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See detailVariability of North Sea pH and CO2 pumping in response to North Atlantic Oscillation forcing
Salt, L; Thomas, H; Prowe, F et al

Poster (2013, April 07)

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See detailModelling ocean acidification in marginal seas: the North Western European shelf case study
Artioli, Y; Blackford, JC; Butenschön, M et al

Conference (2013)

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See detailVariability of North Sea pH and CO2 in response to North Atlantic Oscillation forcing
Salt, L.A.; Thomas, H.; Prowe, A.E.F. et al

in Journal of Geophysical Research. Biogeosciences (2013), 118(1-9),

High biological activity causes a distinct seasonality of surface water pH in the North Sea, which is a strong sink for atmospheric CO 2 via an effective shelf pump. The intimate connection between the ... [more ▼]

High biological activity causes a distinct seasonality of surface water pH in the North Sea, which is a strong sink for atmospheric CO 2 via an effective shelf pump. The intimate connection between the North Sea and the North Atlantic Ocean suggests that the variability of the CO 2 system of the North Atlantic Ocean may, in part, be responsible for the observed variability of pH and CO 2 in the North Sea. In this work, we demonstrate the role of the North Atlantic Oscillation (NAO), the dominant climate mode for the North Atlantic, in governing this variability. Based on three extensive observational records covering the relevant levels of the NAO index, we provide evidence that the North Sea pH and CO 2 system strongly responds to external and internal expressions of the NAO. Under positive NAO, the higher rates of in fl ow of water from the North Atlantic Ocean and the Baltic out fl ow lead to a strengthened north-south biogeochemical divide. The limited mixing between the north and south leads to a steeper gradient in pH and partial pressure of CO 2 (pCO 2 ) between the two regions in the productive period. This is exacerbated further when coinciding with higher sea surface temperature, which concentrates the net community production in the north through shallower strati fi cation. These effects can be obscured by changing properties of the constituent North Sea water masses, which are also in fl uenced by NAO. Our results highlight the importance of examining interannual trends in the North Sea CO 2 system with consideration of the NAO state [less ▲]

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See detailVariability of shelf sea pH and surface water CO2 in response to North Atlantic Oscillation forcing
Salt, L.; Thomas, H.; Prowe, A.E.F. et al

Conference (2012, April 22)

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See detailInorganic carbon dynamics in coastal arctic sea ice and related air-ice CO2 exchanges
Geilfus, Nicolas-Xavier ULg; Tison, J.-L.; Carnat, G. et al

Poster (2012, April)

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See detailDynamics of pCO2 and related air-ice CO2 fluxes in the Arctic coastal zone (Amundsen Gulf, Beaufort Sea)
Geilfus, Nicolas-Xavier ULg; Carnat, G.; Papakyriakou, T. et al

in Journal of Geophysical Research. Oceans (2012), 117(C00G10),

We present an Arctic seasonal survey of carbon dioxide partial pressure (pCO2) dynamics within sea ice brine and related air-ice CO2 fluxes. The survey was carried out from early spring to the beginning ... [more ▼]

We present an Arctic seasonal survey of carbon dioxide partial pressure (pCO2) dynamics within sea ice brine and related air-ice CO2 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 pCO2 (up to 1834 matm) were observed in the sea ice in early April as a consequence of concentration of solutes in brines, CaCO3 precipitation and microbial respiration. CaCO3 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 pCO2 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 CaCO3 and photosynthesis during the sympagic algal bloom. The magnitude of the CO2 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 CO2 fluxes. [less ▲]

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See detailThe carbonate system in the North Sea: sensitivity and model validation
Artioli, Y.; Blackford, J.C.; Butenschön, M. et al

in Journal of Marine Systems (2012), 102-104

The ocean plays an important role in regulating the climate, acting as a sink for carbon dioxide, perturbing the carbonate system and resulting in a slow decrease of seawater pH. Understanding the ... [more ▼]

