Melissa Chierici

A carbon budget for the Arctic Ocean

We present a carbon budget for the Arctic Ocean that is based on estimates of water mass transformation and transport. The budget is constrained by conservation of mass and salt. In the model, the Eurasian and Canadian basins have been divided into five and six boxes, respectively, based on the prevailing water masses. In addition, there are three boxes representing the shelf areas. Total dissolved inorganic (C T ) and organic (TOC) carbon concentrations for the different water masses and different regions are used, together with the volume flows, to calculate the carbon transports. The carbon budget calculation shows that at present the oceanic transport into the Arctic Ocean is larger than out, that is, 3.296±0.008 Gt C yr -1 of C T transported in and 3.287±0.004 Gt C yr - transported out with the corresponding values for TOC being 0.134±0.009 Gt C yr -1 and 0.122±0.006 Gt C yr -1 , respectively. However, the outflowing waters are older than the inflowing waters and had thus been exposed to an atmosphere with lower concentration of anthropogenic carbon dioxide when entering the Arctic Ocean. When recalculating the budget to the preindustrial scenario, assuming steady state, the C T transport changes to 3.243 Gt C yr - in and 3.266 Gt C yr -1 out. To balance the preindustrial transports, assuming no change in the TOC fluxes, a direct input of atmospheric carbon dioxide of 0.011±0.014 Gt C yr -1 is required. Added to this is the burial of organic matter which is calculated as 0.013±0.010 Gt C yr -1 using a recycling efficiency of 80% [Hulth, 1995] and a new production of 0.05 Gt C yr -1 [Anderson et al., 1994]. An indirect contribution of atmospheric carbon dioxide via runoff adds 0.017±0.004 Gt C yr -1 , resulting in a preindustrial total atmospheric input of 0.041±0.018 Gt C yr -1 .

Leads in Arctic pack ice enable early phytoplankton blooms below snow-covered sea ice

The Arctic icescape is rapidly transforming from a thicker multiyear ice cover to a thinner and largely seasonal first-year ice cover with significant consequences for Arctic primary production. One critical challenge is to understand how productivity will change within the next decades. Recent studies have reported extensive phytoplankton blooms beneath ponded sea ice during summer, indicating that satellite-based Arctic annual primary production estimates may be significantly underestimated. Here we present a unique time-series of a phytoplankton spring bloom observed beneath snow-covered Arctic pack ice. The bloom, dominated by the haptophyte algae Phaeocystis pouchetii, caused near depletion of the surface nitrate inventory and a decline in dissolved inorganic carbon by 16 ± 6 g C m−2. Ocean circulation characteristics in the area indicated that the bloom developed in situ despite the snow-covered sea ice. Leads in the dynamic ice cover provided added sunlight necessary to initiate and sustain the bloom. Phytoplankton blooms beneath snow-covered ice might become more common and widespread in the future Arctic Ocean with frequent lead formation due to thinner and more dynamic sea ice despite projected increases in high-Arctic snowfall. This could alter productivity, marine food webs and carbon sequestration in the Arctic Ocean.

Influence of m-cresol purple indicator additions on the pH of seawater samples : correction factors evaluated from a chemical speciation model

Abstract The perturbation of the indicator m -cresol purple on the pH in seawater is illustrated in diagrams, representing measurements in 1-cm and 5-cm cells. The diagrams apply to a measured pH interval of 7.4–8.4 using a 2-mM stock solution of m -cresol purple sodium salt dissolved in seawater. The magnitude of the perturbation is described as correction values, i.e., the change in seawater pH caused by the indicator. The diagrams are based on calculations made by using the equilibrium speciation programme, MARINHALT. From these calculations, and least squares fitting methods, pH correction values are described in terms of the pH difference between each seawater sample and the pH of an indicator stock solution. Calculations are performed for a typical high latitude water and a north Pacific deep water. Diagrams are presented for a salinity of 35 and a temperature of 15°C. Responses to salinities between 32 and 36 and temperatures 15–25°C are illustrated as well. A ±0.05 pH difference between a seawater sample and an indicator stock solution gives a correction of less than 0.001 pH unit for a 1-cm cell. For a 5-cm cell, pH differences between the indicator stock solution and a seawater sample as large as ±0.3 cause corrections smaller than ±0.001 pH unit. Calculations demonstrate that the five-fold lower indicator concentration used with 5-cm cells decreases the perturbation effect by approximately a factor of five relative to 1-cm cells.

