Showing papers by "Woods Hole Oceanographic Institution published in 1983"

The Ventilated Thermocline

Abstract: A simple theoretical model for the oceanic thermocline and the associated field of current is presented. The model consists of a finite but arbitarily large number of inviscid, homogeneous fluid layers each with a different density. The dynamical balances everywhere are Sverdrupian. IN regions where the Ekman pumping is negative (downward) the surface density is specified, i.e., the position of the outcrop of density interfaces is specified. This outcropping of density layers allows deep motion to be excited by the ventilation provided by Ekman pumping even in latitudes far south of the outcrop where the layer is shielded from direct influence of the wind. Analytical solutions are presented in the case where the density-outcrop lines are coincident with latitude circles. The solutions are not self-similar and important sub-domains of the solution are defined by critical potential vorticity trajectories which separate the ventilated from the unventilated regions in the lower thermocline. These cri...

Technique for enumeration of heterotrophic and phototrophic nanoplankton, using epifluorescence microscopy, and comparison with other procedures

Abstract: A new method is described that uses the fluorochrome primulin and epifluorescence microscopy for the enumeration of heterotrophic and phototrophic nanoplankton (2 to 20 μm). Phototrophic microorganisms are distinguished from heterotrophs by the red autofluorescence of chlorophyll a. Separate filter sets are used which allow visualization of the primulin-stained nanoplankton without masking chlorophyll a fluorescence, thus allowing easy recognition of phototrophic cells. Comparison with existing epifluorescence techniques for counting heterotrophic and phototrophic nanoplankton shows that primulin provides more accurate counts of these populations than the fluorescein isothiocyanate or proflavine techniques. Accuracy is comparable to that with the acridine orange technique, but this method requires only one filter preparation for the enumeration of both phototrophic and heterotrophic populations. Images

Metabasalts, axial hot springs, and the structure of hydrothermal systems at mid-ocean ridges

Abstract: Knowledge of the chemical transfer and mineralogical transformations that occur when sea water reacts with basalt at elevated temperatures and pressures can be used along with geological and geophysical data to deduce the typical structure and evolutionary sequence for hydrothermal systems within the oceanic crust along the axis of a mid-ocean ridge. Studies of metabasalt and metadiabase dredged from fault scarps along the axial valley of the Mid-Atlantic Ridge reveal consistent relationships among the bulk chemistry of the altered rocks and their secondary mineralogy, mineral abundances, and mineral compositions, especially for chlorite. These relationships can be interpreted in terms of the distribution of alteration with respect to time, temperature, and water/rock ratio in young crust. Assemblages of chl-ab-ep-act, chl-ab-ep-act-qtz, chl-ab-qtz, and chl-qtz are produced at successively higher effective sea-water to rock ratios within the temperature range of the greenschist facies (−250 to 450 °C). Toward higher ratios, chlorites tend to become more Mg-rich. Pillow basalts of layer 2 are commonly altered under these conditions by sea water on the descending, rather than the ascending, limb of a convection system; this type of alteration, which reflects moderately high water/rock ratios, may characteristically occur above a still partially molten magma chamber. As the magma chamber solidifies and is then penetrated, more pervasive alteration of the deeper part of layer 2 and of layer 3 occurs at lower water/rock ratios, producing solutions such as those recovered from springs on the Galapagos Rift and the East Pacific Rise at 21°N. Localized upwelling limbs of the convection system can produce veins filled with quartz, sulfides, and Fe-rich chlorite.

Fractionation of pyroxene-phyric MORB at low pressure: An experimental study

Abstract: One-atmosphere melting experiments are used to assess the role of clinopyroxene in producing the compositional variations observed in mid-ocean-ridge basalts (MORBs) from the North Atlantic. Analog models of natural glasses and associated phenocrysts show that several possible parental magmas may undergo low pressure fractional crystallization involving olivine and spinel, followed by plagioclase, and then by augite. The phenocryst phase assemblages in natural deep-sea basalts are closely correlated with the major element compositions of their associated quenched glasses, and the projections of these glasses on the Oliv-Cpx-Qtz pseudoternary correspond to the 1-atmosphere phase boundaries and reaction points defined by laboratory experiments. Comparison of natural phenocryst's with experimental phases indicates that the augites preserved in moderately fractionated MORB from the FAMOUS area may have formed at or near the ocean floor and need not be relics of high pressure processes.

