Seasonal field observations show that the North Sea, a Northern European shelf sea, is highly efficient in pumping carbon dioxide from the atmosphere to the North Atlantic Ocean. The bottom topography-controlled stratification separates production and respiration processes in the North Sea, causing a carbon dioxide increase in the subsurface layer that is ultimately exported to the North Atlantic Ocean. Globally extrapolated, the net uptake of carbon dioxide by coastal and marginal seas is about 20% of the world ocean's uptake of anthropogenic carbon dioxide, thus enhancing substantially the open ocean carbon dioxide storage.

.[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.

Abstract.A well-documented, publicly available, global data set of surface ocean carbon dioxide (CO 2 ) parameters has been called for by international groups for nearly two decades. The Surface Ocean CO 2 Atlas (SOCAT) project was initiated by the international marine carbon science community in 2007 with the aim of providing a comprehensive, publicly available, regularly updated, global data set of marine surface CO 2 , which had been subject to quality control (QC). Many additional CO 2 data, not yet made public via the Carbon Dioxide Information Analysis Center (CDIAC), were retrieved from data originators, public websites and other data centres. All data were put in a uniform format following a strict protocol. Quality control was carried out according to clearly defined criteria. Regional specialists performed the quality control, using state-of-the-art web-based tools, specially developed for accomplishing this global team effort. SOCAT version 1.5 was made public in September 2011 and holds 6.3 million quality controlled surface CO 2 data points from the global oceans and coastal seas, spanning four decades . Three types of data products are available: individual cruise files, a merged complete data set and gridded products. With the rapid expansion of marine CO 2 data collection and the importance of quantifying net global oceanic CO 2 uptake and its changes, sustained data synthesis and data access are priorities. Data coverage MotivationThe net absorption of CO 2 by the oceans, caused by rising atmospheric CO 2 concentrations since the industrial revolution, has been responsible for removing CO 2 equivalent to approximately 50 % of the fossil fuel and cement manufacturing emissions or about 30 % of the total anthropogenic emissions, including land use change (Sabine et al., 2004). Because of the availability of the carbonate ion, an important species of the dissolved inorganic carbon pool, and carbonate sediments, the oceans have a tremendous CO 2 uptake capacity and will, on timescales of ten to hundred thousand years, absorb all but a small fraction of the fossil CO 2 that has been and will be emitted (Archer et al., 1997). Meanwhile the changes in ocean CO 2 uptake, relying on factors such as ocean circulation and biology, will be among the decisive factors for the evolution of future atmospheric CO 2 concentrations and climate development (e.g., Friedlingstein et al., 2006;Riebesell et al., 2009). Presently there are two types of globally coordinated efforts that seek to resolve the dynamics of ocean CO 2 uptake through observations: repeat hydrography and surface ocean CO 2 observations (Gruber et al., 2010;Sabine et al., 2010). While repeat hydrography aims to assess variations in the ocean inventory of CO 2 on decadal timescales, surface ocean observations may resolve variations on seasonal to interannual timescales due to the higher sampling frequency. This high sampling frequency has been made possible by the advent of autonomous instruments and sensors for the nearcontinuous determination o...

[1] Observational studies report a rapid decline of ocean CO 2 uptake in the temperate North Atlantic during the last decade. We analyze these findings using ocean physicalbiological numerical simulations forced with interannually varying atmospheric conditions for the period 1979-2004. In the simulations, surface ocean water mass properties and CO 2 system variables exhibit substantial multiannual variability on subbasin scales in response to wind-driven reorganization in ocean circulation and surface warming/cooling. The simulated temporal evolution of the ocean CO 2 system is broadly consistent with reported observational trends and is influenced substantially by the phase of the North Atlantic Oscillation (NAO). Many of the observational estimates cover a period after 1995 of mostly negative or weakly positive NAO conditions, which are characterized in the simulations by reduced North Atlantic Current transport of subtropical waters into the eastern basin and by a decline in CO 2 uptake. We suggest therefore that air-sea CO 2 uptake may rebound in the eastern temperate North Atlantic during future periods of more positive NAO, similar to the patterns found in our model for the sustained positive NAO period in the early 1990s. Thus, our analysis indicates that the recent rapid shifts in CO 2 flux reflect decadal perturbations superimposed on more gradual secular trends. The simulations highlight the need for long-term ocean carbon observations and modeling to fully resolve multiannual variability, which can obscure detection of the long-term changes associated with anthropogenic CO 2 uptake and climate change.

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