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Sea–air CO2 fluxes in the Indian Ocean between 1990 and 2009

DRS at CSIR-National Institute of Oceanography

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Title Sea–air CO2 fluxes in the Indian Ocean between 1990 and 2009
 
Creator Sarma, V.V.S.S.
Lenton, A.
Law, R.M.
Metzl, N.
Patra, P.K.
Doney, S.C.
Lima, I.D.
Dlugokencky, E.
Ramonet, M.
Valsala, V.
 
Subject air-water exchanges
air-sea interaction
surface chemistry
biogeochemical cycle
 
Description The Indian Ocean (44° S–30° N) plays an important role in the global carbon cycle, yet it remains one of the most poorly sampled ocean regions. Several approaches have been used to estimate net sea–air CO2 fluxes in this region: interpolated observations, ocean biogeochemical models, atmospheric and ocean inversions. As part of the RECCAP (REgional Carbon Cycle Assessment and Processes) project, we combine these different approaches to quantify and assess the magnitude and variability in Indian Ocean sea–air CO2 fluxes between 1990 and 2009. Using all of the models and inversions, the median annual mean sea–air CO2 uptake of -0.37 ± 0.06 PgC yr-1 is consistent with the -0.24 ± 0.12 PgC yr-1 calculated from observations. The fluxes from the southern Indian Ocean (18–44° S; -0.43 ± 0.07 PgC yr-1 are similar in magnitude to the annual uptake for the entire Indian Ocean. All models capture the observed pattern of fluxes in the Indian Ocean with the following exceptions: underestimation of upwelling fluxes in the northwestern region (off Oman and Somalia), overestimation in the northeastern region (Bay of Bengal) and underestimation of the CO2 sink in the subtropical convergence zone. These differences were mainly driven by lack of atmospheric CO2 data in atmospheric inversions, and poor simulation of monsoonal currents and freshwater discharge in ocean biogeochemical models. Overall, the models and inversions do capture the phase of the observed seasonality for the entire Indian Ocean but overestimate the magnitude. The predicted sea–air CO2 fluxes by ocean biogeochemical models (OBGMs) respond to seasonal variability with strong phase lags with reference to climatological CO2 flux, whereas the atmospheric inversions predicted an order of magnitude higher seasonal flux than OBGMs. The simulated interannual variability by the OBGMs is weaker than that found by atmospheric inversions. Prediction of such weak interannual variability in CO2 fluxes by atmospheric inversions was mainly caused by a lack of atmospheric data in the Indian Ocean. The OBGM models suggest a small strengthening of the sink over the period 1990–2009 of -0.01 PgC decade-1. This is inconsistent with the observations in the southwestern Indian Ocean that shows the growth rate of oceanic pCO2 was faster than the observed atmospheric CO2 growth, a finding attributed to the trend of the Southern Annular Mode (SAM) during the 1990s.
 
Date 2013-12-10T05:55:43Z
2013-12-10T05:55:43Z
2013
 
Type Journal Article
 
Identifier Biogeosciences, vol.10; 2013; 7035-7052
no
http://drs.nio.org/drs/handle/2264/4402
 
Language en
 
Relation Biogeosciences_10_7035.jpg
 
Rights © Author(s) 2013. CC Attribution 3.0 License.
 
Publisher European Geosciences Union