Abstract
The active carbon flux mediated by diel vertical migration (DVM) of zooplankton is an important component of the downward carbon flux in the ocean. However, active fluxes transported by zooplankton DVM are poorly known in the South China Sea (SCS) and the Western Philippine Sea (WPS). In this study, active carbon fluxes in the SCS and WPS were evaluated on the basis of the data of mesozooplankton community and DVM at two stations of these areas. The mesozooplankton community in the SCS was obviously different from that in the WPS, and higher species number and abundance in the SCS were observed, which may be related to the higher chlorophyll a (Chl a) concentration and the wide gradients of temperature and salinity in this sea. Moreover, shallow depth Chl a maximum and strong thermocline were detected in the SCS, causing lower migration amplitudes of mesozooplankton in the SCS than those in the WPS. However, the migrant biomass of mesozooplankton in the SCS was 98.40 mg C m–2, higher than that in the WPS at 25.12 mg C m–2. The mesozooplankton active carbon flux in the SCS (4.64 mg C m–2⋅d–1) was also higher than that in the WPS (1.80 mg C m–2⋅d–1). The mesozooplankton active fluxes were equivalent to 8.3 and 8.1% of the total flux (active flux plus passive flux) of the SCS and WPS, respectively, and they play an important role in the biological pump functioning in the two regions.
Highlights
The biological pump is one of the most important paths that transport carbon from the euphotic zone to the mesopelagic layer (Hernández-León et al, 2019b; Pakhomov et al, 2019)
The South China Sea (SCS) and the Western Philippine Sea (WPS) are located in the Western Pacific, and they belong to the oligotrophic marginal sea
We addressed two key questions with our study: (1) How much is the active flux contributed by mesozooplankton diel vertical migration (DVM) in SCS and WPS?
Summary
The biological pump is one of the most important paths that transport carbon from the euphotic zone to the mesopelagic layer (Hernández-León et al, 2019b; Pakhomov et al, 2019). Active carbon fluxes transported by zooplankton DVM have been recorded worldwide (Steinberg et al, 2000, 2002; Al-Mutairi and Landry, 2001; Hidaka et al, 2001; Stukel et al, 2013), indicating that active fluxes varied significantly in different marine systems with distinct hydrological properties. The proportion of zooplankton active flux in the total carbon flux is generally higher in the oligotrophic marine systems than in the meso- and eutrophic regions (AlMutairi and Landry, 2001; Steinberg and Landry, 2017; Yebra et al, 2018; Hernández-León et al, 2019b). The knowledge of active fluxes transported by zooplankton DVM in the SCS and WPS is limited, and the difference in zooplankton active flux between the SCS and WPS is not clear
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