Abstract
Based on time-series sediment trap observation at 1003-m depth in the northern South China Sea from 2014 to 2015, we used sinking particle flux combined with remote sensing-derived environmental data to infer mechanisms of the biological carbon pump. Total particle flux, particulate organic carbon, CaCO3, and lithogenic (inorganic)fluxes peaked in winter and autumn but showed minima in summer, ranging from 59.7 to 413.2 mg m−2 d−1, 2.1 to 18.2 mg m−2 d−1, 32.9 to 197.9 mg m−2 d−1, and 12.0 to 73.6 mg m−2 d−1, respectively. Similarly, opal flux varied from 6.9 to 109.6 mg m−2 d−1, with a prominent peak in winter and minimum in summer. However, a secondary maximum of opal in autumn was barely noticeable compared with other components. A deeper mixed-layer depth related to the northeast monsoon and surface cooling, overlapping with the effect of cyclonic eddies, is responsible for the strong winter fluxes. When an anticyclonic eddy suppresses the subsurface nutrient supply, primary production and subsequent export flux in summer were reduced substantially. With respect to maximum lithogenic and CaCO3 fluxes in autumn, a large aerosol optical depth suggests the scavenging and mineral ballast effects as potential causes. This study highlights the importance of intra-seasonal physical processes (e.g., mesoscale eddies and aerosol deposition) to the deep particle flux in the South China Sea as well as monsoonal transition.
Highlights
The overuse of fossil fuels by human activities and the destruction of the natural environment such as deforestation has increased the atmospheric concentration of CO2 from 280 ppm before the Industrial Revolution, to around 406 ppm today1
The mineral can provide physical protection and reduce the microbial degradation of organic matter (Lee et al, 2009). This effect is most relevant to the flux of biogenic minerals, especially CaCO3 (Klaas and Archer, 2002; Barker et al, 2003), but in the marginal seas strongly affected by trade winds, monsoons and large rivers, like the Atlantic coastal regions, particulate organic carbon (POC) export is remarkably influenced by the ballast effect of lithogenic material from atmospheric deposition (Fischer and Karaka, 2009; Salter et al, 2010)
We aroused questions for the seasonal scales like: is monsoon transition being the most contributive and significant factor to the northern South China Sea (SCS) all year around? Are these intra-annual physical processes overlapped with monsoon or functioned separately? Will marginal sea respond to some result of anthropogenic activity like dust deposition just in time? Through 1-year in situ investigation data from sediment traps, our study focuses on seasonal variations of settling particulate flux in the mesopelagic SCS
Summary
The overuse of fossil fuels by human activities and the destruction of the natural environment such as deforestation has increased the atmospheric concentration of CO2 from 280 ppm before the Industrial Revolution, to around 406 ppm today1 This has led to global warming and a rise in sea level. This effect is most relevant to the flux of biogenic minerals, especially CaCO3 (Klaas and Archer, 2002; Barker et al, 2003), but in the marginal seas strongly affected by trade winds, monsoons and large rivers, like the Atlantic coastal regions, POC export is remarkably influenced by the ballast effect of lithogenic material from atmospheric deposition (Fischer and Karaka, 2009; Salter et al, 2010)
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