Interannual sea–air CO2 flux variability from an observation-driven ocean mixed-layer scheme (original) (raw)
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Interannual sea–air CO2 flux variability from an observation-driven ocean mixed-layer scheme
Interannual anomalies in the sea-air carbon dioxide (CO 2 ) exchange have been estimated from surface-ocean CO 2 partial pressure measurements. Available data are sufficient to constrain these anomalies in large parts of the tropical and North Pacific and in the North Atlantic, in some areas covering the period from the mid 1980s to 2011. Global interannual variability is estimated as about 0.31 Pg C yr −1 (temporal standard deviation 1993-2008). The tropical Pacific accounts for a large fraction of this global variability, closely tied to El Niño-Southern Oscillation (ENSO). Anomalies occur more than 6 months later in the east than in the west. The estimated amplitude and ENSO response are roughly consistent with independent information from atmospheric oxygen data. This both supports the variability estimated from surface-ocean carbon data and demonstrates the potential of the atmospheric oxygen signal to constrain ocean biogeochemical processes. The ocean variability estimated from surface-ocean carbon data can be used to improve land CO 2 flux estimates from atmospheric inversions. C. Rödenbeck et al.: Interannual sea-air CO 2 flux variations r) r)
Geophysical Research Letters, 2004
We address an ongoing debate regarding the geographic distribution of interannual variability in ocean-atmosphere carbon exchange. We find that, for 1983-1998, both novel high-resolution atmospheric inversion calculations and global ocean biogeochemical models place the primary source of global CO 2 air-sea flux variability in the Pacific Ocean. In the model considered here, this variability is clearly associated with the El Niño/Southern Oscillation cycle. Both methods also indicate that the Southern Ocean is the second-largest source of air-sea CO 2 flux variability, and that variability is small throughout the Atlantic, including the North Atlantic, in contrast to previous studies.
Air–sea CO2 flux in the Pacific Ocean for the period 1990–2009
Biogeosciences, 2014
Air-sea CO 2 fluxes over the Pacific Ocean are known to be characterized by coherent large-scale structures that reflect not only ocean subduction and upwelling patterns, but also the combined effects of wind-driven gas exchange and biology. On the largest scales, a large net CO 2 influx into the extratropics is associated with a robust seasonal cycle, and a large net CO 2 efflux from the tropics is associated with substantial interannual variability. In this work, we have synthesized estimates of the net air-sea CO 2 flux from a variety of products, drawing upon a variety of approaches in three sub-basins of the Pacific Ocean, i.e., the North Pacific extratropics (18-66 • N), the tropical Pacific (18 • S-18 • N), and the South Pacific extratropics (44.5-18 • S). These approaches include those based on the measurements of CO 2 partial pressure in surface seawater (pCO 2 sw), inversions of ocean-interior CO 2 data, forward ocean biogeochemistry models embedded in the ocean general circulation models (OBGCMs), a model with assimilation of pCO 2 sw data, and inversions of atmospheric CO 2 measurements. Long-term means, interannual variations and mean seasonal variations of the regionally integrated fluxes were compared in each of the sub-basins over the last two decades, spanning the period from 1990 through 2009. A simple average of the long-term mean fluxes obtained with surface water pCO 2 diagnostics and those obtained with ocean-interior CO 2 inversions are −0.47 ± 0.13 Pg C yr −1 in Published by Copernicus Publications on behalf of the European Geosciences Union. 