Showing papers by "Woods Hole Oceanographic Institution published in 1996"

P450 superfamily: Update on new sequences, gene mapping, accession numbers and nomenclature

Abstract: We provide here a list of 481 P450 genes and 22 pseudogenes, plus all accession numbers that have been reported as of October 18,1995. These genes have been described in 85 eukaryote (including vertebrates, invertebrates, fungi, and plants) and 20 prokaryote species. Of 74 gene families so far descr

Bulk parameterization of air‐sea fluxes for Tropical Ocean‐Global Atmosphere Coupled‐Ocean Atmosphere Response Experiment

Abstract: This paper describes the various physical processes relating near-surface atmospheric and oceanographic bulk variables ; their relationship to the surface fluxes of momentum, sensible heat, and latent heat ; and their expression in a bulk flux algorithm. The algorithm follows the standard Monin-Obukhov similarity approach for near-surface meteorological measurements but includes separate models for the ocean's cool skin and the diurnal warm layer, which are used to derive true skin temperature from the bulk temperature measured at some depth near the surface. The basic structure is an outgrowth of the Liu-Katsaros-Businger [Liu et al., 1979] method, with modifications to include a different specification of the roughness/stress relationship, a gustiness velocity to account for the additional flux induced by boundary layer scale variability, and profile functions obeying the convective limit. Additionally, we have considered the contributions of the sensible heat carried by precipitation and the requirement that the net dry mass flux be zero (the so-called Webb correction [Webb et al., 1980]). The algorithm has been tuned to fit measurements made on the R/V Moana Wave in the three different cruise legs made during the Coupled Ocean-Atmosphere Response Experiment. These measurements yielded 1622 fifty-min averages of fluxes and bulk variables in the wind speed range from 0.5 to 10 m s -1 . The analysis gives statistically reliable values for the Charnock [1955] constant (a = 0.011) and the gustiness parameter (β = 1.25). An overall mean value for the latent heat flux, neutral bulk-transfer coefficient was 1.11 x 10 -3 , declining slightly with increasing wind speed. Mean values for the sensible and latent heat fluxes were 9.1 and 103.5 W m -2 ; mean values for the Webb and rain heat fluxes were 2.5 and 4.5 W m -2 . Accounting for all factors, the net surface heat transfer to the ocean was 17.9 ± 10 W m -2 .

Late Proterozoic rise in atmospheric oxygen concentration inferred from phylogenetic and sulphur-isotope studies.

Abstract: The evolution of non-photosynthetic sulphide-oxidizing bacteria was contemporaneous with a large shift in the isotopic composition of biogenic sedimentary sulphides between 0.64 and 1.05 billion years ago. Both events were probably driven by a rise in atmospheric oxygen concentrations to greater than 5-18% of present levels--a change that may also have triggered the evolution of animals.

Cool-skin and warm-layer effects on sea surface temperature

Abstract: To obtain bulk surface flux estimates approaching the ±10 W m−2 accuracy desired for the Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (COARE) program, bulk water temperature data from ships and buoys must be corrected for cool-skin and diurnal warm-layer effects. In this paper we describe two simple scaling models to estimate these corrections. The cool-skin model is based on the standard Saunders [1967] treatment, including the effects of solar radiation absorption, modified to include both shear-driven and convectively driven turbulence through their relative contributions to the near-surface turbulent kinetic energy dissipation rate. Shear and convective effects are comparable at a wind speed of about 2.5 m s−1. For the R/V Moana Wave COARE data collected in the tropical western Pacific, the model gives an average cool skin of 0.30 K at night and an average local noon value of 0.18 K. The warm-layer model is based on a single-layer scaling version of a model by Price et al. [1986]. In this model, once solar heating of the ocean exceeds the combined cooling by turbulent scalar heat transfer and net longwave radiation, then the main body of the mixed layer is cut off from its source of turbulence. Thereafter, surface inputs of heat and momentum are confined to a depth DT that is determined by the subsequent integrals of the heat and momentum. The model assumes linear profiles of temperature-induced and surface-stress-induced current in this “warm layer.” The model is shown to describe the peak afternoon warming and diurnal cycle of the warming quite accurately, on average, with a choice of a critical Richardson number of 0.65. For a clear day with a 10-m wind speed of 1 m s−1, the peak afternoon warming is about 3.8 K with a warm-layer depth of 0.7 m, decreasing to about 0.2 K and 19 m at a wind speed of 7 m s−1. For an average over 70 days sampled during COARE, the cool skin increases the average atmospheric heat input to the ocean by about 11 W m−2; the warm layer decreases it by about 4 W m−2 (but the effect can be 50 W m−2 at midday).

