Spatial distribution of pCO₂, ΔO₂/Ar and dimethylsulfide (DMS) in polynya waters and the sea ice zone of the Amundsen Sea, Antarctica

• Published in: Deep Sea Research Part II: Topical Studies in Oceanography
• Other Authors: Tortell, Philippe (author), Long, Matthew (author), Payne, Christopher (author), Alderkamp, Anne-Carljin (author), Dutrieux, Pierre (author), Arrigo, Kevin (author)
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier Ltd. 2012
• Subjects: Amundsen Sea; Diatoms; Air–sea exchange; Dimethylsulfide; Antarc*; Antarctica; Sea ice
• Online Access: http://nldr.library.ucar.edu/repository/collections/OSGC-000-000-010-415; https://doi.org/10.1016/j.dsr2.2012.03.010

We report the first simultaneous measurements of surface water pCO₂, biological oxygen saturation (ΔO₂/Ar) and dimethylsulfide (DMS) concentrations in polynya waters and the sea ice zone of the Amundsen Sea, Antarctica. Across our survey region, we observed large spatial variability in surface water gas concentrations, tied to strong gradients in hydrography and phytoplankton biomass. Variability in sea surface temperature and salinity was attributed to the interacting effects of surface ocean circulation and heat fluxes, sea ice melt and the upwelling of relatively warm, saline and nutrient-rich modified circumpolar deep water. Phytoplankton biomass ranged from <1 μg L⁻¹ to ~40 μg L⁻¹ chlorophyll a (Chl a), with the highest values observed in regions of shallow mixed layer depths. Phytoplankton assemblages were dominated by the colonial haptophyte Phaeocystis antarctica at most sampling stations, with lesser abundances of diatoms found throughout the polynya and sea ice zone. Cryptophytes were abundant at a few stations along the continental shelf break. Across the open polynya waters and sea ice zone, ΔO₂/Ar ranged from ~-40% to 40% (mean 8.6%), pCO₂ ranged from 80 to 530 μatm (mean 250 μatm) and DMS concentrations varied from <1 nM to ~350 nM. Strong gradients in gas concentrations were observed over short (i.e. <10 km) spatial scales. The distribution of pCO₂ and ΔO₂/Ar across our survey transects reflected the balance between deep water entrainment and net community production, with a significant imprint of air--sea exchange. Chl a concentrations were significantly correlated to both pCO₂ and ΔO₂/Ar, and the slope of the ΔO₂/Ar vs. pCO₂ relationship was consistent with photosynthetic stoichiometry (~1.25 mol O₂ evolved per mol DIC removed). DMS and Chl a concentrations were also correlated in surface waters, but the spatial distribution of DMS was often uncoupled from pCO₂ and ΔO₂/Ar, likely due to complex microbial cycling processes. Sea surface temperature and salinity were related to surface gas ...