Guano core evidence of palaeoenvironmental change and Woodland Indian inhabitance in Fern Cave,Alabama, USA,from the mid‐Holocene to present

Bat guano cores have been used as a source of palaeoenvironmental information to aid in the reconstruction of past climates and vegetation. We collected a 104‐cm‐long (43 cm compacted) guano core from Fern Cave, Alabama, USA, that provided a c. 6000‐year record of guano accumulation. Pollen, nutrients (C, N, P) and stable isotopes (δ¹³C, δ¹⁵N) were measured on the guano core with the objective of reconstructing the environmental history of the area from the mid‐Holocene to present. Our data indicate that bats have utilized Fern Cave for at least 6000 years and that Woodland Indians also utilized the cave for a short period. A 3‐cm charcoal layer was dated to 2720±30 cal. a BP and inferred to be Woodland Indian in origin from microscopic inspection and thickness. Pollen and geochemical data showed that bat diets changed in the late Holocene possibly linked to food supply and climate changes. These results demonstrate that guano cores are a useful tool of palaeoenvironmental reconstruction when other forms of palaeorecords do not exist and can add to local archaeological information.     

A 50-year record of nitrate concentrations in the Slapton Ley Catchment,Devon, United Kingdom

Slapton Ley, a coastal lake, is the largest natural body of fresh water in south-west England. There was concern in the 1960s that the lake was becoming increasingly eutrophic. To quantify inputs of water, sediment and nutrients into the lake, Slapton Ley Field Centre initiated a programme of weekly water quality sampling in September 1970. Of all the chemical properties which have been measured over the decades, the nitrate record has been the subject of more research than any other. The weekly monitoring has been supplemented by research projects aimed at understanding aspects of processes and patterns of nitrate delivery to the stream network. Three aspects of the nitrate record are reviewed: short-term process dynamics; the annual cycle of influent streams and the lake itself; and long-term trends. In the first two decades of monitoring, there was increasing concern about a trend of rising nitrate concentrations, an issue in most lowland rivers in the United Kingdom at the time. In the 1990s, nitrate concentrations levelled off and then have fallen steadily in recent years. In relation to eutrophication, there are clear signs of improvement in the influent streams, but concerns remain about water quality in the lake itself.     

Tenoumer impact crater,Mauritania: Impact melt genesis from a lithologically diverse target

Impact melt rocks from the 1.9 km diameter, simple bowl‐shaped Tenoumer impact crater in Mauritania have been analyzed chemically and petrologically. They are heterogeneous and can be subdivided into three types based on melt matrix color, occurrence of lithic clast components, amount of vesiculation (melt degassing), different proportions of carbonate melt mingled into silicate melt, and bulk rock chemical composition. These heterogeneities have two main causes (1) due to the small size of the impact crater, there was probably no coherent melt pool where a homogeneous mixture of melts, derived from different target lithologies, could be created; and (2) melt rock heterogeneity occurring at the thin section scale is due to fast cooling during and after the dynamic ejection and emplacement process. The overall period of crystal growth from these diverse melts was extremely short, which provides a further indication that complete chemical equilibration of the phases could not be achieved in such short time. Melt mixing processes involved in the generation of impact melts are, thus, recorded in nonequilibrium growth features. Variable mixing processes between chemically different melt phases and the formation of hybrid melts can be observed even at millimeter scales. Due to extreme cooling rates, different mixing and mingling stages are preserved in the varied parageneses of matrix minerals and in the mineral chemistry of microlites. ⁴⁰Ar³⁹Ar step‐heating chronology on specimens from three melt rock samples yielded five concordant inverse isochron ages. The inverse isochron plots show that minute amounts of inherited ⁴⁰Ar* are present in the system. We calculated a weighted mean age of 1.57 ± 0.14 Ma for these new results. This preferred age represents a refinement from the previous range of 21 ka to 2.5 Ma ages based on K/Ar and fission track dating.     

Conduit convection,magma mixing,and melt inclusion trends at persistently degassing volcanoes

Magmas progressively exsolve volatiles as they ascend towards the Earth's surface, such that their volatile content is a function of pressure. Water and carbon dioxide concentrations measured in melt inclusions from degassing volcanoes rarely coincide with modelled degassing trends. I show that observed melt inclusion trends can be reproduced through mixing of magmas, either during convection within the volcanic conduit, or within a subterranean magma reservoir. No fluxing gas phase or post-entrapment loss of water need be invoked. A permeable network allowing gas transport is still required to avoid fragmentation of magma at shallow depths.     

