51 |
Precise north-south oceanographic transect in the Pacific OceanCabrera-Muro, Homero 20 August 1976 (has links)
The Geochemical Ocean Sections Study (GEOSECS) program has carried
out an intensive study of physical and chemical parameters in the
Pacific and Atlantic Ocean. As a result, an enormous collection of high
quality data has been amassed for these two oceans. To analyze the
Pacific data, fourteen stations extending from about 50°N to 69°S near
180°longitude have been selected for this study. The section chosen
provides a good continuous north-south section in the Pacific from near
the Bering Sea to the Antarctic.
To study this massive extent of the oceanic regime, three methods
were adopted. The first was to estimate, using Defant's method, the
approximate level of no motion throughout the section. Secondly, vertical
section plots were contoured for various physical and chemical
parameters to help identify and trace oceanographic features throughout
the Pacific. Finally, calculations for stability were applied to each
station in the section to evaluate the correlation between features of
stability and those seen in the section plots.
The depth of the level of no motion showed strong variability in
the Pacific Ocean, Generally, deeper levels were found in the higher
latitudes with shallowing towards the Equator. In the high southern
latitudes, no level of least motion could be identified. This is
consonant with the condition that the establishment of a level of no
motion involves noticeable stratification of the water column. In high
latitudes, the more nearly uniform distribution of density throughout
the water column inhibits the formation of layers of high stability
and stratified condition.
It is also noted that a good general agreement is found between
the depths of the layer of no motion and the observed oxygen minimum
in the GEOSECS section. This is especially apparent in midlatitudes
where the transition layer between the North and South Intermediate
Waters and the Pacific Deep Waters is the region of the oxygen minimum.
In the layer of the oxygen minimum, biochemical depletion occurs
and there is likely to be minimal replenishment by horizontal and
vertical advection and diffusion. Therefore, it is suggested that the
oxygen minimum layer is closely related to a region of minimal horizontal
movement. The calculation of the level of no motion in the
Pacific GEOSECS sections supports this hypothesis.
The large scale circulation in the Pacific Ocean is clearly
pictured by the parameter section plots obtained from the Pacific
GEOSECS expedition. The North Pacific and Antarctic Intermediate
Waters are clearly defined from their origins to disappearance by low
salinity and high nutrient levels. The extent of the Pacific Deep
Water throughout the Pacific is seen. This large mass of relatively
homogenous water can be seen from the South to the North Pacific.
As the water moves northward, a gradual increase in nutrients and
decrease in oxygen occurs. A third water type seen in the South
Pacific is Antarctic Bottom Water. It intrusion into the South
Pacific can be defined in terms of the 27.86 sigma theta surface or
by such parameters as oxygen, silicate, and apparent oxygen utilization
(AOU).
In an attempt to correlate the various features seen in the vertical
sections, stability profiles were prepared for each station. The
vertical stability profiles did not show any strong features other
than shallow and intermediate stability maxima. Recent discussion
concerning a "benthic front" associated with the Antarctic Bottom
Water intrusion into the South Pacific Ocean is not supported by any
stability feature. Gradients in certain physical and chemical parameters
do occur but the density gradients maximum expected in a
frontal zone is not seen. / Graduation date: 1977
|
52 |
Morphology, shallow structure, and evolution of the Peruvian continental margin, 6⁰ to 18⁰ SMasias Echegaray, Juan Antonio 06 June 1975 (has links)
Detailed bathymetric survey data were collected along the Peruvian
continental margin and were compiled by the author and other
investigators to construct a new bathymetric map for the area between
6° to 18°S latitude. Based on this map and individual bathymetric
profiles, the continental shelf topography is essentially flat. Four
different physiographic provinces (A-D) are defined on the continental
slope. Each province apparently reflects the structural and tectonic
settings in a given area. The trench is separated into three provinces
on the basis of regional depth differences.
Three sedimentary basins, Sechura, Salaverry, and Pisco, are
recognized on the Peruvian continental shelf between 6° to 15°S. The
landward migration on the axis of deposition within these basins is
interpreted to be the sedimentary response to tectonism (uplift) taking
place along the outer edge of the continental margin. Prominent
sedimentary basins also occur on the upper continental slope; these
basins have been named with respect to their geographic position as
the Lima and Arequipa Basins. Landward and seaward migration of
the axis of maximum deposition in these basins is interpreted to be
the result of variable rates of uplift along the outer margin. Uplift
along the seaward edge of these basins suggests that the accretion of
trench and oceanic plate deposits is taking place along the lower and
middle continental slope.
