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  • 1
    Publication Date: 2019-01-17
    Description: We present a new near-global coupled biogeochemical ocean-circulation model configuration. The configuration features a horizontal discretization with a grid spacing of less than 11km in the Southern Ocean and gradually coarsens in meridional direction to more than 200km at 64°N where the model is bounded by a solid wall. The underlying code framework is GFDL's Modular Ocean Model coupled to the Biology Light Iron Nutrients and Gasses (BLING) ecosystem model of Galbraith et al. (2010). The configuration is cutting-edge in that it features both a relatively equilibrated oceanic carbon inventory and a realistic representation of eddy kinetic energy – a combination that has, to-date, been precluded by prohibitive computational cost. Results from a simulation with climatological forcing and a sensitivity experiment with increasing winds suggest that the configuration is suited to explore Southern Ocean Carbon uptake dynamics on decadal timescales. Further, the fidelity of simulated bottom water temperatures off and on the Antarctic Shelf suggest that the configuration may be used to provide boundary conditions to ice-sheet models. The configuration is dubbed MOMSO a Modular Ocean Model Southern Ocean configuration.
    Type: Article , NonPeerReviewed
    Format: text
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  • 2
    Publication Date: 2014-05-05
    Repository Name: EPIC Alfred Wegener Institut
    Type: PANGAEA Documentation , NonPeerReviewed
    Format: application/zip
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  • 3
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    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 56 (9). pp. 1440-1448.
    Publication Date: 2016-11-01
    Description: The phytoplankton distribution off western Australia in the period from April to October is unique in that high biomass is generally associated with anticyclonic eddies and not with cyclonic eddies. As the western Australian region is oligotrophic this anomalous feature must be related to differing nutrient supply pathways to the surface mixed layer of cyclonic and anticyclonic eddies. A suite of modelled abiotic tracers suggests that cyclonic eddies are predominantly supplied by diapycnal processes that remain relatively weak until June–July, when they rapidly increase because of deepening surface mixed layers, which start to tap into the nutrient-replete waters below the euphotic zone. To the contrary, we find that anticyclonic eddies are predominantly supplied by injection of shelf waters, which carry elevated levels of inorganic nutrients and biomass. These injections start with the formation of the eddies in April–May, continue well into the austral winter and reach as far as several hundred kilometers offshore. The diapycnal supply of nutrients is suppressed in anticyclonic eddies since the injection of warm, low-salinity shelf waters delays the erosion of the density gradient at the base of the mixed layer. Our results are consistent with the observed seasonal cycles of chlorophyll a and observation of particulate organic matter export out of the surface mixed layer of an anticyclonic eddy in the region.
    Type: Article , PeerReviewed
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  • 4
    Publication Date: 2012-07-06
    Description: Iron is a key micronutrient for phytoplankton growth in the surface ocean. Yet the significance of volcanism for the marine biogeochemical iron-cycle is poorly constrained. Recent studies, however, suggest that offshore deposition of airborne ash from volcanic eruptions is a way to inject significant amounts of bio-available iron into the surface ocean. Volcanic ash may be transported up to several tens of kilometers high into the atmosphere during large-scale eruptions and fine ash may stay aloft for days to weeks, thereby reaching even the remotest and most iron-starved oceanic regions. Scientific ocean drilling demonstrates that volcanic ash layers and dispersed ash particles are frequently found in marine sediments and that therefore volcanic ash deposition and iron-injection into the oceans took place throughout much of the Earth's history. Natural evidence and the data now available from geochemical and biological experiments and satellite techniques suggest that volcanic ash is a so far underestimated source for iron in the surface ocean, possibly of similar importance as aeolian dust. Here we summarise the development of and the knowledge in this fairly young research field. The paper covers a wide range of chemical and biological issues and we make recommendations for future directions in these areas. The review paper may thus be helpful to improve our understanding of the role of volcanic ash for the marine biogeochemical iron-cycle, marine primary productivity and the ocean-atmosphere exchange of CO2 and other gases relevant for climate in the Earth's history.
    Type: Article , PeerReviewed
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  • 5
    Publication Date: 2017-02-06
    Description: Apparent oxygen utilisation is potentially biased by abiotic, physical processes. Using a coupled 3-D circulation-oxygen model, this potential is quantitatively estimated for a region in the eastern subtropical North Atlantic, called the Beta Triangle, where an inconsistency exists between observational estimates of high carbon export from the euphotic zone, based on oxygen utilisation rates in the thermocline (Jenkins 1982), and those of low nutrient supply to the euphotic zone (Lewis et al. 1986, 2004). Our results indicate that in the upper ocean, the Jenkins (1982) estimate is indeed biased high by approximately 10% due to abiotic processes feigning respiration, thus contributing to the apparent inconsistency. Vertical integration, however, yields an abiotic fraction of less than 3%, so the apparent observational discrepancy can not be resolved.
    Type: Article , PeerReviewed
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  • 6
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 7
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    In:  [Poster] In: EUR-OCEANS Conference - Ocean deoxygenation and implications for marine biogeochemical cycles and ecosystems, 24.-26.10.2011, Toulouse, France .
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 8
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    In:  [Poster] In: EUR-OCEANS Conference - Ocean deoxygenation and implications for marine biogeochemical cycles and ecosystems, 24.-26.10.2011, Toulouse, France .
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 9
    Publication Date: 2012-02-23
    Description: Atmospheric deposition of high N:P material to the subtropical North Atlantic has more than doubled in the past century due to anthropogenic activity, and is increasingly thought to be an important source of essential nutrients to the oligotrophic subtropical gyre. However, the long-term fate of North Atlantic atmospheric nitrogen deposition is not well understood. This modeling study evaluated an observed pool of N in excess of Redfield ratios located in the main thermocline as a potential sink for atmospheric N. Modeled atmospheric deposition was added to a coupled ocean ecosystem and circulation model. Results suggest that nearly half of the atmospheric nitrogen entering the North Atlantic is transported to the main thermocline, contributing ~15% of the annual growth of excess N there. Transport mechanisms include differential remineralization of N and P in sinking biogenic particles and physical transport. If atmospheric nutrient inputs from the year 2000 were maintained for 50 years, the model suggests that nutrient deposition would contribute to an increase in excess N of more than 0.4 μM, or an additional 45% of the present signal. Quantifying the fate and important transport mechanisms of deposited atmospheric nutrients will improve our understanding of N cycle dynamics in the North Atlantic, as well as improve N2 fixation estimates based on mass-balance techniques.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 10
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    In:  [Poster] In: Ocean Sciences Meeting 2012, 20.-24.02.2012, Salt Lake City, USA .
    Publication Date: 2012-03-26
    Description: Ocean biogeochemical models are routinely applied to assess the net global impact of ocean acidification and warming on pelagic CaCO3 cycling. As with respect to the net change of global air-sea carbon fluxes affected by the reduced calcification under future CO2 conditions, these models diverge by a factor of four. The standard method to evaluate modelled CaCO3 cycles is to compare alkalinity and CaCO3 saturation states with observations. In general, state-of-the-art models do feature strong deviations and it is unclear if, or to what extent, these are driven by a deficient representation of physics (ocean circulation) or a deficient representation of biogeochemistry. Here we apply the TA* method (developed to separates the signals of CaCO3 production and dissolution from the large, conservative alkalinity background in observations) to model output. The aim is twofold. First, to assess the method using additional explicit representations of preformed alkalinity, accumulated CaCO3 dissolution, and organic matter remineralisation. And second, we aim to disentangle deficiencies in the physical and biogeochemical module of an ocean biogeochemical model.
    Type: Conference or Workshop Item , NonPeerReviewed
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