bluuebunny/crossref_metadata_2025 huggingface dataset:
A giant landslide on the north flank of Tenerife, Canary Islands
Authors: Watts A. B. , Masson D. G.
Published: February 2004

The extent of mass wasting along the north flank of Tenerife has been mapped using swath bathymetry, GLORIA side‐scan sonar, and 3.5‐kHz echo sounder data. The marine surveys show that, north of Tenerife, a giant landslide is exposed over an area of 5500 km2 of the seafloor, more than twice the surface area of the island. The landslide truncates an older ridge and valley topography that is associated with the shield building basalts on Tenerife. We interpret the ridge and valley topography as the result of subaerial erosion. The landslide is estimated to have a length of 100 km, a width of up to 80 km, and a volume of about 1000 km3. It extends onshore into the Orotava and Icod valleys which have been interpreted as of landslide origin. K‐Ar dating of basaltic flows in the steep headwall of Orotava suggests an age of formation for the valley is younger than 0.78 Ma and may even be younger than 0.27 Ma. The Icod valley is located immediately to the north of the most recent volcano on Tenerife, Las Cañadas, and has been associated with the collapse of its caldera, between 1.2 and 0.2 Ma. A young age for the landslide is supported by the 3.5‐kHz echo sounder data which show that the landslide is draped by a thin (< 10 m) layer of younger sediment. The landslide did not form, however, during a single catastrophic event but represents the amalgamation of a number of separate landslides. The occurrence of the ridge and valley topography in water depths of up to 2.5 km suggests that the shield‐building basalts have subsided by at least this amount since they formed, 3.3–8.0 Ma. We speculate that this subsidence is caused by some form of stress relaxation that occurs in the underlying lithosphere. The giant landslide imaged in our sonar data is associated with the late stages in the development of the most recent volcano on Tenerife, Las Canadas, which only began at about 1.8 Ma. Thus landsliding may be a particular feature of the time soon after emplacement when because of incomplete isostatic adjustment, oceanic volcanoes have their greatest elevations above sea‐level and therefore are most susceptible to slope failure.
Mapping playa evaporite minerals and associated sediments in Death Valley, California, with multispectral thermal infrared images
Authors: Crowley James K. , Hook Simon J.
Published: February 2004

Efflorescent salt crusts and associated sediments in Death Valley, California, were studied with remote‐sensing data acquired by the NASA thermal infrared multispectral scanner (TIMS). Nine spectral classes that represent a variety of surface materials were distinguished, including several classes that reflect important aspects of the playa groundwater chemistry and hydrology. Evaporite crusts containing abundant thenardite (sodium sulfate) were mapped along the northern and eastern margins of the Cottonball Basin, areas where the inflow waters are rich in sodium. Gypsum (calcium sulfate) crusts were more common in the Badwater Basin, particularly near springs associated with calcic groundwaters along the western basin margin. Evaporite‐rich crusts generally marked areas where groundwater is periodically near the surface and thus able to replenish the crusts though capillary evaporation. Detrital silicate minerals were prevalent in other parts of the salt pan where shallow groundwater does not affect the surface composition. The surface features in Death Valley change in response to climatic variations on several different timescales. For example, salt crusts on low‐lying mudflats form and redissolve during seasonal‐to‐interannual cycles of wetting and desiccation. In contrast, recent flooding and erosion of rough‐salt surfaces in Death Valley probably reflect increased regional precipitation spanning several decades. Remote‐sensing observations of playas can provide a means for monitoring changes in evaporite facies and for better understanding the associated climatic processes. At present, such studies are limited by the availability of suitable airborne scanner data. However, with the launch of the Earth Observing System (EOS) AM‐1 Platform in 1998, multispectral visible/near‐infrared and thermal infrared remote‐sensing data will become globally available.
Intraplate deformation in the Japanese Islands: A kinematic study of intraplate deformation at a convergent plate margin
Authors: Shen‐Tu B. , Holt W. E. , Haines A. J.
Published: February 2004

Relative motions within the deforming Japanese Islands with respect to the Sea of Japan are determined using earthquake records over the last 414 years, slip rates on Quaternary faults, and angular change rates obtained from triangulation in the last century. We use a least squares inversion method to match the strain rates on the surface of the Earth with continuous spline functions to recover the velocity gradient tensors. The directions of the principal strain axes obtained from seismic, geological, and geodetic data are in general agreement with each other, with the maximum shortening axis oriented in a WNW direction. Principal strain rate magnitudes obtained from the geodetic data are about 3–5 times larger than the principal strain rates obtained from the seismic and geological data. Intraplate deformation in southwestern Japan determined from the seismic data accommodates a velocity of5.5±2(l σ) mm/yr in a direction parallel to the Nankai trough, which is about 25% of the plate motion velocity component parallel to the Nankai trough between the Philippine Sea and Eurasian plates. In northern Honshu, the velocity vectors from the seismic data are nearly parallel to the plate motion vector at the Japan trench, and the intraplate deformation accommodates about 6% of the total Pacific‐Eurasian or North American plate motion velocity. The velocity vector at Kashima, northern Honshu, calculated from the geodetic data is about 9–12 mm/yr in a direction of N55°W‐N76°W, which is about half of the very long baseline interferometry velocity calculated in the Eurasian reference frame, suggesting that the Sea of Japan may not be rigidly attached to the assumed rigid Eurasian plate.
The dynamics of rapidly emplaced terrestrial lava flows and implications for planetary volcanism
Authors: Baloga Stephen , Spudis Paul D. , Guest John E.
Published: February 2004

