Spatial distribution of pCO₂, 螖O₂/Ar and dimethylsulfide (DMS) in polynya waters and the sea ice zone of the Amundsen Sea, Antarctica

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• 作者：Philippe D. Tortell^a ; ^b ; ^{ptortell@eos.ubc.ca} ; Matthew C. Long^c ; Christopher D. Payne^a ; Anne-Carlijn Alderkamp^d ; Pierre Dutrieux^e ; Kevin R. Arrigo^d
• 关键词：Amundsen Sea ; pCO2 ; O2/Ar ; Dimethylsulfide ; Iron ; Phaeocystis ; Diatoms ; Net community production ; Air&ndash ; sea exchange ; Modified circumpolar deep water
• 刊名：Deep Sea Research Part II ; Topical Studies in Oceanography
• 出版年：2012
• 期刊代码：20_09670645
• 类别：ear
• 出版时间：15 September, 2012
• 卷：71-76
• 期：Complete
• 页码：77-93
• 文件大小：3480 K

摘要

We report the first simultaneous measurements of surface water pCO₂, biological oxygen saturation (螖O₂/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 渭g L^鈭? to 鈭?0 渭g L^鈭? 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, 螖O₂/Ar ranged from 鈭尖垝40%to 40%(mean 8.6%), pCO₂ ranged from 80 to 530 渭atm (mean 250 渭atm) and DMS concentrations varied from <1 nM to 鈭?50 nM. Strong gradients in gas concentrations were observed over short (i.e. <10 km) spatial scales. The distribution of pCO₂ and 螖O₂/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 螖O₂/Ar, and the slope of the 螖O₂/Ar vs. pCO₂ relationship was consistent with photosynthetic stoichiometry (鈭?.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 螖O₂/Ar, likely due to complex microbial cycling processes. Sea surface temperature and salinity were related to surface gas concentrations through their effects on mixed layer depth and as tracers of upwelling. During the time of our cruise, the Amundsen Sea acted as an overall net sink for CO₂ (mean sea-air flux=鈭?5.9 mmol m^鈭? d^鈭?) and a DMS source (mean sea-air flux=23.1 渭mol m^鈭? d^鈭?). Sea-air CO₂ and DMS fluxes were more than 2-fold higher in open polynya waters relative to the overall cruise means. Simple calculations suggest that the Amundsen Sea contributes 鈭?%of total Southern Ocean CO₂ fluxes, and 鈭?%of DMS fluxes.