#12 BIG SCIENCE

R/V Knorr

Monday, July 09, 2001

11'33" N

53'04" W

19:15 ship time (GMT-2)

Steaming SW from Barbados, wind from the east-north-east at 15-20 knots.

Today brought back the science. I also discovered why the water is not so clear blue around here. When we retrieved our net tow, the net, a conical tight mesh ~10' long with a plastic half liter container that screws in the end, was filthy with Trichodesmium (Trico), the little bugger that we're out here looking for. Our CTD scan showed a hefty layering of the ocean waters at 30 meters, with a dramatic salinity increase and temperature decrease right at 30 meters. This is the Amazon effect. We are actually seeing a layer of "fresh" water laying on top of the ocean waters due to fresh water's lower density, thus it tends to float on top of the denser salt water.  This water is also rich in nutrients washed down from the Amazonian basin, thus the heavy load of phyto & zooplankton present. The abundance of this biomass actually captures and retains many wavelengths of the sun's UV light so that's why it warms up, too. Anyway, today I ran some productivity experiments. We placed 10 colonies of the trico (w/ seawater) in 50ml bottles with the little gummy tops, like those that the doctor pulls the medicine from into the syringe.  Then injected gaseous acetylene into the bottles. The trico normally fixes nitrogen available from the seawater, but also is confused by acetylene (it looks molecularly similar to the free nitrogen) and will convert it to ethylene. We place these bottles into a series of baths setting out on the deck, that have seawater pumped through them.  Each bath has a layer of sun filtering film on it to mimic 100%, 50%, 24, 10, & 1, sun exposure.  Every two hours, I take a 100 microliters gas sample from the bottle with a special hypodermic needle and inject it into a gas chromatograph which analyzes the concentration of ethylene giving us an insight into how much nitrogen fixing type metabolism is happening within the bottle. Do that a couple hundred or thousand times, and record all the other variables associated with the water in that local, and you can build up a database on the projected productivity of this particular organism in certain waters. 

Another researcher present on this cruise is working with NASA using satellite imagery, and has generated algorithms that calculate the concentration of our trico organism based on chlorophyll reflectance from the ocean waters. Our samplings and concentration studies here in the field will help him tune his algorithms. Daily, he receives satellite photos, and has schedules of what times, various satellites will be passing our area, and orders  up various shots to be sent to us. 

There is also a whole group involved with trace metal analysis.  Iron has recently been shown to be a limiting growth factor to many phytoplanktons. So we are taking many samples and freezing them for future analysis, but also running experiments by spiking samples of the trico with various concentrations of iron and watching their productivity numbers.  Someone is also using radioactive isotopes to measure something, but I’ve been staying away from that lab. 

There is a gal on board who is working on her PhD thesis studying the DNA of celephapods all over the world. She has been doing net tows at midnight and then picks through all the gunk that comes up and separates out the organism she is looking for, pickles it in alcohol, and stores it for later use. She'll grind it up and extract the DNA and do some sort of comparison based on its origin.  But one of the coolest parts is she has access to samples Charles Darwin collected on his voyages on the Beagle in the 1830’s. 

I find myself asking many of these scientist over and over, what they are doing. Usually, by the 3-4th time, I begin to understand.  Hopefully by the end of the cruise, I’ll know what we have done.

Having fun in Big Science again,

David