[1] A winter time series of the inorganic carbon system above, within, and beneath the landfast sea ice of the southern Beaufort Sea confirmed that sea ice is an active participant in the carbon cycle of polar waters. Eddy covariance measurements above the ice identified significant vertical CO 2 fluxes, mostly upward away from the ice but with short periods of downward fluxes as well. A novel, in situ method revealed extremely high pCO 2 values within the ice that are not inconsistent with theory. The total carbon content of the ice increased slightly through the winter season, and increasing variability in the vertical profiles as spring began indicated that the inorganic carbon became mobile as the ice began to melt. During early winter, as the ice formed, inorganic carbon concentrations in the surface waters increased dramatically, along with salinity, partly because of rejection from the ice and partly from advective mixing. Brine drainage was apparently not sufficient to initiate convection, and the excess carbon remained in the surface waters into the summer.Citation: Miller, L. A., T.
The Canadian Beaufort Sea has been categorized as an oligotrophic system with the potential for enhanced production due to a nutrient‐rich intermediate layer of Pacific‐origin waters. Using under‐ice hydrographic data collected near the ice‐edge of a shallow Arctic bay, we documented an ice‐edge upwelling event that brought nutrient‐rich waters to the surface during June 2008. The event resulted in a 3‐week long phytoplankton bloom that produced an estimated 31 g C m−2 of new production. This value was approximately twice that of previous estimates for annual production in the region, demonstrating the importance of ice‐edge upwelling to the local marine ecosystem. Under‐ice primary production estimates of up to 0.31 g C m−2 d−1 showed that this production was not negligible, contributing up to 22% of the daily averaged production of the ice‐edge bloom. It is suggested that under‐ice blooms are a widespread yet under‐documented phenomenon in polar regions, which could increase in importance with the Arctic's thinning ice cover and subsequent increase in transmitted irradiance to the under‐ice environment.
.[1] We present an Arctic seasonal survey of carbon dioxide partial pressure (pCO 2 ) dynamics within sea ice brine and related air-ice CO 2 fluxes. The survey was carried out from early spring to the beginning of summer in the Arctic coastal waters of the Amundsen Gulf. High concentrations of pCO 2 (up to 1834 matm) were observed in the sea ice in early April as a consequence of concentration of solutes in brines, CaCO 3 precipitation and microbial respiration. CaCO 3 precipitation was detected through anomalies in total alkalinity (TA) and dissolved inorganic carbon (DIC). This precipitation seems to have occurred in highly saline brine in the upper part of the ice cover and in bulk ice. As summer draws near, the ice temperature increases and brine pCO 2 shifts from a large supersaturation (1834 matm) to a marked undersaturation (down to almost 0 matm). This decrease was ascribed to brine dilution by ice meltwater, dissolution of CaCO 3 and photosynthesis during the sympagic algal bloom. The magnitude of the CO 2 fluxes was controlled by ice temperature (through its control on brine volume and brine channels connectivity) and the concentration gradient between brine and the atmosphere. However, the state of the ice-interface clearly affects air-ice CO 2 fluxes.
During a year-round occupation of Amundsen Gulf in the Canadian Arctic Archipelago dissolved inorganic and organic carbon (DIC, DOC), total alkalinity (TA), partial pressure of CO 2 (pCO 2 ) and related parameters were measured over a full annual cycle. A two-box model was used to identify and assess physical, biological, and chemical processes responsible for the seasonal variability of DIC, DOC, TA, and pCO 2 . Surface waters were undersaturated with respect to atmospheric CO 2 throughout the year and constituted a net sink of 1.2 mol C m 22 yr 21 , with ice coverage and ice formation limiting the CO 2 uptake during winter. CO 2 uptake was largely driven by under ice and open-water biological activity, with high subsequent export of organic matter to the deeper water column. Annual net community production (NCP) was 2.1 mol C m 22 yr 21 . Approximately one-half of the overall NCP during the productive season (4.1 mol C m 22 from Apr through Aug) was generated by under-ice algae and amounted to 1.9 mol C m 22 over this period. The surface layer was autotrophic, while the overall heterotrophy of the system was fueled by either sedimentary or lateral inputs of organic matter.
Summertime Arctic shipboard observations of oxygenated volatile organic compounds (OVOCs) such as organic acids, key precursors of climatically active secondary organic aerosol (SOA), are consistent with a novel source of OVOCs to the marine boundary layer via chemistry at the sea surface microlayer. Although this source has been studied in a laboratory setting, organic acid emissions from the sea surface microlayer have not previously been observed in ambient marine environments. Correlations between measurements of OVOCs, including high levels of formic acid, in the atmosphere (measured by an online highresolution time-of-flight mass spectrometer) and dissolved organic matter in the ocean point to a marine source for the measured OVOCs. That this source is photomediated is indicated by correlations between the diurnal cycles of the OVOC measurements and solar radiation. In contrast, the OVOCs do not correlate with levels of isoprene, monoterpenes, or dimethyl sulfide. Results from box model calculations are consistent with heterogeneous chemistry as the source of the measured OVOCs. As sea ice retreats and dissolved organic carbon inputs to the Arctic increase, the impact of this source on the summer Arctic atmosphere is likely to increase. Globally, this source should be assessed in other marine environments to quantify its impact on OVOC and SOA burdens in the atmosphere, and ultimately on climate.Arctic | chemical ionization mass spectrometry | oxygenated volatile organic compounds | sea surface microlayer | marine boundary layer
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