Shifts in Plankton, Nutrient and Light Relationships in Small Tundra Lakes Caused by Localized Permafrost Thaw

Tundra lakes located in the Mackenzie Delta uplands, NWT, Canada, are increasingly being affected by permafrost thaw in the form of shoreline retrogressive thaw slumping. This form of thaw-induced disturbance is used as a surrogate indicator of landscape-related disturbance linked to regional climate warming. We compared 22 lakes, half affected by thaw slumping and half unaffected, to determine whether water column nutrient concentrations, light availability, and plankton biomass differed between these two lake types. Total phosphorus (TP), total dissolved nitrogen (TDN), dissolved organic carbon (DOC), and chlorophyll a concentrations were higher in unaffected lakes than in slump-affected lakes. Absorbance related to water colour of both UV and photosynthetically active radiation in the water column was also higher in unaffected lakes, but bacterioplankton abundance was not different between lake types. UV light absorbance was found to be the best predictor of pelagic chlorophyll a concentrations in unaffected lakes, whereas TDN (and to a lesser extent TP) were the best predictors of pelagic chlorophyll a in slump-affected lakes. These findings indicate that slumping arising from permafrost thaw produces a shift in tundra lake nutrient, light, and phytoplankton relationships. Given the projections of continued warming, this result has significant implications for the future biogeochemical and ecological states of Arctic tundra lakes.Les lacs de toundra situés dans les hautes terres du delta du Mackenzie, dans les Territoires du Nord-Ouest, au Canada, sont de plus en plus touchés par le dégel du pergélisol en ce sens qu’il y a glissement régressif du littoral dû au dégel. Cette forme de perturbation attribuable au dégel sert d’indicateur auxiliaire en matière de perturbation du paysage liée au réchauffement climatique de la région. Nous avons comparé 22 lacs, dont la moitié était touchée par le glissement dû au dégel et l’autre moitié ne l’était pas, afin de déterminer si les concentrations en nutriments des colonnes d’eau, la disponibilité lumineuse et la biomasse du plancton différaient entre ces deux types de lacs. Les concentrations de phosphore total (PT), d’azote dissous total (ADT), de carbone organique dissous (COD) et de chlorophylle a étaient plus élevées dans les lacs non touchés quand dans les lacs où il y avait glissement du littoral. L’absorbance liée à la couleur de l’eau du rayonnement actif photosynthétique et du rayonnement actif ultraviolet dans les colonnes d’eau était également plus élevée dans les lacs non touchés, mais l’abondance du bactérioplancton ne différait pas d’un type de lac à l’autre. On a déterminé que l’absorbance de lumière ultraviolette était le meilleur prédicteur de concentrations de chlorophylle a pélagique dans les lacs non touchés, tandis que l’ADT (et le PT, dans une moindre mesure) constituaient les meilleurs prédicteurs de chlorophylle a pélagique pour ce qui est des lacs faisant l’objet d’un glissement. Ces constatations indiquent que le glissement attribuable au dégel du pergélisol altère les relations qui existent entre les nutriments, la lumière et le phytoplancton des lacs de toundra. Compte tenu des projections à l’égard d’un réchauffement continuel, ce résultat revêt d’importantes incidences sur les états biogéochimiques et écologiques des lacs de la toundra arctique

Dynamic simulation of the THAI heavy oil recovery process

Toe-to-Heel Air Injection (THAI) is a variant of conventional In-Situ Combustion (ISC) that uses a horizontal production well to recover mobilised partially upgraded heavy oil. It has a number of advantages over other heavy oil recovery techniques such as high recovery potential. However, existing models are unable to predict the effect of the most important operational parameters, such as fuel availability and produced oxygen concentration, which will give rise to unsafe designs. Therefore, we have developed a new model that accurately predicts dynamic conditions in the reservoir and also is easily scalable to investigate different field scenarios. The model used a three component direct conversion cracking kinetics scheme, which does not depend on the stoichiometry of the products and, thus, reduces the extent of uncertainty in the simulation results as the number of unknowns is reduced. The oil production rate and cumulative oil produced were well predicted, with the latter deviating from the experimental value by only 4%. The improved ability of the model to emulate real process dynamics meant it also accurately predicted when the oxygen was first produced, thereby enabling a more accurate assessment to be made of when it would be safe to shut-in the process, prior to oxygen breakthrough occurring. The increasing trend in produced oxygen concentration following a step change in the injected oxygen rate by 33 % was closely replicated by the model. The new simulations have now elucidated the mechanism of oxygen production during the later stages of the experiment. The model has allowed limits to be placed on the air injection rates that ensure stability of operation. Unlike previous models, the new simulations have provided better quantitative prediction of fuel laydown, which is a key phenomenon that determines whether, or not, successful operation of the THAI process can be achieved. The new model has also shown that, for completely stable operation, the combustion zone must be restricted to the upper portion of the sand pack, which can be achieved by using higher producer back pressure

