Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 33-40). / The massive marine species turnover at the Cenomanian-Turonian boundary is associated with Oceanic Anoxic Event 11 (OAE II) and is often identified by an increase of a13C in the carbon isotopic record. A high-precision chronology of the Cenomanian- Turonian boundary is needed to better constrain the cause, timing, and extent of OAE II. To create such a timeline, four bentonite samples from the Kaiparowits Plateau, Utah were dated using U/Pb geochronology. The Cenomanian-Turonian boundary is constrained to be 94.040 ± 0.029/0.098/0.14 Ma, in agreement with recent astrochronologic studies of the same time period. This research will help improve the calibration of the astronomical time scale, as well as provide a greater understanding of the Cretaceous environment.. / by Amber M. Stangroom. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2008. / Cataloged from PDF version of thesis. "Appendix B section - Variable Scatter Plots - contains pages with binder punch holes resulting in deleted text"--Disclaimer Notice page. / by Allison R. Brown. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2006. / Includes bibliographical references (p. 85-87). / Recent studies have linked hemispheric climate variability to annular modes, zonally symmetric structures that describe the horizontal redistribution of atmospheric mass. The resulting changes in the pressure patterns consequently alter the atmospheric circulation, including the movement of zonal jets in the atmosphere. While the literature contains much observational evidence describing these annular modes, the fundamental dynamics in the perpetuation of the annular modes still remains poorly understood. We investigate the dynamics of the annular modes using the MITGCM, a semi-hemispheric ocean model. The forcings imposed in the model are an atmospheric wind stress and relaxation to a latitudinal temperature profile, which induces a baroclinically unstable flow. Despite such an idealized setup, the model output shows striking similarities to the observed atmospheric annular modes, where the leading mode of variability is associated with the primary zonal jet's meridional displacement. By convention, when the zonal jet is poleward (equatorward) of its time-mean position, the principal component (PC) of the first empirical orthogonal function (EOF) is positive (negative) and is referred to as the high (low) zonal index. / (cont.) In the model, systematic secondary (weaker) jets migrate equatorward into the primary jet. The total eddy forcing associated with the migrating jets aids in sustaining the primary jet in the presence of frictional forces. Plots of the anomalous eddy fields for both indexes show that the strongest eddy activity in the main jet is associated with the high zonal index. The zonal flow anomalies, which systematically migrate into the poleward flank of the main jet, are largely responsible for causing this positively anomalous eddy forcing. This asymmetrical forcing to the primary jet results in the zonal index variability. In this thesis, the dynamics associated with the secondary jets and its equatorward migration will be examined. We will show that when (1) the sphericity of the earth is accounted for, (2) the interior PV is homogenized, and (3) the width of the baroclinically unstable region exceeds the Rhines scale by several factors, multiple zonal jets emerge and migrate equatorward. / by Cegeon J. Chan. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmosphere and Planetary Sciences, 1988. / Includes bibliographical references. / by Maurizio Fantini. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 161-175). / Mass-independent sulfur isotope signatures are observed in Archean and early Paleoproterozoic sedimentary sulfate and sulfide minerals, and provide the most robust constraints on early atmospheric oxygen levels. Smaller mass-independent sulfur isotope anomalies are observed in ice cores and interpreted as a tracer of stratospheric volcanic loading. Photochemistry of sulfur dioxide (SO2) has been implicated as a possible source of the mass-independent sulfur isotope signatures in both the modern stratosphere and on the early earth. However, the mechanisms responsible for the production of mass-independent sulfur isotope fractionation remain poorly constrained. This thesis investigates the multiple sulfur isotope systematics during photochemical reactions of sulfur dioxide as a function of a variety of experimental conditions. Two absorption regions of SO2 are tested - photolysis in the 190 to 220 nm region and photoexcitation in the 250 to 350 nm region. Experimental conditions modified include temperature, SO2 pressure, bath gas pressure, and addition of reactive gases (C2 H2, 02 and CH4). Results of photochemical experiments are compared with isotope systematics predicted from isotopologue-specific absorption cross-sections to identify potential mechanisms for the production of mass-independent fractionation during photochemical reactions. Strong similarity between the isotope systematics of SO2 photolysis and ice core data suggest that SO2 photolysis is responsible for the production of mass-independent sulfur isotope effects in the modern stratosphere. In contrast, significant discrepancies between the isotope signatures from SO2 photochemistry and those in the Archean record suggest that, although SO2 photolysis was likely an important process in the Archean atmosphere, an additional reaction likely contributes to the mass-independent sulfur isotope signatures preserved in the Archean rock record. / by Andrew Richard Whitehill. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1991. / Includes bibliographical references (p. 117-121). / by Gregory Conrad Johnson. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2008. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 51-55). / Atmospheric blocking disturbs synoptic-scale features from their normal eastward progression, causing extreme weather conditions for the duration of the blocking event. Blocking precursors, as indicators of meridional flow preceding the onset of strong Atlantic blocking episodes, have been identified by using a modified version of the Tibaldi and Molteni blocking index (1990). Hovmoller diagrams of the modified index were found to be particularly useful in finding the potential cases, clearly showing a precursor signal propagating from the western United States down to the Atlantic to initiate the blocking pattern. A composite of the 14 cases identified showed the precursor pattern to be consistent with the positive phase of the PNA, while the composite mature phase of Atlantic blocking resembles the negative NAO and AO phases. The results suggest that blocking is a global, rather than localized, phenomenon. / by Garrett P. Marino. / S.B.

