Coccolithophore blooms occur regularly from April to June in the Bay of Biscay where they have been observed for many years from ocean-colour imagery thanks to the ability of their calcite plates to scatter light. They are easily depicted on interpolated images of non-algal Suspended Particulate Matter (SPM) derived from satellite reflectance data in May, at the time of the PELGAS (PELagique GAScogne) annual surveys. Over the springs 2012 to 2015, the PELGAS surveys provided in-situ data on the turbidity throughout the water column and on the hydrological environment prevailing during the blooms in the vicinity of the continental shelf break. The satellite-derived SPM in the area of coccolithophore blooms was closely related to measured turbidity in the euphotic zone. The deep maxima of coccolithophore-derived biomass were well observed in the turbidity signal throughout the water column. Despite the recurrence of SPM patterns due to coccolithophores in the well-mixed waters over the shelf break in spring, the variability of the satellite-derived SPM and the turbidity profiles was particularly high during the four years studied. The year 2013 showed persistent blooms from mid-April to the end of May over large areas inside and outside the shelf waters, whereas no bloom was observed in 2014, neither on SPM images nor through turbidity profiles. The presence or absence of coccolithophore blooms during the years 2012-2015 seem related to the level of stratification of the water column, with more intense blooms occurring during mixed conditions. These results should improve classification of the PELGAS surveys from those occurring in a coccolith-rich environment, synonymous with mixed and cold waters, to those occurring in a coccolith-poor environment where surface waters are warmer and more stratified. Highlights ► Offshore turbidity in May is associated with coccolithophores in the Bay of Biscay. ► Satellite-derived Suspended Particulate Matter and in-situ turbidity are well related. ► Turbidity profiles together with satellite data result in a better 3-D conception of the blooms. ► Absence of coccolithophores in May is associated with stronger stratification.

Abstract. Evaluate the impact of anthropogenic CO 2 uptake and acidification on the most abundant calcareous phytoplankton, coccolithophores, requires a better knowledge of the temporal and spatial evolution of their blooms. Here we 10 determine, from satellite radiance, the seasonal and interannual variability of coccolithophore blooms for 18 years (1998 to

The paper by Perrot et al. presents a novel analytical method examining satellite reflectance data on the presence and phenology of coccolithophore blooms in the NE Atlantic Ocean (with a focus on shelf seas and shelf break). In parts the paper reads as a methods paper, with some results and new insights gained, though not discussed in depth. At some level the authors need to decide whether the aim of the paper is to validate a new method or to examine the phenology of coccolithophore blooms, and give a clearer focus on that aspect in the revised paper. Although generally well written, there are a number of grammatical and spelling errors which distract from the flow of the paper.