A degradation approach to accelerate simulations to steady-state in a 3-D tracer transport model of the global ocean

1998 ◽  
Vol 14 (2) ◽  
pp. 101-116 ◽  
Author(s):  
O. Aumont ◽  
J. C. Orr ◽  
D. Jamous ◽  
P. Monfray ◽  
O. Marti ◽  
...  
Keyword(s):  
Steady State ◽  
Transport Model ◽  
Global Ocean ◽  
Tracer Transport

scholarly journals Use of experimental isotope-exchange fluxes in reversible enzyme and membrane transport models, assessed by simultaneous computer simulation of unidirectional and net chemical rates

1992 ◽  
Vol 286 (1) ◽  
pp. 295-303 ◽  
Author(s):  
I W Plesner
Keyword(s):  
Steady State ◽  
Exchange Rates ◽  
Membrane Transport ◽  
Isotope Exchange ◽  
Transport Model ◽  
Total Concentration ◽  
Rate Equations ◽  
Tracer Transport ◽  
Transport Models ◽  
Experimental Conditions

Steady-state rate equations for unidirectional (isotope-exchange) rates can become so complex, even for rather simple (reversible) enzyme or membrane transport models, that they are useless for detailed data analysis. In this paper a procedure is described for simultaneous simulation of net (chemical) and isotope-exchange rates. The method employs an expanded version of the basic model to monitor explicitly the fate of the label in an experiment. The procedure is quite general, and can be used for steady-state as well as transient kinetic situations, or it can be used in conjunction with existing interactive computer programs for steady-state model analysis. Three numerical examples are presented. First, it is shown, using the conventional (Post-Albers) model for Na+/K(+)-ATPase, that the change in concentration of a labelled intermediate after a change in experimental conditions does not in general reflect the change in the total concentration of that intermediate, and thus labelled intermediate concentrations may be misleading. Second, using a standard co-transport model and a prototype active-transport model (equivalent to a ligand-ATPase), it is shown that the ratio of tracer transport fluxes at steady state yields transport stoichiometries which depend on the experimental conditions, are different from the net apparent stoichiometries, and whose changes with conditions are also different from that of the net stoichiometries. It follows that conclusions drawn on the basis of experimentally determined tracer fluxes should be viewed with some caution. Specifically, a measured influx stoichiometry ligand/ATP (in the ATPase case) of higher than 1:1 does not necessarily imply the existence of more than one site for either ligand on the enzyme.

scholarly journals CO<sub>2</sub> flux history 1982–2001 inferred from atmospheric data using a global inversion of atmospheric transport

2003 ◽  
Vol 3 (3) ◽  
pp. 2575-2659 ◽  
Author(s):  
C. Rödenbeck ◽  
S. Houweling ◽  
M. Gloor ◽  
M. Heimann
Keyword(s):  
El Niño ◽  
Transport Model ◽  
El Nino ◽  
La Niña ◽  
Global Ocean ◽  
Carbon Uptake ◽  
Interannual Variations ◽  
Co2 Fluxes ◽  
Tracer Transport ◽  
La Nina

Abstract. Based on about 20 years of NOAA/CMDL's atmospheric CO2 concentration data and a global atmospheric tracer transport model, we estimate interannual variations and spatial patterns of surface CO2 fluxes in the period 01/1982–12/2000, by using a time-dependent Bayesian inversion technique. To increase the reliability of the estimated temporal features, particular care is exerted towards the selection of data records that are homogeneous in time. Fluxes are estimated on a grid-scale resolution (~8° latitude×10° longitude), constrained by a-priori spatial correlations, and then integrated over different sets of regions. The transport model is driven by interannually varying re-analysed meteorological fields. We make consistent use of unsmoothed measurements. In agreement with previous studies, land fluxes are estimated to be the main driver of interannual variations in the global CO2 fluxes, with the pace predominantly being set by the El Niño/La Niña contrast. An exception is a 2–3 year period of increased sink of atmospheric carbon after Mt. Pinatubo's volcanic eruption in 1991. The largest differences in fluxes between El Niño and La Niña are found in the tropical land regions, the main share being due to the Amazon basin. The flux variations for the Post-Pinatubo period, the 1997/1998 El Niño, and the 1999 La Niña events are exploited to investigate relations between CO2 fluxes and climate forcing. A rough comparison points to anomalies in precipitation as a prominent climate factor for short-term variability of tropical land fluxes, both through their role on NPP and through promoting fire in case of droughts. Some large flux anomalies seem to be directly related to large biomass burning events recorded by satellite observation. Global ocean carbon uptake shows a trend similar to the one expected if ocean uptake scales proportional to the anthropogenic atmospheric perturbation. In contrast to temporal variations, the longterm spatial flux distribution can be inferred with lesser robustness only. The tentative pattern estimated by the present inversion exhibits a northern hemisphere land sink on the order of 0.4 PgC/yr (for 01/1996–12/1999, non-fossil fuel carbon only) that is mainly confined to North America. Southern hemisphere land regions are carbon neutral, while the tropical land regions are taking up carbon (e.g., at a rate of 0.8 PgC/yr during 01/1996–2/1999). Ocean fluxes show larger uptake in the Northern mid to high latitudes than in the Southern mid latitude regions, in contrast to the estimates by Takahashi et al. (1999) based on in-situ measurements. On a regional basis, results that differ the most from previous estimates are large carbon uptake of 1 to 1.5 PgC/yr by the Southern temperate Pacific ocean region, weak outgassing from the Southern ocean, and a carbon source from eastern Europe.