Estimates of Kinetic Energy Dissipation under Breaking Waves

Abstract: The dissipation of kinetic energy at the surface of natural water bodies has important consequences for many Physical and biochemical processes including wave dynamics, gas transfer, mixing of nutrients and pollutants, and photosynthetic efficiency of plankton. Measurements of dissipation close to the surface obtained in a large lake under conditions of strong wind forcing are presented that show a layer of enhanced dissipation exceeding wall layer values by one or two orders of magnitude. The authors propose a scaling for the rate of dissipation based on wind and wave parameters, and conclude that the dissipation rate under breaking waves depends on depth, to varying degrees, in three stages. Very near the surface, within one significant height, the dissipation rate is high (an order of magnitude greater than that predicted by wall layer theory) and roughly constant. Below this is an intermediate region where the dissipation decays as z−2. The thickness of this layer (relative to the significant...

Methane Hydrate and Free Gas on the Blake Ridge from Vertical Seismic Profiling

Abstract: Seismic velocities measured in three drill holes through a gas hydrate deposit on the Blake Ridge, offshore South Carolina, indicate that substantial free gas exists to at least 250 meters beneath the bottom-simulating reflection (BSR). Both methane hydrate and free gas exist even where a clear BSR is absent. The low reflectance, or blanking, above the BSR is caused by lithologic homogeneity of the sediments rather than by hydrate cementation. The average methane hydrate saturation above the BSR is relatively low (5 to 7 percent of porosity), which suggests that earlier global estimates of methane in hydrates may be too high by as much as a factor of 3.

The Little Ice Age and Medieval warm period in the Sargasso Sea

Abstract: Sea surface temperature (SST), salinity, and flux of terrigenous material oscillated on millennial time scales in the Pleistocene North Atlantic, but there are few records of Holocene variability. Because of high rates of sediment accumulation, Holocene oscillations are well documented in the northern Sargasso Sea. Results from a radiocarbondated box core show that SST was {approximately} 1{degree}C cooler than today {approximately} 400 years ago (the Little Ice Age) and 1700 years ago, and {approximately} 1{degree}C warmer than today 1000 years ago (the Medieval Warm Period). Thus, at least some of the warming since the Little Ice Age appears to be part of a natural oscillation. 39 refs., 4 figs., 1 tab.

Similar rates of modern and last-glacial ocean thermohaline circulation inferred from radiochemical data

Abstract: Today, the ocean thermohaline circulation transports half of the 231Pa produced by radioactive decay in the Atlantic Ocean water column to the Southern Ocean. This export respectively imparts low and high 231Pa/230Th ratios to the surface sediments of these oceans. Ocean sediments from the Last Glacial Maximum bear a similar isotopic fingerprint, implying that advection of North Atlantic Deep/Intermediate Water into the Circumpolar Deep Water of the Southern Ocean occurred at a similar—or slightly higher—rate during the last glacial period.

Dispersal as a regional process affecting the local dynamics of marine and stream benthic invertebrates

Abstract: Recent work has shown that benthic invertebrate assemblages may be influenced in an ongoing fashion by dispersal. Water-column movements of meiofauna, juvenile insects and marine postlarvae are common and can act to alter greatly local dynamics such as predator-prey and competitive interactions in marine and stream ecosystems. These findings are important because past research on the role of dispersal in invertebrate dynamics has focused almost exclusively on how planktonic larval supply influences the establishment and maintenance of local assemblages, on the colonization of newly opened sites, or on the settlement success of new recruits. The emerging framework is that dispersal needs to be viewed as a regional process that may routinely influence local benthic dynamics, because fauna can move to and from water-column dispersal ‘pools' and may do so at frequent intervals.

