ALBERT

Description: Agricultural expansion has resulted in both land use and land cover change (LULCC) across the tropics. However, the spatial and temporal patterns of such change and their resulting impacts are poorly understood, particularly for the pre-satellite era. Here we quantify the LULCC history across the 33.9 million ha watershed of Tanzania's Eastern Arc Mountains, using geo-referenced and digitised historical land cover maps (dated 1908, 1923, 1949 and 2000). Our time series from this biodiversity hotspot shows that forest and savanna area both declined, by 74% (2.8 million ha) and 10% (2.9 million ha), respectively, between 1908 and 2000. This vegetation was replaced by a five-fold increase in cropland, from 1.2 million ha to 6.7 million ha. This LULCC implies a committed release of 0.9 Pg C (95% CI: 0.4-1.5) across the watershed for the same period, equivalent to 0.3 Mg C ha −1 yr −1 . This is at least three-fold higher than previous estimates from global models for the same study area. We then used the LULCC data from before and after protected area creation, as well as from areas where no protection was established, to analyse the effectiveness of legal protection on land cover change despite the underlying spatial variation in protected areas. We found that, between 1949 and 2000, forest expanded within legally protected areas, resulting in carbon uptake of 4.8 (3.8-5.7) Mg C ha −1 , compared to a committed loss of 11.9 (7.2-16.6) Mg C ha −1 within areas lacking such protection. Furthermore, for nine protected areas where LULCC data is available prior to and following establishment, we show that protection reduces deforestation rates by 150% relative to unprotected portions of the watershed. Our results highlight that considerable LULCC occurred prior to the satellite era, thus other data sources are required to better understand long-term land cover trends in the tropics. This article is protected by copyright. All rights reserved.

Description: Key Points We suggest a new Eocene zircon reference material, GHR1. U‐Pb and Hf isotopic systematics in GHR1 zircon are homogeneous with a 206Pb/238U date of 48.106 +/‐ 0.023 Ma (2s) and a 176Hf/177Hf of 0.283050 +/‐ 17 (2s). GHR1 fulfills a need for abundant and easily available Cenozoic zircon reference materials. We present multitechnique U‐Pb geochronology and Hf isotopic data from zircon separated from rapakivi biotite granite within the Eocene Golden Horn batholith in Washington, USA. A weighted mean of twenty‐five Th‐corrected 206Pb/238U zircon dates produced at two independent laboratories using chemical abrasion‐isotope dilution‐thermal ionisation mass spectrometry (CA‐ID‐TIMS) is 48.106 ± 0.023 Ma (2s analytical including tracer uncertainties, MSWD = 1.53) and is our recommended date for GHR1 zircon. Microbeam 206Pb/238U dates from laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) and secondary ion mass spectrometry (SIMS) laboratories are reproducible and in agreement with the CA‐ID‐TIMS date to within 〈 1.5%. Solution multi‐collector ICP‐MS (MC‐ICP‐MS) measurements of Hf isotopes from chemically purified aliquots of GHR1 yield a mean 176Hf/177Hf of 0.283050 ± 17 (2s, n = 10), corresponding to a εHf0 of +9.3. Hafnium isotopic measurements from two LA‐ICP‐MS laboratories are in agreement with the solution MC‐ICP‐MS value. The reproducibility of 206Pb/238U and 176Hf/177Hf ratios from GHR1 zircon across a variety of measurement techniques demonstrates their homogeneity in most grains. Additionally, the effectively limitless reserves of GHR1 material from an accessible exposure suggest that GHR1 can provide a useful reference material for U‐Pb geochronology of Cenozoic zircon and Hf isotopic measurements of zircon with radiogenic 176Hf/177Hf.

Description: Observations of Mercury's local plasma environment by MESSENGER have revealed that the planet hosts a strongly asymmetric magnetosphere as a result of an off-axis dipolar or quadrupolar internal field and significant finite Larmor radius effects at the boundary layer between magnetospheric and solar wind plasma environments. One important asymmetry appears in the growth and evolution of Kelvin-Helmholtz (K-H) waves at the dawn and dusk flanks of the magnetopause. Linear analysis and global hybrid simulations support a dusk-dawn asymmetry in the growth rate caused by finite Larmor radius effects, and indeed K-H waves have been almost exclusively observed at the dusk magnetopause during northward IMF. Observations of these K-H waves at sodium gyro-scales invites investigation into the impact of the hot planetary sodium ion population, itself distributed preferentially on the dusk flank, on the growth of the K-H instability and associated plasma transport. We present local two-dimensional hybrid simulations of the dusk and dawn boundary layer, with varying magnetospheric sodium ion number density, and examine the associated changes in the growth rates of the K-H instability, K-H wave spectra, and cross-boundary particle transport. We show that gyro-resonance between growing K-H vortices and sodium ion gyration introduces a strong spectral peak at sodium gyro-scales at the dusk magnetopause that an increase in sodium ion number density increases dawn-dusk asymmetry of K-H growth rates, and that cross-boundary particle transport decreases with sodium number density at the dawn flank.

