Biogeographical Classification of the Global Ocean From BGC‐Argo Floats

Abstract

Biogeographical classifications of the global ocean generalize spatiotemporal trends in species or biomass distributions across discrete ocean biomes or provinces. These classifications are generally based on a combination of remote‐sensed proxies of phytoplankton biomass and global climatologies of biogeochemical or physical parameters. However, these approaches are limited in their capacity to account for subsurface variability in these parameters. The deployment of autonomous profiling floats in the Biogeochemical Argo network over the last decade has greatly increased global coverage of subsurface measurements of bio‐optical proxies for phytoplankton biomass and physiology. In this study, we used empirical orthogonal function analysis to identify the main components of variability in a global data set of 422 annual time series of Chlorophyll a fluorescence and optical backscatter profiles. Applying cluster analysis to these results, we identified six biomes within the global ocean: two high‐latitude biomes capturing summer bloom dynamics in the North Atlantic and Southern Ocean and four mid‐ and low‐latitude biomes characterized by variability in the depth and frequency of deep chlorophyll maximum formation. We report the distribution of these biomes along with associated trends in biogeochemical and physicochemical environmental parameters. Our results demonstrate light and nutrients to explain most variability in phytoplankton distributions for all biomes, while highlighting a global inverse relationship between particle stocks in the euphotic zone and transfer efficiency into the mesopelagic zone. In addition to partitioning seasonal variability in vertical phytoplankton distributions at the global scale, our results provide a potentially novel biogeographical classification of the global ocean.

Diatom phytochromes integrate the entire visible light spectra for photosensing in marine environments

“…Indeed, DPH can act as a depth sensor, with increasing %PrPr in the entire euphotic zone while photosynthetically active radiation decreases. In addition, the clear spatial biogeography suggests the occurrence of a strong selective pressure in favour of DPH-containing diatoms in temperate and polar oceanic regions, with strong seasonal variations of mixed layer depths and phytoplankton concentration, compared to more stable tropical oligotrophic regions [29][30][31] . The presence of DPH could therefore represent an adaptation to monitor, discriminate and acclimate to light changes when light varies in time, even beyond the daily cycle, such as during vertical movements or changes in optical depth within an algal bloom.…”

Vertically Resolved Global Ocean Light Models Using Machine Learning

“…The NASTG is an oligotrophic environment characterized by low surface nutrients, low Chla, and the presence of a permanent deep chlorophyll maximum (DCM), generally found below 100 m [45,46]. The multi-year time series (more than 6 years of measurement) of the vertical distribution of light variables (PAR, ED380, ED412, and ED490) measured by the NASTG BGC-Argo float (WMO = 6901472) and modeled by SOCA-light are presented in Figure 7 for a direct comparison.…”

Diatom phytochromes integrate the entire visible light spectra for photosensing in marine environments

“…DPH can also work as a sensor of phytoplankton population density, drawing an interesting parallel with phytochrome-mediated neighbor perception in land plants which is however based on R/FR ratio changes (17) . Remarkably, DPH-containing diatoms have been found mostly in temperate and polar regions, which show strong seasonal variations of phytoplankton concentration and mixed layer depths compared to the more stable tropical regions (18–20) . Therefore, the presence of DPH in the marine environment could be an adaptation to the pronounced annual cycles in these regions, allowing physiological acclimation to the different seasons.…”