A comparative study of tree establishment in abandoned pasture and mature forest of eastern Amazonia

Abstract: of heavy use and in a mature forest through a series of field studies in northeastern Amazonia. Tree seedling and sprout emergence was > 20 times lower in the abandoned pasture than in forest understory and forest gaps. Tree emergence was restricted in the abandoned pasture by a lack of tree seeds in the soil (3 tree genera vs 15 in the forest), and a low rate of tree and liana seed deposition by birds and bats in the open vegetation of the abandoned pasture (2 m-2 yr-'). Tree and liana seed deposition in the abandoned pasture was higher beneath treelets (990 m-2 yr-1). Rates of seed removal and consumption by ants and rodents were also higher in the abandoned pasture ( > 80% removal within 20 d for 6 tree species) than in forest understorey and forest gaps. Cutter ants (Atta sexdens) hindered tree seedling survivorship and growth in the abandoned pasture by clipping leaves and stems, and preferred tree seedlings to grass and shrub seedlings. In the absence of herbivores, survivorship and height growth of seedling transplants in the abandoned pasture were generally lower than in experimental treefall gaps, and were correlated with harsh environmental conditions in the former. Air temperature, air vapor pressure deficit and soil moisture stress in the abandoned pasture exceeded conditions measured in both treefall gaps and intact forest during the 5-month dry season. Seedling growth in the abandoned pasture was also restricted during the wet season. These barriers to tree establishment help explain the low density and emergence rates of tree seedlings

Surface Meteorology and Air-Sea Fluxes in the Western Equatorial Pacific Warm Pool during the TOGA Coupled Ocean-Atmosphere Response Experiment

Abstract: A major goal of the Coupled Ocean-Atmosphere Response Experiment (COARE) was to achieve significantly more accurate and complete descriptions of the surface meteorology and air-sea fluxes in the western equatorial warm pool region. Time series of near-surface meteorology from a buoy moored near the center of the COARE Intensive Flux Array (IFA) are described here. The accuracies of the measurements and the derived fluxes are quantified; agreement between average net heat fluxes at the buoy and two nearby research ships is better than 10 W m−2 during three intercomparisons. Variability in the surface meteorology and fluxes associated with westerly wind bursts, periods of low winds, and short-lived, deep convective events characteristic of the region was large compared to the 4-month means. The ECMWF (European Centre for Medium-Range Weather Forecasts) analysis and prediction fields differed most from the buoy data during periods of short-lived, deep convective events, when several day averages of ...

Gas Chromatographic Isolation of Individual Compounds from Complex Matrices for Radiocarbon Dating

Abstract: This paper describes the application of a novel, practical approach for isolation of individual compounds from complex organic matrices for natural abundance radiocarbon measurement. This is achieved through the use of automated preparative capillary gas chromatography (PCGC) to separate and recover sufficient quantities of individual target compounds for 14C analysis by accelerator mass spectrometry (AMS). We developed and tested this approach using a suite of samples (plant lipids, petroleums) whose ages spanned the 14C time scale and which contained a variety of compound types (fatty acids, sterols, hydrocarbons). Comparison of individual compound and bulk radiocarbon signatures for the isotopically homogeneous samples studied revealed that Δ14C values generally agreed well (±10%). Background contamination was assessed at each stage of the isolation procedure, and incomplete solvent removal prior to combustion was the only significant source of additional carbon. Isotope fractionation was addressed thr...

Fluid-mud processes on the Amazon continental shelf

Abstract: A sediment transport study conducted on the Amazon continental shelf as part of AmasSeds (A Multi-disciplinary Amazon Shelf SEDiment Study) revealed extensive regions of dense nearbed suspensions of sediment, known as fluid mud (suspended-sediment concentration > 10 g1−1 ). Fluid mud was found near the river mouth on the inner- and middle-shelf, in the region of the bottom salinity front, and was most extensive during periods of rising and high river discharge. Fluid mud, up to 7.25 m thick, but generally 1–2 m thick, appears to form by processes similar to those occurring at an estuarine turbidity maximum, i.e. enhanced settling and lateral convergence of near-bottom flows. A modeling study showed that vertical mixing was controlled by the suppression of turbulence, due to the stratification induced by suspended sediment, and established an upper bound for the total amount of suspended sediment that may be carried in suspension. Sediment leaving the Amazon River appears to go through cycles of trapping and resuspension at the river mouth, before being partially advected seaward and alongshelf, where it is largely incorporated into fluid mud along the bottom salinity front. The fluid muds have far-reaching effects on the Amazon shelf system by reducing boundary shear stresses, affecting water-column seabed exchange, and serving as the agent of outward growth of the subaqueous delta through episodic offshore transport.