Seismic reflection profiles, extrapolation of regional structural
trends onshore to offshore along the Peruvian margin, and positive
free-air gravity anomalies off southern Peru (Whitsett, 1975), show
that an outer continental shelf high is present off northern and central
Peru. This high is believed to be composed of Paleozoic rocks with
a possible Precambrian core. The high is linked with the Amotape
Mountains in northern Peru and the Coastal Ranges in southern Peru.
It is an important element in the development of the Peruvian continental
margin.
Using all of the data available, a four stage model is proposed
for the Mesozoic-Cenozoic evolution of the Peruvian continental margin.
Stage I describes conditions prior to the formation of the subduction
zone during Triassic time. Plate collision is postulated at the
beginning of Stage II with the formation of a Benioff Zone about 180
m.y. ago (Triassic-Jurassic boundary). Accretion of trench and
oceanic plate deposits occurs as a result of the initiation of under-thrusting
of the South America Block by the Nazca Plate. Stage III
describes the continuous seaward growth of the continental slope
during middle to late Cretaceous time. During late middle (Turonian)
and middle late Cretaceous (Santonian) time diastrophism in
southern Peru restricted the marine conditions to central and
northern Peru. During late Cenozoic time (Stage IV) the Peruvian
margin attained its present configuration through continuous seaward
growth of the continental slope and buildup of the sedimentary
sequences found in the Sechura, Salaverry, and Pisco Basins, in
central and northern Peru. Late Cenozoic volcanism in southern
Peru is apparently associated with the large amount of sediments
that reached the southern Peru Trench since late Cretaceous time.
The Nazca Ridge apparently approached the Peruvian continental
margin during Cenozoic time, and locally changed the morphology of
the continental slope. The proposed model shows that the Peruvian
continental margin is growing seaward and that continental erosion
of the crystalline continental block is not necessary along the
Peruvian continental margin. The model explains and justifies the
presence of the outer continental shelf high off northern and central
Peru. / Graduation date: 1976
|
53 |
The Carnegie Ridge near 86⁰ W. : structure, sedimentation and near bottom observationsMalfait, Bruce Terry 04 September 1974 (has links)
The Carnegie Ridge is a linear, aseismic, submarine ridge
lying between the Galapagos Islands and the coast of South America.
A 2300 meter deep saddle near 86°W. longitude divides the ridge into
western and eastern segments. Surface ship, near bottom, and grain
size studies from the saddle have been used to delineate the present
geological environment and history of the ridge.
Structurally the Carnegie Ridge is rather simple in profile,
being bounded by east-west trending scarps which give the ridge a
block-faulted appearance. Acoustic basement over the ridge appears
smooth on reflection profiles and is composed of chert. The sedimentary
sequence above the chert horizon contains a lower chalk unit
overlain by calcareous ooze. Where erosion has exposed the chalk a
karst-like micro-topography is present which is characterized by
steep walled channels and cliffs and consolidated bed forms undergoing
erosion and dissolution.
The ridge crest has been stripped of almost its entire sediment
cover. Thick sequences of sediment are found only in areas protected
from north or south flowing bottom currents. Evidence of
erosion is provided by extensive channeling on both the north and
south flanks of the ridge. Near bottom observations in one channel on
the north flank revealed a large field of sand dunes indicating northward,
downslope sediment transport. These dunes are found on a
manganese-encrusted chalk which floors the channel. Hydrographic
data suggest that the northward flow across the ridge may be produced
by the spillover of bottom water. Near bottom and surface ship
observations are consistent with a southward sediment transport on
the south flank of the ridge. The mechanism responsible for this
southward flow remains unresolved. Current meters deployed on the
north and south flanks recorded only low speed currents, opposite in
direction to the inferred sediment transport. Apparently the bottom
water flow responsible for erosion and sediment transport over the
ridge is episodic in nature and was not recorded during the present
survey.
