bluuebunny/crossref_metadata_2025 huggingface dataset:
Green icebergs formed by freezing of organic‐rich seawater to the base of Antarctic ice shelves
Authors: Warren Stephen G. , Roesler Collin S. , Morgan Vincent I. , Brandt Richard E. , Goodwin Ian D. , Allison Ian
Published: February 2008

Although most icebergs are blue, green icebergs are seen occasionally in the Antarctic ocean. Chemical and isotopic analysis of samples from green icebergs indicate that the ice consists of desalinated frozen seawater, as does the basal ice from the Amery Ice Shelf. Spectral reflectance of a green iceberg measured near 67°S, 62°E, confirms that the color is inherent to the ice, not an artifact of the illumination. Pure ice appears blue owing to its absorption of red photons. Addition of a constituent that absorbs blue photons can shift the peak reflectance from blue to green. Such a constituent was identified by spectrophotometric analysis of core samples from this iceberg and from the Amery basal ice, and of seawater samples from Prydz Bay off the Amery Ice Shelf. Analysis of the samples by fluorescence spectroscopy indicates that the blue absorption, and hence the inherent green color, is due to the presence of marine‐derived organic matter in the green iceberg, basal ice, and seawater. Thick accumulations of green ice, in icebergs and at the base of ice shelves, indicate that high concentrations of organic matter exist in seawater for centuries at the depth of basal freezing.
A numerical study of sediment transport and event bed genesis during tropical storm Delia
Authors: Keen Timothy R. , Slingerland Rudy L.
Published: February 2008

Some event beds (tempestites) are thought to be emplaced on shallow marine shelves by the combined action of strong coastal currents and high waves during fairly short‐lived storms. To test this hypothesis, a storm sedimentation system has been constructed from six numerical models describing a cyclonic wind field, three‐dimensional coastal circulation, wind waves generated over the continental shelf, the combined effect of steady and oscillatory currents within the benthic boundary layer, suspended and bed load transport of sediment, and conservation of the seafloor. This model system is used to hindcast winds, currents, waves, and resulting sedimentation during Tropical Storm Delia, which passed over the Texas‐Louisiana shelf on September 3–4, 1973. Sensitivity to the initial substrate is investigated in four experiments using uniform silt, uniform sand, a mud line at the 20‐m isobath, and a simplified modern sediment distribution. Modeled coastal currents are vertically uniform and do not reveal the structure predicted by the mid‐latitude geostrophic storm circulation model, because the predicted depth of the wind‐mixed layer is greater than the water depth over the shelf. Shelf currents in excess of 2 m/s flow predominantly along the coast to the southwest during most of the storm, driven by the wind stress and the trapped coastal wave which peaks at 180 cm near Galveston. Significant wave heights reach 8 m on the outer shelf but are less than 4 m over the inner shelf. These waves combine with steady currents to produce bed shear velocities which locally exceed 20 cm/s. The region of highest stresses always lies to the right of the storm track (viewed down the path) and moves across the shelf with the eye of the storm. Three general sediment transport paths are evident: (1) onshore transport of finer sediment over the outer shelf to the right of the storm track, (2) westward‐directed along‐shelf transport of predominantly fine sediment between approximately 40‐m and 20‐m water depths, and (3) minor offshore transport of sand from the shoreface to depths less than 30m. The resulting event bed has a ragged appearance with a maximum thickness of about 20 cm in region 1, and covers an area of approximately 3×104 km2 to the right of the storm track. Aside from local transport associated with finer sediments, these results are relatively insensitive to initial sediment type. Comparison of model results to observed data from Buccaneer platform shows that the different models performed adequately during the peak of the storm, except for a significant underprediction of the significant wave height by the wind sea model. The estimated uncertainty in the calculated combined shear stresses u*, based on errors produced by the individual model components, is most dependent on the wave bottom orbital amplitude. The total uncertainty in u* is estimated to be approximately 7%.
Photochemical oxygen activation: Superoxide radical detection and production rates in the eastern Caribbean
Authors: Micinski Edward , Ball Lary A. , Zafiriou Oliver C.
Published: February 2008

Superoxide ion‐radical, O2‐, the one‐electron reduction product of molecular oxygen, is a long‐suspected first intermediate in chemical reactions using oxygen as the ultimate electron acceptor. We have detected photochemical production of O2‐ in a variety of eastern Caribbean waters studied in Spring and Fall by using a chemically direct O2‐ trapping reaction combined with 15N and/or 18O isotopic labelling of reactants to provide sensitivity and specificity. Photochemical superoxide production rates ranged from 0.1–6 nmol L−1 min−1 of full‐sun irradiation in Spring and from 0.2–8 nmol L−1 min−1 in Fall. These superoxide fluxes correlate well with independently measured total (NO‐scavengeable) radical fluxes in both seasons and account for ∼ 1/3 of the total radical production. Hence we confirm that O2‐ is a quantitatively important, perhaps dominant, reactive transient species in the photochemical radical array. Semiquantitative estimates suggest that O2‐ dismutation to HOOH and O2 can account for most or all of the photochemical HOOH production in surface waters. O2‐ production rates also correlated negatively with salinity.
Atmospheric hydrogen sulfide over the equatorial Pacific (SAGA 3)
Authors: Yvon Shari A. , Cooper David J. , Koropalov Valentin , Saltzman Eric S.
Published: February 2008