Exposing the human nude phenotype [4]

Peer reviewedSubmitted Versio

The Lambda-Lambda Interaction and ^{6}_{Lambda Lambda}He

An OBE potential model for the ^{1}S_0 S = -2 interaction is analyzed with emphasis on the role of coupling between the Lambda Lambda, N Xi, and Sigma Sigma channels. Singlet scalar exchange, an approximation to two-pion exchange, is significant in all channels; surprisingly, the one-pion exchange component is almost negligible. The size of the channel coupling as a function of the overall strength of the OBE model potential is examined. Implications of the analysis for the binding energy of ^{6}_{Lambda Lambda}He are considered; the new experimental datum may suggest a consistency between the extracted Lambda Lambda matrix element and the relation implied by SU(3) among OBE baryon-baryon interactions. \\Comment: 4 pages brief report to Physical Review

Novel Weak Decays in Doubly Strange Systems

The strangeness-changing ($\Delta S = 1$) weak baryon-baryon interaction is studied through the nonmesonic weak decay of double-$\Lambda$ hypernuclei. Besides the usual nucleon-induced decay $\Lambda N \to N N$ we discuss novel hyperon-induced decay modes $\Lambda \Lambda \to \Lambda N$ and $\Lambda \Lambda \to \Sigma N$. These reactions provide unique access to the exotic $\Lambda \Lambda$K and $\Lambda \Sigma$K vertices which place new constraints on Chiral Pertubation Theory ($\chi$PT) in the weak SU(3) sector. Within a meson-exchange framework, we use the pseudoscalar $\pi,\eta,K$ octet for the long-range part while parametrizing the short-range part through the vector mesons $\rho, \omega, K^*$. Realistic baryon-baryon forces for the $S=0,-1$ and -2 sectors account for the strong interaction in the initial and final states. For $^6_{\Lambda \Lambda}$He the new hyperon-induced decay modes account for up to 4% of the total nonmesonic decay rate. Predictions are made for all possible nonmesonic decay modes.Comment: 19 pages, 2 ps figures, 9 table

What Does Free Space Lambda-Lambda Interaction Predict for Lambda-Lambda Hypernuclei?

Data on Lambda-Lambda hypernuclei provide a unique method to learn details on the strangeness S =-2 sector of the baryon-baryon interaction. From the free space Bonn-Julich potentials, determined from data on baryon-baryon scattering in the S=0,-1 channels, we construct an interaction in the S =-2 sector to describe the experimentally known Lambda-Lambda hypernuclei. After including short--range (Jastrow) and RPA correlations, we find masses for these Lambda-Lambda hypernuclei in a reasonable agreement with data, taking into account theoretical and experimental uncertainties. Thus, we provide a natural extension, at low energies, of the Bonn-Julich OBE potentials to the S =-2 channel.Comment: 4 pages, 2 figures, revtex4 style. Minor changes in conclusions. References updated. Accepted in Phys. Rev. Let

The H-Dibaryon and the Hard Core

The H dibaryon, a single, triply magic bag containing two up, two down and two strange quarks, has long been sought after in a variety of experiments. Its creation has been attempted in $K^-$, proton and most recently in relativistic heavy ion induced reactions. We concentrate on the latter, but our conclusions are more generally applicable. The two baryons coalescing to form the single dibaryon, likely $\Lambda \Lambda$ in the case of heavy ions, must penetrate the short range repulsive barrier which is expected to exist between them. We find that this barrier can profoundly affect the probability of producing the H state, should it actually exist.Comment: 9 pages including 4 figure

Warm strange hadronic matter in an effective model with a weak Y-Y interaction

An effective model is used to study the equation of state of warm strange hadronic matter with nucleons, Lambda-hyperons, Xi-hyperons, sigmastar and phi. In the calculation, a newest weak Y-Y interaction deduced from the recent observation of a He double hypernucleus is adopted. Employing this effective model, the results with strong Y-Y interaction and weak Y-Y interaction are compared.Comment: 9 pages, 9 figure