The Kaupulehu 1800–1801 lava flow of Hualalai volcano and the 1823 Keaiwa flow from the Great Crack of the Kilauea southwest rift zone had certain unusual and possibly unique properties for terrestrial basaltic lava flows. Both flows apparently had very low viscosities, high effusion rates, and uncommonly rapid rates of advance. Ultramafic xenolith nodules in the 1801 flow form stacks of cobbles with lava rinds of only millimeter thicknesses. The velocity of the lava stream in the 1801 flow was extremely high, at least 10 m s−1 (more than 40 km h−1). Observations and geological evidence suggest similarly high velocities for the 1823 flow. The unusual eruption conditions that produced these lava flows suggest a floodlike mode of emplacement unlike that of most other present‐day flows. Although considerable effort has gone into understanding the viscous fluid dynamics and thermal processes that often occur in basaltic flows, the unusual conditions prevalent for the Kaupulehu and Keaiwa flows necessitate different modeling considerations. We propose an elementary flood model for this type of lava emplacement and show that it produces consistent agreement with the overall dimensions of the flow, channel sizes, and other supporting field evidence. The reconstructed dynamics of these rapidly emplaced terrestrial lava flows provide significant insights about the nature of these eruptions and their analogs in planetary volcanism.
Holocene paleoseismicity, temporal clustering, and probabilities of future large (M > 7) earthquakes on the Wasatch fault zone, Utah
Authors: McCalpin J. P. , Nishenko S. P.
Published: February 2004

The chronology of M > 7 paleoearthquakes on the central five segments of the Wasatch fault zone (WFZ) is one of the best dated in the world and contains 16 earthquakes in the past 5600 years with an average repeat time of 350 years. Repeat times for individual segments vary by a factor of 2, and range from about 1200 to 2600 years. Four of the central five segments ruptured between ∼620 ± 30 and 1230 ± 60 calendar years B.P. The remaining segment (Brigham City segment) has not ruptured in the past 2120 ± 100 years. Comparison of the WFZ space‐time diagram of paleoearthquakes with synthetic paleoseismic histories indicates that the observed temporal clusters and gaps have about an equal probability (depending on model assumptions) of reflecting random coincidence as opposed to intersegment contagion. Regional seismicity suggests that for exposure times of 50 and 100 years, the probability for an earthquake of M > 7 anywhere within the Wasatch Front region, based on a Poisson model, is 0.16 and 0.30, respectively. A fault‐specific WFZ model predicts 50 and 100 year probabilities for an M > 7 earthquake on the WFZ itself, based on a Poisson model, as 0.13 and 0.25, respectively. In contrast, segment‐specific earthquake probabilities that assume quasi‐periodic recurrence behavior on the Weber, Provo, and Nephi segments are less (0.01–0.07 in 100 years) than the regional or fault‐specific estimates (0.25–0.30 in 100 years), due to the short elapsed times compared to average recurrence intervals on those segments. The Brigham City and Salt Lake City segments, however, have time‐dependent probabilities that approach or exceed the regional and fault specific probabilities. For the Salt Lake City segment, these elevated probabilities are due to the elapsed time being approximately equal to the average late Holocene recurrence time. For the Brigham City segment, the elapsed time is significantly longer than the segment‐specific late Holocene recurrence time.
Seismogenic deformation field in the Mojave block and implications for tectonics of the eastern California shear zone
Authors: Unruh Jeffrey R. , Twiss Robert J. , Hauksson Egill
Published: February 2004

