Direct evidence of fluid mixing in the formation of stratabound Pb–Zn–Ba–F mineralisation in the Alston Block, North Pennine Orefield (England)

The North Pennine Orefield Alston Block has produced approximately 4 Mt Pb, 0.3 Mt Zn, 2.1 Mt fluorite, 1.5 Mt barite, 1 Mt witherite, plus a substantial amount of iron ore and copper ore from predominantly vein-hosted mineralisation in Carboniferous limestones. However, a significant proportion of this production (ca. 20%) came from stratabound deposits. Though much is known about the vein mineralisation, the relationship between the veins and the stratabound mineralisation is not well-understood. New petrographic, isotopic and fluid inclusion data derived from samples of stratabound mineralisation allow us to present a unified model that addresses the genesis of both the vein and stratabound styles of mineralisation. The mineralisation can be considered in terms of three episodes: 1. Dolomitisation and ankeritisation Limestones in the vicinity of the stratabound mineralisation were pervasively dolomitised/ankeritised, and developed vuggy porosity in the presence of a high-salinity brine consistent with fluids derived from adjacent mud and shale-filled basins. 2. Main stage fluorite–quartz–sulphide mineralisation Metasomatism of limestone was accompanied by brecciation, dissolution and hydrothermal karstification with modification of the existing pore system. The open space was filled with fluorite, galena, sphalerite, quartz and barite, formed in response to mixing of lowsalinity sodic groundwater with high-salinity calcic brine with elevated metal contents (particularly Fe up to 7,000 ppm) relative to “normal” high total dissolved solids sedimentary brines. 3. Late-stage barite mineralisation paragenetically appears to represent either the waning stages or the distal portions of the main hydrothermal circulation system under cooler conditions

Regional atmospheric circulation shifts induced by a grand solar minimum

Large changes in solar ultraviolet radiation can indirectly affect climate1 by inducing atmospheric changes. Specifically, it has been suggested that centennial-scale climate variability during the Holocene epoch was controlled by the Sun2, 3. However, the amplitude of solar forcing is small when compared with the climatic effects and, without reliable data sets, it is unclear which feedback mechanisms could have amplified the forcing. Here we analyse annually laminated sediments of Lake Meerfelder Maar, Germany, to derive variations in wind strength and the rate of 10Be accumulation, a proxy for solar activity, from 3,300 to 2,000 years before present. We find a sharp increase in windiness and cosmogenic 10Be deposition 2,759  ±  39 varve years before present and a reduction in both entities 199  ±  9 annual layers later. We infer that the atmospheric circulation reacted abruptly and in phase with the solar minimum. A shift in atmospheric circulation in response to changes in solar activity is broadly consistent with atmospheric circulation patterns in long-term climate model simulations, and in reanalysis data that assimilate observations from recent solar minima into a climate model. We conclude that changes in atmospheric circulation amplified the solar signal and caused abrupt climate change about 2,800 years ago, coincident with a grand solar minimum

The HadGEM2 family of Met Office Unified Model climate configurations

We describe the HadGEM2 family of climate configurations of the Met Office Unified Model, MetUM. The concept of a model "family" comprises a range of specific model configurations incorporating different levels of complexity but with a common physical framework. The HadGEM2 family of configurations includes atmosphere and ocean components, with and without a vertical extension to include a well-resolved stratosphere, and an Earth-System (ES) component which includes dynamic vegetation, ocean biology and atmospheric chemistry. The HadGEM2 physical model includes improvements designed to address specific systematic errors encountered in the previous climate configuration, HadGEM1, namely Northern Hemisphere continental temperature biases and tropical sea surface temperature biases and poor variability. Targeting these biases was crucial in order that the ES configuration could represent important biogeochemical climate feedbacks. Detailed descriptions and evaluations of particular HadGEM2 family members are included in a number of other publications, and the discussion here is limited to a summary of the overall performance using a set of model metrics which compare the way in which the various configurations simulate present-day climate and its variability