Atmospheric H2S concentrations were measured over the equatorial Pacific on leg 1 of the third Soviet‐American Gases and Aerosols (SAGA 3) cruise during February and March 1990. Five N‐S transects were made across the equator between Hawaii and American Samoa. The concentrations ranged from below the detection limit of 0.4 ± 0.5 (1 σ) to 14.4 ppt with an average value of 3.6 ± 2.3 ppt (1σ, n = 72). The highest concentrations were found on the easternmost two transects just south of the equator. The average concentration of 3.6 ppt observed on this cruise is the lowest reported value for background atmospheric H2S over the tropical oceans. A lack of correlation between 222Rn and H2S rules out a significant continental source. Model calculations indicate that the oceanic source of H2S in this region is in the range of 9 to 21 × 10−8 mol m−2 d−1. From this flux the concentration of free sulfide (H2S + S= ) in the surface mixed layer of the ocean is estimated to be in the range of 32 to 67 pmol L−1. In the atmosphere the oxidation of H2S produces SO2 at a rate of 2.1 to 4.4 × 10−11 mol m−3 d−1 which is only a small fraction of that estimated from the oxidation of dimethyl sulfide (DMS) in this region. A diurnal cycle was not observed in the H2S data recorded during this cruise.
Overview of the Stratospheric Aerosol and Gas Experiment II water vapor observations: Method, validation, and data characteristics
Authors: Rind D. , Chiou E.‐W. , Chu W. , Oltmans S. , Lerner J. , Larsen J. , McCormick M. P. , McMaster L.
Published: February 2008

Water vapor observations obtained from the Stratospheric Aerosol and Gas Experiment II (SAGE II) solar occultation instrument for the troposphere and stratosphere are presented and compared with correlative in situ measurement techniques and other satellite data. The SAGE II instrument produces water vapor values from cloud top to approximately 1 mbar, except in regions of high aerosol content such as occurs in the low to middle stratosphere after volcanic eruptions. Details of the analysis procedure, instrumental errors, and data characteristics are discussed. Various features of the data set for the first 5 years after launch (1985–1989) are identified. These include an increase in middle and upper tropospheric water vapor during northern hemisphere summer and autumn, thus at times of warmest sea surface temperature; minimum water vapor values of 2.5–3 ppmv in the tropical lower stratosphere, with lower values during northern hemisphere winter and spring; slowly increasing water vapor values with altitude in the stratosphere, reaching 5–6 ppmv or greater near the stratopause; extratropical values with minimum profile amounts occurring above the conventionally defined tropopause; and higher extratropical than tropical water vapor values throughout the stratosphere except in locations of possible polar stratospheric clouds. SAGE II data will be useful for studying individual water vapor profiles, tropospheric response to climate perturbations, tropospheric‐stratospheric exchange (due to its inherent high vertical resolution), and stratospheric transports. It should also aid in the preparation, for the first time on a global scale, of climatologies of the stratosphere and the upper level cloud‐free troposphere, for use in radiative, dynamical, and chemical studies.
The age of the air in the firn and the ice at Summit, Greenland
Authors: Schwander J. , Barnola J.‐M. , Andrié C. , Leuenberger M. , Ludin A. , Raynaud D. , Stauffer B.
Published: February 2008

In the framework of the Eurocore drilling project 1989 at Summit, Central Greenland, air samples were collected from a drill hole in the firn at several depth levels. The samples have been analyzed for 85Kr, CO2, CH4, CFC's (F‐11 and F‐12) contents and for the isotopic composition of nitrogen and oxygen. The measured data are compared with the results of a diffusion model. CO2, for example, takes 12 years (with a standard deviation of 7.5 years) to diffuse from the surface to the firn‐ice transition under the present climatic conditions at Summit. The difference between the age of the ice and the mean age of the occluded air is approximately 210 years. An enrichment of the heavier isotopes due to separation by gravity has been observed. Molecular diffusion alone suffices to explain the observed concentration trends in the firn column. We can, however, not exclude the existence of a convective zone below the surface. We have also measured the density and closed porosity along the firn core that has been retrieved when drilling the hole. The porosity data reveal that the air is occluded into bubbles mainly between 65 and 80 m, corresponding to densities of 790 and 830 kg/m3, respectively.
Submicron particle, radon, and soot carbon characteristics over the northeast Atlantic
Authors: O'Dowd Colin D. , Smith Michael H. , Jennings S. Gerard
Published: February 2008

