Sinking Rate and Community Structures of Autumn Phytoplankton Responses to Mesoscale Physical Processes in the Western South China Sea

Abstract

To examine the influence of mesoscale eddy on the natural phytoplankton community and its sinking rate changes, a comprehensive investigation cruise was carried out in the western South China Sea in autumn 2016. A total of 108 phytoplankton species were found, which belong to 54 phytoplankton genera; most of them were dominated by Dinophyta (54 genera), followed by Bacillariophyta (50 genera), Cyanophyta (3 genera), and Chrysophyta (1 genus). Bacillariophyta and Dinophyta were the main phytoplankton communities in the investigated sea area. The sinking rate of phytoplankton ranged from 0.12 to 3.17 m day–1, determined by the SETCOL method. The highest phytoplankton sinking rate was found in the 200-m water layer, followed by the DCM layer. No significant correlation was found between phytoplankton sinking rates and most of the environmental parameters during this cruise. At a similar time, we have carried out the estimation of carbon flux in the investigated sea area by using the sinking rate of phytoplankton, which showed that the carbon flux ranged from 2.41 × 10–6 to 0.006 mg C m–2 day–1; in addition, the maximum was at the 200-m layer. Phytoplankton community and sinking rate were significantly affected by the mesoscale eddy processes. The cold eddy could affect the community distribution of diatom and dinoflagellate, and the upwelling mainly affects the community of dinoflagellate. Both of them could contribute to a higher sedimentation rate of phytoplankton in the surface and DCM layers. Warm eddy could reduce the abundance of phytoplankton in the surface layer; simultaneously, the sinking rate of phytoplankton in the shallow water layer above 100 m is also reduced. These results can fill in the knowledge gap of mesoscale eddy processes in the study of phytoplankton community change and sinking rate; furthermore, it can provide insights into phytoplankton carbon and its implementation in further carbon sink.

Response of the Phytoplankton Sinking Rate to Community Structure and Environmental Factors in the Eastern Indian Ocean

“…The ratio of diatoms to dinoflagellates is positively correlated with the sinking rates of phytoplankton in our study, which agreed with a previous investigation reported by Pitcher et al [10], who found that the sinking rate was lower when dinoflagellates rather than the diatoms were the dominant species. In fact, when diatoms bloom, their sinking rate often increases significantly.…”

“…More detailed studies on phytoplankton's sinking rate should examine other factors, such as phytoplankton cell density, cell physiological activity measurement, and sea water characteristics. Some environmental factors, such as nutrient concentration, irradiance, water viscosity, and turbulence, also indirectly affect the sinking rates [8,10].…”

The diel disconnect between cell growth and division inAureococcusis interrupted by giant virus infection

“…To determine the sinking rate of infected cells, A. anophagefferens CCMP1984 was infected with K. quantuckense at an MOI of 100 either 2 h (early infection) or 16 h prior (late infection) to sinking rate assessment. Sinking velocity (Ψ) was calculated using the following formula: In which βs is total exported cells, βt is total cells in the column, l is distance traveled in meters, and T is time in hours (Bienfang, 1981; Mao et al, 2021).…”

“…In which 𝛽𝑠 is total exported cells, 𝛽𝑡 is total cells in the column, 𝑙 is distance traveled in meters, and 𝑇 is time in hours (Bienfang, 1981;Mao et al, 2021).…”