The grain size characteristics of surface sediments respond to
the same processes which control sediment distribution. Where
erosion is evident over the ridge crest, coarse lag deposits of foraminiferal sand are found. Apparently the erosion is most pronounced
at the sill depth on the ridge since the sediments tend to become finer
both upslope and downslope from that point. Three dominant modes
are present in the sand fraction from the ridge. These modes record
the initial input and fragmentation of foraminiferal tests. Continued
fragmentation and dissolution of these tests creates a large number
of finer modes.
The age of true basaltic crust over the ridge is between 10 and
26 million years. This crust was probably created during a period of
very slow spreading on the Galapagos Rift Zone during the Miocene.
Unconformities on the ridge indicate that erosion dates only from the
mid-Pliocene. The initiation of erosion was probably in response to
further uplift of the ridge. This uplift may have been related to slight
southward underthrusting along the north flank of the ridge. / Graduation date: 1975 / Best scan available for figures on p.67, 96. The original is a black and white photocopy.
|
54 |
Sediments and tectonics of the Gorda-Juan de Fuca platePhipps, James B. 05 September 1973 (has links)
Cores taken from the ridge areas of the Gorda-Juan de Fuca
plate have a sedimentation rate that is appropriate for the study of
late Quaternary stratigraphy. An analysis of the clay and silt
mineralogy of the cores using X-ray diffraction methods and by
noting changes in the foraminiferan-radiolarian abundances in the
cores were utilized in developing a stratigraphic sequence.
The clay fractions of these sediments consists of chlorite,
illite and smectite. Cores taken from bathymetric highs contain,
on the average, less smectite than do the turbidites from the adjacent
lowlands. The low smectite content suggests eolian enrichment of
these sediments since dusts collected from the nearby continent also
have low smectite concentrations.
Changes in the relative abundances of radiolaria and foraminifera
are used to put biostratigraphic constraints on the correlation of
mineralogical datums. Two changes in the foraminiferan-radiolarian
ratios, marked by sharp increases in the abundance of radiolaria,
occurred at 12,500 years B.P. and 83,000 years B.P. as dated by
carbon-14 and sedimentation rate extrapolations, respectively. Such
faunal changes serve as an independent check of correlations of the
mineralogical datums.
In the 2 to 20 micron, silt fraction, quartz, chlorite, mica and
feldspar are the predominant minerals. Intervals in which the relative
abundance of quartz changes can be dated by carbon-l4 and
sedimentation rates, and related to late Quaternary climatic events.
The quartz-rich zones are synchronous with periods of high insolation, high stands of sea-level, and to a lesser degree with the
catastrophic floods of the Columbia River. The correlation with high
solar radiation reflects quartz enrichment of the sediment due to an
increased eolian contribution. The coincident high sea level stands
effectively decreased the sedimentation rate of quartz-poor continental
detritus that otherwise dilutes the eolian component. The
periodic floods of the Columbia River, caused by the failure of ice
dams, swept quartz-rich loess from eastern Washington down the
river and injected into the marine environment. Such sediment also
increased the quartz abundance in the quartz-rich zones on the
ridges. Thus, the late Quaternary stratigraphy of the cores can be
related to global late Quaternary climatic variations as well as to
events recorded on the adjacent continents.
The structural development of the Gorda-Juan de Fuca plate
over the last 10 million years can be explained by north-south
shortening coupled with the normal tectonism associated with a
spreading sea floor.