The ocean plays an important role in regulating the climate, acting as a sink for carbon dioxide, perturbing the carbonate system and resulting in a slow decrease of seawater pH. Understanding the dynamics of the carbonate system in shelf sea regions is necessary to evaluate the impact of Ocean Acidification (OA) in these societally important ecosystems. Complex hydrodynamic and ecosystem coupled models provide a method of capturing the significant heterogeneity of these areas. However rigorous validation is essential to properly assess the reliability of such models. The coupled model POLCOMS–ERSEM has been implemented in the North Western European shelf with a new parameterization for alkalinity explicitly accounting for riverine inputs and the influence of biological processes. The model has been validated in a like with like comparison with North Sea data from the CANOBA dataset. The model shows good to reasonable agreement for the principal variables, physical (temperature and salinity), biogeochemical nutrients) and carbonate system (dissolved inorganic carbon and total alkalinity), but simulation of the erived variables, pH and pCO2, are not yet fully satisfactory. This high uncertainty is attributed mostly o riverine forcing and primary production. This study suggests that the model is a useful tool to provide information on Ocean Acidification scenarios, but uncertainty on pH and pCO2 needs to be reduced, particularly when impacts of OA on ecosystem functions are included in the model systems. [less ▲]

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See detailSpatiotemporal variations of fCO(2) in the North Sea
Omar, A. M.; Olsen, A.; Johannessen, T. et al

in Ocean Science (2010), 6(1), 77-89

Data from two Voluntary Observing Ship (VOS) (2005-2007) augmented with data subsets from ten cruises (1987-2005) were used to investigate the spatiotemporal variations of the CO2 fugacity in seawater ... [more ▼]

Data from two Voluntary Observing Ship (VOS) (2005-2007) augmented with data subsets from ten cruises (1987-2005) were used to investigate the spatiotemporal variations of the CO2 fugacity in seawater (fCO(2)(sw)) in the North Sea at seasonal and inter-annual time scales. The observed seasonal fCO(2)(sw) variations were related to variations in sea surface temperature (SST), biology plus mixing, and air-sea CO2 exchange. Over the study period, the seasonal amplitude in fCO(2)(sw) induced by SST changes was 0.4-0.75 times those resulting from variations in biology plus mixing. Along a meridional transect, fCO(2)(sw) normally decreased northwards (-12 mu atm per degree latitude), but the gradient disappeared/reversed during spring as a consequence of an enhanced seasonal amplitude of fCO(2)(sw) in southern parts of the North Sea. Along a zonal transect, a weak gradient (-0.8 mu atm per degree longitude) was observed in the annual mean fCO(2)(sw). Annually and averaged over the study area, surface waters of the North Sea were CO2 undersaturated and, thus, a sink of atmospheric CO2. However, during summer, surface waters in the region 55.5-54.5 degrees N were CO2 supersaturated and, hence, a source for atmospheric CO2. Comparison of fCO(2)(sw) data acquired within two 1 degrees x1 degrees regions in the northern and southern North Sea during different years (1987, 2001, 2002, and 2005-2007) revealed large interannual variations, especially during spring and summer when year-to-year fCO(2)(sw) differences (approximate to 160-200 mu atm) approached seasonal changes (approximate to 200-250 mu atm). The springtime variations resulted from changes in magnitude and timing of the phytoplankton bloom, whereas changes in SST, wind speed and total alkalinity may have contributed to the summertime interannual fCO(2)(sw) differences. The lowest interannual variation (10-50 mu atm) was observed during fall and early winter. Comparison with data reported in October 1967 suggests that the fCO(2)(sw) growth rate in the central North Sea was similar to that in the atmosphere. [less ▲]

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See detailThe North Sea
Thomas, H.; Bozec, Y.; de Baar, Hein J. W. et al

in Carbon and Nutrient Fluxes in Continental Margins (2009)

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See detailEnhanced ocean carbon storage from anaerobic alkalinity generation in coastal sediments
Thomas, H.; Schiettecatte, L.-S.; Suykens, Kim ULg et al

in Biogeosciences (2009), 6

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 ... [more ▼]

