scholarly journals Synoptic evaluation of carbon cycling in the Beaufort Sea during summer: contrasting river inputs, ecosystem metabolism and air–sea CO<sub>2</sub> fluxes

2014 ◽  
Vol 11 (10) ◽  
pp. 2827-2856 ◽  
Author(s):  
A. Forest ◽  
P. Coupel ◽  
B. Else ◽  
S. Nahavandian ◽  
B. Lansard ◽  
...  
Keyword(s):  
Surface Layer ◽  
Organic Carbon ◽  
Sea Ice ◽  
Primary Production ◽  
Arctic Ocean ◽  
Carbon Cycling ◽  
Shelf Break ◽  
The Arctic ◽  
Community Respiration ◽  
Co2 Fluxes

Abstract. The accelerated decline in Arctic sea ice and an ongoing trend toward more energetic atmospheric and oceanic forcings are modifying carbon cycling in the Arctic Ocean. A critical issue is to understand how net community production (NCP; the balance between gross primary production and community respiration) responds to changes and modulates air–sea CO2 fluxes. Using data collected as part of the ArcticNet–Malina 2009 expedition in the southeastern Beaufort Sea (Arctic Ocean), we synthesize information on sea ice, wind, river, water column properties, metabolism of the planktonic food web, organic carbon fluxes and pools, as well as air–sea CO2 exchange, with the aim of documenting the ecosystem response to environmental changes. Data were analyzed to develop a non-steady-state carbon budget and an assessment of NCP against air–sea CO2 fluxes. During the field campaign, the mean wind field was a mild upwelling-favorable wind (~ 5 km h−1) from the NE. A decaying ice cover (< 80% concentration) was observed beyond the shelf, the latter being fully exposed to the atmosphere. We detected some areas where the surface mixed layer was net autotrophic owing to high rates of primary production (PP), but the ecosystem was overall net heterotrophic. The region acted nonetheless as a sink for atmospheric CO2, with an uptake rate of −2.0 ± 3.3 mmol C m−2 d−1 (mean ± standard deviation associated with spatial variability). We attribute this discrepancy to (1) elevated PP rates (> 600 mg C m−2 d−1) over the shelf prior to our survey, (2) freshwater dilution by river runoff and ice melt, and (3) the presence of cold surface waters offshore. Only the Mackenzie River delta and localized shelf areas directly affected by upwelling were identified as substantial sources of CO2 to the atmosphere (> 10 mmol C m−2 d−1). Daily PP rates were generally < 100 mg C m−2 d−1 and cumulated to a total PP of ~ 437.6 × 103 t C for the region over a 35-day period. This amount was about twice the organic carbon delivery by river inputs (~ 241.2 × 103 t C). Subsurface PP represented 37.4% of total PP for the whole area and as much as ~ 72.0% seaward of the shelf break. In the upper 100 m, bacteria dominated (54%) total community respiration (~ 250 mg C m−2 d−1), whereas protozoans, metazoans, and benthos, contributed to 24, 10, and 12%, respectively. The range of production-to-biomass ratios of bacteria was wide (1–27% d−1), while we estimated a narrower range for protozoans (6–11% d−1) and metazoans (1–3% d−1). Over the shelf, benthic biomass was twofold (~ 5.9 g C m−2) the biomass of pelagic heterotrophs (~ 2.4 g C m−2), in accord with high vertical carbon fluxes on the shelf (956 ± 129 mg C m−2 d−1). Threshold PP (PP at which NCP becomes positive) in the surface layer oscillated from 20 to 152 mg C m−2 d−1, with a pattern from low-to-high values as the distance from the Mackenzie River decreased. We conclude that (1) climate change is exacerbating the already extreme biological gradient across the Beaufort shelf–basin system; (2) the Mackenzie Shelf acts as a weak sink for atmospheric CO2, suggesting that PP might exceed the respiration of terrigenous and marine organic matter in the surface layer; and (3) shelf break upwelling can transfer CO2 to the atmosphere, but CO2 outgassing can be attenuated if nutrients brought also by upwelling support diatom production. Our study underscores that cross-shelf exchange of waters, nutrients and particles is a key mechanism that needs to be properly monitored as the Arctic transits to a new state.

