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The export flux of particulate organic carbon (POC) consumes upwelled dissolved inorganic carbon (DIC), which hinders surplus CO being released to the atmosphere. The export flux of POC is therefore crucial to the carbon and biogeochemical cycles. This study aims to model the long-term (1958-2009) variation of export flux and structure of the biological pump in the South China Sea (SCS) using a three-dimensional physical-biogeochemical coupled (ROMS-CoSiNE) model. The modeled POC export flux in the northeastern and north central SCS is high in winter and low in summer, whereas the flux in the central, southwestern and southern SCS varies following a 'W' shape: two maxima in winter and summer, and two minima in spring and autumn. The pattern follows the variation of the East Asian monsoon and is consistent with observations. On the interannual scale, export flux is anti-phased with the El Niño-Southern Oscillation such that El Niño (La Niña) conditions correspond to low (high) export flux. Modeled annual mean POC export flux reaches up to 1.95 mmol m day, which is underestimated comparing with field observations. The f-ratio is estimated to be ~0.4. The b value of the Martin equation for POC is 1.18±0.03. Remineralization rate of POC is greater than the classical Martin equation but is consistent with its subtropical counterparts. The modeled results indicate that the SCS is a weak source of atmospheric CO with a flux estimated at 1.0 mmol m day. The modeled results provide an insight of the temporal and spatial variability of the carbon cycle in this monsoon-driven, semi-enclosed basin. [ABSTRACT FROM AUTHOR]

Primary productivity (PP) and phytoplankton structure play an important role in regulating oceanic carbon cycle. The unique seasonal circulation and upwelling pattern of the South China Sea (SCS) provide an ideal natural laboratory to study the response of nutrients and phytoplankton dynamics to climate variation. In this study, we used a three-dimensional (3D) physical-biogeochemical coupled model to simulate nutrients, phytoplankton biomass, PP, and functional groups in the SCS from 1958 to 2009. The modeled results showed that the annual mean carbon composition of small phytoplankton, diatoms, and coccolithophores was 33.7, 52.7, and 13.6 %, respectively. Diatoms showed a higher seasonal variability than small phytoplankton and coccolithophores. Diatoms were abundant during winter in most areas of the SCS except for the offshore of southeastern Vietnam, where diatom blooms occurred in both summer and winter. Higher values of small phytoplankton and coccolithophores occurred mostly in summer. Our modeled results indicated that the seasonal variability of PP was driven by the East Asian Monsoon. The northeast winter monsoon results in more nutrients in the offshore area of the northwestern Luzon Island and the Sunda Shelf, while the southwest summer monsoon drives coastal upwelling to bring sufficient nutrients to the offshore area of southeastern Vietnam. The modeled PP was correlated with El Niño/Southern Oscillation (ENSO) at the interannual scale. The positive phase of ENSO (El Niño conditions) corresponded to lower PP and the negative phase of ENSO (La Niña conditions) corresponded to higher PP. [ABSTRACT FROM AUTHOR]

While the benthic δ 18 O records from many South China Sea sites mimic the SPECMAP/LR04 standard, their paired planktic δ 18 O curves differ by comparable values at negative peaks corresponding to interstadials, especially between MIS 5.1, 5.3, 5.5, 6.5, and 7.3. Similar planktic δ 18 O records also occur in some other low-latitude oceans under monsoon influence. Because neither temperature nor salinity effects can fully account for the variations of such δ 18 O records after derivation from the SPECMAP/LR04 standard, variations in the rain water δ 18 O affected by regional hydroclimate changes are considered to have played an important role. In contrast to the SPECMAP/LR04 standard δ 18 O curve prevailed by 100-kyr cycles, these regional planktic δ 18 O curves are distinguished by 20-kyr precession signal, showing partial similarity to the δ 18 O records of atmospheric oxygen in polar ice-core bubbles and in stalagmite calcite. We speculate that the common features of these three independent δ 18 O records are indicative of the effect of evolving hydrological cycling driven by monsoon circulation in low latitudes. [ABSTRACT FROM AUTHOR]