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Arctic – Atlantic Exchange of the Dissolved Micronutrients Iron, Manganese, Cobalt, Nickel, Copper and Zinc With a Focus on Fram Strait (2022)

Krisch, Stephan ; Hopwood, Mark J. ; Roig, Stéphane ; [weitere]

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Publikationsdatum: 2022-10-04

Beschreibung: The Arctic Ocean is considered a source of micronutrients to the Nordic Seas and the North Atlantic Ocean through the gateway of Fram Strait (FS). However, there is a paucity of trace element data from across the Arctic Ocean gateways, and so it remains unclear how Arctic and North Atlantic exchange shapes micronutrient availability in the two ocean basins. In 2015 and 2016, GEOTRACES cruises sampled the Barents Sea Opening (GN04, 2015) and FS (GN05, 2016) for dissolved iron (dFe), manganese (dMn), cobalt (dCo), nickel (dNi), copper (dCu) and zinc (dZn). Together with the most recent synopsis of Arctic‐Atlantic volume fluxes, the observed trace element distributions suggest that FS is the most important gateway for Arctic‐Atlantic dissolved micronutrient exchange as a consequence of Intermediate and Deep Water transport. Combining fluxes from FS and the Barents Sea Opening with estimates for Davis Strait (GN02, 2015) suggests an annual net southward flux of 2.7 ± 2.4 Gg·a−1 dFe, 0.3 ± 0.3 Gg·a−1 dCo, 15.0 ± 12.5 Gg·a−1 dNi and 14.2 ± 6.9 Gg·a−1 dCu from the Arctic toward the North Atlantic Ocean. Arctic‐Atlantic exchange of dMn and dZn were more balanced, with a net southbound flux of 2.8 ± 4.7 Gg·a−1 dMn and a net northbound flux of 3.0 ± 7.3 Gg·a−1 dZn. Our results suggest that ongoing changes to shelf inputs and sea ice dynamics in the Arctic, especially in Siberian shelf regions, affect micronutrient availability in FS and the high latitude North Atlantic Ocean.

Beschreibung: Plain Language Summary: Recent studies have proposed that the Arctic Ocean is a source of micronutrients such as dissolved iron (dFe), manganese (dMn), cobalt (dCo), nickel (dNi), copper (dCu) and zinc (dZn) to the North Atlantic Ocean. However, data at the Arctic Ocean gateways including Fram Strait and the Barents Sea Opening have been missing to date and so the extent of Arctic micronutrient transport toward the Atlantic Ocean remains unquantified. Here, we show that Fram Strait is the most important gateway for Arctic‐Atlantic micronutrient exchange which is a result of deep water transport at depths 〉500 m. Combined with a flux estimate for Davis Strait, this study suggests that the Arctic Ocean is a net source of dFe, dNi and dCu, and possibly also dCo, toward the North Atlantic Ocean. Arctic‐Atlantic dMn and dZn exchange seems more balanced. Properties in the East Greenland Current showed substantial similarities to observations in the upstream Central Arctic Ocean, indicating that Fram Strait may export micronutrients from Siberian riverine discharge and shelf sediments 〉3,000 km away. Increasing Arctic river discharge, permafrost thaw and coastal erosion, all consequences of ongoing climate change, may therefore alter future Arctic Ocean micronutrient transport to the North Atlantic Ocean.

Beschreibung: Key Points: Fram Strait is the major gateway for Arctic‐Atlantic exchange of the dissolved micronutrients Fe, Mn, Co, Ni, Cu and Zn. The Arctic is a net source of dissolved Fe, Co, Ni and Cu to the Nordic Seas and toward the North Atlantic; Mn and Zn exchange are balanced. Waters of the Central Arctic Ocean, including the Transpolar Drift, are the main drivers of gross Arctic micronutrient export.

Beschreibung: German Research Foundation

Beschreibung: Netherlands Organization for Scientific Research

Beschreibung: https://doi.pangaea.de/10.1594/PANGAEA.859558

Beschreibung: https://doi.pangaea.de/10.1594/PANGAEA.871030

Beschreibung: https://doi.pangaea.de/10.1594/PANGAEA.868396

Beschreibung: https://doi.pangaea.de/10.1594/PANGAEA.905347

Beschreibung: https://dataportal.nioz.nl/doi/10.25850/nioz/7b.b.jc

Beschreibung: https://doi.pangaea.de/10.1594/PANGAEA.933431

Beschreibung: https://www.bco-dmo.org/dataset/718440

Beschreibung: https://doi.org/10.1594/PANGAEA.936029

Beschreibung: https://doi.org/10.1594/PANGAEA.936027

Beschreibung: https://doi.pangaea.de/10.1594/PANGAEA.927429

Schlagwort(e): ddc:551.9

Sprache: Englisch

Materialart: doc-type:article

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Sediment Release in the Benguela Upwelling System Dominates Trace Metal Input to the Shelf and Eastern South Atlantic Ocean (2022)

