Coupled Changes in Marine Primary Production and Phytoplankton Phenology in a Warming Ocean

Marine ecosystems are experiencing uneven changes in response to the synergistic effects of climate change and anthropogenic pressures. Phytoplankton primary productivity, driven by photosynthesis, fuels marine ecosystems, providing the source material for trophic transfer and carbon export to the ocean interior. This study provides a large-scale assessment of net primary production (NPP) and its temporal variability across different latitudinal bands (40° N–45°S) in the Asia-Pacific region over 25 years (1998 –2022), with emphasis on bloom phenology. NPP is estimated through multi-model inter-fusion using satellite-based observations, which offers practical means for broad regional assessments given the limitations of direct measurement techniques. Our analysis reveals a decline in NPP of −3.2% per decade (equivalent to −15.31 mg C m⁻² day⁻¹ per decade, P < 0.01). NPP decreases with increasing latitude in both hemispheres, reaching minimum values at 20°–25° latitude that are 1.75-fold lower than equatorial values. The observed NPP trends are coupled with changes in phytoplankton phenology. Using three phenological threshold methods, phytoplankton bloom initiation has advanced by approximately −1.1 ± 10.4 days per decade, while termination occurred about −3.3 ± 10.5 days earlier per decade, resulting in shortened bloom durations of around −2.8 ±15.3 days per decade. The seasonal cycle demonstrated increased reproducibility over these temporal shifts, reflecting more stable annual variations. These changes in productivity and phenology patterns reflect the influence of climate change and anthropogenic pressures across the Asia-Pacific waters, with implications for ecosystem energy flow, carbon sequestration processes, and species composition.