Reconciling theories of a mechanically driven meridional overturning circulation with thermohaline forcing and multiple equilibria

It has recently been suggested that the structure and strength of the meridional overturning circulation in the global ocean is governed by the input of mechanical energy to the system by winds and tides. However, it is not clear how this suggestion relates to the existence of multiple equilibria of the meridional overturning circulation, which depends on thermohaline feedbacks and is more consistent with a buoyancy-driven view of the circulation. Both theories have been illustrated by box models in the past (Stommel in Tellus 13:224–230, 1961; Gnanadesikan in Science 283:2077–2079, 1999). Here we incorporate these two theories into a single box model in an attempt to reconcile the roles of mechanical and buoyancy forcing in driving the meridional overturning circulation. The box model has two equilibrium solutions, one with sinking at high northern latitudes as in the present-day Atlantic, and one without. The circulation is mechanically driven, but the northern sinking can be thought of as a release valve which acts as a sink of potential energy when the surface water at high northern latitudes is dense enough to convect. While the source of energy comes from mechanical forcing, the presence or otherwise of multiple equilibria is therefore determined by thermohaline feedbacks. In some areas of parameter space an oscillation between the model’s two circulation regimes occurs, reminiscent of a bipolar seesaw.     

Invasive species and climate change: an agronomic perspective

In the current review we wish to draw attention to an additional aspect of invasive species and climate change, that of agricultural productivity and food security. We recognize that at present, such a review remains, in part, speculative, and more illustrative than definitive. However, recent events on the global stage, particularly in regard to the number of food riots that occurred during 2008, even at a time of record harvests, have prompted additional interest in those factors, including invasive species, which could, through climatic uncertainty, alter food production. To that end, as agricultural scientists, we wish to begin an initial evaluation of key questions related to food production and climate change including: how vulnerable is agriculture to invasive species?; are current pest management strategies sufficient to control invasive outbreaks in the future?; what are the knowledge gaps?; can we provide initial recommendations for scientists, land managers and policy makers in regard to available resources? Our overall goals are to begin a synthesis of potential impacts on productivity, to identify seminal research areas that can be addressed in future research, and to provide the scientific basis to allow agronomists and land managers to formulate mitigation and adaptation options regarding invasive species and climate change as a means to maintain food security.     

Stable carbon isotope analysis on fossil Cedrus pollen shows summer aridification in Morocco during the last 5000 years

Quantitative climate reconstructions from pollen typically rely on empirical relationships between pollen abundances or assemblages and climate, such as the modern analogue technique. However, these techniques may be problematic when applied to fossil sequences, as they cannot separate anthropogenic from climatic influence on pollen assemblages. Here, we reconstruct Mid‐ to Late Holocene summer aridity in the Middle Atlas, Morocco, using stable carbon isotope analysis of isolated fossil Cedrus pollen. This approach is based on well‐documented plant physiological responses to moisture stress and is therefore independent of vegetation composition. We find that there has been a general long‐term trend of increasing summer aridity in the region during the last 5000 years to the present day. The gradual decline of Cedrus atlantica forest in the Late Holocene follows this aridity trend. Additionally, we show how isolating a specific pollen type for carbon isotope analysis yields a robust climate signal, versus using pollen concentrates or bulk sediment. Our findings indicate that climate has become drier in the region and confirms the Mid‐ to Late Holocene aridification trend observed more widely in the western Mediterranean, using a novel proxy for this region with good potential for wider application in other environments.     

Murray Basin Magnetotelluric study

The Murray Basin is geologically featureless, has been sparsely covered by geophysics, and is penetrated by a few scattered wells. Only drilling and reflection seismic work have provided consistently reliable depth information. They have indicated the presence of narrow troughs, which contain more than 3 km of Palaeozoic sediment, covered by basement highs with less than 300 m of Mesozoic and Cainozoic cover.

Six widely spaced magnetotelluric (MT) sites were occupied in the north central Murray Basin. Results showed a 5 km thick horizontal section at Pooncarie, with a probably average porosity of 10%. Higher porosities, and probably a thicker section, were indicated near Little Topar, but the structural complexity there requires that additional data be acquired for positive interpretation.

A persistent conductivity increase near 100 km suggests that the method may respond well to the base of the tectonic plate.

The MT method appears well suited to the onshore exploration problems currently faced in Australia.     

Evolution of a small intraplate basaltic lava field: Jerrabattgulla Creek,upper Shoalhaven River catchment,southeast New South Wales

The Jerrabattgulla Creek basalts are in the upper catchment of the Shoalhaven River of southeastern New South Wales. The basalts erupted into a narrow, north-draining valley and modified the local drainage system, re-routing the paleo-Jerrabattgulla Creek, preserving a series of sub-basaltic quartzose gravels with silcretes in the paleovalley. The paleovalley indicates that a north-flowing drainage existed in this place in the Miocene. The high-relief, narrow valley has preserved a volcanic stratigraphy allowing the magmatic evolution of this small lava field to be determined. The lavas have a large compositional range from olivine nephelinite through to quartz tholeiite, which is unusual in such a small lava field. They represent three distinct magma batches, most likely from an amphibole–apatite metasomatised sub-continental lithospheric mantle, and underwent fractional crystallisation of olivine, clinopyroxene and plagioclase and assimilated upper crust. The lava field underwent temporal change from dominantly alkaline, to mixed alkaline and subalkaline, to dominantly alkaline magmatism over the course of its evolution.     

