Canary in a coal mine

Close-up of a juvenile shrimp

Today our activities were very H20rientated.  After last night’s, or I should say this morning’s, recovery of the pumps around 2am, activities were pushed back for the day.  The CTD cast for water collection started our day off as usual, to gain a solid profile of the water being collected.  Soon after we deployed the GO-Flo bottles, and just wrapped up the In-Situ pumps before dinner.  After our late night plankton tow, we will be steaming back towards the location of the Lander for recovery tomorrow afternoon. 

We have had a very interesting past few days, where we have done more independent inquiry projects on board.  Before coming out to sea, Wessal and I had the opportunity to pitch proposals we wanted to try out on board.  Currently, we have a redox experiment running with a core sample (more to come on a later post…this one has to percolate for some time), have completed a series of plankton tows in different locations , and are now starting to compare data with what the water casts are showing and what we are finding in our nets.

One very interesting species that was immediately identified by Dr. Will Berelson, is Trichodesmium.  These cyanobacteria, bacteria that utilize photosynthesis for energy, are found in tropical and sub tropical waters that are low in nutrients.  Since we have been out here in the clean Gulf waters away from plumes of any run-off from shore, we have noticed these horse-hair-like structures floating on the surface at a few of our stations.  An aptly chosen nick-name for them in bloom is “sea sawdust.”  Their blooms have been found in ship’s records from as early as the 1700’s.  Tricho are found in oligotrophic waters, meaning they are in areas with very little to no nutrients and are usually hypoxic or anoxic as well.  Tricho are also Nitrogen fixers, they pull the gas from the surrounding systems and process it for their own nutrients.  Blooms in the Gulf of Mexico are commonly observed between the

Trichodesmium spp. found in all of our tows so far

 months of May-September.  The reason for these blooms is due to their need for nitrogenase, the enzyme used to fix the Nitrogen, which requires high levels of Iron to be present.  During these months, there are higher levels of Saharan dust, which is high in Iron, deposited in the Gulf of Mexico due to the air masses bringing it across the Atlantic Ocean from Africa.  We cannot wait to see what we find in our tow tonight, knowing that the largest migration of living organisms happens vertically in the Earth’s waters every night; no, not tourists…plankton!

The other fun exploration was ignited by Jesse Muratli’s observations during core sample processing.  He invited us to come and check out the top of one of the deep water samples, from roughly 1,500meters down.  On the very top layer of the sediment you could see minute, delicate structures that resembled tiny fish bones.  Of course we had to grab a sieve and find out what they were.  Once we got through the clay-like mud, we were left with a mesh littered with little spikes, small snail-like shells, and other small structures that looked like a mini prototype for something from “Little Shop of Horrors”(think: Audrey II).  Through some inquiry on board, and some online-searching, I was able to find that they were the shells from pteropods.  These are also a fascinating bunch.  It turns out they are Molluscs, but they use water saturated with carbonate ions and dissolved calcium to form an aragonite shell.  These “sea butterflies” have a split foot, instead of one solid form like the typical garden snail.  This allows them to “fly” through the water.  They catch plankton for food, and are a

Pteropods from sediment sample

part of the vertical migration that plankton routinely follow every day.

What also makes pteropods fascinating is they are sort of the canary in the coal mine, in relation to ocean acidification.  Due to their specific needs for the situation necessary to form their shells, they can thrive only when conditions are right.  Aragonite, however, is not as stable as other forms of carbonate and too low of a pH (lower equals more acidic) will dissolve their shells.  The “acidification of the oceans” is becoming a hot-button due to the high carbon dioxide levels registering world-wide.  If the systems in place cannot process the carbon in a way that keeps the levels balanced in the ocean, and the carbonate and other ions cannot handle the levels of carbon dioxide in the water, the pH turns acidic.  Pteropods, in their usage of carbonate ions to form their shells, are thought to be credited for roughly 50% of the carbon being removed from the atmosphere.  When they die, their shells with the trapped carbon will sink to the sediments, where the carbon should remain trapped for hundreds of thousands of years.  If they do not reach the bottom, that carbon can be rereleased into the system, which perpetuates the acidification process.  A study published in Science Daily in 2008 suggested that these creatures may be gone from our world in the next 30 years, if carbon dioxide in the atmosphere continues to increase.  The Gulf of Mexico is not acidic, per say.  Dr. Berelson has been checking the pH levels with his water samples, and has not noted any indicators or red flags.  He is measuring the pH as an indicator of fluxes

Copepods from plankton tow, before stained for samples

 regarding the exchanges that occur between the sea floor sediment and the water on its surface; he is looking for precipitated trace metals as a result of hypoxia.

Not to be doom and gloom, but these are some of the realities that you cannot escape when studying things like hypoxia or looking at plankton samples while surrounded by oil rigs.  Carbon will always be released by the ocean’s systems; it is a part of the natural cycle of respiration.  However, if we keep adding a bigger load to a system, without giving it more of a support structure…it might eventually crumble.  Through world-wide studies, even some similar to those you have been learning about on this blog, scientists hope to use data to put together plans of stopping and/or reversing some of these levels that have risen over the years.

Echinoderm larvae

Video of plankton sample taken on a Ken-a-Vision digital microscope