1994 Arctic Ocean Section
Tony Gow, Erk
Reimnitz, Bill
Bosworth and Terry
Tucker taking cores
of dirty ice.
Sediment was observed in and on the ice from the ice edge in the Chukchi
Sea to the North Pole. Near the ice edge, sediment covered an estimated 1015%
of the surface of the ice. Farther north it covered less than 1% of the surface and
was extremely "patchy" in occurrence. Sediment was notably absent in the Eura-
sian Arctic, where it has been frequently observed on other expeditions.
Bulk samples of sediment were collected for analysis, and in many locations
ice cores were obtained through the dirty ice. Sediment entrained within the
ice was invariably associated with granular (frazil) ice formation. Frazil ice is
normally associated with turbulent growth conditions. Analyses of the parti-
cle sizes found primarily silt- and clay-sized particles; only 5.3% of the total
sediment collected was sand, while the proportions of silt and clay were 32.7%
and 62.0%, respectively. The few pelecipodes, ostracodes and foraminifera
found in the sediment indicate the shallow circum-Arctic shelves as the source
of the entrained sediment. The combined evidence indicates that sediment is
likely entrained into the ice by ice crystals scavenging suspended sediment
during stormy conditions on the continental shelves. Diffraction analysis of
the clay fine portion showed it to be composed of primarily illite and chlorite,
with smaller amounts of kaolinite and smectite. The smectite proportion increased
from near zero in the south to 1015% in the more northerly samples.
Reverse trajectories calculated for the ice parcels from velocity fields pro-
duced by the International Arctic Buoy Program indicate that the shelf source
areas from the southernmost samples were the Canadian and Alaskan shelves,
while the East Siberian Sea appears to be the source of the more northerly
samples. Comparisons of organic carbon between the ice-borne sediment and
benthic sediments showed that three times more organic carbon (2.6%) was
present in the ice sediments than in the benthos (0.8%). It is likely that the
larger amounts in ice are due to biological activity. Conversely the benthic
sediments had ten times more carbonate than the ice sediments (10.3 vs. 0.9%,
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