Post-Newtonian satellite orbits

The first post-Newtonian approximation of general relativity is used to account for the motion of solar system bodies and near-Earth objects which are slow moving and produce weak gravitational fields. The \(n\)-body relativistic equations of motion are given by the Einstein-Infeld-Hoffmann equations. For \(n=2\), we investigate the associated dynamics of two-body systems in the first post-Newtonian approximation. By direct integration of the associated planar equations of motion, we deduce a new expression that characterises the orbit of test particles in the first post-Newtonian regime generalising the well-known Binet equation for Newtonian mechanics. The expression so obtained does not appear to have been given in the literature and is consistent with classical orbiting theory in the Newtonian limit. Further, the accuracy of the post-Newtonian Binet equation is numerically verified by comparing secular variations of known expression with the full general relativistic orbit equation.     

Determination of Mars crater geometric data: Insights from high-resolution digital elevation models

We review the methods and data sets used to determine morphometric parameters related to the depth (e.g., rim height and cavity depth) and diameter of Martian craters over the past ~45 yr, and discuss the limitations of shadow length measurements, photoclinometry, Earth-based radar, and laser altimetry. We demonstrate that substantial errors are introduced into crater depth and diameter measurements that are inherent in the use of 128th-degree gridded Mars Orbiter Laser Altimeter (MOLA) topography. We also show that even the use of the raw MOLA Precision Engineering Data Record (PEDR) data can introduce errors in the measurement of craters a few kilometers in diameter. These errors are related to the longitudinal spacing of the MOLA profiles, the along-track spacing of the individual laser shots, and the MOLA spot size. Stereophotogrammetry provides an intrinsically more accurate method for measuring depth and diameter of craters on Mars when applied to high-resolution image pairs. Here, we use 20 stereo Context Camera (CTX) image pairs to create digital elevation models (DEMs) for 25 craters in the diameter range 1.5–25.6 km and cover the latitude range of 25^° S to 42^° N. These DEMs have a spatial scale of ~24 m per pixel. Six additional craters, 1.5–3.1 km in diameter, were studied using publically available DEMs produced from High-Resolution Imaging Science Experiment (HiRISE) image pairs. Depth/diameter and rim height were determined for each crater, as well as the azimuthal variation of crater rim height in 1-degree increments. These data indicate that morphologically fresh Martian craters at these diameters are significantly deeper for a given size than previously reported using Viking and MOLA data, most likely due to the improvement in spatial resolution provided by the CTX and HiRISE data.     

Baseline Sediment Trace Metals Investigation: Steinhatchee River Estuary, Florida, Northeast Gulf of Mexico

This Florida Geological Survey U.S. Department of the Interior, Minerals Manage ment Service Cooperative Study provides baseline data for major and trace metal concentrations in the sediments of the Steinhatchee River estuary. These data are intended to provide a benchmark for comparison with future metal concentration data measurements. The Steinhatchee River estuary is a relatively pristine bay located within the Big Bend Wildlife Management Area on the North Central Florida Gulf of Mexico coastline. The river flows 55 km through woodlands and planted pines before emptying into the Gulf at Deadman Harbor. Water quality in the estuary is excellent at present. There is minimal development within the watershed. The estuary is part of an extensive system of marshes that formed along the Florida Gulf coast during the Holocene marine transgression. Sediment accretion rate measurements range from 1.4 to 4.1 mm yr on the basis of lead-210 measurements. Seventy-nine short cores were collected from 66 sample locations, representing four lithofacies: clay- and organic-rich sands, organic-rich sands, clean quartz sands, and oyster bioherms. Samples were analyzed for texture, total organic matter, total carbon, total nitrogen, clay mineralogy, and major and trace-metal content. Follow ing these analyses, metal concentrations were normalized against geochemical reference elements (aluminum and iron) and against total weight percent organic matter. Metals were also normalized granulometrically against total weight percent fines (0.062 mm). Concentrations were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) for all metals except mercury. Mercury concentrations were determined by cold-flameless atomic absorption spectrometry (AAS). Granulo metric measurements were made by sieve and pipette analyses. Organic matter was determined by two methods: weight loss upon ignition and elemental analysis (by Carlo-Erba Furnace) of carbon and nitrogen. X-ray diffraction was used to deter mine clay mineralogy. Trace-metal concentrations were best correlated when normalized with respect to sediment aluminum concentrations. Normalizations indicate that most major and trace-metal concentrations fall within 95 % prediction limits of the expected value. This finding suggests that little significant metal contamination occurred within this system prior to 1994 sediment sampling. Exceptions include lead, mercury, copper, zinc, potassium, and phosphorous. Lead and mercury are elements that generally enter this watershed through atmospheric deposition; thus, anomalous levels of these metals are not necessarily associated with activities within the watershed of the Steinhatchee River estuary. Anomalous concentrations of other metals such as zinc, copper, and phosphorous probably do originate within the Steinhatchee watershed. Copper failed to correlate well with any geochemical or granulometric normalizer, and this condition was not limited to a single facies or area within the estuary. This finding may indicate copper contamination in the system. Increased zinc and copper levels may be attributed to marine paints. Phosphorous levels also appeared to be elevated in a few locations in the two marsh facies sampled. This may be due to nutrient loading from two small communities, Jena and Steinhatchee, or from the application of this element in fertilizer to reduce moisture stress to young planted pines on tree farms within the watershed.     

