We have measured ³He/⁴He ratios and He and Ne concentrations on a suite of 24 basalt glasses from the neovolcanic zone of the Juan de Fuca Ridge (JdFR) from 44.6°N near the Blanco Transform up to 48.0°N on the Endeavour Segment. The helium isotope ratios exhibit a clear geographic variation,...
The Vizcaino block is an anomalously shallow region of the western U.S continental margin located southwest of the Mendocino triple junction. It originated as part of the accretionary prism of the North America plate and was transferred to the Pacific plate in the Miocene as the Pacific-North America plate boundary...
Models of magnetic and gravity anomalies along two E-W transects offshore central Oregon, one of which is coincident with a detailed velocity model, provide quantitative limits on the structure of the subducting oceanic crust and the crystalline backstop. The models indicate that the backstop-forming western edge of the Siletz terrane,...
Analytical and numerical models are used to study the effects of a meridional ridge on the propagation of barotropic Rossby waves produced by distant wind stress forcing. The analytical model illustrates the qualitative aspects of the problem by solving a simplified form of the potential vorticity equation. The analytical results...
The sensitivity of the tropics to climate change, particularly the amplitude of glacial‐to‐interglacial changes in sea surface temperature (SST), is one of the great controversies in paleoclimatology. Here we reassess faunal estimates of ice age SSTs, focusing on the problem of no‐analog planktonic foraminiferal assemblages in the equatorial oceans that...
Benthic foraminiferal δ¹³C data from site 502 in the Caribbean Sea (sill depth 1800 m) indicate that throughout the past 2.6 m.y., glacial δ¹³C values in the middepth Atlantic were higher during glaciations than interglaciations. This is interpreted as indicating a greater proportion of Upper North Atlantic Deep Water (UNADW)...
We evaluate the reliability of statistical estimates of sea surface temperature (SST) derived from planktonic foraminiferal faunas using the modern analog method and the Imbrie‐Kipp method. Global core top faunas provide a calibration data set, while modern sediment trap faunas are used for validation. Linear regression of core top predicted...
Relative humidity (RH) measurements acquired in orographic wave cloud and cirrus environments are used to investigate the temperature‐dependent RH required to nucleate ice crystals in the upper troposphere, RHnuc(T). High ice‐supersaturations in clear air—conducive to the maintenance of aircraft contrails yet below RHnuc and therefore insufficient for cirrus formation—are not...
A temperature spectrum if heterogeneous freezing nuclei concentrations in continental air in the upper troposphere was determined based on airborne measurements. Numerical model simulations incorporating ice formation by heterogeneous and homogeneous freezing of deliquesced soluble aerosol particles were performed to investigate the effect of the heterogeneous freezing nuclei were predicted...
Meanders of the shelf break front in the Mid-Atlantic Bight (MAB) during April and May of 1997 were associated with chlorophyll enhancement along a hydrographic and a topographic feature. The hydrographic feature was the surface outcrop of the front, which ranged from ~10 to >100 km seaward of the shelf...
We use the position fixes and temperature readings from 56 Tristar-II mixed-layer drifters, in conjunction with advanced very high resolution radiometer images, to provide a description of the mesoscale variability of the flows associated with cold-water filaments in the California Current system off northern California in July 1988. We find...
Satellite infrared imagery and coastal meteorological data for March 1984 through February 1985 are used to estimate the net annual surface heat flux for the northern Gulf of California. The average annual surface heat flux for the area north of Guaymas and Santa Rosalia is estimated to be +74 W...
Satellite-derived pigment concentrations from the west coast time series (WCTS) are averaged into monthly mean fields over the California Current system (CCS) for the period July 1979 to June 1986. Errors caused by the scattering algorithm used in the WCTS are reduced by an empirical correction function, although winter values...
A succession of basaltic lavas, volcaniclastic sediments, and lignite beds in the Holmatindur region of eastern Iceland provides the means for tying magnetic reversal stratigraphy and a record of major North Atlantic cooling to a precise radiometric timescale. A prominent part of the section is the Holmatindur classic bed, which...
Evidence for secondary circulation associated with a shelfbreak front is obtained from a high‐resolution, cross‐shelf section of hydrographic, optical and velocity fields. Convergence in the bottom boundary layer on the inshore side of the front and subsequent upwelling into the interior is evident by a mid‐water region of suspended bottom...
Previous simulations of the Martian atmosphere have shown how topography acts to confine the low-level Hadley cell flow into intense jets on the eastern flanks of Tharsis and Syrtis Major. We now conduct detailed studies of these jets using the NASA Ames Mars general circulation model (MGCM). The structure of...
An atmospheric transport model has been used to explore the relationship between source emissions and ambient air quality for individual particle phase organic compounds present in primary aerosol source emissions. An inventory of fine particulate organic compound emissions was assembled for the Los Angeles area in the year 1982. Sources...
