Controlling factors of the delta B-11-pH proxy and its research direction

Significant boron isotope fractionation occurs in nature (-70 aEuro degrees to +75 aEuro degrees) due to the high geochemical reactivity of boron and the large relative mass difference between B-10 and B-11. Since the 1990s, reconstruction of ancient seawater pH using the isotopic composition of boron in bio-carbonates (delta B-11(carb)), and then calculation of the past pCO(2) have become important issues for the international isotope geochemistry community, and are called the delta B-11-pH proxy. Although many achievements have been made by this proxy, various aspects of boron systematics require rigorous evaluation. Based on the previous researches, mechanism of boron isotope fractionation, variation of boron isotope (delta B-11) in nature (especially in bio-carbonates) and controlling factors of the delta B-11-pH proxy, such as the dissociation constant of B(OH)(3) in seawater (pK(a)), the delta B-11 of seawater (delta B-11(SW)), the boron isotopic fractionation factor between B(OH) (4) (-) and B(OH)(3) (alpha (4-3)), and the incorporated species of boron into bio-carbonates, are reviewed in detail and the research directions of this proxy are proposed. Generally, the controversy about pK(a), delta B-11(sw), and alpha (4-3) is relatively less, but whether boron incorporated into bio-carbonates only in the form of B(OH) (4) (-) remains doubtful. In the future, it is required that the physicochemical processes that control boron incorporation into carbonates be rigorously characterized and that the related chemical and isotopic fractionation be quantified. It is also necessary and important to establish a &quot;best-fit empirically equation&quot; between delta B-11(carb) and pH of seawater based on the precipitation experiments of inorganic or culture experiments of corals or foraminifera. In addition, extended application of the delta B-11-pH proxy to the earlier part of the Phanerozoic relying on the Brachiopods is worthy of studying. Like other geochemical indicators, there are limiting factors of delta B-11; however, it remains a very powerful tool in the reconstruction of past seawater pH at present.</p

Boron isotope variations and its geochemical application in nature

The high geochemical reactivity of boron and the large relative mass difference between B-10 and B-11 lead to significant boron isotope fractionation in nature. So far the measured range of boron isotope composition (B-11) varies between -70 and +75 parts per thousand. The negative B-11 values are found in non-marine evaporite borate minerals and tourmalines, whereas positive B-11 values are common in salt lake brines and evaporated seawater. Since the 1980s, with improved measurement methods, applications of boron isotope analysis have increased rapidly. At present, boron isotopes are successfully applied to reconstruct ancient marine environments, to determine depositional environments and ore genesis, to trace groundwater pollution and seawater intrusion, and to study continental erosion. This paper summarises the methods for boron isotope analysis, the mechanisms of boron isotope fractionation and the distribution of boron isotopes in nature, reviews the achievements and the problems of boron isotopes in geochemical applications, and proposes research directions of boron isotopes in geochemical fields.</p

Meta-analysis of individual-patient data from EVAR-1, DREAM, OVER and ACE trials comparing outcomes of endovascular or open repair for abdominal aortic aneurysm over 5 years.

BACKGROUND: The erosion of the early mortality advantage of elective endovascular aneurysm repair (EVAR) compared with open repair of abdominal aortic aneurysm remains without a satisfactory explanation. METHODS: An individual-patient data meta-analysis of four multicentre randomized trials of EVAR versus open repair was conducted to a prespecified analysis plan, reporting on mortality, aneurysm-related mortality and reintervention. RESULTS: The analysis included 2783 patients, with 14 245 person-years of follow-up (median 5·5 years). Early (0-6 months after randomization) mortality was lower in the EVAR groups (46 of 1393 versus 73 of 1390 deaths; pooled hazard ratio 0·61, 95 per cent c.i. 0·42 to 0·89; P = 0·010), primarily because 30-day operative mortality was lower in the EVAR groups (16 deaths versus 40 for open repair; pooled odds ratio 0·40, 95 per cent c.i. 0·22 to 0·74). Later (within 3 years) the survival curves converged, remaining converged to 8 years. Beyond 3 years, aneurysm-related mortality was significantly higher in the EVAR groups (19 deaths versus 3 for open repair; pooled hazard ratio 5·16, 1·49 to 17·89; P = 0·010). Patients with moderate renal dysfunction or previous coronary artery disease had no early survival advantage under EVAR. Those with peripheral artery disease had lower mortality under open repair (39 deaths versus 62 for EVAR; P = 0·022) in the period from 6 months to 4 years after randomization. CONCLUSION: The early survival advantage in the EVAR group, and its subsequent erosion, were confirmed. Over 5 years, patients of marginal fitness had no early survival advantage from EVAR compared with open repair. Aneurysm-related mortality and patients with low ankle : brachial pressure index contributed to the erosion of the early survival advantage for the EVAR group. Trial registration numbers: EVAR-1, ISRCTN55703451; DREAM (Dutch Randomized Endovascular Aneurysm Management), NCT00421330; ACE (Anévrysme de l'aorte abdominale, Chirurgie versus Endoprothèse), NCT00224718; OVER (Open Versus Endovascular Repair Trial for Abdominal Aortic Aneurysms), NCT00094575