7 August, 2003

There's one. Wow! The head of a huge arrow worm- nearly three centimeters long- comes into the microscope's field of view. Craig Aumack expertly zooms-in on the business end of this vicious leviathan of the deep. Thanks to Craig, I get an introduction to their hunting technique, and in parcticular, close-up views of the creature's two tusk-like spines that form its mouth.

Plainly put, the arrow worm is the scourge of the copepods. It lies in wait, but with lightning-quick speed, the arrow worm will seize its unsuspecting prey with its sharp pinchers after sensing the ripples generated in the water by a swimming copepod. Craig speculates that the arrow worm's "jaws," along with other zooplankton species have inspired numerous creatures and their mouth parts in such movies as "Alien" and "Tremors." He goes on to provide more vivid examples that I can't share here, but with interesting anecdotes like that, it's easy to get caught-up in Craig's enthusiasm for his work. (See 21 July for more on copepods.)

Craig is one of the talented graduate students on board from the Marine Botany Lab at the University of Texas Marine Science Institute. Craig possesses a keen intelligence with the ability to grasp concepts quickly, making him a pleasure to work with for everyone on board. As such, he has pitched right in and helps out with just about every thing there is to do. He directs CTD casts, collects various water samples, and helps deploy the Bongo Net. Early on Craig showed some interest in the Lowered Acoustic Doppler Current Profiler gadget (my term), so Electronics Technician Rob Palomares provided the instruction, and Craig has been taking turns with Rob in hooking-up and down-loading the LADCP data ever since.

Interestingly, this is not Craig's first time to the Arctic; in fact, he is just finishing-up his Master's thesis which involved modeling the productivity of kelp beds in the Beaufort Sea north of Prudhoe Bay, Alaska. I thought it was something just working up here on the Palmer, but Craig's field research for his thesis included SCUBA diving in these icy waters!

And Craig is conducting some equally fascinating research during our cruise in addition to his duties described above. In most of his own words:

I am investigating the spatial (location) and temporal (time) changes in the food web by using stable isotopes of carbon and nitrogen. All organisms possess Carbon-12 and Nitrogen-14 as well different forms of carbon and nitrogen, called isotopes, although in much smaller quantities. In this study, I will measure the ratios of Carbon 12 to its isotope Carbon-13, and Nitrogen-14 to its isotope Nitrogen-15. These ratios are unique in each kind of primary producer, so they can be used as a "molecular fingerprint" to identify where the carbon and nitrogen came from. This works because- literally- you are what you eat! A cow's diet of grass, for example, gives it a parcticular Carbon-13/12 ratio, while a fish feeding on phytoplankton will have its own unique C-13/12 ratio. Using this method we can determine the ultimate carbon source(s) of each community of organisms.

I do this by collecting Parcticulate Organic Matter Samples and various zooplankton species for isotopic analysis back in the Botany Lab at the University of Texas. These POM samples are important because they contain the phytoplankton that the zooplanktons are likely feeding on. To process the sample, I must first dry the POM sample in an oven until all the water is gone. Then I grind it into a fine powder using a mortar and pestle. This powder is placed in an elemental analyzer which combusts the material into its basic constituents. These burnt remains are then transferred to a mass spectrometer that measures the various amounts of each isotope from which the appropriate ratios can be determined.

From his earlier work, Craig goes on to explain: So far, in the Arctic basin, we have observed both spatial and temporal changes in the stable isotope values of several organisms. Certain species of copepods have decreasing isotopic compositions in the eastern portion of the basin while there is a noticeable change in the ratios of several populations of copepods between spring and summer. These observations suggest that the copepods are not only changing their diet seasonally, but copepods further to the west. It is our hypothesis that the seasonal and spatial changes of these isotopic signals can be attributed to ice algae entering the food web during the spring months. Ice algae have higher C-13/12 and N-15/14 ratios than most phytoplankton. When ice melts in the spring months the algae falls into the water column, and thus, becomes available for grazing by the larger zooplanktons. This may explain the higher isotopic ratios that we are measuring during the spring.

Indeed, you can be sure this energetic marine botanist will collect and analyze every sample until he tracks down the carbon and nitrogen sources, slowly but surely, POM by POM, plankton by plankton.

Copepod, or put another way, arrow worm food.

Arrow worm head: Note the two pinkish-orange spines that form part of the predator's "jaws."

Craig counting plankton under the Palmer's microscope.

Craig Aumack down-loading the LADCP data after a cast of the rosette.

Craig and marine technician Jenny White recovering the Bongo Net.

Craig repairing cable with electronics technician Rob Palomares's help.