Abstract
The standing stock of phytoplankton carbon is a basic and essential property for understanding oceanic ecosystems, biogeochemical cycles, and regional climates. However, current related algorithms mainly focus on remote-sensed application, which cannot describe the vertical profile of phytoplankton carbon throughout the whole euphotic zone. In this study, we modified a previous absorption-based bio-optical algorithm to acquire vertical variabilities of the total and size-partitioned phytoplankton carbon based on field data from the South China Sea (SCS). The mean absolute errors and the biases between estimated and field picophytoplankton carbon were <2.14 and 0.6–2.0, respectively. The results showed that the vertical profile of total phytoplankton carbon displayed a Gaussian distribution in the stratified SCS basin. The picophytoplankton carbon was always the fundamental component of the total phytoplankton carbon within the whole euphotic zone. The dominant picophytoplankton species changed from Synechococcus-like cyanobacteria at the sea surface to pico-sized haptophytes at the phytoplankton carbon maximum layer. The strong covariation between total phytoplankton carbon and chlorophyll-a concentration suggested that they can be converted into each other through an accurate carbon-to-chlorophyll ratio in the open SCS. These results provide essential information that can be used to decipher the three-dimensional structure of total and size-partitioned phytoplankton carbon in the open SCS.
Highlights
Introduction published maps and institutional affilMarine phytoplankton is a key component of global carbon cycling, accounting for about half (~50 Gt C) of global annual primary production through oxygenic photosynthesis [1,2]
To evaluate the applicability of R17, validation of R17 was carried out using field data (both quantitive filtered technique (QFT)-a∗ph (676) and AC-S-apg (676) data) from the South China Sea (SCS)
These results suggested that the contribution of picophytoplankton still increased while the contributions of nano- and microphytoplankton decreased at the C maximum layer (CML)
Summary
Marine phytoplankton is a key component of global carbon cycling, accounting for about half (~50 Gt C) of global annual primary production through oxygenic photosynthesis [1,2]. Knowledge of the standing stock and dynamics of marine phytoplankton is crucial for understanding the global carbon cycle and climate. The most commonly used indicator of phytoplankton biomass has been the total chlorophyll-a concentration (Chla, in mg m−3 ) [3,4]. Instead of Chla, total phytoplankton carbon biomass (C, in mg m−3 ) is the parameter more directly related to the carbon cycle, biogeochemical cycles, and climate [7,8]. Accurate estimation of C provides a means to observe the standing stocks of phytoplankton and their response to environmental variability [9]
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