Atmospheric aerosol particles (0.05μm ≤ rdry ≤ 1.5μm), 222Rn, and soot carbon mass were measured on a cruise over the Northeast Atlantic (63°N, 8°W) during October and November 1989. An accumulation mode (AM) was present in all particle data and was characterized by a lognormal size distribution with parameters N cm−3 (total number concentration), rg μm (geometric mean radius) and σg (geometric standard deviation). For aerosol associated with the “cleanest” Northeast Atlantic maritime and Arctic air masses, the AM parameters were found to be 16 cm−3 ≤ N ≤ 48 cm−3, 1.32 ≤ σg ≤ 1.46, and 0.08 μm < rg < 0.09 μm, leading to AM masses of between 0.20 μg m−3 and 0.38 μg m−3. Clean background levels of soot carbon mass for maritime and Arctic air were estimated to be around 20 ng m−3 and were associated with particle size radii r ≤ 0.15 μm. Soot carbon mass showed an excellent correlation with AM number concentration (cc=0.93), demonstrating its usefulness as an air mass tracer and as an indicator of anthropogenic pollutant transport. By comparison, radon, which is often used for this purpose, exhibited a significantly poorer correlation (cc=0.60) for this region. Approximately 9% of the total AM mass was accounted for by soot carbon, regardless of air mass origin, suggesting that early winter marine aerosol in the remote North Atlantic is primarily of anthropogenic origin.
Emissions of sulfur gases from marine and freshwater wetlands of the Florida Everglades: Rates and extrapolation using remote sensing
Authors: Hines Mark E. , Pelletier Ramona E. , Crill Patrick M.
Published: February 2008

Rates of emissions of the biogenic sulfur (S) gases carbonyl sulfide (COS), methyl mercaptan (MSH), dimethyl sulfide (DMS), and carbon disulfide (CS2) were measured in a variety of marine and freshwater wetland habitats in the Florida Everglades during a short duration period in October using dynamic chambers, cryotrapping techniques, and gas chromatography. The most rapid emissions of >500 nmol m−2 h−1 occurred in red mangrove‐dominated sites that were adjacent to open seawater and contained numerous crab burrows. Poorly drained red mangrove sites exhibited lower fluxes of ∼60 nmol m−2 h−1 which were similar to fluxes from the black mangrove areas which dominated the marine‐influenced wetland sites in the Everglades. DMS was the dominant organo‐S gas emitted especially in the freshwater areas. Spectral data from a scene from the Landsat thematic mapper were used to map habitats in the Everglades. Six vegetation categories were delineated using geographical information system software and S gas emissions were extrapolated for the entire Everglades National Park. The black mangrove‐dominated areas accounted for the largest portion of S gas emissions to the area. The large area extent of the saw grass communities (42%) accounted for ∼24% of the total S emissions.
Temperature dependence of ν3 and ν4 bandwidths and complex refractive indices for crystalline methane
Authors: Ngoh M. A. , Khanna R. K. , Fox K.
Published: February 2008

Infrared spectra of thin films of pure CH4 have been measured for a range of temperatures from 22 to 68 K. The bandwidth for the fundamental ν3 near 3000 cm−1 (3.3 μm) varies from 12.7 to 33.2 cm−1, while that for ν4 near 1300 cm−1 (7.7 μm) varies from 6.2 to 16.0 cm−1. The real and imaginary parts of the index of refraction also exhibit significant dependence on temperature. These broadband measurements at low temperatures are useful for an understanding of clouds and hazes in the atmosphere of Uranus, clouds and ices in the atmosphere of Titan, and ices on the surfaces of Pluto and Triton.
An assessment of the nature and origins of the carbon‐bearing components in fines collected during the sawing of EET A79001
Authors: Wright I. P. , Hartmetz C. P. , Pillinger C. T.
Published: February 2008

Saw dust obtained from the cutting of EET A79001, a meteorite with a presumed Martian origin, has been analyzed for its carbon content and stable isotopic composition in order to assess the sample's potential value for studies aimed at elucidating Martian surface processes. These fines, which are available in plentiful supply, are a useful source of material and are important since they are a representative whole‐rock sample of this complex meteorite. In addition, the fines give an indication of contamination sources which may affect not only the collected sawings but also the sawn surface of the meteorite. A number of contaminants were identified in the fines (e.g. organic materials, Teflon, diamond, and carbon associated with metal). It is considered that the levels of carbon contamination measured represent a worst possible case and hence provide a valuable reference with which to compare other analyses of this sample, or indeed, other Martian meteorites. Evidence was found for an indigenous carbonate component similar to that observed previously in other fractions of the meteorite. However, based on the results presented herein it is not possible to assert that isotopically distinct carbonate minerals of different origins are present in the meteorite. The levels of trapped Martian atmospheric CO2 calculated for the fines are unexpectedly high (∼1 ppm carbon), but this could be influenced by the presence of other, as yet unknown, carbonaceous materials.
Temperature, N2, and N density profiles of Triton's atmosphere: Observations and model
Authors: Krasnopolsky V. A. , Sandel B. R. , Herbert F. , Vervack R. J.
Published: February 2008

