The Polar seas are changing more rapidly than any other ocean area due to global warming. The melting of the Greenland and West Antarctic ice sheets are expected to already have reached a tipping point and the consequences of the freshwater inflow and ice-free fjords, coastal and open ocean areas are still to be seen. Increased freshwater is predicted to increase stratification of the water column, with potential major consequences for the community composition of plankton and therefore for the polar food webs and carbon flux – an ecosystem tipping point equal to the ones observed in coastal and terrestrial ecosystems. In this session, we welcome presentations on climate-induced changes of biodiversity and biological processes from all polar and sub-polar marine pelagic ecosystems. We are equally interested in observations related to climate-induced regime shifts, process studies on ecosystem functions and modelling studies investigating the changes in marine systems and the ecosystem services that they provide.
Lead Organizer: Sigrun Jonasdottir, Technical University of Denmark (sjo@aqua.dtu.dk)
Co-organizers:
Marja Koski, Technical University of Denmark (mak@aqua.dtu.dk)
Presentations
06:30 PM
Pigments in Greenland shelf waters – comparison of in-situ data and satellite observations (5337)
Primary Presenter: Joanna Stoń-Egiert, Institute of Oceanology Polish Academy of Sciences (aston@iopan.pl)
The climate changes taking place on Earth have substantially modified the physical, chemical, and biological properties of the World Ocean, especially evident in polar regions. The Arctic ecosystem is highly sensitive to climate warming, so monitoring processes in the marine environment require appropriate measurement techniques. Information derived from the models based on satellite data is often used as a tool for mapping changes in the marine environment and providing environmental background for in-situ research. They allow us to look at the phenomenon studying on a larger scale. In the current work, we present the results of measurements of pigment concentrations in samples collected on the Greenland shelf in 2021 and 2022, compared with satellite observations. We used values of chlorophylls and carotenoids concentrations to analyze the biodiversity of the polar ecosystem.
06:30 PM
DISSOLVED ORGANIC MATTER OPTICAL PROPERTIES IN COASTAL WATERS OF GREENLAND (5359)
Primary Presenter: MONIKA ZABLOCKA, INSTITUTE OF OCEANOLOGY POLISH ACADEMY OF SCIENCES (monika_z@iopan.pl)
A study on DOM optical properties was conducted in coastal waters of Greenland during two summer expeditions in 2021 and 2022. Water samples for determination of DOM absorption coefficients, DOM fluorescence intensity and total chlorophyll a concentration were collected at fixed depths (surface, chlorophyll a maximum depth, below chlorophyll a maximum depth) of west and east Greenland shelf waters. Based on 91 EEM spectra and application of the PARAFAC, the 5-component model has been developed and validated. The studies revealed a small differences in both quantitative and qualitative properties of DOM optical characteristics between the waters of the East and West Greenland Shelf. The studies indicated that on average FDOM in investigated areas was equally composed by protein-like and humic-like fluorophores although the contribution of fluorescence intensity of the identified protein-like components (Ip) to the total fluorescence intensity (IT) varied from 30 to 79 % with higher values for surface water samples. The spectral indices: ratio between fluorescence intensity of identified protein-like components to humic-like components, Ip/Ih, humification index, HIX, and biological index, BIX, have been calculated.
06:30 PM
ENRICHMENT OF THE SEA SURFACE MICROLAYER WITH ORGANIC MATTER AND OCCURRENCE OF PHYTOPLANKTON BLOOMS AND POLLUTANTS (5416)
Primary Presenter: Violetta Drozdowska, Institute of Oceanology (drozd@iopan.pl)
The aim of our research - which relates to the SURETY project - is to understand the impact of natural marine and terrestrial organic matter (OM) in the sea on the enrichment of SML in OM, and most importantly to assess the role of SML as a barrier to gas exchange processes, CO2, between the sea and the atmosphere. Optical surveys of the European Arctic surface waters were conducted during three polar research cruises of RV Oceania, in 2018, 2019 and 2021. Sampling of the surface microlayer (SML) and subsurface water (ULW, 1m) allowed us to calculate the enrichment factor (EF) of the SML in organic matter (OM) and in phytoplankton pigments - based on absorption and fluorescence measurements and HPLC analyses of the collected samples. Additionally, the analysis of absorption and fluorescence indices (E2:E3, SR, aCDOM(l), fluorescence intensities of the main chromophoric fractions of DOM in the sea: A, C, M and T, the ratio (M+T)/(A+C), HIX index, composition and concentration of phytoplankton pigments) allow to describe the properties of organic molecules. The analyses of EEMs of sea samples reveals that: (1) concentration of OM fractions - both in the SML and SS – depend on a study-region and a year; (2) enrichment factor of fluorescing fractions of OM yielded higher values in M and T than A and C components. The results reveal the relationships between phytoplankton and the concentration of various optically active organic matter components in the surface layer (0-1m) and microlayer (0-1mm).
