Testing GISS-MM5 physics configurations for use in regional impacts studies

The Mesoscale Modeling System Version 5 (MM5) was one-way nested to the Goddard Institute for Space Studies global climate model (GISS GCM), which provided the boundary conditions for present (1990s) and future (IPCC SRES A2 scenario, 2050s) five-summer “time-slice” simulations over the continental and eastern United States. Five configurations for planetary boundary layer, cumulus parameterization, and radiation scheme were tested, and one set was selected for use in the New York City Climate and Health Project—a multi-disciplinary study investigating the effects of climate change and land-use change on human health in the New York metropolitan region. Although hourly and daily data were used in the health project, in this paper we focus on long-term current and projected mean climate change. The GISS-MM5 was very sensitive to the choice of cumulus parameterization and planetary boundary layer scheme, leading to significantly different temperature and precipitation outcomes for the 1990s. These differences can be linked to precipitation type (convective vs. non-convective), to their effect on solar radiation received at the ground, and ultimately to surface temperature. The projected changes in climate (2050s minus 1990s) were not as sensitive to choice of model physics combination. The range of the projected surface temperature changes at a given grid point among the model versions was much less than the mean change for all five model configurations, indicating relative consensus for simulating surface temperature changes among the different model projections. The MM5 versions, however, offer less consensus regarding 1990s to 2050s changes in precipitation amounts. All of the projected 2050s temperature changes were found to be significant at the 95th percent confidence interval, while the majority of the precipitation changes were not.     

A sediment budget for a grazed semi-arid catchment in the Burdekin basin, Australia

In catchments adjacent to the Great Barrier Reef World Heritage Area in Queensland, Australia, there is a growing concern that sediments and nutrients being exported from the land are having a detrimental effect on coral reef communities. There is a need to determine the processes and rates of erosion from the major land use types, so that management intervention can be initiated to reduce sediment yields where required. This paper presents a sediment budget for Weany Creek, a 13.5 km² grazed semi-arid sub-catchment of the Burdekin River catchment, Australia. A range of field methods was used to measure erosion from hillslopes, gullies and stream banks, as well as identify the amount of sediment being deposited and remobilised on the bed of gullies and the stream network. The data suggests that at least during drought conditions, the primary erosion source in this catchment is gully erosion. However, the largest source of sediment in the budget is actually associated with the remobilisation of in-channel sediment stores. Overall, the sediment budget is comprised of  81% coarse material and 19% fine sediment and an agreement between the fine sediment yield estimated in the sediment budget and the yield measured at the catchment outlet is within 10%. The total sediment yield estimated for this catchment is  4205 t yr^− 1 and is much lower than expected for a catchment of this size. This may reflect the drought conditions during the measurement period; however, there is also the possibility that the primary erosion sources have been exhausted, and the rates of sediment loss may be much lower now than they may have been in the past. Nonetheless, the results show that stored sediment, which may have been deposited in the channel many decades ago, is an important contributor to end of catchment sediment yields and warrants further investigation.     

A concerted research effort to advance the hydrological understanding of tropical páramos

Páramos, a neotropical alpine grassland-peatland biome of the northern Andes and Central America, play an essential role in regional and global cycles of water, carbon, and nutrients. They act as water towers, delivering water and ecosystem services from the high mountains down to the Pacific, Caribbean, and Amazon regions. Páramos are also widely recognized as a biodiversity and climate change hot spots, yet they are threatened by anthropogenic activities and environmental changes. Despite their importance for water security and carbon storage, and their vulnerability to human activities, only three decades ago, páramos were severely understudied. Increasing awareness of the need for hydrological evidence to guide sustainable management of páramos prompted action for generating data and for filling long-standing knowledge gaps. This has led to a remarkably successful increase in scientific knowledge, induced by a strong interaction between the scientific, policy, and (local) management communities. A combination of well-established and innovative approaches has been applied to data collection, processing, and analysis. In this review, we provide a short overview of the historical development of research and state of knowledge of the hydrometeorology, flux dynamics, anthropogenic impacts, and the influence of extreme events in páramos. We then present emerging technologies for hydrology and water resources research and management applied to páramos. We discuss how converging science and policy efforts have leveraged traditional and new observational techniques to generate an evidence base that can support the sustainable management of páramos. We conclude that this co-evolution of science and policy was able to successfully cover different spatial and temporal scales. Lastly, we outline future research directions to showcase how sustainable long-term data collection can foster the responsible conservation of páramos water towers.     

High-P granulites of the Songshugou area (Qinling Orogen,east-central China): Petrography,phase relations,and U/Pb zircon geochronology

High-pressure (HP) granulites provide telling records of mineral reactions at upper mantle to lower crustal levels and key information on the fate of material in subduction systems. The latter especially applies when they abut eclogite and mantle dunite because such rock associations are crucial for understanding the incompletely known processes at the interface of converging plates. A continental arc, active c. 520–395 Ma ago, formed an enigmatic example of such a rock association in the Songshugou area, Qinling Orogen. To unravel the juxtaposition of the distinct rocks, this study combines petrography, phase equilibria modelling, conventional thermobarometry, and zircon U–Th–Pb–Ti–REE analysis. Two mafic HP granulites, which contain the mineral assemblages garnet–clinopyroxene–plagioclase–rutile–mesoperthite–quartz and garnet–clinopyroxene–plagioclase–rutile, experienced peak metamorphic conditions of ≤1.4 GPa, 860°C and ~1.3 GPa, ≥910°C, respectively. During decompression and cooling, at 489 ± 4 Ma, amphibole lamellae unmixed from a clinopyroxene solid solution and orthopyroxene in part replaced garnet. A felsic HP granulite shows equilibration of garnet, perthite, antiperthite, kyanite, quartz, and rutile at 810–860°C, ~1.2 GPa, sillimanite growth during decompression, and upper amphibolite facies cooling at 510 ± 4 Ma. Though the thermobarometric data are just within the methodological errors, the U/Pb zircon ages imply the HP granulites did not evolve coherently. The HP granulites either represent foundered lower arc crust or originated from subduction erosion because their geochemistry is indistinguishable from that of the hanging-wall plate. Published and new pressure–temperature–time–deformation paths converge at ~710°C, ~0.9 GPa, and ≲470 Ma, implying exhumation tectonics juxtaposed the HP granulites with a mélange of eclogite and mantle dunite at lower crustal levels. This study highlights that lower arc crust can comprise material of diverse evolution.     

