Spatiotemporal variability of pCO2 and airsea CO2 uxes in the California Current System

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Author(s) Turi, Giuliana, Lachkar, Zouhair, Gruber, Nicolas
Publication Type Journal Items, Publication Status: Published
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Title Spatiotemporal variability of pCO2 and airsea CO2 uxes in the California Current System
Subtitle An eddy-resolving modeling study
Author(s) Turi, Giuliana
Lachkar, Zouhair
Gruber, Nicolas
Journal or Series Title Biogeosciences discussions
Volume Number 10
Start Page 14043
End Page 14091
Publisher Copernicus
Publication Place Kathlenburg-Lindau
Publication Date 2013
Abstract We quantify the CO2 source/sink nature of the California Current System (CalCS) and determine the drivers and processes behind the mean and spatiotemporal variability of the partial pressure of CO2 (pCO2) in the surface ocean. To this end, we analyze eddy-resolving, climatological simulations of a coupled physical-ecosystem-biogeochemical ocean model on the basis of the Regional Oceanic Modeling System (ROMS). The model-simulated pCO2 agrees very well with in situ observations over the entire domain with virtually no bias, but the model overestimates pCO2 in the nearshore 100 km, and underestimates the observed temporal variability. In the annual mean, the entire CalCS within 800 km of the coast and from ~ 33° N to 46° N is essentially neutral with regard to atmospheric CO2. The model simulates an integrated uptake flux of −0.9 Tg C yr–1, corresponding to a very small average flux density of −0.05 mol C m–2 yr–1, with an uncertainty of the order of ±0.20 mol C m–2 yr–1. This near zero flux is a consequence of an almost complete regional compensation between the strong outgassing in the nearshore region (first 100 km), with flux densities of more than 3 mol C m–2 yr–1 and a weaker, but more widespread uptake flux in the offshore region with an average flux density of −0.17 mol C m–2 yr–1. This pattern is primarily a result of the interaction between upwelling in the nearshore that brings waters with high concentrations of dissolved inorganic carbon (DIC) to the surface, and an intense biological drawdown of this DIC, driven by the nutrients that are upwelled together with the DIC. The biological drawdown occurs too slowly to prevent the escape of a substantial amount of CO2 into the atmosphere, but this is compensated by the biological generation of undersaturated conditions offshore of 100 km, permitting the CalCS to take up most of the escaped CO2. Thus, the biological pump over the entire CalCS is essentially 100% efficient, making the preformed DIC and nutrient concentrations of the upwelled waters a primary determinant of the overall source/sink nature of the CalCS. The comparison of the standard simulation with one for preindustrial conditions show that the CalCS is taking up anthropogenic CO2 at a rate of about −1 mol C m–2 yr–1, implying that the region was a small source of CO2 to the atmosphere in preindustrial times. The air–sea CO2 fluxes vary substantially in time, both on seasonal and sub-seasonal timescales, largely driven by variations in surface ocean pCO2. There are important differences among the subregions. Notably, the total variance of the fluxes in the central nearshore CalCS is roughly 4–5 times larger than elsewhere. Most of the variability in pCO2 is associated with the seasonal cycle, except in the nearshore, where sub-seasonal variations driven by mesoscale processes dominate. In the regions offshore of 100 km, changes in surface temperature are the main driver, while in the nearshore region, changes in surface temperature, as well as anomalies in DIC and alkalinity (Alk) owing to changes in circulation, biological productivity and air–sea CO2 fluxes dominate. The dominance of eddy-driven variability in the nearshore 100 km leads to a complex spatiotemporal mosaic of surface ocean pCO2 and air–sea CO2 fluxes that require a substantial observational effort to determine the source/sink nature of this region reliably.
DOI 10.5194/bgd-10-14043-2013
Additional Notes Received 7 August 2013, Accepted 16 August 2013, Published 26 August 2013
Document Type Article
Publication Status Published
Language English
Assigned Organisational Unit(s) 03731
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Source Database ID FORM-1390473821
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@article{Tr2013,
  author = "Turi, Giuliana and Lachkar, Zouhair and Gruber, Nicolas",
  title = "{S}patiotemporal variability of p{C}{O}2 and airsea {C}{O}2 uxes in the {C}alifornia {C}urrent {S}ystem: {A}n eddy-resolving modeling study",
  journal = "Biogeosciences discussions",
  year = 2013,
  volume = "10",
  pages = "14043--14091",
}


E-Citations record created: Thu, 23 Jan 2014, 10:43:43 CET