Paleomagnetic constraints on the paleogeography and oroclinal bending of the Devonian volcanic arc in Kazakhstan

Numerical modelling, incorporating coupling between surface processes and induced flow in the lower continental crust, is used to address the Quaternary evolution of the Gulf of Corinth region in central Greece. The post-Early Pleistocene marine depocentre beneath this Gulf overlies the northern margin of an older (Early Pleistocene and earlier) lacustrine basin, the Proto Gulf of Corinth Basin or PGCB. In the late Early Pleistocene, relief in this region was minimal but, subsequently, dramatic relief has developed, involving the creation of  900 m of bathymetry within the Gulf and the uplift by many hundreds of metres of the part of the PGCB, south of the modern Gulf, which forms the Gulf's main sediment supply. It is assumed that, as a result of climate change around 0.9 Ma, erosion of this sediment source region and re-deposition of this material within the Gulf began, both processes occurring at spatial average rates of  0.2 mm a^− 1. Modelling of the resulting isostatic response indicates that the local effective viscosity of the lower crust is  4 × 10¹⁹ Pa s, indicating a Moho temperature of  560 °C. It predicts that the  10 mm a^− 1 of extension across this  70 km wide model region, at an extensional strain rate of  0.15 Ma^− 1, is partitioned with  3 mm a^− 1 across the sediment source,  2 mm a^− 1 across the depocentre, and  5 mm a^− 1 across the ‘hinge zone’ in between, the latter value being an estimate of the extension rate on normal faults forming the major topographic escarpment at the southern margin of the Gulf. This modelling confirms the view, suggested previously, that coupling between this depocentre and sediment source by lower-crustal flow can explain the dramatic development in local relief since the late Early Pleistocene. The effective viscosity of the lower crust in this region is not particularly low; the strong coupling interpreted between the sediment source and depocentre results instead from their close proximity. In detail, the effective viscosity of the lower crust is expected to decrease northward across this model region, due to the northward increase in exposure of the base of the continental lithosphere to the asthenosphere; in the south the two are separated by the subducting Hellenic slab. The isostatic consequences of such a lateral variation in viscosity provide a natural explanation for why, since  0.9 Ma, the modern Gulf has developed asymmetrically over the northern part of the PGCB, leaving the rest of the PGCB to act as its sediment source.     

On the ‘Divergence Problem’ in Northern Forests: A review of the tree-ring evidence and possible causes

An anomalous reduction in forest growth indices and temperature sensitivity has been detected in tree-ring width and density records from many circumpolar northern latitude sites since around the middle 20th century. This phenomenon, also known as the “divergence problem”, is expressed as an offset between warmer instrumental temperatures and their underestimation in reconstruction models based on tree rings. The divergence problem has potentially significant implications for large-scale patterns of forest growth, the development of paleoclimatic reconstructions based on tree-ring records from northern forests, and the global carbon cycle. Herein we review the current literature published on the divergence problem to date, and assess its possible causes and implications. The causes, however, are not well understood and are difficult to test due to the existence of a number of covarying environmental factors that may potentially impact recent tree growth. These possible causes include temperature-induced drought stress, nonlinear thresholds or time-dependent responses to recent warming, delayed snowmelt and related changes in seasonality, and differential growth/climate relationships inferred for maximum, minimum and mean temperatures. Another possible cause of the divergence described briefly herein is ‘global dimming’, a phenomenon that has appeared, in recent decades, to decrease the amount of solar radiation available for photosynthesis and plant growth on a large scale. It is theorized that the dimming phenomenon should have a relatively greater impact on tree growth at higher northern latitudes, consistent with what has been observed from the tree-ring record. Additional potential causes include “end effects” and other methodological issues that can emerge in standardization and chronology development, and biases in instrumental target data and its modeling. Although limited evidence suggests that the divergence may be anthropogenic in nature and restricted to the recent decades of the 20th century, more research is needed to confirm these observations.     

Multi-gas Emissions Pathways to Meet Climate Targets

So far, climate change mitigation pathways focus mostly on CO₂ and a limited number of climate targets. Comprehensive studies of emission implications have been hindered by the absence of a flexible method to generate multi-gas emissions pathways, user-definable in shape and the climate target. The presented method ‘Equal Quantile Walk’ (EQW) is intended to fill this gap, building upon and complementing existing multi-gas emission scenarios. The EQW method generates new mitigation pathways by ‘walking along equal quantile paths’ of the emission distributions derived from existing multi-gas IPCC baseline and stabilization scenarios. Considered emissions include those of CO₂ and all other major radiative forcing agents (greenhouse gases, ozone precursors and sulphur aerosols). Sample EQW pathways are derived for stabilization at 350 ppm to 750 ppm CO₂ concentrations and compared to WRE profiles. Furthermore, the ability of the method to analyze emission implications in a probabilistic multi-gas framework is demonstrated. The probability of overshooting a 2 ^∘C climate target is derived by using different sets of EQW radiative forcing peaking pathways. If the probability shall not be increased above 30%, it seems necessary to peak CO₂ equivalence concentrations around 475 ppm and return to lower levels after peaking (below 400 ppm). EQW emissions pathways can be applied in studies relating to Article 2 of the UNFCCC, for the analysis of climate impacts, adaptation and emission control implications associated with certain climate targets. See for EQW-software and data.     

