To examine seasonal and regional variabilities in metabolic status and the coupling of net community production (NCP) and air‐sea CO2fluxes in the western Arctic Ocean, we collected underway measurements of surface O2/Ar and partial pressure of CO2(
The Chukchi Sea is an increasing CO2sink driven by rapid climate changes. Understanding the seasonal variation of air‐sea CO2exchange and the underlying mechanisms of biogeochemical dynamics is important for predicting impacts of climate change on and feedbacks by the ocean. Here, we present a unique data set of underway sea surface partial pressure of CO2(
- Award ID(s):
- 1926158
- NSF-PAR ID:
- 10372602
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 127
- Issue:
- 8
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract p CO2) in the summers of 2016 and 2018. With a box‐model, we demonstrate that accounting for local sea ice history (in addition to wind history) is important in estimating NCP from biological oxygen saturation (Δ(O2/Ar)) in polar regions. Incorporating this sea ice history correction, we found that most of the western Arctic exhibited positive Δ(O2/Ar) and negativep CO2saturation, Δ(p CO2), indicative of net autotrophy but with the relationship between the two parameters varying regionally. In the heavy ice‐covered areas, where air‐sea gas exchange was suppressed, even minor NCP resulted in relatively high Δ(O2/Ar) and lowp CO2in water due to limited gas exchange. Within the marginal ice zone, NCP and CO2flux magnitudes were strongly inversely correlated, suggesting an air to sea CO2flux induced primarily by biological CO2removal from surface waters. Within ice‐free waters, the coupling of NCP and CO2flux varied according to nutrient supply. In the oligotrophic Canada Basin, NCP and CO2flux were both small, controlled mainly by air‐sea gas exchange. On the nutrient‐rich Chukchi Shelf, NCP was strong, resulting in great O2release and CO2uptake. This regional overview of NCP and CO2flux in the western Arctic Ocean, in its various stages of ice‐melt and nutrient status, provides useful insight into the possible biogeochemical evolution of rapidly changing polar oceans. -
Abstract Measurements of pH and nitrate from the Southern Ocean Carbon and Climate Observations and Modeling array of profiling floats were used to assess the ratios of dissolved inorganic carbon (DIC) and nitrate (NO3) uptake during the spring to summer bloom period throughout the Southern Ocean. Two hundred and forty‐three bloom periods were observed by 115 floats from 30°S to 70°S. Similar calculations were made using the Takahashi surface DIC and nitrate climatology. To separate the effects of atmospheric CO2exchange and mixing from phytoplankton uptake, the ratios of changes in DIC to nitrate of surface waters (ΔDIC/ΔNO3) were computed in the Biogeochemical Southern Ocean State Estimate (B‐SOSE) model. Phytoplankton uptake of DIC and nitrate are fixed in B‐SOSE at the Redfield Ratio (RR; 6.6 mol C/mol N). Deviations in the B‐SOSE ΔDIC/ΔNO3must be due to non‐biological effects of CO2gas exchange and mixing. ΔDIC/ΔNO3values observed by floats and in the Takahashi climatology were corrected for the non‐biological effects using B‐SOSE. The corrected, in situ biological uptake ratio (C:N) occurs at values similar to the RR, with two major exceptions. North of 40°S biological DIC uptake is observed with little or no change in nitrate giving high C:N. In the latitude band at 55°S, the Takahashi data give a low C:N value, while floats are high. This may be due to a change in CO2air‐sea exchange in this region from uptake during the Takahashi reference year of 2005 to outgassing of CO2during the years sampled by floats.
