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Optical characteristics of the suspended sediment in the High Energy Benthic Boundary Layer ExperimentSpinrad, Richard W. 02 March 1982 (has links)
Graduation date: 1982
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Sedimentology and micropalaeontology of gravity cores from the N.E. Atlantic continental slope south west of IrelandBuck, P J January 1988 (has links)
Bibliography: pages 45-55. / Eleven gravity cores from the continental margin off Eire and Land's End (SW England) were examined and found to document the major trends of the Late Pleistocene climate. Several stratigraphic indicators; - carbonate content, sediment texture, grain size, composition, nature of terrigenous components, ice-rafted debris and foraminiferal diversity were examined and show that the glacial history of the study area can be closely correlated with the palaeoclimatic evolution of the adjacent European shelf. Sediments deposited during Late Pleistocene glacial conditions show the following characteristics when compared to the surface sediments deposited under Holocene interglacial conditions: an increase in the quantity of ice-rafted debris and percentage of mica, and a notable increase in the degree of frosting and pitting of the quartz grains. Overall grain size was finer resulting in a silty sediment package. Sedimentologically the cores fall into two groups (1 and 2). The major difference being that Group 1 (located on the Pendragon Escarpment) received increased quantities of fine silts from a 'shelf spill-over' mechanism operating on the Fastnet and Western Approaches Basins, during glacial regressions. All sediment samples displayed polymodal characteristics reflecting the interaction of several different physical processes e.g. ice-rafting, contour currents etc. Striking variations in the populations of planktonic foraminifera were noted, alternating between Arctic and Sub-Arctic assemblages, reflecting the waxing and waning of glacial activity. The coccolith-carbonate minima correlate with the Arctic-fauna maxima and the ¹⁸O/¹⁶O maxima of the oxygen-isotope curves. Foraminiferal-test analysis (ratio of whole foraminifera fragmented foraminifera) revealed that no correlation existed with any of the other parameters analysed. However, the cores were severely affected by the presence of bottom currents which were strong enough to remove the fragmented tests. Parallellaminated contourites and evidence of erosion were noted in all cores. Ten cores penetrated sediments deposited during the last glacial maximum of 20,000 B.P - 18,000 B.P. near the 75cm depth mark (Core 1865 was too short to reach such sediments). However sediments reflecting the 11,000 B.P glacial readvance, detected at around the 25cm mark, were not as clearly represented. Bioturbation has smoothed the climatic record throughout the lengths of these cores and has also suppressed the high-frequency oscillations (<10³ B.P).
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Studies of deep-sea sedimentary microtopography in the North Atlantic Ocean.Flood, Roger Donald January 1978 (has links)
Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Science. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: p. 333-347. / Ph.D.
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Observed circulation and inferred sediment transport in Hudson Submarine CanyonHotchkiss, Frances Luellen Stephenson January 1982 (has links)
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1982. / Microfiche copy available in Archives and Science / Vita. / Bibliography: leaves 217-223. / by Frances Luellen Stephenson Hotchkiss. / Ph.D.
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Bottom currents and abyssal sedimentation processes south of IcelandShor, Alexander Noble January 1980 (has links)
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Microfiche copy available in Archives and Science. / Bibliography: leaves 206-211. / by Alexander N. Shor. / Ph.D.
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The biogeochemistry of iron, zinc and cobalt in the Atlantic Ocean : the Atlantic Meridional Transect and UK GEOTRACES sectionsWyatt, Neil January 2014 (has links)
Between 40 % and 50 % of the Earth’s primary production occurs in marine environments, primarily by phytoplankton. The trace metal micronutrients iron, zinc and cobalt are known to exert a significant biological control on phytoplankton productivity by serving as essential active centres in enzymatic processes such as inorganic carbon, nitrogen and phosphorus acquisition. The distributions and biogeochemistries of iron, zinc and cobalt therefore, have the potential to impact upon the global carbon cycle and hence climate. This research involves investigations into the biogeochemical cycling of iron, zinc and cobalt in the Atlantic Ocean. Iron measurements were conducted during October and November 2009 to determine the distribution and biogeochemistry of iron in the upper water column of the Atlantic Ocean along an Atlantic Meridional Transect (AMT-19). In addition, deck board incubation experiments were performed to establish the role of iron in controlling rates of di-nitrogen (N2) fixation in the North Atlantic. The distribution patterns and biogeochemistries of iron, zinc and cobalt in the South Atlantic at 40° S were determined during the UK GEOTRACES Section GA10 cruises of October 2010 and December 2011 to January 2012. Iron distributions in North Atlantic surface waters were primarily controlled by the transport and deposition of atmospheric dust particles. In the North Atlantic, elevated surface dissolved iron concentrations (0.50 - 1.65 nM) were associated with wet and dry deposition of Saharan dust between 4 and 29° N. To the south of 4° N, surface dissolved iron concentrations were markedly reduced (0.14 nM) indicating that high precipitation rates in the Inter-Tropical Convergence Zone (4 - 10° N) formed a barrier to the large-scale transport of Saharan dust particles, thus iron, to the South Atlantic. Here, the low surface dissolved iron concentrations were balanced by a total dissolvable iron flux out of the surface