Satellite data from the Geosat altimeter and the Advanced Very High Resolution Radiometer (AVHRR) are used to show the large-scale structure of the surface circulation of the California Current System in summer. These data show the connection between an equatorward jet and temperature front off Oregon that lies within 100...
Data from Geosat and TOPEX altimeters are used to infer the structure of the Peru-Chile Countercurrent, a jet that flows from at least as far north as 10ºS (historical data suggests 7ºS) to 35º–40ºS, maintaining its position between approximately 100–300 km offshore. Although the annual mean current cannot be determined...
In July 1993 we collected hydrographic data and information on chlorophyll distribution on the continental shelf north of Cape Hatteras and across the shelf break at Cape Hatteras. The data show that a warm, transparent mixed layer lies over much colder, euphotic, chlorophyll-rich bottom water on the shelf. This layer...
The majority of bacteria suspended in seawater do not appear to be metabolically active or in good physiological condition as assessed by various methods. We tested the idea that a large fraction of ‘inactive’ bacterial cells can become ‘active’ with respect to detectable cell-specific electron transport system (ETS) activity, determined...
The location of the Antarctic Polar Front (PF) was mapped over a 7-year period (1987-1993) within images of satellite-deprived sea surface temperature. The mean path of the PF is strongly steered by the topographic features of the Southern Ocean. The topography places vorticity constraints on the dynamics of the PF...
Degradation and release to solution of intracellular dimethylsulfoniopropionate (DMSP) from Emiliania huxleyi 370 was observed during grazing by the heterotrophic dinoflagellate Oxyrrhis marina in 24 h bottle incubations. Between 30 and 70 % of the lost algal DMSP was metabolized by the grazers without production of dimethylsulfide (DMS) when grazer...
A Lagrangian drifter was deployed in a cold filament off northern California as part of the Coastal Transition Zone program. The drifter was equipped with an optical package (consisting of a spectroradiometer, a fluorometer, and a beam transmissometer) suspended at 8.5-m depth and a water sampler suspended at 16.3-m depth....
The sorbed gases at all four Ocean Drilling Program Leg 139 sites (855, 856, 857, and 858) showed the unmistakable presence of thermogenic hydrocarbons. No indication of abiogenic gas was found. The evidence for the thermogenic hydrocarbons includes elevated contents of higher hydrocarbons (i.e., C₁/[C₂ + C₃] ca. 2-20), δ¹³CCH₄...
The shallow sections of most holes drilled during Ocean Drilling Program Leg 139 contain alkenones derived from prymnesiophyte algae. The alkenones indicate a paleotemperature of the photic zone in the upper ocean during primary carbon fixation of 7°-15°C, with an average of 10.7°C. Based on laboratory hydrous pyrolyses these alkenones...
Carbonate nodules and associated sediments from Ocean Drilling Program Leg 139 sites of the Middle Valley, Juan de Fuca Ridge, were studied using a combination of inorganic and organic geochemical techniques. The mineralogy and stable isotopic compositions defined three types of nodules, reflecting the conditions of carbonate precipitation. Nodule ingrowth...
The subduction of the oceanic spreading center at the Chile Triple Junction is marked by a substantial thermal perturbation
and marked changes in the hydrogeologic and aqueous geochemical regimes in the overthrust plate. Ridge subduction substantially
changes the fluid chemistry in the wedge through variably hydrating the oceanic basement, accretionary...
Oxygen and strontium isotopic composition of sedimentary pore fluids obtained by drilling at the Chile Triple Junction have been used to obtain information on the diagenesis and transport mechanisms of fluids. Samples were collected from three sites located on an east-west transect of the pre-collision zone (Sites 859, 860, and...
Ocean Drilling Program (ODP) Leg 138 was designed to study the late Neogene paleoceanography of the equatorial Pacific Ocean at time scales of thousands to millions of years. Crucial to this objective was the acquisition of continuous, high-resolution sedimentary records. It is well known that between successive advanced piston corer...
Sediment spectral reflectance measurements were generated aboard the JOIDES Resolution during Ocean Drilling Program Leg 162 shipboard operations. The large size of the raw data set (over 1.3 gigabytes) and limited computer hard disk storage space precluded detailed analysis of the data at sea, although broad band averages were used...
Benthic foraminifer and δ¹³C data from Site 849, on the west flank of the East Pacific Rise (0°11'N, 110°3l'W; 3851 m), give relatively continuous records of deep Pacific Ocean stable isotope variations between 0 and 5 Ma. The mean sample spacing is 4 k.y. Most analyses are from Cibicides wuellerstorfi>...
Remote-sensing reflectance is easier to interpret for the open ocean than for coastal regions because the optical signals are highly coupled to the phytoplankton (e.g., chlorophyll) concentrations. For estuarine or coastal waters, variable terrigenous colored dissolved organic matter (CDOM), suspended sediments, and bottom reflectance, all factors that do not covary...
