Wind-driven upwelling of iron sustains dense blooms and food webs in the eastern Weddell Gyre.

The Southern Ocean is a major sink of anthropogenic CO2 and an important foraging area for top trophic level consumers. However, iron limitation sets an upper limit to primary productivity. Here we report on a considerably dense late summer phytoplankton bloom spanning 9000 km2 in the open ocean of the eastern Weddell Gyre. Over its 2.5 months duration, the bloom accumulated up to 20 g C m-2 of organic matter, which is unusually high for Southern Ocean open waters. We show that, over 1997-2019, this open ocean bloom was likely driven by anomalies in easterly winds that push sea ice southwards and favor the upwelling of Warm Deep Water enriched in hydrothermal iron and, possibly, other iron sources. This recurring open ocean bloom likely facilitates enhanced carbon export and sustains high standing stocks of Antarctic krill, supporting feeding hot spots for marine birds and baleen whales.

On the impact of wastewater effluent on phytoplankton in the Arctic coastal zone: A case study in the Kitikmeot Sea of the Canadian Arctic.

We present a case study on the impact of effluent from a wastewater lagoon-wetland system on phytoplankton and local primary production near a coastal Arctic community (Cambridge Bay) over spring to fall 2018. Results are also placed within an interannual and regional context for the surrounding Kitikmeot Sea. We find the shallow, relatively fresh Kitikmeot Sea is one of the most nutrient-deplete regions of the Arctic Ocean with NO3- + NO2- concentrations below the surface mixed layer rarely exceeding 2 µmol L-1 and a N:Si:P ratio of 1:6:1. The fjordal-type bathymetry of the main study site and a persistent pycnocline below the bay's exit sill led to slightly elevated N:Si:P of 3:11:1 through trapping of wastewater-sourced N at depth via sinking and remineralization of primary production. Total production in Cambridge Bay over the 3-month open water period was 12.1 g C m-2 with 70% of this production occurring during the 1-month discharge of wastewater into the system. Local primary production responded rapidly to high NO3- + NO2-, NH4+ and PON concentrations provided by wastewater effluent, comprising up to 20% of the production during the discharge period. Remaining production was mostly explained by the deep nutrient pool in the bay, which was only accessed towards the end of the discharge period as the diatom-dominated deep chlorophyll maximum settled below the pycnocline. Although not yet eutrophic, caution is raised at the rapid response of the marine system to wastewater release with a strong recommendation to develop a research and monitoring plan for the bay.

Distribution of small phytoflagellates along an Arctic fjord transect.

Phytoflagellates <10 µm substantially contribute to the abundance, biomass and primary production in polar waters, but information on the distribution of specific groups is scarce. We applied catalysed reporter deposition-fluorescence in situ hybridization to investigate the distribution of total phytoflagellates and of eight specific groups along a 100 km transect west off Kongsfjorden (Spitsbergen) from 29 to 31 July 2010. Phytoflagellates contributed to >75% of the depth-integrated abundance and biomass of total eukaryotes <10 µm at all stations. Their depth-integrated abundance and biomass decreased along the transect from 1.5 × 10(12) cells m(-2) (6.6 × 10(12) pgC m(-2) ) at the outermost station to 1.7 × 10(10) cells m(-2) (4.7 × 10(10) pgC m(-2) ) at the innermost station. Chlorophytes contributed to the total abundance of phytoflagellates with a range from 13% to 87% (0.7-30.5 × 10(3) cells ml(-1) ), and predominated in open waters. The contribution of haptophytes was < 1-38% (10-4500 cells ml(-1) ). The other groups represented <10%. The temperature and salinity positively correlated with the total abundance of phytoflagellates, chlorophytes, haptophytes, bolidophytes and pelagophytes. Cryptophytes, pedinellids and pavlovophytes were negatively associated with the nutrient concentrations. The community composition of phytoflagellates changed along the transect, which could have implications on food web dynamics and biogeochemical cycles between the open ocean environment and Kongsfjorden investigated here.