06:30 PM
CONTRASTING STRUCTURE AND DYNAMICS OF PELAGIC MICROBIAL COMMUNITIES IN FJORDS WITH MARINE- VERSUS LAND-TERMINATING GLACIERS IN GREENLAND (6347)
Primary Presenter: Marta Mikhno, Gent University (marta.mikhno@ugent.be)
Coastal fjord systems around Greenland sustain a high marine productivity and important fisheries, as such fulfill an important ecological and economical function. These fjords are fed by marine-terminating (MTG) and land-terminating glaciers (LTG). Global warming significantly impacts these systems through the accelerated melting of the Greenland ice sheet. This does not only increase total freshwater input into the fjords, but also leads to an accelerated retreat of MTGs, causing them to become LTGs in the near future. Previous studies shown that, in contrast to fjords with LTGs, summer upwelling of deep, nutrient-rich water induced by MTGs significantly increases productivity in their vicinity. It is hypothesized that this phenomenon causes fundamental differences in the structure and function of the pelagic compartment in both fjords types. We will present the results of two sampling campaigns (summer 2021 and spring 2022) carried out in the two main fjord systems near Nuuk, namely Nuup Kangerlua, dominated by MTG, and Ameralik, impacted by a LTG. Analyses of microbial community structure (DNA metabarcoding, Imaging Flow Cytometry, FlowCam, pigments), primary production, marine gel production (TEP), microzooplankton grazing and community respiration rates were carried out to assess differences in dynamics and functioning in the pelagic microbial compartment of the two fjords. Our results may help formulate hypotheses on what the future implications of accelerating melting of the Greenland ice sheet will be on food web structure and the carbon cycle.
06:30 PM
NITROGEN FIXATION AND DIAZOTROPH COMMUNITY COMPOSITION ACROSS ENVIRONMENTAL GRADIENTS IN THE ARCTIC FRAM STRAIT (6404)
Primary Presenter: Stine Zander Hagen, University of Copenhagen (tdn480@alumni.ku.dk)
Nitrogen is a key nutrient limiting primary production in the Arctic Ocean. Knowledge about sources and sinks of nitrogen is, therefore, essential for the understanding of current and future productivity in the region. Nitrogen fixation has been reported in the Arctic Ocean, but data remain sparse. Here, we measured nitrogen fixation rates and examined the diazotroph community composition across the deepest gateway to the Arctic Ocean - the Fram Strait. Samples were obtained from two major currents and their frontal zone: the southbound Arctic-influenced East Greenland Current, the northbound Atlantic-influenced West Spitsbergen Current, and the Polar Front. Nitrogen fixation rates were measurable in 9 of 20 samples (0.02 – 10.15 nmol N l-1 d-1), detected only above 100 m. Rates were highest in the Atlantic-influenced water, positively correlated with temperature and silicate. Amplicon sequencing of the nifH marker gene revealed that non-cyanobacterial diazotrophs dominated across Fram Strait, with Proteobacteria accounting for 66% of all sequences. For samples where nitrogen fixation rates were detected, the dominating classes (<96%) were affiliated with Beta-, Delta- and Gammaproteobacteria. Surprisingly, Cyanobacteria only accounted for 12% of the sequences, mainly affiliated with Nostocales. Our study shows a large potential for nitrogen fixation in this important gateway but with large differences between water masses. Our future work includes identification of the active diazotrophs (nifH gene expression) and the factors driving their activity in Fram Strait.
06:30 PM
SPRINGTIME Si/N DRAWDOWN RATIOS NORTH OF ICELAND 1964-2022 (7361)
Primary Presenter: Solveig Olafsdottir, Marine and Freshwater Research Inst (solveig.rosa.olafsdottir@hafogvatn.is)
Shifting fronts between temperate Atlantic and Arctic influences north and northwest of Iceland cause large interannual hydrographic variations where the relatively warm North Atlantic water may shift from being almost negligible to be the dominant surface layer water mass. We present data on nutrients and hydrography from springtime surveys conducted from 1964 to 2022. The timing of the observations is from late May to early June each year. Temperature and salinity of the surface waters in spring have been highly variable in this period. The stoichiometry of N:P utilization has in general been close to 16 but the Si:N uptake ratio has varied. In years normally characterised by high Polar Water influence, nitrate and phosphate are nearly depleted whilst silicate remains near winter concentration. We relate the resultant anomalous Si:N ratios to the observed dominance of the non-silicious species <em>Phaeocystis pouchetii </em> in the phytoplankton assemblages. This trophic pathway has impact on the carbon cycling in the ecosystem and the microbial food web and could be an indication of future conditions in rapidly changing Arctic marginal areas in spring. Trophic responses to <em>phaeocystis</em> blooms have been shown to differ from those of diatom dominated blooms with possible food chain effects. We evaluate the interannual variability in the euphotic layer nutrient utilization and examine the variability in relation to the differing dominant water masses and hydrographic surface layer structure.
SS059P Ecosystem Tipping Points in the Open Ocean Ecosystem in Polar Seas
Description
Time: 6:30 PM
Date: 6/6/2023
Room: Mezzanine