Abstract
Abstract. A 21 year (1998–2018) continuous monthly data set of the global distribution of light (photosynthetically available radiation, PAR, or irradiance) reaching the seabed is presented. This product uses ocean color and bathymetric data to estimate benthic irradiance, offering critical improvements on a previous data set. The time series is 4 times longer (21 versus 5 years), the spatial resolution is better (pixel size of 4.6 versus 9.3 km at the Equator), and the bathymetric resolution is also better (pixel size of 0.46 versus 3.7 km at the Equator). The paper describes the theoretical and methodological bases and data processing. This new product is used to estimate the surface area of the seafloor where (1) light does not limit the distribution of photosynthetic benthic organisms and (2) net community production is positive. The complete data set is provided as 14 netCDF files available on PANGAEA (Gentili and Gattuso, 2020a, https://doi.org/10.1594/PANGAEA.910898). The R package CoastalLight, available on GitHub (https://github.com/jpgattuso/CoastalLight.git, last access: 29 July 2020), allows us (1) to download geographical and optical data from PANGAEA and (2) to calculate the surface area that receives more than a given threshold of irradiance in three regions (nonpolar, Arctic, and Antarctic). Such surface areas can also be calculated for any subregion after downloading data from a remotely and freely accessible server.
Highlights
Light plays a major role in the global carbon cycle by controlling primary production, the main source of new organic carbon in the ocean (Assis et al, 2018)
Sunlight is rapidly absorbed by the water column, and primary production is restricted to the shallow photic zone above 200 m depth
Data availability is higher in the present study which used multiple sensors compared to a previous study that only used Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) data (Gattuso et al, 2006)
Summary
It shapes the composition of benthic and pelagic communities by controlling the threedimensional distribution of primary producers, the lowest levels of the food webs. Light plays a major role in the global carbon cycle by controlling primary production, the main source of new organic carbon in the ocean (Assis et al, 2018). Sunlight is rapidly absorbed by the water column, and primary production is restricted to the shallow photic zone above 200 m depth (except for localized chemoautotrophic communities). Marine diazotrophs, which fix dinitrogen into organic forms, are light-dependent. Many marine ecosystem engineers require light because they are either plants (mangrove, salt marshes, seagrass, coralline algae) or animals living in symbiosis with endosymbiotic algae (e.g., some mollusks and zooxanthellate reef-building corals)
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