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This modelling study shows that chemical weathering of continental surfaces—which removes carbon dioxide from the atmosphere—is highly sensitive to a carbon dioxide doubling for the Mackenzie River Basin, the most important Arctic watershed. The findings highlight the potential role of chemical weathering processes in mitigating global warming. According to future anthropogenic emission scenarios, the atmospheric CO 2 concentration may double before the end of the twenty-first century 1 . This increase is predicted to result in a global warming of more than 6 °C in the worst case 1 . The global temperature increase will promote changes in the hydrologic cycle through redistributions of rainfall patterns and continental vegetation cover 1 , 2 . All of these changes will impact the chemical weathering of continental rocks. Long considered an inert CO 2 consumption flux at the century timescale, recent works have demonstrated its potential high sensitivity to the ongoing climate and land-use changes 3 , 4 . Here we show that the CO 2 consumption flux related to weathering processes increases by more than 50% for an atmospheric CO 2 doubling for one of the most important Arctic watersheds: the Mackenzie River Basin. This result has been obtained using a process-based model of the chemical weathering of continental surfaces forced by models describing the atmospheric general circulation and the dynamic of the vegetation 5 , 6 under increased atmospheric CO 2 . Our study stresses the potential role that weathering may play in the evolution of the global carbon cycle over the next centuries.

The recently developed Norwegian Earth System Model (NorESM) is employed for simulations contributing to the CMIP5 (Coupled Model Intercomparison Project phase 5) experiments and the fifth assessment report of the Intergovernmental Panel on Climate Change (IPCC-AR5). In this manuscript, we focus on evaluating the ocean and land carbon cycle components of the NorESM, based on the preindustrial control and historical simulations. Many of the observed large scale ocean biogeochemical features are reproduced satisfactorily by the NorESM. When compared to the climatological estimates from the World Ocean Atlas (WOA), the model simulated temperature, salinity, oxygen, and phosphate distributions agree reasonably well in both the surface layer and deep water structure. However, the model simulates a relatively strong overturning circulation strength that leads to noticeable model-data bias, especially within the North Atlantic Deep Water (NADW). This strong overturning circulation slightly distorts the structure of the biogeochemical tracers at depth. Advancements in simulating the oceanic mixed layer depth with respect to the previous generation model particularly improve the surface tracer distribution as well as the upper ocean biogeochemical processes, particularly in the Southern Ocean. Consequently, near-surface ocean processes such as biological production and air-sea gas exchange, are in good agreement with climatological observations. The NorESM adopts the same terrestrial model as the Community Earth System Model (CESM1). It reproduces the general pattern of land-vegetation gross primary productivity (GPP) when compared to the observationally based values derived from the FLUXNET network of eddy covariance towers. While the model simulates well the vegetation carbon pool, the soil carbon pool is smaller by a factor of three relative to the observational based estimates. The simulated annual mean terrestrial GPP and total respiration are slightly larger than observed, but the difference between the global GPP and respiration is comparable. Model-data bias in GPP is mainly simulated in the tropics (overestimation) and in high latitudes (underestimation). Within the NorESM framework, both the ocean and terrestrial carbon cycle models simulate a steady increase in carbon uptake from the preindustrial period to the present-day. The land carbon uptake is noticeably smaller than the observations, which is attributed to the strong nitrogen limitation formulated by the land model.

In this contribution, a reactive‐transport model describing weathering in soil profiles and at the watershed scale is coupled to a dynamic global vegetation model to calculate the dissolved load of continental waters on a 0.5° latitude × 0.5° longitude grid. The so‐called Biosphere‐Weathering at the Catchment Scale (B‐WITCH) model is applied to the Orinoco watershed (South America). We show that B‐WITCH is able to reproduce the main cation composition of the surface waters over the watershed. Sensitivity tests demonstrate that clay mineral reactivities are key factors controlling the calculated discharge of dissolved species. More specifically, our simulations show that the dissolution and precipitation rates of clay minerals in the weathering profiles are strongly intertwined, and that this coupling must be accurately described when modeling the weathering fluxes at the continental scale. A second set of sensitivity tests show that, for the tropical environment, land plants control the total base cation discharge through their impact on the soil hydrology, rather than through enhanced soil CO2 pressures. Indeed, the complete removal of the continental vegetation leads to an increase in the dissolved fluxes to the ocean by 80% because of the collapse in the evapotranspiration, resulting in a more efficient drainage of the weathering profiles. On the other hand, neglecting the root respiration and setting the soil CO2 pressure to the atmospheric level forces the total base cation discharge to decrease by only 20%.

