.[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.

Abstract. The coastal ocean is a crucial link between land, the open ocean and the atmosphere. The shallowness of the water column permits close interactions between the sedimentary, aquatic and atmospheric compartments, which otherwise are decoupled at long time scales ( ∼ =1000 yr) in the open oceans. Despite the prominent role of the coastal oceans in absorbing atmospheric CO 2 and transferring it into the deep oceans via the continental shelf pump, the underlying mechanisms remain only partly understood. Evaluating observations from the North Sea, a NW European shelf sea, we provide evidence that anaerobic degradation of organic matter, fuelled from land and ocean, generates total alkalinity (A T ) and increases the CO 2 buffer capacity of seawater. At both the basin wide and annual scales anaerobic A T generation in the North Sea's tidal mud flat area irreversibly facilitates 7-10%, or taking into consideration benthic denitrification in the North Sea, 20-25% of the North Sea's overall CO 2 uptake. At the global scale, anaerobic A T generation could be accountable for as much as 60% of the uptake of CO 2 in shelf and marginal seas, making this process, the anaerobic pump, a key player in the biological carbon pump. Under future high CO 2 conditions oceanic CO 2 storage via the anaerobic pump may even gain further relevance because of stimulated ocean productivity.

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.

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[1] Underway and in situ observations of surface ocean pCO 2 , combined with satellite data, were used to develop pCO 2 regional algorithms to analyze the seasonal and interannual variability of surface ocean pCO 2 and sea-air CO 2 flux for five physically and biologically distinct regions of the eastern North American continental shelf: the South Atlantic Bight (SAB), the Mid-Atlantic Bight (MAB), the Gulf of Maine (GoM), Nantucket Shoals and Georges Bank (NSþGB), and the Scotian Shelf (SS). Temperature and dissolved inorganic carbon variability are the most influential factors driving the seasonality of pCO 2 . Estimates of the sea-air CO 2 flux were derived from the available pCO 2 data, as well as from the pCO 2 reconstructed by the algorithm. Two different gas exchange parameterizations were used. The SS, GBþNS, MAB, and SAB regions are net sinks of atmospheric CO 2 while the GoM is a weak source. The estimates vary depending on the use of surface ocean pCO 2 from the data or algorithm, as well as with the use of the two different gas exchange parameterizations. Most of the regional estimates are in general agreement with previous studies when the range of uncertainty and interannual variability are taken into account. According to the algorithm, the average annual uptake of atmospheric CO 2 by eastern North American continental shelf waters is found to be between À3.4 and À5.4 Tg C yr À1 (areal average of À0.7 to À1.0 mol CO 2 m À2 yr À1 ) over the period

Abstract.We develop an algorithm to compute pCO 2 in the Scotian Shelf region (NW Atlantic) from satellite-based estimates of chlorophyll-a concentration, sea-surface temperature, and observed wind speed. This algorithm is based on a high-resolution time-series of pCO 2 observations from an autonomous mooring. There is a gradient in the air-sea CO 2 flux between the northeastern Cabot Strait region which acts as a net sink of CO 2 with an annual uptake of 0.50 to 1.00 mol C m −2 yr −1 , and the southwestern Gulf of Maine region which acts as a source ranging from −0.80 to −2.50 mol C m −2 yr −1 . There is a decline, or a negative trend, in the air-sea pCO 2 gradient of 23 µatm over the decade, which can be explained by a cooling of 1.3 • C over the same period. Regional conditions govern spatial, seasonal, and interannual variability on the Scotian Shelf, while multi-annual trends appear to be influenced by larger scale processes.

[1] From sea-ice formation in November 2007 to onset of ice melt in May 2008, we studied the carbonate system in first-year Arctic sea ice, focusing on the impact of calcium-carbonate (CaCO 3 ) saturation states of aragonite (XAr) and calcite (XCa) at the ice-water interface (UIW). Based on total inorganic carbon (C T ) and total alkalinity (A T ), and derived pH, CO 2 , carbonate ion ( [CO 3 22 ]) concentrations and X, we investigated the major drivers such as brine rejection, CaCO 3 precipitation, bacterial respiration, primary production and CO 2 -gas flux in sea ice, brine, frost flowers and UIW. We estimated large variability in sea-ice C T at the top, mid, and bottom ice. Changes due to CaCO 3 and CO 2 -gas flux had large impact on C T in the whole ice core from March to May, bacterial respiration was important at the bottom ice during all months, and primary production in May. It was evident that the sea-ice processes had large impact on UIW, resulting in a five times larger seasonal amplitude of the carbonate system, relative to the upper 20 m. During ice formation, [CO 2 ] increased by 30 mmol kg 21 , [CO 3 22 ] decreased by 50 mmol kg 21, and the XAr decreased by 0.8 in the UIW due to CO 2 -enriched brine from solid CaCO 3 . Conversely, during ice melt, [CO 3 22 ] increased by 90 mmol kg 21 in the UIW, and X increased by 1.4 between March and May, likely due to CaCO 3 dissolution and primary production. We estimated that increased ice melt would lead to enhanced oceanic uptake of inorganic carbon to the surface layer.

[1] Dense shelf water formed in the Mertz Polynya supplies the lower limb of the global overturning circulation, ventilating the abyssal Indian and Pacific Oceans. Calving of the Mertz Glacier Tongue (MGT) in February 2010 altered the regional distribution of ice and reduced the size and activity of the polynya. The salinity and density of dense shelf water declined abruptly after calving, consistent with a reduction of sea ice formation in the polynya. Breakout and melt of thick multiyear sea ice released by the movement of iceberg B9B and the MGT freshened near-surface waters. The input of meltwater likely enhanced the availability of light and iron, supporting a diatom bloom that doubled carbon uptake relative to precalving conditions. The enhanced biological carbon drawdown increased the carbonate saturation state, outweighing dilution by meltwater input. These observations highlight the sensitivity of dense water formation, biological productivity, and carbon export to changes in the Antarctic icescape.