Fundamental limitations in passive time delay estimation--Part I: Narrow-band systems

Abstract: Time delay estimation of a noise-like random signal observed at two or more spatially separated receivers is a problem of considerable practical interest in passive radar/sonar applications. A new method is presented to analyze the mean-square error performance of delay estimation schemes based on a modified (improved) version of the Ziv-Zakai lower bound (ZZLB). This technique is shown to yield the tightest results on the attainable system performance for a wide range of signal-to-noise ratio (SNR) conditions. For delay estimation using narrow-band (ambiguity-prone) signals, the fundamental result of this study is illustrated in Fig. 3. The entire domain of SNR is divided into several disjoint segments indicating several distinct modes of operation. If the available SNR does not exceed SNR 1 , signal observations from the receiver outputs are completely dominated by noise thus essentially useless for the delay estimation. As a result, the attainable mean-square error \bar{\epsilon}^{2} is bounded only by the a priori parameter domain. If SNR 1 2 , the modified ZZLB coincides with the Barankin bound. In this regime differential delay observations are subject to ambiguities. If SNR > SNR 3 the modified ZZLB coincides with the Cramer-Rao lower bound indicating that the ambiguity in the differential delay estimation can essentially be resolved. The transition from the ambiguity-dominated mode of operation to the ambiguity-free mode of operation starts at SNR 2 and ends at SNR 3 . This is the threshold phenomenon in time delay estimation. The various deflection points SNR i and the various segments of the bound (Fig. 3) are given as functions of such important system parameters as time-bandwidth product (WT), signal bandwidth to center frequency ratio (W/ω 0 ) and the number of half wavelengths of the signal center frequency contained in the spacing between receivers. With this information the composite bound illustrated in Fig. 3 provides the most complete characterization of the attainable system performance under any prespecified SNR conditions.

How rapidly is a passive scalar mixed within closed streamlines

Abstract: The homogenization of a passive ‘tracer’ in a flow with closed mean streamlines occurs in two stages: first, a rapid phase dominated by shear-augmented diffusion over a time ≈P1/3(L/U), where the Peclet number P=LU/κ (L,U and κ are lengthscale, velocity scale and diffusivity), in which initial values of the tracer are replaced by their (generalized) average about a streamline; second, a slow phase requiring the full diffusion time ≈ L2/κ. The diffusion problem for the second phase, where tracer isopleths are held to streamlines by shear diffusion, involves a generalized diffusivity which is proportional to κ, but exceeds it if the streamlines are not circular. Expressions are also given for flow fields that are oscillatory rather than steady.

Phenotypic Plasticity in Life-History Traits: Demographic Effects and Evolutionary Consequences

Abstract: Although much life-history theory assumes otherwise, most life-history traits exhibit phenotypic plasticity in response to environmental factors during development. Plasticity has long been recognized as a potentially important factor in evolution, is known to be under genetic control, and may or may not be adaptive. The notion of adaptive plasticity contrasts with the idea that developmental homeostasis is a major evolutionary goal. The conflict was resolved in principle by Ashby's cybernetic analysis of homeostasis, which showed how plasticity in “response variables” might act to screen “essential variables” from the impact of environmental disturbance. To apply this analysis to life-history plasticity, it must be incorporated into a demographic model. An approach is presented here using life cycle graphs and matrix projection models. Plasticity in response to temporal variation leads to time-varying matrix models: plasticity in response to spatial variation leads to models structured by criteria other than age. The adaptive value of such plasticity can be assessed by calculating its effects on a suitable measure of fitness: long-term growth rate for time-invariant models, expected growth rate discounted by variance for time-varying models. Three examples are analyzed here: plasticity in the rate of development from one instar to the next in a stage-classified model, plasticity in multiplicative yield components, and plasticity in dormancy as a response to environmental cues. Development rate plasticity is adaptive if reproductive value increases from the instar in question to the next, maladaptive otherwise. Plasticity in yield components reduces fitness variance, and hence is adaptive, if the responses of successive developmental steps ( e.g. , flowers/stem, seeds/flower) are negatively correlated. Plasticity in dormancy is adaptive if it responds to the same factor(s) influencing mortality, but with opposite sign. A number of important problems, including trade-offs between genetic and phenotypic adaptation and the distinction between continuous and discontinous plasticity remain to be solved.

