The onset of the spring phytoplankton bloom in the coastal North Sea supports the Disturbance Recovery Hypothesis

[摘要] The spring phytoplankton bloom is a key event intemperate and polar seas, yet the mechanisms that trigger it remain underdebate. Some hypotheses claim that the spring bloom onset occurs when lightis no longer limiting, allowing phytoplankton division rates to surpass acritical threshold. In contrast, the Disturbance Recovery Hypothesis (DRH)proposes that the onset responds to an imbalance between phytoplanktongrowth and loss processes, allowing phytoplankton biomass to startaccumulating, and this can occur even when light is still limiting. Althoughseveral studies have shown that the DRH can explain the spring bloom onsetin oceanic waters, it is less certain whether and how it also applies tocoastal areas. To address this question at a coastal location in theScottish North Sea, we combined 21 years (1997–2017) of weekly in situchlorophyll and environmental data with meteorological information.Additionally, we also analyzed phytoplankton cell counts estimated usingmicroscopy (2000–2017) and flow cytometry (2015–2017). The onset ofphytoplankton biomass accumulation occurred around the same date each year,16  ±  11 d (mean  ±  SD) after the winter solstice, when lightlimitation for growth was strongest. Also, negative and positive biomassaccumulation rates ( r ) occurred respectively before and after the wintersolstice at similar light levels. The seasonal change from negative topositive r was mainly driven by the rate of change in light availabilityrather than light itself. Our results support the validity of the DRH forthe studied coastal region and suggest its applicability to other coastalareas.

[学科分类] 大气科学