SEASONAL CHANGES IN POLAR PHYTOPLANKTON - RELATION TO HYDROGRAPHIC CONDITIONS ALONG THE WESTERN ANTARCTIC PENINSULA

CUSICK, ALLISON; MASCIONI, MARTINA; PINPOKINTR, ANESSE; JOHNSON, CHRISTIAN; ALMANDOZ, GASTÓN; RICK REYNOLDS; VERNET, MARIA

Congreso; Ocean Sciences Meeting 2022; 2022

ASLO

Along the Western Antarctic Peninsula (WAP), diatoms have been described as the main contributors to primary productivity; however, small flagellates and cryptophytes also play a significant role in the contribution of carbon biomass. Relatively little is known about how and when the diversity of the community composition shifts during the 5-month solar season (November to March) and how this may relate to melting glaciers in the nearshore. Along the WAP 87% of the glaciers are in retreat providing a net input of freshwater. This study examined the hypothesis that freshwater input would be observed earliest in spring-summer season along the northern WAP, and meltwater occurrence extends southward as the season progresses. In addition, a shift toward smaller flagellate abundance, particularly that of cryptophytes, will be more present when more freshwater is present. Sampling was conducted along the nearshore (62°-68°S) from tour vessels through the citizen science project Fjord Phyto during austral summer from 2017 – 2020. Measurements of salinity, temperature, and Secchi depth were taken to calculate mixed layer depth, meltwater fraction, and euphotic depth. Surface phytoplankton samples were analyzed via microscopy and next-generation sequencing (18S v9) for identification, cell abundance and estimated carbon biomass. Results from each season are highly variable regarding the inputs of freshwater to the coast. Diatoms dominated followed by cryptophytes, dinoflagellates. Small flagellates remained at background levels throughout the season. Cryptophytes were present when temperature was lower, and salinity was higher in some seasons which contradicts previous studies. This study highlights the spatial extent and timing of glacial meltwater input during the season and identifies concomitant shifts in phytoplankton presence and species diversity.