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
05:00 PM
Detecting changes in phytoplankton functional types in the Arctic over past 20 years through combined in situ and satellite observations (5665)
Primary Presenter: Katarzyna Dragańska-Deja, Institute of Oceanology Polish Academy of Science (katarzynadraganska@gmail.com)
While the use of satellite data has revolutionised our ability to study the Arctic, there are significant limitations in the ability to estimate changes in biological processes, biodiversity and ecosytem functions.The development of algorithms for remote sensing of water quality, including productivity and phytoplankton community composition, requires a large amount of in situ data, such as pigment data, to calibrate and validate. However, there is a shortage of in situ data published, and those existing for the Arcitc that can match up in situ pigment data with satellite measurements are very limited due to high cloud cover in this region. This study explores the value of a large, previously unpublished, dataset of historical phytoplankton pigment data from the Arctic region collected over the 2000-2022 period and analyzed by High-Performance Liquid Chromatography (HPLC). A total of 900 sets of pigment data were used in the analyses which compares the spatio-temporal variability in the distribution of phytoplankton functional types in the Arctic between 2000-2005 and 2014-2022. By acquiring an unprecedented number of match-ups with satellite ocean colour measurements, we provide preliminary results from relating the observed patterns in pigment data with patterns detected from large scale satellite-based estimates of phytoplankton biomass and sea surface temperature among other environmental variables. The newly available dataset with satellite match-ups exhibits potential for significantly improving existing capacity to model changing distributions of phytoplankton functional types from space.
05:15 PM
NITROGEN FIXATION ACROSS CONTRASTING HYDROGRAPHICAL AND SEA ICE REGIMES IN THE CENTRAL AND EASTERN ARCTIC OCEAN (5129)
Primary Presenter: Lisa von Friesen, University of Copenhagen (lisa.vonfriesen@bio.ku.dk)
Nitrogen fixation – the conversion of nitrogen gas to bioavailable ammonia by a group of prokaryotes called diazotrophs – was previously not thought to occur in the Arctic Ocean. However, studies have now reported considerable nitrogen fixation rates from western Arctic shelf seas. This is of relevance as the often nitrogen-limited Arctic is undergoing rapid change with unknown consequences for nutrient availability and thus primary productivity. In this study, nitrogen fixation and the underpinning diazotroph communities were mapped over contrasting hydrographical and sea ice regimes in the unexplored central and eastern Arctic Ocean. Non-cyanobacterial diazotrophs are putative key players in the Arctic and may take up dissolved organic carbon. We therefore targeted the chlorophyll a maximum to achieve highest biomass and experimentally investigate organic carbon limitation. Strikingly, we detected nitrogen fixation below sea ice in the central Arctic Ocean ranging from 0.5-2.6 nmol N L-1 d-1. Across the marginal ice zone, rates varied with regime and time, reaching up to 6.0 ± 1.4 nmol N L-1 d-1 in the area between open water and pack ice. Very low rates of 0.4 ± 0.2 nmol N L-1 d-1 were detected below land-fast sea ice in northeast Greenland. The response to organic carbon amendments was strongest in the central Arctic, indicating carbon limitation of diazotrophs in this region. The surprisingly high rates of nitrogen fixation in the low-productive central Arctic Ocean suggest it could be a regionally significant process partially supporting local primary production.
05:30 PM
SEASONAL PREY COMPOSITION OF THREE SMALL ARCTIC COPEPODS ASSESSED BY METABARCODING (4646)
Primary Presenter: Snorre Flo, University Centre in Svalbard (UNIS) (snorreflo@gmail.com)
Although the small size-fraction of copepods (<1 mm) are important constituents of the Arctic food-web, their trophic interactions remain largely unexplored, partly due to methodological limitations. We here characterize the prey of the cyclopoid Oithona similis, harpacticoid Microsetella norvegica and calanoid Microcalanus spp. from the Arctic Barents Sea and Nansen Basin in March, April-May, August, and December using brute force prey metabarcoding of the 18S rRNA gene. Of the prey identified, chaetognaths were the most consistently identified taxa and composed 47% of all prey reads. Reads from diatoms (16%), dinoflagellates (11%) and urochordates (8%) were likewise abundant, but these taxa were more prevalent during specific seasons. Diatoms composed 43% of prey reads in April-May, dinoflagellates 15% in December and 17% in March, and urochordates 20% in August. Although some species differences were also discernible, we show that the dietary composition varied more among seasons than among species. This was observed despite the taxonomic and behavioural differences that distinguish the ambush-predator O. similis, chemosensoric particle-chaser M. norvegica and current-feeding Microcalanus spp. The results thus indicate that dietary plasticity is common in small Arctic copepods, regardless of their behaviours or strategies for finding food. We moreover hypothesize that such plasticity is an important adaptation in systems where prey availability is highly seasonal.