Description: Many metrics can be used to capture trends in biodiversity, and in turn these metrics inform biodiversity indicators. Sampling biases, genuine differences between metrics, or both, can often cause indicators to appear to be in conflict. This lack of congruence confuses policy makers and the general public, hindering effective responses to the biodiversity crisis. We show how different and seemingly incongruous metrics of biodiversity can in fact emerge from the same scenario of biodiversity change. We develop a simple, evidence-based narrative of biodiversity change and implement it in a simulation model. The model demonstrates how, for example, species richness can remain stable in a given landscape whereas other measures (e.g., compositional similarity) can be in sharp decline. We suggest that linking biodiversity metrics in a simple model will support more robust indicator development, enable stronger predictions of biodiversity change, and provide policy-relevant advice at a range of scales. This article is protected by copyright. All rights reserved

Description: Author(s): S. Servidio, C. T. Haynes, W. H. Matthaeus, D. Burgess, V. Carbone, and P. Veltri Particle dynamics are investigated in plasma turbulence, using self-consistent kinetic simulations, in two dimensions. In the steady state, the trajectories of single protons and proton pairs are studied, at different values of plasma β (ratio between kinetic and magnetic pressure). For single-parti… [Phys. Rev. Lett. 117, 095101] Published Wed Aug 24, 2016

Description: The Cancún Agreements provide strong backing for a REDD+ (Reducing Emissions from Deforestation and Forest Degradation) mechanism whereby developed countries pay developing ones for forest conservation. REDD+ has potential to simultaneously deliver cost-effective climate change mitigation and human development. However, most REDD+ analysis has used coarse-scale data, overlooked important opportunity costs to tropical forest users and failed to consider how to best invest funds to limit leakage, that is, merely displacing deforestation. Here we examine these issues for Tanzania, a REDD+ country, by comparing district-scale carbon losses from deforestation with the opportunity costs of carbon conservation. Opportunity costs are estimated as rents from both agriculture and charcoal production (the most important proximate causes of regional forest conversion). As an alternative we also calculate the implementation costs of alleviating the demand for forest conversion—thereby addressing the problem of leakage—by raising agricultural yields on existing cropland and increasing charcoal fuel-use efficiency. The implementation costs exceed the opportunity costs of carbon conservation (medians of US$6.50 versus US$3.90 per Mg CO2), so effective REDD+ policies may cost more than simpler estimates suggest. However, even if agricultural yields are doubled, implementation is possible at the competitive price of ~US$12 per Mg CO2.

Description: Author(s): A. H. Sulaiman, A. Masters, M. K. Dougherty, D. Burgess, M. Fujimoto, and G. B. Hospodarsky Shock waves exist throughout the Universe and are fundamental to understanding the nature of collisionless plasmas. Reformation is a process, driven by microphysics, which typically occurs at high Mach number supercritical shocks. While ongoing studies have investigated this process extensively both… [Phys. Rev. Lett. 115, 125001] Published Wed Sep 16, 2015

Description: Africa is predicted to be highly vulnerable to 21 st century climatic changes. Assessing the impacts of these changes on Africa's biodiversity is, however, plagued by uncertainties, and markedly different results can be obtained from alternative bioclimatic envelope models or future climate projections. Using an ensemble forecasting framework, we examine projections of future shifts in climatic suitability, and their methodological uncertainties, for over 2,500 species of mammals, birds, amphibians and snakes in sub-Saharan Africa. To summarise a priori the variability in the ensemble of 17 general circulation models, we introduce a consensus methodology that combines co-varying models. Thus we quantify and map the relative contribution to uncertainty of seven bioclimatic envelope models, three multi-model climate projections and three emissions scenarios, and explore the resulting variability in species turnover estimates. We show that bioclimatic envelope models contribute most to variability, particularly in projected novel climatic conditions over Sahelian and southern Saharan Africa. To summarise agreements among projections from the bioclimatic envelope models we compare five consensus methodologies, which generally increase or retain projection accuracy and provide consistent estimates of species turnover. Variability from emissions scenarios increases towards late-century and affects southern regions of high species turnover centred in arid Namibia. Two-fold differences in median species turnover across the study area emerge among alternative climate projections and emissions scenarios. Our ensemble of projections underscores the potential bias when using a single algorithm or climate projection for Africa, and provides a cautious first approximation of the potential exposure of sub-Saharan African vertebrates to climatic changes. The future use and further development of bioclimatic envelope modelling will hinge on the interpretation of results in the light of methodological as well as biological uncertainties. Here, we provide a framework to address methodological uncertainties and contextualise results.