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 CO2 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 (AT) and increases the CO2 buffer capacity of seawater. At both the basin wide and annual scales anaerobic AT 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 CO2 uptake. At the global scale, anaerobic AT generation could be accountable for as much as 60% of the uptake of CO2 in shelf and marginal seas, making this process, the anaerobic pump, a key player in the biological carbon pump. Under future high CO2 conditions oceanic CO2 storage via the anaerobic pump may even gain further relevance because of stimulated ocean productivity. [less ▲]

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See detailMechanisms controlling the air-sea CO2 flux in the North Sea
Prowe, F. A. E.; Thomas, H.; Pätsch, J. et al

in Continental Shelf Research (2009), 29

The mechanisms driving the air–sea exchange of carbon dioxide (CO2) in the North Sea are investigated using the three-dimensional coupled physical–biogeochemical model ECOHAM (ECOlogical model, HAMburg ... [more ▼]

The mechanisms driving the air–sea exchange of carbon dioxide (CO2) in the North Sea are investigated using the three-dimensional coupled physical–biogeochemical model ECOHAM (ECOlogical model, HAMburg). We validate our simulations using field data for the years 2001–2002 and identify the controls of the air–sea CO2 flux for two locations representative for the North Sea’s biogeochemical provinces. In the seasonally stratified northern region, net CO2 uptake is high (2:06molm 2 a 1) due to high net community production (NCP) in the surface water. Overflow production releasing semi labile dissolved organic carbon needs to be considered for a realistic simulation of the low dissolved inorganic carbon (DIC) concentrations observed during summer. This biologically driven carbon drawdown outcompetes the temperature-driven rise in CO2 partial pressure (pCO2) during the productive season. In contrast, the permanently mixed southern region is a weak net CO2 source (0:78molm 2 a 1). NCP is generally low except for the spring bloom because remineralization parallels primary production. Here, the pCO2 appears to be controlled by temperature. [less ▲]

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See detailA revised carbon budget for the North Sea
Paetsch, J.; Kuehn, W.; Borges, Alberto ULg et al

Conference (2009)

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See detailHigh temporal coverage of carbon dioxide measurements in the Southern Bight of the North Sea
Schiettecatte, L. S.; Thomas, H.; Bozec, Y. et al

in Marine Chemistry (2007), 106(1-2), 161-173

A monthly survey of the partial pressure of CO2 (pCO2) was carried in the Southern Bight of the North Sea (SBNS) from June 2003 to May 2004. The spatial variability of the surface distribution of the pCO2 ... [more ▼]

A monthly survey of the partial pressure of CO2 (pCO2) was carried in the Southern Bight of the North Sea (SBNS) from June 2003 to May 2004. The spatial variability of the surface distribution of the pCO2 was relatively small (within a range of 10–70 μatm) compared to the amplitude in the seasonal signal (∼260 μatm). On an annual scale, the pCO2 dynamics appeared to be controlled by biological processes (primary production in springtime and respiratory processes in summer), rather than temperature (in summer). The comparison with measurements carried out in 2001 and 2002 (13 cruises) shows that the inter-annual variability of pCO2 was close to the range of the spatial variability and mostly observed in spring, associated to biological processes (primary production). Net ecosystem production estimated from dissolved inorganic carbon (DIC) temporal variations showed that the SBNS is autotrophic, at an annual rate of 6.3 mol C m−2 yr−1. The decoupling in time between autotrophy in spring and heterotrophy in summer, associated to the relatively rapid flushing time of the water mass in the area (∼70 days), might allow the export of a fraction of the springtime synthesized organic matter to the adjacent areas of the North Sea. The SBNS was on a yearly basis a sink of atmospheric CO2 at a rate of −0.7 mol C m−2 yr−1. [less ▲]

