Showing papers by "Woods Hole Oceanographic Institution published in 1991"

Reconstruction of Caribbean climate change over the past 10,500 years

Abstract: A high-resolution reconstruction of Caribbean climate is presented based on O-18/O-16 ratios in ostracod shells from Lake Miragoane, Haiti. The variations which are found can be largely explained by orbitally induced variations in seasonal insolation which modified the intensity of the annual cycle.

Cytochrome P-450 Monooxygenase Systems in Aquatic Species: Carcinogen Metabolism and Biomarkers for Carcinogen and Pollutant Exposure

Abstract: High levels of polynuclear aromatic hydrocarbon (PAH) carcinogens commonly occur in aquatic systems where neoplasms arise in fish and other animals. Enzymes that transform PAHs can act in initiatin...

Methanopyrus kandleri, gen. and sp. nov. represents a novel group of hyperthermophilic methanogens, growing at 110°C

Abstract: A novel group of hyperthermophilic rod-shaped motile methanogens was isolated from a hydrothermally heated deep sea sediment (Guaymas Basin, Gulf of California) and from a shallow marine hydrothermal system (Kolbeinsey ridge, Iceland). The grew between 84 and 110°C (opt: 98°C) and from 0.2% to 4% NaCl (opt. 2%) and pH 5.5 to 7 (opt: 6.5). The isolates were obligate chemolithoautotrophes using H2/CO2 as energy and carbon sources. In the presence of sulfur, H2S was formed and cells tended to lyse. The cell wall consisted of a new type of pseudomurein containing ornithin in addition to lysine and no N-acetylglucosamine. The pseudomurein layer was covered by a detergent-sensitive protein surface layer. The core lipid consisted exclusively of phytanyl diether. The GC content of the DNA was 60 mol%. By 16S rRNA comparisons the new organisms were not related to any of the three methanogenic lineages. Based on the physiological and molecular properties of the new isolates, we describe here a new genus, which we name Methanopyrus (the “methane fire”). The type species is Methanopyrus kandleri (type strain: AV19; DSM 6324).

Do upper-ocean sediment traps provide an accurate record of particle flux?

Abstract: SEDIMENT traps are widely used to measure the vertical flux of particulate matter in the oceans. In the upper ocean, sediment traps have been used to determine the extent to which CO2 Axed by primary producers is exported as particulate organic carbon1–3. In addition, the observed decrease of particle flux with depth has been used to predict regeneration rates of organic matter and associated elements3. Over seasonal or annual timescales, the import of limiting nutrients into the upper ocean (new production) should be balanced by particle export4,5. Given the importance of accurately determining the sinking particle flux, it has been suggested that 234Th might be used to 'calibrate' shallow-trap fluxes6. Here I present a re-evaluation of existing 234Th data which indicates that trap-derived and model-derived 234Th particle fluxes can differ by a factor of ±3–10, suggesting that shallow traps may not provide an accurate measure of particle fluxes.

Seasonal and depth-related changes in the source of sinking particles in the North Atlantic

Abstract: LARGE, fast-sinking particles are important in the downward transport and redistribution of biogeochemical species in the deep ocean. Using nitrogen isotope ratio, 15N/14N, as an in situ tracer, we investigate the source and transformation of these particles in the North Atlantic ocean. We observe seasonal variations in δ15N associated with seasonal changes in near-surface nitrate concentration and particle flux; the nitrogen isotope variations are consistent with, but much larger than, previously observed variability1,2. Our results show that the signal from these near-surface changes propagates rapidly into the deep ocean, but is modified depending on the phase of the seasonal production cycle. Surprisingly, we find that δ15N values for sinking particles decrease with depth during low-flux periods—behaviour that may occur generally in the open ocean. The sinking particles must therefore be either gaining light nitrogen or losing heavy nitrogen, an effect that we believe requires there to be another source of sinking particles, apart from recent surface production.

Sulfide oxidation in the anoxic Black Sea chemocline

Abstract: The depth distributions of O2 and H2S and of the activity of chemical or bacterial sulfide oxidation were studied in the chemocline of the central Black Sea. Relative to measurements from earlier studies, the sulfide zone had moved upwards by 20–50 m and was now (May 1988) situated at a depth of 81–99 m. Oxygen in the water column immediately overlying the sulfide zone was depleted to undetectable levels resulting in a 20–30-m deep intermediate layer of O2 - and H2S-free water. Radiotracer studies with 35S-labelled H2S showed that high rates of sulfide oxidation, up to a few micromoles per liter per day, occurred in anoxic water at the top of the sulfide zone concurrent with the highest rates of dark CO2 assimilation. The main soluble oxidized products of sulfide were thiosulfate (68–82%) and sulfate. Indirect evidence was presented for the formation of elemental sulfur which accumulated to a maximum of 200 nmol l−1 at the top of the sulfide zone. Sulfide oxidation was stimulated by particles suspended at the chemocline, probably by bacteria. Green phototrophic sulfur bacteria were abundant in the chemocline, suggesting that photosynthetic H2S oxidation took place. Flux calculations showed that the measured H2S oxidation rates were 4-fold higher than could be explained by the downward flux of organic carbon and too high to balance the availability of electron acceptors such as oxidized iron or manganese. A nitrate maximum at the lower boundary of the O2 zone did not extend down to the sulfide zone.