Description: Current classifications of carbonate platforms use depositional gradient as the main criterion for separating systems into two end-member types, ramps and flat-topped platforms (FTPs). However, many examples do not conform to this simple classification. To investigate why this is and to better understand probable controls on platform development, we have used a series of 2D numerical forward model runs to investigate how sediment production, diffusional sediment transport, and other controls such as tectonic subsidence, antecedent topography, and relative sea-level oscillation interact to determine platform geometry. Modeling results reaffirm that rates of down-dip sediment transport relative to rates of autochthonous production are a critical factor in maintaining a ramp profile in stable cratonic settings under a constant rate of relative sea-level rise. Type of carbonate production versus water-depth curve, for example euphotic versus oligophotic, is not a significant control in our model cases. Both euphotic and oligophotic production profiles produce FTPs when diffusion coefficients are low relative to production rates, and ramps when diffusion coefficients are relatively high. These results suggest a continuum of platform types, ranging from transport-dominated, low-gradient systems at one end of the spectrum, to in situ accumulation dominated systems at the other. A system may be transport-dominated because high-energy processes are able to break down and transport even bound sediment, or because carbonate factories produce only sediment that is easily transportable under even low-energy conditions. Time evolution is also probably important. Initially low gradient systems will, in the absence of sufficiently high sediment transport rates, tend to evolve towards high-gradient flat-topped steep-margined platforms. Many observed or inferred platform geometries are therefore likely to be transient forms, and this could complicate interpretation. Investigating how basin bathymetry and style of subsidence control platform geometry suggests that, in transport-dominated systems, strata simply drape the underlying topography, and that pre-existing breaks of slope and differential fault subsidence are a stronger control on platform geometry in in situ accumulation dominated systems. Rotational subsidence tends to create transport-dominated systems during rotation as the topographic gradient increases and transport rate increases and outpaces in situ production rate. Relative sea-level oscillations tend to move the locus of sediment production laterally along any slope present on the platform, distributing the sediment accumulation across the whole width of the platform, suppressing progradation and steepening, and so favoring development of low-gradient systems. Based on all these results, we suggest that a simple cutoff classification into ramp and flat-topped platform types can still be useful in some circumstances, but a more meaningful approach may be to describe and predict platform strata in terms of a multiple-dimension platform parameter space containing a continuum of geometries controlled by sediment production, sediment diffusion coefficient, antecedent topography, differential subsidence effects, relative sea-level oscillations and perhaps other as yet unappreciated controls.

Description: Abstract Glacier and ice sheet mass loss as a result of climate change is driving important coastal changes in Arctic fjords. Yet limited information exists for Arctic coasts regarding the influence of glacial erosion and ice mass loss on the occurrence and character of turbidity currents in fjords, which themselves affect delta dynamics. Here we show how glacial erosion and the production of meltwaters and sediments associated with the melting of retreating glaciers control the generation of turbidity currents in fjords of eastern Baffin Island (Canada). The subaqueous parts of 31 river mouths along eastern Baffin Island were mapped by high‐resolution swath bathymetry in order to assess the presence or absence of sediment waves formed by turbidity currents on delta fronts. By extracting glaciological and hydrological watershed characteristics of these river mouths, we demonstrate that the presence and areal extent of glaciers are a key control for generating turbidity currents in fjords. However, lakes formed upstream during glacial retreat significantly alter the course of sediment routing to the deltas by forming temporary sinks, leading to the cessation of turbidity currents in the fjords. Due to the different deglaciation stages of watersheds in eastern Baffin Island, we put these results into a temporal framework of watershed deglaciation to demonstrate how the retreat pattern of glaciers, through the formation and filling of proglacial lakes, affects the turbidity current activity of deltas.