2,841 research outputs found
The paleoceanography of the Bering Sea during the last glacial cycle
No full textThesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (leaves 117-126).In this thesis, I present high-resolution stable-isotope and planktonic-fauna records from Bering Sea sediment cores, spanning the time period from 50,000 years ago to the present. During Marine Isotope Stage 3 (MIS3) at 30-20 ky BP (kiloyears before present) in a core from 1467m water depth near Umnak Plateau, there were episodic occurrences of diagenetic carbonate minerals with very low 13C (-22.4%), high 18O (6.5%), and high [Mg]/[Ca], which seem associated with sulfate reduction of organic matter and possibly anaerobic oxidation of methane. The episodes lasted less than 1000 years and were spaced about 1000 years apart. During MIS3 at 55-20 ky BP in a core from 2209m water depth on Bowers Ridge, N. pachyderma (s.) and Uvigerina 18O and 13C show no coherent variability on millennial time scales. Bering Sea sediments are dysoxic or laminated during the deglaciation. A high sedimentationrate core (200 cm/ky) from 1132m on the Bering Slope is laminated during the Blling warm phase, Allerd warm phase, and early Holocene, where the ages of lithological transitions agree with the ages of those climate events in Greenland (GISP2) to well within the uncertainty of the age models. The subsurface distribution of radiocarbon was estimated from a compilation of published and unpublished North Pacic benthic-planktonic 14C measurements (475{2700 m water depth). There was no consistent change in 14C probles between the present and the Last Glacial Maximum, Blling-Allerd, or the Younger Dryas cold phase. N. pachyderma (s.) 18O in the Bering Slope core decreases rapidly (in less than 220 y) by 0.7-0.8h at the onset of the Blling and the end of the Younger Dryas. These isotopic shifts are accompanied by transient decreases in the relative abundance of N. pachyderma (s.), suggesting that the isotopic events are transient warnings and sustained freshenings.by Mea S. Cook.Ph.D
(Table S1) Stable isotope composition of Neogloboquadrina pachyderma s of sediment core HLY02-02-51
No full text(Table S1) Stable isotope composition of Neogloboquadrina pachyderma s of sediment core HLY02-02-5
(Table S2) Stable isotope composition of Neogloboquadrina pachyderma s of sediment core HLY02-02-57
No full text(Table S2) Stable isotope composition of Neogloboquadrina pachyderma s of sediment core HLY02-02-5
The deglacial history of surface and intermediate water of the Bering Sea
No full textAuthor Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B. V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 52 (2005): 2163-2173, doi:10.1016/j.dsr2.2005.07.004.The lithology of deglacial sediments from the Bering Sea includes intervals of laminated
or dysaerobic sediments. These intervals are contemporaneous with the occurrence
of laminated sediments from the California margin and Gulf of California,
which suggests widespread low-oxygen conditions at intermediate depths in the
North Pacific Ocean. The cause could be reduced intermediate water ventilation,
increased organic carbon
flux, or a combination of the two. We infer abrupt decreases
of planktonic foraminifer δ18O at 14,400 y BP and 11,650 y BP, which may
be a combination of both freshening and warming. On the Shirshov Ridge, the abundance
of sea-ice diatoms of the genus Nitzschia reach local maxima twice during the
deglaciation, the latter of which may be an expression of the Younger Dryas. These
findings expand the extent of the expression of deglacial millennial-scale climate
events to include the northernmost Pacific.The Oak Foundation of Boston, Massachusetts,
and the WHOI Academic Programs Office provided support for Mea Cook.
This project was funded by NSF grant OPP-9912122
Numerical simulation of the mechanical behaviour of ultrafine - and coarse - grained Zr-Nb alloys over s wide range of strain rates
No full textThis paper presents the results on the development of theoretical methods of evaluation and prediction of mechanical properties of Zr–Nb alloys over a range of strain rates from 10−3 to 103 s−1. The mechanical behavior of coarse- and ultrafine-grained Zr–1Nb (E110) was investigated numerically. The ranges of strain rates and temperatures in which the mechanical behavior of Zr–1Nb alloy can be described using modified models of Johnson–Cook and Zerilli–Armstrong were defined. The results can be used in engineering analysis of designed technical systems for nuclear reactors
The paleoceanography of the Bering Sea during the last glacial cycle
No full textSubmitted in partial fulfillment of the requirements for the degree of
Doctor of Philosophy at the Massachusetts Institute of Technology and the
Woods Hole Oceanographic Institution February, 2006In this thesis, I present high-resolution stable-isotope and planktonic-fauna records from Bering Sea sediment cores, spanning the time period from 50,000 years ago to the present.
During Marine Isotope Stage 3 (MIS3) at 30-20 ky BP (kiloyears before present) in a core
from 1467m water depth near Umnak Plateau, there were episodic occurrences of diagenetic
carbonate minerals with very low δ13C (-22:4h), high δ18O (6.5h), and high [Mg]/[Ca], which seem associated with sulfate reduction of organic matter and possibly anaerobic oxidation of methane. The episodes lasted less than 1000 years and were spaced about 1000 years apart. During MIS3 at 55-20 ky BP in a core from 2209m water depth on Bowers Ridge, N. pachyderma (s.) and Uvigerina δ18O and δ13C show no coherent variability on millennial time scales.
Bering Sea sediments are dysoxic or laminated during the deglaciation. A high sedimentation
rate core (200 cm/ky) from 1132m on the Bering Slope is laminated during the
Bolling warm phase, Allerod warm phase, and early Holocene, where the ages of lithological transitions agree with the ages of those climate events in Greenland (GISP2) to well within the uncertainty of the age models. The subsurface distribution of radiocarbon was estimated
from a compilation of published and unpublished North Pacific benthic-planktonic
14C measurements (475-2700 m water depth). There was no consistent change in 14C profiles between the present and the Last Glacial Maximum, Bolling-Allerod, or the Younger Dryas cold phase. N. pachyderma (s.) δ18O in the Bering Slope core decreases rapidly (in less than 220 y) by 0.7-0.8% at the onset of the Bolling and the end of the Younger Dryas.
These isotopic shifts are accompanied by transient decreases in the relative abundance of N. pachyderma (s.), suggesting that the isotopic events are transient warmings and sustained freshenings.The work in this thesis was supported by the National Science Foundation award OPP-9912122 to Lloyd Keigwin, the Oak Foundation of Boston, Massachusetts, the Stanley
Watson Fellowship, the Paul Fye Fellowship, and the Academic Programs Office at WHOI
(Table S5) Absolute abundance of benthic foraminifera in sediment core HLY02-02-51
No full text(Table S5) Absolute abundance of benthic foraminifera in sediment core HLY02-02-5
(Table 1) Age determination of sediment cores HLY02-02-51 and HLY02-02-57
No full textMeasured on Neogloboquadrina pachyderma sinistral
(Table S4) Stable isotope composition of Uvigerina peregrina of sediment core HLY02-02-57
No full text(Table S4) Stable isotope composition of Uvigerina peregrina of sediment core HLY02-02-5
(Table S7) Geochemistry of sediment core HLY02-02-51
No full text(Table S7) Geochemistry of sediment core HLY02-02-5
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