Liu, Te ; Krisch, Stephan ; Xie, Ruifang C. ; [weitere]

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Publikationsdatum: 2023-01-21

Beschreibung: Upwelling of subsurface waters injects macronutrients (fixed N, P, and Si) and micronutrient trace metals (TMs) into surface waters supporting elevated primary production in Eastern Boundary Upwelling Regions. The eastern South Atlantic features a highly productive shelf sea transitioning to a low productivity N‐Fe (co)limited open ocean. Whilst a gradient in most TM concentrations is expected in any off‐shelf transect, the factors controlling the magnitude of cross‐shelf TM fluxes are poorly constrained. Here, we present dissolved TM concentrations of Fe, Co, Mn, Cd, Ni, and Cu within the Benguela Upwelling System from the coastal section of the GEOTRACES GA08 cruise. Elevated dissolved Fe, Co, Mn, Cd, Ni, Cu and macronutrient concentrations were observed near shelf sediments. Benthic sources supplied 2.22 ± 0.99 μmol Fe m−2 day−1, 0.05 ± 0.03 μmol Co m−2 day−1, 0.28 ± 0.11 μmol Mn m−2 day−1 and were found to be the dominant source to shallow shelf waters compared to atmospheric depositions. Similarly, off‐shelf transfer was a more important source of TMs to the eastern South Atlantic Ocean compared to atmospheric deposition. Assessment of surface (shelf, upper 200 m) and subsurface (shelf edge, 200–500 m) fluxes of Fe and Co indicated TM fluxes from subsurface were 2–5 times larger than those from surface into the eastern South Atlantic Ocean. Under future conditions of increasing ocean deoxygenation, these fluxes may increase further, potentially contributing to a shift toward more extensive regional limitation of primary production by fixed N availability.

Beschreibung: Key Points: Shelf sediments release redox‐sensitive trace metals (TMs) to overlying oxygen‐depleted waters in the Benguela Upwelling System. Sediment‐derived TMs are upwelled and laterally transported constituting a major source to shelf waters and to the eastern South Atlantic. Subsurface fluxes of dissolved Fe and Co from the shelf edge play an important role in supplying Fe and Co to the eastern South Atlantic.

Beschreibung: China Scholarship Council, CSC http://dx.doi.org/10.13039/501100004543

Beschreibung: GEOMAR and German Research Foundation

Beschreibung: German DFG

Beschreibung: German Research Foundation

Beschreibung: https://doi.pangaea.de/10.1594/PANGAEA.947275

Schlagwort(e): ddc:551 ; dissolved trace metals ; Benguela Upwelling Systems ; fluxes ; Eastern Boundary Upwelling Systems Regions

Sprache: Englisch

Materialart: doc-type:article

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Quantifying Ice‐Sheet Derived Lead (Pb) Fluxes to the Ocean; A Case Study at Nioghalvfjerdsbræ (2022)

Krisch, Stephan ; Huhn, Oliver ; Al‐Hashem, Ali ; [weitere]

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Publikationsdatum: 2023-11-17

Beschreibung: Concentrations of the toxic element lead (Pb) are elevated in seawater due to historical emissions. While anthropogenic atmospheric emissions are the dominant source of dissolved Pb (dPb) to the Atlantic Ocean, evidence is emerging of a natural source associated with subglacial discharge into the ocean but this has yet to be constrained around Greenland. Here, we show subglacial discharge from the cavity underneath Nioghalvfjerdsbræ floating ice tongue, is a previously unrecognized source of dPb to the NE Greenland Shelf. Contrasting cavity‐inflowing and cavity‐outflowing waters, we constrain the associated net‐dPb flux as 2.2 ± 1.4 Mg·yr−1, of which ∼90% originates from dissolution of glacial bedrock and cavity sediments. We propose that the retreat of the floating ice tongue, the ongoing retreat of many glaciers on Greenland, associated shifts in sediment dynamics, and enhanced meltwater discharges into shelf waters may result in pronounced changes, possibly increases, in net‐dPb fluxes to coastal waters.

