A model of the spring bloom in the North Atlantic and its impact on ocean optics

TLDR

Phytoplankton are the primary absorbers and scatterers of light in the open ocean, enabling chlorophyll concentration to predict time‑varying light attenuation. The study presents a model of the spring phytoplankton bloom in the North Atlantic and its impact on water‑column light attenuation. The model incorporates climatological mixed‑layer depth, surface solar irradiance, and basin‑scale nitrate distribution to compute the spatial variability of the downwelling irradiance attenuation coefficient K490. Simulations show the bloom advances from mid‑ to high latitudes between March and June, first appearing in shallow coastal waters and later in the open ocean, with local peak phytoplankton concentrations lasting 1–2 weeks.

Abstract

A model of the development of the spring phytoplankton bloom in the North Atlantic and its effect on light attenuation in the water column is presented. The model uses as input data on the climatological mixed‐layer depth, solar irradiance at the sea surface, and basin‐scale distribution of nitrate at standard depths. The simulated phytoplankton bloom progresses from mid‐ to high latitudes following the shallowing of the mixed layer during March through June. The bloom occurs first in coastal waters where the mixed layer is shallow and later in the open ocean. Local peak concentrations of phytoplankton last 1–2 weeks. As phytoplankton are the major absorbers and scatterers of light in the open ocean, the relationship between chlorophyll concentration and light attenuation can be used to predict time‐varying fields of light extinction. The basin‐scale variability in the attenuation coefficient for downwelling irradiance at 490 nm ( K 490) in May is computed as an example.