Improved analysis of the Voyager Ultraviolet Spectrometer (UVS) observations of the solar occultation by Triton yields the isothermal temperature and N2 number densities in the altitude range 475–675 km: T = 102 ± 3 K, [N2]= (4 ± 0.4) × 108 cm−3 at 575 km. A distinct steplike absorption feature at 850 Å is due to the atomic nitrogen ionization continuum. It allows a measurement of N number densities in the range from 170 to 570 km, which correspond to diffusive equilibrium above 300 km with [N] = (1±0.25) ×108 cm−3 at 400 km and T = 100±7 K. Deviations from diffusive equilibrium become important below 300 km, and [N] = (5 ± 2.5) × 108 cm−3 at 200 km. The exobase altitude is 870 km, and the total escape rate of atomic nitrogen is (1±0.3) × 1025 s−1. The main condensible product of methane chemistry is ethylene, C2H4, with a peak number density of 6 × 106 cm−3 near 25 km. The striking similarity of the thermospheric properties at both occultation sites despite substantial differences in latitudes, seasons, local time, and incoming flux of magnetospheric electrons implies very effective winds and suggests that one‐dimensional modeling is applicable. Temporal variations of the temperature profile should be rather small in spite of strong variations of the electron flux. The presence of CO in the atmosphere as suggested by recent measurements of the CO absorption bands in the surface ice results in cooling by the rotational lines, deactivation and radiation of vibrational excitation of N2, and heating by quenching of N(2D). Heating efficiencies of electron precipitation and solar EUV radiation in the ranges of the N2 continuum and bands are calculated equal to 0.2–0.29, 0.24, and 0.19, respectively. The column integrated cooling by the CO lines is weaker than the thermospheric heating and cannot form a mesosphere. A CO mixing ratio of up to 10−2 is consistent with thermal balance calculations. Sixteen optimized versions of the model are considered with profiles of T and [N2] which agree with the measurements. Profiles of N, H2, and H densities are calculated. The calculated profile of atomic nitrogen and its escape rate are in excellent agreement with the measured values. Mixing ratios of H2 and H at 400 km are equal to 240 and 23 ppm, respectively. The total escape rate of hydrogen atoms (H + 2H2) is determined by photolysis of methane by H Lyman α radiation, does not depend on the ionospheric processes which transform H2 to H, and is equal to 2.3 × 1026 s−1. The ratio of H to N escape rates on Triton, 20, does not correspond to the measured ratio H+/N+∼ 2–3 in Neptune's magnetosphere and should be taken into account in its modeling. The recommended model for Triton's atmosphere is based on the temperature profile calculated for a CO mixing ratio of 10−3, a ratio of the average to the maximum electron fluxes of 0.162, and includes data on temperature, N2, N, CH4, H2, and H number densities.
The reaction of atomic hydrogen with germane: Temperature dependence of the rate constant and implications for germane photochemistry in the atmospheres of Jupiter and Saturn
Authors: Nava David F. , Payne Walter A. , Marston George , Stief Louis J.
Published: February 2008

Germane (GeH4) has been suggested to be a chemical tracer of atmospheric dynamics on Jupiter and Saturn. The observed abundance of germanium as GeH4 in the atmosphere of Saturn is dramatically low compared to the predicted GeH4 abundance. In order to provide data to help determine the major chemical form in which germanium exists in these planetary atmospheres, studies of the formation and loss processes for GeH4 are required. One of the important reactions to consider is that of hydrogen atom reaction with germane; H + GeH4. Two previous measurements of the rate constant for this reaction, made only at 298 K, yielded values differing by a factor of 200. We have undertaken a study to determine the absolute rate constant for this reaction for the first time as a function of temperature and pressure. The method employed to measure the rate of this reaction is that of flash photolysis of dilute mixtures of GeH4 in argon, combined with time‐resolved detection of H atoms via Lyman α resonance fluorescence. Results of this study show the reaction to be moderately rapid, independent of total pressure, but possessing a positive temperature dependence. Rate constant data over the temperature range 210 ≤ T ≤ 450 K yield the Arrhenius expression k1 = (1.94 ± 0.39) × 10−10 exp [(−1130 ± 50)/T] cm3 s−1. Implications for modeling the germane photochemistry in the atmospheres of Jupiter and Saturn derived from the present temperature dependent kinetic study are (1) low‐temperature reaction rate data relevant for these atmospheric conditions are provided, and (2) limits may be placed on the role of GeH4 production and loss processes in the modeler's efforts to elucidate the respective chemical forms and abundances in which the total germanium exists in the atmospheric systems of Jupiter and Saturn.
Mars atmospheric dynamics as simulated by the NASA Ames General Circulation Model: 1. The zonal‐mean circulation
Authors: Haberle Robert M. , Pollack James B. , Barnes Jeffrey R. , Zurek Richard W. , Leovy Conway B. , Murphy James R. , Lee Hilda , Schaeffer James
Published: February 2008

This is the first in a series of papers that will discuss Mars atmospheric dynamics as simulated by the NASA Ames General Circulation Model (GCM). This paper describes the GCM's zonal‐mean circulation and how it responds to seasonal variations and dust loading. The results are compared to Mariner 9 and Viking observations, and the processes responsible for maintaining the simulated circulation are discussed. At the solstices the zonal‐mean circulation consists of a single cross‐equatorial Hadley circulation between 30°S and 30°N. For relatively modest dust loadings (τ=0.3), the associated peak mass flux is 100 × 108 kg s−1 at northern winter solstice and 55 × 108 kg s−1 at southern winter solstice. At both seasons, westerlies dominate the winter hemisphere, and easterlies dominate the summer hemisphere. Maximum zonal winds occur near the model top (∼47 km) and are about the same at both seasons: 120 m s−1 in the winter hemisphere and 60 m s−1 in the summer hemisphere. Mean surface westerlies of 10–20 m s−1 are predicted at the middle and high latitudes of the winter hemisphere, as well as in the summer hemisphere near the rising branch of the Hadley circulation. The latter has the structure of a “jet” and is particularly strong (>20 m s−1) at northern winter solstice. With increasing amounts of dust (up to τ=5), the zonal mean circulation at northern winter solstice intensifies and gives no indication of a negative feedback. Dust can easily double the mass flux of the Hadley circulation. In the solstice simulations, the mean meridional circulation is the main dynamical contributor to the heat and momentum balance; the eddies play a relatively minor role. There is no evidence in these simulations for a polar warming. At the equinoxes the zonal mean circulation is more Earth‐like and consists of two roughly symmetric Hadley cells with westerly winds in the mid‐latitudes of each hemisphere and easterlies in the tropics. The simulated zonal winds are about half as strong as they are at solstice. However, the strength of the mean meridional circulation is much less than at solstice and averages between 5 and 10 × 108 kg s−1. At these seasons, the eddies and mean circulation make comparable, but opposing, contributions to the heat and momentum balances.
Evidence for a bathyal front at 2000‐M depth in the glacial Pacific, based on a depth transect on Ontong Java Plateau
Authors: Herguera J. C. , Jansen E. , Berger W. H.
Published: February 2008