mixed layer (3.2 µmol m-2 y-1) that was comparable to atmospheric input estimates. Nitrogen fixation rates in the North Atlantic were highest (0.3 – 1.1 nmol L-1 d-1) where surface dissolved iron concentrations were elevated (1.02 nM) and decreased with increasing latitude as iron decreased. Hence, iron variability in the North Atlantic was sufficient to influence nitrogen fixation over a large spatial scale. In the South Atlantic Ocean at 40° S, the vertical and horizontal distributions of dissolved zinc and cobalt showed distinct gradients associated with the water masses present. Zinc concentrations ranged from 15 pM in open ocean surface waters to 8 nM in Antarctic Bottom Waters, whilst cobalt ranged from 2 pM to 80 pM in intermediate waters and was scavenged in deeper waters. Growth limiting mixed layer zinc concentrations resulted from the lack of a direct return path for zinc to the South Atlantic pycnocline with Sub-Antarctic Mode Water. Low zinc in this return path was identified by a linear correlation between zinc and soluble reactive phosphorus that showed a kink at ~ 500 m, much deeper than that observed in other oceanographic regimes. A seasonal study in the Southeast Atlantic revealed that the depletion of zinc over spring-summer periods resulted in an increase in the nutritional importance of cobalt and a shift towards phytoplankton with a cellular preference for cobalt over zinc and/or the ability to co-substitute these two trace metals at the molecular level. These key findings demonstrate the physico-chemical and biological influences that interact to control the distributions and biogeochemistries of iron, zinc and cobalt across diverse oceanographic regimes of the Atlantic Ocean, provide the first examination of zinc and cobalt biogeochemistries along the productive 40° S parallel and highlight the need for additional research in this region.
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The biology of certain terns, with special reference to the black noddy, Anoüs tenuirostris, and the wideawake, Sterna fuscata on Ascension IslandAshmole, N. Philip January 1961 (has links)
No description available.
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Analysis of meteorological observations from an array of buoys during JASINIshida, Hiroshi 14 December 1979 (has links)
Observations of wind speed and direction, air and sea temperature,
and solar radiation were obtained from an array of buoys in
JASIN. The observations were analyzed to show spatial and temporal
variability. Spectra of wind speed and air and sea temperature were
computed to illustrate the distribution of variance over periods
ranging from 3.5 minutes to 40 days. When plotted on log-log graphs
the spectral estimates generally decrease with increasing frequency
with slopes between -3/2 and -2. Spectra of air and sea temperature
have a peak at the diurnal frequency. When plotted in variance-preserving
form, the spectrum of wind speed is consistent with a spectral
gap and is qualitatively similar to other observations of low
frequency spectra. On the basis of a cross-correlation analysis, it
appears that mesoscale eddies propagated with the mean wind speed
except during frontal passages. Based on the cross-correlation
between wind speed and air temperature, there is evidence of horizontal
roll vortices or organized convection. / Graduation date: 1980
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Palaeobiogeography of Early Cretaceous calcareous nannoplanktonStreet, Christianne January 1999 (has links)
No description available.
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Ecology And Evolution Of Heavily Exploited Fish PopulationsRicard, Daniel 25 May 2012 (has links)
Commercial harvest of sh stocks and their appropriate management requires an understanding
of their population dynamics and of their ability to sustain exploitation.
Here, some ecological and evolutionary consequences of excessive exploitation are
examined.
In Chapter 2 I evaluate the knowledge base and status of commercially exploited
marine populations that undergo formal stock assessment. Despite a bias towards industrialised
countries and stocks of commercial importance, I show the pervasiveness
of overexploitation and, by using reference points of stock status, identify important
regional di erences in the e ectiveness of sheries management.
In Chapter 3 I develop a data format suitable for ecological analyses to best disseminate
the valuable information contained in scienti c trawl surveys. This data
format is suitable for inclusion into the public Ocean Biogeographic Information System
(OBIS) and provides detailed observations that are suitable to the reconstruction
of important sheries-independent stock indices.
In Chapter 4 I examine the spatiotemporal dynamics of ground sh populations. A
positive abundance-occupancy relationship was estimated for the majority of ground-
sh populations examined suggesting that this well-described terrestrial pattern is
also pervasive in the marine environment. Spatial hysteresis was exhibited by numerous
populations, indicating that the spatial distribution of individuals failed to
recover despite recoveries in abundance.
In Chapter 5 I estimate the demographic consequences of changes in growth and
maturation characteristics. The ability of a population to sustain harvest, and its
ability to recover from previous depletions can be overestimated because of trends
towards earlier maturation and slower growth.
In Chapter 6 I conclude the thesis by discussing the implications of my research to
sheries science and management. I argue that trends in the spatial distribution and
the overall productivity of populations must be accounted for when determining sustainable
shing levels and when predicting recovery trajectories under various catch
abatement scenarios. While successful management measures have been implemented
in a number of marine ecosystems, this thesis highlights the importance of improving
our capacity to understand the dynamics of exploited populations and to fully use
the wealth of available monitoring and assessment data.
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