Interannual variability of the initiation of the phytoplankton growing period in two French coastal ecosystems

[摘要] Decadal time series of chlorophyll  a concentrations sampled at highand low frequencies are explored to study climate-induced impacts on theprocesses inducing interannual variations in the initiation of thephytoplankton growing period (IPGP) in early spring. We specifically detailthe IPGP in two contrasting coastal temperate ecosystems under the influenceof rivers highly rich in nutrients: the Bay of Brest and the Bay of Vilaine.In both coastal ecosystems, we observed a large interannual variation inthe IPGP influenced by sea temperature, river inputs, light availability(modulated by solar radiation and water turbidity), and turbulent mixinggenerated by tidal currents, wind stress, and river runoff. We show that theIPGP is delayed by around 30 d in 2019 in comparison with 2010. In situ observationsand a one-dimensional vertical model coupling hydrodynamics,biogeochemistry, and sediment dynamics show that the IPGP generally does notdepend on one specific environmental factor but on the interaction betweenseveral environmental factors. In these two bays, we demonstrate that the IPGPis mainly caused by sea surface temperature and available light conditions,mostly controlled by the turbidity of the system before first blooms. Whileboth bays are hydrodynamically contrasted, the processes that modulate the IPGPare similar. In both bays, the IPGP can be delayed by cold spells and floodevents at the end of winter, provided that these extreme events last severaldays.

[学科分类] 大气科学