Aging-like Spontaneous Epigenetic Silencing Facilitates Wnt Activation,Stemness, and BrafV600E-Induced Tumorigenesis

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Global silicate weathering flux overestimated because of sediment–water cation exchange

Rivers carry the dissolved and solid products of silicate mineral weathering, a process that removes CO2 from the atmosphere and provides a key negative climate feedback over geological timescales. Here we show that, in some river systems, a reactive exchange pool on river suspended particulate matter, bonded weakly to mineral surfaces, increases the mobile cation flux by 50%. The chemistry of both river waters and the exchange pool demonstrates exchange equilibrium, confirmed by Sr isotopes. Global silicate weathering fluxes are calculated based on riverine dissolved sodium (Na⁺) from silicate minerals. The large exchange pool supplies Na⁺ of nonsilicate origin to the dissolved load, especially in catchments with widespread marine sediments, or where rocks have equilibrated with saline basement fluids. We quantify this by comparing the riverine sediment exchange pool and river water chemistry. In some basins, cation exchange could account for the majority of sodium in the river water, significantly reducing estimates of silicate weathering. At a global scale, we demonstrate that silicate weathering fluxes are overestimated by 12 to 28%. This overestimation is greatest in regions of high erosion and high sediment loads where the negative climate feedback has a maximum sensitivity to chemical weathering reactions. In the context of other recent findings that reduce the net CO2 consumption through chemical weathering, the magnitude of the continental silicate weathering fluxes and its implications for solid Earth CO2 degassing fluxes need to be further investigated.

For decades, silicate weathering has been postulated to provide the negative climate feedback on Earth that prevents a runaway greenhouse climate like on Venus (1). Silicate mineral dissolution with carbonic acid converts atmospheric CO2 into carbonate, and releases essential nutrients to the terrestrial and marine biosphere (2). There have been many attempts to quantify the silicate weathering flux (3), mostly assuming that riverine dissolved sodium (Na+) is derived only from silicate minerals and rock salt. Here we show that there is a major addition of nonsilicate Na+ to the critical zone from ancient seawater, weakly bonded to sedimentary rocks and supplied to waters via the cation exchange process. The implication is not only that the silicate weathering flux is overestimated at a global scale, but that this nonsilicate Na+ is most important in regions previously thought to have the highest silicate weathering fluxes (so called weathering-limited regions) and greatest climate sensitivity.Cation exchange is a rapid chemical reaction between cations in the dissolved phase and mineral surfaces, particularly clays (4). Major and trace cations such as calcium (Ca2+), magnesium (Mg2+), sodium (Na+), potassium (K+), and strontium (Sr2+) form the cation exchange pool, which balances negative charges on river-borne clay particle surfaces. This exchange takes place on interlayer sites, between the tetrahedral and octahedral layers, or on exposed surfaces (4). The importance of the cation exchange pool is well recognized in soils and aquifers (4, 5), has significant implications for enhanced weathering (6), and has been proposed as an important mechanism for buffering the composition of river waters (7–9). However, data on the riverine exchange pool are only available for two large river systems [Amazon and Ganges-Brahmaputra (10, 11)], despite its significance in providing a source of elements that are immediately bioavailable (12), and their potential for biasing the quantification of silicate weathering (9).It is increasingly recognized that rapidly reactive phases have a strong influence on the chemistry of river waters (13, 14). Cation exchange is a rapid reaction occurring continuously in soils, as riverine freshwaters evolve downstream interacting with particulate matter, and when they mix with seawater (15, 16). Important examples of cation exchange are the “swapping” of divalent cations Ca2+ and Mg2+ with Na+, in particular when there is a major change in water composition such as when fluvial clays reach the ocean,Caclay2++2Nawater+⇋2Naclay++Cawater2+.[1]As a result, marine sediments have an exchange pool that is dominated by Na+ (17). Subsequently, these marine sediments are uplifted and emplaced on the continents where Na+ in the exchange pool is released by cation exchange with Ca-rich fresh waters (9). This has major implications for estimates of silicate weathering fluxes and associated CO2 consumption, because they are calculated using the Na+ content of rivers (3). Cerling et al. (9) proposed that the Na+-rich exchange pool exerts an important control on natural waters, based on charge balance arguments from river water chemistry, but this hypothesis has never been rigorously tested (18) by determining the flux and composition of the exchange pool of rivers around the world.In this contribution, we present a large dataset of fluvial sediment cation exchange capacity (CEC) and composition in several of the world’s largest river basins. By comparing with the concomitant dissolved load chemistry, we demonstrate that 1) the exchange pool in river sediments is in equilibrium with the river water; 2) the fraction of mobile elements in the exchange pool relative to the dissolved pool can be significant, particularly in rapidly eroding, weathering-limited catchments; and 3) given reasonable inferences on the composition of old marine sedimentary rocks, modern-day silicate weathering has been overestimated and carbonate weathering has been underestimated. The results reduce the estimated magnitude of the silicate weathering flux, but increase the supply of base cations (e.g., Ca2+, which can be a limiting nutrient) to the biosphere, suggesting a greater role of organic carbon burial compared with silicate weathering for the long-term atmospheric CO2 sink.     

