2012 Shelfwide Cruise: July 22 - July 28

With so much rain, it is hard to remember that we are in a drought. And by we I mean, pretty much the entire United States. As a result, river flow from the Mississippi River this year is low, really low, and a few days of rain in Cocodrie, LA will not to change that. This year, the flow rate from the Mississippi River is well below the roughly 80 year (1938-2011) average flow and is hovering right above the minimum flow for that time period.

River flow from the Mississippi is important, as it is a critical determinant for hypoxia and the size of the Dead Zone. The river flushes nutrients into the Gulf, sparking phytoplankton blooms. These provide the organic matter to fuel oxygen consumption in the bottom water. The fresh water itself is also very important. As fresh water is less dense (i.e., lighter) than salt water, when a large amount of fresh water enters the Gulf it will stay above the saltier water effectively partitioning, or stratifying the water column. Under these conditions, the oxygen rich surface water is not able to mix down to the oxygen depleted bottom water and hypoxia occurs. Without the river input this spring and especially summer, the Gulf may have a bit of a reprieve from hypoxia, and we're all gripping the wheel tight, waiting to see how much.

Occurrences of hypoxia have so far been sparse, mainly closer to shore, and we will just have to wait and see what the regions to the West have in store for us.

Along the Shelfwide Mapping Cruise, we examine several different gradients: East to West, offshore to inshore, surface to bottom. East to West, allows us to examine the reach of the Mississippi River outflow as it enters the Gulf of Mexico and moves west hugging the coast. Similarly, inshore to offshore provides the perspective of deeper, offshore stations, closer to slope waters and shallower inshore stations more impacted by the Mississippi River and other tributaries. Surface to bottom tracks from the fresher, warmer, more oxygenated surface waters down to the saltier, cooler, and more oxygen poor waters.

Tonight the night shifters sampled the length of the D-transect marveling at the differences between the sites on this transect and previous transects. Starting offshore we saw deep, deep blue waters so clear we could watch the rosette of Niskin bottles as it descended several meters below the surface. We were greeted by schools of fish, jellyfish, needlefish, a shark, and a very small flying fish in these offshore waters. Closer to shore, the water took on a greenish hue from high chlorophyll levels; laughing gulls and oilrigs surrounded us. The brilliant green of these inshore waters are a stark contrast to the brown murky waters to the east in previous transects, closer to the river outflow, full of suspended solids. In such a way, even without looking at the data we can see the differences between regions in the Gulf.

For others, monitoring the system in both hypoxic and oxic environments adds variability that teaches us more about what drives the system such as with the sampling of water column chlorophyll and nutrients, carbon dioxide exchange between the air and the sea, light attenuation through the water column, and carbon cycling from inorganic to particulate forms.

One study in particular on the cruise actually benefits from the almost universal presence of oxygen, the study of aerobic respiration. Respiration referring to the process of metabolizing organic matter, and Aerobic referring to the use of oxygen in this process. This is what we, humans (as well as kittens and ponies, etc.), do we break down organic matter (i.e., our food) using oxygen in the process (why else would we breathe it in?)

The Roberts laboratory from LUMCON is examining how aerobic respiration varies across the gradients of the cruise East to West, inshore to offshore, and surface to bottom. In addition to examining how respiration changes, his lab is also examining potential drivers of respiration including different forms of organic matter (dissolved and particulate) as well as nutrients in the water column. Respiration is an important part of the hypoxia puzzle, as it is the process that ultimately draws down oxygen in the bottom water under conditions of stratification.

Though we previously had thought that we would sample only out to the K-transect, if we find hypoxia in the K-transect, we will continue to sample until we reach the edge of the Dead Zone. So tonight the Night Shifters go to sleep as if it were Christmas Eve, anxious for what we will find when we wake up the next morning(evening?), either the ship heading home, or more sampling to be done.

Other highlights from the night include a school of about a hundred Blue Runners that came into our spot light, attracted by the accumulating plankton, drawn to the light. Numerous acrobatic fish - Needlefish and Flying Fish - were seen jumping out of the water tonight. Overall, however, the number of fauna tonight was much less than we had seen previously in the trip.

Either way, this was the last shift for the Night Shifters. As if the Gulf knew, she bade us a fond farewell by washing a wave over the side of the boat on our last station, flooding all of our boots.

Though we are looking forward to getting back on land and seeing loved ones, we can all agree on things that we will miss from the cruise. A big one is watching the water for fish under the lights at night while we wait for the CTD to descend to the bottom and back up. Tonight we saw a couple Mahi Mahi, several very long needlefish in groups of up to 10, moon jellies, and menhaden. It goes without saying that we will miss the delicious food cooked every night. Less delicious, more intrinsic, we will miss being a part of something so big. These surveys have been going on for 28 years and we wish them a happy 28 more.

As amazing as this rare sighting was, it came with its own dangers. Researchers stipulate that this subspecies was not formed through evolution, rather through a mutating virus (you know...like vampires). Though we were far away from the ship, we were not outside the airborne range of the virus. It took 2 crew members to hold down one of the scientists on board as she came under the influence of the virus. The whole time she screamed, "They have a casino on board! Where are my singles! If I jump over, they have to save me, its Maritime law!" Fortunately, she was not exposed long enough for the virus to have a lasting impact.

[N.B., the editor of the daily log gave carte blanche to the Night Shifters and cannot be held responsible for their actions.]