Net Community Production and Carbon Exchange From Winter to Summer in the Atlantic Water Inflow to the Arctic Ocean

Abstract

The eastern Fram Strait and area north of Svalbard, are influenced by the inflow of warm Atlantic water, which is high in nutrients and CO 2 , influencing the carbon flux into the Arctic Ocean. However, these estimates are mainly based on summer data and there is still doubt on the size of the net ocean Arctic CO 2 sink. We use data on carbonate chemistry and nutrients from three cruises in 2014 in the CarbonBridge project (January, May, and August) and one in Fram Strait (August). We describe the seasonal variability and the major drivers explaining the inorganic carbon change (C DIC ) in the upper 50 m, such as photosynthesis (C BIO ), and air-sea CO 2 exchange (C EXCH ). Remotely sensed data describes the evolution of the bloom and net community production. The focus area encompasses the meltwater-influenced domain (MWD) along the ice edge, the Atlantic water inflow (AWD), and the West Spitsbergen shelf (SD). The C BIO total was 2.2 mol C m −2 in the MWD derived from the nitrate consumption between January and May. Between January and August, the C BIO was 3.0 mol C m −2 in the AWD, thus C BIO between May and August was 0.8 mol C m −2 . The ocean in our study area mainly acted as a CO 2 sink throughout the period. The mean CO 2 sink varied between 0.1 and 2.1 mol C m −2 in the AWD in August. By the end of August, the AWD acted as a CO 2 source of 0.7 mol C m −2 , attributed to vertical mixing of CO 2 -rich waters and contribution from respiratory CO 2 as net community production declined. The oceanic CO 2 uptake (C EXCH ) from the atmosphere had an impact on C DIC between 5 and 36%, which is of similar magnitude as the impact of the calcium carbonate (CaCO 3 , C CALC ) dissolution of 6-18%. C CALC was attributed to be caused by a combination of the sea-ice ikaite dissolution and dissolution of advected CaCO 3 shells from the south. Indications of denitrification were observed, associated with sea-ice meltwater and bottom shelf processes. C BIO played a major role (48-89%) for the impact on C DIC .

Terrestrial Inputs Drive Seasonality in Organic Matter and Nutrient Biogeochemistry in a High Arctic Fjord System (Isfjorden, Svalbard)

“…Concentrations of PO 4 were also high, reaching 1.7 µmol L −1 in river samples in August. These concentrations are higher than concentrations measured from AW advected from the shelf (maximum of 2 µmol L −1 for NO 2 + NO 3 and 0.4 µmol L −1 for PO 4 in this study, but other observations from Svalbard show 6-11 µmol L −1 for N and 0.8 µmol L −1 for P (Chierici et al, 2019;Halbach et al, 2019). While SiO 2 has been associated with glacial meltwater from contact with silica-rich bedrock in Isfjorden (Fransson et al, 2015), Kongsfjorden (Halbach et al, 2019) and Greenland fjords (Meire et al, 2016;Kanna et al, 2018;Hendry et al, 2019), N and P have been linked primarily to advected deep water.…”

Estimates of net community production from multiple approaches surrounding the spring ice-edge bloom in Baffin Bay

“…These values are much higher than our maximum NCP rate in eastern Baffin Bay of 5.7 mol C m -2 ; however, given the declining NCP and primary production trends over the past decade within the North Water region (Bélanger et al, 2013;Bergeron and Tremblay, 2014;Blais et al, 2017;, such high rates of NCP are no longer occurring within that region. Our reported seasonal NCP rates within the Atlantic sector of Baffin Bay (1.4-5.7 mol C m -2 ) fall in the same approximate range as those reported more recently in the productive Barents Sea (2.3-4.2 mol C m -2 ; Fransson et al, 2001;Codispoti et al, 2013;Chierici et al, 2019).…”

Seasonal dynamics of carbonate chemistry, nutrients and CO2 uptake in a sub-Arctic fjord

“…The mean atmospheric CO 2 uptake of 0.86 ± 0.63 mmol m −2 day −1 is similar to that of 0.73 ± 0.40 mmol m −2 day −1 estimated for a marginal Arctic coastal environment of Hudson Bay, Canada (Else et al, 2008b). Wind speeds in Kaldfjorden were dampened due to orographic steering, compared to measurements off the shelf (Nordby et al, 1999); thus, atmospheric CO 2 uptake in Kaldfjorden of 2.7 mmol m -2 day -1 is weak compared with the CO 2 influx of >15 mmol m −2 day −1 for the Norwegian Sea (Yasunaka et al, 2016) and the nonice-covered Arctic shelf seas that generally absorb CO 2 at between 1 and 15 mmol m −2 day −1 (Omar et al, 2005;Cai et al, 2006;Else et al, 2008aElse et al, , 2013Ericson et al, 2018;Chierici et al, 2019). Enhanced CO 2 uptake in higher latitude waters results from substantial blooms, greater biological productivity and subsequent export of organic matter to deeper waters, coupled to strong winds enhancing oceanic CO 2 uptake.…”

“…Calcium carbonate (CaCO 3 ) saturation state (Ω) for the biomineral aragonite and the surface water fugacity of CO 2 (fCO 2 ) were determined from C T and A T , and in situ temperature, salinity, pressure and macronutrient concentrations using the CO 2 system program CO2SYS (Lewis and Wallace, 1998;van Heuven, 2011). The carbonic acid dissociation constants (pK 1 and pK 2 ) of Mehrbach et al (1973) as refit by Dickson and Millero (1987) were selected, as they have shown good agreement between measured and calculated values in Arctic waters (Chen et al, 2015;Woosley et al, 2017) and were selected for similar studies in sub-Arctic/Arctic regions (Chierici et al, 2019;Ericson et al, 2019). Ω is used as an indicator for changes in carbonate chemistry in relation to ocean acidification.…”