Satellite-derived global-ocean phytoplankton phenology indices

Abstract. Phytoplankton bloom phenology is an important indicator for the monitoring and management of marine resources and the assessment of climate change impacts on ocean ecosystems. Despite its relevance, there is no long-term and sustained observational phytoplankton phenological product available for global-ocean implementation. This need is addressed here by providing a phenological data product (including among other seasonal metrics, the bloom initiation, termination, duration, and amplitude timing) using satellite-derived chlorophyll-a data from the Ocean Colour Climate Change Initiative. This multi-decadal data product provides the phenology output from three widely used bloom detection methods at three different spatial resolutions (4, 9, and 25 km), allowing for both regional- and global-scale applications. When compared to each other on global scales, there is general agreement between the detection methods and between the different resolutions. Regional differences are evident in coastal domains (particularly for different resolutions) and in regions with strong physical–biogeochemical transitions (notably for different detection methods). This product can be used towards the development of national and global biodiversity assessments, for pelagic ecosystem mapping, and for monitoring change in climate sensitive regions relevant for ecosystem services. The data set is published in the Zenodo repository under the following DOIs: https://doi.org/10.5281/zenodo.8402932 for 4 km, https://doi.org/10.5281/zenodo.8402847 for 9 km, and https://doi.org/10.5281/zenodo.8402823 for 25 km (Nicholson et al., 2023a, b, c). It will be updated on an annual basis.