Assessing the presence of discontinuities in the ocean color satellite record and their effects on chlorophyll trends and their uncertainties

Ocean color sensors are crucial for understanding global phytoplankton dynamics. However, the limited life spans of sensors make multisensor data sets necessary for estimating long‐term trends. Discontinuities may be introduced when merging data between sensors, potentially affecting trend estimates and their uncertainties. We use a Bayesian spatiotemporal model to investigate the presence of discontinuities and their impacts on estimated chlorophyll trends. The discontinuities considered are the introduction of Medium Resolution Imaging Spectrometer, Moderate Resolution Imaging Spectroradiometer‐Aqua, and Visible Infrared Imaging Radiometer Suite and the termination of Sea‐Viewing Wide Field‐of‐View Sensor. Discontinuities are detected in ~70% of regions, affecting trend estimates (~60% of regions have statistically different trends) and potentially even biasing trend estimates (opposite sign in ~13% of regions). Considering a single discontinuity increases trend uncertainty by an average of 0.20%/year (0.59%/year for two discontinuities). This difference in trend magnitude and uncertainty highlights the importance of minimizing discontinuities in multisensor records and taking into account discontinuities when analyzing trends. Plain Language Summary Ocean color sensors are crucial for understanding global phytoplankton dynamics as they detect chlorophyll, a proxy for phytoplankton abundance. However, the limited life spans of sensors make multisensor data sets necessary for estimating long‐term trends. Differences between sensors may be seen when combining them to form multisensor data sets, creating discontinuities in the record (a point in the record representing a sudden change) which could potentially affect estimates of trend and their uncertainties. We use a statistical model that explicitly considers the spatial relationship between observation locations to investigate the presence of discontinuities and their impacts on estimated chlorophyll trends. We consider three discontinuities relating to the introduction and termination of important ocean color sensors. Discontinuities are detected in the majority of regions, affecting trend estimates and potentially even changing the direction of trend. Considering a single discontinuity increases trend uncertainty, and considering multiple discontinuities increases this further. This difference in trend magnitude and uncertainty highlights the importance of minimizing discontinuities in multisensor data sets and taking into account discontinuities when analyzing trends.