Search

As current global temperatures continue to rise at an accelerated pace, it is becoming increasingly important to examine how the planet has responded to previous periods of global warming in order to gain valuable insights into how the Earth system may react in the future. The mid-Cretaceous (~101-91 Ma) provides an excellent case study of a prolonged greenhouse climatic state, where high rates of oceanic crust production and enhanced large igneous province-related volcanism released vast quantities of greenhouse gases into the atmosphere. Consequently, global temperatures reached their highest level for the past 450 Myr during the Cenomanian to Turonian stages, and peak sea levels led to the development of epeiric seas such as the Western Interior Seaway (WIS), which extended southwards from the northern Boreal Ocean, across central North America, and into the Tethys Ocean. Superimposed upon this greenhouse climate were a series of even more extreme climate perturbations, of which Oceanic Anoxic Event 2 (OAE 2), spanning the Cenomanian-Turonian boundary (94.1 Ma), was the most prominent, globally widespread, extreme climatic event of the Late Cretaceous. OAE 2 represents a major global carbon cycle perturbation, during which enhanced marine productivity coupled with the expansion of oxygen minimum zones across global oceans led to the extensive deposition of organic-rich black shale deposits. An earlier Mid-Cenomanian Event (MCE I; ~96.5 Ma) is taken to be a precursor to OAE 2, as it marks the beginning of a ~2 Myr oceanographic reorganisation during which bottom waters started to become increasingly oxygen-depleted. MCE I is identified on a global scale by a distinct dual-peaked positive carbon isotope excursion. However, with little evidence of widespread organic-rich mudrock deposition, most studies of MCE I are from carbonate-rich successions, thus limiting the range of analyses that can be undertaken. Here, a high-resolution, integrated organic and inorganic multi-proxy study of the Rebecca K Bounds-1 core from western Kansas has been undertaken in order to elucidate environmental and oceanographic changes during MCE I and the interval leading up to OAE 2 in the central-eastern WIS. MCE I is identified in an organic-rich sequence through a dual-peaked, positive organic carbon isotope excursion (MCE 1a and MCE 1b, respectively), and is determined to coincide with the establishment of a fully connected seaway that extended from the northern Boreal Ocean to the Tethyan Ocean in the south via the WIS in the mid-Cenomanian, as evidenced by diversified palynological, foraminiferal, and geochemical changes between MCE 1a and MCE 1b. Periodically enhanced planktic productivity is linked to ~50 kyr obliquity cycles across MCE I through cyclostratigraphic analysis. This heightened productivity is attributed to the strengthening of meridional winds during obliquity maxima, which may have increased upwelling-related nutrient input into Tethyan surface waters in equatorial regions. Palynological, redox-sensitive trace metal, lipid biomarker, and sedimentological data reveal that a complex dynamic oceanographic system prevailed in the central region of the WIS, with mixed early Cenomanian Tethyan-Boreal waters eventually being replaced by a northward migrating Tethyan water mass in the mid- to late Cenomanian. This situation prevailed until OAE 2 set in, when a rapid southward incursion of Boreal waters extended as far as the southern margin of the seaway. This multi-faceted study provides a new in-depth, high-resolution example of how Earth systems and environmental conditions reacted to periods of stressed, greenhouse climatic conditions.

The physiological response to environmental hypoxia encountered at high altitude has a wide range of cardiovascular and pulmonary effects. The insertion allele of the angiotensin converting enzyme (ACE) gene polymorphism has been found to be more prevalent in endurance athletes and is associated with beneficial anabolic and functional responses in muscle. Furthermore, the insertion allele of this functional genetic polymorphism has been associated with enhanced physical performance at altitude, as defined by the successful ascent of peaks over 4800 metres. This thesis examines the cardiopulmonary responses during exercise and hypoxia in order to elucidate any genotype dependent differences in cardiopulmonary response that could explain this observation. The main body of this work was carried out between August 1999 and September 2001. The studies involved 60 healthy subjects performing a maximal cardiopulmonary exercise test to determine ventilatory threshold (VT). At the second visit the subjects underwent a second set of steady state exercise tests, performed at 50% of the work rate attained at VT, under normoxic and hypoxic conditions (FiO2 12.5%). Metabolic and ventilatory measurements were made during tests and the changes between normoxic and hypoxic response during rest and exercise were analysed. A second smaller study examined cardiac output response during hypoxia and exercise using bioimpedance cardiography. These studies were performed simultaneously with the cardiopulmonary exercise tests and included 31 subjects. Similar analyses were performed on cardiac output variables between normoxia and hypoxia. The repeatability of the steady state cardiopulmonary exercise experimental protocol was verified by repeat testing and analyses. Bioimpedance cardiography measurements were validated against simultaneous measurements during pulmonary catheter studies and thermodilution cardiac output measurement. The results of the tests and the comparison of response demonstrated a larger increase in ventilation during exercise from normoxia to hypoxia in the insertion homozygous group. This was accompanied by a genotype dependent decrease in end-tidal carbon dioxide, suggesting a higher alveolar ventilation. There was no increase in oxygen saturations in the insertion homozygous group, which may have been due to the technical limitations of the oximeters. The cardiac output studies did not reveal any significant difference between genotype. The ventilatory study has demonstrated a response that may contribute to enhanced performance during prolonged hypoxic exposure, as experienced at high altitude.

With multimedia communication growing in popularity, it has become important to develop techniques that will allow a multimedia application to access multimedia files from local as well as remote sites. This thesis describes the methodology used in the design of the Network Multimedia File System (NMFS) protocol. The protocol provides “transparent access to shared files across networks” much like Sun’s Network File System (NFS) protocol. However, NMFS differs from NFS in that it provides a connection-oriented service that allows the user to specify quality of service (QOS) parameters and reserve resources to achieve the desired QOS. NMFS is an application layer protocol and is intended to work with existing multimedia applications, unaltered, on multiple platforms. NMFS will provide real-time delivery of multimedia data over networks both designed and not designed to carry multimedia traffic. A unique feature of this protocol is that it uses an anticipated delivery schedule (ADS) to guide prefetch of portions of files that are likely to be requested in the future. This prefetched data is stored in a local buffer which reduces the need to transfer the data over the variable latency network when the application actually requests it. Thus NMFS provides most unaltered application programs with almost constant latency accesses over a network with variable latency.