Early Last Interglacial Greenland Ice Sheet melting and a sustained period of meridional overturning weakening: a model analysis of the uncertainties     

Pepijn Bakker  Hans Renssen  Cédric J. Van Meerbeeck 《Climate Dynamics》2014,43(3-4):1025-1039

Proxy-data suggest that the Last Interglacial (LIG; ~130–116 ka BP) climate was characterized by higher temperatures, a partially melted Greenland Ice Sheet (GIS) and a changed Atlantic meridional overturning circulation (AMOC). Notwithstanding the uncertainties in LIG palaeoclimatic reconstructions, this setting potentially provides an opportunity to evaluate the relation between GIS melt and the AMOC as simulated by climate models. However, first we need to assess the extent to which a causal relation between early LIG GIS melt and the weakened AMOC is plausible. With a series of transient LIG climate simulations with the LOVECLIM earth system model, we quantify the importance of the major known uncertainties involved in early LIG GIS melt scenarios. Based on this we construct a specific scenario that is within the parameter space of uncertainties and show that it is physically consistent that early LIG GIS melting kept the AMOC weakened. Notwithstanding, this scenario is at the extreme end of the parameter space. Assuming that proxy-based reconstructions of early LIG AMOC weakening offer a realistic representation of its past state, this indicates that either (1) the AMOC weakening was caused by other forcings than early LIG GIS melt or (2) the early LIG AMOC was less stable than indicated by our simulations and a small amount of GIS melt was sufficient to keep the AMOC in the weak state of a bi-stable regime. We argue that more intensive research is required because of the high potential of the early LIG to evaluate model performance in relation to the AMOC response to GIS melt.  相似文献   

Can the vapour phase be neglected to estimate bulk salinity of halite bearing aqueous fluid inclusions?     

Ronald J. Bakker 《Central European Journal of Geosciences》2012,4(2):238-245

The bulk salinity cannot be directly obtained from the dissolution temperatures of halite in highly saline fluid inclusions that contain solid, liquid, and vapour at room temperature. At least two of the following independent parameters must be determined to estimate the bulk composition and density of these inclusions: 1. dissolution temperature of halite in the presence of vapour; 2. total homogenization temperature of liquid and vapour; and 3. volume fraction of the vapour phase. A new V ^m -x diagram for phase stabilities in the H₂O-NaCl system has been constructed to obtain these bulk fluid properties from inclusions that homogenize liquid and vapour phase at higher temperatures than dissolution of halite.  相似文献   

Package FLUIDS. Part 4: thermodynamic modelling and purely empirical equations for H2O-NaCl-KCl solutions   总被引：1，自引：0，他引：1  

Ronald J. Bakker 《Mineralogy and Petrology》2012,105(1-2):1-29

A H₂O-NaCl-KCl-rich fluid occurs occasionally in fluid inclusions in a variety of geological environments. The properties of this fluid provide information about the conditions of entrapment, and thereby, conditions that have affected the rock. New purely empirical and thermodynamic models are developed in this study to reproduce the properties of the H₂O-NaCl-KCl fluid system, especially the liquidus at variable pressures (the solid–liquid-vapour surface, i.e. SLV), and at constant pressures (the solid–liquid surface, i.e. SL). The SLV surface is modelled according to “best-fit” polynomial equations, which relate temperature, pressure and composition. The SL surfaces, at constants pressures, are modelled according to thermodynamic principles, i.e. the equality of chemical potentials of components (NaCl and KCl) in each phase at equilibrium. The models are valid up to 400?MPa and 900°C and can be applied to fluid inclusions studies to obtain salinities from dissolution temperatures of salt crystals. The new models are included in the program AqSo WHS that forms part of the software package FLUIDS (Bakker, Chem Geol 194:3–23, 2003), to be able to apply directly the mathematical functions in fluid inclusion studies and in general fluid properties investigations.  相似文献   

Multilayer analytic element modeling of radial collector wells   总被引：1，自引：0，他引：1  

Bakker M  Kelson VA  Luther KH 《Ground water》2005,43(6):926-934

A new multilayer approach is presented for the modeling of ground water flow to radial collector wells. The approach allows for the inclusion of all aspects of the unique boundary condition along the lateral arms of a collector well, including skin effect and internal friction losses due to flow in the arms. The hydraulic conductivity may differ between horizontal layers within the aquifer, and vertical anisotropy can be taken into account. The approach is based on the multilayer analytic element method, such that regional flow and local three-dimensional detail may be simulated simultaneously and accurately within one regional model. Horizontal flow inside a layer is computed analytically, while vertical flow is approximated with a standard finite-difference scheme. Results obtained with the proposed approach compare well to results obtained with three-dimensional analytic element solutions for flow in unconfined aquifers. The presented approach may be applied to predict the yield of a collector well in a regional setting and to compute the origin and residence time, and thus the quality, of water pumped by the collector well. As an example, the addition of three lateral arms to a collector well that already has three laterals is investigated. The new arms are added at an elevation of 2 m above the existing laterals. The yield increase of the collector well is computed as a function of the lengths of the three new arms.  相似文献   