Introduction: Geographic Contributions to Agrobiodiversity Conservation

Abstract

Since the period of bank deregulation in the 1980s, deferred deposit loan operations, better known as payday lenders, have become commonplace in the landscapes of many American cities. At the same time, traditional banking facilities have become less common, especially in the inner city. Growing disparities in the type of and accessibility to credit in the inner city has generated calls for greater regulation to curb practices by payday lenders that critics claim disproportionately affect poor and minority consumers. Payday lenders argue that they serve communities neglected by traditional banks. This article analyzes the site-location strategies of banks and payday lenders in metropolitan Louisiana, and in Cook County, Illinois, and finds that disenfranchised neighborhoods are simultaneously targeted by payday lenders and neglected by traditional banks. The implications these findings have for public policy and for ongoing discourses on the urban condition, race, and class are briefly discussed.

     

Mapping the physiography of Michigan with GIS

Abstract

We present a new physiographic map of Michigan, that is also available interactively, online. Only four, small-scale physiographic maps of Michigan had been previously published. Our mapping project made use of a wide variety of spatial data, in a GIS environment, to visualize and delineate the physical landscape in more detail than has been done previously. We also examined many of the unit boundaries in the field, using a GIS running on a GPS-enabled laptop. Unlike previous physiographic maps, the online version of the map enables users to query the criteria used to define each of the 224 boundaries of its 10 major and 91 minor physiographic units. The interactive nature of the online version of the map is a unique enhancement to physiographic maps and mapping. Our study also provides data on the number and types of criteria used to define each of the 224 unit boundaries within the map. Most of our unit boundaries are based on data derived from 10-m raster elevation data and NRCS soils data, e.g., relief, soil wetness, escarpments, landscape fabric, and parent material characteristics. Data gleaned from NRCS SSURGO county-scale soil maps were a strength of the project. [Key words: Michigan, physiography, landforms, soils, GIS, mapping]     

Spatial video and GIS

GIS elemental unit representations of spatial data are often defined in terms of points, lines and areas. However, another type of spatial data that is becoming frequently captured, but as yet is largely ignored in GIS, is that of video. While digital video recording is a commonly encountered medium in modern society and encompasses many forms, from simple personal camcorders through to sophisticated survey and surveillance systems, its geographical representation in a GIS has not been fully examined or realised. In the majority of cases the video footage is usually captured while the device and/or the objects being viewed are in motion. What is of particular interest is when video streams can be, or have been, associated with spatial data such as location and orientation to create geographically referenced videographic data, which, for simplicity, will be defined as spatial video. Fundamentally, the nature of video is to record space, so when spatial properties can be accurately acquired and associated with this footage, an important geographical element can be considered for integration and analysis within a GIS.

Existing spatial video systems, both commercial and research, are predominantly used in survey or LBS roles and are usually bespoke and application specific. These systems do not model spatial video to any recognised standards that is generalised to be both data and platform independent. They do not support GIS integration and/or analysis from a purely spatial content perspective. A video-image/remote-sensing centric approach prevails where usage options range from simple visualisation interfaces to interactive computer vision systems. What has been largely overlooked is a spatial approach where the inherent geographical extent recorded in each video frame can be modelled and used in a geo-spatial analysis context. While this modelling approach has not been fully realised, it does exist in a GIS form based on Open Geospatial Consortium standards, where the spatial context of video is defined in a structure called a ViewCone. However, a ViewCone only defines a 2D model of the geographical extent of each frame and is restricted to a three-or-five sided polygon representation.

Thus, this article examines the potential of modelling spatial video through the use of elemental data types within GIS; gives some examples of using this approach; describes some problems in using spatial video within GIS; and then demonstrates how these problems are being solved. This is done in three stages: Firstly, a detailed overview of spatial video in its current GIS role is provided – this is achieved through a complete introduction to the distinct elements of spatial video followed by a review of its use in both commercial and academic application areas. Secondly, a brief theoretical overview of an alternative GIS-constrained ViewCone data structure is given that defines a more flexible spatial video model for both 2D and 3D GIS analysis and visualisation. Thirdly, a selective sample of results is presented based on an implementation of this approach being applied to a constrained spatial video data source in a specific study area.     

Computational advances in gravitational microlensing: A comparison of CPU,GPU, and parallel,large data codes

To assess how future progress in gravitational microlensing computation at high optical depth will rely on both hardware and software solutions, we compare a direct inverse ray-shooting code implemented on a graphics processing unit (GPU) with both a widely-used hierarchical tree code on a single-core CPU, and a recent implementation of a parallel tree code suitable for a CPU-based cluster supercomputer. We examine the accuracy of the tree codes through comparison with a direct code over a much wider range of parameter space than has been feasible before. We demonstrate that all three codes present comparable accuracy, and choice of approach depends on considerations relating to the scale and nature of the microlensing problem under investigation. On current hardware, there is little difference in the processing speed of the single-core CPU tree code and the GPU direct code, however the recent plateau in single-core CPU speeds means the existing tree code is no longer able to take advantage of Moore’s law-like increases in processing speed. Instead, we anticipate a rapid increase in GPU capabilities in the next few years, which is advantageous to the direct code. We suggest that progress in other areas of astrophysical computation may benefit from a transition to GPUs through the use of “brute force” algorithms, rather than attempting to port the current best solution directly to a GPU language – for certain classes of problems, the simple implementation on GPUs may already be no worse than an optimised single-core CPU version.