This hypothesis for the development of the plate is based on the
presently known magnetic anomaly pattern. A series of reconstructions
of this pattern back through the past 10 million years shows
that both the Gorda and Juan de Fuca portions of the plate have grown
steadily smaller. The incorporation of sequentially shorter Gorda
ridge anomalies into the Pacific plate appears to have led to the
northwest-southeast orientation of the Blanco Fracture Zone, with
consequent changes in the direction of spreading of the Juan de Fuca
Ridge. On the Juan de Fuca portion of the plate, the shortening was
accomplished by shear faulting in Cascadia Basin. Furthermore,
this faulting resulted in the rapid subduction of this portion of the
plate, which, in turn, produced a disconformity in the sediments of
Cascadia Basin. The reconstruction strengthens the notion that right
lateral strike slip motion between the Pacific and Gorda-Juan de Fuca
plate does, indeed, exist. / Graduation date: 1974
|
55 |
Biogenic silica sedimentation in the central equatorial Pacific during the CenozoicLeinen, Margaret, 1946- 18 September 1975 (has links)
A new technique for determining the amount of opal in deep-sea
sediments of any age is described. Using a normative calculation, a
portion of the analytical silica concentration of sediments is subtracted
as non-biogenic in proportion to the concentration of aluminum in the
sample. The ratio of SiO₂:Al₂O₃ used to characterize the non-biogenic
sediment fraction was determined by X-ray diffraction analysis of
opal-free sediments. The procedure was tested against the X-ray
diffraction method for determining opal in deep-sea sediments
The biogenic silica content of Cenozoic sediments from 20 Deep
Sea Drilling Project sites in the central equatorial Pacific was determined
using the normative calculation technique for opal determination.
The equatorial Pacific lies beneath the equatorial current
system where upwelling of nutrient-rich waters results in high
plankton productivity. Accumulation rates of biogenically produced
silica were calculated from the opal contents. Maps of these accumulation
rates for time intervals during the Cenozoic show that opal
accumulation was highest near the equator or paleoequator during the
last 50 m.y. Superimposed on this pattern are fluctuations in the
rate of opal accumulation in the entire area with time. Regional
maxima in opal accumulation in the entire area with time. Regional
maxima in opal accumulation occurred during the middle Eocene
(42-45 m.y. ago) and the late Miocene (7-10 m.y. ago). The
accumulation rates during these maxima are an order of magnitude
higher than those during times of minimum accumulation: the late
Oligocene (25 m.y. ago) and the present. The percent of biogenic
silica in the sediments varies synchronously with the accumulation
rates, but is low to the east due to dilution by non-biogenic sediment
from terrigenous and volcanic sources.
Surface productivity controls the accumulation of opal in the
equatorial Pacific and opaline sediments are not subject to differential
solution with depth. The opal productivity indicated by opal accumulation
rates is not related to changes in sea surface or bottom water
temperatures and is therefore not directly governed by climate. The
association of equatorial productivity and upwelling suggests that
changes in circulation which cause upwelling were the principal factors
controlling productivity and accumulation of biogenic silica in the
past. / Graduation date: 1976
|
56 |
Peruvian deep-sea sediments : evidence for continental accretionRosato, Victor Joseph 28 December 1973 (has links)
In order to determine whether the sediments found on the landward
wall of the Peru Trench are accreted Nazca Plate sediments,
the clay mineralogy and organic carbon contents of 52 surface
samples were submitted to factor analysis. Q-mode factor analysis
resolved the data from the Nazca Plate and Peru continental margin
into three factors. The most important factor (oceanic assemblage)
is strongly associated with Nazca Plate sediments and is comprised
of smectite and aeolian illite. In contrast, upper continental margin
sediments are dominated by either of the two continental factors (A or
B). The principal difference between the continental factors is that
mixed-layer smectite-chlorite clays are characteristic only of continental
assemblage A. Lower continental margin sediments are
characterized by either an oceanic or continental factor dominance.
The boundary between sediments dominated by the oceanic
factor and those dominated by the continental factor was as much as
100 km to the west of its present position earlier in the Quaternary.
The seaward shift in the boundary is attributed to westward shoreline
displacement in response to glacially-induced sea level changes,
increased erosion rates on land during more humid times, and
deposition of continental factor dominated sediments seaward of the
present Peru Trench axis.
Quaternary sediments from 27 cores reveal minor fluctuations
with time in factor loadings in Nazca Plate and upper continental
margin cores and significant variations in some areas near the trench
axis and on the middle to lower continental slope. Displacement of
oceanic sediments into areas with continental sediments is determined
with respect to the factor dominance boundary. Using this
method, continental accretion is indicated for five cores, located up
to 3000 m above the trench floor. One core on the middle continental
slope off Lima, Peru, contains diatom-rich Quaternary dolomite
that probably originated as calcareous sediment on the Nazca Ridge.
If this is true, left-lateral strike-slip motion of the Nazca Ridge along
the Peru Trench axis is indicated.