Matching carbon pools and fluxes for the Southern Ocean Iron Release Experiment (SOIREE)     

Dorothee C.E. Bakker  Philip W. Boyd  Edward R. Abraham  Matthew A. Charette  Mark P. Gall  Julie A. Hall  Cliff S. Law  Scott D. Nodder  Karl Safi  Dick J. Singleton  Kim Tanneberger  Thomas W. Trull  Anya M. Waite  Andrew J. Watson  John Zeldis 《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(12):1941-1960

The Lagrangian Southern Ocean Iron Release Experiment (SOIREE) allowed study of a gradually evolving iron-mediated phytoplankton bloom in water labelled with the inert tracer sulfur hexafluoride, SF₆. This article describes a pelagic carbon budget for the mixed layer in SOIREE and assesses the extent to which closure of the budget is achieved. Net community production (NCP) converted 837 mmol m⁻² of inorganic carbon to organic carbon in 12.0 d after the first iron addition. A large fraction (41%) of NCP remained as particulate organic carbon in the mixed layer of the iron-enriched patch, while 23% was lost by horizontal dispersion and 0–29% was exported. The closure of the carbon budget is hampered by the lack of measurements of dissolved organic carbon (DOC), by a major uncertainty in carbon export, and by use of empirical conversion factors in estimates of carbon biomass and metabolic rates. Lagrangian carbon-budget studies may be improved by direct measurement of all major carbon parameters and conversion factors. Carbon cycling in the SOIREE bloom resembled that in ‘natural’ algal blooms in the open Southern Ocean in some respects, but not in all. Daily NCP in the SOIREE bloom (70 mmol m⁻² d⁻¹) was higher than in natural blooms, partly because other studies did not account for horizontal dispersion, were for longer periods or included less productive areas. The build-up of POC stock and carbon export as a fraction of NCP in SOIREE were in the lower range of observations elsewhere.  相似文献   

Temperature dependence of the hyperfine parameters of maghemite and al-substituted maghemites     

G. M. da Costa  E. De Grave  L. H. Bowen  P. M. A. de Bakker  R. E. Vandenberghe 《Physics and Chemistry of Minerals》1995,22(3):178-185

Synthetic aluminum-substituted maghemite samples, -(Al _y Fe_1-y )₂O₃ with y=0, 0.032, 0.058, 0.084, 0.106 and 0.151 have been studied by Mössbauer spectroscopy at 8 K and in the range 80 K to 475 K at steps of 25 K. The spectra have been analysed as a superposition of two sextets composed of asymmetrical Lorentzians. The A- and B-site isomer shifts were constrained as: _A=_B-0.12 mm/s. From the temperature dependence of _B it was possible to determine the characteristic Mössbauer temperature and the intrinsic shift. Both quantities clearly increase with increasing Al content, at least up to 10 mole%. The temperature dependence of the A-and B-sites hyperfine fields could be satisfactorily reproduced using the molecular-field theory assuming an antiparallel spin configuration. The exchange integrals were found as: J _AB =-25 K; J _AA =-18 K and J _BB = -3 K. The hyperfine fields show a crossing in the vicinity of 300 K as a result of the relatively strong A-A interaction. The Curie temperature for the non-substituted sample was calculated to be 930 K and decreases to 765 K for the sample with 15 mol% Al. The gradual decrease of the saturation value of the A-site hyperfine field with increasing Al substitution and the constancy of this quantity for the B sites, suggest that the Al cations occupy the B sites.Research Director, National Fund for Scientific Research, Belgium  相似文献   

Analytic modeling of groundwater dynamics with an approximate impulse response function for areal recharge     

Mark Bakker  Kees Maas  Frans Schaars  Jos R. von Asmuth 《Advances in water resources》2007

An analytic approach is presented for the simulation of variations in the groundwater level due to temporal variations of recharge in surficial aquifers. Such variations, called groundwater dynamics, are computed through convolution of the response function due to an impulse of recharge with a measured time series of recharge. It is proposed to approximate the impulse response function with an exponential function of time which has two parameters that are functions of space only. These parameters are computed by setting the zeroth and first temporal moments of the approximate impulse response function equal to the corresponding moments of the true impulse response function. The zeroth and first moments are modeled with the analytic element method. The zeroth moment may be modeled with existing analytic elements, while new analytic elements are derived for the modeling of the first moment. Moment matching may be applied in the same fashion with other approximate impulse response functions. It is shown that the proposed approach gives accurate results for a circular island through comparison with an exact solution; both a step recharge function and a measured series of 10 years of recharge were used. The presented approach is specifically useful for modeling groundwater dynamics in aquifers with shallow groundwater tables as is demonstrated in a practical application. The analytic element method is a gridless method that allows for the precise placement of ditches and streams that regulate groundwater levels in such aquifers; heads may be computed analytically at any point and at any time. The presented approach may be extended to simulate the effect of other transient stresses (such as fluctuating surface water levels or pumping rates), and to simulate transient effects in multi-aquifer systems.  相似文献   

