Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Bibliography: leaves 173-176. / by Rui Xin Huang. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1997. / Includes bibliographical references (p. 225-234). / by Dennis J. Boccippio. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1986. / Microfiche copy available in Archives and Science. / Bibliography: leaves [54]-[55]. / by Sarah Dawn Saltzer. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2005. / Includes bibliographical references (leaves 96-107). / The Eocene era was a warm, climatically dynamic transitional period between the Paleocene greenhouse world and the Oligocene icehouse world. This study details carbon and hydrogen isotopic and biomarker analyses of samples of lignite (bulk fossil leaves), wood, paleosol, and resinite from the Middle to Late Eocene age fossil forest stratigraphy on Axel Heiberg Island, Nunavut, Canada. Bulk carbon isotopes show a record of frequent, large fluctuations on the scale of the Paleocene-Eocene Thermal Maximum benthic carbon excursion of [approx.] 2.6%₀ (Zachos 1999). However, terrestrial flora are less sensitive to CO₂ fluctuations given their capacity to regulate stomatal intake and the comparatively easy diffusion of CO₂ in air. Resinites (-22.8 +/- 1.7%₀) are enriched relative to bulk lignite (-24.7 +/- 0.75%₀), and wood (-21.66 +/- 0.45%₀) is also enriched relative to bulk lignite. Both 1) a scenario of periodic methane hydrate pulses and 2) a scenario of fluctuating forest stand LAI (leaf area index) are not inconsistent with our data. Either mechanism could be responsible for large carbon isotope shifts. Higher plant input dominated the n-alkane signature. Compound-specific hydrogen isotopes in n-alkanes show a record of marked secular change, with isotopes becoming generally lighter over the time span of the stratigraphy, though punctuated by singular fluctuations as large as 32%₀. / (cont.) Polycyclic isoprenoid lipids (-266%₀ to -375%₀, mean 300%₀ +/- 38%₀) are characteristically depleted relative to n-alkanes (-238%₀ to -295%₀, mean -268%₀ +/- 10%₀). From the n-alkanes, we estimate that environmental water in the Eocene on Axel Heiberg Island was depleted -150%o +/- 24.8%o, which agrees with an estimate derived from cellulose, [delta]D-environmental = -133%₀ (Jahren 2003). (For comparison, modern precipitation at the site has a [delta]D value of [approx.] -213%₀, though precipitation should not be considered equivalent to environmental water.) This datum is consistent with a meridional weather patterns that may have carried moisture over continents towards high latitudes in the absence of a polar front, isotopically depleting precipitation to a greater extent than occurs today. However, seasonality cannot be discounted as a mechanism, given that colder temperatures would lead to colder condensation temperatures and thus, isotopically lighter precipitation. / Monica C. Byrne. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 199-210). / The four chloromethanes - methyl chloride (CH3Cl), dichloromethane (CH2Cl2), chloroform (CHCl3), and carbon tetrachloride (CCl4), are chlorine-containing gases contributing significantly to stratospheric ozone depletion and having adverse health effects. Large uncertainties in estimates of their source and sink magnitudes and temporal and spatial variations currently exist. GEIA inventories and other bottom-up emission estimates are used to construct a priori maps of surface fluxes of these species. The Model of Atmospheric Transport and CHemistry (MATCH), driven by NCEP interannually varying meteorological fields, is then used to simulate the trace gas mole fractions using the a priori emissions and to quantify the time series of sensitivities of tracer concentrations to different aseasonal, seasonal, and regional sources and sinks.We implement the Kalman filter (with the unit pulse response method) to estimate both constant (if applicable) and time-varying surface fluxes on regional/global scales at a monthly resolution for the three short-lived species between 2000-2004, and the continental industrial emissions and global oceanic sink for CCl4 at a 3-month resolution between 1996-2004. The high frequency observations from AGAGE, SOGE, NIES and NOAA/GMD HATS and other low frequency flask observations are used to constrain the source and sink magnitudes estimated as multiplying factors for the a priori fluxes and contained in the state vector in the Kalman filter. The CH3Cl inversion results indicate large CH3Cl emissions of 2240 ± 370 Gg yr-1 from tropical plants. The inversion implies greater seasonal oscillations of the natural sources and sink of CH3Cl compared to the a priori. Seasonal cycles have been derived for both the oceanic (for CHCl3 and CH2Cl2) and terrestrial (for CHCl3) sources, with summer maxima and winter minima emissions. Our inversion results show significant industrial sources of CH2Cl2 and CCl4 from the Southeast Asian region. Our inversions also exhibit the strong effects of the 2002/2003 globally wide-spread heat and drought conditions on the emissions of CH3Cl from tropical plants and global salt marshes, on the soil fluxes of CH3Cl and CHCl3, on the biomass burning sources of CH3Cl and CH2Cl2, and on the derived oceanic flux of CHCl3. / by Xue Xiao. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1992. / Includes bibliographical references (p. 321-337). / by William Sam Douglas Wilcock. / Ph.D.

