1994 Arctic Ocean Section
Late Quaternary Paleoceanography of the Canada Basin,
Central Arctic Ocean
William M. Briggs and Thomas M. Cronin
This project is based on quantitative analysis of the ostracodes present in
seafloor boxcores and piston cores collected during AOS-94. Ostracodes are
small, bivalved crustaceans whose shells, or valves, are made up of calcium
carbonate in the form of the mineral calcite, which also contains trace amounts
of magnesium.
Seafloor sediments of the central Arctic Ocean (CAO) contain two types of
deep-sea ostracodes: cladocopids and podocopids. Cladocopid ostracodes are
extremely abundant in the CAO, where they are represented by about 13 species
of the genus Polycope. Cladocopids are part of the epifaunal bottom commun-
ity, and they can swim for short distances just a few centimeters above the sea
bottom. The podocopid ostracodes of Arctic Ocean sediments, with one excep-
tion, are bottom-dwelling species, some living at the sedimentseawater interface
(epifaunal) and others living in the substrate just below the interface (infaunal).
The exception is the genus Acetabulastoma, which has a lifestyle of com-
mensalism on at least two species of gammarid amphipods that are part of the
under-ice community in Arctic marine environments. Whether due to the
death of the host amphipod species or the release of ostracode shells from the
host species by accidental detachment, death or molting, the shells of Acetabu-
lastoma eventually sink through the water column and come to rest on the sea-
floor, where they become part of the ostracode bottom fauna. Their shells are
therefore not indicative of the ostracode assemblages used to characterize cer-
tain water masses. The presence or absence of Acetabulastoma in downcore
ostracode assemblages can be used as a proxy indicator of the magnitude and
extent of ice cover in the CAO. This has important implications for CAO ice-
cover history and its linkages to paleoceanography, paleoclimatology and glo-
bal change.
Many ostracodes in the marine realm live within narrowly defined envi-
ronmental tolerance limits, and their distribution on the seafloor is governed
by variables such as the temperature, salinity, oxygen concentration and nutri-
ents in the overlying water column and the type of sediments on the seafloor.
William Briggs is with the Institute of Arctic and Alpine Research at the University of Colorado at Boulder,
Colorado, U.S.A. Thomas Cronin is with the U.S. Geological Survey at Reston, Virginia, U.S.A.
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