Daily Journal

June 27, 2010

By David M. Lawrence

We are at the midpoint of our cruise. We've been at sea 17 days, and we have 17 days to go. Spirits are high, energy is often low, but we are working more efficiently and more often than not getting more done in a 24-hour period that we were at the beginning of the expedition.

Today has been a day of work instead of rest. We postponed field day yesterday because of Dylan Meyer's birthday, but the ship needs to be cleaned, and we met the mung this afternoon and gave it our worst. B Watch is running the ship, while A and C watches are taking advantage of some down time to relax, shower, and maybe even do laundry. Personally, I hope to do my inaugural laundry at sea tomorrow. My shipmates would probably appreciate it as much as I expect I will.

Yesterday we began our zag to the southwest in our attempt to cover as much of the Sargasso Sea between 30°N and 26°N. Plastic counts have continued to be relatively low compared to what we were finding when we were steaming along latitude 32°N out of Bermuda. I don't know if we should be heartened by the low numbers we've been seeing, if the plastic is mixed into deeper waters because of the sustained wind and wave action we've been experiencing, or if we're just missing the patches of it.

The Sargasso Sea is often described as something of a marine desert in that – because of the relatively few nutrients available – it can't support the numbers and diversity of organisms that areas with greater nutrient availability such as coastal areas, upwelling areas, and polar seas can. We have hit patches with relatively low biomass – a measure of the amount of biological material – and relatively low diversity, which is consistent with the Sargasso-as-desert idea.

Earlier (on June 12) I discussed the main ways we sampled the ocean – neuston tows, surface stations, and carousels. On June 15 I discussed Tucker trawls, which are similar to neuston tows, but at depth rather than at the surface. What I didn't discuss is what we do with what we find. Today I will begin explaining all that – and hope that I finish by the time we arrive back in Bermuda.

I start with neuston tows and Tucker trawls. Once the nets are retrieved, the cod end (tip) of the net and collecting jar are placed in a bucket. The collecting jar is removed and dumped in the bucket. The cod end is gently rinsed to wash most of the trapped organisms and plastic into the bucket without minimal disturbance. This bucket, containing the "pristine rinse," is taken to the lab. Another bucket is brought over, and the net is subjected to a more vigorous rinse from mouth to tip. This "rinse sample" is likewise taken to the lab for analysis.

With both the pristine and rinse samples of the neuston tows and Tucker trawls, we pick out the plastic pieces. Some we can get floating on the surface before filtering, others after we filter the sample through a fine mesh (0.333 mm) sieve. For the neuston tows we pick out certain organisms, like large jellies and Portuguese man-o-war, for safety as well as for counting and measuring biomass. Other organisms we remove and preserve for scientific purposes, such as Halobates (the only pelagic, or open ocean, insect) and leptocephali (eel larvae). For both the neuston tows and Tucker trawls we measure the biomass contained in the sample. From the pristine rinses of the neuston tows, we remove a small amount of the biomass for a 100 count, in which we identify and count the first 100 organisms we see in the sample. A portion of the biomass obtained in the neuston tows is preserved in ethanol for later scientific study.

For me, the most interesting part is the 100 counts. Some centuries ago I was trained as an old-school biologist with an emphasis on being able to identify the plants, animals, and organisms I see in the field. The science of identification, taxonomy, is one that I hold dear, and one that I used to emphasize whenever I had the opportunity to cover it in my biology, geography, or oceanography classes. When I look through the lens of the microscope during a count, I am transported back to that sense of curiosity and wonder I felt as an undergraduate student 30 years ago. But what's best, I'm seeing these organisms as living, skittering beings rather than as illustrations in a musty, worn-out textbook.

Stay tuned. I'm not through talking about the rich microscopic life of the ocean...