Abstract
Measurements of net community production (NCP) provide an upper constraint on the strength of the oceanic biological pump, the dominant mechanism for removing CO2 from the ocean surface and sequestering it at depth. In this investigation, our objectives were to describe the spatial and temporal variability of NCP associated with the spring ice-edge bloom in Baffin Bay and to identify the key environmental drivers controlling its variability. Using data collected between June 9 and July 10, 2016, we estimated NCP based on (1) underway measurements of surface water oxygen to argon ratios (O2:Ar), (2) underway measurements of the partial pressure of CO2, and (3) seasonal nitrate drawdown from discrete samples. These multiple approaches displayed high NCP (up to 5.7 mol C m–2) in eastern Baffin Bay, associated with modified Atlantic waters, and low NCP (<1 mol C m–2) in the presence of Arctic outflow waters in western Baffin Bay. Arctic outflow waters were characterized by low surface salinities and nitrate concentrations, suggesting that high freshwater content may have limited the nutrient availability of these waters. Different integration depths and timescales associated with each NCP approach were exploited to understand the temporal progression and succession of the bloom, revealing that the bloom was initiated under ice up to 15 days prior to ice retreat and that a large portion of NCP in eastern Baffin Bay (potentially up to 70%) was driven by primary production occurring below the surface-mixed layer.
Highlights
Like other Arctic Seas, the waters of Baffin Bay are currently transforming under the influence of anthropogenic climate change
Other studies have shown large uncertainties in estimated transfer velocities in the presence of partial sea-ice cover (Rutgers van der Loeff et al, 2014; Butterworth and Miller, 2016; Prytherch et al, 2017). Taking these reported uncertainties into consideration and acknowledging that this large uncertainty is again applied by our residencetime multiplier to report seasonal Net community production (NCP) in units of mol C m–2, we find that the relative uncertainty of our N CPO2=Ar estimates may be more than 100%
We were able to use interpolated FPWMLD values as a proxy for winter mixed layer conditions, as we found that only small differences in fraction of Pacific water (FPW) existed between the MLD and depth of winter convection and that these differences did not result in a change of classification between Atlantic or Arctic domains at any station
Summary
Like other Arctic Seas, the waters of Baffin Bay are currently transforming under the influence of anthropogenic climate change. Freshwater inputs to Baffin Bay continue to increase from various sources including increasingly fresh surface waters exported from the central Arctic Ocean (Haine et al, 2015; Carmack et al, 2016) and increasing glacial meltwater inputs from the Greenland ice sheet (Dahl-Jensen et al, 2011; Bamber et al, 2018). Combined, these changes will no doubt affect the primary production regime in Baffin Bay and have consequent effects for marine ecosystems and the marine carbon cycle in this region. NCP represents an upper constraint on the amount of organic carbon exported to depth (the biological pump), assuming that the storage of organic carbon in the surface-mixed layer is modest over large spatial and temporal scales (Falkowski et al, 2003)
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