Data on oxygen and carbon isotope compositions of the benthic foraminifer Planulina wüllerstorfi from 18 cores (17 box cores and one piston core) from Ontong Java Plateau provide proxy depth profiles for temperature, water mass, and nutrient content for the late Holocene, the last transition, and the last glacial. The δ18O profile during glacial time shows an increased gradient at a depth near 2000 m. The corresponding δ13C data suggest that a bathyal nutricline existed close to the same depth level. The δ13C values provide limits on the global change in carbon content of the glacial ocean, which may be estimated as distinctly less than 1 atmospheric carbon mass (1 ACM = 700 GtC). The greater CO2 content of glacial deep waters, which is reflected in the more negative δ13C values, may be at least in part due to a more sluggish renewal of (abyssal) deep waters. If so, the water of the deep Pacific was up to 400 years older than now. In turn, ventilation in the upper waters, above 2000 m, may have been more vigorous than today.
North Atlantic Deep Water cools the southern hemisphere
Authors: Crowley Thomas J.
Published: February 2008

A standard explanation for coupling climate variations in the northern and southern hemispheres involves fluctuations in North Atlantic Deep Water (NADW) production. However, I suggest that the “NADW‐Antarctic” connection may work opposite to that conjectured by many investigators; that is, when NADW production rates are high, southern hemisphere temperatures decrease rather than increase. The revised interpretation is consistent with observations and ocean modeling studies which demonstrate that, although upwelling of relatively warm NADW water around Antarctica promotes sea ice meltback, a second and more important negative feedback is also operating. In order to conserve volume, southward export of NADW across the equator is accompanied by import of an equivalent volume of considerably warmer water from shallower oceanic layers in the South Atlantic. The southern hemisphere loses heat as a result of this exchange. The hemispherically averaged net heat loss may be as high as 4 W/m², an amount comparable to a CO2 doubling. It is suggested that this more comprehensive view of the role of NADW may explain both decadal‐scale variations in South Atlantic sea surface temperatures in this century and two significant problems in Pleistocene climatology: why southern hemisphere temperatures decreased before CO2 levels decreased at the end of the last interglacial and why southern hemisphere temperature changes precede changes in northern hemisphere ice volume. It is shown that when NADW production was reinitiated during the last interglacial (120,000 B.P.), high‐latitude southern hemisphere temperatures decreased. The estimated magnitude of altered southern hemisphere heat export is comparable to the ice‐age CO2 signal and may be able to account for the observed cooling even when CO2 levels were high. When cast into a frequency domain framework, this interpretation may also help explain why southern hemisphere temperatures lead global ice volume changes.
Sedimentation history of the South Pacific pelagic clay province over the last 85 million years Inferred from the geochemistry of Deep Sea Drilling Project Hole 596
Authors: Zhou Lei , Kyte Frank T.
Published: February 2008

Geochemical analyses of sediments from the top 24.5 m of Deep Sea Drilling Project hole 596 (23°51.20′S, 169°39.27′W) show great variability in the composition of pelagic clays accumulated in the South Pacific since the late Cretaceous. Elemental associations indicate that most of this variability can be attributed to variations in abundances of six sediment end‐member components: detrital (eolian), andesitic (volcanic), hydrothermal, hydrogenous, phosphate (fish debris), and biogenic silica. We develop a sedimentation model which is used to infer processes that might have influenced the accumulation rates of these components over the last 85 million years. The accumulation of eolian detritus in the South Pacific shows some similarities to that observed in the North Pacific and has been largely controlled by global climate trends in the Cenozoic. Much of the variation in the accumulation of other sediment components likely reflects the paleoceanographic evolution of the South Pacific. The most notable change in the sedimentary environment occurred at about the Paleogene/Neogene boundary. At that time, significant changes in the color, mineralogy, and chemistry of the sediment probably reflect major shifts in climate mode as well as oceanic circulation in the central South Pacific region.
Glacial to interglacial changes in surface nitrate utilization in the Indian Sector of the Southern Ocean as recorded by sediment δ15N
Authors: Francois Roger , Altabet Mark A. , Burckle Lloyd H.
Published: February 2008