710 M. Ishii et al.: Air-sea CO 2 flux in the Pacific Ocean the North Pacific extratropics, +0.44 ± 0.14 Pg C yr −1 in the tropical Pacific, and −0.37 ± 0.08 Pg C yr −1 in the South Pacific extratropics, where positive fluxes are into the atmosphere. This suggests that approximately half of the CO 2 taken up over the North and South Pacific extratropics is released back to the atmosphere from the tropical Pacific. These estimates of the regional fluxes are also supported by the estimates from OBGCMs after adding the riverine CO 2 flux, i.e., −0.49 ± 0.02 Pg C yr −1 in the North Pacific extratropics, +0.41 ± 0.05 Pg C yr −1 in the tropical Pacific, and −0.39 ± 0.11 Pg C yr −1 in the South Pacific extratropics. The estimates from the atmospheric CO 2 inversions show large variations amongst different inversion systems, but their median fluxes are consistent with the estimates from climatological pCO 2 sw data and pCO 2 sw diagnostics. In the South Pacific extratropics, where CO 2 variations in the surface and ocean interior are severely undersampled, the difference in the air-sea CO 2 flux estimates between the diagnostic models and ocean-interior CO 2 inversions is larger (0.18 Pg C yr −1). The range of estimates from forward OBGCMs is also large (−0.19 to −0.72 Pg C yr −1). Regarding interannual variability of air-sea CO 2 fluxes, positive and negative anomalies are evident in the tropical Pacific during the cold and warm events of the El Niño-Southern Oscillation in the estimates from pCO 2 sw diagnostic models and from OBGCMs. They are consistent in phase with the Southern Oscillation Index, but the peak-to-peak amplitudes tend to be higher in OBGCMs (0.40 ± 0.09 Pg C yr −1) than in the diagnostic models (0.27 ± 0.07 Pg C yr −1).
Ocean Science, 2013
A temporally and spatially resolved estimate of the global surface-ocean CO 2 partial pressure field and the sea-air CO 2 flux is presented, obtained by fitting a simple data-driven diagnostic model of ocean mixed-layer biogeochemistry to surface-ocean CO 2 partial pressure data from the SOCAT v1.5 database. Results include seasonal, interannual, and short-term (daily) variations. In most regions, estimated seasonality is well constrained from the data, and compares well to the widely used monthly climatology by Takahashi et al. (2009). Comparison to independent data tentatively supports the slightly higher seasonal variations in our estimates in some areas. We also fitted the diagnostic model to atmospheric CO 2 data. The results of this are less robust, but in those areas where atmospheric signals are not strongly influenced by land flux variability, their seasonality is nevertheless consistent with the results based on surface-ocean data. From a comparison with an independent seasonal climatology of surface-ocean nutrient concentration, the diagnostic model is shown to capture relevant surface-ocean biogeochemical processes reasonably well. Estimated interannual variations will be presented and discussed in a companion paper. Ocean Sci., 9, 193-216, 2013 www.ocean-sci.net/9/193/2013/ C. Rödenbeck et al.: Global surface-ocean p CO 2 and sea-air CO 2 flux variability 195 22 C. Rödenbeck et al.: Sea-air CO 2 flux estimated from CO 2 partial pressure data Atm. mixing ratio [ppm]:
Journal of geophysical …, 1983
Based on atmospheric data and models, the tropical CO2 source anomaly reaches up to 2 GtC yr−1, but the respective contributions of the terrestrial biosphere and the oceans to this flux are difficult to quantify. Here we present a new method for estimating CO2 fluxes from oceanic observations based on the surprisingly good predictive skill of temperature and salinity for surface dissolved inorganic carbon. Using historical temperature and salinity data, we reconstruct the basin scale CO2 flux to the atmosphere in the equatorial Pacific from 1982 to 1993. We find that interannual anomalies do not exceed 0.4±0.2 GtC yr−1 which suggests that up to 80% of the tropical CO2 source anomaly is due to the terrestrial biosphere.
