A single peer-reviewed satellite analysis found that declining surface chlorophyll after the seasonal peak is lasting longer at northern high latitudes. Data from 2007–2022 combined ocean colour and laser observations, with independent float measurements used for validation. The Southern Ocean showed a more variable pattern. The observed timing shift does not directly measure carbon storage or cell death.
The seasonal decline in surface chlorophyll is taking longer at northern high latitudes, according to a single peer-reviewed observational study. Its baseline analysis found that the increasing phase gained 2.3–5.5 days over a decade; the post-peak declining phase gained 5.7–6.2 days. The ratio of those phases fell by approximately 5.3 per cent per decade. The Southern Ocean showed more balanced, spatially variable changes.[1]
Zhenhua Zhang, Peng Chen and colleagues analysed global satellite observations from 2007–2022. Phytoplankton are microscopic ocean organisms that photosynthesise. The team combined Aqua ocean-colour measurements with laser observations to reduce gaps in low-light and polar conditions. Independent profiling floats validated the chlorophyll product. The phases run from seasonal initiation to the chlorophyll maximum, and from that maximum to the season’s end; they do not directly measure cell growth or mortality rates.[1]
Sea ice, temperature, light and mixed-layer characteristics were examined together. Their covariation limits isolation of individual effects. The paper also discusses contrasting nutrient regimes alongside the hemispheric pattern. The team also summed surface chlorophyll over the season. That measure leaves contributions from concentration and vertical redistribution partly unresolved and does not measure carbon export to the deep ocean.[1]
