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  • 1
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    Declining oxygen in the global ocean and coastal waters (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-01-05
    Description: Oxygen is fundamental to life. Not only is it essential for the survival of individual animals, but it regulates global cycles of major nutrients and carbon. The oxygen content of the open ocean and coastal waters has been declining for at least the past half-century, largely because of human activities that have increased global temperatures and nutrients discharged to coastal waters. These changes have accelerated consumption of oxygen by microbial respiration, reduced solubility of oxygen in water, and reduced the rate of oxygen resupply from the atmosphere to the ocean interior, with a wide range of biological and ecological consequences. Further research is needed to understand and predict long-term, global- and regional-scale oxygen changes and their effects on marine and estuarine fisheries and ecosystems.
    Keywords: Geochemistry, Geophysics, Online Only
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Uncertainty in the response of transpiration to CO 2 and implications for climate change (2015)
    Institute of Physics (IOP)
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    Publication Date: 2015-08-29
    Description: While terrestrial precipitation is a societally highly relevant climate variable, there is little consensus among climate models about its projected 21st century changes. An important source of precipitable water over land is plant transpiration. Plants control transpiration by opening and closing their stomata. The sensitivity of this process to increasing CO 2 concentrations is uncertain. To assess the impact of this uncertainty on future climate, we perform experiments with an intermediate complexity Earth System Climate Model (UVic ESCM) for a range of model-imposed transpiration-sensitivities to CO 2 . Changing the sensitivity of transpiration to CO 2 causes simulated terrestrial precipitation to change by −10% to +27% by 2100 under a high emission scenario. This study emphasises the importance of an improved assessment of the dynamics of environmental impact on vegetation to better predict future changes of the terrestrial hydrological and carbo...
    Print ISSN: 1748-9318
    Electronic ISSN: 1748-9326
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering
    Published by Institute of Physics (IOP)
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  • 3
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    A new perspective on environmental controls of marine nitrogen fixation (2015)
    Wiley
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    Publication Date: 2015-05-15
    Description: Growing slowly, marine N 2 fixers are generally expected to be competitive only where nitrogen (N) supply is low relative to that of phosphorus (P) with respect to the cellular N:P ratio (R) of non-fixing phytoplankton. This is at odds with observed high N 2 fixation rates in the oligotrophic North Atlantic where the ratio of nutrients supplied to the surface is elevated in N relative to the average R (16:1). In this study, we investigate several mechanisms to solve this puzzle: iron limitation, phosphorus enhancement by preferential remineralization or stoichiometric diversity of phytoplankton, and dissolved organic phosphorus (DOP) utilization. Combining resource competition theory and a global coupled ecosystem-circulation model we find that the additional N and energy investments required for exo-enzymatic break-down of DOP gives N 2 fixers a competitive advantage in oligotrophic P-starved regions. Accounting for this mechanism expands the ecological niche of N 2 -fixers also to regions where the nutrient supply is high in N relative to R, yielding, in our model, a pattern consistent with the observed high N 2 -fixation rates in the oligotrophic North Atlantic.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Quantification of ocean heat uptake from changes in atmospheric O2 and CO2 composition (2018)
    Springer Nature
    In: Nature
    Details
    Publication Date: 2018
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 5
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    A revised global estimate of dissolved iron fluxes from marine sediments (2015)
    Wiley
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    Publication Date: 2015-04-09