Air–sea CO2 flux in the Pacific Ocean for the period 1990–2009
Biogeosciences, 2014
Air-sea CO 2 fluxes over the Pacific Ocean are known to be characterized by coherent large-scale structures that reflect not only ocean subduction and upwelling patterns, but also the combined effects of wind-driven gas exchange and biology. On the largest scales, a large net CO 2 influx into the extratropics is associated with a robust seasonal cycle, and a large net CO 2 efflux from the tropics is associated with substantial interannual variability. In this work, we have synthesized estimates of the net air-sea CO 2 flux from a variety of products, drawing upon a variety of approaches in three sub-basins of the Pacific Ocean, i.e., the North Pacific extratropics (18-66 • N), the tropical Pacific (18 • S-18 • N), and the South Pacific extratropics (44.5-18 • S). These approaches include those based on the measurements of CO 2 partial pressure in surface seawater (pCO 2 sw), inversions of ocean-interior CO 2 data, forward ocean biogeochemistry models embedded in the ocean general circulation models (OBGCMs), a model with assimilation of pCO 2 sw data, and inversions of atmospheric CO 2 measurements. Long-term means, interannual variations and mean seasonal variations of the regionally integrated fluxes were compared in each of the sub-basins over the last two decades, spanning the period from 1990 through 2009. A simple average of the long-term mean fluxes obtained with surface water pCO 2 diagnostics and those obtained with ocean-interior CO 2 inversions are −0.47 ± 0.13 Pg C yr −1 in Published by Copernicus Publications on behalf of the European Geosciences Union. 710 M. Ishii et al.: Air-sea CO 2 flux in the Pacific Ocean
Tellus B, 2010
The interannual variability of net sea-air CO 2 flux for the period 1982-2007 is obtained from a diagnostic model using empirical subannual relationships between climatological CO 2 partial pressure in surface seawater (pCO 2SW ) and sea surface temperature (SST), along with interannual changes in SST and wind speed. These optimum subannual relationships show significantly better correlation between pCO 2SW and SST than the previous relationships using fixed monthly boundaries. Our diagnostic model yields an interannual variability of ±0.14 PgC yr −1 (1σ ) with a 26-year mean of −1.48 PgC yr −1 . The greatest interannual variability is found in the Equatorial Pacific, and significant variability is also found at northern and southern high-latitudes, depending in part, on which wind product is used. We provide an assessment of our approach by applying it to pCO 2SW and SST output from a prognostic global biogeochemical ocean model. Our diagnostic approach applied to this model output shows reasonable agreement with the prognostic model net sea-air CO 2 fluxes in terms of magnitude and phase of variability, suggesting that our diagnostic approach can capture much of the observed variability on regional to global scale. A notable exception is that our approach shows significantly less variability than the prognostic model in the Southern Ocean.
Seasonal and interannual variability of CO2 in the equatorial Pacific
Deep Sea Research Part II: Topical Studies in Oceanography, 2002
As part of the JGOFS field program, extensive CO 2 partial-pressure measurements were made in the atmosphere and in the surface waters of the equatorial Pacific from 1992 to 1999. For the first time, we are able to determine how processes occurring in the western portion of the equatorial Pacific impact the sea-air fluxes of CO 2 in the central and eastern regions. These 8 years of data are compared with the decade of the 1980s. Over this period, surface-water pCO 2 data indicate significant seasonal and interannual variations. The largest decreases in fluxes were associated with the 1991-94 and 1997-98 El Ni * no events. The lower sea-air CO 2 fluxes during these two El Ni * no periods were the result of the combined effects of interconnected large-scale and locally forced physical processes: (1) development of a lowsalinity surface cap as part of the formation of the warm pool in the western and central equatorial Pacific, (2) deepening of the thermocline by propagating Kelvin waves in the eastern Pacific, and (3) the weakening of the winds in the eastern half of the basin. These processes serve to reduce pCO 2 values in the central and eastern equatorial Pacific towards near-equilibrium values at the height of the warm phase of ENSO. In the western equatorial Pacific there is a small but significant increase in seawater pCO 2 during strong El Ni * no events (i.e., 1982-83 and 1997-98) and little or no change during weak El Ni * no events . The net effect of these interannual variations is a lower-than-normal CO 2 flux to the atmosphere from the equatorial Pacific during El Ni * no. The annual average fluxes indicate that during strong El Ni * nos the release to the atmosphere is 0.2-0.4 Pg C yr À1 compared to 0.8-1.0 Pg C yr À1 during non-El Ni * no years. r (R.A. Feely). 0967-0645/02/$ -see front matter r 2002 Published by Elsevier Science Ltd. PII: S 0 9 6 7 -0 6 4 5 ( 0 2 ) 0 0 0 4 4 -9
