Sympagic-pelagic coupling and vertical export in two seasonally ice-covered fjords. Study of the physical and biological drivers in the sub-Arctic Ramfjorden (Norwegian mainland) and the Arctic Van Mijenfjorden (Svalbard archipelago) during early spring bloom.

Fjords are important high latitudes ecosystems, many have beside planctonic ones, a unique ecosystem associated with seasonal ice cover. During the development of the spring season conditions, two major type of primary producers contribute highly to the biomass production: sea-ice algae inhabiting brine channels and bottom surface of the ice (sympagic algae) and phytoplankton, living in the water column (pelagic algae). The biomass produced by algae is the base of the food web in the fjord ecosystem and is commonly exported to the benthic realm and sequestered at the sea floor. It is still not resolved 1) if autotrophic biomass in the sea-ice, and suspended in or exported from the water column differ in fjords on a short time scale, and 2) how physical processes drive the sympagic-pelagic coupling and sinking biomass in fjords on different latitudes. This study compared the seasonally ice-covered sub-Arctic, Ramfjorden (RMF, 69 °N, 19 °E) in March 2019 with the high Arctic, Van Mijenfjorden (VMF, 77 °N, 16 °E) in April 2019 during the early spring bloom to investigate these questions. Physical oceanographic and meteorologic data, ice cores and water column samples were collected as well as deployment of short-term sediment trap brought together with the chlorophyll a (Chl a), particulate organic carbon and nitrogen (POC and PON) concentration and the algal community composition in the ice and water column. This revealed that the two fjord systems differed with regard to sympagic-pelagic coupling and export of biomass. Ramfjorden was more impacted by river run-off than Van Mijenfjorden, the truly Arctic fjord. The sea-ice in Ramfjorden was fresher and hold a lower autotrophic biomass and a less rich sea-ice algae community, than the thicker and more saline sea-ice in Van Mijenfjorden. Thus, while the export in Ramfjorden was driven by pelagic species, in the high Arctic Van Mijenfjorden a tighter coupling between the sympagic, pelagic system and the vertical export was found. The short time scale, meteorological and hydrographical factors (e.g., air temperature and under-ice currents) seemed important drivers on the sea-ice, suspended and sinking biomass. In conclusion, the sympagic-pelagic coupling and the link to the vertical export of biomass seems to be very different in seasonally ice-covered fjords on different latitudes and in fjords with unlike freshwater impact

Sympagic-pelagic coupling and vertical export in two seasonally ice-covered fjords. Study of the physical and biological drivers in the sub-Arctic Ramfjorden (Norwegian mainland) and the Arctic Van Mijenfjorden (Svalbard archipelago) during early spring bloom.

Fjords are important high latitudes ecosystems, many have beside planctonic ones, a unique ecosystem associated with seasonal ice cover. During the development of the spring season conditions, two major type of primary producers contribute highly to the biomass production: sea-ice algae inhabiting brine channels and bottom surface of the ice (sympagic algae) and phytoplankton, living in the water column (pelagic algae). The biomass produced by algae is the base of the food web in the fjord ecosystem and is commonly exported to the benthic realm and sequestered at the sea floor. It is still not resolved 1) if autotrophic biomass in the sea-ice, and suspended in or exported from the water column differ in fjords on a short time scale, and 2) how physical processes drive the sympagic-pelagic coupling and sinking biomass in fjords on different latitudes. This study compared the seasonally ice-covered sub-Arctic, Ramfjorden (RMF, 69 °N, 19 °E) in March 2019 with the high Arctic, Van Mijenfjorden (VMF, 77 °N, 16 °E) in April 2019 during the early spring bloom to investigate these questions. Physical oceanographic and meteorologic data, ice cores and water column samples were collected as well as deployment of short-term sediment trap brought together with the chlorophyll a (Chl a), particulate organic carbon and nitrogen (POC and PON) concentration and the algal community composition in the ice and water column. This revealed that the two fjord systems differed with regard to sympagic-pelagic coupling and export of biomass. Ramfjorden was more impacted by river run-off than Van Mijenfjorden, the truly Arctic fjord. The sea-ice in Ramfjorden was fresher and hold a lower autotrophic biomass and a less rich sea-ice algae community, than the thicker and more saline sea-ice in Van Mijenfjorden. Thus, while the export in Ramfjorden was driven by pelagic species, in the high Arctic Van Mijenfjorden a tighter coupling between the sympagic, pelagic system and the vertical export was found. The short time scale, meteorological and hydrographical factors (e.g., air temperature and under-ice currents) seemed important drivers on the sea-ice, suspended and sinking biomass. In conclusion, the sympagic-pelagic coupling and the link to the vertical export of biomass seems to be very different in seasonally ice-covered fjords on different latitudes and in fjords with unlike freshwater impact