scholarly journals Synoptic evaluation of carbon cycling in Beaufort Sea during summer: contrasting river inputs, ecosystem metabolism and air–sea CO<sub>2</sub> fluxes

2013 ◽  
Vol 10 (10) ◽  
pp. 15641-15710
Author(s):  
A. Forest ◽  
P. Coupel ◽  
B. Else ◽  
S. Nahavandian ◽  
B. Lansard ◽  
...  
Keyword(s):  
Surface Layer ◽  
Organic Carbon ◽  
Sea Ice ◽  
Primary Production ◽  
Arctic Ocean ◽  
Carbon Cycling ◽  
Shelf Break ◽  
The Arctic ◽  
Community Respiration ◽  
Co2 Fluxes

Abstract. The accelerated decline in Arctic sea ice combined with an ongoing trend toward a more dynamic atmosphere is modifying carbon cycling in the Arctic Ocean. A critical issue is to understand how net community production (NCP; the balance between gross primary production and community respiration) responds to changes and modulates air–sea CO2 fluxes. Using data collected as part of the ArcticNet-Malina 2009 expedition in southeastern Beaufort Sea (Arctic Ocean), we synthesize information on sea ice, wind, river, water column properties, metabolism of the planktonic food web, organic carbon fluxes and pools, as well as air–sea CO2 exchange, with the aim of identifying indices of ecosystem response to environmental changes. Data were analyzed to develop a non-steady-state carbon budget and an assessment of NCP against air–sea CO2 fluxes. The mean atmospheric forcing was a mild upwelling-favorable wind (~5 km h−1) blowing from the N-E and a decaying ice cover (<80% concentration) was observed beyond the shelf, the latter being fully exposed to the atmosphere. We detected some areas where the surface mixed layer was net autotrophic owing to high rates of primary production (PP), but the ecosystem was overall net heterotrophic. The region acted nonetheless as a sink for atmospheric CO2 with a mean uptake rate of −2.0 ± 3.3 mmol C m−2d−1. We attribute this discrepancy to: (1) elevated PP rates (>600 mg C m−2d−1) over the shelf prior to our survey, (2) freshwater dilution by river runoff and ice melt, and (3) the presence of cold surface waters offshore. Only the Mackenzie River delta and localized shelf areas directly affected by upwelling were identified as substantial sources of CO2 to the atmosphere (>10mmol C m−2d−1). Although generally <100 mg C m−2d−1, daily PP rates cumulated to a total PP of ~437.6 × 103 t C, which was roughly twice higher than the organic carbon delivery by river inputs (~241.2 × 103 t C). Subsurface PP represented 37.4% of total PP for the whole area and as much as ~72.0% seaward of the shelf break. In the upper 100 m, bacteria dominated (54%) total community respiration (~250 mg C m−2d−1), whereas protozoans, metazoans, and benthos, contributed to 24%, 10%, and 12%, respectively. The range of production-to-biomass ratios of bacteria was wide (1–27% d−1), while we estimated a narrower range for protozoans (6–11% d−1) and metazoans (1–3 % d−1). Over the shelf, benthic biomass was twice higher (~5.9 g C m−2) than the biomass of pelagic heterotrophs (~2.4 g C m−2), in accord with high vertical carbon fluxes on the shelf (956 ± 129 mg C m−2d−1). Threshold PP (PP at which NCP becomes positive) in the surface layer oscillated from 20–152 mg C m−2d−1, with a pattern from low-to-high values as the distance from the Mackenzie River decreased. We conclude that: (1) climate change is exacerbating the already extreme biological gradient across the Arctic shelf-basin system; (2) the Mackenzie Shelf acts as a weak sink for atmospheric CO2, implying that PP exceeds the respiration of terrigenous and marine organic matter in the surface layer; and (3) shelf break upwelling can transfer CO2 to the atmosphere, but massive outgassing can be attenuated if nutrients brought also by upwelling support diatom production. Our study underscores that cross-shelf exchange of waters, nutrients and particles is a key mechanism that needs to be properly monitored as the Arctic transits to a new state.