Interannual and decadal changes in the sea-air CO2 flux from atmospheric CO2 inverse modeling
Global Biogeochemical Cycles, 2005
1] The atmosphere-land-ocean fluxes of CO 2 were derived for 64 partitioned areas of the globe (22 over the ocean and 42 over the land) using a time-dependent inverse (TDI) model for the period of January 1988 to December 2001. The model calculation partially follow the TransCom-3 protocol, and is constrained by atmospheric CO 2 concentration data from 87 stations and fully time-dependent atmospheric transport model simulations. The air-to-land and air-to-sea fluxes averaged over the 1990s are estimated at 1.15 ± 0.74 and 1.88 ± 0.53 Pg-C yr À1 , respectively. These estimates, however, remain uncertain owing to sampling biases arising from the sparse distribution of atmospheric CO 2 data, are compared with other estimates by various methods. The sensitivity analysis indicates that the differences in fluxes and flux variability caused by the choices of initial conditions for the TDI model are smaller compared to those due to the selection of measurement networks. Our model results capture interannual variations in global and regional CO 2 fluxes realistically. The estimated oceanic CO 2 flux anomalies appear to be closely related to prominent climate modes such as El Niño-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), and the Pacific Decadal Oscillation (PDO). The results from the correlation analyses show that the oceanic CO 2 flux in the tropics is strongly influenced by the ENSO dynamical cycle, and that in the sub-polar regions by upwelling of sub-surface waters in the winter and plankton blooms in the spring.
Interannual variability of the oceanic sink of CO2from 1979 through 1997
Global Biogeochemical Cycles, 2000
We have estimated the interannual variability in the oceanic sink of CO2 with a three-dimensional global-scale model which includes ocean circulation and simple biogeochemistry. The model was forced from 1979 to 1997 by a combination of daily to weekly data from the European Centre for Medium-Range Weather Forecast and the National Centers for Environmental PredictionSNational Center for Atmospheric Research reanalysis as well as European Remote Sensing satellite observations. For this period, the ocean sink of CO2 is estimated to vary between 1.4 and 2.2 Pg C yr-1, as a result of annually averaged interannual variability of 4.0.4 Pg C yr-1 that fluctuates about a mean of 1.8 Pg C yr-•. Our interannual variability roughly agrees in amplitude with previous ocean-based estimates but is 2 to 4 times less than estimates based on atmospheric observations. About 70% of the global variance in our modeled flux of CO• originated in the equatorial Pacific. In that region, our modeled variability in the flux of CO• generally agreed with that observed to 4-0.1 Pg C yr-•. The predominance of the equatorial Pacific for interannual variability is caused by three factors: (1) interannual variability associated with E1 Nifio events occurs in phase over the entire basin, whereas elsewhere positive and negative anomalies partly cancel each other out (e.g., for events such as Antarctic Circumpolar Wave and the North Atlantic Oscillation); (2) dynamic processes dominate in the equatorial Pacific, whereas dynamic, thermodynamic, and biological processes partly cancel one another at higher latitudes; and (3) our model underestimates the variability in ocean dynamics and biology at high latitudes. 1. Introduction Interannual variability in atmospheric CO2 provides clues which can be exploited to help unravel the relative roles of the ocean and terrestrial biosphere in absorbing and releasing atmospheric CO2. Although changes in atmospheric CO2 are well documented [Keeling et al., 1989; Conway et al., 1994; Tans et al., 1996], interannual changes in sea-air flux of CO2 are poorly constrained. Figure i illustrates the present controversy. Relatively small interannual variability in the sea-air flux of CO2 (+0.1 to +0.5 Pg C yr-1) is deduced from measurements of oceanic partial pressure of CO2