Thesis: S.M. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2018. / Cataloged from PDF version of thesis. "June 2018." / Includes bibliographical references (pages 18-24). / Carboxysomes provide an avenue for narrowing the timing of evolutionary events in groups of cyanobacteria that are ecologically dominant in modem marine environments - groups that may have an integral role in oxygenating the Earth's atmosphere. Here I show that using concatenated phylogenies of carbon fixation proteins better informs the horizontal gene transfer event that brought carboxysomes from purple sulfur bacteria into marine cyanobacteria and that this gene history aids in constraining the evolutionary timing of carbon fixation. Genes encoding the proteins for the a-carboxysomal shell as well as RuBisCO and carbonic anhydrase are co-located on the genomes of various cyanobacteria in the Prochlorococcus and Synechococcus groups. Previous studies have shown that these genes were likely horizontally transferred together from Chromatiales (purple sulfur bacteria), a group of phototrophic Gammaproteobacteria. While many of these genes are highly conserved and thus yield poorly resolved phylogenies, their concatenation clarifies a shared evolutionary history. This work integrates gene transfer with molecular clock calibration methods to determine divergence times. Accordingly, I evaluate the relationship between atmospheric evolution and the ecology of important groups of phototrophs. / by Makayla N. Betts. / S.M. in Geophysics

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1999. / Includes bibliographical references (p. 195-202). / This work attempts to understand the dynamics of the genesis of concentric eyewall hurricanes. More specifically, we focus on the effects of external eddy forcing associated with upper-level wave asymmetries in the environment of tropical cyclones, and through what processes these effects can be achieved. Our approach is a combination of numerical modeling and observational case studies. We have made use of two numerical models, namely a simple two-layer model and a two-dimensional cloud resolving non-hydrostatic model. The latter is called the full physics model for short. Owing to the lack of direct measurements of upper-level atmospheric conditions, we choose to use reanalysis data from National Centers for Environmental Prediction (NCEP) and National Center for Atmospheric Research (NCAR) and European Center for Medium-Range Weather Forecasts (ECMWF). A somewhat lengthy evaluation suggests that both datasets are marginally suitable for case studies of tropical cyclones. Our major conclusions are as follows: ** Numerical simulations from the simple and full physics models suggest that the genesis of concentric eyewall hurricane results from finite-amplitude wind induced surface heat exchange (WISHE) instability of the tropical atmosphere. ** The results from the full physics model suggest that the role of the eddy forcing is like the catalyst in a chemical reaction. The forcing helps manifest internal finite-amplitude instabilities which themselves are driven by surface enthalpy fluxes. ** The results from our extensive case studies suggest that a causal relationship does not always exist between environmental forcing and genesis of a secondary eyewall. Some cases, for example, Hurricane Allen of 1980, Hurricane Elena of 1985 and Hurricane Opal of 1995, show a good and clear relationship between their eyewall replacement cycles and their external forcings. Some cases, for example, Hurricane Gilbert of 1998 and Hurricane Andrew of 1992, show some degree of causal relationship. Some cases, for example, Hurricane Emily of 1993 and Hurricane Gabrielle of 1989, show a weak or close to no causal relationship. ** With the results of Hurricane Frederic of 1979 and results from concentric eyewall hurricanes, we can conclude that the interaction between a tropical cyclone and its upper-level synoptic environment is neither sufficient nor necessary for the genesis and development of concentric eyewall cycles in reality. ** The maps of isentropic potential vorticity (PV) only provide qualitative information on the occurrence of the interaction. The strength of the interaction should be determined quantitatively by the eddy PV fluxes which should be calculated in a storm-moving coordinate system. The discrepancy between the numerical results and the case studies' results leads us to hypothesis two mechanisms of the genesis. One is the interaction between a hurricane and the ocean underneath. The other is the tilting of high PV inner core with the storm and followed up projection of cyclonic vorticity down to the ocean surface. / by Shangyao Nong. / Ph.D.