Tortell, P.D., Long, M.C., Payne, C.D., Alderkamp, A.-C., Dutrieux, P. and Arrigo, K.R. 2012. Spatial distribution of pCO2, ΔO2/Ar and dimethylsulfide (DMS) in polynya waters and the sea ice zone of the Amundsen Sea, Antarctica. Deep-Sea Research II 71-76: 77-93.
In an analysis of several aspects of coastal polynyas that yearly receive iron (Fe) inputs from melting sea ice and continental shelf sediments - as described by Sedwick and DiTullio (1997) and Coale et al. (2005) - Tortell et al. (2012) note that primary productivity in these systems can account for about 40% of total Southern Ocean C-fixation, citing Arrigo et al. (1998) and Arrigo and van Dijken (2003). They further write that "high primary productivity in polynya surface waters lowers the partial pressure of CO2 below atmospheric saturation (Sweeney et al., 2000; Arrigo et al., 2008), driving an influx of CO2 and the subsequent export of particulate and dissolved organic C into subsurface waters (Dunbar et al., 1998)," such that "the global impact of this biological C pump is enhanced by the formation of deep water masses over the Antarctic continental shelf (Jacobs, 2004), which carry carbon into the ocean interior and sequester CO2 from the atmosphere on 100-1000 year timescales (Marinov et al., 2006)," with the consequence that this sea ice formation "impedes sea-air exchange with pCO2 supersaturated polynya waters during winter (Gibson and Trull, 1999; Sweeney, 2003; Arrigo and Van Dijken, 2007), ensuring that these regions are a net sink for CO2 on annual timescales (Arrigo et al., 2008)."
What was done
In further exploring this region of the planet and its unique characteristics, while on a cruise from 11 January to 16 February 2009 as part of the DynaLiFe program, the six scientists acquired new field data pertaining to the surface water distribution of DMS (dimethylsulfide) and pCO2 within the polynya and beneath the pack ice of the Amundsen Sea, using ship-board membrane inlet mass spectrometry for high spatial resolution analysis.
What was learned
Tortell et al. report that during the time of their cruise, the Amundsen Sea acted as an overall net sink for CO2 and a source for DMS. In fact, they found that the air-to-sea flux of CO2 and sea-to-air flux of DMS were both "more than 2-fold higher in open polynya waters relative to the overall cruise means."
What it means
In harmony with the findings of Alderkamp et al. (2012), Tortell et al. conclude that the "exceptionally high productivity in the Amundsen Sea polynyas [was] likely due to the high glacially-derived Fe concentrations of this water mass." And this exceptionally high productivity ensures an exceptionally high organic matter sinking flux, which would be expected to have a cooling effect on the planet, due to the CO2 it extracted from the atmosphere and incorporated into its tissues sinking with it. In addition, the much higher sea-to-air flux of DMS would be expected to also have a cooling effect on the planet, as described by the CLAW hypothesis of Charlson et al. (1987). And for more on that phenomenon, we direct you to Dimethyl Sulphide in our Subject Index.
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