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See detailAssessment of the processes controlling the seasonal variations of dissolved inorganic carbon in the North Sea
Bozec, Y.; Thomas, H.; Schiettecatte, L. S. et al

in Limnology & Oceanography (2006), 51(6), 27462762

We used a seasonal North Sea data set comprising dissolved inorganic carbon (DIC), partial pressure of CO2 (pCO2), and inorganic nutrients to assess the abiotic and biological processes governing the ... [more ▼]

We used a seasonal North Sea data set comprising dissolved inorganic carbon (DIC), partial pressure of CO2 (pCO2), and inorganic nutrients to assess the abiotic and biological processes governing the monthly variations of DIC. During winter, advection and air–sea exchange of CO2 control and increase the DIC content in the surface and deeper layers of the northern and central North Sea, with the atmosphere supplying CO2 on the order of 0.2 mol C m22 month21 to these areas. From February to July, net community production (NCP) controls the seasonal variations of DIC in the surface waters of the entire North Sea, with a net uptake ranging from 0.5 to 1.4 mol C m22 month21. During the August–December period, NCP controls the seasonal variations of DIC in the southern North Sea, with a net release ranging from 0.5 to 0.8 mol C m22 month21. Similarly, during the April–August period in the deeper layer of the northern North Sea, the NCP was the main factor controlling DIC concentrations, with a net release ranging from 0.5 to 5.5 mol C m22 month21. In the surface layer of the North Sea, NCP on the basis of DIC was 4.3 6 0.4 mol C m22 yr21, whereas, NCP on the basis of nitrate was 1.6 6 0.2 mol C m22 yr21. Under nutrient-depleted conditions, preferential recycling (extracellular) of nutrients and intracellular mechanisms occurred and were responsible for the non-Redfield uptake of DIC versus nitrate and phosphate. [less ▲]

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See detailControls of the surface water partial pressure of CO2 in the North Sea
Thomas, H.; Bozec, Y.; de Baar, Hein J. W. et al

in Biogeosciences (2005), 2(4), 323-334

The seasonal variability of the partial pressure of CO2 (pCO2) has been investigated in the North Sea, a northwest European shelf sea. Based on a seasonal and high spatial resolution data set the main ... [more ▼]

The seasonal variability of the partial pressure of CO2 (pCO2) has been investigated in the North Sea, a northwest European shelf sea. Based on a seasonal and high spatial resolution data set the main controlling factors – biological processes and temperature - have been identified and quantified. In the central and northern parts being a CO2- sink all year round, the biological control dominates the temperature control. In the southern part, the temperature control dominates the biological control at an annual scale, since the shallow water column prevents stronger net-CO2 removal from the surface layer due to the absence of seasonal stratification. The consequence is a reversal of the CO2 seato- air flux during the spring bloom period, the only time, when CO2 is taken up from the atmosphere in the southern region. Net community production in the mixed layer has been estimated to 4mol Cm−2 yr−1 with higher values (4.3 mol Cm−2 yr−1) in the northern part and lower values in the southern part (2.6 mol Cm−2 yr−1). [less ▲]

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See detailThe Carbon budget of the North Sea
Thomas, H.; Bozec, Y.; de Baar, Hein J. W. et al

in Biogeosciences (2005), 2(1), 87-96

A carbon budget has been established for the North Sea, a shelf sea on the NW European continental shelf. The carbon exchange fluxes with the North Atlantic Ocean dominate the gross carbon budget. The net ... [more ▼]

A carbon budget has been established for the North Sea, a shelf sea on the NW European continental shelf. The carbon exchange fluxes with the North Atlantic Ocean dominate the gross carbon budget. The net carbon budget – more relevant to the issue of the contribution of the coastal ocean to the marine carbon cycle – is dominated by the carbon inputs from rivers, the Baltic Sea and the atmosphere. The North Sea acts as a sink for organic carbon and thus can be characterised as a heterotrophic system. The dominant carbon sink is the final export to the North Atlantic Ocean. More than 90% of the CO2 taken up from the atmosphere is exported to the North Atlantic Ocean making the North Sea a highly efficient continental shelf pump for carbon. [less ▲]

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