Definition and detailed characterization of Lunar surface units using remote observations

Remote sensing techniques and data may be subdivided into three principal types according to how they are used: (1) defining techniques help to define unit boundaries and extent; (2) characterizing techniques allow classification and characterization of physical features, lithology, or chemical composition; (3) supporting techniques provide additional useful information but are not fundamental to the definition or characterization of units. Defined units represent a fundamental subdivision of the rocks in a planetary crust and thus represent processes and sequences of events. The definition and characterization of units provides a framework for the interpretation of planetary processes and history. Detailed consideration of unit definition and characterization is presented using the mare deposits of the Imbrium basin as an example. This example provides guidelines for the utilization of remote sensing techniques in geologic mapping of the Moon and other planets.     

A new technique for the determination of coronal magnetic fields: A fixed mesh solution to Laplace's equation using line-of-sight boundary conditions

A new method for computing potential magnetic field configurations in the solar atmosphere is described. A discrete approximation to Laplace's equation is solved in the domain R r R ₁, 0 , 0 2 (R ₁being an arbitrary radial distance from the solar center). The method utilizes the measured line-of-sight magnetic fields directly as the boundary condition at the solar surface and constrains the field to become radial at the outer boundary, R ₁. First the differential equation and boundary conditions are reduced to a set of two-dimensional equations in r, by Fourier transforming out the periodic dependence. Next each transformed boundary condition is converted to a Dirichlet surface condition. Then each two-dimensional equation with standard Dirichlet-Dirichlet boundary conditions is solved for the Fourier coefficient it determines. Finally, the solution of the original three dimensional equation is obtained through inverse Fourier transformation. The primary numerical tools in this technique are the use of a finite fast Fourier transform technique and also a generalized cyclic reduction algorithm developed at NCAR. Any extraneous monopole component present in the data can be removed if so desired.The code was developed for the HAO solar-interplanetary modeling effort in response to the following specific requirements:

Constraints on Infrasound Scaling and Attenuation Relations from Soviet Explosion Data

—?The Institute for the Dynamics of the Geospheres (IDG) in Moscow, Russia, contains an archive of infrasound recordings from Soviet atmospheric nuclear tests that were conducted in 1957 and 1961, and has digitized the highest quality records from this data set. We have measured the infrasound signals from these records and compared them with previously developed scaling and attenuation relations. We find that the data are in best agreement with a scaling and attenuation relation developed by the Los Alamos National Laboratory (LANL) which can be written as logP = 3.37 + 0.68 logW? 1.36logR where P is zero to peak pressure amplitude in Pascals, W is the yield in kilotons, and R is the source to receiver distance in kilometers. We use the scaling relations to define an infrasound magnitude, and to estimate the detection capability of the International Monitoring System (IMS) being developed as part of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The detection threshold for the proposed 60-station IMS network is estimated to be slightly higher than the CTBT design goal of 1 kiloton in some locations.     

Response of a hypersaline salt marsh to a large flood and rainfall event along the west coast of southern Africa

The Orange Estuary lost 27% (276 ha) of its wetland area near the mouth as a result of bad management practices during the 1980s. The salt marsh has been unable to recover over the last 20 years because of the persistently high soil and groundwater salinity. In 2006, a 1 in 5 year flood occurred that completely covered the desertified salt marsh and floodplain with freshwater. The flood was followed by an above average (>45 mm) winter rainfall. Soil and groundwater sampled in April and August 2004 were compared with 2006 data to quantify the impact of the flood and rainfall event. It was hypothesised that the two freshwater events would significantly reduce the soil and groundwater salinity. However, the results showed no significant difference in sediment electrical conductivity throughout the soil profile over the four sampling periods. Soil moisture and organic content however increased significantly after these events in the surface soil layer. The flood deposited silt and scoured sand from the surface layers in significant quantities. The depth to groundwater in the desertified marsh retained a similar pattern after the flood despite 15 cm changes in depth in places. In 2004 a clear groundwater electrical conductivity gradient was present extending from the less saline north part of the marsh (0–15 mS cm⁻¹) to the central part (120–135 mS cm⁻¹) and decreasing again towards the south (60–75 mS cm⁻¹). The flood served to even out the groundwater salinity across the desertified marsh (60–90 mS cm⁻¹). The flood and high rainfall had a limited impact on the soil and groundwater characteristics. The few significant changes that were recorded were mostly restricted to the surface soil layers and on a small spatial scale. The rainfall did however create numerous pools of low salinity (<60 mS cm⁻¹) water on the marsh surface that provided a brief opportunity for salt marsh seeds to germinate. A further benefit of the flood was the increased tidal reach into the desertified marsh importing freshwater from the river mouth and exporting salt. Despite these responses it is unlikely that the hypersaline salt marsh will revegetate naturally. Human intervention is needed to ensure the rehabilitation of this important Ramsar site.     