Human perturbations on the global biogeochemical cycles of coupled Si–C and responses of terrestrial processes and the coastal ocean

We present a model of the global biogeochemical cycle of silicon (Si) that emphasizes its linkages to the carbon cycle and temperature. The Si cycle is a crucial part of global nutrient biogeochemistry regulating long-term atmospheric CO₂ concentrations due to silicate mineral weathering reactions involving the uptake of atmospheric CO₂ and production of riverine dissolved silica, cations and bicarbonate. In addition and importantly, the Si cycle is strongly coupled to the other nutrient cycles of N, P, and Fe; hence siliceous organisms represent a significant fraction of global primary productivity and biomass. Human perturbations involving land-use changes, burning of fossil fuel, and inorganic N and P fertilization have greatly altered the terrestrial Si cycle, changing the river discharge of Si and consequently impacting marine primary productivity primarily in coastal ocean waters.     

Hydrologic processes on tree islands in the Everglades (Florida, USA): tracking the effects of tree establishment and growth

The hydrodynamics of tree islands during the growth of newly planted trees has been found to be influenced by both vegetation biomass and geologic conditions. From July 2007 through June 2009, groundwater and surface-water levels were monitored on eight recently planted tree islands at the Loxahatchee Impoundment Landscape Assessment (LILA) facility in Boynton Beach, Florida, USA. Over the 2-year study, stand development coincided with the development of a water-table depression in the center of each of the islands that was bounded by a hydraulic divide along the edges. The water-table depression was greater in islands composed of limestone as compared to those composed of peat. The findings of this study suggest that groundwater evapotranspiration by trees on tree islands creates complex hydrologic interactions between the shallow groundwater in tree islands and the surrounding surface water and groundwater bodies.     

Burial and Preservation of Carbonate Rocks Over Phanerozoic Time

Comparison of results for the original burial rate of carbonate sediments over Phanerozoic time, as calculated using the GEOCARBSULFvolc model, with their rate of preservation to the present (survival rate) shows a considerable loss of mass, partly by subduction of oceanic crust, during the past 250 million years. Before that time, despite the evidence that preserved Paleozoic carbonates appear to have been deposited only in shallow water, we contend that there was also inorganic deposition of carbonates in the Paleozoic deep sea with subsequent loss by subduction. Inorganic carbonate deposition may have been abetted by the vastly different seawater and atmospheric composition for most of the Paleozoic than those of post-Cretaceous and end Paleozoic–early Mesozoic times. The hypothesis helps to explain the loss of mass greater than that predicted for shallow-water carbonates prior to 250 Ma.     

Environmental change and seasonal behavior of mastodons in the Great Lakes region inferred from stable isotope analysis

We investigate seasonal variations in the diet and drinking water of four Great Lakes mastodon (Mammut americanum) specimens using stable isotope analysis of serially sampled inner-enamel bioapatite structural carbonate (δ¹³C_sc, δ¹⁸O_sc), and previously published bulk analyses. Isotopic analyses and thin section measurements showed that mastodon tooth enamel extension rates (~ 12–4 mm/yr, decreasing toward the cervix) were lower than those of mammoths or modern elephants. Mastodons had distinct and highly regular seasonal variations in δ¹³C_sc and δ¹⁸O_sc, which we interpret in the context of local glacial history and vegetation changes. Seasonal variations in δ¹⁸O were large but variations in δ¹³C were small, and may have been obscured if coarser sampling methods than our inner-enamel sampling approach were used. Thus, our approach may be particularly useful for understanding relatively small seasonal changes in δ¹³C within C₃ environments. The seasonal patterns, though not entirely conclusive, suggest that the Ontario mastodons did not migrate over very long distances. Rather, the climate and seasonal dietary patterns of mastodons within the region changed over time, from ~ 12,400 to 10,400 ¹⁴C yr BP (~ 15,000 – 12,000 cal yr BP). Insights gained using these methods can contribute to a better understanding of megafaunal extinctions and Paleoamerican lifeways.     

A re-assessment of the nearest neighbour alignment of the X-ray isophotes of galaxy clusters

Alignment is defined as the tendency of the distribution of pointing angles between the major axes of clusters and their nearest neighbours to be more concentrated towards small values for small nearest neighbour distances, whereas the distribution is expected to be uniform over all angles at larger distances. Conflicting pronouncements on the reality of this effect have been published in the astronomy literature. A re-assessment of the evidence for alignment is presented, based on three recently published X-ray data sets. We find that whereas there is evidence for alignment, it is not as convincing as previously claimed. In particular, the scale to which the effect has been claimed to extend seems to have been severely overstated.