The bulk of the 28 cores recovered from the acoustically complex
landward wall of the Peru Trench contain sand-silt turbidites of
continental origin. Even though there is a distinct overprint of
terrigenous sedimentation, accreted oceanic sediments can be
recovered in a tectonically active convergent plate boundary. / Graduation date: 1974
|
57 |
Trace element studies of metalliferous sediments in cores from the East Pacific Rise and Bauer Deep, 10⁰ SKendrick, John William 02 October 1973 (has links)
Major (Fe, Mn, Al) and minor (Cr, Mo, Pb, Zn, Cd) element
analyses of metalliferous sediments in cores from the East Pacific
Rise and Bauer Deep indicate that the Bauer Deep sediments are
similar in chemistry and origin to metalliferous sediments of the
East Pacific Rises.
Fe, Pb, and Zn are strongly associated in both cores and are
probably related to the hydrothermal processes which are postulated
to occur on the East Pacific Rise. Incomplete Cd data suggest that
Cd may also be released during hydrothermal leaching of basalt
Mn may originate by precipitation from hydrothermal solutions or by
normal authigenic precipitation from sea water. The similar
accumulation rates of Mo in both cores, and poor correlation of Mo
with Fe imply that Mo is being extracted from sea water. The low
abundances of Cr and Al in metalliferous sediments suggest that
detritus is a minor component of the sediments.
Poorly crystalline smectites constitute a major mineralogical
phase of metalliferous sediments. Chemical and mineralogical
studies indicate that the smectite is an iron-rich montmorillonite,
similar in composition to the bulk sediment.
Information on sedimentation rates in the two cores indicate
that most elements are accumulating faster on the East Pacific Rise
than in the Bauer Deep. Accumulation rates of metals in the Bauer
Deep have decreased up to the present and are currently similar to
those for normal pelagic sediments. It is inferred that the sedimentation
rates in the Bauer Deep are influenced by the proximity of the
East Pacific Rise, It appears that sediments in the Bauer Deep are
largely the product of hydrothermal processes on the East Pacific
Rise, and that the precipitates are transported in suspension to the
Bauer Deep. Authigenic precipitation of elements from sea water
also occurs, having a stronger influence on the sediments as the
precipitation of rise-crest material decreases away from the ridge. / Graduation date: 1974
|
58 |
Host-parasite relationships of the staghorn sculpin Leptocottus armatus Girard in OregonBurreson, Eugene Michael 29 September 1972 (has links)
The staghorn sculpin Leptocottus armatus is abundant in the
Yaquina Bay estuary on the central Oregon coast and also occurs
offshore in shallow water. A total of 560 L. armatus were collected
at three locations in Yaquina Bay and between 7 and 11 kilometers
offshore in depths of 40 to 80 meters. Staghorn sculpins were present
in all areas where collections were made throughout the year except
during the summer when most offshore sculpins moved into Yaquina
Bay. Leptocottus armatus spawned primarily in the bay during the
fall and early winter. The young fish remained in Yaquina Bay for
about one year at which time they were about 12.0 cm in length.
Subsequently, some of them moved offshore.
Seventeen different species of parasites were collected from
the 526 L. armatus examined.
Genolinea laticauda was collected from the stomachs of 25.1%
of the fish and had greater incidence and intensity in larger fish.
Recruitment of immature forms began in April and the average life
span was about seven months. The life cycle was most efficient in the
lower estuary.
Tubulovesicula lindbergi occurred in the stomachs of 50.8% of
the fish and had greater incidence and intensity in small fish. Recruitment
of immature individuals occurred all year, but was greatest in
June. The life cycle was most efficient in the upper estuary.
Podocotyle atomon was found in 42.6% of the fish and was most
abundant in the larger fish.
Bucephalopsis ozakii was collected in 38.8% of the L. armatus
and was more abundant in large fish, as were larval tetraphyllidean
cestodes which were present in 40.7% of the fish. These two parasites
were found to be positively associated because they were both
more likely to parasitize larger fish.
Nematodes believed to be Contracaecum cornutum were found
in ulcers in the stomach of 28.0% of the fish. This was the only
parasite that was obviously pathogenic.
Echinorhynchus gadi occurred in 47.4% of the fish. Immature
worms were obtained all year, but only from fish in the upper estuary.
