2013 Shelfwide Cruise: July 21 - July 28

Once away from the mouth of the river, we started as usual on the inshore side of transect A'. And, the first station is always one of the longest while we get things straightened out. Hypoxia was extremely low at the two inshore stations less than 10 m deep, but further offshore to a depth of 50 m values ranged between 2 and 4 mg/L. Don't give up the ship yet.

For the next 7 days, the R/V Pelican will be home to 13 scientists and 7 crew members as they map the extent of the low oxygen area, a.k.a. the "Dead Zone" along the shelf of the Gulf of Mexico.

Sampling will take place from roughly the Mississippi River delta to Galveston, TX. In order to survey this area, the boat will travel night and day along consecutive north to south transects, similar to how one would mow a lawn.

The size of the Dead Zone varies each year depending on several factors. Dr. Turner from LSU, present on board, has been able to predict the extent of the low oxygen area using a relationship between two factors, Mississippi River nutrient load and river flow.

These factors reflect the dominant mechanisms that cause the Dead Zone. Elevated nutrients increase phytoplankton (one-celled plants) growth in the water column, again think of lawn care and fertilizer application. High riverflow stratifies (layers) the Gulf of Mexico with warm fresh water on the surface and cool salty water on the bottom. When the phytoplankton die and sink to the bottom, the bacteria that consume them breathe in oxygen in the process. Under stratified conditions the bottom water is not re-aerated by surface water and the bacteria decrease the oxygen concentration in the bottom water - think James Bond in a bank vault. The result is low oxygen in the bottom water, concentrations below 2 mg O2/L are considered hypoxic.

Every year presents unique circumstances, however, as tropical storms with their high winds can mix the water column, breaking up stratification and re-aerating the bottom water. These tropical storms also make for a very exciting boat ride for the scientists and crew.

So far we sail with calm seas and a full moon to guide our way; but are ever on the alert for what the dynamic ocean may bring. Stay tuned on the blog for tales of our adventures on board. We are excited for you to join us along the way.

~The Night Shifters.

Moving on to transect C, we expected at least some hypoxia in the 10-20 m range, but no. Values in the range of 3 to 5 mg/L from 30 m offshore to 10 m inshore. There is always transect D'.

There are many different types of platforms in the Gulf, both manned and unmanned. The one we approached was a manned platform that we affectionately call "C6C," really for no better reason than it comes right after C6B in the C-Transect. The station is particularly important, however, as the Rabalais lab attaches sensors that continuously measure water column parameters to one of the platform's support pilings.

C6C is a massive platform with dorms for workers to live in as well as a helicopter pad. Though we all kept an eye out for Bruce Willis hitting golf balls off of the helicopter pad, he was nowhere to be found. There were some other workers out on the deck though as our boat approached and we waved a hello. Again, no Ben Affleck out there either, sigh.

In addition to C6C our sunset vista included oil rigs dotting the sky line, surrounding the boat. Just a subtle reminder of the delicate balance within which humans and the Gulf live; like that neighbor who always comes over to borrow something, or whose kids are perpetually chasing your cats.

After murmurs through the last few days as to the state of the bottom oxygen, namely that there was so much of it, hypoxia abounded during tonight's shift. Not only was this seen on the real-time output from sensors at depth, but also in the fauna at the surface.

At several stations, bottom dwelling lesser blue crabs (Callinectes similis), and in one case a benthic eel, were seen on the surface. These critters are not normally seen in surface waters, but likely came to the surface searching for oxygen-rich water. Being able to move away from low oxygen areas is a luxury only mobile species have. Some species, however, are not mobile and instead find themselves stuck in the mud (pun intended).

Another new sight for the Nightshifters was clear blue waters. Transects now take us into deeper, offshore waters. With these clear waters, we were able to see the rosette sampler for several meters as it descended down through the water column. Much further than in the murky green-ish, brown waters closer to the river delta and the coast.

We were welcomed into this new realm by flying fish, needlefish, schools of squid, and a pod of dolphins. We have been very hopeful that both the full moon and boat lights would help attract sea fauna and are very excited for what the rest of our blue water encounters will hold.

One of the favorite tasks at each station is to visual survey the surface waters near the boat for flora and fauna, while we wait for the rosette sampler to descend (sometimes over 50-meters!). Not only is this a lot of fun, but it also serves as an important aspect of data collection. By noting what critters are on the surface we can help characterize what is going on in the water column. Tonight we saw squid, needlefish, Sargassum seaweed, flying fish, AND a "chicken dolphin."

A note on "chicken dolphins." Neither a chicken (bird) nor a dolphin (mammal), this beautiful, brightly colored creature is small Mahi Mahi (fish). "Chicken dolphin" is its local nickname. We saw individuals at several stations and they were very active, zipping around the boat and leaping out of the water.

The seas began to calm early afternoon and we are at 1 to 2 ft now.

We've been seeing large rafts of Sargassum weed during the day when we were out of the turbid coastal current.

Box coring was finally a success at stations I3 and I4. This area had been cored between 1989 and 1997 for various projects and station I3 had an accumulation rate of 0.41 cm y-1. Box coring on transects B and C was unsuccessful, and was not attempted along transect A because the area was disturbed by Hurricane Katrina in 2005. The new cores will be split so that material for dating the core and for conducting dinoflagellate cyst analysis could be from the same horizons. Additional measurements representing indicators for increased productivity or worsening hypoxia will also be made. The dinoflagellate work will be done by a Ph.D. student, Andrea Price, from McGill University (a student of former LSU colleague, Dr. Gail Chmura).

