Detection of phytoplankton blooms in Antarctic coastal water with an online mooring system during summer 2010/11

In order to continuously monitor the phytoplankton growth in Antarctic coastal waters, an online mooring system was deployed in Great Wall Bay (unofficial name), King George Island, and both chlorophyll a (chl a) concentrations and environmental variables were monitored in a period between December 2010 and March 2011. Water temperatures showed a significant increasing trend (0.27-2.52 degrees C), whereas the salinities displayed a decreasing trend (34.19-33.86). In general, phytoplankton biomass accumulated from mid-December and two significant blooms developed in January (3.18 mu g l(-1) and 4.75 mu g l(-1)) and were then maintained at a relatively high level, with a transient bloom in late February (4.93 mu g l(-1)). Sea-ice meltwater and terrestrial freshwater input caused by the increase of temperature played an important role in inducing phytoplankton blooms in early summer. The variation and stratification of temperature and salinity signals in different water layers, without total mixing, suggested lateral intrusion of oceanic waters with alternating levels of temperature and salinity and, presumably, phytoplankton as well. Meanwhile, chl a concentrations initially decreased with an increase in irradiance, indicating the shade-adapted characteristic of phytoplankton in early summer, and then gradually adapted to the increasing irradiance. Our results demonstrated the effectiveness and reliability of the online coastal mooring system for the monitoring of Antarctic coastal phytoplankton bloom and environmental conditions.