ORCID Profile
0000-0002-4706-295X
Current Organisations
Shiraz University
,
University of Sydney
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Publisher: Research Square Platform LLC
Date: 31-08-2021
DOI: 10.21203/RS.3.RS-824230/V1
Abstract: Retrograde clay mineral reactions (i.e., reverse weathering), including glauconite formation, are first-order controls on element (re)cycling vs sequestration in modern and ancient marine sediments. Here, we report substantial K–Mg–Fe sequestration by glauconite formation in shallow marine settings from the Triassic to the Holocene, averaging 4 ± 3 mmol K·cm − ²·kyr − 1 , 4 ± 2 mmol Mg·cm − ²·kyr − 1 and 10 ± 6 mmol Fe·cm − ²·kyr − 1 , which is ~ 2 orders of magnitude higher compared to deep-sea settings. Upscaling of glauconite abundances in shallow-water ( 200 m) environments predicts a global K–Mg–Fe uptake of ~ 0.05–0.06 Tmol K·yr − 1 , ~ 0.04–0.06 Tmol Mg·yr − 1 and ~ 0.11–0.14 Tmol Fe·yr − 1 . We conclude that authigenic clay elemental uptake had a large impact on the global marine K, Mg and Fe cycles throughout Earth`s history, in particular during ‘greenhouse’ periods with sea level highstand. Quantifying authigenic clay formation is key for better understanding past and present geochemical cycling in marine sediments.
Publisher: Copernicus GmbH
Date: 23-02-2017
Abstract: Abstract. Past warm periods provide an opportunity to evaluate climate models under extreme forcing scenarios, in particular high ( 800 ppmv) atmospheric CO2 concentrations. Although a post hoc intercomparison of Eocene ( ∼ 50 Ma) climate model simulations and geological data has been carried out previously, models of past high-CO2 periods have never been evaluated in a consistent framework. Here, we present an experimental design for climate model simulations of three warm periods within the early Eocene and the latest Paleocene (the EECO, PETM, and pre-PETM). Together with the CMIP6 pre-industrial control and abrupt 4 × CO2 simulations, and additional sensitivity studies, these form the first phase of DeepMIP – the Deep-time Model Intercomparison Project, itself a group within the wider Paleoclimate Modelling Intercomparison Project (PMIP). The experimental design specifies and provides guidance on boundary conditions associated with palaeogeography, greenhouse gases, astronomical configuration, solar constant, land surface processes, and aerosols. Initial conditions, simulation length, and output variables are also specified. Finally, we explain how the geological data sets, which will be used to evaluate the simulations, will be developed.
Publisher: Annual Reviews
Date: 29-06-2016
DOI: 10.1146/ANNUREV-EARTH-060115-012211
Abstract: We present a revised global plate motion model with continuously closing plate boundaries ranging from the Triassic at 230 Ma to the present day, assess differences among alternative absolute plate motion models, and review global tectonic events. Relatively high mean absolute plate motion rates of approximately 9–10 cm yr −1 between 140 and 120 Ma may be related to transient plate motion accelerations driven by the successive emplacement of a sequence of large igneous provinces during that time. An event at ∼100 Ma is most clearly expressed in the Indian Ocean and may reflect the initiation of Andean-style subduction along southern continental Eurasia, whereas an acceleration at ∼80 Ma of mean rates from 6 to 8 cm yr −1 reflects the initial northward acceleration of India and simultaneous speedups of plates in the Pacific. An event at ∼50 Ma expressed in relative, and some absolute, plate motion changes around the globe and in a reduction of global mean plate speeds from about 6 to 4–5 cm yr −1 indicates that an increase in collisional forces (such as the India–Eurasia collision) and ridge subduction events in the Pacific (such as the Izanagi–Pacific Ridge) play a significant role in modulating plate velocities.
Publisher: Elsevier BV
Date: 06-2020
Publisher: Society of Exploration Geophysicists and American Association of Petroleum Geologists
Date: 16-09-2015
Publisher: Elsevier BV
Date: 09-2020
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-10847
Abstract: The recycling of oceanic lithosphere at subduction zones constitutes the largest driving force of plate tectonic motion. The angle at which subducting plates enter the mantle influences the magnitude of this force, the distribution of subduction-related earthquakes, intensity of volcanism, and mountain building. However, the factors that control subduction angle remain unresolved. We develop a novel formulation for calculating the subduction angle based on trench migration, convergence rate, slab thickness, and plate density which reproduces the present-day dynamics of global subduction zones. Applying this formulation to reconstructed subduction boundaries from the Jurassic to present day, we relate subduction angle combined with slab flux to pulses in kimberlite eruptions. High rates of subducting slab material trigger mantle return flow that stimulates fertile reservoirs in the mantle. These convective instabilities transport slab-influenced melt to the surface at a distance inbound from the trench corresponding to the subduction angle. Our deep-time slab dip formulation has numerous potential applications including modelling the deep carbon and water cycles, and an improved understanding of subduction-related mineral deposits.