Anthropogenic sources are widely accepted as the dominant cause for the increase in atmospheric CO2 concentrations since the beginning of the industrial revolution. Here we use the B‐WITCH model to quantify the impact of increased CO2 concentrations on CO2 consumption by weathering of continental surfaces. B‐WITCH couples a dynamic biogeochemistry model (LPJ) and a process‐based numerical model of continental weathering (WITCH). It allows simultaneous calculations of the different components of continental weathering fluxes, terrestrial vegetation dynamics, and carbon and water fluxes. The CO2 consumption rates are estimated at four different atmospheric CO2 concentrations, from 280 up to 1120 ppmv, for 22 sites characterized by silicate lithologies (basalt, granite, or sandstones). The sensitivity to atmospheric CO2 variations is explored, while temperature and rainfall are held constant. First, we show that under 355 ppmv of atmospheric CO2, B‐WITCH is able to reproduce the global pattern of weathering rates as a function of annual runoff, mean annual temperature, or latitude for silicate lithologies. When atmospheric CO2 increases, evapotranspiration generally decreases due to progressive stomatal closure, and the soil CO2 pressure increases due to enhanced biospheric productivity. As a result, vertical drainage and soil acidity increase, promoting CO2 consumption by mineral weathering. We calculate an increase of about 3% of the CO2 consumption through silicate weathering (mol ha−1 yr−1) for 100 ppmv rise in CO2. Importantly, the sensitivity of the weathering system to the CO2 rise is not uniform and heavily depends on the climatic, lithologic, pedologic, and biospheric settings.

During glacial periods, dust deposition rates and inferred atmospheric concentrations were globally much higher than present. According to recent model results, the large enhancement of atmospheric dust content at the last glacial maximum (LGM) can be explained only if increases in the potential dust source areas are taken into account. Such increases are to be expected, due to effects of low precipitation and low atmospheric (CO^sub 2^) on plant growth. Here the modelled three-dimensional dust fields from Mahowald et al. and modelled seasonally varying surface-albedo fields derived in a parallel manner, are used to quantify the mean radiative forcing due to modern (non-anthropogenic) and LGM dust. The effect of mineralogical provenance on the radiative properties of the dust is taken into account, as is the range of optical properties associated with uncertainties about the mixing state of the dust particles. The high-latitude (poleward of 45°) mean change in forcing (LGM minus modern) is estimated to be small (-0.9 to +0.2 W m^sup -2^), especially when compared to nearly -20 W m^sup -2^ due to reflection from the extended ice sheets. Although the net effect of dust over ice sheets is a positive forcing (warming), much of the simulated high-latitude dust was not over the ice sheets, but over unglaciated regions close to the expanded dust source region in central Asia. In the tropics the change in forcing is estimated to be overall negative, and of similarly large magnitude (-2.2 to -3.2 W m^sup -2^) to the radiative cooling effect of low atmospheric (CO^sub 2^). Thus, the largest long-term climatic effect of the LGM dust is likely to have been a cooling of the tropics. Low tropical sea-surface temperatures, low atmospheric (CO^sub 2^) and high atmospheric dust loading may be mutually reinforcing due to multiple positive feedbacks, including the negative radiative forcing effect of dust.[PUBLICATION ABSTRACT]

Background:In patients with ischaemic cardiomyopathy and viable myocardium, left ventricular ejection fraction (LVEF) does not always improve after revascularisation. Whether this may affect prognosis is unclear.Objective:To evaluate the prognosis of viable patients with and without improvement of LVEF after coronary revascularisation.Methods:Before revascularisation, radionuclide ventriculography (RNV) and dobutamine stress echocardiography were performed to assess LVEF and myocardial viability, respectively. Nine to 12 months after revascularisation, LVEF improvement was assessed by RNV. Patients were divided into three groups: group 1, viable patients with LVEF improvement (n = 27); group 2, viable patients without LVEF improvement (n = 15), group 3, non-viable patients (n = 48). Cardiac events were evaluated during a 4-year follow-up.Results:After revascularisation, the mean (SD) LVEF improved from 32 (9)% to 42 (10)% in group 1, but did not change significantly in group 2 and in group 3, p<0.001 by analysis of variance (ANOVA). Heart failure symptoms improved in both groups 1 (mean (SD) NYHA class from 3.1 (0.9) to 1.7 (0.7)) and 2 (from 3.2 (0.7) to 1.7 (0.9)), but not in group 3 (from 2.8 (1.0) to 2.7 (0.5)), p<0.001 by ANOVA. During follow-up, the cardiac event rate was low (4%) in group 1, intermediate (21%) in group 2 and high (33%) in group 3 (p = 0.01).Conclusion:The best prognosis after revascularisation may be expected in those viable patients whose LVEF improves. Conversely, viable patients without functional improvement have an intermediate prognosis.

