Seasonal to decadal variations of sea surface pCO₂ and sea‐air CO₂ flux in the equatorial oceans over 1984–2013: A basin‐scale comparison of the Pacific and Atlantic Oceans

Abstract

The equatorial Pacific and Atlantic Oceans release significant amount of CO 2 each year. Not much attention has been paid to evaluating the similarities and differences between these two basins in terms of temporal variability. Here we employ a basin-scale, fully coupled physical-biogeochemical model to study the spatial and temporal variations in sea surface pCO 2 and air-sea CO 2 flux over the period of 1984-2013 in the equatorial Pacific and Atlantic Oceans. The model reproduces the overall spatial and temporal variations in the carbon fields for both basins, including higher values to the south of the equator than to the north, the annual maximum sea surface pCO 2 in boreal spring, and the annual peak in sea-to-air CO 2 flux in boreal fall in the upwelling regions. The equatorial Pacific reveals a large interannual variability in sea surface pCO 2 , which is associated with the El Niño-Southern Oscillation. As a contrast, there is a strong seasonality but little interannual variability in the carbon fields of the equatorial Atlantic. The former is driven by the variability of dissolved inorganic carbon but the latter by sea surface temperature. Our model estimates an average sea-to-air CO 2 flux of 0.521 ± 0.204 Pg C yr À1 for the tropical Pacific (18°S-18°N, 150°E-90°W), which is in good agreement with the observation-based estimate (0.51 ± 0.24 Pg C yr À1 ). On average, sea-to-air CO 2 flux is 0.214 ± 0.03 Pg C yr À1 in the tropical Atlantic (10°S-10°N), which compares favorably with observational estimates.

A Coupled Ocean Physics‐Biology Modeling Study on Tropical Instability Wave‐Induced Chlorophyll Impacts in the Pacific

“…The model configurations are described by Wang, Behrenfeld, et al (), Wang et al (). The model contains an explicit bulk ML model and 19 vertical layers below the ML.…”

“…The coupled ocean physics-biology model is detailed by Christian et al (2001) and Wang et al (2006Wang et al ( , 2008Wang et al ( , 2015. A brief description is presented in this section.…”

Variability and trends in surface seawater pCO2 and CO2 flux in the Pacific Ocean

“…For example, El Niño–Southern Oscillation (ENSO) induced CO 2 flux changes in the tropical Pacific Ocean are the major source of interannual variability in the net annual global ocean CO 2 sink and results in measureable impacts on atmospheric CO 2 growth rates [ Feely et al , ; Feely et al , ; Rayner et al , ; Wanninkhof et al , ]. Decadal‐scale variability in the climate system has also been shown to influence CO 2 flux in the tropical Pacific [ Feely et al , ; Ishii et al , ; Sutton et al , ; Takahashi et al , ; Wang et al , ], North Pacific [ Takahashi et al , ], North Atlantic [ McKinley et al , ], and Southern Ocean [ Landschützer et al , ]. However, there remain significant uncertainties in the magnitude of these variations in ocean CO 2 flux and even disagreements as to the direction of sea‐air CO 2 flux in some regions.…”

A New Hybrid Coupled Model of Atmosphere, Ocean Physics, and Ocean Biogeochemistry to Represent Biogeophysical Feedback Effects in the Tropical Pacific

“…The model consists of 12 components, including six nutrients (nitrate, silicon, dissolved inorganic carbon (DIC), ammonium, dissolved oxygen, and dissolved iron) and six biogeochemical components (large and small phytoplankton (Pl and Ps), large and small zooplankton (Zl and Zs), and large and small detritus (Dl and Ds)). The trend for each biogeochemical component (N) is related to advection, mixing, sources, and other factors (Wang et al, ). The ocean biogeochemical fields include 12 prognostic variables that are calculated from their time‐dependent equations with consistent units of mol N m −3 .…”

“…For the atmosphere‐ocean component of the model, a hybrid coupled modeling approach is taken: an oceanic GCM (OGCM) is coupled to a simple statistical model for interannual wind stress variability (τ inter ) derived from a singular value decomposition (SVD) analysis, and this component is thus called a hybrid coupled model (HCM). For the biogeochemistry component, an ocean biogeochemistry model is adopted in which detailed biogeochemical processes are considered to represent biogeochemical heating effects on the climate system (Wang et al, ). Such an HCM framework can offer an extremely efficient modeling tool for ocean physics‐biogeochemistry systems and the coupling thereof with the atmosphere in the tropical Pacific, allowing a large number of experiments to be performed feasibly and affordably.…”