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  • 1
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    A red tide in the pack ice of the Arctic Ocean (2019)
    Nature
    In:  EPIC3Scientific Report, Nature
    Details
    Publication Date: 2020-04-01
    Description: In the Arctic Ocean ice algae constitute a key ecosystem component and the ice algal spring bloom a critical event in the annual production cycle. The bulk of ice algal biomass is usually found in the bottom few cm of the sea ice and dominated by pennate diatoms attached to the ice matrix. Here we report a red tide of the phototrophic ciliate Mesodinium rubrum located at the ice-water interface of newly formed pack ice of the high Arctic in early spring. These planktonic ciliates are not able to attach to the ice. Based on observations and theory of fluid dynamics, we propose that convection caused by brine rejection in growing sea ice enabled M. rubrum to bloom at the ice-water interface despite the relative flow between water and ice. We argue that red tides of M. rubrum are more likely to occur under the thinning Arctic sea ice regime.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 2
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    Leads in Arctic pack ice enable early phytoplankton blooms below snow-covered sea ice (2017)
    Nature
    In:  EPIC3Scientific Reports, Nature, 7(40850), ISSN: 2045-2322
    Details
    Publication Date: 2017-01-24
    Description: The Arctic icescape is rapidly transforming from a thicker multiyear ice cover to a thinner and largely seasonal first-year ice cover with significant consequences for Arctic primary production. One critical challenge is to understand how productivity will change within the next decades. Recent studies have reported extensive phytoplankton blooms beneath ponded sea ice during summer, indicating that satellite-based Arctic annual primary production estimates may be significantly underestimated. Here we present a unique time-series of a phytoplankton spring bloom observed beneath snow-covered Arctic pack ice. The bloom, dominated by the haptophyte algae Phaeocystis pouchetii, caused near depletion of the surface nitrate inventory and a decline in dissolved inorganic carbon by 16 ± 6 g C m−2. Ocean circulation characteristics in the area indicated that the bloom developed in situ despite the snow-covered sea ice. Leads in the dynamic ice cover provided added sunlight necessary to initiate and sustain the bloom. Phytoplankton blooms beneath snow-covered ice might become more common and widespread in the future Arctic Ocean with frequent lead formation due to thinner and more dynamic sea ice despite projected increases in high-Arctic snowfall. This could alter productivity, marine food webs and carbon sequestration in the Arctic Ocean.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    Deep carbon export from a Southern Ocean iron-fertilized diatom bloom. (2012)
    Nature
    In:  EPIC3Nature, Nature, 487(7407), pp. 313-319
    Details
    Publication Date: 2019-07-16
    Description: Fertilization of the ocean by adding iron compounds has induced diatom-dominated phytoplankton blooms accompanied by considerable carbon dioxide drawdown in the ocean surface layer. However, because the fate of bloom biomass could not be adequately resolved in these experiments, the timescales of carbon sequestration from the atmosphere are uncertain. Here we report the results of a five-week experiment carried out in the closed core of a vertically coherent, mesoscale eddy of the Antarctic Circumpolar Current, during which we tracked sinking particles from the surface to the deep-sea floor. A large diatom bloom peaked in the fourth week after fertilization. This was followed by mass mortality of several diatom species that formed rapidly sinking, mucilaginous aggregates of entangled cells and chains. Taken together, multiple lines of evidence—although each with important uncertainties—lead us to conclude that at least half the bloom biomass sank far below a depth of 1,000 metres and that a substantial portion is likely to have reached the sea floor. Thus, iron-fertilized diatom blooms may sequester carbon for timescales of centuries in ocean bottom water and for longer in the sediments.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    First phytoplankton community assessment of the Kong Håkon VII Hav, Southern Ocean during austral autumn (2022)
    COPERNICUS GESELLSCHAFT MBH
    In:  EPIC3Biogeosciences, COPERNICUS GESELLSCHAFT MBH, ISSN: 1726-4170
    Details
    Publication Date: 2022-07-10
    Description: We studied phyto- and protozooplankton community composition based on light microscopy, flow cytometry and photosynthetic pigment data in the Atlantic sector of the Southern Ocean during March 2019 (early austral autumn). Sampling was focused on the area east of the prime meridian in the Kong Håkon VII Hav, including Astrid Ridge, Maud Rise and a south-north transect at 6° E. Phytoplankton community composition throughout the studied area was characterized by oceanic diatoms typical of the iron-deplete High-Nutrient Low-Chlorophyll (HNLC) Southern Ocean. Topography and wind-driven iron supply likely sustained blooms dominated by the centric diatom Chaetoceros dichaeta at Maud Rise and at a station north of the 6° E transect. For the remainder of the 6° E transect diatom composition was similar to the previously mentioned bloom stations but flagellates dominated in abundance suggesting a post-bloom situation and likely top-down control by krill on the bloom-forming diatoms. Among flagellates, species with haptophyte-type pigments were the dominating group. At Astrid Ridge, overall abundances were lower and pennate were more numerous than centric diatoms, but the community composition was nevertheless typical for HNLC areas. The observations described here show that C. dichaeta can form blooms beyond the background biomass level and fuels both carbon export and upper trophic levels also within HNLC areas. This study is the first thorough assessment of phytoplankton communities in this region and can be compared to other seasons in future studies.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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