ORCID Profile
0000-0002-5000-7863
Current Organisation
Consiglio Nazionale delle Ricerche
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Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-1892
Abstract: & & Forty percent of the plastic produced annually ends up in the ocean. What happens to the plastic after that is poorly understood, though a growing body of data suggests it is rapidly spreading throughout the ocean. The mechanisms of this spread are not straightforward for small, weakly or neutrally buoyant plastic size fractions (the microplastics), in part because they aggregate in marine snow and are consumed by zooplankton. This biological transport pathway is suspected to be a primary surface microplastic removal mechanism, but exactly how it might work in the real ocean is unknown. We search the parameter space of a new microplastic model embedded in an earth system model to show biological uptake significantly shapes global microplastic inventory and distributions, despite its being an apparently inefficient removal pathway.& &
Publisher: Springer Science and Business Media LLC
Date: 21-04-2021
DOI: 10.1038/S41467-021-22554-W
Abstract: Global warming has driven a loss of dissolved oxygen in the ocean in recent decades. We demonstrate the potential for an additional anthropogenic driver of deoxygenation, in which zooplankton consumption of microplastic reduces the grazing on primary producers. In regions where primary production is not limited by macronutrient availability, the reduction of grazing pressure on primary producers causes export production to increase. Consequently, organic particle remineralisation in these regions increases. Employing a comprehensive Earth system model of intermediate complexity, we estimate this additional remineralisation could decrease water column oxygen inventory by as much as 10% in the North Pacific and accelerate global oxygen inventory loss by an extra 0.2–0.5% relative to 1960 values by the year 2020. Although significant uncertainty accompanies these estimates, the potential for physical pollution to have a globally significant biogeochemical signal that exacerbates the consequences of climate warming is a novel feedback not yet considered in climate research.
Publisher: Springer Science and Business Media LLC
Date: 07-10-2020
DOI: 10.1038/S41598-020-72898-4
Abstract: Every year, about four percent of the plastic waste generated worldwide ends up in the ocean. What happens to the plastic there is poorly understood, though a growing body of evidence suggests it is rapidly spreading throughout the global ocean. The mechanisms of this spread are straightforward for buoyant larger plastics that can be accurately modelled using Lagrangian particle models. But the fate of the smallest size fractions (the microplastics) are less straightforward, in part because they can aggregate in sinking marine snow and faecal pellets. This biologically-mediated pathway is suspected to be a primary surface microplastic removal mechanism, but exactly how it might work in the real ocean is unknown. We search the parameter space of a new microplastic model embedded in an earth system model to show that biological uptake can significantly shape global microplastic inventory and distributions and even account for the budgetary “missing” fraction of surface microplastic, despite being an inefficient removal mechanism. While a lack of observational data h ers our ability to choose a set of “best” model parameters, our effort represents a first tool for quantitatively assessing hypotheses for microplastic interaction with ocean biology at the global scale.
Publisher: Copernicus GmbH
Date: 26-11-2018
DOI: 10.5194/BG-2018-467
Abstract: Abstract. Phytoplankton calcifiers contribute to global carbon cycling through their dual formation of calcium carbonate and particulate organic carbon (POC). The carbonate might provide an efficient export pathway for the associated POC to the deep ocean, reducing the particles' exposure to biological degradation in the upper ocean and increasing the particle settling rate. Previous work has suggested ballasting of POC by carbonate might increase in a warming climate, in spite of increasing carbonate dissolution rates, because calcifiers benefit from the widespread nutrient limitation arising from stratification. We compare the biogeochemical responses of three models containing 1) a single mixed phytoplankton class, 2) additional explicit small phytoplankton and calcifiers, and 3) additional explicit small phytoplankton and calcifiers with a prognostic carbonate ballast model, to two rapid changes in atmospheric CO2. The first CO2 scenario represents a rapid (150 year) transition from a stable icehouse climate (285 ppm) into a greenhouse climate (1257 ppm) the second represents a symmetric rapid transition from a stable greenhouse climate into an icehouse climate. We identify a slope change in the global net primary production response with a transition point at about 3.5 °C global mean sea surface temperature change in all models, driven by a combination of physics and biology. We also find that in both warming and cooling scenarios, the application of a prognostic carbonate ballast model moderates changes in carbon export production, suboxic volume, and nitrate sources and sinks, reducing the long-term model response to about one-third that of the calcifier model without ballast. Explicit small phytoplankton and calcifiers, and carbonate ballasting, increase the physical separation of nitrate sources and sinks through a combination of phytoplankton competition and lengthened remineralization profile, resulting in a significantly higher global nitrate inventory in this model compared to the single phytoplankton type model (15 % and 32 % higher, for icehouse and greenhouse climates). Higher nitrate inventory alleviates nitrate limitation, increasing phytoplankton sensitivity to changes in physical limitation factors (light and temperature). This larger sensitivity to physical forcing produces stronger shifts in ocean phosphate storage between icehouse and greenhouse climates. The greenhouse climate is found to hold phosphate and nitrate deeper in the ocean, despite a shorter remineralization length scale than the icehouse climate, because of the longer residence times of the deep water masses. We conclude the global biogeochemical impact of calcifiers extends beyond their role in global carbon cycling, and that the ecological composition of the global ocean can affect how ocean biogeochemistry responds to climate forcing.
