and 2008.
I can provide some additional thoughts with pretty HD video to boot. The eastern stations, as seen in the chlorophyll map, were predominantly green water, with considerable phyotoplankton mass present in the water column. We could observe significant green-colored biomass both on the GF/D pre-filters and the 0.22 µm Sterivex filters. This is also what you see if you are actually in the water, and the video from the green-water CTD cast at station B6 confirms what was seen with the CTD instrumentation and the filters. Convenient, eh? There is dense, murky greenness at the surface. Deeper, the visibility improves as we get below the highest biomass concentration, but towards the bottom, where hypoxia was observed, we again see increased turbidity, but of a different sort. It’s much whiter than that at the surface. On the return trip, considerable marine snow can be seen (along with a jelly or two and other marine invertebrates).
The western stations, as you might imagine by looking at the surface chlorophyll data, were blue water, with very little phyotplankton mass compared to the eastern stations. The cast at station K3 shows beautiful blue water with high visibility (diver’s paradise), but as you descend, you again pick up the whitish turbidity at the bottom layer where hypoxia was observed.
Sterivex filters from this section were light pink, a phenomenon we observed last year as well. The 16S rRNA and metagenomic data will, among other things, help us uncover a bit more about the variant prokaryotic taxa seen in these contrasting zones of hypoxia.
Well, that’s all folks. We’re headed home. We only found isolated pockets of hypoxia found a smaller coastal patch of hypoxia west of the F line. We searched western transects all the way to the P line, which is off the map I posted below in the first update. All in all, Lauren and I collected over 100 samples. It’s going to be an exciting dataset, for sure. I’ll update the blog with higher quality images when I get back, and look for some cool CTD cast videos, brought to you by Mike Henson’s GoPro.
We’ve finished the H transect and are motoring westward to I. As of now, we have observed no hypoxia west of the F line. However Nancy and Gene have described situations in the past where the hypoxia is discontinuous. We will know soon enough. The last couple days have been very calm, with almost glassy seas. It hasn’t been terribly hot either, so all in all, it’s a pretty ideal situation for sampling. Lauren and I have filtered 3-12 liters from the surface and the oxygen minimum at over 35 sites so far. This will be combined with lots of additional metadata being collected via the CTD and other researchers on board.
This morning we’re transiting from the E to the F line. As of now we’ve found stratification and bottom water hypoxia (dissolved oxygen < 2 mg/L) at almost all stations from A, B, and C 6 shoreward, and D' and D 3, E 2A shoreward. Which is many more stations than at this point on the cruise last year. It's not hard to see why. Surface water has been filled with phytoplankton blooms (I've taken to calling it shelfwide Gatorade, because of the green color) and some of my GoPro recordings of our CTD casts (I'll post video when I get back to shore) show marine snow raining down. This is yummy yummy candy for aerobic heterotrophs that will respire the carbon, and in doing so, draw down the dissolved oxygen (DO) in the water. This process will have been going for some time to reduce bottom water DO to hypoxic levels. I'll keep you posted!
Saturday night we shoved off in the R/V Pelican from LUMCON a little after midnight, as per the usual shelfwide cruise routine. We motored eastward through the night and arrived at the southwest pass of the Mississippi River Sunday morning, one of its several engineered mouths. After collecting samples through the salinity gradient a little upriver, we turned around and proceeded immediately to the A’ line. We finished the A’ line last night as I went off shift and Lauren took over and this morning. The A line was sampled through the night more exhaustively, including multiple casts per site and box cores. We’re running 12 hour shifts, 7-7. I’m on in the day and my night counterpart is Lauren Gilles (@GillesLE), a PhD student in Olivia Mason’s (@OUMasonJar) lab who was also my partner in crime last year. We’re significantly ramping up our sampling frequency and this year collecting from multiple depths at each site as well. Right now we’re transiting to the B line. For more information on the shelfwide cruise, head over to the gulfhypoxia.net site on the topic.
Yesterday I joined Jim Lee and Charlie Milan to help them execute sampling for the monthly Barataria Transect, one of Eugene Turner’s projects. His lab has been doing this transect, monthly, since 1994 to monitor water chemistry and some of the biology that occurs across this contiguous estuarine system. Over the years, various other sampling has been done, including work on the Macondo oil spill and toxic algal blooms. They brought me along so I could collect samples at the beginning of the transect in support of our microbial community survey of the Southern Louisiana coastline and our high-throughput culturing activities. I also brought my camera.