scholarly journals Contrasting trends in sea ice and primary production in the Bering Sea and Arctic Ocean

2012 ◽  
Vol 69 (7) ◽  
pp. 1180-1193 ◽  
Author(s):  
Zachary W. Brown ◽  
Kevin R. Arrigo
Keyword(s):  
Sea Ice ◽  
Primary Production ◽  
Arctic Ocean ◽  
Bering Sea ◽  
Net Primary Productivity ◽  
Remote Sensing Data ◽  
Ice Cover ◽  
The Arctic ◽  
Light Limitation ◽  
The Bering Sea

Abstract Brown, Z. W., and Arrigo, K. R. 2012. Contrasting trends in sea ice and primary production in the Bering Sea and Arctic Ocean. – ICES Journal of Marine Science, 69: . Satellite remote sensing data were used to examine recent trends in sea-ice cover and net primary productivity (NPP) in the Bering Sea and Arctic Ocean. In nearly all regions, diminished sea-ice cover significantly enhanced annual NPP, indicating that light-limitation predominates across the seasonally ice-covered waters of the northern hemisphere. However, long-term trends have not been uniform spatially. The seasonal ice pack of the Bering Sea has remained consistent over time, partially because of winter winds that have continued to carry frigid Arctic air southwards over the past six decades. Hence, apart from the “Arctic-like” Chirikov Basin (where sea-ice loss has driven a 30% increase in NPP), no secular trends are evident in Bering Sea NPP, which averaged 288 ± 26 Tg C year−1 over the satellite ocean colour record (1998–2009). Conversely, sea-ice cover in the Arctic Ocean has plummeted, extending the open-water growing season by 45 d in just 12 years, and promoting a 20% increase in NPP (range 441–585 Tg C year−1). Future sea-ice loss will likely stimulate additional NPP over the productive Bering Sea shelves, potentially reducing nutrient flux to the downstream western Arctic Ocean.

Changes in phytoplankton concentration now drive increased Arctic Ocean primary production

Science ◽  
2020 ◽  
Vol 369 (6500) ◽  
pp. 198-202 ◽  
Author(s):  
K. M. Lewis ◽  
G. L. van Dijken ◽  
K. R. Arrigo
Keyword(s):  
Sea Ice ◽  
Primary Production ◽  
Arctic Ocean ◽  
Open Water ◽  
Water Area ◽  
The Arctic ◽  
Carbon Export ◽  
Phytoplankton Primary Production ◽  
Open Water Area ◽  
The Arctic Ocean

Historically, sea ice loss in the Arctic Ocean has promoted increased phytoplankton primary production because of the greater open water area and a longer growing season. However, debate remains about whether primary production will continue to rise should sea ice decline further. Using an ocean color algorithm parameterized for the Arctic Ocean, we show that primary production increased by 57% between 1998 and 2018. Surprisingly, whereas increases were due to widespread sea ice loss during the first decade, the subsequent rise in primary production was driven primarily by increased phytoplankton biomass, which was likely sustained by an influx of new nutrients. This suggests a future Arctic Ocean that can support higher trophic-level production and additional carbon export.

scholarly journals Nitrate supply and uptake in the Atlantic Arctic sea ice zone: seasonal cycle, mechanisms and drivers