Stable isotope studies of the carbon, nitrogen and sulfur cycles in the Black Sea and the Cariaco Trench

Abstract: Samples for stable isotope studies of possible chemosynthesis in anoxic basins were collected in 1986 in the Cariaco Trench and May 1988 in the Black Sea. POM (particulate organic matter) collected at oxic/anoxic interfaces in the water column showed no distinctive carbon or nitrogen isotopic compositions that could be associated with chemosynthetic bacteria. Carbon and nitrogen isotopic compositions at POM concentration maxima near the top of the sulfide zone were −23%o and 4.5%o, respectively, in both the Black Sea and the Cariaco Trench. Measurements of dissolved inorganic carbon (DIC) in the Black Sea indicated that carbon respired during decomposition at depth had an isotopic composition of −23%o and was isotopically similar to phytoplankton, with no distinctive component that could be attributed to chemosynthetic carbon. These results indicate that either the biomass of chemosynthetic bacteria in the oxic/anoxic interface zones is low relative to sinking phytoplankton or that chemoautotrophic bacteria have isotopic compositions similar to those of phytoplankton. In the uppermost 50 m of sulfidic waters in the Black Sea, sulfide isotopic compositions changed significantly in a region of sulfide consumption, increasing up to 5%o vs deep-water background values of −40.5%o. These increases in sulfide isotopic compositions may be due to sulfide oxidation mediated by MnO 2 or oxygen, but are not consistent with sulfide oxidation by photosynthetic bacteria. Growth experiments with sulfate-reducing bacteria suggested that part of the increase in sulfide isotopic compositions could be due to rapid rates of sulfate reduction in the oxic/anoxic interface regions.

Enhanced particle fluxes in Bay of Bengal induced by injection of fresh water

Abstract: THE melting of ice sheets during deglaciation results in the injection of large amounts of fresh water into the oceans1. To investigate how such injections might influence particle fluxes in the ocean, and hence the uptake of atmospheric CO2, we deployed three sediment-trap moorings (two traps in each mooring) in the northern, central and southern parts of the Bay of Bengal, respectively. The Bay of Bengal is suitable for such a study, because some of the world's largest rivers2 supply pulses of fresh water and sediment to the bay, resulting in large seasonal changes in surface salinity3. We find that the maximum river discharge, which occurs during the southwest monsoon, coincides with the maximum observed flux of participate matter. From north to south, the carbonate flux increases, whereas fluxes of opal, organic carbon and particulate matter decrease. The overall flux pattern seems to be controlled by the seasonally varying input from the rivers and the accompanying shift in marine biogenic production. We conclude that fresh-water pulses during deglaciation may therefore have caused similar shifts in marine biogenic production, resulting in short-term episodes of increased oceanic uptake of atmospheric CO2.

A Simple Kinematic Mechanism for Mixing Fluid Parcels across a Meandering Jet

Abstract: Recent observations of fluid parcel pathways in the Gulf Stream using isopycnal RAFOS floats revealed a striking pattern of cross-stream and vertical motion associated with meanders (Bower and Rossby 1989). In an attempt to explain the observed pattern, a two-dimensional kinematic model of a meandering jet has been developed which enables examination of the relationship between streamfunction patterns and fluid parcel trajectories. The streamfunction fields are displayed in a reference frame moving with the wave pattern so motions of fluid parcels relative to the jet can be seen more easily. The results suggest that the observed pattern of cross-stream motion results primarily from the downstream phase propagation of meanders. The model successfully reproduces several of the most distinctive features of the float observations: 1 ) entrainment of fluid into the Gulf Stream occurs at the leading edges of meander extrema while detrainment takes place at the trailing edges; 2) exchange between the Gu...