Publisher: Springer Science and Business Media LLC
Date: 22-03-2022
DOI: 10.1038/S41467-022-29223-6
Abstract: Retrograde clay mineral reactions (reverse weathering), including glauconite formation, are first-order controls on element sequestration in marine sediments. Here, we report substantial element sequestration by glauconite formation in shallow marine settings from the Triassic to the Holocene, averaging 3 ± 2 mmol·cm − ²·kyr −1 for K, Mg and Al, 16 ± 9 mmol·cm − ²·kyr −1 for Si and 6 ± 3 mmol·cm − ²·kyr −1 for Fe, which is ~2 orders of magnitude higher than estimates for deep-sea settings. Upscaling of glauconite abundances in shallow-water (0–200 m) environments predicts a present-day global uptake of ~≤ 0.1 Tmol·yr −1 of K, Mg and Al, and ~0.1–0.4 Tmol·yr −1 of Fe and Si, which is ~half of the estimated Mesozoic elemental flux. Clay mineral authigenesis had a large impact on the global marine element cycles throughout Earth’s history, in particular during ‘greenhouse’ periods with sea level highstand, and is key for better understanding past and present geochemical cycling in marine sediments.
Publisher: Copernicus GmbH
Date: 04-07-2023
DOI: 10.5194/EGUSPHERE-2023-1398
Abstract: Abstract. In drought-prone Australia, multi-year droughts have detrimental impacts on both the natural environment and human societies. For responsible water management, we need a thorough understanding of the full range of variability in multi-year droughts and how this might change in a warming world. But research into the long-term frequency, persistence, and severity of Australian droughts is limited. This is partly due to the length of the observational record, which is short relative to the time scales of hydroclimatic variability, and hence may not capture the range of possible variability. Using simulations of Australian precipitation over the last millennium (850–2000 CE), we characterise the nature of multi-year meteorological droughts across Australia, and including a particular focus on the Murray-Darling Basin (MDB) the largest agricultural region in Australia. We find that simulated Australian droughts in the twentieth century (1900–2000) are within the bounds of pre-industrial natural variability in terms of drought intensity, severity, and frequency. A tendency to longer droughts in southwestern and eastern Australia (including the MDB) in the 20th century compared with the pre-industrial period suggests an emerging anthropogenic influence, consistent with projected rainfall changes in these regions. Large volcanic eruptions tend to promote drought-free intervals in the MDB. Model simulations suggest future droughts across Australia could be much longer than what has been experienced in the twentieth century, even without any human influence. With the addition of anthropogenic climate change—which favours drought conditions across much of southern Australia, due to reduced cool season rainfall—it is likely that future droughts in Australia will exceed historical experience.
Publisher: Copernicus GmbH
Date: 29-11-2021
DOI: 10.5194/CP-2021-156
Abstract: Abstract. The Southern Annular Mode (SAM) is the leading mode of climate variability in the extratropical Southern Hemisphere, with major regional climate impacts. Observations, reconstructions, and historical climate simulations all show positive trends in the SAM since the 1960s however, earlier trends in palaeoclimate SAM reconstructions cannot be reconciled with last millennium simulations. Here we investigate the sensitivity of the SAM to solar irradiance variations using simulations with a range of constant solar forcing values, and last millennium transient simulations with varying litude solar forcing scenarios. We find the mean SAM state can be significantly altered by solar irradiance changes, and that transient last millennium simulations using a high- litude solar scenario have an improved and significant agreement with proxy-based SAM reconstructions. Our findings suggest that the effects of solar forcing on high-latitude climate may not be adequately incorporated in most last millennium simulations, due to solar irradiance changes that are too small and/or the absence of interactive atmospheric chemistry in global climate models.