From the aftershocks of the 1992 Landers earthquake, we infer the orientation of the principal strain rate axes (d1 > d2 > d3; d1 lengthening), their relative magnitude, and the relative spin of fault blocks by using a micropolar continuum model to invert the seismic P and T axes. The seismogenic deformation is consistent with the geodetic measurements of the coseismic displacement and with the secular deformation of the central Mojave block. Regionally, the aftershock data define two major domains within the central Mojave block: (1) the western Mojave block, including the San Bernardino Mountains and the epicentral area of the Big Bear earthquake, which is characterized by E‐W d1 (lengthening) and N‐S d3 (shortening); and (2) the central Mojave block, including the Landers surface rupture zone, which is characterized by NW‐SE d1 and NE‐SW d3. Inversion for the principal strain axes of geodetically measured coseismic displacements across the Big Bear and Landers seismogenic zones gives results similar to the aftershock inversions for those areas, indicating that the aftershocks accommodate a deformation similar to the main rupture and do not reflect elastic rebound or residual stresses. The background seismicity for 1981 to 1991 shows the same characteristic d1 and d3 orientations for the two domains, indicating that the secular seismogenic strain has the same regional geometry as the 1992 coseismic deformation. The micropolar inversion also provides values of the relative vorticity parameter W, which reflects a difference between the vorticity of a shearing continuum and the vorticity of fault‐bounded blocks rotating within tabular seismogenic shear zones. The observed fault geometry along the Kickapoo fault suggests a pinned‐block model for the local block rotation that is consistent with the values of W obtained from our inversions. We interpret the regional NW‐SE orientation of d1 in the central Mojave block to be characteristic of the dextral eastern California shear zone, which transfers approximately 22% of the Pacific‐North American plate motion from the San Andreas system to the Walker Lane Belt in eastern California. Our results and geodetic determinations of the secular shear strain in the central Mojave block indicate that the locus of NW dextral shear generally lies between the San Bernardino Mountains and the Pisgah fault.
Potbellies, wasp‐waists, and superparamagnetism in magnetic hysteresis
Authors: Tauxe L. , Mullender T. A. T. , Pick T.
Published: February 2004

Because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material, much can be learned by monitoring that response through what is known as a “magnetic hysteresis loop”. The measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research. Yet the interpretation of hysteresis loops is not simple. It has become apparent that although classic “single‐domain”, “pseudo‐single‐domain”, and “multidomain” loops described in textbooks occur in natural samples, loops are frequently distorted, having constricted middles (wasp‐waisted loops) or spreading middles and slouching shoulders (potbellies). Such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions. The physics of the problem have been understood for nearly half a century, yet numerical simulations appropriate to geological materials are almost unavailable. In this paper we discuss results of numerical simulations using the simplest of systems, the single‐domain/superparamagnetic (SD/SP) system. Examination of the synthetic hysteresis loops leads to the following observations: (1) Wasp‐waisting and potbellies can easily be generated from populations of SD and SP grains. (2) Wasp‐waisting requires an SP contribution that saturates quickly, resulting in a steep initial slope, and potbellies require low initial slopes (the SP contribution approaching saturation at higher fields). The approach to saturation is dependent on volume, hence the cube of grain diameter. Therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size. (3) We were unable to generate potbellies using an SP/SD threshold size as large as 30 nm, and wasp waists cannot be generated using a threshold size as small as 8 nm. The occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm (±5). (4) Simulations using a threshold size of 15–20 nm with populations dominated by SP grain sizes, that is with a small number of SD grains, produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass. (5) Simulations and measurements using two populations with distinct coercivity spectra can also generate wasp‐waisted loops. A relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp‐waisting resulting from SP/SD behavior.
Gravity field over the Sea of Galilee: Evidence for a composite basin along a transform fault
Authors: Ben‐Avraham Zvi , ten Brink Uri , Bell Robin , Reznikov Margaret
Published: February 2004

The Sea of Galilee (Lake Kinneret) is located at the northern portion of the Kinneret‐Bet Shean basin, in the northern Dead Sea transform. Three hundred kilometers of continuous marine gravity data were collected in the lake and integrated with land gravity data to a distance of more than 20 km around the lake. Analyses of the gravity data resulted in a free‐air anomaly map, a variable density Bouguer anomaly map, and a horizontal first derivative map of the Bouguer anomaly. These maps, together with gravity models of profiles across the lake and the area south of it, were used to infer the geometry of the basins in this region and the main faults of the transform system. The Sea of Galilee can be divided into two units. The southern half is a pull‐apart that extends to the Kinarot Valley, south of the lake, whereas the northern half was formed by rotational opening and transverse normal faults. The deepest part of the basinal area is located well south of the deepest bathymetric depression. This implies that the northeastern part of the lake, where the bathymetry is the deepest, is a young feature that is actively subsiding now. The pull‐apart basin is almost symmetrical in the southern part of the lake and in the Kinarot Valley south of the lake. This suggests that the basin here is bounded by strike‐slip faults on both sides. The eastern boundary fault extends to the northern part of the lake, while the western fault does not cross the northern part. The main factor controlling the structural complexity of this area is the interaction of the Dead Sea transform with a subperpendicular fault system and rotated blocks.
Hydrogeology of the Hawaii Scientific Drilling Project borehole KP‐1: 1. Hydraulic conditions adjacent to the well bore
Authors: Paillet F. L. , Thomas D. M.
Published: February 2004

