Phytoplankton blooms during austral summer in the Ross Sea, Antarctica: Driving factors and trophic implications

Abstract

During the austral summer of 2014, an oceanographic cruise was conducted in the Ross Sea in the framework of the RoME (Ross Sea Mesoscale Experiment) Project. Forty-three hydrological stations were sampled within three different areas: the northern Ross Sea (RoME 1), Terra Nova Bay (RoME 2), and the southern Ross Sea (RoME 3). The ecological and photophysiological characteristics of the phytoplankton were investigated (i.e., size structure, functional groups, PSII maximum quantum efficiency, photoprotective pigments), as related to hydrographic and chemical features. The aim was to identify the mechanisms that modulate phytoplankton blooms, and consequently, the fate of organic materials produced by the blooms. The observed biomass standing stocks were very high (e.g., integrated chlorophyll-a up to 371 mg m-2 in the top 100 m). Large differences in phytoplankton community composition, relative contribution of functional groups and photosynthetic parameters were observed among the three subsystems. The diatoms (in different physiological status) were the dominant taxa in RoME 1 and RoME 3; in RoME 1, a post-bloom phase was identified, whereas in RoME 3, an active phytoplankton bloom occurred. In RoME 2, diatoms co-occurred with Phaeocystis antarctica, but were vertically segregated by the upper mixed layer, with senescent diatoms dominating in the upper layer, and P. antarctica blooming in the deeper layer. The dominance of the phytoplankton micro-fraction over the whole area and the high Chl-a suggested the prevalence of non-grazed large cells, independent of the distribution of the two functional groups. These data emphasise the occurrence of significant temporal changes in the phytoplankton biomass in the Ross Sea during austral summer. The mechanisms that drive such changes and the fate of the carbon production are probably related to the variations in the limiting factors induced by the concurrent hydrological modifications to the Ross Sea, and they remain to be fully clarified. The comparison of conditions observed during summer 2014 and those reported for previous years reveal considerably different ecological assets that might be the result of current climate change. This suggests that further changes can be expected in the future, even at larger oceanic scales.

Austral Summer Bloom of Loricate Choanoflagellates in the Central Ross Sea Polynya

“…Our observations support the recent trend of changes in the plankton succession that are potentially restructuring trophic relationships in the Antarctic food web (Mangoni et al. ; Rivaro et al. ).…”

Fe and Nutrients in Coastal Antarctic Streams: Implications for Primary Production in the Ross Sea

“…Normalized to an SRP detection limit of 0.17 μM, Garwood had an average stoichiometry of 6N:1P:210Si:2Fe. Recent work in the coastal waters of the Ross Sea, north of Taylor Valley found that the mean N:P:Si ratio in the surface mixed layer was observed to be 21.5:1:63 (Mangoni et al, ). Thus, these coastal streams with their enhanced P (relative to N) concentrations may be very consequential in affecting macronutrient stoichiometry during the austral summer.…”

Reconstruction of Ocean Color Data Using Machine Learning Techniques in Polar Regions: Focusing on Off Cape Hallett, Ross Sea

“…To avoid this noise, a deep understanding of the factors that influence the class is needed. We, therefore, referred to previous studies [11,[33][34][35][36][37][56][57][58][59][60][61][62][63][64][65][66] on the growth/limitation of phytoplankton that determine CHL in this region and finally selected the predictors.…”

“…In the western Ross Sea including Cape Hallett, distinct phytoplankton blooms are recurrent from year to year during austral spring and summer, especially around the Terra Nova Bay [11,63]. The phytoplankton growth results from the combinations of many factors such as sea ice, temperature, wind, nutrients, and light [37,[64][65][66].…”