1994 Arctic Ocean Section
Distribution of Iron and Aluminum
in the Surface Waters of the Arctic Ocean
Chris Measures
Extremely low concentrations of dissolved iron in the surface waters of
parts of the remote ocean such as the sub-Arctic Pacific are believed to play a
crucial role in limiting the biological productivity of these regions, despite an
abundance of the major nutrients in the surface waters. Phytoplankton require
iron for various biochemical processes, including the conversion of sunlight
energy and the reduction of the nutrient nitrate.
The levels at which iron becomes limiting to phytoplankton growth, and
the effects of its sporadic introduction into surface waters on growth rate, spe-
cies dominance and carbon export, are the subject of intense study in various
oceanic regimes.
While iron is delivered to the edges of the ocean in copious quantities
through fluvial run-off, little of this material escapes the intense scavenging
removal of these high-productivity regions to reach the surface waters of the
gyres. In the temperate and tropical oceans, iron is delivered to the surface
ocean by the dissolution of eolian-transported continental dust; the regions in
which iron is found to be limiting are those that receive only low inputs of this
eolian material.
Mineral dust inputs to the Arctic are low, and with its annual cycle of varia-
ble ice cover, the supply of iron by this route to the surface waters is likely to
be low and highly sporadic in both time and space. Little or nothing is known
of the distribution of iron in the surface waters of the Arctic Ocean, because it
is difficult to collect uncontaminated samples for an element that is ubiqui-
tous in manufactured materials and because of analytical difficulties associated
with determining iron at extremely low concentrations.
Recent advances have resulted in the development of analytical methodol-
ogy that can be operated onboard ship and is capable of determining iron at
ambient surface water concentrations. AOS-94 provided an opportunity to
deploy this system to investigate the input of the eolian-transported trace metals
iron and aluminum across the surface waters of the basin. Since sampling
close to the ship raises questions of contamination from the ship's iron hull,
Chris Measures is from the Department of Oceanography at the University of Hawaii in Honolulu, Hawaii,
U.S.A.
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