Ocean Circulation and Geochemistry
Nansen
Makarov
Basin
Basin
Amundsen
Mendeleyev
Chukchi
Basin
Ridge
Sea
8
25
Al
Fe
Dirty Ice
20
6
15
Al
Fe
(nM)
(nM) 4
10
2
5
0
0
10
20
30
40
Station Number
Concentrations of iron and aluminum in the surface waters vs. Louis S. St-Laurent
station numbers.
surface samples were obtained at stations by hand-dipping bottles from the
edge of ice floes located upwind of the ship.
The results indicate that concentrations of iron in the surface waters across
the basin are relatively high and quite variable, with generally higher values
(3.2 nM) in the western Arctic dropping to relatively low values (0.75 nM) in
the Nansen Basin. Within this general trend, though, are localized regions of
extremely high iron concentrations (>8 nM), particularly in the vicinity of the
Mendeleyev Ridge. These highest values occur in regions where the ice floes
were observed to contain significant quantities of sediment on their surface,
known as "dirty ice." The suggestion that ice-rafted sediment is the source of
these high iron values in the surface water is further supported by the enrich-
ment of aluminum in the same regions.
The entrainment of sediments into ice floes during freezing at the edge of
the basin and the subsequent advection and partial melting of the ice in the
center of the basin represents a unique pathway for delivering reactive trace
metals such as iron to the center of a basin. The partial melting of ice floes
during the summer apparently is capable of delivering high levels of iron to
the surface stratified waters. This delivery mechanism results in relatively high
concentrations of iron, which may favor the development of the ice algae
community that grows on the underside of the ice floes and is thought to
make a major contribution to the primary productivity of the Arctic Ocean.
Large organisms such as ice algae require higher ambient iron concentrations
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