Sunlight and tidal interaction as a mechanism of carbon transport in an ice-covered region: Results of a coupled ice–ocean ecosystem model

In order to clarify the mechanism of carbon transport in an ice-covered ecosystem in Lake Saroma (44^°N${44}^{°}\mathrm{N}$, 143^°E${143}^{°}\mathrm{E}$, Hokkaido, Japan), a three-dimensional numerical calculation using a coupled ice–ocean ecosystem model was conducted. This model comprises an ocean ecosystem model, an ice ecosystem model, and equations for the coupling between ice and ocean. Comparisons of calculated results with observational data confirm that the calculation well reproduced the in situ phenomena with respect to tides, tidal currents, concentrations of POC and chlorophyll a in ice and in water, and sinking fluxes beneath the ice. The analysis of the organic carbon budget based on the calculation reveals that tide-induced transport, the enhancement of biological production in a pelagic system, and the physical release of organic matter from ice associated with ice-melting are important factors affecting the carbon transport during the ice-melting season. The carbon transport has a one-day time cycle. This is because principal driving forces are sunlight, and diurnal tides. The described mechanism of “sunlight and tidal pumping” is one of the most important features of carbon transport in a coupled ice–water ecosystem.     

The relationship between reference canopy conductance and simplified hydraulic architecture

Terrestrial ecosystems are dominated by vascular plants that form a mosaic of hydraulic conduits to water movement from the soil to the atmosphere. Together with canopy leaf area, canopy stomatal conductance regulates plant water use and thereby photosynthesis and growth. Although stomatal conductance is coordinated with plant hydraulic conductance, governing relationships across species has not yet been formulated at a practical level that can be employed in large-scale models. Here, combinations of published conductance measurements obtained with several methodologies across boreal to tropical climates were used to explore relationships between canopy conductance rates and hydraulic constraints. A parsimonious hydraulic model requiring sapwood-to-leaf area ratio and canopy height generated acceptable agreement with measurements across a range of biomes (r²=0.75)$(r^2=0.75)$. The results suggest that, at long time scales, the functional convergence among ecosystems in the relationship between water-use and hydraulic architecture eclipses inter-specific variation in physiology and anatomy of the transport system. Prognostic applicability of this model requires independent knowledge of sapwood-to-leaf area. In this study, we did not find a strong relationship between sapwood-to-leaf area and physical or climatic variables that are readily determinable at coarse scales, though the results suggest that climate may have a mediating influence on the relationship between sapwood-to-leaf area and height. Within temperate forests, canopy height alone explained a large amount of the variance in reference canopy conductance (r²=0.68)$(r^2=0.68)$ and this relationship may be more immediately applicable in the terrestrial ecosystem models.     

A new epsilon-dominance hierarchical Bayesian optimization algorithm for large multiobjective monitoring network design problems

This study focuses on the development of a next generation multiobjective evolutionary algorithm (MOEA) that can learn and exploit complex interdependencies and/or correlations between decision variables in monitoring design applications to provide more robust performance for large problems (defined in terms of both the number of objectives and decision variables). The proposed MOEA is termed the epsilon-dominance hierarchical Bayesian optimization algorithm (ε$\epsilon$-hBOA), which is representative of a new class of probabilistic model building evolutionary algorithms. The ε$\epsilon$-hBOA has been tested relative to a top-performing traditional MOEA, the epsilon-dominance nondominated sorted genetic algorithm II (ε$\epsilon$-NSGAII) for solving a four-objective LTM design problem. A comprehensive performance assessment of the ε$\epsilon$-NSGAII and various configurations of the ε$\epsilon$-hBOA have been performed for both a 25 well LTM design test case (representing a relatively small problem with over 33 million possible designs), and a 58 point LTM design test case (with over 2.88×10¹⁷$2.88\times {10}^{17}$ possible designs). The results from this comparison indicate that the model building capability of the ε$\epsilon$-hBOA greatly enhances its performance relative to the ε$\epsilon$-NSGAII, especially for large monitoring design problems. This work also indicates that decision variable interdependencies appear to have a significant impact on the overall mathematical difficulty of the monitoring network design problem.     

Computation of oceanic vertical stability (Brunt-Väisäläfrequency) with an improved density equation

Vertical stability of a water column can be computed from the formula: $N^2=g^2\left[\frac{d\rho }{dP}?\frac{1}{c^2}\right]$ where ρ is density, P is pressure, g is gravity, and c is sound speed.Because Ekman's density equation is not consistent with Wilson's sound speed equation, large errors are introduced by combining these two equations to calculate the vertical stability. However, this difficulty can be overcome with the Wang and Millero density equation derived consistently from Wilson's sound speed equation. In addition to its simplicity, the computation of vertical stability from the above formula using Wilson's sound speed equation and Wand and Millero's density equation can be shown to generally give the most accurate results.     

Permeability of 3D discontinuity networks: New tensors from boundary-conditioned homogenisation

Two equivalent permeability tensors are defined for 3D heterogeneous media, K^p${\mathbf{K}}^p$ and K^q${\mathbf{K}}^q$, valid respectively for linear pressure and constant flux conditions at the block boundary. Both tensors are symmetric and positive-definite and the second one produces lower magnitude of directional permeability than the first one. These tensors only depends upon the internal block structure and 3D distribution of the local permeability values. On this basis, we develop first a straightforward method for evaluating the coefficients of the 2D tensor for the problem of flow through fracture traces in a cross-section, subject to linear pressure conditions. A quartzite rock mass is used as an example to illustrate this method. Then, an approximated method is proposed to build up the 3D permeability tensor of the fractured block from the ellipses within cross-sections in varied orientations.