2020 ◽  
Vol 378 (2181) ◽  
pp. 20190361 ◽  
Author(s):  
Sian F. Henley ◽  
Marie Porter ◽  
Laura Hobbs ◽  
Judith Braun ◽  
Robin Guillaume-Castel ◽  
...  
Keyword(s):  
Sea Ice ◽  
Primary Production ◽  
Arctic Ocean ◽  
Nutrient Availability ◽  
Seasonal Cycle ◽  
Nitrate Uptake ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Surface Ocean ◽  
Nitrate Supply

Nutrient supply to the surface ocean is a key factor regulating primary production in the Arctic Ocean under current conditions and with ongoing warming and sea ice losses. Here we present seasonal nitrate concentration and hydrographic data from two oceanographic moorings on the northern Barents shelf between autumn 2017 and summer 2018. The eastern mooring was sea ice-covered to varying degrees during autumn, winter and spring, and was characterized by more Arctic-like oceanographic conditions, while the western mooring was ice-free year-round and showed a greater influence of Atlantic water masses. The seasonal cycle in nitrate dynamics was similar under ice-influenced and ice-free conditions, with biological nitrate uptake beginning near-synchronously in early May, but important differences between the moorings were observed. Nitrate supply to the surface ocean preceding and during the period of rapid drawdown was greater at the ice-free more Atlantic-like western mooring, and nitrate drawdown occurred more slowly over a longer period of time. This suggests that with ongoing sea ice losses and Atlantification, the expected shift from more Arctic-like ice-influenced conditions to more Atlantic-like ice-free conditions is likely to increase nutrient availability and the duration of seasonal drawdown in this Arctic shelf region. The extent to which this increased nutrient availability and longer drawdown periods will lead to increases in total nitrate uptake, and support the projected increases in primary production, will depend on changes in upper ocean stratification and their effect on light availability to phytoplankton as changes in climate and the physical environment proceed. This article is part of the theme issue ‘The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

scholarly journals Effects of sea ice cover on satellite-detected primary production in the Arctic Ocean

2016 ◽  
Vol 12 (11) ◽  
pp. 20160223 ◽  
Author(s):  
Mati Kahru ◽  
Zhongping Lee ◽  
B. Greg Mitchell ◽  
Cynthia D. Nevison
Keyword(s):  
Sea Ice ◽  
Primary Production ◽  
Arctic Ocean ◽  
Barents Sea ◽  
Net Primary Production ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Primary Input ◽  
High Productivity ◽  
The Arctic Ocean

The influence of decreasing Arctic sea ice on net primary production (NPP) in the Arctic Ocean has been considered in multiple publications but is not well constrained owing to the potentially large errors in satellite algorithms. In particular, the Arctic Ocean is rich in coloured dissolved organic matter (CDOM) that interferes in the detection of chlorophyll a concentration of the standard algorithm, which is the primary input to NPP models. We used the quasi-analytic algorithm (Lee et al . 2002 Appl. Opti. 41 , 5755−5772. ( doi:10.1364/AO.41.005755 )) that separates absorption by phytoplankton from absorption by CDOM and detrital matter. We merged satellite data from multiple satellite sensors and created a 19 year time series (1997–2015) of NPP. During this period, both the estimated annual total and the summer monthly maximum pan-Arctic NPP increased by about 47%. Positive monthly anomalies in NPP are highly correlated with positive anomalies in open water area during the summer months. Following the earlier ice retreat, the start of the high-productivity season has become earlier, e.g. at a mean rate of −3.0 d yr −1 in the northern Barents Sea, and the length of the high-productivity period has increased from 15 days in 1998 to 62 days in 2015. While in some areas, the termination of the productive season has been extended, owing to delayed ice formation, the termination has also become earlier in other areas, likely owing to limited nutrients.

scholarly journals Modelling the impact of riverine DON removal by marine bacterioplankton on primary production in the Arctic Ocean