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1988. / Includes bibliographical references. / by Steven John Ghan. / Sc.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2000. / Includes bibliographical references (p. 121-128). / The dynamics of the oceanic large-scale meridional overturning circulation are investigated through a series of numerical experiments using an idealized single-hemisphere general circulation model. In addition to the system's scaling behavior, the consequences of diapycnal mixing location, the impact of deep buoyancy fluxes, and the importance of the surface restoring timescale are considered. As required by advective-diffusive balance, upwelling across isopycnals in low latitudes occurs where diapycnal mixing is specified. Downward mass transport into the abyss is relatively buoyant; the abyssal heat budget is such that this flow is subsequently cooled through deep convective mixing and re-warmed by diapycnal heat fluxes. Thus, mixing below the thermocline affects the abyssal stratification and upwelling profile, but does not contribute significantly to the zonally averaged circulation through the thermocline or the meridional oceanic heat transport. Boundary mixing is more efficient than interior mixing at driving the meridional overturning circulation; with interior mixing, the planetary vorticity constraint interferes with the communication of interior water mass properties and the eastern boundary. The results are consistent with thermodynamic considerations that suggest the strength of the overturning is a function of the vertical heat fluxes through the thermocline. Accordingly, diapycnal mixing must result in surface heat input to influence the portion of large scale overturning that effects the meridional heat transport. When a buoyancy flux (e.g., geothermal heating) is applied to the ocean floor, a perturbation deep meridional overturning cell on the order of several Sv is produced. The surface flow is also perturbed at high latitudes, allowing the additional heat to be released to the atmosphere. Rising motion is concentrated near the equator. The upward penetration of the deep cell is limited by the thermocline, analogous to the role of the stratosphere in limiting the upward penetration of convective plumes in the atmosphere. The magnitude of the advective response is inversely proportional to the deep stratification; with a weaker meridional overturning circulation and hence a less stratified abyss, the overturning maximum of the deep cell is increased. These results suggest that geothermal heat fluxes, typically ignored in general circulation models, might play a more significant role than thought in the determining the abyssal circulation. For the lowest two decades of changes to diapycnal mixing diffusivity (K), the system's response is largely "self-similar", but experiences a transition to a different regime at very high values of diffusivity. The maximum in overturning circulation obeys an approximate 2/3 power scaling law over both regimes. In contrast, given changes in the imposed equator-to-pole temperature difference AT, the behavior is not self-similar except in the meridional pro.- file of surface heat exchange. Moreover, the power law scaling of overturning with AT is similar to that of K, in contradiction with the 1/3 law predicted by scaling arguments and the Marotzke (1997) theory. The ocean's dynamical behavior is also strongly influenced by the restoring timescale at which the surface temperature is restored; with weaker restoring, the deep sinking region of the ocean becomes more narrow in the zonal mean, and the maximum in meridional heat flux declines even though the maximum in overturning remains nearly constant. These results are interpreted by considering the fundamental thermodynamics of the system. / by Jeffery R. Scott. / Ph.D.