Diagnosis of physical and biological controls on phytoplankton distribution in the Sargasso Sea

Abstract

The linkage between physical and biological processes is studied by applying a one-dimensional physical-biological coupled model to the Sargasso Sea. The physical model is the Princeton Ocean Model and the biological model is a five-component system including phytoplankton, zooplankton, nitrate, ammonium, and detritus. The coupling between the physical and biological model is accomplished through vertical mixing which is parameterized by the level 2.5 Mellor and Yamada turbulence closure scheme. The coupled model investigates the annual cycle of ecosystem production and the response to external forcing, such as heat flux, wind stress, and surface salinity, and the relative importance of physical processes in affecting the ecosystem. Sensitivity experiments are also carried out, which provide information on how the model bio-chemical parameters affect the biological system. The computed seasonal cycles compare reasonably well with the observations of the Bermuda Atlantic Time-series Study (BATS). The spring bloom of phytoplankton occurs in March and April, right after the weakening of the winter mixing and before the establishment of the summer stratification. The bloom of zooplankton occurs about two weeks after the bloom of phytoplankton. The sensitivity experiments show that zooplankton is more sensitive to the variations of biochemical parameters than phytoplankton.

Long-read powered viral metagenomics in the Oligotrophic Sargasso Sea

“…Depth-specific niches are occupied by ecologically important heterotrophs, such as Pelagibacter (SAR11), Chloroflexi (SAR202), Deltaproteobacteria (SAR324) and Marinomicrobia (SAR406) (Giovannoni, 1990); (Giovannoni et al, 1996;Gordon & Giovannoni, 1996); (Gordon & Giovannoni, 1996); (Wright et al, 1997) and the phototrophs Prochlorococcus ( (Moore & Rocap, 1998) and Synechococcus (Lomas et al, 2013). Prochlorococcus and SAR11 (Pelagibacter) are the dominant phototrophs and heterotrophs in epipelagic surface waters, respectively (Treusch et al, 2009); (Wang & Malanotte-Rizzoli, 2014). The extremely low levels of nutrients in the Sargasso Sea photic zone have constrained the diversity of the microbial communities, as revealed by 16S rRNA community profiling (Treusch et al, 2009).…”