2015 ◽  
Vol 12 (11) ◽  
pp. 3385-3402 ◽  
Author(s):  
V. Le Fouest ◽  
M. Manizza ◽  
B. Tremblay ◽  
M. Babin
Keyword(s):  
Sea Ice ◽  
Primary Production ◽  
Arctic Ocean ◽  
Dissolved Organic Nitrogen ◽  
Organic Nitrogen ◽  
The Arctic ◽  
Biogeochemical Model ◽  
The Impact ◽  
Ice Model ◽  
Annual Flux

Abstract. The planktonic and biogeochemical dynamics of the Arctic shelves exhibit a strong variability in response to Arctic warming. In this study, we employ a biogeochemical model coupled to a pan-Arctic ocean–sea ice model (MITgcm) to elucidate the processes regulating the primary production (PP) of phytoplankton, bacterioplankton (BP), and their interactions. The model explicitly simulates and quantifies the contribution of usable dissolved organic nitrogen (DON) drained by the major circum-Arctic rivers to PP and BP in a scenario of melting sea ice (1998–2011). Model simulations suggest that, on average between 1998 and 2011, the removal of usable riverine dissolved organic nitrogen (RDON) by bacterioplankton is responsible for a ~ 26% increase in the annual BP for the whole Arctic Ocean. With respect to total PP, the model simulates an increase of ~ 8% on an annual basis and of ~ 18% in summer. Recycled ammonium is responsible for the PP increase. The recycling of RDON by bacterioplankton promotes higher BP and PP, but there is no significant temporal trend in the BP : PP ratio within the ice-free shelves over the 1998–2011 period. This suggests no significant evolution in the balance between autotrophy and heterotrophy in the last decade, with a constant annual flux of RDON into the coastal ocean, although changes in RDON supply and further reduction in sea-ice cover could potentially alter this delicate balance.

Lagrangian measurements in the West Spitsbergen Current by Argo floats

2021 ◽  
Author(s):  
Waldemar Walczowski ◽  
Agnieszka Beszczyńska-Möller ◽  
Małgorzata Merchel
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Atlantic Water ◽  
Shelf Break ◽  
The Arctic ◽  
Time Data ◽  
The West ◽  
Argo Floats ◽  
The Arctic Ocean ◽  
West Spitsbergen

&lt;p&gt;Almost 4000 operational Argo floats covering the world's ocean provide near-real-time data on its state. The Arctic is less covered than other waters, but observations collected by Argo floats are gaining in importance. By delivering year-round measurements from the water column down to 2000 m (or to the bottom) along float trajectories, they complement and enhance the synoptic data collected during ship campaigns or by fixed moorings. However, oceanographic measurements with autonomous platforms are significantly limited in the Arctic regions by the presence of sea ice.&lt;/p&gt;&lt;p&gt;Here we present results obtained by Argo floats deployed in 2012-2020 by the Institute of Oceanology Polish Academy of Sciences (IOPAN) during summer campaigns of RV Oceania. In most years, the Argo floats were launched in the eastern branch (core) and in the western branch of the West Spitsbergen Current (WSC) within the Atlantic water inflow towards the Arctic Ocean. Floats deployed in the WSC core drift predominantly northward over the shelf break and upper slope west of Svalbard. After passing Fram Strait the floats usually turn eastward and continue over the northern Svalbard shelf brake, being advected with the Svalbard Branch of the Atlantic inflow into the Arctic Ocean Boundary Current. The easternmost position reached by the IOPAN Argo float was 39.6&amp;#176;E. Ultimately all deployed floats submerge under the sea ice north of Svalbard or farther to the east and die under the ice. Argo floats deployed in the western WSC branch over the underwater ridges, usually recirculate to the west and continue southward with the East Greenland Current. The float WMO 3901851 that drifted to the Labrador Sea, reached the southernmost latitude of 52.5&amp;#176;N and have been working until now for 4.5 years, which is unusual in the Arctic conditions.&amp;#160;&amp;#160; &amp;#160;&lt;/p&gt;&lt;p&gt;The measurements collected in the Marginal Ice Zone are particularly interesting for studying the ocean-atmosphere-ice interactions at the boundary between open and ice-covered ocean as well as they can be used for developing the ice avoidance algorithms for the Argo floats and other under ice sensors and platforms. A number of profiles obtained by Argo floats under the sea ice provide unique measurements in the upper ocean layer that is usually inaccessible from other platforms (e.g., moorings). In 2020 several profiles were collected under the ice cover by Argo floats north of Svalbard and transmitted after the float emerged in the polynya. The eastward flow of warm (up to 4&amp;#176; C at 80 m depth) Atlantic water was observed along the float trajectory over the shelf break. Measurements by Argo floats, revealing the dynamics and transformation of the Atlantic water entering the Arctic Ocean, are compared with ship-borne observations collected during the IOPAN long-term observational program AREX and year-round data from IOPAN moorings deployed north of Svalbard under the A-TWAIN and INTAROS projects.&lt;/p&gt;

