Local Energetic Constraints on Walker Circulation Strength

The weakening of tropical overturning circulations is a robust response to global warming in climate models and observations. However, there remain open questions on the causes of this change and the extent to which this weakening affects individual circulation features such as the Walker circulation. The study presents idealized GCM simulations of a Walker circulation forced by prescribed ocean heat flux convergence in a slab ocean, where the longwave opacity of the atmosphere is varied to simulate a wide range of climates. The weakening of the Walker circulation with warming results from an increase in gross moist stability (GMS), a measure of the tropospheric moist static energy (MSE) stratification, which provides an effective static stability for tropical circulations. Baroclinic mode theory is used to determine changes in GMS in terms of the tropical-mean profiles of temperature and MSE. The GMS increases with warming, owing primarily to the rise in tropopause height, decreasing the sensitivity of the Walker circulation to zonally anomalous net energy input. In the absence of large changes in net energy input, this results in a rapid weakening of the Walker circulation with global warming

Constraining the date of a seasonally ice-free Arctic using a simple model

State-of-the-art climate models simulate a large spread in the projected decline of Arctic sea-ice area (SIA) over the 21st century. Here we diagnose causes of this intermodel spread using a model that approximates future SIA based on present SIA and the sensitivity of SIA to Arctic temperatures. This model accounts for 70-95% of the intermodel variance, with the majority of the spread arising from present-day biases. The remaining spread arises from model differences in Arctic warming, with some contribution from the local sea-ice sensitivity. Using observations to constrain the projections moves the probability of an ice-free Arctic forward by 10-35 years. Under a high-emissions scenario, an ice-free Arctic will likely (66% probability) occur in September around 2046 and from July-October around 2059. Under a medium-emissions scenario, this date occurs around 2051 in September and 2080 from July-October. These observation-based constraints imply ice-free Arctic summers are approaching faster than previously thought

Is the surface salinity difference between the Atlantic and Indo–Pacific a signature of the Atlantic Meridional Overturning Circulation?

The high Atlantic surface salinity has sometimes been interpreted as a signature of the Atlantic Meridional Overturning Circulation and an associated salt advection feedback. Here, the role of oceanic and atmospheric processes for creating the surface salinity difference between the Atlantic and Indo–Pacific is examined using observations and a conceptual model. In each basin, zonally averaged data are represented in diagrams relating net evaporation (E ̃) and surface salinity (S). The data-pair curves in the E ̃–S plane share common features in both basins. However, the slopes of the curves are generally smaller in the Atlantic than in the Indo–Pacific, indicating a weaker sensitivity of the Atlantic surface salinity to net evaporation variations. To interpret these observations, a conceptual advective-diffusive model of the upper-ocean salinity is constructed. Notably, the E ̃–S relations can be qualitatively reproduced with only meridional diffusive salt transport. In this limit, the inter-basin difference in salinity is caused by the spatial structure of net evaporation, which in the Indo–Pacific oceans contains lower meridional wavenumbers that are weakly damped by the diffusive transport. The observed Atlantic E ̃–S relationship at the surface reveals no clear influence of northward advection associated with the meridional overturning circulation; however a signature of northward advection emerges in the relationship when the salinity is vertically averaged over the upper kilometer. The results indicate that the zonal-mean near-surface salinity is shaped primarily by the spatial pattern of net evaporation and the diffusive meridional salt transport due to wind-driven gyres and mesoscale ocean eddies, rather than by salt advection within the meridional overturning circulation

Spectropolarimetry of 3CR 68.1: A Highly Inclined Quasar

We present Keck spectropolarimetry of the highly polarized radio-loud quasar 3CR 68.1 (z=1.228, V=19). The polarization increases from 5 in the red (4000 A rest-frame) to >10% in the blue (1900 A rest-frame). The broad emission lines are polarized the same as the continuum, which shows that 3CR 68.1 is not a blazar as it has sometimes been regarded in the past. We also present measurements of the emission lines and a strong, blueshifted, associated absorption line system, as well as a detection at the emission-line redshift of Ca II K absorption, presumably from stars in the host galaxy. 3CR 68.1 belongs to an observationally rare class of highly polarized quasars that are neither blazars nor partially obscured radio-quiet QSOs. Taking into account 3CR 68.1's other unusual properties, such as its extremely red spectral energy distribution and its extreme lobe dominance, we explain our spectropolarimetric results in terms of unified models. We argue that we have a dusty, highly inclined view of 3CR 68.1, with reddened scattered (polarized) quasar light diluted by even more dust-reddened quasar light reaching us directly from the nucleus.Comment: 20 pages, includes 3 tables, 6 figures. Accepted by Ap

Caffeine and Progression of Parkinson Disease: A Deleterious Interaction With Creatine.