scholarly journals Measuring and modelling the isotopic composition of soil respiration: insights from a grassland tracer experiment

2011 ◽  
Vol 8 (5) ◽  
pp. 1333-1350 ◽  
Author(s):  
U. Gamnitzer ◽  
A. B. Moyes ◽  
D. R. Bowling ◽  
H. Schnyder
Keyword(s):  
Steady State ◽  
Isotopic Composition ◽  
Transport Model ◽  
Tracer Experiment ◽  
Atmospheric Co2 ◽  
Soil Co2 ◽  
Soil Air ◽  
Co2 Transport ◽  
Atmosphere System

Abstract. The carbon isotopic composition (δ13C) of CO2 efflux (δ13Cefflux) from soil is generally interpreted to represent the actual isotopic composition of the respiratory source (δ13CRs). However, soils contain a large CO2 pool in air-filled pores. This pool receives CO2 from belowground respiration and exchanges CO2 with the atmosphere (via diffusion and advection) and the soil liquid phase (via dissolution). Natural or artificial modification of δ13C of atmospheric CO2 (δ13Catm) or δ13CRs causes isotopic disequilibria in the soil-atmosphere system. Such disequilibria generate divergence of δ13Cefflux from δ13CRs (termed "disequilibrium effect"). Here, we use a soil CO2 transport model and data from a 13CO2/12CO2 tracer experiment to quantify the disequilibrium between δ13Cefflux and δ13CRs in ecosystem respiration. The model accounted for diffusion of CO2 in soil air, advection of soil air, dissolution of CO2 in soil water, and belowground and aboveground respiration of both 12CO2 and 13CO2 isotopologues. The tracer data were obtained in a grassland ecosystem exposed to a δ13Catm of −46.9 ‰ during daytime for 2 weeks. Nighttime δ13Cefflux from the ecosystem was estimated with three independent methods: a laboratory-based cuvette system, in-situ steady-state open chambers, and in-situ closed chambers. Earlier work has shown that the δ13Cefflux measurements of the laboratory-based and steady-state systems were consistent, and likely reflected δ13CRs. Conversely, the δ13Cefflux measured using the closed chamber technique differed from these by −11.2 ‰. Most of this disequilibrium effect (9.5 ‰) was predicted by the CO2 transport model. Isotopic disequilibria in the soil-chamber system were introduced by changing δ13Catm in the chamber headspace at the onset of the measurements. When dissolution was excluded, the simulated disequilibrium effect was only 3.6 ‰. Dissolution delayed the isotopic equilibration between soil CO2 and the atmosphere, as the storage capacity for labelled CO2 in water-filled soil pores was 18 times that of soil air. These mechanisms are potentially relevant for many studies of δ13CRs in soils and ecosystems, including FACE experiments and chamber studies in natural conditions. Isotopic disequilibria in the soil-atmosphere system may result from temporal variation in δ13CRs or diurnal changes in the mole fraction and δ13C of atmospheric CO2. Dissolution effects are most important under alkaline conditions.

scholarly journals Multi-grid algorithm for passive tracer transport in the NEMO ocean circulation model: a case study with the NEMO OGCM (version 3.6)

2020 ◽  
Vol 13 (11) ◽  
pp. 5465-5483
Author(s):  
Clément Bricaud ◽  
Julien Le Sommer ◽  
Gurvan Madec ◽  
Christophe Calone ◽  
Julie Deshayes ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Ocean Circulation ◽  
Circulation Model ◽  
Ocean Model ◽  
Ocean Dynamics ◽  
Global Ocean ◽  
Passive Tracer ◽  
Tracer Transport ◽  
Ocean Circulation Model ◽  
Grid Algorithm

Abstract. Ocean biogeochemical models are key tools for both scientific and operational applications. Nevertheless the cost of these models is often expensive because of the large number of biogeochemical tracers. This has motivated the development of multi-grid approaches where ocean dynamics and tracer transport are computed on grids of different spatial resolution. However, existing multi-grid approaches to tracer transport in ocean modelling do not allow the computation of ocean dynamics and tracer transport simultaneously. This paper describes a new multi-grid approach developed for accelerating the computation of passive tracer transport in the Nucleus for European Modelling of the Ocean (NEMO) ocean circulation model. In practice, passive tracer transport is computed at runtime on a grid with coarser spatial resolution than the hydrodynamics, which reduces the CPU cost of computing the evolution of tracers. We describe the multi-grid algorithm, its practical implementation in the NEMO ocean model, and discuss its performance on the basis of a series of sensitivity experiments with global ocean model configurations. Our experiments confirm that the spatial resolution of hydrodynamical fields can be coarsened by a factor of 3 in both horizontal directions without significantly affecting the resolved passive tracer fields. Overall, the proposed algorithm yields a reduction by a factor of 7 of the overhead associated with running a full biogeochemical model like PISCES (with 24 passive tracers). Propositions for further reducing this cost without affecting the resolved solution are discussed.