The ichnology of carbonate drifts

Carbonate drifts have so far not been as intensely investigated as their siliciclastic equivalents, especially from an ichnological perspective. The aim of this work is therefore to provide an overview of the different bioturbation styles in carbonate drifts for ichnologists and sedimentologists working in such deposits. Different types of carbonate drifts from the Maldives were studied to address this objective. The cores recovered during International Ocean Discovery Program Expedition 359 were examined to provide the sedimentological and ichnological data for a detailed analysis of the ichnology of carbonate drifts. The ichnological characteristics of the Maldives drifts are compared to other carbonate drifts in order to discuss similarities and differences, and thus provide an overview of the general characteristics of carbonate drift ichnology. These drifts are located in the Santaren Channel which lines Great Bahama Bank, along the Marion Plateau in Australia, in the Limassol and Larnaca basins in Cyprus and in the Danish Basin in Denmark. The common characteristics of bioturbation in carbonate drifts are: (i) the complete bioturbation of the sediment with bioturbation indexes between four and six; (ii) the occurrence of distinctive trace fossils limited to facies contacts or condensed intervals; (iii) a typical ichnoassemblage consisting of Thalassinoides, Scolicia, Planolites, Zoophycos, Chondrites, Phycosiphon and Palaeophycus; (iv) the contiguous occurrence of ichnogenera from different tiers, with only Zoophycos and Chondrites as deep tiers; and (v) distinct infills of the traces including particulate organic matter, pyrite, silica and celestine. In addition, the main ichnofacies of carbonate drifts is the Zoophycos ichnofacies. Ichnofabrics grade from coarse‐grained and completely bioturbated to ichnofabrics with present to rare trace fossils and preserved sedimentary structures. The type and intensity of the bioturbation is controlled by the amount of organic matter and the oxygenation at the sea floor that is determined by the action of bottom currents and the sea‐level fluctuations affecting the carbonate factory in carbonate platforms bordering the basins where the carbonate drifts form. The study of the bioturbation in core and outcrop provides palaeoenvironmental information about carbonate‐drift deposits that complement the classical sedimentological data.     

History of scoria-cone eruptions on the eastern shoulder of the Kenya–Tanzania Rift revealed in the 250-ka sediment record of Lake Chala near Mount Kilimanjaro

Reconstructions of the timing and frequency of past eruptions are important to assess the propensity for future volcanic activity, yet in volcanic areas such as the East African Rift only piecemeal eruption histories exist. Understanding the volcanic history of scoria-cone fields, where eruptions are often infrequent and deposits strongly weathered, is particularly challenging. Here we reconstruct a history of volcanism from scoria cones situated along the eastern shoulders of the Kenya–Tanzania Rift, using a sequence of tephra (volcanic ash) layers preserved in the ~250-ka sediment record of Lake Chala near Mount Kilimanjaro. Seven visible and two non-visible (crypto-) tephra layers in the Lake Chala sequence are attributed to activity from the Mt Kilimanjaro (northern Tanzania) and the Chyulu Hills (southern Kenya) volcanic fields, on the basis of their glass chemistry, textural characteristics and known eruption chronology. The Lake Chala record of eruptions from scoria cones in the Chyulu Hills volcanic field confirms geological and historical evidence of its recent activity, and provides first-order age estimates for seven previously unknown eruptions. Long and well-resolved sedimentary records such as that of Lake Chala have significant potential for resolving regional eruption chronologies spanning hundreds of thousands of years.     

Coesite and pure pyrope in high-grade blueschists of the Western Alps: a first record and some consequences

A pyrope-quartzite originally described by Vialon (1966) from the Dora Maira massif was resampled and reinvestigated. Garnet (up to 25 cm in size), phengite, kyanite, talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz. The garnet is a pyrope-almandine solid solution with 90 to 98 mol % Mg end-member. It contains inclusions of coesite which has partially inverted to quartz, resulting in a typical radial cracking of the host garnet around the inclusions. Several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite. The formidable pressures of formation implied (≧28 kbar) are independently indicated by i) the coexistence of nearly pure pyrope with free silica and talc, ii) the coexistence of jadeite with kyanite, iii) the high Si content of phengite. Water activity must have been low. The stability of talc-phengite and the presence of rare glaucophane inclusions in pyrope point to low formation temperatures (about 700 °C) and to a probable Alpine age for the assemblage. This is evidence that low temperature gradients, how essentially transient they are, may nevertheless persist to considerable depths. Moreover, the upper crustal (evaporite-related?) origin of the quartzite and its interbedding within a continental unit implies that continental crust may also be subducted to depths of 90 km or more. The return back to the surface is problematic; the retrograde assemblages observed show that it must be tectonic. If the rocks remain at depth, new perspectives open for the genesis of intermediate to acidic magmas. Eventually, the role of continental crust in geodynamics may have to be reconsidered.