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  • 1
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    Non-linear response of summertime marine productivity to increased meltwater discharge around Greenland (2018)
    Nature Research
    In:  Nature Communications, 9 (3256).
    Details
    Publication Date: 2021-04-23
    Description: Runoff from the Greenland Ice Sheet (GrIS) is thought to enhance marine productivity by adding bioessential iron and silicic acid to coastal waters. However, experimental data suggest nitrate is the main summertime growth-limiting resource in regions affected by meltwater around Greenland. While meltwater contains low nitrate concentrations, subglacial discharge plumes from marine-terminating glaciers entrain large quantities of nitrate from deep seawater. Here, we characterize the nitrate fluxes that arise from entrainment of seawater within these plumes using a subglacial discharge plume model. The upwelled flux from 12 marine-terminating glaciers is estimated to be 〉1000% of the total nitrate flux from GrIS discharge. This plume upwelling effect is highly sensitive to the glacier grounding line depth. For a majority of Greenland’s marine-terminating glaciers nitrate fluxes will diminish as they retreat. This decline occurs even if discharge volume increases, resulting in a negative impact on nitrate availability and thus summertime marine productivity.
    Type: Article , PeerReviewed
    Format: text
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    DOI: 10.1038/s41467-018-05488-8
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Iron from ice (2018)
    Nature Research
    In:  Nature Geoscience, 11 (7). p. 462.
    Details
    Publication Date: 2021-02-08
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/s41561-018-0167-8
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Hydrogen peroxide in deep waters from the Mediterranean Sea, South Atlantic and South Pacific Oceans (2017)
    Nature Research
    In:  Scientific Reports, 7 (43436).
    Details
    Publication Date: 2021-04-23
    Description: Hydrogen peroxide (H2O2) is present ubiquitously in marine surface waters where it is a reactive intermediate in the cycling of many trace elements. Photochemical processes are considered the dominant natural H2O2 source, yet cannot explain nanomolar H2O2 concentrations below the photic zone. Here, we determined the concentration of H2O2 in full depth profiles across three ocean basins (Mediterranean Sea, South Atlantic and South Pacific Oceans). To determine the accuracy of H2O2 measurements in the deep ocean we also re-assessed the contribution of interfering species to ‘apparent H2O2’, as analysed by the luminol based chemiluminescence technique. Within the vicinity of coastal oxygen minimum zones, accurate measurement of H2O2 was not possible due to interference from Fe(II). Offshore, in deep (〉1000 m) waters H2O2 concentrations ranged from 0.25 ± 0.27 nM (Mediterranean, Balearics-Algeria) to 2.9 ± 2.2 nM (Mediterranean, Corsica-France). Our results indicate that a dark, pelagic H2O2 production mechanism must occur throughout the deep ocean. A bacterial source of H2O2 is the most likely origin and we show that this source is likely sufficient to account for all of the observed H2O2 in the deep ocean.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1038/srep43436
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    The influence of Arctic Fe and Atlantic fixed N on summertime primary production in Fram Strait, North Greenland Sea (2020)
    Nature Research
    Details
    Publication Date: 2023-02-08
    Description: Climate change has led to a ~ 40% reduction in summer Arctic sea-ice cover extent since the 1970s. Resultant increases in light availability may enhance phytoplankton production. Direct evidence for factors currently constraining summertime phytoplankton growth in the Arctic region is however lacking. GEOTRACES cruise GN05 conducted a Fram Strait transect from Svalbard to the NE Greenland Shelf in summer 2016, sampling for bioessential trace metals (Fe, Co, Zn, Mn) and macronutrients (N, Si, P) at ~ 79°N. Five bioassay experiments were conducted to establish phytoplankton responses to additions of Fe, N, Fe + N and volcanic dust. Ambient nutrient concentrations suggested N and Fe were deficient in surface seawater relative to typical phytoplankton requirements. A west-to-east trend in the relative deficiency of N and Fe was apparent, with N becoming more deficient towards Greenland and Fe more deficient towards Svalbard. This aligned with phytoplankton responses in bioassay experiments, which showed greatest chlorophyll-a increases in + N treatment near Greenland and + N + Fe near Svalbard. Collectively these results suggest primary N limitation of phytoplankton growth throughout the study region, with conditions potentially approaching secondary Fe limitation in the eastern Fram Strait. We suggest that the supply of Atlantic-derived N and Arctic-derived Fe exerts a strong control on summertime nutrient stoichiometry and resultant limitation patterns across the Fram Strait region.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Unprecedented Fe delivery from the Congo River margin to the South Atlantic Gyre (2020)
    Nature Research
    Details
    Publication Date: 2023-02-08
    Description: Rivers are a major supplier of particulate and dissolved material to the ocean, but their role as sources of bio-essential dissolved iron (dFe) is thought to be limited due to rapid, efficient Fe removal during estuarine mixing. Here, we use trace element and radium isotope data to show that the influence of the Congo River margin on surface Fe concentrations is evident over 1000 km from the Congo outflow. Due to an unusual combination of high Fe input into the Congo-shelf-zone and rapid lateral transport, the Congo plume constitutes an exceptionally large offshore dFe flux of 6.8 ± 2.3 × 108 mol year−1. This corresponds to 40 ± 15% of atmospheric dFe input into the South Atlantic Ocean and makes a higher contribution to offshore Fe availability than any other river globally. The Congo River therefore contributes significantly to relieving Fe limitation of phytoplankton growth across much of the South Atlantic.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Highly variable iron content modulates iceberg-ocean fertilisation and potential carbon export (2019)
    Nature Research
    In:  Nature Communications, 10 (1). Art.Nr. 5261.
