“Nuts” (pronounced ‘newts!’) in the Ross Sea

My name is Meredith and I am a first year graduate student studying biogeochemistry in the Hansell Lab at the University of Miami (RSMAS). Lucky for me, my first significant research cruise has brought me to a region of the world more mysterious and wonderful than I could have ever imagined!

Terra Nova Bay. Photo Credit: G. McDonald.

Emperors on Sulzberger Ice Shelf near Cape Colbeck. Photo Credit: R. Dunbar.

Sunset over pancake ice. Photo credit: M. Jennings.

Cape Colbeck Emperors checking us out at Sulzberger Ice Shelf. Photo Credit: A. Westman.

However, I frequently have to remind myself that I did not travel all the way to the edge of the world from Florida just for amazing sightseeing! I spend a portion of my time learning from other research groups on board as a crash course in 'Oceanography 101' but I also have my own responsibilities in the lab. Primarily, I collect seawater samples from a device that collects water from great depths (called a CTD rosette) to analyze for “nuts” or nutrients (namely phosphate, silicic acid and nitrate), which are essential players in the biogeochemistry of the Ross Sea.

Biogeochemistry is the study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment. It deals with 1) how biological and geochemical processes affect organic matter and its principle components (carbon, nitrogen, phosphorus, etc.) in the biosphere, and 2) how chemical elements and compounds (such as nutrients) cycle between the living and non-living parts of an ecosystem.

Acting as biogeochemical fingerprints, nutrient distributions can help us explain and characterize properties in the marine environment such as phytoplankton productivity and seasonal turnover of the water column. For example, we expect lower nutrient concentrations in the surface layer because available nutrients have been consumed by phytoplankton to fuel a summer bloom. Below the surface layer, concentrations of nutrients are typically higher due to the recycling of organic material by bacteria and should be similar to the nutrient pool available prior to a bloom. Therefore, we can get an idea of the flux of nutrients during phytoplankton blooms. If none of this is making sense, just think of nutrients available to phytoplankton as fresh chocolate chip cookies available to a bunch of graduate students (and Roberta)...

A schematic of the biological pump in action! Image from Ocean Biogeochemical Dynamics, by Drs. Jorge L. Sarmiento and Nicolas Gruber, used in the marine biogeochemistry course that my advisor Dennis Hansell is teaching us aboard the Palmer.

Analyzing the concentrations and fluxes of nutrients will help us understand the broader picture of the biological pump, which is the cycle of organic matter production, its export from the surface ocean as sinking particles (downward transport), and finally its remineralization (conversion from organic carbon to dissolved CO₂). On board, I have been analyzing silicic acid in seawater using a reaction that produces a beautiful blue color in the presence of the nutrient by adding a few chemicals [an acidified molybdate reagent and a reducing mixed reagent (electron donor)].

This blue acidified and reduced complex displays a max absorbance at 810 nm. Photo credit: M. Jennings.

After letting the blue color develop for a couple hours, I use an instrument called a spectrophotometer to detect the light absorbed by this blue solution to calculate silicic acid concentrations after calibrating the instrument with known concentrations of the nutrient. A similar method using a colored chemical complex is also used to analyze phosphate (performed onboard by Sarah).  Nitrate, the third nutrient we are considering, requires a completely different method for analysis, which we will perform back in our lab in Miami.

Amanda and me (front right) working hard at the spectrophotometer. Photo credit: A. Lee.

The Ross Sea is an extremely productive system, making it a very interesting place to study (if our pictures of the gorgeous views and magnificent animals haven't already convinced you!). Even after intense phytoplankton blooms, the nutrient concentrations are much higher in these surface waters than in many parts of the world. Our proposed work has been very exciting to watch unfold as we are discovering what is happening to the system's biogeochemistry at the end of the productive season. I feel fortunate to be a part of this process and am excited to learn more in the weeks to come!

Party in the ice fort (complete with hot cocoa)!  Photo credit: D. Mucciarone.

–Meredith