Modern Pine Island and Thwaites Glaciers, which both drain into Pine Island Bay, are some of the fastest moving portions of the cryosphere and may be the most unstable ice streams in Antarctica. I examined over 133 cores to conduct a detailed sedimentological facies analysis. These data, augmented by new radiocarbon and 210Pb dates, and bathymetric data, are used to reconstruct the post-LGM deglacial history of PIB and gain a better understanding of the causes of ice sheet retreat. My results record a clear retreat stratigraphy in PIB composed of, from top to base; terrigenous sandy silt (plumite), pebbly sandy mud (ice-proximal glacimarine), and till. Initial retreat from the outer-continental shelf began shortly after the LGM and before 16.4 k cal yr BP, in response to rising sea level. Bedforms in outer PIB document episodic retreat in the form of back-stepping grounding zone wedges and are associated with proximal glacimarine sediments. A sub-ice shelf facies is observed in central PIB that spans ∼12.3–10.6 k cal yr BP. Widespread impingement of warm water onto the continental shelf caused an abrupt change from sub-ice shelf sedimentation to distal glacimarine sedimentation dominated by dispersal of terrigenous silt between 7.8 and 7.0 k cal yr BP. The uppermost sediments in Pine Island Bay were hydrodynamically sorted by meltwater plumes. Inner Pine Island Bay contains several large basins that are linked by channels. The most recent release of sediment coincides with rapid retreat of the grounding line, and has an order of magnitude greater flux relative to the entire unit, indicating episodic sedimentation. This is the first identification of a meltwater-derived deposit in Antarctica and demonstrates that punctuated meltwater-intensive glacial retreat occurred at least three times throughout the Holocene in this region. Quartz sand grains were used to conduct an analysis of mode of transport for sediments in the Antarctic Peninsula region from the Eocene to present to record the onset of glaciation. Glacial transport imparts a unique suite of microtextures on quartz grains from high shear-stresses. Eocene samples are free of glacial influence. Late Eocene samples show the inception of glacially derived high-stress microtextures, marking the onset of alpine glaciation. Oligocene grains are similar to the late Eocene samples. Middle Miocene microtextures are characteristic of transport from far-field large ice sheets, originating from ice rafting from the West Antarctic Ice Sheet. The Pliocene and Pleistocene samples indicate the existence of the northern Antarctic Peninsula Ice Sheet at this time, consistent with other proxies.

Declines in glacier area and volume are widespread. These changes will have important hydrologic consequences since glaciers store tremendous amounts of fresh water and buffer seasonally low flows in many densely populated regions. In this thesis I focus on a region that is hydrologically vulnerable to glacier change, namely the Cordillera Blanca, Peru. I present three manuscripts that focus on measuring glacier area change, modeling the effect of this area change on the hydrology of one watershed, and isotopic sampling to elucidate hydrologic processes in this watershed and the entire Cordillera Blanca. In the first manuscript, I describe a methodology for mapping glaciers using satellite imagery. Satellite data, in conjunction with automated glacier mapping methods, are being used more frequently to map changes in glacier size. In contrast to the majority of studies using automated methods, I correct satellite images for atmospheric effects. Mapping glaciers with atmospherically-corrected satellite images resulted in an approximately 5% increase in glacier area, relative to glaciers mapped with non-atmospherically-corrected images. I also applied a consistent threshold that was validated using high-resolution satellite imagery. This helps to reduce error associated with change analysis. For the entire Cordillera Blanca, I calculated a 25% decrease in glacier area from 1987 to 2010. The rate of glacier area loss has increased significantly based on the most recent estimates. In the second manuscript, I use a physically-based, hydrologic model, the Distributed Hydrology Soil Vegetation Model (DHSVM) with a newly-coupled dynamic glacier model to simulate stream discharge and glacier change in the Llanganuco watershed of the Cordillera Blanca. I also examined statistical trends associated with historical records of temperature, precipitation, and discharge. I observed significant positive trends in annual temperature, but no trends in precipitation or discharge despite a 25% reduction in glacier area in this watershed over the same time. The model setup process and the results of sensitivity analyses are described. Of the input parameters I examined, I found that the model was particularly sensitive to changes in albedo and precipitation. Based on established efficiency criteria, the newly-coupled model did a decent job of simulating historical stream discharge and glacier area during 10 year calibration and validation periods. However, due to the lack of additional validation data and an inability to quantify uncertainty associated with model output, the model is not yet ready to be used for predicting future discharge based on different climate projections. In the third manuscript I describe the knowledge gained about hydrologic processes from isotopic sampling in the Llanganuco watershed, as well as other watersheds of the Cordillera Blanca. Thirty water samples from Llanganuco were collected in July 2011 and measured for stable isotopes of water, δ¹⁸O and δ²H. I first calculated the isotopic lapse rate, or the relationship between isotopic values and elevation. Lapse rates from this watershed are slightly more positive than global averages. This observation is best explained by the influence of glaciers. I also calculated the strength of the relationship between isotopic values and percent glacier cover. For Llanganuco, glacier cover is a better predictor of isotopic value than elevation. Based on examination of the same relationships at larger scales in the Cordillera Blanca, this relationship appears to be persistent at a regional scale. Finally, I used a simple two-component mixing model to estimate the relative contributions of glacier meltwater and groundwater in the Llanganuco watershed. Glacier meltwater made up approximately three-fourths of surface water that exited the watershed during this two week period in July, 2011. The importance of glacier meltwater is clearly demonstrated using stable isotopes, but further, more detailed monthly sampling is necessary to accurately determine annual and dry season streamflow contributions from glacier meltwater and groundwater. / Graduation date: 2013