    Details
    Publication Date: 2022-01-31
    Description: Marine phytoplankton growth at high latitudes is extensively limited by iron availability. Icebergs are a vector transporting the bioessential micronutrient iron into polar oceans. Therefore, increasing iceberg fluxes due to global warming have the potential to increase marine productivity and carbon export, creating a negative climate feedback. However, the magnitude of the iceberg iron flux, the subsequent fertilization effect and the resultant carbon export have not been quantified. Using a global analysis of iceberg samples, we reveal that iceberg iron concentrations vary over 6 orders of magnitude. Our results demonstrate that, whilst icebergs are the largest source of iron to the polar oceans, the heterogeneous iron distribution within ice moderates iron delivery to offshore waters and likely also affects the subsequent ocean iron enrichment. Future marine productivity may therefore be not only sensitive to increasing total iceberg fluxes, but also to changing iceberg properties, internal sediment distribution and melt dynamics.
    Type: Article , PeerReviewed
    Format: text
    Format: other
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    DOI: 10.1038/s41467-019-13231-0
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    The 79°N Glacier cavity modulates subglacial iron export to the NE Greenland Shelf (2021)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Approximately half of the freshwater discharged from the Greenland and Antarctic Ice Sheets enters the ocean subsurface as a result of basal ice melt, or runoff draining via the grounding line of a deep ice shelf or marine-terminating glacier. Around Antarctica and parts of northern Greenland, this freshwater then experiences prolonged residence times in large cavities beneath floating ice tongues. Due to the inaccessibility of these cavities, it is unclear how they moderate the freshwater associated supply of nutrients such as iron (Fe) to the ocean. Here, we show that subglacial dissolved Fe export from Nioghalvfjerdsbrae (the ‘79°N Glacier’) is decoupled from particulate inputs including freshwater Fe supply, likely due to the prolonged ~162-day residence time of Atlantic water beneath Greenland’s largest floating ice-tongue. Our findings indicate that the overturning rate and particle-dissolved phase exchanges in ice cavities exert a dominant control on subglacial nutrient supply to shelf regions.
    Type: Article , PeerReviewed
    Format: text
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    Format: other
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Lab-on-chip analyser for the in situ determination of dissolved manganese in seawater (2021)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: A spectrophotometric approach for quantification of dissolved manganese (DMn) with 1-(2-pyridylazo)-2-naphthol (PAN) has been adapted for in situ application in coastal and estuarine waters. The analyser uses a submersible microfluidic lab-on-chip device, with low power (~ 1.5 W) and reagent consumption (63 µL per sample). Laboratory characterization showed an absorption coefficient of 40,838 ± 1127 L⋅mol−1⋅cm−1 and a detection limit of 27 nM, determined for a 34.6 mm long optical detection cell. Laboratory tests showed that long-term stability of the PAN reagent was achieved by addition of 4% v/v of a non-ionic surfactant (Triton-X100). To suppress iron (Fe) interferences with the PAN reagent, the Fe(III) masking agents deferoxamine mesylate (DFO-B) or disodium 4,5-dihydroxy-1,3-benzenedisulfonate (Tiron) were added and their Fe masking efficiencies were investigated. The analyser was tested during a deployment over several weeks in Kiel Fjord (Germany), with successful acquisition of 215 in situ data points. The time series was in good agreement with DMn concentrations determined from discretely collected samples analysed via inductively coupled plasma mass spectrometry (ICP-MS), exhibiting a mean accuracy of 87% over the full deployment duration (with an accuracy of 〉 99% for certain periods) and clear correlations to key hydrographic parameters.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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