Publisher: Copernicus GmbH
Date: 04-07-2023
Publisher: Emerald
Date: 04-03-2019
DOI: 10.1108/COMPEL-06-2017-0229
Abstract: This paper aims to achieve an optimal design for distribution transformers considering cost and power losses. Particle swarm optimization (PSO) algorithm is used as an optimization tool for minimizing the objective functions of design procedure which are cost and electrical and iron losses. In this paper, distribution transformer losses are considered as operating costs. Also, transformer construction cost which depends on the amount of iron and copper in the structure is assumed as its initial cost. In addition, some other important constraints such as appropriate ranges of transformer efficiency, voltage regulation, temperature rise, no-load current, and winding fill factor are investigated in the design procedure. The PSO algorithm is applied to find optimum amount of needed copper and iron for a typical distribution transformer. Moreover, transformer impedance considered as a constraint to achieve an acceptable voltage regulation in the design process. It is shown that the proposed design procedure provides a simple and effective approach to estimate the flux and current densities for minimizing the active part cost and active power losses which means reduction in amount of transformer total owning cost (TOC). The methodology advances a proposal for reducing distribution transformers costs using PSO algorithm. The approach considers the aforementioned constraints and TOC to minimize the active part cost and maximize the efficiency. It is demonstrated that a designed transformer will not be optimum when the transformer losses over years are not considered in design procedure. Finally, the results prove the effectiveness of the proposed procedure in designing cost-effective distribution transformers from its initial cost until its whole life.
Publisher: Springer Science and Business Media LLC
Date: 18-05-2009
DOI: 10.1155/2009/786291
Publisher: Elsevier BV
Date: 03-2016
Publisher: American Geophysical Union (AGU)
Date: 10-2020
DOI: 10.1029/2020GC009214
Publisher: American Geophysical Union (AGU)
Date: 12-2017
DOI: 10.1002/2017GC007258
Publisher: American Geophysical Union (AGU)
Date: 02-2018
DOI: 10.1002/2017PA003238
Publisher: Springer Science and Business Media LLC
Date: 12-01-2022
Publisher: Springer Science and Business Media LLC
Date: 06-06-2023
DOI: 10.1038/S41598-023-36250-W
Abstract: Kimberlites are sourced from thermochemical upwellings which can transport diamonds to the surface of the crust. The majority of kimberlites preserved at the Earth’s surface erupted between 250 and 50 million years ago, and have been attributed to changes in plate velocity or mantle plumes. However, these mechanisms fail to explain the presence of strong subduction signatures observed in some Cretaceous kimberlites. This raises the question whether there is a subduction process that unifies our understanding of the timing of kimberlite eruptions. We develop a novel formulation for calculating subduction angle based on trench migration, convergence rate, slab thickness and density to connect the influx of slab material into the mantle with the timing of kimberlite eruptions. We find that subduction angles combined with peaks in slab flux predict pulses of kimberlite eruptions. High rates of subducting slab material trigger mantle return flow that stimulates fertile reservoirs in the mantle. These convective instabilities transport slab-influenced melt to the surface at a distance inbound from the trench corresponding to the subduction angle. Our deep-time slab dip formulation has numerous potential applications including modelling the deep carbon and water cycles, and an improved understanding of subduction-related mineral deposits.
Publisher: Geological Society of America
Date: 22-03-2016
DOI: 10.1130/G37828Y.1
Publisher: Geological Society of America
Date: 05-2015
DOI: 10.1130/G36303.1
Publisher: Copernicus GmbH
Date: 07-03-2013
Abstract: Abstract. A variety of paleogeographic reconstructions have been published, with applications ranging from paleoclimate, ocean circulation and faunal radiation models to resource exploration yet their uncertainties remain difficult to assess as they are generally presented as low-resolution static maps. We present a methodology for ground-truthing the digital Palaeogeographic Atlas of Australia by linking the GPlates plate reconstruction tool to the global Paleobiology Database and a Phanerozoic plate motion model. We develop a spatio-temporal data mining workflow to validate the Phanerozoic Palaeogeographic Atlas of Australia with paleoenvironments derived from fossil data. While there is general agreement between fossil data and the paleogeographic model, the methodology highlights key inconsistencies. The Early Devonian paleogeographic model of southeastern Australia insufficiently describes the Emsian inundation that may be refined using biofacies distributions. Additionally, the paleogeographic model and fossil data can be used to strengthen numerical models, such as the dynamic topography and the associated inundation of eastern Australia during the Cretaceous. Although paleobiology data provide constraints only for paleoenvironments with high preservation potential of organisms, our approach enables the use of additional proxy data to generate improved paleogeographic reconstructions.