Initial contact, exploration and attachment of barnacle ( Balanus amphitrite ) cyprids settling in flow

Abstract: Settlement responses of barnacle (Balanus amphitrite) cyprids to boundary-layer flows were examined in laboratory flume-experiments. The leading-edge configuration of flat plates was altered in order to manipulate flows without changing surface topography or freestream velocity. Settlement along the plates correlated strongly with downstream gradients in shear stress. Analyses of video images taken during the experiments indicate that cyprids first contact plates in regions where plate-ward advection is high, and subsequent exploratory movement along the plate is oriented with flow direction at the plate surface. After exploration, cyprids reject a surface more frequently in a fast flow (10 cm s−1 freestream velocity) than in a slow flow (5 cm s−1), but rejection occurs in shear stresses well below the threshold that would prevent attachment and exploration. A higher rejection rate does not result in lower settlement, however, since contact rate is higher in fast than slow flows. The movement of cyprids in flow thus appears to be a passive transport process during the initial contact stage of settlement, but an active behavioral response to flow direction and shear stress during later stages of exploration and attachment.

Passive mechanical gravity compensation for robot manipulators

Abstract: A simple mechanical method for passively compensating for gravitationally induced joint torques is presented. This energy-conservative gravity-compensation method is suitable for a variety of manipulator designs. With cables and appropriate pulley profiles, changes in potential energy associated with link motion through a gravity field can be mapped to changes in strain energy storage in spring elements. The resulting system requires significant energy input only for acceleration and deceleration or to resist external forces. A testbed with both single- and double-link configurations has demonstrated the efficiency and accuracy of this gravity compensation method, as well as its robustness under dynamic loading conditions. >

Performance of a broad-band acoustic Doppler current profiler

Abstract: A new broadband acoustic Doppler current profiler (ADCP) is described, with a useful range comparable to that of a commercially available narrowband (incoherent) system of the same acoustic frequency, but having enhanced performance. The extra performance may be traded off among (1) reduced velocity variance, (2) reduced averaging time, and (3) finer depth resolution. This improvement permits the observation of phenomena with smaller time and space scales than is now possible with available ADCPs. An expression predicting r.m.s. velocity error in terms of system parameters and the measured acoustic data is given and is shown to be consistent with the independently measured velocity error among redundant beams. Two major sources of bias error in incoherent ADCPs are shown to be much reduced for the broadband system. Field data demonstrating the improved performance over the existing incoherent ADCP are shown for cases of both strong and weak shear. >

Immunohistochemical localization of cytochrome P-450IA1 induced by 3,3',4,4'-tetrachlorobiphenyl and by 2,3,7,8-tetrachlorodibenzoafuran in liver and extrahepatic tissues of the teleost Stenotomus chrysops (scup).

Abstract: The regulation of different cytochrome P-450 forms and their functions in different organs and cell types could determine the susceptibility of those cells and organs to toxic effects of xenobiotics, including chemical carcinogenesis. Here we describe the cellular localization of cytochrome P-450E (P-450IA1) induced in 10 major organs or organ systems of a marine vertebrate species, the fish, Stenotomus chrysops (scup). Scup were injected ip with 3,3',4,4'-tetrachlorobiphenyl (TCB) at 1 mg/kg, or with 2,3,7,8-tetrachlorodibenzofuran (TCDF) at 3 micrograms/kg. Induction was verified by Western blot analysis of microsomes from selected organs (liver, kidney, and gill) using monoclonal antibody (MAb) 1-12-3 to scup P-450IA1. The localization of P-450IA1 was subsequently determined in sections prepared by standard histological methods (10% buffered formalin fixation, paraffin embedding), and stained with MAb 1-12-3 and peroxidase-labeled second antibody. P-450IA1 was induced in epithelial and endothelial cells in liver (including pancreatic tissue), kidney, gill, gut, spleen, testis, and ovary. Induction also was detected in endothelial cells, but not other types, in heart, brain, and red muscle. In heart, the staining was present in the endocardium as well as in the endothelium of the coronary vasculature and great vessels. Although TCDF and TCB both induced P-450IA1 in various cells of all organs examined, the effect of TCB was in most cases greater than that of TCDF. This may be due to a relatively higher TCB dosage. A wider staining distribution was seen in gut, gill, kidney, and gonad of TCB-treated fish, which might be explained by a greater penetration, or by excretion of parent TCB, as opposed to TCDF. In any case, the results show that these important environmental agents induce P-450IA1 in generally similar patterns in all organs examined. The common finding of a strong induction of P-450IA1 in endothelial cells in all organs examined supports the suggestion that the endothelium may be a primary site of P-450IA1 induction.