Chapter 158 Marine chemistry and geochemistry of the lanthanides

Abstract: Publisher Summary This chapter discusses the characteristics and properties of lanthanides in seawater and presents the rationale for studying the lanthanide composition of natural waters. The lanthanides are composed of a group of fourteen elements (La, Ce, Pf, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu). There are anthropogenic sources of lanthanides to the atmosphere (and presumably to the ocean) in the form of particles produced during the cracking of oil and the combustion of oil and gasoline products. A major objective of chemical oceanography is to understand processes controlling the concentration, distribution, speciation, and flux of elements in the oceans. The chapter describes and discusses lanthanide distributions in the oceans and the biogeochemical and physical processes responsible for these distributions. It presents the profiles of lanthanide concentrations in the water column and their variations within and between ocean basins. The redox geochemistry of Ce as revealed by vertical and horizontal variations in the Ce anomaly is discussed. The inter-oceanic mass fractionation of the strictly trivalent lanthanides is also described.

Production of strong, extracellular Cu chelators by marine cyanobacteria in response to Cu stress

Abstract: Copper speciation in the upper marine water column is dominated b>, strong ligands thought to be of recent biological origin. Cultures of the marine cyanobacteria Synechococcu.? spp., a ubiquitous and important group of phytoplankton highly sensitive to Cu toxicity, were previously shown to produce chelators comparable in strength to those detected in the water column. Here we shoyw that cultures of Synechococcus exposed to toxic concentrations of Cu produce an extracellular ligand with a binding constant comparable to constants for ligands found in the water column. Coordination of Cu by this compound decreases the concentration of free cupric ion (the toxic form) in the culture media to le-rels that do not inhibit growth. A tight linear correlation between chelator and Cu concentration suggests l.hat production of this substance may be regulated by the concentration of free Cu in the media in a feeldback mechanism. Similarly, the concentrations of Cu and Cu-binding ligands in the water column are o?ten closely related. These results suggest that cyanobacteria modify Cu chemistry in seawater, creating conditions more favorable for growth.

A new coupled, one-dimensional biological-physical model for the upper ocean: Applications to the JGOFS Bermuda Atlantic Time-series Study (BATS) site

Abstract: This paper presents a new coupled, one dimensional biological-physical model applied to the subtropical region near Bermuda. The physical component of the model, which is driven by smooth climatological forcing, successfully reproduces the long-term seasonal cycles of upper ocean temperature, salinity and boundary layer depth from Hydrostation S. The nitrogen-based biological model, which includes the effects of photoadaptation, phytoplankton aggregation, and particle remineralization in the aphotic zone, shows significant skill in capturing the major features of the annual chlorophyll field (e.g. spring bloom, deep chlorophyll maximum) and depth-integrated chlorophyll and primary production as exhibited by the U.S. JGOFS Bermuda Atlantic Time-series Study (BATS) data. The introduction of variable phytoplankton chlorophyll-to-nitrogen ratios is found to be important for simulating the subsurface chlorophyll maximum, and the model solutions show a realistic deep nitracline in the summer and a low annual average f -ratio of ∼0.21 compared to previous modeling work. The performance of the model solutions are weakest during the late summer, when the model can not supply enough nutrients to support the high production observed in the stratified near-surface waters. The coupled model has large winter production values, leading to a substantial export of organic material from the euphotic zone via downward turbulent mixing. The model predicts a total export production from the euphotic zone of 0.24 mol N m −2 year −1 , approximately equally partitioned between particle sinking and suspended matter detrainment. The bulk of the export production is remineralized in the shallow aphotic zone, and only a small fraction is transported below the depth of the maximum winter mixed layer and thus contributes to “biological pump”.

