UC Berkeley

Earth’s topography is constantly evolving in response to surface processes that are modulated by changes in climate, tectonics, and sea level. Geochronology can used to identify the timing and rates of past Earth surface change and thereby advance our understanding of how these changes relate to different Earth processes that interplay over different geologic timescales. In this thesis, I contribute new geochronologic constraints on the extent to which Earth surface processes varied in the past and how that variation relates to past climate change. Chapter 1 describes the fundamentals of geochronology and provides an overview of the specific techniques used in this thesis. In Chapter 2, I present a quantitative framework for determining the timing and patterns of km-scale topographic change at the high-latitude Antarctic Peninsula using detrital apatite (U-Th)/He thermochronometry and 3D thermo-kinematic numerical modeling. While Plio-Pleistocene cooling accelerated glacial erosion rates at many mid-latitude glacial landscapes, my results reveal that Plio-Pleistocene cooling suppressed glacial erosion at the Antarctic Peninsula. These results highlight that landscapes at different latitudes had different responses to global cooling. In Chapter 3, I apply the approach developed in Chapter 2 to seven additional fjords along a latitudinal transect at the Antarctic Peninsula to investigate how the timing of km-scale topographic change relates to changes in climate and tectonics. At this site, the onset of km-scale topographic change occurs more than 15 million years after the initiation of glaciation and generally covaries with the arrival time of spreading ridge. These are among the first empirical results to show that a tectonic history, and its control on the regional topography of a landscape, has influenced glacial erosion rates over geologic timescales. In Chapter 4, I use the uranium-series comminution age technique to constrain sediment transport times to the Bengal Fan over the last 200 thousand years. I find pronounced variability in transport time that appears to be modulated by the climate and hydrological changes associated with the Late Pleistocene climate cycles. Because sediment transport times are more than 100 times smaller than the age of the Bengal Fan, Himalayan sediment transport keeps pace with erosion on million-year timescales. Each chapter demonstrates that the response of Earth surface processes to climate change depends on the geologic history of landscape. Thus, the past not only informs on the extent to which climate change can perturb Earth surface processes; the past influences how Earth surface processes will respond to future climate change.