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-6151
Abstract: & & Increasing the complexity& of the representation of iron in an earth system model can lead to significant differences in surface ocean nutrient pathways in a pre-industrial climate. These differences persist even after automated calibration forces the models to achieve similar fit to the same observational data. We explore the impact of these nutrient pathway differences in the context of climate change by forcing the models (one without iron, one with a seasonally-cyclic iron mask, and one with a fully dynamic iron module) with the RCP8.5 business-as-usual atmospheric CO& sub& & /sub& concentration scenario from years 1800 until 2100. We find that while the global oxygen inventory drops across all models over this period, different trends in the oxygen minimum zone (OMZ) volume arise. Models with iron represented simulate decreases between 60 and 80 percent in OMZ volume, while the model without iron simulates an OMZ volume increase of 10 percent. The difference is attributed to the role of iron limitation in regulating the low latitude primary production response to warming and stratification. We further quantify the corresponding denitrification trends and impact on ocean nitrate inventory.& This study illustrates that model structural uncertainty further challenges predictions under a changing climate, and highlights the strong role of iron in regulating nutrient cycling and ocean deoxygenation.& &
Publisher: Springer Science and Business Media LLC
Date: 07-10-2020
DOI: 10.1038/S41586-020-2780-0
Abstract: Nitrous oxide (N
Publisher: American Geophysical Union (AGU)
Date: 24-02-2022
DOI: 10.1029/2020GB006851
Abstract: Biological nitrogen fixation is an important oceanic nitrogen source, potentially stabilizing marine fertility in an increasingly stratified and nutrient‐depleted ocean. Iron limitation of low latitude primary producers has been previously demonstrated to affect simulated regional ecosystem responses to climate warming or nitrogen cycle perturbation. Here we use three biogeochemical models that vary in their representation of the iron cycle to estimate change in the marine nitrogen cycle under a high CO 2 emissions future scenario (RCP8.5). The first model neglects explicit iron effects on biology (NoFe), the second utilizes prescribed, seasonally cyclic iron concentrations and associated limitation factors (FeMask), and the third contains a fully dynamic iron cycle (FeDyn). Models were calibrated using observed fields to produce near‐equivalent nutrient and oxygen fits, with productivity ranging from 49 to 75 Pg C yr −1 . Global marine nitrogen fixation increases by 71.1% with respect to the preindustrial value by the year 2100 in NoFe, while it remains stable (0.7% decrease in FeMask and 0.3% increase in FeDyn) in explicit iron models. The mitigation of global nitrogen fixation trend in the models that include a representation of iron originates in the Eastern boundary upwelling zones, where the bottom‐up control of iron limitation reduces export production with warming, which shrinks the oxygen deficient volume, and reduces denitrification. Warming‐induced trends in the oxygen deficient volume in the upwelling zones have a cascading effect on the global nitrogen cycle, just as they have previously been shown to affect tropical net primary production.
Publisher: Copernicus GmbH
Date: 14-03-2019
Abstract: Abstract. Phytoplankton calcifiers contribute to global carbon cycling through their dual formation of calcium carbonate and particulate organic carbon (POC). The carbonate might provide an efficient export pathway for the associated POC to the deep ocean, reducing the particles' exposure to biological degradation in the upper ocean and increasing the particle settling rate. Previous work has suggested ballasting of POC by carbonate might increase in a warming climate, in spite of increasing carbonate dissolution rates, because calcifiers benefit from the widespread nutrient limitation arising from stratification. We compare the biogeochemical responses of three models containing (1) a single mixed phytoplankton class, (2) additional explicit small phytoplankton and calcifiers, and (3) additional explicit small phytoplankton and calcifiers with a prognostic carbonate ballast model, to two rapid changes in atmospheric CO2. The first CO2 scenario represents a rapid (151-year) transition from a stable icehouse climate (283.9 ppm) into a greenhouse climate (1263 ppm) the second represents a symmetric rapid transition from a stable greenhouse climate into an icehouse climate. We identify a slope change in the global net primary production response with a transition point at about 3.5 ∘C global mean sea surface temperature change in all models, driven by a combination of physical and biological changes. We also find that in both warming and cooling scenarios, the application of a prognostic carbonate ballast model moderates changes in carbon export production, suboxic volume, and nitrate sources and sinks, reducing the long-term model response to about one-third that of the calcifier model without ballast. Explicit small phytoplankton and calcifiers, and carbonate ballasting, increase the physical separation of nitrate sources and sinks through a combination of phytoplankton competition and lengthened remineralization profile, resulting in a significantly higher global nitrate inventory in this model compared to the single phytoplankton type model (15 % and 32 % higher for icehouse and greenhouse climates). Higher nitrate inventory alleviates nitrate limitation, increasing phytoplankton sensitivity to changes in physical limitation factors (light and temperature). This larger sensitivity to physical forcing produces stronger shifts in ocean phosphate storage between icehouse and greenhouse climates. The greenhouse climate is found to hold phosphate and nitrate deeper in the ocean, despite a shorter remineralization length scale than the icehouse climate, because of the longer residence times of the deep water masses. We conclude the global biogeochemical impact of calcifiers extends beyond their role in global carbon cycling, and that the ecological composition of the global ocean can affect how ocean biogeochemistry responds to climate forcing.
Location: United Kingdom of Great Britain and Northern Ireland
Location: No location found
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