Prognostic Value of Dobutamine Stress Echocardiography in Patients With Diabetes Fabiola B. Sozzi , MD, PHD 1 , Abdou Elhendy , MD, PHD 1 , Jos R.T.C. Roelandt , MD, PHD 1 , Ron T. van Domburg , PhD 1 , Arend F.L. Schinkel , MD 1 , Eleni C. Vourvouri , MD 1 , Jeroen J. Bax , MD, PHD 1 , Johan De Sutter , MD, PHD 1 , Alberico Borghetti , MD 2 and Don Poldermans , MD, PHD 1 1 Erasmus Medical Centre, Rotterdam, the Netherlands 2 Department of Internal Medicine, Parma University, Parma, Italy Abstract OBJECTIVE —The aim of this study was to assess the incremental value of dobutamine stress echocardiography (DSE) for the risk stratification of diabetic patients who are unable to perform an adequate exercise stress test. Exercise capacity is frequently impaired in patients with diabetes. The role of pharmacologic stress echocardiography in the risk stratification of diabetic patients has not been well defined. RESEARCH DESIGN AND METHODS —We studied 396 diabetic patients (mean age 61 ± 11 years, 252 men [64%]) with limited exercise capacity who underwent DSE for evaluation of known or suspected coronary artery disease (CAD). End points were hard cardiac events (cardiac death and nonfatal myocardial infarction) and all causes of mortality. RESULTS —During a median follow-up of 3 years, 97 patients (24%) died (55 cardiac deaths), and 27 patients had nonfatal myocardial infarction. In an incremental multivariate analysis model, clinical predictors of hard cardiac events were history of congestive heart failure, previous myocardial infarction, hypercholesterolemia, and ejection fraction at rest. The percentage of ischemic segments was incremental to the clinical model in the prediction of hard cardiac events (χ 2 = 37 vs. 18, P < 0.05). Clinical predictors of all causes of mortality were history of congestive heart failure, age, hypercholesterolemia, and ejection fraction at rest. Wall motion score index at peak stress was incremental to the clinical model in the prediction of mortality (χ 2 = 52 vs. 43, P < 0.05). CONCLUSIONS —DSE provides incremental data for the prediction of mortality and hard cardiac events in patients with diabetes who are unable to perform an adequate exercise stress test. CAD, coronary artery disease DSE, dobutamine stress echocardiography LV, left ventricular Footnotes Address correspondence and reprint requests to Don Poldermans, MD, Thoraxcenter, BA 302, 3015 GD Rotterdam, The Netherlands. E-mail: poldermans{at}hlkd.azr.nl . Received for publication 4 December 2001 and accepted in revised form 9 September 2002. A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances. DIABETES CARE

The European and American guidelines state the need for echocardiography in patients with syncope. 50% of older adults with syncope present with a fall. Nonetheless, up to now no data have been published addressing echocardiographic abnormalities in older fallers. In order to determine the association between echocardiographic abnormalities and falls in older adults, we performed a prospective cohort study, in which 215 new consecutive referrals (age 77.4, SD 6.0) of a geriatric outpatient clinic of a Dutch university hospital were included. During the previous year, 139 had experienced a fall. At baseline, all patients underwent routine two-dimensional and Doppler echocardiography. Falls were recorded during a three-month follow-up. Multivariate adjustment for confounders was performed with a Cox proportional hazards model. 55 patients (26%) fell at least once during follow-up. The adjusted hazard ratio of a fall during follow-up was 1.35 (95% CI, 1.08-1.71) for pulmonary hypertension, 1.66 (95% CI, 1.01 to 2.89) for mitral regurgitation, 2.41 (95% CI, 1.32 to 4.37) for tricuspid regurgitation and 1.76 (95% CI, 1.03 to 3.01) for pulmonary regurgitation. For aortic regurgitation the risk of a fall was also increased, but non-significantly (hazard ratio, 1.57 [95% CI, 0.85 to 2.92]). Trend analysis of the severity of the different regurgitations showed a significant relationship for mitral, tricuspid and pulmonary valve regurgitation and pulmonary hypertension. Echo (Doppler) cardiography can be useful in order to identify risk indicators for falling. Presence of pulmonary hypertension or regurgitation of mitral, tricuspid or pulmonary valves was associated with a higher fall risk. Our study indicates that the diagnostic work-up for falls in older adults might be improved by adding an echo (Doppler) cardiogram in selected groups.

Objective: To determine the diagnostic potential of a hand carried cardiac ultrasound (HCU) device (OptiGo, Philips Medical Systems) in a cardiology outpatient clinic and to compare the HCU diagnosis with the clinical diagnosis and diagnosis with a full featured standard echocardiography (SE) system. Methods: 300 consecutive patients took part in the study. The HCU examination was performed by an experienced echocardiographer before patients visited the cardiologist. The echocardiographer noted whether the HCU device was able to confirm or reject the referral diagnosis, which abnormality was detected, and whether SE investigation was necessary. Physical examination by a cardiologist followed and thereafter, whenever required, a complete study with an SE was carried out. The HCU data were compared with the clinical diagnosis of the cardiologist and the SE diagnosis in a blinded manner. Results: The cardiologist referred 203 of 300 patients for an SE study and 13 patients for transoesophageal echocardiography. In 84 patients no further examination was considered necessary. HCU echocardiography was able to confirm or reject the suspected clinical diagnosis in 159 of 203 (78%) patients. In 44 of 203 (22%) patients SE Doppler was needed. Agreement between the HCU device and the SE system for the detection of major abnormalities was excellent (98%). The HCU device missed 4% of the major findings. Among the 84 patients not referred for an SE, the HCU device detected unsuspected major abnormalities missed with the physical examination in 14 (17%). Conclusion: Integration of an HCU device with the physical examination augments the yield of information.

Tissue Doppler imaging is a recently introduced echocardiographic tool for measuring myocardial velocities. In this article the physical principles and different myocardial velocity imaging modalities are discussed. Examples of practical applications and clinical use of this non-invasive imaging technique are provided.