English
norskBlar i forfatter "Randelhoff, Achim"
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Carbon export in the seasonal sea ice zone north of Svalbard from winter to late summer
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-01-21)Phytoplankton blooms in the Arctic Ocean's seasonal sea ice zone are expected to start earlier and occur further north with retreating and thinning sea ice cover. The current study is the first compilation of phytoplankton bloom development and fate in the seasonally variable sea ice zone north of Svalbard from winter to late summer, using short-term sediment trap deployments. Clear seasonal patterns ... -
Leads in Arctic pack ice enable early phytoplankton blooms below snow-covered sea ic
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-01-19)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 ... -
Nutrients vs. turbulence, and the future of Arctic Ocean primary production
(Conference object; Konferansebidrag, 2016-11)This poster presents estimates of nitrate fluxes in the Arctic Ocean and speculates on the associated primary production in a future climate. -
Regional patterns in current and future export production in the central Arctic Ocean quantified from nitrate fluxes
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-08-24)Due to severe nutrient and light limitation, the central Arctic Ocean has been characterized as a region of low primary productivity, with high retention of carbon in the surface waters. Using an in-depth analysis of published and new measurements of turbulent microstructure and high-resolution profiles of nitrate concentration, we reassess the vertical supply of nitrate to the Polar Mixed Layer and ... -
Seasonal variability and fluxes of nitrate in the surface waters over the Arctic shelf slope
(Conference object; Konferansebidrag, 2015-03)Understanding the present state and possible future scenarios of Arctic Ocean primary productivity has been hampered by the scarcity of year-round nutrient measurements. Here, the first year-long moored timeseries of near-surface nitrate concentrations in the Eastern Arctic, together with hydrography, currents and chlorophyll-a fluorescence, is reported from ... -
Seasonality of the Physical and Biogeochemical Hydrography in the Inflow to the Arctic Ocean Through Fram Strait
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-06-29)Eastern Fram Strait and the shelf slope region north of Svalbard is dominated by the advection of warm, salty and nutrient-rich Atlantic Water (AW). This oceanic heat contributes to keeping the area relatively free of ice. The last years have seen a dramatic decrease in regional sea ice extent, which is expected to drive large increases in pelagic primary production and thereby changes in marine ... -
Turbulent heat and momentum fluxes in the upper ocean under Arctic sea ice
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-02-25)We report observations of heat and momentum fluxes measured in the ice-ocean boundary layer from four drift stations between January and June 2015, covering from the typical Arctic basin conditions in the Nansen Basin to energetic spots of interaction with the warm Atlantic Water branches near the Yermak Plateau and over the North Spitsbergen slope. A wide range of oceanic turbulent heat flux values ... -
Vertical fluxes of nitrate in the seasonal nitracline of the Atlantic sector of the Arctic Ocean
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-07-31)<p>This study compiles colocated oceanic observations of high-resolution vertical profiles of nitrate concentration and turbulent microstructure around the Svalbard shelf slope, covering both the permanently ice-free Fram Strait and the pack ice north of Svalbard. The authors present an overview over the seasonal evolution of the distribution of nitrate and its relation to upper ocean stratification. ... -
Vertical nitrate fluxes in the Arctic Ocean
(Doctoral thesis; Doktorgradsavhandling, 2017-03-16)Upward mixing of remineralized nutrients is essential for photosynthesis in the upper ocean. Weak vertical mixing, which restricts nutrient supply, and sea ice, which leads to low light levels, conspire to severely inhibit marine primary productivity in the Arctic Ocean. However, little has been known about their relative contributions. No large-scale quantitative estimates of the vertical nutrient ... -
Winter storms accelerate the demise of sea ice in the Atlantic sector of the Arctic Ocean
(Journal article; Peer reviewed, 2019-06-25)A large retreat of sea-ice in the ‘stormy’ Atlantic Sector of the Arctic Ocean has become evident through a series of record minima for the winter maximum sea-ice extent since 2015. Results from the Norwegian young sea ICE (N-ICE2015) expedition, a five-month-long (Jan-Jun) drifting ice station in first and second year pack-ice north of Svalbard, showcase how sea-ice in this region is frequently ...