Sea ice phenology and timing of primary production pulses in the Arctic Ocean

2012 ◽  
Vol 19 (3) ◽  
pp. 734-741 ◽  
Author(s):  
Rubao Ji ◽  
Meibing Jin ◽  
Øystein Varpe
Keyword(s):  
Sea Ice ◽  
Primary Production ◽  
Arctic Ocean ◽  
The Arctic ◽  
The Arctic Ocean ◽  
Ice Phenology

scholarly journals Regional variability of acidification in the Arctic: a sea of contrasts

2013 ◽  
Vol 10 (2) ◽  
pp. 2937-2965 ◽  
Author(s):  
E. E. Popova ◽  
A. Yool ◽  
A. C. Coward ◽  
T. R. Anderson
Keyword(s):  
Sea Ice ◽  
Primary Production ◽  
Arctic Ocean ◽  
Canadian Arctic ◽  
Atmospheric Co2 ◽  
The Arctic ◽  
Canadian Arctic Archipelago ◽  
Climate Feedbacks ◽  
Regional Variability ◽  
The Arctic Ocean

Abstract. The Arctic Ocean is a region that is particularly vulnerable to the impact of ocean acidification driven by rising atmospheric CO2, negatively impacting calcifying organisms such as coccolithophorids and foraminiferans. In this study, we use an ocean general circulation model, with embedded biogeochemistry and a full description of the carbon cycle, to study the response of pH and saturation states of calcite and aragonite to changing climate in the Arctic Ocean. Particular attention is paid to the strong regional variability within the Arctic and, for comparison, simulation results are contrasted with those for the global ocean. Simulations were run to year 2099 using the RCP 8.5 (the highest IPCC AR5 CO2 emission scenario). The separate impacts of the direct increase in atmospheric CO2 and indirect effects via climate feedbacks (changing temperature, stratification, primary production and fresh water fluxes) were examined by undertaking two simulations, one with the full system and the other in which ocean-atmosphera exchange of CO2 was prevented from increasing beyond the flux calculated for year 2000. Results indicate that climate feedbacks, and spatial heterogeneity thereof, play a strong role in the declines in pH and carbonate saturation (Ω) seen in the Arctic. The central Arctic, Canadian Arctic Archipelago and Baffin Bay show greatest rates of acidification and Ω decline as a result of melting sea ice. In contrast, areas affected by Atlantic inflow including the Greenland Sea and outer shelves of the Barents, Kara and Laptev seas, had minimal decreases in pH and Ω because weakening stratification associated with diminishing ice cover led to greater mixing and primary production. As a consequence, the predicted onset of undersaturation is highly variable regionally within the Arctic, occurring during the decade of 2000–2010 in the Siberian shelves and Canadian Arctic Archipelago, but as late as the 2080s in the Barents and Norwegian Seas. We conclude that, in order to make future projections of acidification and carbon saturation state in the Arctic, regional variability needs to be adequately resolved, with particular emphasis on reliable predictions of the rates of retreat of the sea-ice which are a major source of uncertainty.

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