Deep circulation in the eastern South Atlantic Ocean

Abstract: Tracer properties on sections of closely spaced hydrographic stations across the Angola Basin of the South Atlantic Ocean along Lats 11° and 24°S suggest a three-layer description of the deep circulation there. Below 4 km the basin is closed off in the south, so water enters only from the north; the interior flow is southward, and the western-boundary current (above the eastern flank of the Mid-Atlantic Ridge) is southward at 11°S but northward at 24°S, as required by the Stommel-Arons dynamics. At depths roughly between 2400 and 4000 m the basin seems to be supplied only from the south, the western-boundary current is everywhere northward, and the interior flow is southward. Near the 2-km level the Mid-Atlantic Ridge is too deep to be an effective western boundary; the flow seems to he broadly southeastward across the full basin at l1°S, but at 24°S a topographically guided current flows northward above the ridge to supply southward interior flow. A hydrographic section along the Greenwich meridian illustrates an eastward jet at depths between 1300 and 3200 m that extends near Lat. 22°S from the western-boundary curent to a gap in the Walvis Ridge, through which the jet introduces water to the Cape Basin. Geostrophic estimates of the volume transports of these circulation clements, calculated with reference to zero-velocity surfaces construed from the tracer fields, are consistent in direction with the inferred flow patterns, but the values may be somewhat erroneously high, as they imply dubiously large upward velocities. A tongue of oxygen-poor, nutrient-rich water is found at depths between 3000 and 4500 m at 11°S but not at 24°S. It is strongest at the African continental rise, and extends some 1000 km westward. Its origin is attributed to decay within the ~ediment of detritus originating mainly from the Congo River plume, and its form to the deep horizontal flow field.

Hydrodynamic facilitation of gregarious settlement of a reef-building tube worm.

Abstract: Experiments testing the effects of hydrodynamic processes and chemical cues on substrate selection were conducted with larvae of the marine tube worm Phragmatopoma lapidosa californica. In flume experiments, larvae were presented an array of sand treatments, including two substrates previously shown to induce metamorphosis in this species, under fast and slow flow regimes. Larvae preferentially metamorphosed on the inductive substrates in both flows. Delivery to the array was higher in fast flow because larvae tumbled along the bottom, whereas in slow flow, larvae were observed swimming in the water column. Thus, in addition to chemical cues, behavioral responses to flow conditions may play an important role in larval recruitment to the benthos.

The Bottom Boundary Layer Over the Northern California Shelf

Abstract: Moored temperature and shipboard CTD observations from a northern California coastal upwelling region reveal variable bottom mixed-layer heights that are typically 5–15 m, but occasionally exceed 50 m. Observations from Oregon, northern California, and Peru, indicate that in coastal upwelling regions, maximum bottom mixed-layer heights tend to increase with water depth over the shelf, but rarely exceed half the water depth. Over the northern California shelf the bottom mixed-layer height is shown to depend on the stratification, the current magnitude, and the current direction. The dependence on current direction tends to dominate the response, with thicker bottom mixed layers during poleward flows and thinner bottom mixed layers during equatorward flows. This asymmetric response to poleward and equatorward currents is consistent with model results which indicate that the asymmetric response is due to the up- or downslope Ekman transport of buoyancy along the bottom.

Diel vertical migration in zooplankton: rapid individual response to predators

Abstract: While diel vertical migration in zooplankton has been shown recently to be a predator avoidance behavior, the mechanism by which predators induce and maintain such behavior has been debated. We report results of an in situ predator manipulation experiment during which enclosed populations of the marine planktomc copepod Acaraa hudsonica rapidly changed their vertical distribution and diel migration behavior depending on presence or absence of the planktivorous fish Casterosteus aculeatus These results point unambiguously to phenotypic behavioral plasticity of individual planktomc prey, not, as previously hypothesized, population-genetic level behavioral changes caused by selective fish predation, as the mechanism underlying changes in diel vertical migration in this copepod.

The tholeiite to alkalic basalt transition at Haleakala Volcano, Maui, Hawaii

Abstract: Previous studies of alkalic lavas erupted during the waning growth stages (<0.9 Ma to present) of Haleakala volcano identified systematic temporal changes in isotopic and incompatible element abundance ratios. These geochemical trends reflect a mantle mixing process with a systematic change in the proportions of mixing components. We studied lavas from a 250-m-thick stratigraphic sequence in Honomanu Gulch that includes the oldest (∼1.1 Ma) subaerial basalts exposed at Haleakaka. The lower 200 m of section is intercalated tholeiitic and alkalic basalt with similar isotopic (Sr, Nd, Pb) and incompatible element abundance ratios (e.g., Nb/La, La/Ce, La/Sr, Hf/Sm, Ti/Eu). These lava compositions are consistent with derivation of alkalic and tholeiitic basalt by partial melting of a compositionally homogeneous, clinopyroxene-rich, garnet lherzolite source. The intercalated tholeiitic and alkalic Honomanu lavas may reflect a process which tapped melts generated in different portions of a rising plume, and we infer that the tholeiitic lavas reflect a melting range of ∼10% to 15%, while the intercalated alkalic lavas reflect a range of ∼6.5% to 8% melting. However, within the uppermost 50 m of section. 87Sr/86Sr decreases from 0.70371 to 0.70328 as eruption age decreased from ∼0.97 Ma to 0.78 Ma. We infer that as lava compositions changed from intercalated tholeiitic and alkalic lavas to only alkalic lavas at ∼0.93 Ma, the mixing proportions of source components changed with a MORB-related mantle component becoming increasingly important as eruption age decreased.

