Influence of atmospheric teleconnections and Upper Circumpolar Deep Water on phytoplankton biomass around Elephant Island, Antarctica

Abstract

Using 18 years of hydrographic data collected during austral summer from 1990 to 2007, we examined the association between atmospheric teleconnections, seasonal mean water column properties and phytoplankton biomass around Elephant Island (EI), Antarctica. We developed an index of the extent of Upper Circumpolar Deep Water (UCDW) in the EI region, defined as the mean temperature at the 27.6 kg m -3 (σt) isopycnal. We found a positive correlation (r = 0.60; p < 0.001) between this index of UCDW extent and the magnitude of the seasonal Southern Oscillation Index (SOI). No linear secular trend was observed in temperature at the 27.6 σt isopycnal, but significant interannual patterns of variability were observed and polynomial regression suggested that potential long-term decadal (or longer) scale variability was captured. Mean Upper Mixed Layer (UML) chlorophyll a (chl a) concentration was not correlated with this UCDW index, but was positively cor- related with the strength of the SOI. Mean integrated chl a biomass of the UML was positively corre- lated (r = 0.88; p < 0.001) with the mean UML chl a concentration. Stepwise regression showed that variability in mean UML chl a concentration over the 18-yr time series was more strongly correlated with UML temperature than UML depth. Although the correlations were weak, these results suggest that the deepening of the UML during El Nino conditions was likely the result of colder temperatures within the UML that limited bloom conditions over this 18-yr time series, with the opposite pattern during La Nina.