    Description: Literature data on benthic dissolved iron (DFe) fluxes (µmol m −2 d −1 ), bottom water oxygen concentrations (O 2BW , μM) and sedimentary carbon oxidation rates (C OX , mmol m −2 d −1 ) from water depths ranging from 80 to 3700 m were assembled. The data were analyzed with a diagenetic iron model to derive an empirical function for predicting benthic DFe fluxes: where γ (=170 µmol m −2 d −1 ) is the maximum flux for sediments at steady state located away from river mouths. This simple function unifies previous observations that C OX and O 2BW are important controls on DFe fluxes. Upscaling predicts a global DFe flux from continental margin sediments of 109 ± 55 Gmol yr −1 , of which 72 Gmol yr −1 is contributed by the shelf (〈200 m) and 37 Gmol yr −1 by slope sediments (200–2000 m). The predicted deep-sea flux (〉2000 m) of 41 ± 21 Gmol yr −1 is unsupported by empirical data. Previous estimates of benthic DFe fluxes derived using global iron models are far lower (ca. 20–30 Gmol yr −1 ). This can be attributed to (i) inadequate treatment of the role of oxygen on benthic DFe fluxes, and (ii) improper consideration of continental shelf processes due to coarse spatial resolution. Globally-averaged DFe concentrations in surface waters simulated with an intermediate-complexity Earth system climate model (UVic ESCM) were a factor of two higher with the new function. We conclude that (i) the DFe flux from marginal sediments has been underestimated in the marine iron cycle, and (ii) iron scavenging in the water column is more intense than currently presumed.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Sensitivity analysis of simple global marine biogeochemical models (2012)
    Wiley
    Details
    Publication Date: 2012-06-05
    Description: This study presents results from 46 sensitivity experiments carried out with three structurally simple (2, 3, and 6 biogeochemical state variables, respectively) models of production, export and remineralization of organic phosphorus, coupled to a global ocean circulation model and integrated for 3000 years each. The models' skill is assessed via different misfit functions with respect to the observed global distributions of phosphate and oxygen. Across the different models, the global root-mean square misfit with respect to observed phosphate and oxygen distributions is found to be particularly sensitive to changes in the remineralization length scale, and also to changes in simulated primary production. For this metric, changes in the production and decay of dissolved organic phosphorus as well as in zooplankton parameters are of lesser importance. For a misfit function accounting for the misfit of upper-ocean tracers, however, production parameters and organic phosphorus dynamics play a larger role. Regional misfit patterns are investigated as indicators of potential model deficiencies, such as missing iron limitation, or deficiencies in the sinking and remineralization length scales. In particular, the gradient between phosphate concentrations in the northern North Pacific and the northern North Atlantic is controlled predominantly by the biogeochemical model parameters related to particle flux. For the combined 46 sensitivity experiments performed here, the global misfit to observed oxygen and phosphate distributions shows no clear relation to either simulated global primary or export production for either misfit metric employed. However, a relatively tight relationship that is very similar for the different model of different structural complexity is found between the model-data misfit in oxygen and phosphate distributions to simulated meso- and bathypelagic particle flux. Best agreement with the observed tracer distributions is obtained for simulated particle fluxes that agree most closely with sediment trap data for a nominal depth of about 1000 m, or deeper.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Phytoplankton niche generation by interspecific stoichiometric variation (2012)
    Wiley
    Details
    Publication Date: 2012-05-03
    Description: For marine biogeochemical models used in simulations of climate change scenarios, the ability to account for adaptability of marine ecosystems to environmental change becomes a concern. The potential for adaptation is expected to be larger for a diverse ecosystem compared to a monoculture of a single type of (model) algae, such as typically included in biogeochemical models. Recent attempts to simulate phytoplankton diversity in global marine ecosystem models display remarkable qualitative agreement with observed patterns of species distributions. However, modeled species diversity tends to be systematically lower than observed and, in many regions, is smaller than the number of potentially limiting nutrients. According to resource competition theory, the maximum number of coexisting species at equilibrium equals the number of limiting resources. By simulating phytoplankton communities in a chemostat model and in a global circulation model, we show here that a systematic underestimate of phytoplankton diversity may result from the standard modeling assumption of identical stoichiometry for the different phytoplankton types. Implementing stoichiometric variation among the different marine algae types in the models allows species to generate different resource supply niches via their own ecological impact. This is shown to increase the level of phytoplankton coexistence both in a chemostat model and in a global self-assembling ecosystem model.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Sensitivity of simulated extent and future evolution of marine suboxia to mixing intensity (2011)