Beschreibung: Plain Language Summary: Lead (Pb) is a toxic element. Hundreds of thousands of tons have historically been emitted into the atmosphere through use of leaded gasoline, ore‐smelting and coal‐combustion which led to large‐scale deposition of Pb into the ocean and onto the Greenland Ice Sheet. Since the phase‐out of leaded gasoline, concentrations of dissolved Pb in the surface ocean have declined, increasing the relative importance of other, natural sources of Pb to the marine environment. In 2016, we conducted a survey near Nioghalvfjerdsbræ, one of Greenland’s largest marine‐terminating glaciers, to investigate if Greenland Ice Sheet discharge is a source of Pb to the Northeast Greenland Shelf. We observed elevated dissolved Pb concentrations at intermediate depths within a ⁓60 km radius downstream of the Nioghalvfjerdsbræ terminus. The Pb enrichment originates from underneath the glacier’s floating ice tongue. Lead sources underneath Nioghalvfjerdsbræ likely include Pb from eroded bedrock and exchange with fjord sediments. Our calculations suggest that Nioghalvfjerdsbræ dissolved Pb discharge is comparable to that from small Arctic rivers. Given the widespread occurance of Pb‐rich minerals across Greenland, observed increases in meltwater discharge and the retreat of marine‐terminating glaciers could increase dPb supply to Greenlandic shelf regions.

Beschreibung: Key Points: Helium and neon show strong evidence for a subglacial source of Pb discharging onto the NE Greenland Shelf. Contrasting inflowing and outflowing waters beneath the floating ice tongue of Nioghalvfjerdsbræ shows a 2‐3‐fold dPb enrichment. The dissolved Pb flux from Nioghalvfjerdsbræ (2.2 ± 1.4 Mg·yr−1) is comparable to small Arctic rivers, with ∼90% of a sedimentary origin.

Beschreibung: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659

Beschreibung: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347

Beschreibung: Kuwait Institute for Scientific Research http://dx.doi.org/10.13039/501100005074

Beschreibung: Swiss Polar Foundation

Beschreibung: https://doi.pangaea.de/10.1594/PANGAEA.871028

Beschreibung: https://doi.pangaea.de/10.1594/PANGAEA.871030

Beschreibung: https://doi.pangaea.de/10.1594/PANGAEA.879197

Beschreibung: https://doi.pangaea.de/10.1594/PANGAEA.905347

Beschreibung: https://doi.pangaea.de/10.1594/PANGAEA.933431

Beschreibung: https://doi.pangaea.de/10.1594/PANGAEA.931336

Beschreibung: https://doi.org/10.5194/essd-8-543-2016

Schlagwort(e): ddc:551 ; Greenland ice sheet ; Arctic ; marine‐terminating glacier ; Nioghalvfjerdsbrae ; lead fluxes ; GEOTRACES

Sprache: Englisch

Materialart: doc-type:article

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The influence of Arctic Fe and Atlantic fixed N on summertime primary production in Fram Strait, North Greenland Sea (2020)

Krisch, Stephan ; Browning, Thomas J. ; Graeve, Martin ; [weitere]

Springer Nature SharedIt

In: EPIC3Scientific Reports, Springer Nature SharedIt, 10(1), ISSN: 2045-2322

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Publikationsdatum: 2020-09-22

Beschreibung: 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.

Repository-Name: EPIC Alfred Wegener Institut

Materialart: Article , isiRev

Format: application/pdf

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The 79°N Glacier cavity modulates subglacial iron export to the NE Greenland Shelf (2021)

Krisch, Stephan ; Hopwood, Mark J. ; Schaffer, Janin ; [weitere]

In: EPIC3Nature Communications, 12(3030)

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Publikationsdatum: 2021-05-28

Repository-Name: EPIC Alfred Wegener Institut

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Nutrient regulation of late spring phytoplankton blooms in the midlatitude North Atlantic (2021)

Browning, Thomas J. ; Al-Hashem, Ali A. ; Hopwood, Mark J. ; [weitere]

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Publikationsdatum: 2021-12-01

Beschreibung: The duration and magnitude of the North Atlantic spring bloom impacts both higher trophic levels and oceanic carbon sequestration. Nutrient exhaustion offers a general explanation for bloom termination, but detail on which nutrients and their relative influence on phytoplankton productivity, community structure, and physiology is lacking. Here, we address this using nutrient addition bioassay experiments conducted across the midlatitude North Atlantic in June 2017 (late spring). In four out of six experiments, phytoplankton accumulated over 48–72 h following individual additions of either iron (Fe) or nitrogen (N). In the remaining two experiments, Fe and N were serially limiting, that is, their combined addition sequentially enhanced phytoplankton accumulation. Silicic acid (Si) added in combination with N + Fe led to further chlorophyll a (Chl a) enhancement at two sites. Conversely, addition of zinc, manganese, cobalt, vitamin B12, or phosphate in combination with N + Fe did not. At two sites, the simultaneous supply of all six nutrients, in combination with N + Fe, also led to no further Chl a enhancement, but did result in an additional 30–60% particulate carbon accumulation. This particulate carbon accumulation was not matched by a Redfield equivalent of particulate N, characteristic of high C:N organic exudates that enhance cell aggregation and sinking. Our results suggest that growth rates of larger phytoplankton were primarily limited by Fe and/or N, making the availability of these nutrients the main bottom-up factors contributing to spring bloom termination. In addition, the simultaneous availability of other nutrients could modify bloom characteristics and carbon export efficiency.