Temperature and formation resistivity logs obtained in borehole KP‐1 of the Hawaii Scientific Drilling Project indicate that the adjacent formation is characterized by several zones of distinctly different average temperature and water salinity. A series of hydraulic analyses and water sampling programs were conducted to rule out the possibility of local hydraulic effects associated with the presence of the borehole in the generation of these apparent groundwater zones. Hydraulic tests and sampling with the borehole cased to a depth of 710 m and open below that depth indicate that the deep aquifer contains seawater at a temperature nearly identical to that of the open ocean at the same depth. Various analyses give estimates of aquifer transmissivity of about 10−3 m2/s in the vicinity of the borehole. Isolation of this deeper aquifer from the overlying groundwater zones was investigated by perforating the casing at six locations and then measuring the changes in water level in the borehole, in the salinity of the fluid column, in the temperature profile of the fluid column, and in the rate of flow in the fluid column induced by the perforations. These results positively confirm that the zones of distinctly different formation properties indicated on the temperature and resistivity logs are not caused by flow in or around casing. Flow and fluid column salinity induced by the perforations also confirm significant differences between the hydraulic heads and geochemistry of the different groundwater zones inferred from the well logs.
Thermal and mass implications of magmatic evolution in the Lassen volcanic region, California, and minimum constraints on basalt influx to the lower crust
Authors: Guffanti Marianne , Clynne Michael A. , Muffler L. J. Patrick
Published: February 2004

We have analyzed the heat and mass demands of a petrologic model of basalt‐driven magmatic evolution in which variously fractionated mafic magmas mix with silicic partial melts of the lower crust. We have formulated steady state heat budgets for two volcanically distinct areas in the Lassen region: the large, late Quaternary, intermediate to silicic Lassen volcanic center and the nearby, coeval, less evolved Caribou volcanic field. At Caribou volcanic field, heat provided by cooling and fractional crystallization of 52 km3 of basalt is more than sufficient to produce 10 km of rhyolitic melt by partial melting of lower crust. Net heat added by basalt intrusion at Caribou volcanic field is equivalent to an increase in lower crustal heat flow of ∼7 mW m−2, indicating that the field is not a major crustal thermal anomaly. Addition of cumulates from fractionation is offset by removal of erupted partial melts. A minimum basalt influx of 0.3 km3 (km2 Ma)−1 is needed to supply Caribou volcanic field. Our methodology does not fully account for an influx of basalt that remains in the crust as derivative intrusives. On the basis of comparison to deep heat flow, the input of basalt could be ∼3 to 7 times the amount we calculate. At Lassen volcanic center, at least 203 km3 of mantle‐derived basalt is needed to produce 141 km3 of partial melt and drive the volcanic system. Partial melting mobilizes lower crustal material, augmenting the magmatic volume available for eruption at Lassen volcanic center; thus the erupted volume of 215 km3 exceeds the calculated basalt input of 203 km3. The minimum basalt input of 1.6 km3 (km2 Ma)−1 is >5 times the minimum influx to the Caribou volcanic field. Basalt influx high enough to sustain considerable partial melting, coupled with locally high extension rate, is a crucial factor in development of Lassen volcanic center; in contrast, Caribou volcanic field has failed to develop into a large silicic center primarily because basalt supply there has been insufficient.
Seismic anisotropy around the Gulf of Corinth, Greece, deduced from three‐component seismograms of local earthquakes and its relationship with crustal strain
Authors: Bouin Marie‐Paule , Téllez Julia , Bernard Pascal
Published: February 2004

Several thousand three‐component seismograms from local earthquakes recorded during two field experiments in August 1991 and November 1992 in the Gulf of Corinth have been analyzed to detect shear wave splitting. After a first selection of the events located in the S window of the considered stations, a second very strict selection of the records is applied in order to avoid the effect of scattered or converted phases which can mimic the behavior of shear wave splitting. Two main directions of fast S wave polarization have been detected: one oriented N105°E–N120°E, the other N55°E–N75°E. The first one is perpendicular to the main direction of extension of the Gulf provided by focal mechanism, Global Positioning System measurements, and tectonic studies, and is thus consistent with the extensive‐dilatancy anisotropy (EDA) model. The second direction is subparallel to the direction of the active normal fault closest to the sites. This suggests a local control of the anisotropy by these active faults, either by a local rotation of the total stress field, in which case the EDA model may still explain the anisotropy, or by the existence of a specific microstructure or macrostructure generated by the long‐term fault activity (set of secondary fault planes parallel to the major one), in which case the anisotropy direction would be significantly rotated from the stress direction (about 50°). The anisotropic signature does not seem to be affected by the geology of the site (pre‐Tertiary limestone and Pleistocene sediments), except for a station located on the thick Plio‐Quaternary deposits of a delta, where the time delay is significantly larger.
The S reflector west of Galicia (Spain): Evidence from prestack depth migration for detachment faulting during continental breakup
Authors: Reston T. J. , Krawczyk C. M. , Klaeschen D.
Published: February 2004

