Friday, March 23, 2012

Trophic BATS: Post # 12 (Day 10 - Final)

Sunrise shortly before our return to Bermuda.

As we were spooling off the lines I got a rare sensation of dock rock. There are two kinds of dock rock, the first kind is what happens after a cruise in evening – it involves a BBQ and a Karaoke player (and its on a dock). The second kind is the sensation where you still feel like you’re swaying back and forth like you’re on the boat. The ground can interestingly look like seismic pulses, slowly lifting up the ground like periods of sea swell.

Jojo and June spooling off the sediment trap lines from the winch.

We arrived back to BIOS at 0930 this morning and shortly after lunch almost all of our cruise gear was off-loaded. The majority of it was hiked up into the laboratories for inventory before crates and boxes are stored until July. The spooling of the array lines was last on the to-do list and shortly after 1430, the cruise has almost officially wrapped up.

Science party watches the Atlantic Explorer navigating Ferry Reach, where the BIOS dock is located.

Now, some of the science party will take the weekend to relax in Bermuda before heading back to their respective institutions. In just about 4 months, the summer Trophic BATS cruise will commence. 2011 and 2012 were funded for field work, with 23 cruise days each year. In the summer, the cruise will be 13 days and likely, the majority of scientists will be returning for the fun. The scientific plan will be roughly the same: sample cyclonic or anticylonic eddies to determine their differences in food web processes, but ultimately focusing on how carbon transfers from the autotrophic community to export from the euphotic zone.

Once again, let’s revisit our research question.

How does plankton community composition and trophic interactions modify carbon export from the euphotic zone?

Now let’s recap the routes we took to measure each portion of the research question. Hopefully the food web from NASA’s Earth Observatory can put help put it into visual perspective.

First, phytoplankton, the base of the food web, need nutrients to grow. We measured these elemental stocks using CTD casts which gave us physical measurements of the water column (temperature, salinity, dissolved oxygen, and density) by using in-situ sensors. We collected water from the cast to process the chemical stocks such as carbon, nitrogen, phosphorous, and silica in both inorganic/organic and dissolved/particulate forms. Now we have a sense of the substrate in which the autotrophic community converts sunlight and inorganic nutrients into organic matter.

Samplers at the CTD.

To investigate the phytoplankton community structure, we took samples for chlorophyll, pigments (HPLC), and flow cytometry. We can get cell counts through flow cytometry that give us a good picture of the proportions of the dominate phytoplankton in the Sargasso Sea. We also made rate measurements using Carbon-14 to give us an estimate of primary production. One of the future challenges will be determining if these primary production measurements can be sorted using the cytometer to give us taxon-specifc measurements of production.

Primary Produciton/Grazing Array getting deployed.

Now, we have an idea (or will have an idea once all the samples are run) of who’s in the water, how fast they are growing, and what their source of nutrition looks like. From there we move up a trophic level to the grazers. Conducting net tows will give us a measure of zooplankton biomass. With the primary production experiments, micro-zooplankton experiments were carried out as well to measure the overall grazing rate. Separate grazing experiments were made to determine stable isotope fractions of the zooplankton’s food source and then the zooplankton’s organic matter. This will be used to answer the more specific question of who’s eating who. Additionally, DNA analysis of gut content and fecal pellets will be another indicator of zooplankton diet.

Naomi and Molly haul in the zoop net.

This simplified explanation (I didn’t focus on the cycling aspect, which will be absolutely part of the analysis) gives us a general idea of plankton community composition and a few of the trophic interactions. Our sediment traps will hopefully provide us with the answers to how much and what type of organic matter is being exported. The sediment traps will be measured for carbon, nitrogen, phosphorous, thorium, and silica. We also sampled for DNA and pigments in the trap material, giving us clues to the sources of the zooplankton diet, which was converted into fecal pellets and exported to depth.

Sediment traps making their way back on deck.

This research will hopefully provide a quantified model of how carbon flows through each of these relationships starting from the primary producers to the exported flux. Of course, there is much more work to be done. One more research cruise, much more sample analysis, and finally data synthesis and presentation.

This will be the last post, so to summarize – oceanography is awesome. And to generalize, science is awesome.

Thanks for reading.

Doug Bell
Research Technician, Phytoplankton Ecology Lab
I’m going to the beach.

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