Role of protozoan grazing in relieving iron limitation of phytoplankton

Abstract: RECENT evidence indicates that iron is a limiting factor in primary production in some areas of the oceans1,2. In sea water, iron is largely present in the form of particulate and colloidal phases which are apparently unavailable for uptake by phytoplankton3–5. Several mechanisms have been proposed whereby non-reactive iron may be converted into more labile forms (for example, thermal dissolution6, photochemical reactions7,8 and ligand complexation9). Here we report that digestion of colloidal iron in the acidic food vacuoles of protozoan grazers may be a mechanism for the generation of 'bioavailable' iron from refractory iron phases. We have demonstrated several grazer-mediated effects on colloidal ferrihydrite, including a decrease in colloid size, an increase in colloid lability as determined by competitive ligand-exchange techniques, and an increase in the bioavailability of colloids to iron-limited diatoms. These results indicate that protozoan grazers may significantly enhance the supply of iron to marine phytoplankton from terrestrial sources.

Surface Buoyancy Forcing and the Mixed Layer of the Western Pacific Warm Pool: Observations and 1D Model Results

Abstract: The broad, shallow body of warm (>29°C) water found in the western tropical Pacific Ocean plays an important role in the coupled ocean-atmosphere dynamics and thermodynamics associated with the El Nino-Southern Oscillation phenomenon. Thus, it is important to understand the processes that maintain and perturb that warm pool. Measurements from a buoy moored in the center of the warm pool during the TOGA Coupled Ocean-Atmosphere Response Experiment show that the exchange of mass between the ocean and atmosphere is as important as the exchange of heat. Rain forms a shallow, buoyant layer that does not mix with the water below except during infrequent strong wind events. Using a one-dimensional mixed layer model, it is demonstrated that the rate of local precipitation governs the mixed layer depth and can thus alter the rates of change in sea surface temperature during both warming and cooling periods. The observed mixed layer depth in the warm pool is at a depth that allows for maximum warming by ca...

Phytodetritus at the abyssal seafloor across 10 of latitude in the central equatorial Pacific

Abstract: Fresh phytoplankton detritus (or phytodetritus) has been reported from numerous deep seafloor sites in the temperate North Atlantic and Pacific Oceans following seasonal phytoplankton blooms. Here we report the first strong evidence for abyssal accumulations of phytodetritus in the tropics, in the central equatorial Pacific. In November–December 1992 we obtained photographs and/or sediment-core samples from 61 abyssal stations (water depths of 4280–5012 m) between 12°S and 9°N along ∼ 140°W. Greenish flocculent material was recovered from the top of multiple-core samples from 5°S to 5°N; this material was most abundant from 2°S to 2°N, in some areas forming continuous layers at least 5 mm thick, and individual aggregates > 1 cm in diameter. The greenish material was clearly visible in bottom photographs as a green veneer that covered >95% of the seafloor near the equator, and as individual cm-scale aggregates covering <1% of the seafloor. Occasionally, thick accumulations of cm-scale aggregates occurred in biogenic pits. Cleared trails and feeding traces suggest that surface-deposit-feeding holothurians and echiurans grazed the greenish material. Microscopic examination of greenish material recovered from core tops and a burrow lumen revealed relatively intact diatoms (including Rhizosolenia sp.) and other microalgae with chloroplasts containing chlorophyll. The greenish material was 1–12.5% organic carbon by weight, i.e. 5–39 times richer than associated seafloor sediments. It also contained high excess activities of 234Th, suggesting arrival from the water column in the previous 100 days. Samples of the greenish flocculent material from 0° and 5°N incubated at simulated environmental pressure and temperature with 14C-labeled glutamate exhibited ⩾ 5-fold higher rates of microbial activity than underlying sediments or brown floc from 9°N. Surface-sediment samples (which included the greenish flocculent material) from 5°S to 5°N also contained significant concentrations of chlorophyll a and other chloropigments; the chloropigment concentrations were roughly comparable to deep-sea phytodetritus collected in the North Atlantic. We conclude that fresh, organic-rich phytodetritus was present on the seafloor from 5°S to 5°N along 140°W in November–December 1992, with highest concentrations within 2–3° of the equator. This material is likely to be a concentrated, high-quality food resource for deep-sea microbes and metazoans. We estimate an upper limit for the standing stock of this phytodetritus to be ∼2.6 mmol Corg/m2; this corresponds to ∼3% of the annual flux of organic carbon to the seafloor at these latitudes in 1992. Because the degradation rate of this material appears to be very high, its presence at the seafloor for several months per year could yield significant phytodetrital contributions to the annual seafloor organic-carbon budget. We also suggest that the phytodetrital aggregates are formed at intense convergence zones resulting from seasonal passage of tropical instability waves within 5° of the equator; if so, phytodetrital accumulations are likely to recur seasonally over broad areas of the abyssal equatorial Pacific.