Schlagwort(e): 577.7 ; mid-latitude North Atlantic ; phytoplankton ; diatom blooming ; experiments

Sprache: Englisch

Materialart: map

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Characteristic depths, fluxes and timescales for Greenland’s tidewater glacier fjords from subglacial discharge‐driven upwelling during summer (2022)

Slater, Donald A. ; Carroll, Dustin ; Oliver, Hilde ; [weitere]

American Geophysical Union

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Publikationsdatum: 2022-10-21

Beschreibung: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Slater, D., Carroll, D., Oliver, H., Hopwood, M., Straneo, F., Wood, M., Willis, J., & Morlighem, M. Characteristic depths, fluxes and timescales for Greenland’s tidewater glacier fjords from subglacial discharge‐driven upwelling during summer. Geophysical Research Letters, 49(10),(2022): e2021GL097081, https://doi.org/10.1029/2021gl097081.

Beschreibung: Greenland's glacial fjords are a key bottleneck in the earth system, regulating exchange of heat, freshwater and nutrients between the ice sheet and ocean and hosting societally important fisheries. We combine recent bathymetric, atmospheric, and oceanographic data with a buoyant plume model to show that summer subglacial discharge from 136 tidewater glaciers, amounting to 0.02 Sv of freshwater, drives 0.6–1.6 Sv of upwelling. Bathymetric analysis suggests that this is sufficient to renew most major fjords within a single summer, and that these fjords provide a path to the continental shelf that is deeper than 200 m for two-thirds of the glaciers. Our study provides a first pan-Greenland inventory of tidewater glacier fjords and quantifies regional and ice sheet-wide upwelling fluxes. This analysis provides important context for site-specific studies and is a step toward implementing fjord-scale heat, freshwater and nutrient fluxes in large-scale ice sheet and climate models.

Beschreibung: DAS acknowledges support from NERC Independent Research Fellowship NE/T011920/1. DAS and FS acknowledge support from NSF award 2020547. HO acknowledges support from a WHOI Postdoctoral Scholar award. MW and JKW performed this work at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Schlagwort(e): Greenland Ice Sheet ; Fjord ; Subglacial discharge ; Plume ; Tidewater glacier ; Freshwater

Repository-Name: Woods Hole Open Access Server

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Review article: How does glacier discharge affect marine biogeochemistry and primary production in the Arctic? (2020)

Hopwood, Mark J. ; Carroll, Dustin ; Dunse, Thorben ; [weitere]

Copernicus

In: The Cryosphere. 2020; 14(4): 1347-1383. Published 2020 Apr 24. doi: 10.5194/tc-14-1347-2020.

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Publikationsdatum: 2020-04-24

Beschreibung: Freshwater discharge from glaciers is increasing across the Arctic in response to anthropogenic climate change, which raises questions about the potential downstream effects in the marine environment. Whilst a combination of long-term monitoring programmes and intensive Arctic field campaigns have improved our knowledge of glacier–ocean interactions in recent years, especially with respect to fjord/ocean circulation, there are extensive knowledge gaps concerning how glaciers affect marine biogeochemistry and productivity. Following two cross-cutting disciplinary International Arctic Science Committee (IASC) workshops addressing the importance of glaciers for the marine ecosystem, here we review the state of the art concerning how freshwater discharge affects the marine environment with a specific focus on marine biogeochemistry and biological productivity. Using a series of Arctic case studies (Nuup Kangerlua/Godthåbsfjord, Kongsfjorden, Kangerluarsuup Sermia/Bowdoin Fjord, Young Sound and Sermilik Fjord), the interconnected effects of freshwater discharge on fjord–shelf exchange, nutrient availability, the carbonate system, the carbon cycle and the microbial food web are investigated. Key findings are that whether the effect of glacier discharge on marine primary production is positive or negative is highly dependent on a combination of factors. These include glacier type (marine- or land-terminating), fjord–glacier geometry and the limiting resource(s) for phytoplankton growth in a specific spatio-temporal region (light, macronutrients or micronutrients). Arctic glacier fjords therefore often exhibit distinct discharge–productivity relationships, and multiple case-studies must be considered in order to understand the net effects of glacier discharge on Arctic marine ecosystems.

Print ISSN: 1994-0416

Digitale ISSN: 1994-0424

Thema: Geographie , Geologie und Paläontologie