Optical dating and soil micromorphology at MacCauley's Beach,New South Wales,Australia

The ability to position landscapes in a context of time and space is a particular goal of Quaternary science research. The lack of context for dating samples published previously for MacCauley's Beach, an important site for the reconstruction of Australian sea levels, warranted a re‐evaluation of both the site stratigraphy and chronology. In this study, we combined optically stimulated luminescence (OSL) dating of sedimentary quartz grains and soil micromorphology of the same samples to improve our understanding of the depositional history and chronology of the sediments. This combination allowed the contextualization of samples not only in time and space, but also in terms of their depositional histories. The latter is important in OSL dating, where pre‐, syn‐ and post‐depositional processes can all influence the accuracy and precision of the final age estimates. The sediment profile at MacCauley's Beach is made up of three major units. The basal mottled mud layer has undergone extensive pedogenesis since deposition, and only a minimum age of 14.7 ± 2.7 ka could be calculated. The overlying grey mud, with OSL ages from the bottom and top of the unit of 10.0 ± 0.7 and 7.7 ± 0.5 ka, respectively, shows evidence of soil structure collapse. This unit correspond to the onset of the mid‐Holocene sea‐level high stand for this region. The overlying sand layer was first deposited at 7.5 ± 0.4 ka, with deposition continuing beyond 6.6 ± 0.4 ka. Not only does the chronology presented constrain the timing of deposition (and the extent of post‐depositional processes) at MacCauley's Beach, but the methodological approach used here can be applied to any site to aid in the interpretation of formation processes and assess their influence on OSL age determination. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluating local population dynamics of the American lobster,Homarus americanus,with trap‐based mark‐recapture methods and seabed mapping

Seabed mapping, spatially referenced trapping, and mark‐recapture methods have all been useful tools in ecological studies of lobsters and other benthic animals. Here we integrate the three methods to evaluate local population dynamics and movements of American lobsters, Homarus americanus, in coastal fishing grounds in Maine, United States. The study was conducted on five study areas of different size, and used two different sampling protocols. At one site (1 km² in area) we used a monthly mark‐recapture sampling interval over a 6‐month period, only tagging a subsample of the catch. At four smaller sites (0.3 km²) we used a shorter‐term approach, sampling at 3–4‐day intervals for a 2‐week duration, tagging the entire catch. Tagging data were analysed with a modified Jolly‐Seber model adapted for continuous sampling to estimate population abundance, gains (immigration), and losses (emigration and mortality). Side‐scan sonar surveys of the seabed combined with diver‐based population surveys, stratified by substrate type, provided an independent comparison to mark‐recapture‐based estimates of abundance over the same areas. Spatial referencing of trap catch also allowed us to relate catch rates and lobster movements directly to seabed features. The longer‐term tagging data on the larger study area provided abundance estimates that were more consistent with the diver observations, and estimates of gains and losses statistically more robust, than those derived from the shorter‐term effort on the smaller sites. The flux of lobsters followed the well known seasonal movements on these fishing grounds, with gains and losses from the larger study area ranging over 1000 individuals per day, and an estimated mid‐summer peak density of >65 000 lobsters per km² (individuals >50 mm carapace length). This approach may lend itself to broader application with the American lobster.     

A changing nutrient regime in the Gulf of Maine

Recent oceanographic observations and a retrospective analysis of nutrients and hydrography over the past five decades have revealed that the principal source of nutrients to the Gulf of Maine, the deep, nutrient-rich continental slope waters that enter at depth through the Northeast Channel, may have become less important to the Gulf's nutrient load. Since the 1970s, the deeper waters in the interior Gulf of Maine (>100 m) have become fresher and cooler, with lower nitrate (NO₃) but higher silicate (Si(OH)₄) concentrations. Prior to this decade, nitrate concentrations in the Gulf normally exceeded silicate by 4–5 μM, but now silicate and nitrate are nearly equal. These changes only partially correspond with that expected from deep slope water fluxes correlated with the North Atlantic Oscillation, and are opposite to patterns in freshwater discharges from the major rivers in the region. We suggest that accelerated melting in the Arctic and concomitant freshening of the Labrador Sea in recent decades have likely increased the equatorward baroclinic transport of the inner limb of the Labrador Current that flows over the broad continental shelf from the Grand Banks of Newfoundland to the Gulf of Maine. That current system now brings a greater fraction of colder and fresher deep shelf waters into the Gulf than warmer and saltier offshore slope waters which were previously thought to dominate the flux of nutrients. Those deep shelf waters reflect nitrate losses from sediment denitrification and silicate accumulations from rivers and in situ regeneration, which together are altering the nutrient regime and potentially the structure of the planktonic ecosystem.     

Does geographic location impact the survival differential between screen- and interval-detected breast cancers?