Publisher: Elsevier BV
Date: 03-2020
Publisher: Springer Science and Business Media LLC
Date: 09-03-2020
DOI: 10.1038/S41586-020-2084-4
Abstract: The Indian Ocean Dipole (IOD) affects climate and rainfall across the world, and most severely in nations surrounding the Indian Ocean
Publisher: Copernicus GmbH
Date: 07-2022
Abstract: Abstract. The Southern Annular Mode (SAM) is the leading mode of climate variability in the extratropical Southern Hemisphere, with major regional climate impacts. Observations, reconstructions, and historical climate simulations all show positive trends in the SAM since the 1960s however, earlier trends in palaeoclimate SAM reconstructions cannot be reconciled with last millennium simulations. There are also large differences in the magnitude of solar irradiance change between various solar reconstructions, although most last millennium climate simulations have relied on a low- litude solar-forcing scenario. Here we investigate the sensitivity of the SAM to solar irradiance variations using simulations with a range of constant solar-forcing values and last millennium transient simulations with varying litude solar-forcing scenarios. We find the mean SAM state can be significantly altered by solar irradiance changes and that transient last millennium simulations using a high- litude solar scenario have an improved and significant agreement with proxy-based SAM reconstructions. Our findings suggest that the effects of solar forcing on high-latitude climate may not be adequately incorporated in most last millennium simulations due to solar irradiance changes that are too small and/or the absence of interactive atmospheric chemistry in the global climate models used for these palaeoclimate simulations.
Publisher: American Geophysical Union (AGU)
Date: 04-2014
DOI: 10.1002/2013GC005176
Publisher: Wiley
Date: 14-03-2023
DOI: 10.1002/GDJ3.185
Abstract: PyGPlates is an open‐source Python library to visualize and edit plate tectonic reconstructions created using GPlates. The Python API affords a greater level of flexibility than GPlates to interrogate plate reconstructions and integrate with other Python workflows. GPlately was created to accelerate spatio‐temporal data analysis leveraging pyGPlates and PlateTectonicTools within a simplified Python interface. This object‐oriented package enables the reconstruction of data through deep geologic time (points, lines, polygons and rasters), the interrogation of plate kinematic information (plate velocities, rates of subduction and seafloor spreading), the rapid comparison between multiple plate motion models, and the plotting of reconstructed output data on maps. All tools are designed to be parallel‐safe to accelerate spatio‐temporal analysis over multiple CPU processors.
Publisher: American Geophysical Union (AGU)
Date: 04-2020
DOI: 10.1029/2019GC008869
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-10133
Abstract: The reconstruction of paleobathymetry, in particular the evolution of oceanic gateways, has important implications for paleo-ocean circulation, paleoclimate, as well as biotic and faunal exchanges. During the past ~250 million years there have been major changes in paleobathymetry and oceanic gateways associated with the breakup of the Pangaea supercontinent, including the development of the North and South Atlantic ocean basins and the Central Atlantic seaway. Considerable research effort has been invested into better understanding the global evolution of paleobathymetry and oceanic gateways during the Cenozoic, but there remain large uncertainties about the timing of opening, closure, and physiographic evolution of Mesozoic oceanic gateways and seaways.Here, we present new paleobathymetry reconstructions based on a recent global plate tectonic model (M& #252 ller et al., 2019) spanning the Triassic (~250 Ma) to the present. We reconstruct presently-preserved oceanic crust using new functionality developed in pybacktrack v1.4, a python module for backstripping and reconstructing paleobathymetry. For present-day submerged continental crust we use pybacktrack to reconstruct paleobathymetry based on its rifting and deformation history and assuming a single lithology for the progressive decompaction of sediments. In regions where ancient seafloor is now subducted, we use an established approach of synthetically reconstructing paleobathymetry based on the age-area distribution of oceanic crust (& #8216 age grids& #8217 ) convolved with an age-depth relationship to reconstruct basement depths followed by modelling effects from sediment thickness and seafloor volcanism including large igneous provinces. Our methodology additionally allows for alternative plate tectonic models (and/or absolute reference frames) to be integrated into reconstructions of paleobathymetry. Further, we use our new paleobathymetry reconstructions to explore the formation and evolution of pre-Cenozoic oceanic gateways. We find significant differences in the development and physiography of Mesozoic oceanic gateways and seaways in our new reconstructions compared to a widely used paleogeographic model, which has major implications for paleoceanographic models and interpretations of paleoclimate proxies.
Location: Iran (Islamic Republic of)
No related grants have been discovered for Mehdi Allahbakhshi.