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Spatiotemporal characteristics of seasonal to multidecadal variability of p CO 2 and air‐sea CO 2 fluxes in the equatorial P acific O cean
Author(s) -
Valsala Vinu K.,
Roxy Mathew Koll,
Ashok Karumuri,
Murtugudde Raghu
Publication year - 2014
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2014jc010212
Subject(s) - climatology , pacific decadal oscillation , environmental science , empirical orthogonal functions , biogeochemical cycle , oceanography , annual cycle , pacific ocean , el niño southern oscillation , flux (metallurgy) , la niña , atmospheric sciences , geology , chemistry , organic chemistry , environmental chemistry
Seasonal, interannual, and multidecadal variability of seawater pCO 2 and air‐sea CO 2 fluxes in the equatorial Pacific Ocean for the past 45 years (1961–2005) are examined using a suite of experiments performed with an offline biogeochemical model driven by reanalysis ocean products. The processes we focus on are: (a) the evolution of seasonal cycle of pCO 2 and air‐sea CO 2 fluxes during the dominant interannual mode in the equatorial Pacific, i.e., the El Niño‐Southern Oscillation (ENSO), (b) its spatiotemporal characteristics, (c) the combined and individual effects of wind and ocean dynamics on pCO 2 and CO 2 flux variability and their relation to canonical (eastern Pacific) and central Pacific (Modoki) ENSOs and (d) the multidecadal variability of carbon dynamics in the equatorial Pacific and its association with the Pacific Decadal Oscillations (PDO). The simulated mean and seasonal cycle of pCO 2 and CO 2 fluxes are comparable with the observational estimates and with other model results. A new analysis methodology based on the traditional Empirical Orthogonal Functions (EOF) applied over a time‐time domain is employed to elucidate the dominant mode of interannual variability of pCO 2 and air‐sea CO 2 fluxes at each longitude in the equatorial Pacific. The results show that the dominant interannual variability of CO 2 fluxes in the equatorial Pacific (averaged over 5°N–10°S) coevolves with that of ENSO. Generally a reduced CO 2 source in the central‐to‐eastern equatorial Pacific evident during June–July of the El Niño year (Year:0) peaks through September of Year:0 to February of Year:+1 and recovers to a normal source thereafter. In the region between 160°W and 110°W, the canonical El Niño controls the dominant variability of CO 2 fluxes (mean and RMS of anomaly from 1961 to 2005 is 0.43±0.12 PgC yr −1 ). However, in the western (160°E–160°W) and far eastern (110°W–90°W) equatorial Pacific, CO 2 flux variability is dominantly influenced by the El Niño‐Modoki (0.3±0.06 and 0.11±0.04 PgC yr −1 , respectively). On the other hand, the interannual variability of pCO 2 is correlated with the canonical El Niño mostly to the east of 140°W and with El Niño‐Modoki to the west of 140°W. Decoupling of CO 2 flux and pCO 2 variability at various locations in the equatorial Pacific is attributable to the differences in the combined and individual effects of ocean dynamics and winds associated with these two types of ENSO. A multidecadal variability in the equatorial Pacific sea‐air CO 2 fluxes and pCO 2 exhibits a positive phase during the 1960s, a negative phase during the 1980s, and then positive again by the 2000s. Within the ocean, the dissolved inorganic carbon (DIC) anomalies are traceable to the northern Pacific via thermocline pathways at decadal timescales. The multidecadal variability of equatorial Pacific CO 2 fluxes and pCO 2 are determined by the phases of the PDO and the corresponding scale of the El Niño‐Modoki variability, whereas canonical El Niño's contribution is to mainly determine the variability at interannual timescales. This study segregates the impacts of different types of ENSOs on the equatorial Pacific carbon cycle and sets the framework for analysing its spatiotemporal variability under global warming.