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Life Around the Iceberg

ICEBERG A43K, SOUTHERN OCEAN– Many birds, seals and whales are living around Iceberg A43K. We saw several of them as we approached the iceberg two days ago. In comparison, we had fewer sightings at SS-1, the smaller iceberg.

Crabeater seals resting on a small ice floe.

Jake Ellena and Ken Smith are our bird surveyors. They count birds in flight while the ship is transiting between stations or during iceberg circumnavigation. Snow petrels are the most abundant of them; they are attracted to the iceberg, feeding on the zooplankton congregating within a few miles of the iceberg.

A Snow Petrel near Iceberg A43K.

Our sampling targets the study of the wildlife’s food source and the concept that birds and marine mammals are found in association with icebergs thanks to the physical and chemical modification of the ocean by the presence of the bergs. The icebergs enrich the water, promoting phytoplankton and zooplankton growth.

Ron Kaufmann and Bruce Robison have been monitoring some of this growth by using large nets to sample the macrozooplankton and micronekton around the iceberg. Salps (Salpa thompsoni) have dominated most of the samples at various distances from the berg. Many of these salps had highly colored guts, perhaps indicative of recent feeding, and representative salps have been analyzed for gut contents and pigments. Small phytoplankton cells, abundant at this time of the year, are preferred by salps.

One of the crustacean species that we are catching near Iceberg A43K.

Conspicuously rare in the samples have been large Antarctic Krill (Euphausia superba), though large numbers of young or juvenile krill have been collected. Krill typically feed on diatoms which are not abundant in winter.

The nets also contain large numbers of vertically migrating mesopelagic fishes as well as hyperiid amphipods, small krill and occasional large medusae.

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