-
Abstract The Southern Ocean, an important region for the uptake of anthropogenic carbon dioxide (CO2), features strong surface currents due to substantial mesoscale meanders and eddies. These features interact with the wind and modify the momentum transfer from the atmosphere to the ocean. Although such interactions are known to reduce momentum transfer, their impact on air‐sea carbon exchange remains unclear. Using a 1/20° physical‐biogeochemical coupled ocean model, we examined the impact of the current‐wind interaction on the surface carbon concentration and the air‐sea carbon exchange in the Southern Ocean. The current‐wind interaction decreased winter partial pressure of CO2(
p CO2) at the ocean surface mainly south of the northern subantarctic front. It also reducedp CO2in summer, indicating enhanced uptake, but not to the same extent as the winter loss. Consequently, the net outgassing of CO2was found to be reduced by approximately 17% when including current‐wind interaction. These changes stem from the combined effect of vertical mixing and Ekman divergence. A budget analysis of dissolved inorganic carbon (DIC) revealed that a weakening of vertical mixing by current‐wind interaction reduces the carbon supply from below, and particularly so in winter. The weaker wind stress additionally lowers the subsurface DIC concentration in summer, which can affect the vertical diffusive flux of carbon in winter. Our study suggests that ignoring current‐wind interactions in the Southern Ocean can overestimate winter CO2outgassing. -
Abstract The Arctic Ocean has turned from a perennial ice‐covered ocean into a seasonally ice‐free ocean in recent decades. Such a shift in the air‐ice‐sea interface has resulted in substantial changes in the Arctic carbon cycle and related biogeochemical processes. To quantitatively evaluate how the oceanic CO2sink responds to rapid sea ice loss and to provide a mechanistic explanation, here we examined the air‐sea CO2flux and the regional CO2sink in the western Arctic Ocean from 1994 to 2019 by two complementary approaches: observation‐based estimation and a data‐driven box model evaluation. The
p CO2observations and model results showed that summer CO2uptake significantly increased by about 1.4 ± 0.6 Tg C decade−1in the Chukchi Sea, primarily due to a longer ice‐free period, a larger open area, and an increased primary production. However, no statistically significant increase in CO2sink was found in the Canada Basin and the Beaufort Sea based on both observations and modeled results. The reduced sea ice coverage in summer in the Canada Basin and the enhanced wind speed in the Beaufort Sea potentially promoted CO2uptake, which was, however, counteracted by a rapidly decreased air‐seap CO2gradient therein. Therefore, the current and future Arctic Ocean CO2uptake trends cannot be sufficiently reflected by the air‐seap CO2gradient alone because of the sea ice variations and other environmental factors. -
Abstract The carbonate chemistry in the Dalton Polynya in East Antarctica (115°–123°E) was investigated in summer 2014/2015 using high‐frequency underway measurements of CO2fugacity (
f CO2) and discrete water column measurements of total dissolved inorganic carbon (TCO2) and total alkalinity. Air‐sea CO2fluxes indicate this region was a weak net source of CO2to the atmosphere (0.7 ± 0.9 mmol C m−2day−1) during the period of observation, with the largest degree of surface water supersaturation (Δf CO2= +45 μatm) in ice‐covered waters near the Totten Ice Shelf (TIS) as compared to the ice‐free surface waters in the Dalton Polynya. The seasonal depletion of mixed‐layer TCO2(6 to 51 μmol/kg) in ice‐free regions was primarily driven by sea ice melt and biological CO2uptake. Estimates of net community production (NCP) reveal net autotrophy in the ice‐free Dalton Polynya (NCP = 5–20 mmol C m−2day−1) and weakly heterotrophic waters near the ice‐covered TIS (NCP = −4–0 mmol C m−2day−1). Satellite‐derived estimates of chlorophylla (Chla ) and sea ice coverage suggest that the early summer season in 2014/2015 was anomalous relative to the long‐term (1997–2017) record, with lower surface Chla concentrations and a greater degree of sea ice cover during the period of observation; the implications for seasonal primary production and air‐sea CO2exchange are discussed. This study highlights the importance of both physical and biological processes in controlling air‐sea CO2fluxes and the significant interannual variability of the CO2system in Antarctic coastal regions.