    Wiley
    Details
    Publication Date: 2011-03-31
    Description: Geological and hydrographic records contain evidence of substantial past variations in the oxygenation of the global ocean. Numerical models predicts a future decrease of marine oxygen levels under global warming. Using a global biogeochemical-climate model in which diapycnal mixing is parametrised as the sum of the regionally heterogenous tidal and homogenous background vertical mixing, we here show that simulated total oceanic oxygen content and the extent of marine suboxia are both sensitive to the strength of background vertical mixing. Eight otherwise identical configurations of the model were spun up under pre-industrial conditions for different vertical diffusivities ranging from background values of 0.01 cm2/s to 0.5 cm2/s. This range corresponds to various observational estimates and to values currently used in numerical ocean circulation models. Whereas the simulated total oceanic oxygen content is larger for larger mixing intensities, the simulated suboxic volume displays a maximum at intermediate diffusivities of about 0.2 cm2/s. The intensity of vertical mixing also determines the evolution of suboxic areas under projected 21st century CO2 emissions: while all model configurations predict a decline in total oceanic oxygen, the simulated extent of marine suboxia shows a 21st century expansion only for mixing rates higher than 0.2 cm2/s, whereas the suboxic volume declines for lower mixing rates despite an overall loss of marine oxygen. Differences in the poorly constrained mixing parameterisation can thus lead to qualitatively different estimates about the future evolution of marine suboxia under projected climate change.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Can we predict the direction of marine primary production change under global warming? (2011)
    Wiley
    Details
    Publication Date: 2011-01-21
    Description: A global Earth System model is employed to investigate the role of direct temperature effects in the response of marine ecosystems to climate change. While model configurations with and without consideration of explicit temperature effects can reproduce observed current biogeochemical tracer distributions and estimated carbon export about equally well, carbon flow through the model ecosystem reveals strong temperature sensitivities. Depending on whether biological processes are assumed temperature sensitive or not, simulated marine net primary production (NPP) increases or decreases under projected climate change driven by a business-as-usual CO2 emission scenario for the 21st century. This suggests that indirect temperature effects such as changes in the supply of nutrients and light are not the only relevant factors to be considered when modeling the response of marine ecosystems to climate change. A better understanding of direct temperature effects on marine ecosystems is required before even the direction of change in NPP can be reliably predicted.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
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    The viscosity effect on marine particle flux – a climate relevant feedback mechanism (2014)
    Wiley
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    Publication Date: 2014-03-14
    Description: Oceanic uptake and long-term storage of atmospheric carbon dioxide (CO 2 ) are strongly driven by the marine ‘biological pump’, i.e. sinking of biotically fixed inorganic carbon and nutrients from the surface into the deep ocean [ Sarmiento and Bender , 1994; Volk and Hoffert , 1985]. Sinking velocity of marine particles depends on seawater viscosity, which is strongly controlled by temperature [ Sharqawy et al. , 2010]. Consequently, marine particle flux is accelerated as ocean temperatures increase under global warming [ Bach et al. , 2012]. Here we show that this previously overlooked 'viscosity effect' could have profound impacts on marine biogeochemical cycling and carbon uptake over the next centuries to millennia. In our global-warming simulation, the viscosity effect accelerates particle sinking by up to 25%, thereby effectively reducing the portion of organic matter that is respired in the surface ocean. Accordingly, the biological carbon pump's efficiency increases, enhancing the sequestration of atmospheric CO 2 into the ocean. This effect becomes particularly important on longer timescales when warming reaches the ocean interior. At the end of our simulation (4000 AD) oceanic carbon uptake is 17% higher, atmospheric CO 2 concentration is 180 ppm lower, and the increase in global average surface temperature is 8% weaker when considering the viscosity effect. Consequently, the viscosity effect could act as a long-term negative feedback mechanism in the global climate system.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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