Sensitivity of Limulus amebocyte lysate (LAL) to LAL-reactive glucans.

Abstract: The sensitivity of Limulus amebocyte lysate (LAL) to LAL-reactive glucans (LRGs) and lipid A was tested by using commercially available and experimentally formulated LAL reagents. The glucans included two kinds of beta-(1,3)-D-glucans, laminarin and curdlan, and cellulosic material, LAL-reactive material (LAL-RM), extracted from a hollow-fiber (Cuprophan) hemodialyzer. LAL-RM loses its LAL activity when it is digested with cellulase and thus appears to be a beta-(1,4)-D-glucan or a mixed glucan containing a substantial proportion of beta-(1,4) linkages. All LAL reagents tested were at least 1,000-fold more sensitive to endotoxin than to LRGs. The presence of the surfactant Zwittergent was shown to interfere with reactivity to LRGs; LAL reagents without added Zwittergent reacted more strongly to LRGs than did the same reagents containing Zwittergent. Chloroform extraction of LAL increased the reagents9 sensitivity to both endotoxin and LRGs, but it was not responsible for LRG reactivity. The addition of Zwittergent significantly reduced the sensitivity of LAL reagents to lipid A. LAL without the surfactant was equally sensitive to endotoxin and lipid A. Both curdlan and LAL-RM amplified or enhanced the LAL response to endotoxin. Kinetic turbidimetric studies demonstrated that the enhancement was dependent on the glucan concentration.

Asymmetric Behavior of an Oceanic Boundary Layer above a Sloping Bottom

Abstract: The effects of stratification, planetary rotation and a sloping bottom combine to produce an asymmetric response in which the characteristics of an oceanic bottom boundary layer depend on the direction, in addition to the magnitude, of the along-isobath velocity in the inviscid interior. The asymmetric response is examined theoretically under idealized conditions in which the motion begins from rest, the flow is uniform in the along-isobath and cross-isobath directions, and the water column is initially uniformly stratified. The analysis is based on an integrated model, in which the bottom stress is determined from a quadratic drag law, and the height of the boundary layer is determined from a Pollard–Rhines–Thompson mixing criterion. The model indicates rapid mixing at the onset of forcing to a height limited by planetary rotation and interior stratification, followed by evolution in which the height of the boundary layer may either increase or remain fixed near its initial value, depending on t...

Initiation of Fennoscandian ice-sheet retreat during the last deglaciation

Abstract: ALTHOUGH the retreat history of the southern margin of the Laurentide ice sheet during the last deglaciation has been well known for several decades1–3 and recently supported by evidence from accelerator mass spectrometer (AMS) radiocarbon dating of meltwater in the Gulf of Mexico4 and the North Atlantic subtropical gyre5, the retreat history of the Fennoscandian ice sheet before 13kyr ago is still poorly documented. From AMS 14C dating and isotopic analysis of a rapidly deposited series of supra-till sediments in the Norwegian Channel (North Sea), we find that the southern margin of the Fennoscandian ice sheet was in retreat by 15 kyr BP (before present), approximately 2,000 yr earlier than previously supposed. Oxygen isotope analyses in the channel sediments confirm earlier evidence from deep Norwegian Sea sediment cores for low salinity due to ice sheet discharge beginning ∼15–14.5 kyr BP (ref. 6). Recent recalibration of the 14C timescale indicates that the onset of deglaciation within the Norwegian Sea occurred during an interval of rapidly increasing summer insolation beginning∼18,000 calendar yr BP (ref. 7), suggesting that ice-sheet retreat may have been caused by increasing insolation acting on a particularly climate-sensitive ice-sheet configuration. Fresh water and icebergs discharged into the Norwegian Sea at this time reached the North Atlantic and may have contributed to a brief interval of extreme oceanic cooling8 and reduced production of North Atlantic Deep Water9,10. These factors may also have helped to briefly reverse the deglaciation trend (Erie Interstade) already underway in North America.