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Teaming up on the Iceberg Project
11/22/2010 | Benjamin Twining, Bigelow Laboratory for Ocean Sciences (Ocean Systems)
Tags: 10.20.10 webinar, scientist post, icebergs

One of my favorite aspects of oceanography is its collaborative nature. Most projects are collaborations between multiple science groups—often located at different institutions and occasionally on different sides of the globe. A great collaborator can teach you about their field of research, provide an independent view of your own data, and help generate novel models and hypotheses.

The Iceberg Project involved 9 principal investigators at 7 different institutions across the country, including Monterey Bay Aquarium Research Institute, UC-San Diego, University of San Diego, Desert Research Institute, University of South Carolina and Brigham Young University, in addition to myself at Bigelow Laboratory for Ocean Sciences. Each of these leaders then recruited and hired additional students, post-docs and science staff, so that the whole project involved more than 30 scientists on the research cruise.

The research team on the Nathaniel B. Palmer. (Photo by Debbie Nail Meyer)
The research team on the Nathaniel B. Palmer. (Photo by Debbie Nail Meyer)

While my work was focused on the effects of icebergs on iron in the water, our interest in iron is motivated by its potential to affect the growth of plankton. Thus the response of the biological community to the presence of icebergs was studied at several trophic levels. Starting with the smallest organisms, Alison Murray was responsible for examining the identity and behavior of heterotrophic bacteria around icebergs.

Alison’s group
Micrograph of stained cells. (Ben Twining)
Micrograph of stained cells. (Ben Twining)
collected water from throughout the water column in order to determine the abundance of bacteria. To do this, they used microscopy and flow cytometry. For microscopy, the cells are collected onto a filter and the DNA of the cells is stained with a chemical that fluoresces when excited with a specific type of light. This allows them to count the cells and also determine their size with digital imaging. The Murray group used genetics to determine the identity of the bacteria, and they also measured the activities of various enzymes produced by the bacteria to determine what organic compounds the cells were using to grow.

Some Antarctic diatoms (Adrian Cefarelli - Deep-Sea Research II, in press)
Some Antarctic diatoms (Adrian Cefarelli - Deep-Sea Research II, in press)
Moving up the size scale, the abundance, identity and activity of phytoplankton was studied by Maria Vernet and her group. They measured the concentration of chlorophyll (the most abundant plant pigment) in various size classes to determine relatively quickly what types of cells were present. They also used microscopy to visually identify certain types of diatoms and other groups of interest. In order to determine the rates at which phytoplankton were converting carbon dioxide into cellular material through photosynthesis, the Vernet group incubated water in incubators on the ship and measured the rate of incorporation of C-14, a radioactive isotope of carbon.

Images of fish captured by ROV cameras.
Images of fish captured by ROV cameras. (Sherlock et al., Deep-Sea Research II, in press)
Moving further up the food web, the zooplankton and micronekton (small fish) were studied by Ron Kaufmann and Bruce Robison. In order to obtain animals for counting, identification and further measurements, large nets were towed each night to collect krill, other crustaceans, and gelatinous zooplankton. These samples were sorted every morning by a virtual army of ‘pickers’, and some of the animals were tested for the contents of their guts in order to determine how much they were eating. Additionally, grazing organisms living right at the face of the iceberg were counted and identified in situ (in the water) using the high-definition video capabilities of the remotely-operated vehicle.

Zooplankton sorters, hard at work. (photo by Debbie Nail Meyer)
Zooplankton sorters, hard at work. (photo by Debbie Nail Meyer)

Pulling it all together, biology results indicate that larger phytoplankton (mostly diatoms) were growing at the face of the iceberg, however these cells were also likely getting eaten at a faster rate than cells farther from the iceberg. The growth of these cells may have been stimulated by iron or other nutrients released from the iceberg, but growth may also be enhanced by changes in water column mixing caused by the iceberg. The story is still unfolding as results are added.

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