scholarly journals Differentiation of Glucose Transport in Human Brain Gray and White Matter

2001 ◽  
Vol 21 (5) ◽  
pp. 483-492 ◽  
Author(s):  
Robin A. de Graaf ◽  
Jullie W. Pan ◽  
Frank Telang ◽  
Jing-Huei Lee ◽  
Peter Brown ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Steady State ◽  
White Matter ◽  
Magnetic Resonance ◽  
Human Brain ◽  
Glucose Transport ◽  
Gray Matter ◽  
Transport Model ◽  
Transport Activity ◽  
Brain Glucose

Localized 1H nuclear magnetic resonance spectroscopy has been applied to determine human brain gray matter and white matter glucose transport kinetics by measuring the steady-state glucose concentration under normoglycemia and two levels of hyperglycemia. Nuclear magnetic resonance spectroscopic measurements were simultaneously performed on three 12-mL volumes, containing predominantly gray or white matter. The exact volume compositions were determined from quantitative T1 relaxation magnetic resonance images. The absolute brain glucose concentration as a function of the plasma glucose level was fitted with two kinetic transport models, based on standard (irreversible) or reversible Michaelis-Menten kinetics. The steady-state brain glucose levels were similar for cerebral gray and white matter, although the white matter levels were consistently 15% to 20% higher. The ratio of the maximum glucose transport rate, Vmax, to the cerebral metabolic utilization rate of glucose, CMRGlc, was 3.2 ± 0.10 and 3.9 ± 0.15 for gray matter and white matter using the standard transport model and 1.8 ± 0.10 and 2.2 ± 0.12 for gray matter and white matter using the reversible transport model. The Michaelis-Menten constant Km was 6.2 ± 0.85 and 7.3 ± 1.1 mmol/L for gray matter and white matter in the standard model and 1.1 ± 0.66 and 1.7 ± 0.88 mmol/L in the reversible model. Taking into account the threefold lower rate of CMRGlc in white matter, this finding suggests that blood–brain barrier glucose transport activity is lower by a similar amount in white matter. The regulation of glucose transport activity at the blood–brain barrier may be an important mechanism for maintaining glucose homeostasis throughout the cerebral cortex.

The Fingerprint of Indian Ocean Rain and River Water in Salinity and Circulation

2021 ◽  
Author(s):  
Vinu Valsala
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Climate Models ◽  
Transport Model ◽  
Tropical Indian Ocean ◽  
Quasi Equilibrium ◽  
Tracer Transport ◽  
Tropical Ocean ◽  
Cumulative Impact ◽  
Circulation Anomalies

Abstract Per unit area of the tropical Indian Ocean receives the world’s largest tropical ocean rain and river runoff (RRW). The 3-dimensional spreading of RRW entering the tropical Indian Ocean and associated salinity and circulation anomalies are explored for 60 years using ocean reanalysis data tailored to a tracer transport model. Over 60 years, the cumulative impact of RRW entering the tropical Indian Ocean is to freshen the Indian Ocean basin as large as 2-0.1 p.s.u from the surface to 500m. The RRW has propagated to a vast extent of the Atlantic and Pacific Oceans via general circulation pathways. A quasi-equilibrium model of accumulation of RRW over the tropical Indian Ocean suggests that it induces clockwise geostrophic currents from the Bay of Bengal to the Arabian Sea over 0-500m depths, a net inter-basin transport tendency of 0.8±0.14 Sv year-1. The study implies that coupled climate models with apparent precipitation biases may miscalculate such salinity and circulation anomalies due to RRW and aggravating biases in simulated climate dynamics.

scholarly journals Liquid Brine in Ice Shelves

1975 ◽  
Vol 14 (70) ◽  
pp. 125-136 ◽  
Author(s):  
R. H. Thomas
Keyword(s):  
Steady State ◽  
Heat Transport ◽  
Thermal Equilibrium ◽  
Transport Model ◽  
Percolation Model ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Brine Layer ◽  
Good Agreement

Holes drilled into thin areas of the Brunt Ice Shelf encounter a layer of liquid brine less than 1 m thick approximately at sea-level. Assuming the brine to be moving horizontally, analysis of its effects on thermal equilibrium gives an estimate of steady-state annual brine flow that is in good agreement with the value deduced from a percolation model. The effect of firn density on percolation rates is such that the slope of an active brine layer increases rapidly as ice thickness increases. However, the heat transport model predicts that brine layers are unlikely to be active in both very thick and very thin ice shelves.

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