The mechanism of continental extension and breakup, and the role of detachment faults in these processes, are currently the subject of intense debate. One possible detachment fault is the S reflector, imaged as an undulating (in time), locally discontinuous reflection on existing seismic profiles west of Iberia. Here we present new images in depth of the four margin‐normal profiles across the west Galicia rifted margin, where the S reflector was originally defined and is best imaged. It is shown that faults bounding wedge‐shaped units of late synrift sediments, which hence were active during rifting immediately prior to breakup, appear to detach at shallow levels onto the S reflector. S itself appears as a continuous, locally domal feature and does not generally appear offset. The waveform of S is compatible with a reflection from a single interface such as a sharp tectonic boundary. The depth sections show that S was active at 1–3 km below the seafloor during final rifting; S is interpreted as a brittle detachment fault which controlled the final breakup of the continent west of Galicia. Furthermore, the data provide constraints on the sense of shear of S: analogy with detachment terranes, the present, synrift and structural dips of S, and the identification of a breakaway to S imply that S accommodated top‐to‐the‐west shear. Toward the east of the profiles, S becomes more complex, possibly because of different phases of detachment faulting and the development of both incisement and excisement structures. From the geometry of wedge‐shaped sedimentary units deposited during faulting above S it also appears that S was active at an angle of 20° or less and hence may be considered a genuine low‐angle normal fault.
Effective elastic thickness of the continental lithosphere in South Africa
Authors: Doucouré C. Moctar , de Wit Maarten J. , Mushayandebvu Martin F.
Published: February 2004

We have estimated the effective elastic thickness of the continental lithosphere beneath South Africa using the coherence technique. This involves (1) estimating the coherence between Bouguer gravity anomalies and topography in the spectral domain and (2) comparing the coherence with that predicted by an elastic plate model that flexes under loads placed on, within and beneath the lithosphere. The depth to the base of this elastic layer which gives the best root‐mean‐square fit between estimated and predicted coherence is the effective elastic thickness (Te). Two major tectonic provinces, namely, the Archean Kaapvaal Craton and the Mesoproterozoic Namaqua‐Natal Mobile Belt (which together form the Kalahari Craton in southern Africa), are found to have Te values of 72 km and 38 to 48 km, respectively. There is indication from the coherence data that over the Kalahari Craton, topographic features with equivalent wavelengths less than ∼200–300 km are supported by the rigidity of the lithosphere while features with wavelengths greater than 700 km are compensated. It is implied from the present findings that each of the two South African tectonic provinces can be considered as separate coherent domains. On the basis of geotherms from both provinces, the effective elastic thicknesses obtained point to a lithospheric basal temperature of about 600°C. Geologic and geophysical considerations suggest that the contrast in flexural rigidity of the lithosphere between the two provinces can be attributed to the combined effects of compositional and thickness differences of the lithosphere, as well as variation in present‐day asthenospheric heat flow. Our Te estimates of the Namaqua‐Natal Mobile Belt are similar to those of the Mesoproterozoic Grenville belt, corroborating tectonic models which suggest that these two belts may once have been part of the same mobile belt. In contrast, the Te estimate of the Kaapvaal Craton fall below average global Archean cratonic values; the reasons for this are not clear.
Extensive distribution of hydrothermal plumes along the superfast spreading East Pacific Rise, 13°30′–18°40′S
Authors: Baker Edward T. , Urabe Tetsuro
Published: February 2004

A general model relating relative hydrothermal activity to the rate of plate creation requires data from the full spectrum of mid‐ocean ridge spreading rates. To obtain data from a superfast spreading environment, the Japanese/U.S. Ridge Flux Project used continuous hydrographic/optical tow‐yos in 1993 to map the distribution of hydrothermal plumes along the southern East Pacific Rise from 13°30′ to 18°40′S. Plume incidence, the fraction of the spreading axis length overlain by a significant plume, was 0.6, including a virtually continuous vent field stretching 150 km from 17°20′ to 18°40′S. Hydrothermal venting was most concentrated along portions of the ridge crest with an inflated cross‐sectional area and an observable axial magma chamber reflector. This pattern agrees with previous results from the northern East Pacific Rise. Such consistency implies that hydrothermal circulation on fast spreading ridges is vigorous where the relative volume of partial melt is high and meager where melt volume is low or undetectable; “hot rock” alone is generally insufficient to drive significant hydrothermal circulation. Using a mean temperature anomaly of 0.014 ± 0.010°C, we estimated the hydrothermal heat flux from the study area as (1.5 ± 1.1 × 107 MW)Ux, where Ux is the cross‐axis flow at the ridge crest. No direct measurements of Ux are yet available. Combining the plume distribution found here with prior data from slow, intermediate, and fast spreading ridges yields a significant linear correlation between plume incidence and spreading rate that extends across the full range of plate motion. This correlation, which mirrors that for near‐axis heat flux calculated by recent models, implies that magma supply rate is the principal control on the large‐scale distribution of axial hydrothermal venting.
Wind and thermohaline circulation of the Black Sea driven by yearly mean climatological forcing
Authors: Oguz T. , Malanotte‐Rizzoli P. , Aubrey D.
Published: February 2004