Although mammography screening programs aim to diagnose breast cancer at an early stage, not all tumours are detected during the regular screening examination. This study examines the influence of various characteristics, including geographical residence, on the survival between screen- and interval-detected breast cancers among participants of a public population-based breast screening program in Queensland, Australia. The investigation was performed using the linked population-based datasets from BreastScreen Queensland and the Queensland Cancer Registry for the period of 1997–2008 for women aged 40–89 years at diagnosis. A Bayesian spatial relative survival modelling approach that accommodates rare outcomes in small geographic regions was adopted, with the use of Markov chain Monte Carlo computation, to evaluate the relative excess risk of breast cancer. In the multivariate Bayesian spatial model, higher relative excess risk of mortality was observed in interval-detected cancer (RER = 1.59, 95 % credible interval = [1.33, 1.89]) compared to screen-detected cancer. Higher cancer survival among the study cohort was also observed among younger women (40–59 years), those of non-Indigenous ethnicity, with localised (stage I) tumour stage as well as those not in the work force. There was no independent association with marital status. Moreover, there was no substantive evidence of either measured geographical or latent random spatial inequalities in survival among screening participants across Queensland, meaning the higher survival for screen-detected breast cancer patients compared to interval-detected women was consistent across the state. These results provide suggestive evidence supporting the effectiveness of the BreastScreen Queensland screening program in reaching socio-economically disadvantaged women as well as those living in rural and remote areas of the state, but also highlights the need for any interval cancer awareness programs to be geographically widespread.     

Function of Soils for Human Societies and Environment

This study assessed the spatial distribution of vulnerability to extreme heat in 1990 and 2000 within metropolitan Phoenix based on an index of seven equally weighted measures of physical exposure and adaptive capacity. These measures were derived from spatially interpolated climate, normalized differential vegetation index, and U.S. Census data. From resulting vulnerability maps, we also analyzed population groups living in areas of high heat vulnerability. Results revealed that landscapes of heat vulnerability changed substantially in response to variations in physical and socioeconomic factors, with significant alterations to spatial distribution of vulnerability especially between eastern and western sectors of Phoenix. These changes worked to the detriment of Phoenix's Hispanic population and the elderly concentrated in urban-fringe retirement communities.     

Stability and stable modes of coastal fronts

Abstract

The stability of a single layer, geostrophic front of zero potential vorticity bounded by a vertical coast (wall) is investigated by means of a Rayleigh integral. It is proved that the flow of the density-driven current is stable at all wavenumbers provided the mean velocity of basic flow exceeds fL (where f is the Coriolis parameter and L is the distance between the wall and the free streamline). The frequency of the stable long waves is either zero or super-inertial.     

A note on the use of zero potential vorticity models

Abstract

The acceptability of zero potential vorticity models as approximations for natural systems of small, but finite, potential vorticity is studied for bounded frontal flows of arbitrary profile. It is demonstrated that all (infinitely) long-wave solutions of the zero potential vorticity front are asymptotic limits for some (not necessarily long-wave) solutions of the small potential vorticity front. In contrast, for downstream-varying solutions there is no simple way of demonstrating this property. These findings suggest that the use of zero potential vorticity models should be carefully examined in other, non-frontal, problems as well. Finally we show that the longwave solutions of the zero potential vorticity flow are at most neutral (quasi-stable).     

Solitary Rossby Waves in Zonally Varying Jet Flows

The dynamics of solitary Rossby waves (SRWs) embedded in a meridionally sheared, zonally varying background flow are examined using a non-divergent barotropic model centered on a midlatitude g -plane. The zonally varying background flow, which is produced by an external potential vorticity (PV) forcing, yields a modified Korteweg-de Vries (K-dV) equation that governs the spatial-temporal evolution of a disturbance field that contains both Rossby wave packets and SRWs. The modified K-dV equation differs from the classical equation in that the zonally varying background flow, which varies on the same scale as the disturbance field, directly affects the disturbance linear translation speed and linear growth characteristics. In the limit of a locally parallel background flow, equations governing the amplitude and propagation characteristics of SRWs are derived analytically. These equations show, for example, that a sufficiently large (small) translation speed and/or a sufficiently weak (strong) background zonal shear favor transmission (reflection) of the SRW through (from) the jet. Conservation equations are derived showing that time changes in the domain averaged amplitude ("mass") or squared amplitude ("momentum") are due to zonal variation in both the linear, long-wave phase speed and linear growth; dispersion and nonlinearity do not affect the "mass" or "momentum". Provided (1) the background PV forcing is sufficiently small, or (2) the background PV forcing is meridionally symmetric and the disturbance is a SRW, the dynamics of the disturbance field is Hamiltonian and mass and energy are thus conserved. Numerical solutions of the K-dV equation show that the zonally varying background flow yields three general classes of behavior: reflection, transmission, or trapping. Within each class there exists SRWs and Rossby wave packets. SRWs that become trapped within the zonally localized jet region may exhibit the following behaviors: (1) an oscillatory decay to a steady state at the jet center, (2) the creation of additional SRWs within the jet region, or (3) a steady-state wherein the solution has a smoothed step-like structure located downstream along the jet axis.