No description available.

The increased temperatures in the Arctic accelerate the loss of land based ice stored in glaciers. The Greenland Ice Sheet is the largest ice mass in the Northern Hemisphere and holds ~10% of all the freshwater on Earth, equivalent to ~7 metres of global sea level rise. A few decades ago, the mass balance of the Greenland Ice Sheet was poorly known and assumed to have little impact on global sea level rise. The development of regional climate models and remote sensing of the ice sheet during the past decade have revealed a significant mass loss. To monitor how the Greenland Ice Sheet will affect sea levels in the future requires understanding the physical processes that govern its mass balance and movement. In the southeastern and central western regions, mass loss is dominated by the dynamic behaviour of ice streams calving into the ocean. Changes in surface mass balance dominate mass loss from the Greenland Ice Sheet in the central northern, southwestern and northeastern regions. Little is known about what the hydrological system looks like beneath the ice sheet; how well the hydrological system is developed decides the water’s impact on ice movement. In this thesis, I have focused on radar sounding measurements to map the subglacial topography in detail for a land-terminating section of the western Greenland Ice Sheet. This knowledge is a critical prerequisite for any subglacial hydrological modelling. Using the high-resolution ice thickness and bed topography data, I have made the following specific studies: First, I have analysed the geological setting and glaciological history of the region by comparing proglacial and subglacial spectral roughness. Second, I have analysed the subglacial water drainage routing and revealed a potential for subglacial water piracy between adjacent subglacial water catchments with changes in the subglacial water pressure regime. Finally, I have looked in more detail into englacial features that are commonly observed in radar sounding data from western Greenland. In all, the thesis highlights the need not only for accurate high-resolution subglacial digital elevation models, but also for regionally optimised interpolation when conducting detailed hydrological studies of the Greenland Ice Sheet. / De ökade temperaturerna i Arktis påskyndar förlusten av landbaserad is lagrad i glaciärer och permafrost. Grönlands inlandsis är den största ismassan på norra halvklotet och lagrar ca 10% av allt sötvatten på jorden, vilket motsvarar ca 7 meter global havsnivåhöjning. För ett par decennier sedan var inlandsisens massbalans dåligt känd och antogs ha liten inverkan på dagens havsnivåhöjning. Utvecklingen av regionala klimatmodeller och satellitbaserad fjärranalys av inlandsisen har under de senaste decenniet påvisat en betydande massförlust. För att förutse vilken inverkan inlandsisen har på framtida havsnivåhöjningar krävs en förståelse för de fysikaliska processerna som styr dess massbalans och isrörelse. I de sydöstra och centrala västra delarna av inlandsisen domineras massförlusten av dynamiska processer i isströmmar som kalvar ut i havet. Massförlusten i de centrala norra, sydvästra och nordöstra delarna domineras av isytans massbalans. Ytterst lite är känt om hur det hydrologiska systemet ser ut under inlandsisen; hur väl det hydrologiska systemet är utvecklat avgör vattnets påverkan på isrörelsen. I denna doktorsavhandling har jag använt markbaserade radarmätningar för att kartlägga den subglaciala topografin för en del av den västra landbaserade inlandsisen. Denna kunskap är en viktig förutsättning för att kunna modellera den subglaciala hydrologin. Med hjälp av rumsligt högupplöst data över istjockleken och bottentopografin har jag gjort följande specifika studier: Först har jag analyserat de geologiska och glaciologiska förhållandena i regionen genom att jämföra proglacial och subglacial spektralanalys av terrängens ytojämnheter. Sedan har jag analyserat den subglaciala vattenavrinningen och påvisat en potential för att avrinningsområdena kan ändras beroende på vattentryckförhållandena på botten. Slutligen har jag tittat mer i detalj på englaciala radarstrukturer som ofta observerats i radardata från västra Grönland. Sammanfattningsvis belyser avhandlingen behovet av inte bara noggranna rumsligt högupplösta subglaciala digitala höjdmodeller, utan även regionalt optimerad interpolering när detaljerade hydrologiska studier ska utföras på Grönlands inlandsis.

No Abstract Provided / Thesis / Bachelor of Arts (BA)