Warren G. Lee

The Effect of Terrestrial Photosynthesis Down Regulation on the Twentieth-Century Carbon Budget Simulated with the CCCma Earth System Model

Abstract The simulation of atmospheric–land–ocean CO2 exchange for the 1850–2000 period offers the possibility of testing and calibrating the carbon budget in earth system models by comparing the simulated changes in atmospheric CO2 concentration and in land and ocean uptake with observation-based information. In particular, some of the uncertainties associated with the treatment of land use change (LUC) and the role of down regulation in affecting the strength of CO2 fertilization for terrestrial photosynthesis are assessed using the Canadian Centre for Climate Modelling and Analysis Earth System Model (CanESM1). LUC emissions may be specified as an external source of CO2 or calculated interactively based on estimated changes in crop area. The evidence for photosynthetic down regulation is reviewed and an empirically based representation is implemented and tested in the model. Four fully coupled simulations are performed: with and without terrestrial photosynthesis down regulation and with interactively ...

The Combined Effect of Tidally and Eddy-Driven Diapycnal Mixing on the Large-Scale Ocean Circulation

Several recent studies have shown that ocean western boundaries are the primary regions of eddy energy dissipation.Globally,theeddyenergysinkshavebeenestimatedtointegratetoabout0.2TW.Thisisasizable fraction of the tidal energy dissipation in the deep oceanic interior, estimated at about 1.0 TW and contributing to diapycnal mixing. The authors conduct sensitivity experiments with an ocean general circulation model assuming that the eddy energy is scattered into high-wavenumber vertical modes, resulting in energy dissipation and locally enhanced diapycnal mixing. When only the tidal energy dissipation maintains diapycnal mixing, the overturning circulation, and stratification in the deep ocean are too weak. With the addition of the eddy dissipation, the deep-ocean thermal structure becomes closer to that observed and the overturning circulation and stratification in the abyss become stronger. Furthermore, the mixing associated with the eddy dissipation can, on its own, drive a relatively strong overturning. The stratification and overturning in the deep ocean are sensitive to the vertical structure of diapycnal mixing. When most of this energy dissipates within 300 m above the bottom, the abyssal overturning and stratification are too weak. Allowing forthedissipationtopenetratehigherinthewatercolumn,suchassuggestedbyrecentobservations,resultsin stronger stratification and meridional circulation. Zonal circulation is also affected. In particular, the Drake Passage transport becomes closer to its observational estimates with the increase in the vertical scale for turbulence above topography. Consistent with some theoretical models, the Drake Passage transport increases with the increase in the mean upper-ocean diffusivity.

Progress and Challenges in Biogeochemical Modeling of the Pacific Arctic Region

At this early stage of modeling marine ecosystems and biogeochemical cycles in the Pacific Arctic Region (PAR), numerous challenges lie ahead. Observational data used for model development and validation remain sparse, especially across seasons and under a variety of environmental conditions. Field data are becoming more available, but at the same time PAR is rapidly changing. Biogeochemical models can provide the means to capture some of these changes. This study introduces and synthesizes ecosystem modeling in PAR by discussing differences in complexity and application of one-dimensional, regional, and global earth system models. Topics include the general structure of ecosystem models and specifics of the combined benthic, pelagic, and ice PAR ecosystems, the importance of model validation, model responses to climate influences (e.g. diminishing sea ice, ocean acidification), and the impacts of circulation and stratification changes on PAR ecosystems and biogeochemical cycling. Examples of modeling studies that help place the region within the context of the Pan-Arctic System are also discussed. We synthesize past and ongoing PAR biogeochemical modeling efforts and briefly touch on decision makers’ use of ecosystem models and on necessary future developments.

Subduction and Transport in the Indian and Pacific Oceans in a 2 × CO2 Climate

Abstract Subduction, water mass transformation, and transport rates in the Indo-Pacific Ocean are diagnosed in a recent version of the Canadian Centre for Climate Modelling and Analysis coupled model. It is found that the subduction across the base of the winter mixed layer is dominated by the lateral transfer, particularly within the relatively dense water classes corresponding to the densest mode and intermediate waters. However, within lighter densities, including those characterizing the lighter varieties of mode waters, the vertical transfer has a strong positive input to the net subduction. The upper-ocean volume transports across 30°N and 32°S are largest within the density classes that correspond to mode waters. In the North Pacific, the buoyancy flux converts the near-surface waters mostly to denser water classes, whereas in the Southern Ocean the surface waters are transformed both to lighter and denser water classes, depending on the density. In response to a doubling of CO2, the subduction, tr...