Steady-state solutions for subsurface chlorophyll maximum in stratified water columns with a bell-shape vertical profile of chlorophyll

Abstract

Abstract. A bell-shape vertical profile of chlorophyll a (Chl a) concentration, conventionally referred as Subsurface Chlorophyll Maximum (SCM) phenomenon, has frequently been observed in stratified oceans and lakes. This profile is assumed to be a general Gaussian distribution in this study. By substituting the general Gaussian function into ecosystem dynamical equations, the steady-state solutions for SCM characteristics (i.e. SCM layer depth, thickness, and intensity) in various scenarios are derived. These solutions indicate that: (1) The maximum in Chl a concentrations occurs at or below the depth with the maximum in growth rates of phytoplankton locating at the transition from nutrient limitation to light limitation, and the depth of SCM layer deepens logarithmically with an increase in surface light intensity; (2) The shape of SCM layer (thickness and intensity) is mainly influenced by nutrient supply, but independence of surface light intensity; (3) The intensity of SCM layer is proportional to the diffusive flux of nutrient from below, getting stronger as a result of this layer being shrank by a higher light attenuation coefficient or a larger sinking velocity of phytoplankton. The analytical solutions can be useful to estimate environmental parameters difficultly obtained from on-site observations.

A strong summer phytoplankton bloom southeast of Vietnam in 2007, a transitional year from El Niño to La Niña

“…Under influence of strong solar radiation and weak wind conditions in summer, the stable stratification in the euphotic layer in the SCS inhibits transport of nutrients from the subsurface layer into the near-surface layer. Consequently, a summer subsurface Chl-a maximum (SCM) layer typically appears at a depth between 65 and 85 m, with the euphotic layer reaching a depth of about 120 m [ 41 – 43 ] in the offshore deep water areas of the SCS, due to the absence of nutrients at the near-surface layer and a relatively deep nutricline in the offshore SCS. Therefore, upwelling could not only increase nutrients in the near-surface layer through transporting high nutrients water from the deep layer, but also increase the Chl-a concentrations near the sea surface by shoaling the SCM in a way.…”

Contributions of physical and biogeochemical processes to phytoplankton biomass enhancement in the surface and subsurface layers during the passage of Typhoon Damrey

“…Subsurface chlorophyll a maximum (SCM) has been observed frequently in tropical and subtropical oceans throughout the whole year, while it occurs during the warm season in temperate ocean zones. The subsurface layer has been reported to be the most productive layer among the whole water column in tropical and subtropical oceans throughout the year and in temperate ocean zones during summer [ Gong et al ., ; Liu et al ., ; Ardyna et al ., ; Gong et al ., ]. However, satellite data can only indicate the distribution of Chl a in the surface layer.…”

“…The upper water is permanently stratified and oligotrophic in the basin area due to strong solar radiation throughout the year. In addition, a significant phytoplankton biomass is generally observed in the subsurface, which is the most productive layer [ Gong et al ., ; Liu et al ., ; Gong et al ., ]. The primary production depends mainly on the supply of nutrients from deeper nutrient‐rich water to the euphotic zone by turbulent vertical transport [ Tang et al ., ].…”

Statistical Characteristics of the Response of Sea Surface Temperatures to Westward Typhoons in the South China Sea

“…It is the largest marginal sea on the east coast of Asia in the Western Pacific Ocean and one of the regions with the most frequent tropical cyclones and typhoons, with an average of 10.3 typhoons passing through each year [46,47]. As much of the South China Sea is located in the tropics, where high evaporation causes seawater to layer and hinders the transport of nutrient salts from the bottom up, the upper sea water is in a nutrient-innocencing state throughout the year [48,49]. According to the revised national standard "tropical cyclone classification" issued by China Meteorological Administration in 2006, tropical cyclone can be divided into six grades according to the maximum average wind speed near the bottom center: tropical depression (TD), tropical storm (TS), severe tropical storm (STS), typhoon (TY), strong typhoon (STY) and super typhoon (Super TY) [50].…”