Using an eddy‐resolving ocean circulation model endowed with active thermodynamics and a turbulence closure parameterization, a hierarchy of numerical experiments is carried out to investigate the relative contributions of the wind forcing, the surface thermohaline fluxes, the river runoff, and the Bosphorus inflow/outflow in driving the yearly mean circulation in the Black Sea. The model accommodates a topographic and boundary‐fitted curvilinear coordinate system and resolves steep topographical changes around the periphery of the basin using O(10 km) grid spacing and 18 stretched vertical levels. Model experiments show that topography, wind forcing, and buoyancy forcing are all first‐order contributors to the primary circulation of the Black Sea. If any of these features are neglected, significant elements of the model circulation do not reproduce observations. Subbasin scale gyres are caused by both wind and thermohaline forcing. Annual mean wind stress is sufficient to produce the major interior cyclonic gyres. Stronger winds produce more defined interior flow than the weaker winds of the Hellermann and Rosenstein (1983) fields. Heat flux is an important contributor to subbasin scale cyclonic circulation. However, the annual mean heat flux with spatial structure given by the climatology produces unrealistic features in the interior circulation. The latter ones disappear when including the seasonal heat flux variability. This results strongly suggests that the seasonal cycle of the wind stress is much less crucial than the heat flux seasonal cycle in producing a realistic basin circulation. The Rim Current is locked to the steep topographic shelf slope, regardless of the forcing mechanism. Without including the strong topography the Rim Current is absent for all forcings. Mesoscale variability arises from the dynamic evolution of the Rim Current. This variability is enhanced by the Danube inflow and the Bosphorus inflow/outflow, demonstrating the importance of these buoyancy sources in enhancing the mesoscale. The deep‐layer circulation is controlled by the barotropic pressure gradient and is insensitive to the magnitude, seasonality, or strength of the surface forcing. A transition zone separates the surface and deep‐layer circulation patterns. Its circulation is mainly driven by the slope of the pycnocline developed as a response to the surface forcing.
A theoretical derivation of the dependence of the remotely sensed reflectance of the ocean on the inherent optical properties
Authors: Zaneveld J. Ronald V.
Published: February 2004

An expression for the ratio of the upwelling nadir radiance L(π, z) and the downwelling scalar irradiance Eod(Z) is derived from the following equation of radiative transfer. This expression is given by RSR(z) = [L(π, z)]/Eod(z) = [ƒb(z)bb(z)]/2π[k(π, z) + c(z) − ƒL(z)bf(z)], where bb(z) is the backscattering coefficient, k(π, z) is the vertical attenuation coefficient of the nadir radiance, c(z) is the beam attenuation coefficient, and ƒb(z) and ƒL(z) are shape parameters that depend on the shape of the volume scattering function and the radiance distribution. Successive approximations are subsequently applied to the above exact equation. These are ƒb(z) = [2πβ(π − θm, z)]/[bb(z)], where β(π − θm, z) is the volume scattering function at 180° minus the zenith angle of the maximum radiance, and k(π, z) = am = c[1 − 0.52 b/c − 0.44 (b/c)2], where m is a parameter that is numerically equal to the inverse of the average cosine of the asymptotic light field for a medium with the same inherent optical properties, α is the absorption coefficient, and b/c is the single scattering albedo. Together with ƒL(z) = 1.05 and application of Gershun's equation, it is shown that for nearly all oceanic cases RSR(z) ≡ L(π, z)/Eod(z) = [β(π − θm, z)]/{a(z)[1 + m(z)]}.
In situ phytoplankton absorption, fluorescence emission, and particulate backscattering spectra determined from reflectance
Authors: Roesler Collin S. , Perry Mary Jane
Published: February 2004

An inverse model was developed to extract the absorption and scattering (elastic and inelastic) properties of oceanic constituents from surface spectral reflectance measurements. In particular, phytoplankton spectral absorption coefficients, solar‐stimulated chlorophyll a fluorescence spectra, and particle backscattering spectra were modeled. The model was tested on 35 reflectance spectra obtained from irradiance measurements in optically diverse ocean waters (0.07 to 25.35 mg m−3 range in surface chlorophyll a concentrations). The universality of the model was demonstrated by the accurate estimation of the spectral phytoplankton absorption coefficients over a range of 3 orders of magnitude (ρ = 0.94 at 500 nm). Under most oceanic conditions (chlorophyll a<3 mg m−3) the percent difference between measured and modeled phytoplankton absorption coefficients was <35%. Spectral variations in measured phytoplankton absorption spectra were well predicted by the inverse model. Modeled volume fluorescence was weakly correlated with measured chl a; fluorescence quantum yield varied from 0.008 to 0.09 as a function of environment and incident irradiance. Modeled particle backscattering coefficients were linearly related to total particle cross section over a twentyfold range in backscattering coefficients (ρ = 0.996, n = 12).
Comparison of optically‐derived spectral densities and microwave cross sections in a wind‐wave tank
Authors: Keller Mary Ruth , Gotwols Bruce L. , Plant William J. , Keller William C.
Published: February 2004