Tectonics of ridge-transform intersections at the Kane fracture zone

Abstract: The Kane Transform offsets spreading-center segments of the Mid-Atlantic Ridge by about 150 km at 24° N latitude In terms of its first-order morphological, geological, and geophysical characteristics it appears to be typical of long-offset (>100 km), slow-slipping (2 cm yr-1) ridge-ridge transform faults High-resolution geological observations were made from deep-towed ANGUS photographs and the manned submersible ALVIN at the ridge-transform intersections and indicate similar relationships in these two regions These data indicate that over a distance of about 20 km as the spreading axes approach the fracture zone, the two flanks of each ridge axis behave in very different ways Along the flanks that intersect the active transform zone the rift valley floor deepens and the surface expression of volcanism becomes increasingly narrow and eventually absent at the intersection where only a sediment-covered ‘nodal basin’ exists The adjacent median valley walls have structural trends that are oblique to both the ridge and the transform and have as much as 4 km of relief These are tectonically active regions that have only a thin (<200 m), highly fractured, and discontinuous carapace of volcanic rocks overlying a variably deformed and metamorphosed assemblage of gabbroic rocks Overprinting relationships reveal a complex history of crustal extension and rapid vertical uplift In contrast, the opposing flanks of the ridge axes, that intersect the non-transform zones appear to be similar in many respects to those examined elsewhere along slow-spreading ridges In general, a near-axial horst and graben terrain floored by relatively young volcanics passes laterally into median valley walls with a simple block-faulted character where only volcanic rocks have been found Along strike toward the fracture zone, the youngest volcanics form linear constructional volcanic ridges that transect the entire width of the fracture zone valley These volcanics are continuous with the older-looking, slightly faulted volcanic terrain that floors the non-transform fracture zone valleys These observations document the asymmetric nature of seafloor spreading near ridge-transform intersections An important implication is that the crust and lithosphere across different portions of the fracture zone will have different geological characteristics Across the active transform zone two lithosphere plate edges formed at ridge-transform corners are faulted against one another In the non-transform zones a relatively younger section of lithosphere that formed at a ridge-non-transform corner is welded to an older, deformed section that initially formed at a ridge-transform corner

Reverse Diel Vertical Migration: An Escape from Invertebrate Predators

Abstract: The marine copepod Pseudocalanus sp. exhibits an unusual reverse diel vertical migration in Dabob Bay, Washington, concurrently with a normal vertical migration by nocturnal invertebrate predators. Reduced spatial overlap with predators appears to decrease mortality rate of adult female Pseudocalanus. A life table analysis suggests that the demographic disadvantage associated with daily migration across a thermal gradient can be overcome if mortality is reduced by as little as 16 percent.

Internal Wave Wake of a Moving Storm. Part I. Scales, Energy Budget and Observations

Abstract: The ocean's baroclinic response to a steadily moving storm is analyzed using a numerical model for an inviscid, multi-layered fluid. This first part of a two-part study gives a detailed account of the response to a rapidly moving hurricane, while parameter dependence is examined in the second part. A central theme of both parts is the coupling between wind-forcing, the surface mixed layer, and the thermocline. The baroclinic response is made up of a geostrophic component and a three-dimensional wake of inertial-internal waves which is emphasized. These waves initially have large horizontal spatial scales set directly by the storm. Their along-storm track wavelength is the storm translation speed times the wave period, which is typically five percent less than the local inertial period. Their cross-track scale is the storm scale. If the storm is intense as it is here, finite amplitude effects soon produce a double inertial frequency wave and smaller spatial scales. An important qualitative result ...

Rare-earth distributions with a positive Ce anomaly in the Western North Atlantic Ocean

Abstract: From the vertical distributions of the rare-earth elements (REE) in the Sargasso Sea we now report the first profiles of Pr, Tb, Ho, Tm and Lu in seawater, together with profiles for La, Ce, Sm, Eu and Yb The first observations of positive Ce anomalies in seawater are ascribed to reducing inshore sediments as a source for Ce (ref 1) All vertical profiles are consistent with adsorption of trivalent rare earths by settling particles, possibly siliceous or calcareous, followed by their release at or near the sea floor on dissolution of the carriers The very different Ce profile demonstrates the additional effects of oxidation–reduction reactions

A cellulolytic nitrogen-fixing bacterium cultured from the gland of deshayes in shipworms (bivalvia: teredinidae).

Abstract: A novel bacterium has been isolated in pure culture from the gland of Deshayes in six species of teredinid bivalves. It is the first bacterium known to both digest cellulose and fix nitrogen, and it is a participant in a unique symbiotic relation with shipworms that may explain how teredinids are able to use wood as their principal food source.

