Phaeocystis antarctica unusual summer bloom in stratified antarctic coastal waters (Terra Nova Bay, Ross Sea)

This study focuses on the potential explanations for a Phaeocystis antarctica summer bloom occurred in stratified waters of Terra Nova Bay (TNB) - which is part of the Antarctic Special Protected Area (n.161) in the Ross Sea - trough a multi-parameter correlative approach. Many previous studies have highlighted that water column stratification typically favors diatom dominance compared to the colonial haptophyte P. antarctica, in the Ross Sea, and this correlation has often been used to explain the historic dominance of diatoms in TNB. To explore the spatial and temporal progression of P. antarctica bloom in coastal waters, four stations were sampled three times each between December 31, 2009 and January 13, 2010. Taxonomic and pigment composition of phytoplankton communities, macro-nutrient concentrations and various different indices, all indicated the relative dominance of P. antarctica. Cell abundances revealed that P. antarctica contributed 79% of total cell counts in the upper 25 m and 93% in the lower photic zone. Similarly, a strong correlation was observed between Chl-a and the Hex:Fuco pigment ratio, corroborating the microscopic analyses. Recent studies have shown that iron can trigger colonial P. antarctica blooms. Based on the Hex:Chl-c3 proxy for iron limitation in P. antarctica, we hypothesize that anomalously higher iron fluxes were responsible for the unusual bloom of colonial P. antarctica observed in TNB

Spatial-Related Community Structure and Dynamics in Phytoplankton of the Ross Sea, Antarctica

The Ross Sea exhibits the largest continental shelf and it is considered to be the most productive region in Antarctica, with phytoplankton communities that have so far been considered to be driven by the seasonal dynamics of the polynya, producing the picture of what is considered as the classical Antarctic food web. Nevertheless, the Ross Sea is made up of a complex mosaic of sub-systems, with physical, chemical, and biological features that change on different temporal and spatial scales. Thus, we investigated the phytoplankton community structure of the Ross Sea with a spatial scale, considering the different ecological sub-systems of the region. The total phytoplankton biomass, maximum quantum efficiency (Fv/Fm), size classes, and main functional groups were analyzed in relation to physical–chemical properties of the water column during the austral summer of 2017. Data from our study showed productivity differences between polynyas and other areas, with high values of biomass in Terra Nova Bay (up to 272 mg chl a m–2) and the south-central Ross Sea (up to 177 mg chl a m–2) that contrast with the HNLC nature of the off-shore waters during summer. Diatoms were the dominant group in all the studied subsystems (relative proportion ≥ 50%) except the southern one, where they coexisted with haptophytes with a similar percentage. Additionally, the upper mixed layer depth seemed to influence the level of biomass rather than the dominance of different functional groups. However, relatively high percentages of dinoflagellates (∼30%) were observed in the area near Cape Adare. The temporal variability observed at the repeatedly sampled stations differed among the sub-systems, suggesting the importance of Long-Term Ecological Research (L-TER) sites in monitoring and studying the dynamics of such an important system for the global carbon cycle as the Ross Sea. Our results provide new insights into the spatial distribution and structure of phytoplankton communities, with different sub-systems following alternative pathways for primary production, identifiable by the use of appropriate sampling scales

Diversity in zooplankton and sympagic biota during a period of rapid sea ice change in Terra Nova Bay, Ross Sea, Antarctica

Sea ice is a major driver of biological activity in the Southern Ocean. Its cycle of growth and decay determines life history traits; food web interactions; and populations of many small, ice-associated organisms. The regional ocean modelling system (ROMS) for sea ice in the western Ross Sea has highlighted two modes of sea ice duration: fast-melting years when water temperature warms quickly in early spring and sea ice melts out in mid-November, and slow-melting years when water temperature remains below 0 °C and sea ice persists through most of December. Ice-associated and pelagic biota in Terra Nova Bay, Ross Sea, were studied intensively over a 3-week period in November 1997 as part of the PIPEX (Pack-Ice Plankton Experiment) campaign. The sea ice environment in November 1997 exhibited features of a slow-melting year, and the ice cover measured 0.65 m in late November. Phytoplankton abundance and diversity increased in the second half of November, concomitant with warming air and water temperatures, melting sea ice and progressive deepening of a still weak pycnocline. Water column phytoplankton was dominated by planktonic species, both in abundance and diversity, although there was also some input from benthic species. Pelagic zooplankton were typical of a nearshore Antarctic system, with the cyclopoid copepod Oithona similis representing at least 90% of total abundance. There was an increase in numbers coinciding with the period of ice thinning. Conversely, ice-associated species such as the calanoid copepods Stephos longipes and Paralabidocera antarctica decreased over time and were found in low numbers once the water temperatures increased. Stratified sampling under the sea ice, to 20 m, revealed that P. antarctica was mainly found in close association with the under-ice surface, while S. longipes, O. similis, and the calanoid copepod Metridia gerlachei were dispersed more evenly

Metal induced folding: Synthesis and conformational analysis of the lanthanide complexes of two 44-membered hydrazone macrocycles

Six new lanthanide complexes of two 44-membered macrocycles have been prepared and characterised in solution. An analysis of the conformations of the free macrocycles and their lanthanide complexes both in solution (2D NMR) and in solid state (X-ray crystallography) demonstrate that the complexation induces changes in folding of the macrocycles