Early diagenetic alteration of chlorophyll-a and bacteriochlorophyll-a in a contemporaneous marl ecosystem; Florida Bay

This report covers the analyses of tetrapyrrole pigments in sediments and numerous source biota from northern central Florida Bay. Sediment cores were all carbonate marls and ‘bedrock’ (Pleistocene limestones) was typically at 0.6–1.2 m bsf. (below sea floor). Extraction of the sediments was performed using tetrahydrofuran, shown to be 3–7 times as effective as more common solvents. Surficial sediments were found to contain a pigment distribution indicating a diatomaceous-cyanobacterial biofilm/mat underlain with purple sulfur bacteria as the microphytobenthos. Downhole trends in pigment diagenesis revealed differences due to paleoenvironment. That is, when bacteriochlorophyll-a (BCHLa) plus derivatives were elevated, indicating strong syn-depositional anoxia, the pheophytins-a (PTINsa) were the major chlorophyll-a (CHLa) derivatives. Conversely, when BCHL-a plus derivatives were low, indicating oxic to dys-oxic syn-depositional conditions, then pyropheophorbide-a (pPBIDa) and 13², 17²-cyclopheophorbide-a (CYCLO) were strongly dominant. The generation of cyclopheophorbide in carbonate marls with weakly anoxic to dysoxic syn-depositional conditions may yield an oil-source paleoenvironmental marker for bitumen containing compounds such as bicycloalkanoporphyrins (BiCAPs). Downhole conversions were observed for the following diagenetic steps; CHLa to pheophytin-a (PTINa), PTINa to pyropheophytin-a (pPTINa), pPBIDa to CYCLO, BCHLa to bacteriopheophytin-a (BPTINa), and BPTINa to bacteriopyropheophytin-a (BpPTINa).     

Recent bottom-current activity in the deep western Bay of Bengal

We present several types of data which show that strong geostrophic bottom currents are present in a broad valley in the deep western Bay of Bengal adjacent to the Indian margin. Sea-floor photographs show well-developed current lineations with scour marks on the northern sides and sediment deposition tails on the southern sides of some objects (such as fecal pellets) suggesting strong southward-flowing bottom currents. A direct current measurement made in the region confirms this inferred flow direction. The nepheloid layer is much stronger in the western Bay of Bengal than in any other region of the northern Indian Ocean and indicates strong turbulence and a high concentration of suspended sediment at or near the sea floor. Additional data which do not provide unequivocal evidence for, but may also be indicative of, the existence of the bottom currents are as follows: the dispersal of the peninsular Indian rivers-derived smectite-rich sediments all along the valley to as far as south of Sri Lanka; a zone of sediment waves (as recorded on 3.5-kHz echograms) parallel to the regional trend of bathymetric contours along the Indian margin; and the frequent occurrence of thin, sharp and uniform layers of fine sand and silt beds rather than thick graded turbidite beds in the cores from the broad valley in the deep western Bay of Bengal.     

