Science Results : Daily Update

Daily Update | Current SEA Research

June 30, 2010

By Giora Proskurowski

Last night during midwatch (2300 to 0300 hours) we analyzed all the chlorophyll-a samples that we have been collecting. At every neuston station we filter 1000 mL of surface seawater through a 0.45 micron filter to retain the phytoplankton that use chlorophyll-a, a pigment, to capture sunlight for photosynthesis. The filters are then placed in glass vials and frozen until we're ready for a batch analysis.

Once we've collected a large number of samples (in this case 65), we fill the tubes with acetone (nail polish remover) that dissolves the filter and splits open the phytoplankton cells, spilling the pigments into the fluid. After a quick spin on a centrifuge, which pushes all the particles to the bottom of the tube, we place the tube in a fluorometer. This devices shines a blue light through the tube. The pigments absorb this light and re-emit a red light, which is detected. The more chlorophyll-a, the more red light emitted by the sample. What is neat about this analysis is that it simulates one of the most important reactions ever, all in a little glass test tube. The pigment's ability to absorb light energy and turn it into chemical energy (and re-emit a fraction of that energy) is fundamental to life on this planet – producing most of the oxygen in our atmosphere, and converting some of the carbon dioxide in the atmosphere into biomass at the base of the food chain.

We are in the Sargasso Sea, which – for the same reasons plastics accumulate here – is a region of very low productivity. This means that despite the abundant sunlight, there is not much phytoplankton, and in turn, not much zooplankton, small fish, bigger fish, and so on up the food chain. Thus, the water here is a deep, stunning clear blue.

At first glance, last night's chlorophyll-a analyses were not a surprise – most of the values were very low. However, by collecting the samples, and making the analyses, we will be able to evaluate the question: Is there a connection between primary productivity and plastic concentration?

Other factors also affect primary productivity, such as nutrient concentration – for which we have also been collecting samples that we plan to analyze late next week. Without these data any claims regarding the relationship between productivity and plastic concentration are mere speculation.