Randomized,double-blind,controlled trial of pneumococcal vaccination in renal transplant recipients

Renal transplant recipients are at increased risk for developing invasive pneumococcal disease but may have a poor response to pneumococcal polysaccharide vaccine (PPV23). For them, pneumococcal conjugate vaccine (PCV7) may be more immunogenic. Patients were given a single dose of PPV23 or PCV7 in our randomized, controlled, double-blind trial. Immunogenicity was assessed 8 weeks after vaccination by serotype-specific enzyme-linked immunosorbent assay (ELISA) and opsonophagocytic assay (OPA). Baseline demographics, renal function, time since transplantation, and immunosuppression were comparable. In the PCV7 group, the vaccine response rate was improved for serotypes 23F (P=.046) and 6B (P=.067), and mean fold increases in antibody titer were higher for serotypes 23F (P=.046) and 9V (P=.09). The response rate and mean fold increase in OPA titers were not significantly different between groups. There was a trend toward enhanced immunogenicity for PCV7 by ELISA. However, functional antibody responses were not different.     

Radioiodine ablation of the thyroid to prevent recurrence of amiodarone-induced thyrotoxicosis in patients with resistant tachyarrhythmias.

Amiodarone-induced thyrotoxicosis (AIT) is a common complication of amiodarone therapy. Although permanent withdrawal of amiodarone is recommended due notably to the risk of worsening of tachyarrhythmias, some patients may require the reintroduction of amiodarone several months after normalizing their thyroid function. We, retrospectively, assessed the effects of (131)I therapy to prevent recurrence of AIT in euthyroid patients requiring reintroduction of amiodarone. SUBJECTS AND METHODS: Amiodarone was required in 10 cases of recurrent symptomatic paroxysmal atrial fibrillation (AF) and in 5 cases of ventricular tachycardia (VT) (M = 12, F = 3, mean age: 63 +/- 14). The underlying heart disease was dilated cardiomyopathy (n = 4), ischaemic heart disease (n = 4), hypertensive heart disease (n = 2), arrhythmogenic right ventricular dysplasia (n = 27) and valvulopathy (n = 1). Two patients had idiopathic paroxysmal AF. RESULTS: A mean (131)I dose of 579 +/- 183 MBq was administered 34 +/- 37 after the episode of AIT. Amiodarone was reintroduced in 14 of 15 patients after a mean interval of 103 +/- 261 d. Fourteen patients developed definite hypothyroidism necessitating l-thyroxine but we observed no late recurrence of AIT. After a mean follow-up of 22 +/- 16 months, tachyarrhythmias were controlled in 12 of 14 patients. CONCLUSION: (131)I therapy appears to be an effective and safe approach to prevent the recurrence of AIT in a patient requiring the reintroduction of amiodarone for tachyarrhythmias.     

Occupational therapy with people with depression: Using nominal group technique to collate clinician opinion

Aims. This aim of this study was to obtain a consensus from clinicians regarding occupational therapy for people with depression, for the assessments and practices they use that are not currently supported by research evidence directly related to functional performance. The study also aimed to discover how many of these assessments and practices were currently supported by research evidence. Methods. Following a previously reported systematic review of assessments and practices used in occupational therapy for people with depression, a modified nominal group technique was used to discover which assessments and practices occupational therapists currently utilize. Three online surveys gathered initial data on therapeutic options (survey 1), which were then ranked (survey 2) and re-ranked (survey 3) to gain the final consensus. Twelve therapists completed the first survey, whilst 10 clinicians completed both the second and third surveys. Major findings. Only 30% of the assessments and practices identified by the clinicians were supported by research evidence. A consensus was obtained on a total of 35 other assessments and interventions. These included both occupational-therapy-specific and generic assessments and interventions. Principle conclusion. Very few of the assessments and interventions identified were supported by research evidence directly related to functional performance. While a large number of options were generated, the majority of these were not occupational therapy specific.