We present a new approach for paleoceanographic reconstruction of surface nutrient utilization in the southern ocean. It has been observed in the contemporary ocean that, due to preferential uptake of 14NO3− during photosynthesis, the δ15N of planktonic organic matter increases with increasing nitrate depletion in surface waters. Our results demonstrate that the δ15N signal produced in surface waters is reflected in the underlying surface sediments; core top δ15N is inversely correlated with surface nitrate concentration along a transect across the Subtropical Convergence and the Polar Front in the southeast Indian Ocean. These results are consistent with a four‐box model showing that the nitrogen isotopic composition of sinking organic matter depends on percent nitrate utilization in the euphotic zone. By comparing the δ15N of surface sediments with that measured in the glacial sections of several cores, we infer changes in the intensity and latitudinal distribution of nitrate uptake in this region during the last glacial maximum. These preliminary results argue against increased biological uptake of nutrients in southern polar waters as a major mechanism for glacial lowering of atmospheric CO2. They also suggest that Subantarctic waters in the SE Indian sector became more nutrient depleted as they migrated northward. Increased nitrate depletion might have also occurred slightly south of the glacial Polar Front. We use a six‐box model to explore the possible impact of this observation on atmospheric CO2.
A high‐resolution diatom record of the last deglaciation from the SE Norwegian Sea: Documentation of rapid climatic changes
Authors: Karpuz Nalân Koç , Jansen Eystein
Published: February 2008

Although the pulsating nature and the abruptness of the last deglaciation are well documented in marine and land records, very few marine records have so far been able to capture the high‐frequency climatic changes recorded in the Greenland ice core Dye 3. We studied high‐resolution sediment cores from SE Norwegian Sea, which display a detailed climatic record during the last deglaciation comparable to that of Dye 3. Accelerator mass spectrometry age control of the cores enables us to correlate this record in detail with continental records. The results indicate that the surface waters of the SE Norwegian Sea were seasonally ice free after 13,400 B.P. The Bølling/Allerød interstadial complex (13,200–11,200 B.P.) was a climatically unstable period with changing Arctic‐Subarctic conditions. This period was punctuated by four progressively more severe sea surface temperature (SST) minima: between 12,900–12,800 B.P. (BCP I); 12,500–12,400 B.P. (BCP II); 12,300–12,000 B.P. (OD I); and 11,800–11,500 B.P. (OD II). The Younger Dryas (YD) (11,200–10,200 B.P.) represents the severest and most prolonged cold episode of this series of climatic deteriorations. It was bounded by very rapid SST changes and characterized by Arctic‐Polar conditions. The first true warm Atlantic water incursion to the SE Norwegian Sea took place around 10,100 B.P., followed by a brief cooler condition between 9900–9600 B.P. (YD II). The early Holocene climatic optimum occurred between 8000–5000 B.P. A conceptual model is proposed where meltwater fluxes are suggested to cause the observed instability in the SST record.
Surface ocean variability at Galapagos from 1936–1982: Calibration of geochemical tracers in corals
Authors: Shen Glen T. , Cole Julia E. , Lea David W. , Linn Laura J. , McConnaughey Ted A. , Fairbanks Richard G.
Published: February 2008

A variety of geochemical tracers has been developed in reef corals as a means of reconstructing the natural variability of the tropical surface ocean over wide ranging time frames. The purpose of this paper is to calibrate the performance of five of these tracers in a modern coral colony, over an extended period. A 47‐year growth interval (1936–1982) in a colony of Pavona clavus taken from San Cristobal Island, Galapagos Islands, was sectioned into 187 quarterly intervals and analyzed for δ18O, δ13O, Ba/Ca, Cd/Ca, and Mn/Ca. The resulting time series are compared with eastern Pacific sea surface temperatures—one of few instrumental data bases available for calibration over this time period. Linear least squares regressions of four of the tracers (δ18O, δ13O, Ba/Ca, Cd/Ca) against Peruvian SST show highly significant correlations (p<0.0001). Over the annual, biennial, and ENSO (3.8 years) frequency bands, cross‐spectral comparisons show even stronger coherency, with SST frequently accounting for 70–80% of the variance in these tracers. These results as well as the phase relationships determined from the spectral analyses suggest that the coupling between SST and δ18O and the nutrientlike tracers Ba and Cd is controlled principally by seasonal upwelling cycles and interannual interruptions of these cycles brought about by El Niño and anti‐El Niño phenomena. An inverse relationship between SST and δ13C has its primary origins in the co‐occurrence of the warm SST phase with high light levels during the first half of the calendar year. The association with sunlight derives from the photosynthetic response of algal symbionts which results in fractionation of light and heavy carbon isotopes between soft tissues and CaCO3 skeleton. The fifth tracer, the transition metal Mn, exhibits poorer correlations against both SST and the other tracers. Slight shifts in phasing of the historical Mn/Ca annual cycle suggest that the general water column distribution of this tracer, which is the reverse of a nutrient, may not be stable. The erratic behavior of Mn illustrates how complex hydrography near Galapagos may influence tracers with diverse source signatures.
Reevaluation of Early Oligocene, Eocene, and Paleocene Seawater Strontium Isotope Ratios Using Outcrop Samples from The U.S. Gulf Coast
Authors: Denison R. E. , Koepnick R. B. , Fletcher A. , Dahl D. A. , Baker M. C.
Published: February 2008

