Response to changing oceanography in the Dove Time Series : a Northumberland plankton community study

Abstract

The Dove Time Series is a plankton monitoring station in the Northumberland coastal sea which has been sampled since 1969. Over the 20th century, major changes have occurred in the North Sea plankton which have in part correlated with oscillation in atmospheric mass over the Northern Hemisphere, the North Atlantic Oscillation (NAO). Westerly winds when the NAO is positive phase block northern low pressure systems and transport warm Atlantic water into the North Sea extending stratification, leading to greater phytoplankton biomass. Phytoplankton biomass in the central North Sea reached a sustained higher level after 1985. Phytoplankton, zooplankton and ichthyoplankton datasets were created or extended from the Dove Time Series to study the effect of oceanographic change at this location. There was a change to a high abundance community 10 years later, in 1995. The most important predictor of phytoplankton abundance was not the NAO index, but the Atlantic Meridional Oscillation (AMO), which exhibits 60-100 year and subordinate 11 and 14 year periodicity, describing a deviation from the long term sea surface temperature (SST) mean in the North Atlantic. Phytoplankton periodicity partly matched the 14 year period in the AMO, which correlates with a feedback mechanism of westerly versus northerly wind in the North Atlantic, regulating ocean-atmosphere heat flux. Zooplankton abundance was predicted by SST and ratio of maximum to minimum abundance by phytoplankton/AMO. Oceanographic conditions that were contemporary with the state of the AMO anomaly after 1995 promoted higher spring phytoplankton abundance and neritic copepod abundance peaks. Ichthyoplankton variability was not synchronous with these lower order changes, probably as a result of different effects on adult fish. The cyclical nature of the AMO means both low and high biomass communities observed in the Dove Time Series are part of one regime.