Potential climate-change impacts on the Chesapeake Bay

We review current understanding of the potential impact of climate change on the Chesapeake Bay. Scenarios for CO₂ emissions indicate that by the end of the 21^st century the Bay region will experience significant changes in climate forcings with respect to historical conditions, including increases in CO₂ concentrations, sea level, and water temperature of 50–160%, 0.7–1.6 m, and 2–6 °C, respectively. Also likely are increases in precipitation amount (very likely in the winter and spring), precipitation intensity, intensity of tropical and extratropical cyclones (though their frequency may decrease), and sea-level variability. The greatest uncertainty is associated with changes in annual streamflow, though it is likely that winter and spring flows will increase. Climate change alone will cause the Bay to function very differently in the future. Likely changes include: (1) an increase in coastal flooding and submergence of estuarine wetlands; (2) an increase in salinity variability on many time scales; (3) an increase in harmful algae; (4) an increase in hypoxia; (5) a reduction of eelgrass, the dominant submerged aquatic vegetation in the Bay; and (6) altered interactions among trophic levels, with subtropical fish and shellfish species ultimately being favored in the Bay. The magnitude of these changes is sensitive to the CO₂ emission trajectory, so that actions taken now to reduce CO₂ emissions will reduce climate impacts on the Bay. Research needs include improved precipitation and streamflow projections for the Bay watershed and whole-system monitoring, modeling, and process studies that can capture the likely non-linear responses of the Chesapeake Bay system to climate variability, climate change, and their interaction with other anthropogenic stressors.     

Estimating the carbon transfer between the ocean, atmosphere and the terrestrial biosphere since the last glacial maximum

Carbon dioxide records from polar ice cores and marine ocean sediments indicate that the last glacial maximum (LGM) atmosphere CO₂ content was 80–90 ppm lower than the mid-Holocene. This represents a transfer of over 160 GtC into the atmosphere since the LGM. Palaeovegetation studies suggest that up to 1350 GtC was transferred from the oceans to the terrestrial biosphere at the end of the last glacial. Evidence from carbon isotopes in deep sea sediments, however, indicates a smaller shift of between 400 and 700 GtC. To understand the functioning of the carbon cycle this apparent discrepancy needs to be resolved. Thus, older data have been reassessed, new data provided and the potential errors of both methods estimated. New estimates of the expansion of terrestrial biomass between the LGM and mid-Holocene are 700 GtC ± > 300 GtC, using the ocean carbon isotope-based method, compared with of 1100 GtC ± > 500 GtC using the palaeovegetation estimate. If these estimates of the carbon shift to the terrestrial biosphere are equilibrated with the dissolved carbon in the oceans, and the CaCO₃ compensation of the ocean is taken into account, then the glacial atmospheric CO₂ would have been between 50 (± 30) ppm and 95 (± 50) ppm higher. The glacial atmosphere therefore should have had a CO₂ partial pressure of between 330 and 375 μatm. Hence, a rise of between 130 and 175 μatm in atmospheric CO₂, rather than 80 μatm, at the end of the last glacial must be accounted for.     

Efficacy of PIT tags and an autonomous antenna system to study the juvenile life stage of an estuarine-dependent fish

Many marine fishes use spatially distinct habitats as juveniles and adults. Determining which juvenile habitats are most important to sustaining adult populations (i.e., which habitats are nurseries) has proven difficult, in part due to challenges in estimating survival of juveniles in putative nursery habitats. Recent technological advances have made largescale tagging efforts a viable approach to estimating survival of juvenile fishes by increasing recapture rates and enabling the use of individual-identification tags. These techniques, using Passive Integrated transponder (PIT) tags and autonomous antenna detection systems (antenna), have been successfully applied in freshwater environments. This paper reports the adaptation of these techniques to estuarine mangrove creeks (salinity: 2–28‰) for research of the juvenile life stage on an estuarine-dependent marine fish,Centropomus undecimalis. Retention rate of PIT tags in juveniles >120 mm standard length was 100%, with no mortality. The antenna detection field covered 48% of the creek water column, and the antenna was experimentally determined to detect approximately 67% of tagged fish that swam through. Overall recapture rate of tagged fish by the antenna was >40%. This recapture rate is higher than the sparse data typical of traditional tag-recapture studies. A time-dependent Jolly-Seber model was fit to the data, providing estimates of capture probability (0.8) and weekly apparent survival (0.41) that will be invaluable in comparing juvenile habitats of different quality (e.g., natural versus anthropogenically degraded). This research demonstrates the viability of this approach to fish research in estuarine habitats.