Thursday, March 15, 2012

Trophic BATS: Post # 3 (Day 1)

This is a good sign. There is a BBQ on our ship’s back deck. March in the North Atlantic around Bermuda still brings about periods of rough weather. Oceanographers may refer to this period as winter mixing, where strong winds sweep away surface waters, encouraging mixing with deeper water masses. This is important because these deep waters are nutrient rich which provide the elements required for phytoplankton growth. However, Today there is no such sign of any winter mixing. The weather is calm, with winds blowing between 5-10 knots and the sea swell reaching about 4-6ft. We would be lucky to have three days like this at this time of the year. Right now, we are staring at a solid week of nice weather, which is great news for any cases of motion sickness, but more importantly the ability to get our work done efficiently and with safety. Science operations cease to exist on a variety of factors, but typically when winds begin to hit over 40-45 kts and the sea state reaches over 15ft, we enforce a mandatory break from science. So, this mentioned BBQ is great tidings for good weather and delicious food. And I don’t believe in jinxes.

Four hours ago, our main engines were shut off once we arrived to our first station, just seven and a half hours after departing from Bermuda. Our first sediment trap array is in the water (and will be for almost 4 days) and now zooplankton tows are under way. Here, at 32o 49’ N, 63o27’ W, we will remain for about 4 days.

The research team is addressing almost all aspects of the open ocean food web and their interactions with each trophic level, focusing on the transfer of carbon. Starting with the physical and chemical features of the water, nutrient stocks are measured. Nutrient stocks are the food source required for photosynthetic metabolism in the first trophic level. Autotrophic phytoplankton convert inorganic matter (nutrients) into their own cellular organic matter. This transfer of carbon from inorganic to organic is termed primary production and it is here we start the base of our food web.

From there, hetrotrophic phytoplankton and zooplankton (zoo = animal, phyto = plant, plankton = general locomotion dependent on water movement) may graze on primary producers. Zooplankton of larger size classes will feed on those smaller, thus putting them at a higher trophic level. Larger organisms like fish may feed on these organisms, but in the oligotrophic (low biomass) open ocean, like the Sargasso, much of the transfer of carbon exists between primary producers, zooplankton, and the subsequent excretion of grazing by zooplankton. The excreted material/fecal pellets along with grazed cells and broken down zooplankton will now either sink to depth or become remineralized. This sinking of matter from the surface ocean is called export. This concept of carbon transfer from production to export is called the biological carbon pump. Scientists look at the efficiency and the strength of this pump to determine impacts of elevated atmospheric CO2 and the response by phytoplankton to convert CO2 into organic carbon and ultimately if this organic carbon is sequestered to depth.

The significance of this particular research is due to the fact that we are making as many measurements as possible within the same time and space. The measurements such as primary production, export, grazing, nutrient stock and plankton community assessment has yet to be completed in the Sargasso Sea at a high resolution, with multiple replications, within the same short time – frame and water mass. As we’re able to make measurements as close together in time and space, it allows researchers to rely on fewer assumptions when synthesizing raw data into ecosystem models.

Heading this research cruise is Dr. Richardson. Her team will measure primary production by using the radioisotope Carbon -14 to track its incorporation as a nutrient substrate into organic matter. Graduate students Bridget Bachman and Eric Lachenmeyer, both hailing from the University of South Carolina, will lead these measurements. To determine what types of phytoplankton are growing, research technician, Emily Goldman, will filter water sampled from the CTD rosette in collection for HPLC analysis. HPLC analysis measures pigments (pigments convert light energy used in photosynthesis). Specific pigments relate to a specific taxon of phytoplankton.

As I am wrapping up my day (0000 – Thursday), the Richardson group is up deck next. They will begin sampling for their primary production experiments. These experiments will last for 24 hrs. In short, water is collected from the CTD and then spiked with Carbon – 14. Each individual bottle spiked with C-14 will be brought out to the back deck and attached to line that we will be deployed into the water. While attached to the line, these bottles will sit at ambient temperature and available light. 24hrs later, we will recover the floating array, and the samples are processed back in the lab.

So, good night for now and speak with you tomorrow.

Doug Bell
Research Technician, Phytoplankton Ecology Lab
Sediment Trapper

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