Other parasites encountered were the protozoans Scyphidia sp.,
Trichodina sp. and Ceratomyxa sp.; the trematodes Gyrodactylus sp.,
Neopodocotyloides sinusaccus and Derogenes sp.; the nematode
Contracaecum aduncum; a piscicolid leech; the copepod
Acanthochondria rectangularis and the isopod Lironeca vulgaris.
It was concluded that all the parasites of L. armatus could be
acquired in Yaquina Bay, although it was more likely that the larval
cestode was acquired offshore.
The parasite data could not be used to determine movements
of L. armatus in and out of Yaquina Bay, but the data were utilized
to show that movements between the upper and lower estuary were
not extensive. / Graduation date: 1973
|
59 |
Late Quaternary radiolarian paleo-oceanography of the Panama Basin, eastern equatorial PacificDinkelman, Menno Gustaaf 20 July 1973 (has links)
A total of 57 core top samples from the Panama Basin were
used in a quantitative study of complete radiolarian thanatocoenoses
to determine whether surface oceanographic conditions are reflected
in the microplankton faunas deposited onto and buried in the sea floor.
Information obtained from this study was used to resolve the sequence
of temporal fluctuations in oceanographic and climatologic conditions
in the eastern equatorial Pacific. Four piston cores from within the
basin were sampled on the basis of carbonate stratigraphies to levels
no older than 130,000 years B.P. Although the sample intervals are
irregular and samples are not closely spaced, this procedure
allowed reasonably good stratigraphic resolution. Because of high
diversity at low latitudes, the 131 radiolarian taxa recognized in this
study accounted for only 37-61% of the individuals encountered in
counts of >1000 specimens.
Q-mode factor analysis of the surface sediment samples
yielded three end member samples, which allowed recognition of
three different assemblages. The dominant assemblage can be
identified with a tropical fauna and the least important assemblage is
considered to be associated with the Peru Current fauna, The distribution
of the tropical assemblage does not reflect surface oceanographic
conditions whereas the distribution of the Peru Current
assemblage shows a weak association with surface conditions, The
other assemblage shows no coherent distribution pattern. The nature
of this assemblage is best explained by considering it to be a
residual of the tropical fauna resulting from chemical and mechanical
modification in the water column and at the sea floor. All evidence
suggests that solution, winnowing and lateral transport are
major processes in determining the distribution of the faunal
assemblages in the sediments of the Panama Basin.
The signal of the Peru Current assemblage in the surface
study was used for a quantitative analysis of the subsurface samples.
This analysis yielded the following results: 1) During most of the
last glacial, assemblages associated with the Peru Current.were
deposited in the Panama Basin, indicating a northward shift of
current boundaries, This has important climatological implications
since such a shift must be associated with a shift of the major wind
belts and of the South Pacific high pressure cell towards the
equator. 2) At least once during, the last glacial, from approximately
50,000 to 40,000 years B.P., warmer conditions are indicated by a
re-appearance of tropical assemblages. 3) The previous interglacial
appears to have been slightly cooler than present interglacial conditions.
4) The warming trend towards present conditions began
between 15,000 and 20,000 years B.P. This is earlier than observed
in the North Atlantic.
These results are correlative with records of oceanographic
and climatic changes in the southeast Pacific, northwestern South
America and the Galapagos Islands. / Graduation date: 1974
|
60 |
Vertical distribution patterns in a subarctic Pacific zooplankton communityMarlowe, Christopher J. 13 February 1974 (has links)
A study has been made of the vertical distributions and
migrations of a large number of zooplankton species at Weather
Station "P" in the Subarctic Pacific. Simultaneously towed horizontal
opening-closing nets were used for the study. The distributions
and migrations of 104 taxa have been subjectively grouped
into seven basic patterns. A few taxa could not be so grouped.
Examination of hydrographic features reveals correlations between
animal distributions and strong hydrographic gradients.
It is concluded that: 1. In boreal oceanic waters, few
animals perform diurnal migrations, 2. Depth ranges for most
zooplankton are on the order of hundreds of meters, and 3. Hydrographic
features may influence the vertical distributions and
migrations of zooplankton. / Graduation date: 1974
|
Page generated in 0.0244 seconds