The Cenozoic strontium isotope (87Sr/86Sr) variation in seawater is largely defined using Deep Sea Drilling Project (DSDP) samples. Examination of non‐DSDP results, particularly for the Paleogene, suggest that the original seawater curve of Burke et al. (1982) may lie above the true seawater ratio during this time. To investigate this possibility, we analyzed the 87Sr/86Sr for 230 Paleogene rock and shell samples from the 83 sites in Alabama, Mississippi, and Louisiana. Many of the samples are from classic sections on which the Gulf Coast Paleogene stratigraphy was originally defined. Multiple analyses of samples from these units show very little scatter, and in most cases, precise agreement is obtained among geographically separated collection sites. We believe that analysis of multiple samples from a unit of established age, collected at more than one site, yields results that most accurately define the actual seawater Sr isotope ratio at any given time. Results from these units define a seawater variation line that tracks well within the range of DSDP data, but is generally below the original seawater line of Burke et al. (1982). It is often assumed that samples from continental settings will exchange with high‐ratio Sr thereby raising 87Sr/86Sr values. Our Gulf Coast samples, which are derived from a continental setting, yield individual 87Sr/86Sr values that are both higher and lower than the estimated contemporaneous seawater ratio. An analysis of our Gulf Coast data and DSDP results show that the direction of isotopic exchange cannot be confidently predicted for individual samples based solely on their derivation from either continental or oceanic settings.
Controls and Development of Late Quaternary Periplatform Carbonate Stratigraphy in Walton Basin (Northeastern Nicaragua Rise, Caribbean Sea)
Authors: Glaser Karen Sullivan , Droxler André W.
Published: February 2008

The late Quaternary sedimentary record in periplatform oozes and muds deposited on the northern Nicaragua Rise results from the interplay of four main controls: (1) input of pelagic carbonates and bank‐derived fine aragonite and magnesian calcite; (2) input of siliciclastic sediments; (3) dispersal and removal of sediments by the Caribbean Current; and (4) partial seafloor dissolution of metastable carbonates. High accumulation rates of the calcite coarse sediment fraction throughout the study area demonstrate that planktonic foraminiferal productivity peaked during interglacial stages. Neritic carbonate productivity also peaked during interglacial stages, when bank and shelf tops along the Nicaragua Rise were submerged within the photic zone. Because the bank and shelf tops remained mostly exposed during glacial stages, the surface area available for the neritic carbonate productivity was drastically reduced to a narrow band along the margins of Pedro Bank and the southern shelf of Jamaica. A large volume of siliciclastic sediments, transported from the coastal area of South America and the eastern and western regions of Jamaica, were deposited during glacial stages within the eastern and western deep extensions of Walton Basin. This finding contrasts with the input pattern of siliciclastic sediments in Walton Basin itself, where the largest input of siliciclastic sediments occurred at each of the interglacial climatic optima, corresponding to intervals of maximum sea level transgression. Finally, cores in water depths exceeding 1100 m display during interglacial stages aragonite accumulation rates systematically lower than rates in cores from water depths shallower than 1100 m. This indicates that some bank‐derived aragonite and magnesian calcite has been partially removed by seafloor dissolution in areas from water depths exceeding 1100 m. Results from this study on the northeastern Nicaragua Rise indicate that not only do offbank transport and water column saturation state influence the late Quaternary record but also that the variable strength of the Caribbean Current and the proximity of sources for siliciclastic sediments have played a major role in the development of the late Quaternary periplatform high resolution stratigraphy.
HF radio wave field strength on long mid‐latitude paths
Authors: Tsedilina Elena E.
Published: February 2008

Analyses are presented of experimental field strength values on two long mid‐latitude circuits, Fort Collins to Hiraiso and Hawaii to Hiraiso on a frequency of 15 MHz, for the different seasons of the 1975–1986 solar cycle and for different ratios of the wave frequency to the MUF. It is shown that on average the field strength during the night and twilight increases with solar activity and the electron concentration and also with MUF increase or wave frequency decrease. Comparison of experimental field strength values with values calculated by the adiabatic invariant method for equinoctial conditions shows the existence of extra energy losses on the circuits. The losses arise when f < MUF during night and twilight. They are not related to radio wave absorption in the ionosphere. Their average value is 20 to 30 dB, and the values decrease with solar activity and electron concentration increase or with radio wave frequency decrease. Strong leakage of the radio waves into the skip zone for f > MUF is also observed during the night, sunrise, and sunset. The observed phenomena are explained in terms of multiple radio wave scattering by irregularities in the ionosphere. A similar, but smaller, effect also occurs during the day.
Oblique frequency domain interferometry measurements using the middle and upper atmosphere radar
Authors: Palmer R. D. , Fukao S. , Larsen M. F. , Yamamoto M. , Tsuda T. , Kato S.
Published: February 2008

First results are presented from oblique frequency domain interferometry (FDI) measurements conducted using the middle and upper atmosphere radar in Japan in October 1990. Using the idea of Doppler sorting, an equation is derived which shows a parabolic variation of the oblique FDI cross‐spectral phase as a function of Doppler velocity. However, because of the small range of Doppler velocities observed with the measured cross spectra, the phase has an approximate linear variation; that is, the cross spectra sample only a small portion of the parabolic structure and are therefore approximately linear and are shown to follow the model closely. Using the oblique FDI configuration, a comparison is drawn between simultaneous measurements of signal‐to‐noise ratio, coherence, three‐dimensional wind, and profiles of FDI cross spectra. We find that the regions that exhibit a well‐defined scattering layer correspond to those regions of high aspect sensitivity. An explanation is suggested based on the anisotropy of the turbulence.
Pulse propagation on a semiinfinite horizontal wire above ground: Near‐zone fields
Authors: Dvorak Steven L. , Dudley Donald G.
Published: February 2008

