skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Improved atmospheric constraints on Southern Ocean CO 2 exchange
We present improved estimates of air–sea CO2exchange over three latitude bands of the Southern Ocean using atmospheric CO2measurements from global airborne campaigns and an atmospheric 4-box inverse model based on a mass-indexed isentropic coordinate (Mθe). These flux estimates show two features not clearly resolved in previous estimates based on inverting surface CO2measurements: a weak winter-time outgassing in the polar region and a sharp phase transition of the seasonal flux cycles between polar/subpolar and subtropical regions. The estimates suggest much stronger summer-time uptake in the polar/subpolar regions than estimates derived through neural-network interpolation of pCO2data obtained with profiling floats but somewhat weaker uptake than a recent study by Long et al. [Science374, 1275–1280 (2021)], who used the same airborne data and multiple atmospheric transport models (ATMs) to constrain surface fluxes. Our study also uses moist static energy (MSE) budgets from reanalyses to show that most ATMs tend to have excessive diabatic mixing (transport across moist isentrope, θe, or Mθesurfaces) at high southern latitudes in the austral summer, which leads to biases in estimates of air–sea CO2exchange. Furthermore, we show that the MSE-based constraint is consistent with an independent constraint on atmospheric mixing based on combining airborne and surface CO2observations.  more » « less
Award ID(s):
1839218
PAR ID:
10528641
Author(s) / Creator(s):
; ; ; ; ; ; ; ;
Publisher / Repository:
National Academy of Sciences
Date Published:
Journal Name:
Proceedings of the National Academy of Sciences
Volume:
121
Issue:
6
ISSN:
0027-8424
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; (, Global Biogeochemical Cycles)
    Abstract Seasonal change of atmospheric potential oxygen (APO ∼ O2 + CO2) is a tracer for air‐sea O2flux with little sensitivity to the terrestrial exchange of O2and CO2. In this study, we present the tropospheric distribution and inventory of APO in each hemisphere with seasonal resolution, using O2and CO2measurements from discrete airborne campaigns between 2009 and 2018. The airborne data are represented on a mass‐weighted isentropic coordinate (Mθe) as an alternative to latitude, which reduces the noise from synoptic variability in the APO cycles. We find a larger seasonal amplitude of APO inventory in the Southern Hemisphere relative to the Northern Hemisphere, and a larger amplitude in high latitudes (lowMθe) relative to low latitudes (highMθe) within each hemisphere. With a box model, we invert the seasonal changes in APO inventory to yield estimates of air‐sea flux cycles at the hemispheric scale. We found a larger seasonal net outgassing of APO in the Southern Hemisphere (518 ± 52.6 Tmol) than in the Northern Hemisphere (342 ± 52.1 Tmol). Differences in APO phasing and amplitude between the hemispheres suggest distinct physical and biogeochemical mechanisms driving the air‐sea O2fluxes, such as fall outgassing of photosynthetic O2in the Northern Hemisphere, possibly associated with the formation of the seasonal subsurface shallow oxygen maximum. We compare our estimates with four model‐ and observation‐based products, identifying key limitations in these products or in the tools used to create them. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al (, Science)
    The Southern Ocean plays an important role in determining atmospheric carbon dioxide (CO 2 ), yet estimates of air-sea CO 2 flux for the region diverge widely. In this study, we constrained Southern Ocean air-sea CO 2 exchange by relating fluxes to horizontal and vertical CO 2 gradients in atmospheric transport models and applying atmospheric observations of these gradients to estimate fluxes. Aircraft-based measurements of the vertical atmospheric CO 2 gradient provide robust flux constraints. We found an annual mean flux of –0.53 ± 0.23 petagrams of carbon per year (net uptake) south of 45°S during the period 2009–2018. This is consistent with the mean of atmospheric inversion estimates and surface-ocean partial pressure of CO 2 ( P co 2 )–based products, but our data indicate stronger annual mean uptake than suggested by recent interpretations of profiling float observations. 
    more » « less
  3. ; ; ; ; ; ; ; ; ; ; et al (, Journal of Geophysical Research: Oceans)
    Abstract 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(pCO2) and discrete samples of biogeochemical properties collected in five consecutive cruises in 2014 and examine the seasonal variations in air‐sea CO2flux and net community production (NCP). We found that thermal and non‐thermal effects have different impacts on sea surfacepCO2and thus the air‐sea CO2flux in different water masses. The Bering summer water combined with meltwater has a significantly greater atmospheric CO2uptake potential than that of the Alaskan Coastal Water in the southern Chukchi Sea in summer, due to stronger biological CO2removal and a weaker thermal effect. By analyzing the seasonal drawdown of dissolved inorganic carbon (DIC) and nutrients, we found that DIC‐based NCP was higher than nitrate‐based NCP by 66%–84% and attributable to partially decoupled C and N uptake because of a variable phytoplankton stoichiometry. A box model with a non‐Redfield C:N uptake ratio can adequately reproduce observedpCO2and DIC, which reveals that, during the intensive growing season (late spring to early summer), 30%–46% CO2uptake in the Chukchi Sea was supported by a flexible stoichiometry of phytoplankton. These findings have important ramification for forecasting the responses of CO2uptake of the Chukchi ecosystem to climate change. 
    more » « less
  4. ; ; ; ; (, Journal of Geophysical Research: Oceans)
    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(pCO2) at the ocean surface mainly south of the northern subantarctic front. It also reducedpCO2in 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. 
    more » « less
  5. ; ; ; ; ; ; ; ; (, Global Biogeochemical Cycles)
    Abstract 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(pCO2) 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 negativepCO2saturation, Δ(pCO2), 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 lowpCO2in 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. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email