The most popular model of microwave backscatter from rough water surfaces at mid‐incidence angles (20° < θi < 70°) is composite surface theory. This theory holds that the backscattered return is directly proportional to the spectral density of centimetric, Bragg‐resonant water waves which are tilted and advected by longer waves. A stringent test of this theory is to measure, independently and from the same surface area, the normalized microwave cross section (σ0) and the Bragg wave spectral density, and compare them using the theory. In this paper, we use a calibrated optical slope imaging system in a wind‐wave tank to measure the two‐dimensional wavenumber spectrum of short waves. From these spectra, we calculate both the pure Bragg scattering σ0 which neglects longwave effects and the more complex composite surface σ0. The results are compared with σ0 obtained from backscatter measurements at X band (10 GHz) and Ka band (35 GHz) made between 28° and 68° incidence angle. We find that composite surface theory generally shows better agreement with experiment at both frequencies than pure Bragg scattering theory. The agreement seems best for friction velocities above 40 cm s−1. For all friction velocities up to 70 cm s−1, however, composite surface theory somewhat underpredicts the actual σ0 in a majority of the cases. This is especially true for horizontal polarization at large incidence angles. We conclude that while composite surface theory accounts for much of the backscatter at both frequencies in the incidence angle range we examined, the discrepancy between the predicted and measured cross sections is sufficiently large that contributions from other scattering processes cannot be ruled out.
Evidence for platelet ice accretion in Arctic sea ice development
Authors: Jeffries M. O. , Schwartz K. , Morris K. , Veazey A. D. , Krouse H. R. , Gushing S.
Published: February 2004

Moderate quantities of platelet ice are reported in ice cores obtained from floes in the central and western Beaufort Sea, Arctic Ocean. The crystal structure characteristics include a fabric of long, thin, ragged‐edged crystals with randomly oriented c axes. The cellular substructure that is characteristic of congelation ice is not evident in individual platelet ice crystals, but they do occur together with congelation ice in layers ranging from 0.05 to 0.6 m thick. Platelet ice crystals are observed primarily in second‐year and multiyear floes. The structural characteristics of Arctic platelet ice are similar to those of Antarctic platelet ice. The platelet ice layers have a minimum δ 18O value of −5.3‰, and in some cases the platelet ice layers have more negative δ 18O values than the ice layers above and below them. The salinity of platelet ice layers is not significantly different from other ice layers. A number of platelet ice growth mechanisms and sources are discussed. Processes associated with the Ellesmere ice shelves, nearshore processes such as anchor ice growth in shallow waters off the north coast of Alaska, and ice growth in freshwater impounded behind grounded ice dams might be locally important but are unlikely to contribute significant quantities of platelet ice to pack ice floes. Two processes probably account for the presence of platelet ice. The first is growth in underice melt ponds which form in inverted depressions at the base of floes when meltwater floes off the ice surface. The second is the operation of ice pumps in which ice that is melted off the deeper parts of floes and ridges is deposited as platelet ice at a higher level. In either case, initially loose accumulations of platelet crystals are entrained in the floes by the growth of congelation ice. The widespread occurrence of platelet ice in the central and western Beaufort Sea suggests that ice growth in both underice melt ponds and associated with the operation of ice pumps might be more common than was previously realized.
Antarctic Intermediate Water circulation in the tropical and subtropical South Atlantic
Authors: Suga Toshio , Talley Lynne D.
Published: February 2004

Recent hydrographic data from the South Atlantic Ventilation Experiment cruises and others are combined with historical data and used to map the isopycnal properties corresponding to the Antarctic Intermediate Water (AAIW) in the Atlantic Ocean. The low salinity of the AAIW extends eastward across the South Atlantic just south of the equator (3–4°S). Evidence of a weak eastward flow just north of the equator (1–2°N) is also shown. Lateral and vertical homogenization of properties in the AAIW is found at the equator between 2°S and 2°N; there is no clear zonal gradient in salinity just along the equator. These observations suggest enhanced mixing within the equatorial baroclinic deformation radius. The South Atlantic tropical gyre is shown to consist of the following three cells: one cyclonic cell centered at about 7°S, another centered at about 19°S in the west and 23°S in the east, and one anticyclonic cell centered at about 13°S. These cells are associated with a westward extension at 10°S of high salinity and low oxygen which originates in the eastern tropical South Atlantic and a front in these properties at about 15°S in the west and about 20°S in the east.
A fine resolution numerical model of the Iceland‐Farœ front with open boundary conditions
Authors: Griffiths Catherine
Published: February 2004