Eigenshape analysis of microfossils: A general morphometric procedure for describing changes in shape

Abstract: A general morphometric procedure is described that organizes collections of microfossil outlines according to their shape It involves representing the greatest proportion of variation observed among a collection of shapes by the least number of different shapes Since these are determined as empirical orthogonal shape functions—eigenfunctions—of the observed shapes, the procedure is termed eigenshape analysis Observed shapes are arranged and their shape differences systemized by reference to these determined eigenshape functions The well-known ecophenotypic shape variation with latitude exhibited by the Pleistocene planktonic foraminifer Globorotalia truncatulinoides (d'Orbigny)serves as an example

Importance of life cycle events in the population dynamics of Gonyaulax tamarensis

Abstract: Life cycle changes that allow populations of the toxic dinoflagellate Gonyaulax tamarensis Lebour to inhabit the benthos and the plankton alternately are important factors regulationg the initiation and decline of blooms in restricted embavments. When the dynamics of these estuarine populations were monitored during “bloom” and “non bloom” years, it was shown that: (1) each year, germination of benthie cysts inoculated the overlying waters during the vernal warming period, but a large residual population remained in the sediments throughout the blooms; (2) the resulting planktonic population began growth under suboptimal temperature conditions; (3) the populations developed from this inoculum through asexual reproduction until sexuality (and cyst formation) were induced; (4) encystment was not linked to any obvious environmental cue and occurred under apparently optimal conditions; and (5) an increase in the number of non-mitotic swimming cells (planozygotes, the precursors to dormant cysts) accompanied the rapid decline of the planktonic population. Thus encystment, in combination with hypothesized losses due to advection and grazing, contributed substantiatly to the decline of the vegetative cell population. We conclude that the encystment/excystment cycle temporally restricts the occurrence of the vegetative population and may not be optimized for rapid or sustained vegetative growth and bloom formation in shallow embayments. The factors that distinguish “bloom” from “non-bloom” years thus appear to be operating on the growth of the planktonic population.

Chemoautotrophic growth of a marine Beggiatoa in sulfide-gradient cultures

Abstract: A recently isolated strain of Beggiatoa, MS-81-6 (cf. alba), was tested for chemoautotrophic growth in semi-solid (0.2% agar) sulfide/oxygen gradient cultures. The organism grew in a horizontal layer, the distance from the air/medium interface depending on sulfide concentrations and changing with time. Optimal growth as a gradient organism was based on a preference for reduced oxygen concentrations and a limited sulfide tolerance in combination with gliding motility. In gradient cultures chemoautotrophic growth was demonstrated by the following criteria: (1) biomass yield (protein) increased with increasing sulfide concentration, and estimated molar growth yields agreed with those for other sulfide-grown chemoautotrophs; (2) approximately 90% of total cell carbon and protein carbon were fixed from carbon dioxide; (3) the CO2-fixing enzyme, ribulosebisphosphate carboxylase, was present in cell-free extracts at a level typical of chemoautotrophs; (4) acidification of the medium, apparently linked to utilization of internal So granules, accompanied the later phase of growth. The ability to grow on acetate in the absence of a source of reduced sulfur renders the organism facultatively chemoautotrophic.

Biological control of the removal of abiogenic particles from the surface ocean.

Abstract: Concurrent measurements of particle concentrations in the near-surface water and of particle fluxes in the deep water of the Sargasso Sea show a close coupling between the two for biogenic components. The concentrations of suspended matter appear to follow an annual cycle similar to that of primary production and deepwater particle flux. Although the concentration of particulate aluminum in the surface water appears to vary randomly with respect to that cycle, the removal of aluminum to deep water is intimately linked to the rapid downward transport of organic matter.

Evidence for punctuated gradualism in the Late Neogene Globorotalia tumida lineage of planktonic foraminifera