Large submarine slide (olistostrome) associated with Sunda Arc subduction zone,northeast Indian Ocean

Reflection profiling in a region of anomalous topography and structure in the Bay of Bengal off Burma has revealed the presence of a large submarine slide (olistostrome) at the base of the continental slope off the Bassein River. The slide overlies a thick section of Bengal Deep-Sea Fan turbidites and has a complex internal structure consisting of two primary elements. The lower element is pervasively disturbed and is interpreted as a mudflow generated at the time of the slide which spread over a large area to as much as 35 km beyond the topographic toe. This mudflow poured into a distributary channel on the Bengal Fan and virtually filled it for 145 km along its length. The upper element comprises a series of relatively coherent blocks of stratified sediments (olistoliths) bounded by curved fault planes. The blocks have been transported as much as 55 km from the original Sunda Trench wall. Their dimensions, up to 360 m thick and 2.8 km between faults, are similar to olistoliths of the slide terrain in the Apennines. The blocks are blanketed by younger slope strata. The total area covered by the slide, including the mudflow, is almost 4,000 km², and total volume of the slide is over 900 km³. Material of the slide consists of Bengal Fan turbidites offscraped above the Sunda Subduction zone and blanketed by rapidly deposited slope sediments from a western Irrawaddy River distributary (the Bassein River) during Late Quaternary glacial low sea level. This rapid loading, probably coupled with a large earthquake, triggered the slide.     

Evaporites, petroleum exploration, and the Cenozoic evolution of the Libyan shelf margin, central North Africa

The Mediterranean margin of Libya can be divided into three physiographic provinces, the Pelagian Shelf, the Sirt Embayment, and Offshore Cyrenaica. The petroleum potential of the Pelagian Shelf has been investigated but the Sirt Embayment and Offshore Cyrenaica are almost unexplored. During 2004–2005, new 2D pre-stack time-migrated seismic data were acquired and used to examine the large-scale structural, depositional, and salt tectonic features of the Libyan shelf and slope. The data cover approximately 38,000 line kilometers in water depths ranging from under 50 to over 3000 m.Cenozoic strata along much of the Libyan margin have a demonstrable progradational character punctuated by surfaces of erosion and margin failure. Within the Sirt Embayment the most visible retrogradational surface becomes seismically coincident with the top of Messinian unconformity. This retrogradational surface extends for over 700 km along strike and cuts both sides of the Sirt Embayment. Over 5000 cubic kilometers of material are missing from above this surface. There are two ideas for how retrogradation occurred. One idea relates the retrogradation to margin erosion during the Messinian salinity crisis. The other idea suggests that a large part of the Libyan margin experienced a cataclysmic failure during the late Miocene.Some existing models for offshore Libya have interpreted a widespread layer of halite lying within the Messinian which thickens basinward. This interpretation was probably based on the fact seismic reflection continuity was lost over much of the Sirt Embayment on older data beneath the top Messinian unconformity. The loss of good reflection character adversely affected exploration efforts by obscuring deep structures. Recent seismic data and a current understanding of salt behavior do not support the interpretation of thick halite within the Messinian section. Regional observations do not indicate any mobile halite present in the Sirt Embayment. There is a relatively thin, high amplitude and high velocity layer of non-halite evaporites (mainly anhydrite) which caps the Messinian section. Where this high amplitude and high velocity layer is absent or eroded, seismic continuity within the Messinian interval is restored. Limited available well data support this interpretation.True mobile halite is interpreted to exist in offshore Libya only in the far west of the Pelagian Shelf near the Tunisian border. Beneath the Pelagian Shelf are a series of tight contractional folds that are interpreted to be salt cored. Basins adjacent to the folds display geometries characteristic of salt withdrawal. The fold crests formed bathymetric highs which served as nucleation sites for nummulitic shoal development. These shoals are the principal reservoirs of the Pelagian Shelf.     

Impact of halides on the photobleaching of dissolved organic matter

Understanding absorbance photobleaching of marine dissolved organic matter (DOM) is important because DOM chromophores impact oceanic primary productivity by affecting the depth of the photic zone, absorb UV radiation and affect ocean color used in remote sensing. However, the fundamental mechanisms which account for this bleaching are largely unknown. Controlled laboratory studies demonstrated that the presence of seawater concentrations of chloride and bromide ions enhanced absorbance photobleaching reaction rates by ~ 40%, regardless of DOM source or the presence or absence of carbonate ions. In contrast, halide ions generally did not affect fluorescence bleaching rates. Variations in ionic strength did not alter the enhancement in absorbance photobleaching by halide ions. Accordingly, the enhancement in absorbance photobleaching was specific to halide ions, rather than a generalized salinity effect. We confirmed the formation of hydroxyl radical (HO^•) in illuminated samples, and its significant scavenging in the presence of halide salts. Gamma-radiolysis experiments and associated modeling indicated that a small component (~ 12%) of the photobleaching enhancement by halides was consistent with the hypothesis that halide scavenging of HO^• will form reactive halogen radicals that target electron-rich chromophores within DOM more selectively than HO^•. The mechanism responsible for the major component of absorbance photobleaching rate enhancement by halides remains unresolved.