Simulating groundwater flow to surface water features with leaky beds using analytic elements     

Mark Bakker 《Advances in water resources》2007

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A magmatic-hydrothermal transition in Arkaroola (northern Flinders Ranges, South Australia): from diopside–titanite pegmatites to hematite–quartz growth     

Ronald J. Bakker  Marlina A. Elburg 《Contributions to Mineralogy and Petrology》2006,152(5):541-569

A set of Palaeozoic diopside–titanite veins are present in Mesoproterozoic metagranites and metasediments that constitute the basement (Mt Painter Inlier) of the Adelaide Fold Belt (South Australia). These massive veins (up to 1 m) of pegmatitic nature contain large crystals of diopside, LREE–Y-enriched titanite (up to 40 cm in length) and minor amounts of quartz. They can be used to trace the system’s development from a high-temperature magmatic stage through to a massive hydrothermal event. The pegmatitic origin of these veins is evident from a complex fluid-melt inclusion assemblage, consisting of a highly saline inhomogeneous fluid and relicts of melt. Immiscibility of melt and heterogeneous highly saline fluids (exceeding 61 eq. mass% NaCl) is preserved in primary inclusions in diopside and secondary inclusions in titanite, indicating relatively shallow conditions of formation (510 ± 20°C and 130 ± 10 MPa). Graphic intergrowth of diopside and albite occurs at the contact with granitic pegmatites. The system evolved into hydrothermal conditions, which can be deduced from a later population of only fluid inclusions (homogeneous and less saline, ≈ 40 eq. mass% NaCl), trapped around 350 ± 20°C and 80 ± 10 MPa. During quartz crystallization, the conditions moved across the halite liquidus resulting in a heterogeneous mixture of brine and halite crystals, which were trapped at 200 ± 20°C and 50 ± 10 MPa. Brecciation and a palaeo-geothermal system overprinted the pegmatitic veins with an epithermal hematite–quartz assemblage and lesser amounts of bladed calcite and fluorite, in an intermittently boiling hydrothermal system of fairly pure H₂O at 100–140°C and 1–5 MPa. Remobilization of LREEs and Y from titanite and/or the granitic host rock is evidenced by precipitation of apatite, allanite and wakefieldite in an intermediate stage. Occasional incorporation of radioactive elements or minerals, presumably U-rich, in the fluorite is responsible for radiolysis of H₂O to H₂.  相似文献   

The sediment budget and dynamics of a delta‐canyon‐lobe system over the Anthropocene timescale: The Rhone River delta,Lake Geneva (Switzerland/France)     

Tiago A. Silva  Stphanie Girardclos  Laura Stutenbecker  Maarten Bakker  Anna Costa  Fritz Schlunegger  Stuart N. Lane  Peter Molnar  Jean‐Luc Loizeau 《Sedimentology》2019,66(3):838-858

Deltas are important coastal sediment accumulation zones in both marine and lacustrine settings. However, currents derived from tides, waves or rivers can transfer that sediment into distal, deep environments, connecting terrestrial and deep marine depozones. The sediment transfer system of the Rhone River in Lake Geneva is composed of a sublacustrine delta, a deeply incised canyon and a distal lobe, which resembles, at a smaller scale, deep‐sea fan systems fed by high discharge rivers. From the comparison of two bathymetric datasets, collected in 1891 and 2014, a sediment budget was calculated for eastern Lake Geneva, based on which sediment distribution patterns were defined. During the past 125 years, sediment deposition occurred mostly in three high sedimentation rate areas: the proximal delta front, the canyon‐levée system and the distal lobe. Mean sedimentation rates in these areas vary from 0·0246 m year^?1 (distal lobe) to 0·0737 m year^?1 (delta front). Although the delta front–levées–distal lobe complex only comprises 17·0% of the analysed area, it stored 74·9% of the total deposited sediment. Results show that 52·5% of the total sediment stored in this complex was transported toward distal locations through the sublacustrine canyon. Namely, the canyon–levée complex stored 15·9% of the total sediment, while 36·6% was deposited in the distal lobe. The results thus show that in deltaic systems where density currents can occur regularly, a significant proportion of riverine sediment input may be transferred to the canyon‐lobe systems leading to important distal sediment accumulation zones.  相似文献