Seasonal patterns of vertical flux in the northwestern Barents Sea under Atlantic Water influence and sea-ice decline

The northern Barents Sea is a productive Arctic inflow shelf with a seasonal ice cover and as such, a location with an efficient downward export of particulate organic matter through the biological carbon pump. The region is under strong influence of Atlantification and sea-ice decline, resulting in a longer open water and summer period. In order to understand how these processes influence the biological carbon pump, it is important to identify the seasonal and spatial dynamics of downward vertical flux of particulate organic matter. In 2019 and 2021, shortterm sediment traps were deployed between 30 and 200 m depth along a latitudinal transect in the northwestern Barents Sea during March, May, August and December. Vertical flux of particulate organic carbon, δ13C and δ15N values, Chl-a, protists and fecal pellets were assessed. We identified a clear seasonal pattern, with highest vertical flux in May and August (178 ± 202 and 159 ± 79 mg C m− 2 d− 1 , respectively). Fluxes in December and March were − 2 d− 1 . May was characterized by diatom- and Chl a-rich fluxes and high spatial variability, while fluxes in August had a higher contribution of fecal pellets and small flagellates, and were spatially more homogenous. Standing stocks of suspended particulate organic matter were highest in August, suggesting a more efficient retention system in late summer. The strong latitudinal sea-ice gradient and the influence of Atlantic Water probably led to the high spatial variability of vertical flux in spring, due to their influence on primary productivity. We conclude that the efficiency of the biological carbon pump in a prolonged open-water period depends on the reworking of small, slow sinking material into efficiently sinking fecal pellets or aggregates, and the occurrence of mixing

Seasonal dynamics of sea-ice protist and meiofauna in the northwestern Barents Sea

The rapid decline of Arctic sea ice makes understanding sympagic (ice-associated) biology a particularly urgent task. Here we studied the poorly known seasonality of sea-ice protist and meiofauna community composition, abundance and biomass in the bottom 30 cm of sea ice in relation to ice properties and ice drift trajectories in the northwestern Barents Sea. We expected low abundances during the polar night and highest values during spring prior to ice melt. Sea ice conditions and Chlorophyll a concentrations varied strongly seasonally, while particulate organic carbon concentrations were fairly stable throughout the seasons. In December to May we sampled growing first-year ice, while in July and August melting older sea ice dominated. Low sea-ice biota abundances in March could be related to the late onset of ice formation and short time period for ice algae and uni- and multicellular grazers to establish themselves. Pennate diatoms, such as Navicula spp. and Nitzschia spp., dominated the bottom ice algal communities and were present during all seasons. Except for May, ciliates, dinoflagellates, particularly of the order Gymnodiales, and small-sized flagellates were co-dominant. Ice meiofauna (here including large ciliates and foraminifers) was comprised mainly of harpacticoid copepods, copepod nauplii, rotifers, large ciliates and occasionally acoels and foraminifers, with dominance of omnivore species throughout the seasons. Large ciliates comprised the most abundant meiofauna taxon at all ice stations and seasons (50–90 %) but did not necessarily dominate the biomass. While ice melt might have released and reduced ice algal biomass in July, meiofauna abundance remained high, indicating different annual cycles of protist versus meiofauna taxa. In May highest Chlorophyll a concentrations (29.4 mg m− 2 ) and protist biomass (107 mg C m− 2 ) occurred, while highest meiofauna abundance was found in August (23.9 × 103 Ind. m− 2 ) and biomass in December (0.6 mg C m− 2 ). The abundant December ice biota community further strengthens the emerging notion of an active biota during the dark Arctic winter. The data demonstrated a strong and partially unexpected seasonality in the Barents Sea ice biota, indicating that changes in ice formation, drift and decay will significantly impact the functioning of the ice-associated ecosystem