Macronutrients persist in the surface layer of the equatorial Pacific Ocean because the production of phytoplankton is limited; the nature of this limitation has yet to be resolved. Measurements of photosynthesis as a function of irradiance (P-I) provide information on the control of primary productivity, a question of great biogeochemical...
A drifter equipped with bio-optical sensors and an automated water sampler was deployed in the California Current as part of the coastal transition zone program to study the biological, chemical, and physical dynamics of the meandering filaments. During deployments in 1987 and 1988, measurements were made of fluorescence, downwelling irradiance,...
Condensed water content (CWC) measured using a counterflow virtual impactor (CVI) with a Lyman-α hygrometer downstream is compared with that measured by other airborne instruments (a hot-wire probe, a PMS FSSP, and a PMS 2D-C). Results indicate that the CVI system provides a reliable measurement of CWC in both liquid-...
Due to distortion of airflow streamlines, flow velocities and droplet size distributions measured around a moving aircraft can differ from freestream conditions. This can complicate measurements made from aircraft platforms. Potential flow calculations were used to predict airflow characteristics and the spatial distribution of different-sized droplets around the Lockheed Electra...
A series of automated tests is developed for tower and aircraft time series to identify instrumentation problems, flux sampling problems, and physically plausible but unusual situations. The automated procedures serve as a safety net for quality controlling data. A number of special flags are developed representing a variety of potential...
Accurate ship velocity is important for determining absolute currents from acoustic Doppler current profiler (ADCP) measurements. In this paper, the authors describe the application of two methods to improve the quality of ship velocity estimates. The first uses wide-area differential global positioning system (WADGPS) navigation to improve ship positioning. During...
Several simple laboratory experiments have been conducted to study the dynamic behavior of the vector-averaging current meter (VACM) compass and vane follower. They demonstrate that the behavior of the compass and vane follower can be modeled as a damped linear harmonic oscillator for small-amplitude forcing. The combined eddy-current and bearing-friction...
We examine and compare near-forward light scattering that is caused by turbulence and typical particulate assemblages in the ocean. The near-forward scattering by particles was calculated using Mie theory for homogeneous spheres and particle size distributions representative of natural assemblages in the ocean. Direct numerical simulations of a passive scalar...
Calculation of vector winds from spaceborne fan-beam scatterometers requires that backscatter measurements from different antennas be relatively calibrated to high accuracy. A method is developed to perform postlaunch antenna calibration using global mean ocean backscatter measurements in conjunction with estimates of the statistical distribution of near-surface wind velocity and the...
Wind-generated inertial currents can radiate from the mixed layer as horizontally and vertically propagating new-inertial internal gravity waves. To study the timescale of the decay of mixed layer energy and the magnitude of the energy transfer to the ocean below, the authors developed a numerical, linear model on a β...
Motivated by satellite altimeter observations of enhanced sea level variability near steep topographic slopes in the Southern Ocean, effects of topography on the spatial distribution of mesoscale eddies and on eddy–mean flow interaction are investigated using a two-layer, wind-forced, quasigeostrophic channel model. The principal topography, a zonal ridge with a...
A simple theory is presented for steady geostrophic circulation of a stratified fluid in a rectangular basin with a circumpolar connection. The interior flow obeys the β-plane Sverdrup vorticity balance, and the circulation is closed by geostrophic boundary currents. The circulation is forced by surface thermal gradients and wind-driven Ekman...
Appearing in this issue of the Journal of Physical Oceanography are three papers that present new observations of a distinct, narrow band, and diurnally varying signal in temperature records obtained in the low Richardson number shear flow above the core of the equatorial undercurrent. Moored data suggest that the intrinsic...
We undertook an interlaboratory comparison of techniques used to extract and analyze trapped gases in ice cores. The intercomparison included analyses of standard reference gases and samples of ice from the Greenland Ice Sheet Project 2 (GISP2) site. Concentrations of CO₂, CH₄, the δ¹⁸O of O₂, the δ¹⁵N of N₂,...
The oceanic circulation near the eastern margin of the African continent is dominated by the poleward flow of the Agulhas Current. The Agulhas Current separates from the African coast near the southern tip of the continent, makes an abrupt turn to the east (known as the Agulhas Retroflection), and flows...
Datasets taken near the coasts of Peru and California have been analyzed to explore the evidence of a correlation between the high frequency (period < 10.8 hour) and low frequency (period > 4 day) motions. A large part of the high frequency current is consistent with internal wave dynamics. They...
The European Centre for Medium-Range Weather Forecasts (ECMWF) and Institut Francais Pour la Recherche et l’Exploitation de la Mer European Remote-Sensing Satellite, named IFR2, surface wind velocity data products are compared during July 1995 over the Arabian Sea. Substantial differences were found. The central positions of the maximum isotach were...