Daily Journal

June 12, 2010

By David M. Lawrence

Today has been our first day completely beyond the sight of any land, or of any neighboring ships. Overnight, we had a companion on radar – a sailboat – but sometime after midnight, our courses had diverged to the point where they could no longer be located on the display. This morning we awoke to a mild rollercoaster ride as well from a storm system far to the north that prevented the SSV Corwith Cramer from maintaining anything like straight and level sailing. For those of us who haven't found our sea legs yet, it has been interesting moving about the ship. For those who haven't found their sea stomachs yet, it has been something other than interesting.

Yesterday around sunset we began the scientific part of our program. At 2000 hours we deployed a neuston net and conducted a surface station at 32°21'N, 64°28'W, or 6.7 nautical miles east of our official starting point – where we cleared Bermuda's coral reef.

Neuston refers to the interface between the ocean surface and the air above. During a neuston tow, a fine-mesh net with a collecting jar attached at the tip is towed along the surface to collect phytoplankton (plants), zooplankton (animals that float or drift at the mercy of currents and wind), nekton (free-swimming animals), and anything else that happens to get in the way of the net, such as plastic or other debris.

During a surface station, a small sample of filtered ocean water is collected for other types of analysis – in this case, measurement of chlorophyll a (a proxy measurement for the amount of phytoplankton present), and measurement of nitrate, nitrite, and phosphate concentrations. In many ways, these data reveal the productivity of the marine ecosystem. Nutrients typically limit phytoplankton populations, the foundation of the marine ecosystem.

Once the neuston net is retrieved, anything that is still trapped in the webbing is rinsed into a collecting jar. The sample is run through a sieve. Plant material, such as seagrass fragments or sargassum weed, is removed. Animals trapped in the sieve are identified, counted, and their overall biomass – a measure of the amount of animal material collected – is determined. All bits of plastic debris are removed, counted, and saved for later studies.

The scientific watches worked through the night to pick through and analyze the collected samples. During my watch, we found medusae (jellyfish), various crustaceans such as copepods and amphipods, and fish eggs.

We also collected hourly weather, water, and position data.

This morning at about 0830 hours, we conducted another neuston tow and surface station. Our location was 32°29'N, 63°18'W, 55 nautical miles from our starting point. We also deployed a carousel – a device designed to measure physical and chemical characteristics of the water at various depths. These data are important because characteristics such as temperature, salinity, and oxygen concentrations may change rapidly with depth. These changes are critical influences on the distribution of marine organisms as well as on the rate and efficiency of biological and chemical processes that maintain the marine ecosystem.

This afternoon we had our first "class" session. Classes are an important part of the Sea Education Association tradition. On most cruises, they are literally classes. In our case, it is an excellent opportunity to share preliminary results and assess the expedition's progress.