OBJECTIVE: Increased caffeine intake is associated with a lower risk of Parkinson disease (PD) and is neuroprotective in mouse models of PD. However, in a previous study, an exploratory analysis suggested that, in patients taking creatine, caffeine intake was associated with a faster rate of progression. In the current study, we investigated the association of caffeine with the rate of progression of PD and the interaction of this association with creatine intake. METHODS: Data were analyzed from a large phase 3 placebo-controlled clinical study of creatine as a potentially disease-modifying agent in PD. Subjects were recruited for this study from 45 movement disorders centers across the United States and Canada. A total of 1741 subjects with PD participated in the primary clinical study, and caffeine intake data were available for 1549 of these subjects. The association of caffeine intake with rate of progression of PD as measured by the change in the total Unified Parkinson Disease Rating Scale score and the interaction of this association with creatine intake were assessed. RESULTS: Caffeine intake was not associated with the rate of progression of PD in the main analysis, but higher caffeine intake was associated with significantly faster progression among subjects taking creatine. CONCLUSIONS: This is the largest and longest study conducted to date that addresses the association of caffeine with the rate of progression of PD. These data indicate a potentially deleterious interaction between caffeine and creatine with respect to the rate of progression of PD

Wind-driven evolution of the North Pacific subpolar gyre over the last deglaciation

North Pacific atmospheric and oceanic circulations are key missing pieces in our understanding of the reorganisation of the global climate system since the Last Glacial Maximum (LGM). Here, using a basin-wide compilation of planktic foraminiferal δ18O, we show that the North Pacific subpolar gyre extended ~3 degrees further south during the LGM, consistent with sea surface temperature and productivity proxy data. Analysis of an ensemble of climate models indicates that the expansion of the subpolar gyre was associated with a substantial gyre strengthening. These gyre circulation changes were driven by a southward shift in the mid-latitude westerlies and increased wind-stress from the polar easterlies. Using single-forcing model runs, we show these atmospheric circulation changes are a non-linear response to the combined topographic and albedo effects of the Laurentide Ice Sheet. Our reconstruction suggests the gyre boundary (and thus westerly winds) began to migrate northward at ~17-16 ka, during Heinrich Stadial 1

Identification of a mammalian silicon transporter.

Silicon (Si) has long been known to play a major physiological and structural role in certain organisms, including diatoms, sponges, and many higher plants, leading to the recent identification of multiple proteins responsible for Si transport in a range of algal and plant species. In mammals, despite several convincing studies suggesting that silicon is an important factor in bone development and connective tissue health, there is a critical lack of understanding about the biochemical pathways that enable Si homeostasis. Here we report the identification of a mammalian efflux Si transporter, namely Slc34a2 (also termed NaPiIIb), a known sodium-phosphate cotransporter, which was upregulated in rat kidney following chronic dietary Si deprivation. Normal rat renal epithelium demonstrated punctate expression of Slc34a2, and when the protein was heterologously expressed in Xenopus laevis oocytes, Si efflux activity (i.e., movement of Si out of cells) was induced and was quantitatively similar to that induced by the known plant Si transporter OsLsi2 in the same expression system. Interestingly, Si efflux appeared saturable over time, but it did not vary as a function of extracellular [Formula: see text] or Na+ concentration, suggesting that Slc34a2 harbors a functionally independent transport site for Si operating in the reverse direction to the site for phosphate. Indeed, in rats with dietary Si depletion-induced upregulation of transporter expression, there was increased urinary phosphate excretion. This is the first evidence of an active Si transport protein in mammals and points towards an important role for Si in vertebrates and explains interactions between dietary phosphate and silicon