Long-term iceshelf-covered meiobenthic communities of the Antarctic continental shelf resemble those of the deep sea

Since strong regional warming has led to the disintegration of huge parts of the Larsen A and B ice shelves east of the Antarctic Peninsula in 1995 and 2002, meiofaunal communities covered by ice shelves for thousands of years could be investigated for the first time. Based on a dataset of more than 230,000 individuals, meiobenthic higher taxa diversity and composition of Larsen continental shelf stations were compared to those of deep-sea stations in the Western Weddell Sea to see whether the food-limiting conditions in the deep sea and the food-poor shelf regime at times of iceshelf coverage has resulted in similar meiobenthic communities, on the premises that food availability is the main driver of meiobenthic assemblages. We show here that this is indeed the case; in terms of meiobenthic communities, there is greater similarity between the deep sea and the inner Larsen embayments than there is similarity between the deep sea and the former Larsen B iceshelf edge and the open continental shelf. We also show that resemblance to Antarctic deep-sea meiofaunal communities was indeed significantly higher for communities of the innermost Larsen B area than for those from intermediate parts of Larsen A and B. Similarity between communities from intermediate parts and the deep sea was again higher than between those of the ice-edge and the open shelf. Meiofaunal densities were low at the inner parts of Larsen A and B, and comparable to deep-sea densities, again likely owing to the low food supply at both habitats. We suggest that meiobenthic communities have not yet recovered from the food-limiting conditions present at the time of iceshelf coverage. Meiofaunal diversity on the other hand seemed driven by sediment structure, being higher in coarser sediments.

Effects of environmental conditions on the seasonal distribution of phytoplankton biomass in the North Sea

We study the spatial and seasonal variability of phytoplankton biomass (as phytoplankton color) in relation to the environmental conditions in the North Sea using data from the Continuous Plankton Recorder survey. By using only environmental fields and location as predictor variables we developed a nonparametric model (generalized additive model) to empirically explore how key environmental factors modulate the spatio-temporal patterns of the seasonal cycle of algal biomass as well as how these relate to the ,1988 North Sea regime shift. Solar radiation, as manifest through changes of sea surface temperature (SST), was a key factor not only in the seasonal cycle but also as a driver of the shift. The pronounced increase in SST and in wind speed after the 1980s resulted in an extension of the season favorable for phytoplankton growth. Nutrients appeared to be unimportant as explanatory variables for the observed spatio-temporal pattern, implying that they were not generally limiting factors. Under the new climatic regime the carrying capacity of the whole system has been increased and the southern North Sea, where the environmental changes have been more pronounced, reached a new maximum.