An eddy‐resolving limited area primitive equation model of the Iceland‐Farœ frontal region is developed. The spatial and temporal evolution of the front is examined on time‐scales of up to 2 months. Experiments are performed changing the open boundary conditions at the lateral boundaries, using passive and active open boundary conditions. The experiment with the passive open boundary conditions reproduces many observed features of the Iceland‐Farœ frontal region. Discrepancies between these results and observations in the area are noted. In particular, the western end of the front drifts too far north. The model is then forced at the lateral boundaries using two contrasting barotropic velocity fields. Improvements in the results are noted. Comparison of the results illustrate to what extent and how, far‐field currents can affect the dynamics of this frontal region. The East Icelandic current is found to have the following important effect on the front: maintaining its vertical structure and confining the western end of the front to more southerly latitudes.
Mississippi River flood waters that reached the Gulf Stream
Authors: Ortner Peter B. , Lee Thomas N. , Milne Peter J. , Zika Rod G. , Clarke M. Elizabeth , Podesta Guillermo P. , Swart Peter K. , Tester Patricia A. , Atkinson Larry P. , Johnson Walter R.
Published: February 2004

Distributions of physical, biological, and chemical parameters in Florida Keys coastal waters seaward of the reef track were surveyed on September 9 to 13, 1993, as part of a coordinated multidisciplinary study of surface transport processes. A band of low‐salinity water was observed along the shoreward side of the Florida Current over the downstream extent of the survey from Miami to Key West. Biological and chemical indicators within the band, together with its large volume, satellite imagery, and a surface drifter trajectory suggested the recent Mississippi River flood as the source.
Internal wave generation by ice floes moving in stratified water: Results from a laboratory study
Authors: Waters Jennifer Kehl , Bruno Michael S.
Published: February 2004

A series of tests has been conducted to investigate the increased ice‐water drag exhibited by ice floes in two‐layer, salinity‐stratified water. Scaled model tests are used to quantify the additional drag due to internal wave creation at the fresh water‐salt water interface. This additional drag is shown to have a peak value five times the drag in similar unstratified conditions and to have a strong dependence on a few well‐defined nondimensional parameters describing the ice and water characteristics.
Upper ocean modeling in a coastal bay
Authors: Gan Jianping , Ingram R. Grant , Greatbatch Richard J. , Chen Ping
Published: February 2004

A numerical model of the upper ocean is developed to study the dynamics and thermodynamics of the Baie des Chaleurs (Gulf of St. Lawrence, Canada). The model has primitive equation dynamics with two active layers embedded with a Niiler‐Kraus (Niller and Kraus, 1977) type mixed layer model at the top. Proper open boundary conditions and forcing functions are constructed. The model is eddy‐permitting, with a horizontal grid spacing of 2×4 km. An Arakawa C grid scheme is used. Forced by observed wind, atmospheric heat fluxes, river runoff, and appropriate remote forcing (in particular, the Gaspé Current, (GC)), the model demonstrates that the mean cyclonic general circulation pattern in the bay is a consequence of the intrusion of the GC. The strength of the circulation depends on the resultant stress of prevailing westerly winds and the opposing GC intrusion. In the mixed layer, atmospheric heat fluxes and horizontal thermal advection play a key role in the thermal balance at the eastern part of the bay. The local mixed layer fluctuations are controlled by wind and GC induced divergence. The entrainment (and its corresponding heat flux) is important at the western part of the bay and changes the mean mixed layer depth on a timescale of more than a week. Varying GC intensifies the flow variations induced by the wind in the bay and improves simulation results as compared with observations.
Chemical tracers of productivity and respiration in the subtropical Pacific Ocean
Authors: Emerson S. , Quay P. D. , Stump C. , Wilbur D. , Schudlich R.
Published: February 2004

We determine annual rates of net biological oxygen production in the euphotic zone and respiration in the upper thermocline of the subtropical North Pacific ocean using mass balances of oxygen, argon, and nitrogen measured at the U.S. Joint Global Ocean Flux Study time series station ALOHA. Net evasion of nitrogen and argon to the atmosphere caused by warming of surface waters is balanced by supply primarily from cross‐isopycnal transport. Mixing rates between the euphotic zone and the top of the permanent thermocline required to balance the inert gas flux are 1–2 cm2 s−1 when transformed to units of an eddy diffusion coefficient. Application of mixing rates derived from the inert gas mass balance to the oxygen field yields a net annual euphotic zone production rate of 1.4±1.0 moles O2 m−2 yr−1, one half of which is lost to the atmosphere, with most of the rest mixed into the top of the thermocline. Since cross‐isopycnal gradients of dissolved organic carbon (DOC) are about half to those of oxygen, we estimate that at least one quarter of the carbon flux out of the euphotic zone is via DOC. Because surface ocean dissolved organic matter has a relatively high C/N ratio, the stoichiometry among O2, C, and inorganic N in the upper ocean should be different than that observed in deeper waters.