POSTER Session 3

CHANGES IN PHYTOPLANKTON COMPOSITION OF THE EAST GREENLAND SEA AS OBSERVED BY HIGH RESOLUTION UNDERWAY SPECTROPHOTOMETRY

Hyperspectral underway spectrophotometry data measured at yearly spring/summer RV Polarstern expeditions from 2015 to 2024 along the ship’s transect surface waters in eastern Greenland Sea. The chlorophyll-a concentrations (chl-a) of the major phytoplankton groups have been determined by spectrally decomposing the data and then developing models based on regression to matchups with HPLC phytoplankton pigment data. The unique high-resolution data set was analyzed to assess the composition of phytoplankton particularly within the Fram Strait area in the Greenland Sea and assess its variability and trends. The data set reflects well the different composition of the phytoplankton community to be related to the to the two main water masses, Atlantic and polar waters. From the beginning of the time series haptophytes (most probably mainly dominated by Phaeocystis) have steadily increased within the phytoplankton community and became nearly as dominant as diatoms in phytoplankton blooms until 2021. In contrast, the data of the last three years show that now in phytoplankton blooms diatoms contribute up to 90% while rather green algae than haptophytes play the role of the second major group. This is accompanied by a strong increase in total chl-a which is more than double the values compared to the years before as derived from our data set and previous literature.

Astrid Bracher, Alfred Wegener Institute for Polar and Marine Research, Germany, [email protected], https://orcid.org/0000-0003-3025-5517

Hongyan Xi, Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Germany, [email protected], https://orcid.org/0000-0003-2827-0603

Ehsan Mehdipour, Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Germany, [email protected]

Alexandra Kraberg, Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Germany, [email protected], https://orcid.org/0000-0003-2571-2074

Katja Metfies, Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Germany, [email protected], https://orcid.org/0000-0003-3073-8033

Eva-Maria Nöthig, Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Germany, [email protected], https://orcid.org/0000-0002-7527-7827

Ilka Peeken, Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Germany, [email protected], https://orcid.org/0000-0003-1531-1664

Wilken von Appen, Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Germany, [email protected], https://orcid.org/0000-0002-7200-0099

Sonja Wiegmann, Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Germany, [email protected]

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