Widespread phagocytosis of ciliates and other protists by marine mixotrophic and heterotrophic thecate dinoflagellates1

Abstract: An electron microscopic examination of large amorphous inclusions located in a variety of photosynthetic thecate dinoflagellates (Alexandrium ostenfeldii (Paulsen) Balech et Tangen, Gonyaulax diegensis Kofoid, Scrippsiella sp., Ceratium longipes (Bailey) Gran, and Prorocentrum micans Ehrenberg) and a nonphotosynthetic thecate species (Amylax sp.) revealed each inclusion to be a food vacuole, the majority of which were ingested ciliate prey. Recognizable features of these ciliates included linear arrays of basal bodies and cilia consistent with oligotrich polykinetid structure, characteristic macronuclei, chloroplasts (evidently kleptoplastids), cup-shaped starch plates, and cylindrical extrusomes. Three species contained (apparent) nonciliate prey: Scrippsiella sp., whose food vacuoles consistently contained unusual and complex extrusome-like cylindrical bodies having a distinctive six-lobed, multilayered structure; P. micans, which contained an unidentified encysted cell; and a single A. ostenfeldii cell, containing a Dinophysis sp. dinoflagellate cell. Several food vacuoles of ciliate origin had a red hue. This, together with the resemblance of A. ostenfeldii cells to planozygotes, suggests that similar structures previously identified as accumulation bodies may in fact be food vacuoles and that feeding may in some cases be associated with sexual processes.

Export flux of carbon at the equator during the EqPac time-series cruises estimated from 234Th measurements

Abstract: Distributions of 234 Th were determined in three particle-size classes ( > 53, 1–53 and 0.7–1.0 μm) and in filtered seawater during each of the two time-series cruises of the U.S. JGOFS Process Study in the equatorial Pacific. Four vertical profiles were measured on the equator at 140°W from the sea surface to 400 m depth between 24 March and 9 April 1992 (Time-series I) and again between 3 and 18 October 1992 (Time-series II). In addition, both organic and inorganic carbon were measured in each of the particle fractions. The results were used with a one-dimensional model, which includes the equatorial upwelling, to estimate the flux of particulate carbon sinking out of the surface layer. The flux of particulate organic carbon (POC) at the base of the euphotic zone (0.1 % light level, 120 m depth) was estimated to average 1.9 mmol m −2 day −1 during El Nino (Time-series I) and 2.4 mmol m −2 day −1 during the cold period that followed (Time-series II). These values amount to only ∼ 2% of the primary production measured during each of the same periods and are insufficient to balance the new production, estimated previously to be ∼ 17% of primary production. These results are consistent with the hypothesis that the major part of the new production is removed from the region by advection in the form of dissolved organic matter. The POC flux profile indicates a net remineralization below the 1 % light level (80 m depth) such that the flux reaching 200 m depth has been reduced by ∼ 55%, giving a remineralization length scale of ∼ 155 m. For particulate inorganic (carbonate) carbon the flux at 200 m averaged 0.54 mmol m −2 day −1 during Time-series I and 0.71 mmol m −2 day −1 during Time-series II, very similar to the fluxes reported in deep sediment traps deployed at the same time. Estimates of the average large-particle sinking velocity give values −1 in the upper part of the euphotic zone, show a sharp increase near the base of the euphotic zone and level off to values of 30–60 m day −1 at 200 m depth.

