Influence of El Niño on the sea‐to‐air CO₂ flux at the SEATS time‐series site, northern South China Sea

Abstract

The eastern equatorial Pacific is the predominant source area for atmospheric CO2, and the size of this source is significantly reduced during El Niño events. Here we apply a newly constructed 1999–2008 time series carbon chemistry trend to show a similar reduction can also be identified in the northern South China Sea. The net sea‐to‐air CO2 flux during the 2002–2003 El Niño event (1.57 ± 0.13∼1.61 ± 0.28 g C m−2 a−1) at the SEATS time series site was significantly lower than that during the 2007–2008 La Niña event (10.35 ± 0.66∼10.67 ± 0.93 g C m−2 a−1). The appreciable reduction (by ∼85%) is a direct response to the diminished vertical mixing of CO2‐rich subsurface waters from below and, possibly, an increase in the lateral flow transport from the western Pacific during the weakening winter monsoon in the El Niño years. Thus, the suppression of CO2 efflux during the El Niño events is a basin‐wide phenomenon across from the eastern equatorial Pacific to the western subtropical Pacific including the northern South China Sea.

Seasonal variations of sea–air CO<sub>2</sub> fluxes in the largest tropical marginal sea (South China Sea) based on multiple-year underway measurements

“…Previous estimates of annual sea-air CO 2 fluxes in the SCS proper are either based on limited transects/stations (Zhai et al, 2005a; or spatially extrapolated from time-series observations at a single site (Chou et al, 2005;Tseng et al, 2007;Sheu et al, 2010b). We contend that this limited spatial coverage has hampered the better assessment of pCO 2 variability in the SCS (Fig.…”

“…In shaping this source term, at least in the basin area of the SCS, the inflow of the CO 2 -enriched North Pacific deep water through the Luzon Strait and its subsequent upward transport into the thermocline through vertical mixing and upwelling may have played a critically important role . In contrast, based on time series observations at the SEATS (South-East Asian Time Series Study) station (18 • 15 N, 115 • 35 E), Chou et al (2005), Tseng et al (2007), and Sheu et al (2010b) noted seasonal/interannual variability in carbon chemistry including computed sea surface partial pressure of CO 2 (pCO 2 ) between 1999 and 2008, and report that the northern SCS serves as a very weak sink of atmospheric CO 2 by extrapolating the SEATS results to the entire region.…”

“…All published studies related to sea-air CO 2 fluxes in the SCS proper are summarized (see the text for details). Note that the sea-air CO 2 fluxes at the SEATS station have been well studied in Chou et al (2005), Tseng et al (2007), and Sheu et al (2010b).…”

Variability of oceanic carbon cycle in the North Pacific from seasonal to decadal scales

“…Locations of the five measurement sites are shown in Figure 3. pCO 2 data at the SEATS are from Sheu et al [2010]; those at the MB are from the MBARI Annual Report 2010 (http://www.mbari.org/news/ publications/pubs.html); those at the HOT are from Dore et al [2009]; and those at the NWP and GOA are from the LDEO database [Takahashi et al, 2012]. representative.…”

Surface Chlorophyll-a Concentration Spatio-Temporal Variations in the Northern South China Sea Detected Using MODIS Data

“…There were one minor (2004) (Sheu et al 2010). El Niño events mainly strengthened the seasonal mean pattern, strengthened the cyclonic gyre in summer, but weakened the entire cyclonic gyre in winter.…”