Abstract: The warm-water planktonic foraminiferal Globorotalia tumida lineage has been studied in a 10-Myr-long stratigraphic sequence (Late Miocene through Recent) from the Indian Ocean to determine long-term evolutionary patterns through the lineage's history, and particularly to study in great detail the evolutionary transition from G. plesiotumida to G. tumida across the Miocene/Pliocene boundary. Sampling resolution was very good, between 5 × 103 and 15 × 103 yr across the Miocene/Pliocene boundary and about 2 × 105 yr otherwise. The test shape was analyzed in edge view, permitting determinations of variation in inflation and elongation of the test. Shape was analyzed quantitatively using eigenshape analysis. This method represents the greatest proportion of variation observed among a collection of shapes by the least number of different shapes. The Late Miocene (10.4-5.6 Myr B.P.) populations exhibited only minor fluctuations in shape that did not result in any net phyletic change. This period of stasis was followed by an 0.6-Myr-long period (between 5.6 and 5.0 Myr B.P.) of gradual transformation of the Late Miocene morphotype (G. plesiotumida) into the Early Pliocene morphotype (G. tumida). The populations were again more or less in stasis in the Pliocene and Pleistocene (5.0 Myr to the present day), so that no major modifications of the newly evolved Early Pliocene morphotype occurred during these 5 Myr. Thus it would appear that the G. tumida lineage, while remaining in relative stasis over a considerable part of its total duration underwent periodic, relatively rapid, morphologic change that did not lead to lineage branching. This pattern does not conform to the gradualistic model of evolution, because that would assume gradual changes throughout the history of the lineage. It also does not conform to the punctuational model, because (1) there was no speciation (lineage branching) in this lineage and (2) the transition was not rapid enough (<1% of the descendant species' duration according to definition). For this evolutionary modality we propose the term “punctuated gradualism” and suggest that this may be a common norm for evolution—at least within the planktonic foraminifera.

Long-term biological consequences of nuclear war

Abstract: Subfreezing temperatures, low light levels, and high doses of ionizing and ultraviolet radiation extending for many months after a large-scale nuclear war could destroy the biological support systems of civilization, at least in the Northern Hemisphere. Productivity in natural and agricultural ecosystems could be severely restricted for a year or more. Postwar survivors would face starvation as well as freezing conditions in the dark and be exposed to near-lethal doses of radiation. If, as now seems possible, the Southern Hemisphere were affected also, global disruption of the biosphere could ensue. In any event, there would be severe consequences, even in the areas not affected directly, because of the interdependence of the world economy. In either case the extinction of a large fraction of the Earth's animals, plants, and microorganisms seems possible. The population size of Homo sapiens conceivably could be reduced to prehistoric levels or below, and extinction of the human species itself cannot be excluded.

Reduced advection into Atlantic Ocean deep eastern basins during last glaciation maximum

Abstract: Causes of change in deep water δ13C can be either global or local in extent. Global causes include (1) climatically-induced changes in the amount of terrestrial biomass which alter the average carbon isotopic composition of the oceanic reservoir1, and (2) erosion and deposition of organic-rich, continental shelf sediments during sea level fluctuations which change the mean oceanic carbon: phosphorus ratio2. Regional gradients of δ13C are created by remineralization of organic detritus within the deep ocean itself thus reflecting the distribution of water masses and modern thermohaline flow. Changes in a single geological record of benthic foraminiferal δ13C can result from any combination of these global and abyssal circulation effects. By sampling a large number of cores collected over a wide bathymetric range yet confined to a small geographical region we have minimized the ambiguity. We can assume that each δ13C record was equally affected by global causes of δ13C variation. The differences seen between the δ13C records must, therefore, reflect changes in the distribution of δ13C in the deep ocean. We interpret these differences in distribution in terms of changes in the ocean's abyssal circulation. Benthic foraminiferal carbon isotopic evidence from a suite of Sierra Leone Rise cores indicates that the deeper parts of the eastern Atlantic basins underwent a reduction in [O2] during the maximum of the last glaciation. Reduced advection of O2-rich deep water through low-latitude fracture zones, associated with increased delivery of organic matter to the deep ocean, lowered the δ13C of deep water ΣCO2 at all depths below the sill separating the eastern and western Atlantic basins.3 This decreased advection into the eastern Atlantic Ocean coincides with the overall decrease in deep water production in the North Atlantic during the last glacial maximum4–7.

Differential response of humpback whales, Megaptera novaeangliae, to playback of song or social sounds

Abstract: Playback experiments were performed with wild humpback whales, Megaptera novaeangliae, during their breeding and calving season off the island of Maui, Hawaii. Singing whales usually stopped singing upon playback of either songs recorded from lone whales or social sounds recorded from groups of five to eight humpback whales in which males were fighting, probably for access to a female in the group. Three out of four lone singers and six of the eight groups of one or two adults exposed to social sounds charged the playback boat, but the two cows with calves and two groups of three of more adults exposed to social sounds moved away.