Distributed, active extension in Bransfield basin Antarctic Peninsula: Evidence from multibeam bathymetry

Abstract: Bransfield basin, a marginal basin off the west coast of the northern Antarctic Peninsula, lies in a unique tectonic environment with a basement of Paleozoic to Mesozoic accretionary wedge material. Although active subduction occurred during most of the past 200 m.y., it stopped or slowed dramatically at about 4 Ma when the Phoenix-Antarctic spreading center was abandoned offshore, leaving a small remnant of the former Phoenix plate incorporated in the Antarctic plate. Even though geochemical data indicate that unaltered basalt dredged from Bransfield basin is like midocean ridge basalt, there is no clear evidence for normal seafloor spreading. In November 1995, RVIB N.B. Palmer spent three weeks mapping the seafloor in Bransfield basin and searching for hydrothermal activity. The multibeam bathymetric chart of the Central Bransfield basin shows submarine volcanoes and striking, lineated seafloor features that dredging indicated were vesicular basalt. The chemistry of the rocks, combined with high heat flow and evidence for active hydrothermal circulation, strongly suggests present-day extension. At least four parallel zones of linear extrusions can be seen in the multibeam data. Whereas the bathymetry provides new insight into the mode of extension in the basin, it does not explain why or how extension is occurring. The evidence strongly supports active extension in accretionary wedge–derived continental crust that produces linear cracks that leak magma. The present extensional regime may lead to seafloor spreading, but the thickness of the crust in Bransfield basin suggests that normal seafloor spreading is yet to occur and any attempt to correlate magnetic anomalies is premature. INSIDE • Presidential Conference, p. 6 • North-Central Section Meeting, p. 20 • Cordilleran Section Meeting, p. 22 Vol. 6, No. 11 November 1996

Oceanic Turbulence Dissipation Measurements in SWADE

Abstract: Recent experiments measuring turbulence dissipation rates in the upper ocean can be divided into two types: those supporting an analogy between the upper ocean and lower atmosphere, with dissipation rates following wall layer behavior, and those finding oceanic dissipation rates to be much higher than wall layer predictions. In an attempt to reconcile these two diverse acts of observations, Terray et al. proposed a wave-dependent scaling of the dissipation rate based on the significant wave height and the rate of energy input from the wind to the waves. Their parameterization was derived from observations of strongly forced, fetch-limited waves, although they conjectured that it would apply in typical oceanic conditions as well. This paper reports new measurements of turbulent kinetic energy dissipation made in the North Atlantic Ocean from a SWATH ship during the recent Surface Waves Dynamics Experiments (SWADE).These data support the scaling of Terray et al., verifying its validity when applied...

Rapid assessment of induced cytochrome P4501A protein and catalytic activity in fish hepatoma cells grown in multiwell plates : Response to TCDD, TCDF, and two planar PCBs

Abstract: Induction of cytochrome P450 1A1 (CYP1A1) in cultured cells can be used to determine taxon-specific relative potencies of Ah receptor agonists. This report describes optimized methods for growth and treatment of PLHC-1 fish hepatoma cells in multiwell plates, in situ analysis of ethoxyresorufin O-deethylase (EROD) activity, and measurement of CYP1A protein by immunoblotting of cell lysates. EROD activity was undetectable (< 1 pmol min{sup {minus}1} mg{sup {minus}1}) in untreated or dimethyl sulfoxide-treated cells, but was highly induced (up to 150 pmol min{sup {minus}1} mg{sup {minus}1}) in cells exposed to Ah receptor agonists such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), or plant chlorobiphenyls (CB). Addition of exogenous NADPH was not required for measurement of EROD activity in PLHC-1 cells. As inducers of EROD activity, TCDD, TCDF, 3,3{prime},4,4{prime},5-pentachlorobiphenyl (CB-126), and 3,3{prime},4,4{prime}-tetrachlorobiphenyl (CB-77) differed both in potency and in apparent efficacy (maximal level of induced activity). In each case, EROD induction was biphasic, with stronger induction at lower concentrations and an attenuated response at higher concentrations. In contrast, the content of immunodetectable CYP1A protein increased monotonically with dose of CB, and the maximum level achieved was similar for all inducers. The discrepancy in results obtained for EROD activity versus CYP1A protein may result frommore » inhibition or inactivation of catalytic function at high concentrations of inducer. By reducing peak EROD values, this inhibition leads to lower apparent EC50 values and thus the overestimation of relative potencies or toxic equivalency factors (TEFs) for many inducers. These studies demonstrate the necessity of measuring both EROD activity and immunodetectable CYP1A protein for the accurate assessment of CYP1A induction and relative potencies in cultured cells.« less