Abstract
Abstract. The Arctic Ocean accounts for only 4% of the global ocean area, but it contributes significantly to the global carbon cycle. Recent observations of seawater CO2-carbonate chemistry in shelf waters of the western Arctic Ocean, primarily in the Chukchi Sea, from 2009 to 2011 indicate that bottom waters are seasonally undersaturated with respect to calcium carbonate (CaCO3) minerals, particularly aragonite. Nearly 40% of sampled bottom waters on the shelf have saturation states less than one for aragonite (i.e., Ωaragonite < 1.0), thereby exposing the benthos to potentially corrosive water for CaCO3-secreting organisms, while 80% of bottom waters present had Ωaragonite values less than 1.5. Our observations indicate seasonal reduction of saturation states (Ω) for calcite (Ωcalcite) and aragonite (Ωaragonite) in the subsurface in the western Arctic by as much as 0.8 and 0.5, respectively. Such data indicate that bottom waters of the western Arctic shelves were already potentially corrosive for biogenic and sedimentary CaCO3 for several months each year. Seasonal changes in Ω are imparted by a variety of factors such as phytoplankton photosynthesis, respiration/remineralization of organic matter and air–sea gas exchange of CO2. Combined, these processes either increase or enhance in surface and subsurface waters, respectively. These seasonal physical and biological processes also act to mitigate or enhance the impact of Anthropocene ocean acidification (OA) on Ω in surface and subsurface waters, respectively. Future monitoring of the western Arctic shelves is warranted to assess the present and future impact of ocean acidification and seasonal physico-biogeochemical processes on Ω values and Arctic marine ecosystems.
Highlights
; Doney et al, 2009; Feely et al, 2009)
The inflow of Pacific Ocean water (∼ 1 Sv during summer; 1 Sv = 106 m3 s−1) from the Bering Sea into the Chukchi Sea through Bering Strait is comprised of three different water sources associated with the Alaskan Coastal Current (ACC), Bering Sea water (BSW) and Anadyr Current (AW) waters (Fig. 1)
During the 2009–2011 RUSALCA/ICESCAPE expeditions, shelf water temperatures varied from −1.8 to +7.5 ◦C, while salinity ranged from ∼ 24 to 33.5
Summary
As the CO2 contion states ( ) for calcite ( calcite) and aragonite ( aragonite) in the subsurface in the western Arctic by as much as 0.8 tent of seawater increases in response to uptake of anthropogenic CO2, readjustment of seawater CO2-carbonate equiand 0.5, respectively Such data indicate that bottom waters of the western Arctic shelves were already potentially corrosive for biogenic and sedimentary CaCO3 for several months each year. Seasonal changes in are imparted by a varilibria results in the reduction of pH, carbonate ion concentration [CO23−] and (CaCO3) minerals saturation state ( ) of calcium carbonate such as cSalcoitleid(i.eE.,arctahlcite) and aragonite (i.e., aragonite) Such changes have been observed in the ety of factors such as phytoplankton photosynthesis, respi- open ocean over the past thirty years, with the CO2 partia
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