Biogeosciences
www.biogeosciences.net
1726-4170
1726-4189
6
11
2009
10.5194/bg-6-2421-2009
http://www.biogeosciences.net/6/2421/2009/
http://www.biogeosciences.net/6/2421/2009/bg-6-2421-2009.html
http://www.biogeosciences.net/6/2421/2009/bg-6-2421-2009.pdf
2421
2431
2009-11-04
Calcium carbonate saturation in the surface water of the Arctic Ocean: undersaturation in freshwater influenced shelves
M. Chierici
melissa@chem.gu.se
A. Fransson
University of Gothenburg, Department of Chemistry, Marine Chemistry, 412 96 Göteborg, Sweden
University of Gothenburg, Department of Earth Sciences, Oceanography, 403 50 Göteborg, Sweden
In the summer of 2005, we sampled surface water and measured pH and total
alkalinity (A<sub>T</sub>) underway aboard <i>IB Oden</i> along the Northwest Passage from Cape
Farewell (South Greenland) to the Chukchi Sea. We investigated the
variability of carbonate system parameters, focusing particularly on
carbonate concentration [CO<sub>3</sub><sup>2−</sup>] and calcium carbonate
saturation states, as related to freshwater addition, biological processes
and physical upwelling. Measurements on A<sub>T</sub>, pH at 15°C, salinity
(S) and sea surface temperature (SST), were used to calculate total
dissolved inorganic carbon (C<sub>T</sub>), [CO<sub>3</sub><sup>2−</sup>] and the
saturation of aragonite (ΩAr) and calcite (ΩCa) in the
surface water. The same parameters were measured in the water column of the
Bering Strait. Some surface waters in the Canadian Arctic Archipelago (CAA)
and on the Mackenzie shelf (MS) were found to be undersaturated with respect
to aragonite (ΩAr<1). In these areas, surface water was low in
A<sub>T</sub> and C<sub>T</sub> (<1500 μmol kg<sup>−1</sup>) relative to seawater and
showed low [CO<sub>3</sub><sup>2−</sup>]. The low saturation states were probably due to
the likely the effect of dilution due to freshwater addition by sea ice melt
(CAA) and river runoff (MS). High A<sub>T</sub> and C<sub>T</sub> and low pH,
corresponded with the lowest [CO<sub>3</sub><sup>2−</sup>], ΩAr and ΩCa,
observed near Cape Bathurst and along the South Chukchi Peninsula. This was
linked to the physical upwelling of subsurface water with elevated CO<sub>2</sub>.
The highest surface ΩAr and ΩCa of 3.0 and 4.5,
respectively, were found on the Chukchi Sea shelf and in the cold water
north of Wrangel Island, which is heavily influenced by high CO<sub>2</sub>
drawdown and lower C<sub>T</sub> from intense biological production. In the
western Bering Strait, the cold and saline Anadyr Current carries water that
is enriched in A<sub>T</sub> and C<sub>T</sub> from enhanced organic matter
remineralization, resulting in the lowest ΩAr (~1.2) of the
area.
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