05:45 PM
EXPLORING SEASONAL ENERGETICS OF BARENTS SEA MACROZOOPLANKTON AND THE IMPACT OF BOREALIZATION (6701)
Primary Presenter: Robynne Nowicki, The University Centre in Svalbard (robynneno@unis.no)
Arctic zooplankton develop large energy reserves, as an adaptation to strong seasonality, making them valuable prey items. We quantified the energy content (kJ g−1 dry weight) of abundant krill (arcto-boreal, Thysanoessa inermis and boreal, Meganyctiphanes norvegica) and amphipods (Arctic, Themisto libellula and sub-Arctic-boreal, Themisto abyssorum) in the Barents Sea in late summer (August) and early winter (December). Variation in energy content was attributed to species-specific traits and body size categories, the latter in part as a proxy for ontogeny. T. inermis had the highest energy content, which remained similar from summer to winter. Energy content increased in M. norvegica and decreased in both amphipod species, with the lowest energy content being in T. abyssorum. The effect of body size varied between species, with energy content increasing with size in T. inermis and T. libellula, and no change with size in M. norvegica and T. abyssorum. Energy content varied with species’ dependence on energy storage. Our findings highlight how phylogenetically and morphologically similar prey items cannot necessarily be considered equal from a predator´s perspective. Energetically, the northern T. inermis was higher quality compared to the more southern M. norvegica, and mostly so during summer. Ecological models and management strategies should consider such variation in prey quality, especially as Arctic borealization is expected to change species composition and the energetic landscape for predators.
06:00 PM
WHERE TO OVERWINTER? THE DETAIL IN THE <em>CALANUS HYPERBOREUS</em> LIPIDS (4926)
Primary Presenter: Sigrun Jonasdottir, Technical University of Denmark (sjo@aqua.dtu.dk)
Lipid accumulation and (long) periods of diapause are the key traits ensuring successful life history strategy of polar copepods. The lipids have several functions, where the most obvious function is to supply the animal with sufficient energy for survival during overwintering and to fuel gonad development and even egg production. However, lipids are also essential as a buoyancy regulator allowing the copepod to stay torpid at great depths for a long period in a state of diapause. The type of lipids copepods accumulate before entering diapause are wax esters, and their compressibility (thus buoyancy) is dependent on the saturation level of the wax ester. We present results from an ongoing analysis on the molecular composition of intact wax esters of the Arctic copepod <em>Calanus hyperboreus</em> from several locations; West and East of Greenland and the Nansen and Amundsen basins in the Arctic Ocean. The overarching questions we seek to answer is if there is a relationship between wax ester structure and the overwintering habitat at which the copepod parks? We focus on the relationship is between the depth (pressure) of overwintering and the saturation of the wax esters and if there is a relationship between the details in the wax esters and seawater density. Any change in the physical environment can affect the depth and length of overwintering of the copepods and therefore the survival during diapause. Results from ongoing analyses will be presented.
06:15 PM
Metazoans, vertical migrations, carbon sequestration and oxygen. (5164)
Primary Presenter: Andre Visser, DTU Aqua (awv@aqua.dtu.dk)
The vertical structure of mesopelagic ecosystems is characterized by Vinogradov’s ladder, a trophic relay of vertical migrants spanning from the sunlit surface ocean to the sea floor. This vertical structure is imprinted further by seasonal migrants, light, temperature and nutrient profiles, particulate organic matter fluxes, global ocean circulation and oxygen minima zones (OMZ). Here we disentangle some to the key pathways (respiration, fecal pellets, deadfalls) by which passive and active fluxes impact the oceanic carbon sequestration of the biological carbon pump (BCP). Specifically we compare estimates to the ~1300 PgC of dissolved inorganic carbon (DIC) sequestered in the world’s oceans by the respiration of organic carbon. We draw on recent modelling results for metazoan migrants in the mesopelagic ocean as well as observation driven estimates for selected seasonally migrating copepods stocks and krill fecal pellet production in the Southern Ocean. Throughout we are mindful of the oxygen demand associated with DIC sequestration via the BCP, and point to a potential tipping process associated with expanding OMZ’s and interruptions to Vinogradov’s ladder.
SS059 Ecosystem Tipping Points in the Open Ocean Ecosystem in Polar Seas
Description
Time: 5:00 PM
Date: 5/6/2023
Room: Sala Menorca A