Uptake of atmospheric carbon dioxide in the Barents Sea

The uptake of atmospheric carbon dioxide has been estimated from data collected in 1999 along a transect in the Barents Sea ranging from 72.5jN, 31jE to 78.2jN, 34jE. The uptake has been calculated from the change in total dissolved inorganic carbon, total alkalinity, nitrate and salinity in the water column and from the conservation of mass. The average uptake of carbon dioxide in Atlantic water from late winter until the time of investigation (about 3 months) was estimated to be 29F11 g Cm � 2 . The uptake estimate has been compared with integrated air–sea flux calculated from the wind speed and the difference in fCO2 between the atmosphere and the ocean. The computed air–sea flux has been compared to estimates of new production, with the latter having a clearer trend of decreasing values with increasing latitude than for the air–sea flux. This could be explained by the decreasing surface water temperature with increasing latitude, indicating that cooling (increasing the solubility of CO2) is an important factor in driving the air–sea flux. This fact might be different if our study had been performed later in the season. D 2002 Elsevier Science B.V. All rights reserved.

Anthropogenic carbon dioxide in the Arctic Ocean - inventory and sinks

An inventory and sequestering rate of anthropogenic carbon dioxide CTanthro in the Arctic Ocean, calculated by a plume-entrainment model, are presented. The plume is initiated by a fraction rj leaving the shelf break at 200 m, followed by an entrainment of rj for every 150 m depth the plume descends. The model is constrained by the CFC-12 and carbon tetrachloride (CCl4) distributions, with the concentrations of CFC-12, CCl4, and CTanthro in the source water calculated assuming a water in 100% equilibrium with the atmosphere. The model is run from 1750 to 1991, the latter being the year in which measurements of the transient tracers in the water column of the central Arctic Ocean were made. The output from the model gives sinks of anthropogenic carbon dioxide in 1991 of 0.026±0.009 Gt C yr−1, of which 0.0194 Gt C yr−1 is in the Eurasian Basin and 0.0070 Gt C yr−1 in the Canadian Basin. This amounts to about 1% of the total oceanic uptake of anthropogenic CO2. The Arctic Ocean inventory of anthropogenic carbon dioxide in 1991 was 1.35(+0.12/−0.06) Gt C, which is about 1% of the total oceanic inventory. The sensitivity of the computed sinks and inventories to various model assumptions was estimated.

Impact of sea-ice processes on the carbonate system and ocean acidification at the ice-water interface of the Amundsen Gulf, Arctic Ocean

[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 calciumcarbonate (CaCO3) saturation states of aragonite (XAr) and calcite (XCa) at the ice-water interface (UIW). Based on total inorganic carbon (CT) and total alkalinity (AT), and derived pH, CO2, carbonate ion ([CO3 22 ]) concentrations and X, we investigated the major drivers such as brine rejection, CaCO3 precipitation, bacterial respiration, primary production and CO2-gas flux in sea ice, brine, frost flowers and UIW. We estimated large variability in seaice CT at the top, mid, and bottom ice. Changes due to CaCO3 and CO2-gas flux had large impact on CT 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, [CO2] 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 CO2-enriched brine from solid CaCO3. Conversely, during ice melt, [CO3 22 ] increased by 90 mmol kg 21 in the UIW, and X increased by 1.4 between March and May, likely due to CaCO3 dissolution and primary production. We estimated that increased ice melt would lead to enhanced oceanic uptake of inorganic carbon to the surface layer.