Detecting changing river temperatures in England and Wales

Changes in water temperature can have important consequences for aquatic ecosystems, with some species being sensitive even to small shifts in temperature during some or all of their life cycle. While many studies report increasing regional and global air temperatures, evidence of changes in river water temperature has, thus far, been site specific and often from sites heavily influenced by human activities that themselves could lead to warming. Here we present a tiered assessment of changing river water temperature covering England and Wales with data from 2773 locations. We use novel statistical approaches to detect trends in irregularly sampled spot measurements taken between 1990 and 2006. During this 17‐year period, on average, mean water temperature increased by 0.03 °C per year (±0.002 °C), and positive changes in water temperature were observed at 2385 (86%) sites. Examination of catchments where there has been limited human influence on hydrological response shows that changes in river flow have had little influence on these water temperature trends. In the absence of other systematic influences on water temperature, it is inferred that anthropogenically driven climate change is driving some of this trend in water temperature. © 2014 The Authors. Hydrological Processes published by John Wiley & Sons Ltd.     

Growth and linkage of a segmented normal fault zone; the Late Jurassic Murchison–Statfjord North Fault, northern North Sea

The structure of the 25 km long northeastern portion of the Murchison–Statfjord North Fault Zone and adjacent syn-rift stratigraphy are integrated to reconstruct the temporal and spatial evolution during c. 30.5 myr of Late Jurassic, North Sea rifting. Based on a structural analysis (D–d data) alone, approximately 14 precursor fault strands are identified. Incorporation of stratigraphic data shows that only six of these strands were important in controlling stratal architecture and distribution. Three main stages in the evolution of the fault zone are recorded in the syn-rift stratigraphy and are biostratigraphically constrained. These are: (1) following initiation of rifting, six isolated fault strands developed (each <4 km long) and controlled the stratigraphy for c. 13 myr; (2) the isolated strands linked along-strike forming two >9 km long fault segments separated by a 2 km wide relay ramp, that controlled the stratigraphy for at least the following c. 10.5 myr; and (3) the two fault segments hard-linked forming a single, continuous fault trace during the final c. 7 myr of rifting. The results of this study reveal the necessity to adopt an integrated structural and stratigraphic approach when reconstructing the evolution of normal fault zones. The results may also help to further constrain models of fault evolution.     

Linearly Organized Turbulence Structures Observed Over a Suburban Area by Dual-Doppler Lidar

Dual-Doppler lidar observations are used to investigate the structure and evolution of surface-layer flow over a suburban area. The observations were made during the Joint Urban 2003 (JU2003) field experiment in Oklahoma City, U.S.A. in the summer of 2003. This study focuses specifically on a 10-h sequence of scan data beginning shortly after noon local time on 7 July 2003. During this period two coherent Doppler lidars performed overlapping low elevation angle sector scans upwind and south of Oklahoma City’s central business district. Radial velocity data from the two lidars are processed to reveal the structure and evolution of the horizontal velocity field in the surface layer throughout the afternoon and during the evening transition period. The retrieved velocity fields clearly show a tendency for turbulence structures to be elongated in the direction of the mean flow throughout the entire 10-h study period. In order to quantify the observed anisotropy and its dependence on stability, integral length scales are estimated directly from the spatially resolved velocity retrievals. As the flow became more stably stratified the characteristic cross-stream dimension of the linear structures decreased. The streamwise component was consistently more anisotropic than the cross-stream component, and both velocity components exhibited maximum anisotropy under neutral conditions. The ratio of the streamwise to cross-stream length scale was estimated to be about eight for the streamwise component, and four for the cross-stream component under neutral conditions.     

Discriminant analysis for estimation of groundwater age from hydrochemistry and well construction: application to New Zealand aquifers

Concentrations of tritium, chlorofluorocarbons and sulfur hexafluoride have been measured at over 100 groundwater monitoring sites across New Zealand, followed by interpretation of groundwater age distribution using the exponential-piston flow model. Interpreted mean residence times ranged from less than 1 year to more than 100 years, with the 25th, 50th (median) and 75th percentiles being approximately 10, 40 and 100 years, respectively. Classification functions derived from discriminant analysis and based on nine input variables (well depth, electrical conductivity and the concentrations of the ions Na, K, Ca, Mg, HCO₃, Cl and SO₄) allowed assignment of 71% of the sites to the correct of four age categories (mean residence time 10 years or less, 11–40 years, 41–100 years, or more than 100 years). The discriminant analysis classification functions were more effective than regression methods for estimating groundwater age from hydrochemistry and well depth, and can thus be used to predict the groundwater age category for any monitoring site in New Zealand.