In honor of our flying friends we dedicate this blog post to flyingfish. Check out the photo gallery for a flying fish photo!

There are over 50 species of flyingfish, living mainly in the tropics and subtropics. Eight of these species live in the Gulf of Mexico. Some flyingfish species are monoplanes with just one set of "wings", only their pectoral fins (just behind their head) are enlarged. Other species are biplanes with two set of "wings", both the pelvic and pectoral fins are enlarged. We have seen primarily monoplanes at our stations, with a few biplanes.

Please note here that the use of the term "wings" is more for a mental image of the fish rather than a functional description. Flyingfish do not flap their wings like birds, but instead glide through the air. To take flight, the fish accelerates to top speeds using its tailfin and as its body leaves the water, it spreads its large pectoral fins. It then gains lift using winds, or updrafts from waves. This take off process is similar to an airplane taking off as it speeds down the runway.

Flying is an important predator avoidance mechanism for the flyingfish. Flyingfish are an important food for several speedy predators including dolphin, tuna, and billfish, as well as slower predators like humans. Flyingfish are actually a delicacy in Barbados where they are the official national fish, the author has dined on flyingfish in Barbados.

Flyingfish are predators themselves, feeding on small fish and crustaceans in the surface waters. They are further connected to the surface ecosystem as they lay their eggs in mats of Sargassum, a type of seaweed named for its prevalence in the Sargasso Sea. We also saw lots of Sargassum at the blue water stations this evening where we saw the flyingfish.

I know an entry discussing lush life in the surface waters seems a bit odd for a blog about a cruise mapping the "Dead Zone" on the bottom. But it serves as a reminder of the delicate Gulf ecosystem and the importance of its protection. On our cruise, we seek to not only describe the extent of the Dead Zone, but also to gain a better understanding of the mechanisms behind its formation. I doing so we can learn how to better protect the Gulf as an amazing natural resource.

Our journey to map the extent of the Dead Zone has taken the R/V Pelican across Louisiana, the sportsman's paradise, into Texas, the lone star state. We could tell when we crossed the border into Texas as everything seemed a bit bigger, particularly the waves. The entire way across Louisiana we had 1 to 2 foot seas (liar, liar pants on fire; day shift had seas up to 5 ft), and once we entered Texas waters, the seas increased to 3 to 4 feet.

In actuality, what we encountered was a cold front coming down from the Midwest, moving east across the western upper Gulf Coast to Louisiana. By Sunday the weather, and waves, should calm down.

With the ship rockin' and rollin' the Nightshifters frantically scurried around securing equipment. Additionally with the increased seas, ordinary things have become very exciting, like getting a glass of water, or walking to the bathroom. Our greatest sympathies are for the cook, trying to make us breakfast under these conditions.

The remainder of the day was spent heading east to the vicinity of transect D' for re-occupation of some stations there and likely to transect C for some resampling. The time to steam from J5 to D'3 is about 14 hours, but closer to port. We know that the dissolved oxygen at station C6C has fallen from 4.8 mg/L on 22 July to less than 2 mg/L on 27 July, and we may re-occupy the transect.

Our not so peaceful summer seas were further disturbed with a cold front moving in early this morning. It is chase us as we headed east. Prediction is for increased sloppiness today.

Great news on oxygen probes. The Winkler titrations (full range from near zero to over 8 mg/L) were a perfect match for the SeaBird primary DO sensor. The YSI 6820 readings were over by 0.1 mg/L, which is within range. However, a correction to the YSI DO data was made for developing the bottom-water hypoxia map, which basically remained unchanged.

I'VE GOT THE NUMBER. Shhhhhh.....

Amidst large swells and driving horizontal sheets of rain, the Nightshifters battled their way through their last shift. The sea was angry last night, my friends, but science does not wait for sunny days or fair weather. It was as if we had trained all week for this shift, gaining our sea legs, and perfecting our sampling techniques. What a great way to say goodbye to the Gulf.

As we finish our shift, the Nightshifters cannot help but start to feel like scientific summer camp is almost over. On this last nightshift we take a moment to reflect on the wonderful adventures we had on this cruise. From the delicious meals served by the cook, to the interesting fish observed, and the great research that was conducted, this was a great cruise.

Though the cruise ends tonight, it will leave lasting impressions on all of us over the next several years as we process samples, and sort through data to tell the story of the Gulf in 2013; part of the greater story of the science of the Gulf shelf, 29 years in the making.

Thank you to all of the blog followers. It was a pleasure to once again take you along with us to map the Dead Zone.

Sincerely yours,

The Nighshifters

D'3 and D'2 were not hypoxic, but similar to the values earlier in the cruise. So much for intuition. But Nancy's intuition was correct as we worked transect C from C9 to shore. C8 and C9 were lower than earlier in the week and C7 was hypoxic at 1.8 mg/L. Hypoxia continued into the shallower waters for the remainder of transect C. This will change the map and the overall bottom area estimate of hypoxia some but not by much.

Dock at 2 pm. End of the 2013 shelfwide cruise. 29 years.