The near zone electric field distribution due to a transient current pulse propagating on a semiinfinite wire above the ground is investigated. A quasi‐transverse electromagnetic approximation to the modal equation for the propagation wave number is used to obtain the time history of the pulse on the wire. Spectral domain techniques are then used to obtain an expression for the electric field. In the resulting two‐dimensional Sommerfeld integrals, representation of the angular integral in terms of incomplete Lipschitz‐Hankel integrals allows for the efficient computation of the frequency domain near and intermediate zone fields. A numerical inverse Fourier transform is then applied to obtain the transient response. Numerical results, presented in both the time and frequency domains, are used to determine when the previously obtained far zone approximations can be applied. The results in this paper are for the quasi‐transverse electromagnetic component of current; however, similar techniques can be applied to the Earth‐attached and continuous modes.
Generalized boundary and transition conditions and the question of uniqueness
Authors: Senior Thomas B. A.
Published: February 2008

To better simulate the material properties of a surface, a method that is attracting attention is to include higher derivatives in the boundary specification of the field. In the case of a thin layer, the result is a generalized boundary or transition condition whose order is specified by the highest (Nth) derivative present. The conditions are logical extensions of the first order ones corresponding to the usual surface impedance or sheet conditions, but when applied to a surface with discontinuities, they do not produce a unique solution to the problem if N > 1. The standard edge conditions alone are no longer sufficient and additional constraints are necessary. It is shown how these can be obtained from a rather general derivation of the conditions, applicable for conditions through at least the third order.
Use of a combined expansion scheme to analyze microstrip antennas with the method of moments
Authors: Vandenbosch G. A. E. , Van de Capelle A. R.
Published: February 2008

A new expansion scheme is introduced to solve the integral equations describing a microstrip antenna with the method of moments. The scheme offers both flexibility and a low number of expansion functions and thus an acceptable calculation time. The basic idea consists of constructing secondary entire domain expansion functions as fixed combinations of primary expansion functions. This special concept allows the solution of several problems concerning rapid variations of the currents on the patches in an efficient way without having to deal with an unacceptable number of expansion functions to describe the mutual coupling between the patches. The efficiency of the combined scheme is illustrated by a comparison of measured and calculated results for a linear eight‐element microstrip array antenna.
A Multibeam Vorticity Measurement Technique for Modular MST Radars
Authors: Kudeki Erhan , Rastogi Prabhat K.
Published: February 2008

A multibeam Doppler radar technique for atmospheric vorticity measurements is presented and analyzed. The technique is applicable with steerable and modular radars with three or four independent modules centered about the vertices of an equilateral triangle or a square. An accuracy of ∼10−3–10−2 s−1 is predicted in stratospheric vorticity measurements, depending on the available module separations and observation zenith angles.
Application of volumetric multiple scattering approximations to foliage media
Authors: Tamasanis Douglas
Published: February 2008

Vegetation media may be viewed as two or more different types of dielectric scatterers arranged in a random geometric configuration in a surrounding “host” medium. This allows the vegetation to be treated as a continuous medium where the propagation of the waves through that medium is governed by an effective dielectric constant, (ε*). In this paper, several multiple scattering approximation techniques were used to quantitatively estimate the values of the effective dielectric constants for vegetation media based on the foliage density and dielectric properties of the scattering elements composing the vegetation. Because this formalism is not computationally intensive, it is useful for modeling the propagation losses experienced by an electromagnetic wave propagating through vegetation media in electromagnetic scattering or radar simulations. The theoretical approximations of ε* are compared with data at three levels. First, the calculated values of ε* were compared with values reported in the literature. Second, the effective dielectric constants for a foliage environment were used to calculate attenuation coefficients of coherent waves propagating through dense vegetation. The calculated attenuation constants were compared with experimental measurements reported by various authors at frequencies between 50 MHz and 3.2 GHz, resulting in good agreement. Finally, the values of ε* were incorporated into a bistatic scattering model which was used to calculate an effective normalized scattering cross section σ0 for a grass‐ and forest‐covered terrain. This was compared with L band data resulting in excellent agreement between theory and experimental data.
Strike‐slip tectonics and granite petrogenesis
Authors: Hutton D. H. W. , Reavy R. J.
Published: February 2008

Transpression is a process that thickens the crust and therefore in obliquely convergent orogens as in normally convergent orogens there is the potential to generate granitic melts. Individual transcurrent shear zones may not only control the ascent paths, siting, and emplacement mechanisms of plutons, but they may also cause the genesis of the granitoids themselves. Two contrasting situations are examined. In the Hercynian shear zones of Iberia, thickening together with hydrous fluxing along shear zones created intracrustal wet melting of fertile Gondwanan sediments to produce syntectonic granites. In the northern part of the British Caledonides, the association of compositionally expanded granitoids with a major mantle component and transcurrent shear zones may be explained by melting of continental crust at the lower limits of crustal transpressional faults detaching into the Moho.