Thesis (S.M. in Geophysics)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 21-23). / I show that perchlorate hydrates, which have been indirectly detected at high Martian circumpolar latitudes by the Phoenix Mars Lander, have a dramatic effect upon the rheological behavior of polycrystalline water ice under conditions applicable to the north polar layered deposits (NPLD). I conducted subsolidus creep tests on mixtures of ice and magnesium perchlorate hexahydrate (MP6) of 0.02, 0.05, 0.10, and 0.47 volume fraction MP6. I found these mixtures to be increasingly weak with increasing MP6 content. For mixtures with </= 0.10 volume fraction MP6, I resolved a stress exponent of n ~~ 2 at low stresses transitioning to n ~~ 4 above 10 MPa. Scanning electron microscopy of deformed specimens revealed MP6 to be distributed as an interconnected film between ice grains. These results suggest that grain boundary sliding (GBS) may be enhanced with respect to pure ice. As the enhancement of GBS is expected in polycrystalline aggregates containing a few percent melt or otherwise weak material distributed along grain boundaries, the observed n~~ 2 is consistent with the mutual accommodation of basal slip and GBS. If ice containing trace concentrations of MP6 is also much weaker than pure ice at low stresses, flow in the NPLD could be significantly enhanced, particularly at the warmer basal temperatures associated with higher Martian obliquities. / by Hendrik J. Lenferink. / S.M.in Geophysics

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 29-31). / This study aimed to evaluate the presence of spectral slope variations of B-type asteroids in the near-ultraviolet wavelength range and further compare variations to those found in the near-infrared (de Leon et al., 2012) and infrared (All-Lagoa et al., 2013). New observations of 19 B-type asteroids were obtained using the Telescopio Nazionale Galileo (TNG) and additional observations were collected on the William Herschel Telescope (WHT) and Isaac Newton Telescope (INT). After identifying appropriate solar analogs for spectral reduction, it was found that 1) not all asteroids are B-types as classified by the M4AST online tool (Popescu et al., 2012), and 2) spectral slope variations were present amongst the B-type asteroids. These spectral slope variations could not be traced to the use of certain solar analogs or differences in airmass during observations. Furthermore, these variations were in good agreement spectral slope variations of carbonaceous chondrites, particularly in the near-UV region. These results support the work of de Leon et al. (2012) and Alf-Lagoa et al. (2013) in identifying spectral slope variations and contributing to a three-part survey of B-type asteroids across different wavelengths. / by Ashley J. Peter. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 106-119). / Portland, Oregon, lies within an active tectonic margin, which puts the city at risk to hazards from earthquakes and volcanic eruptions. The young Juan de Fuca microplate is subducting under North America, introducing not only arc magmatism into the overlying plate, but also interplate and intraplate seismicity related to the subduction zone. Large crustal earthquakes are also probable in Portland because of the oblique strike-slip Portland Hills Fault zone. These hazards create risk to Portland residents and infrastructure because of pre-existing vulnerabilities. Much of Portland's downtown area, including the government and business districts, is at risk of ground shaking infrastructure damage, liquefaction and landslides due to earthquakes. Additionally, the city is within 110 km of three active Cascadia stratovolcanoes, two of which pose hazards from tephra and lahars. Though the city is under the umbrella of four emergency response plans-city, county, state and federal-there are critical gaps in mitigation strategies, emergency exercises and community education and outreach. Portland cannot prevent earthquakes or volcanic eruptions, but the city can reduce its vulnerability to these hazards. / by Alexandra M. Jordan. / S.B.