Annual carbon fluxes in the upper Greenland Sea based on measurements and a box-model approach

Annual carbon flux in the upper Greenland Sea based on measurements and a box model approach

Ocean Acidification Effects on Atlantic Cod Larval Survival and Recruitment to the Fished Population

How fisheries will be impacted by climate change is far from understood. While some fish populations may be able to escape global warming via range shifts, they cannot escape ocean acidification (OA), an inevitable consequence of the dissolution of anthropogenic carbon dioxide (CO2) emissions in marine waters. How ocean acidification affects population dynamics of commercially important fish species is critical for adapting management practices of exploited fish populations. Ocean acidification has been shown to impair fish larvae’s sensory abilities, affect the morphology of otoliths, cause tissue damage and cause behavioural changes. Here, we obtain first experimental mortality estimates for Atlantic cod larvae under OA and incorporate these effects into recruitment models. End-of-century levels of ocean acidification (~1100 μatm according to the IPCC RCP 8.5) resulted in a doubling of daily mortality rates compared to present-day CO2 concentrations during the first 25 days post hatching (dph), a critical phase for population recruitment. These results were consistent under different feeding regimes, stocking densities and in two cod populations (Western Baltic and Barents Sea stock). When mortality data were included into Ricker-type stock-recruitment models, recruitment was reduced to an average of 8 and 24% of current recruitment for the two populations, respectively. Our results highlight the importance of including vulnerable early life stages when addressing effects of climate change on fish stocks.

Barium and carbon fluxes in the Canadian Arctic Archipelago

The seasonal and spatial variability of dissolved Barium (Ba) in the Amundsen Gulf,southeastern Beaufort Sea, was monitored over a full year from September 2007 to September 2008. Dissolved Ba displays a nutrient・type behavior: the maximum water column concentration is located below the surface layer. The highest Ba concentrations are typically observed at river mouths, the lowest concentrations are found in water masses of Atlantic origin. Barium concentrations decrease eastward through the Canadian Arctic Archipelago. Barite (BaSO 4 ) saturation is reached at the maximum dissolved Ba concentrations in the subsurface layer, whereas the rest of the water column is undersaturated. A three end‐member mixing model comprising freshwater from sea・ice melt and rivers, as well as upper halocline water, is used to establish their relative contributions to the Ba concentrations in the upper water column of the Amundsen Gulf. Based on water column and riverine Ba contributions, we assess the depletion of dissolved Ba by formation and sinking of biologically bound Ba (bio・Ba), from which we derive an estimate of the carbon export production. In the upper 50 m of the water column of the Amundsen Gulf, riverine Ba accounts for up to 15% of the available dissolved Ba inventory, of which up to 20% is depleted by bio-Ba formation and export. Since riverine inputs and Ba export occur concurrently, the seasonal variability of dissolved Ba in the upper water column is moderate. Assuming a fixed organic carbon to bio・Ba flux ratio, carbon export out of the surface layer is estimated at 1.8 ・ 0.45 mol C m −2 yr −1 . Finally, we propose a climatological carbon budget for the Amundsen Gulf based on recent literature data and our findings, the latter bridging the surface and subsurface water carbon cycles.

Flux of anthropogenic carbon into the deep Greenland Sea

Measurements of the carbonate system and the transient tracers, CFC-11 and carbon tetrachloride (CCl4), in the Greenland Sea and western Eurasian Basin are used to deduce the sources and magnitude of excess dissolved inorganic carbon in the deep Greenland Sea. The salinity in the deep Greenland Sea has increased during the past 20 years as a result of Arctic Ocean water advecting into the area. From salinity and temperature data the relative amount of advective water below 1500 m is estimated to ∼2% yr−1 between 1982 and 1994. Data from the western Eurasian Basin, collected during the Oden 91 cruise, are used as the advective source waters. A mixing box model is applied to estimate the evolution of CFCs and anthropogenic total dissolved inorganic carbon in the deep waters of the Greenland Sea since preindustrial times. The source functions are the surface water concentrations of CFC-11, CCl4, and total dissolved inorganic carbon CT, which are the result of anthropogenic emission. In order to explain the measured CFC data in the Greenland Sea an annual percent renewal by deep water formation of between 0.5 and 1.2% is needed below 1500 m, corresponding to a mean ventilation of 0.17±0.05 Sv, considering realistic uncertainties in the calculations. This ventilation gives a sequestering of anthropogenic carbon dioxide, which in 1994 equaled 2.4±0.7×1012 g C yr−1.