Ice flow produces morphological features at the bed and on the surface of ice sheets. These ‘flow signatures’ provide us with an insight into the mechanisms, history and characteristics of ice sheet flow. In this thesis I examine the characteristics of basal and surficial ice sheet flow signatures, as well as possible links between them. The first chapter introduces ice sheet flow signatures. At the bed, a suite of landforms known as subglacial bedforms are found. The surface of an ice sheet is home to longitudinal surface structures (LSSs) and transverse surface structures (TSSs). Whilst the two environments are mostly considered in isolation, links between the sets of flow signatures found at each have been suggested. Section A deals with basal flow signatures. Chapter 2 asks whether subglacial bedforms are patterned. Drumlins are found to be regularly placed within the landscape, and likely grow or shrink over time. Chapter 3 examines whether subglacial bedforms conform to a size and shape continuum. By collating and analysing a dataset of 96,900 measurements of size and shape it is found that 3 continua of subglacial bedforms exist: flutes, lineations and ribs. The latter two are joined by an understudied class of quasi-circular bedforms. Section B deals with surficial flow signatures. In Chapter 4 I present and analyse a map of the LSSs of the Antarctic Ice Sheet. The morphology, spatial distribution and glaciological context of LSSs leads to the proposal of a model for their formation. Chapter 5 presents the first systematic study of TSSs. Mapping and analysis reveals that TSSs are regularly spaced, differ little in their morphology between ice streams and are most likely stationary. Section C compares basal and surficial ice sheet flow signatures. In Chapter 6, morphological comparisons, a case study of the Rutford Ice Stream, analysis of ice penetrating radar and examination of ice flow modelling lead to the conclusion that the majority of basal and surficial flow signatures are separate entities. Chapter 7 concludes the thesis and provides suggestions for future research.

The last British Ice Sheet has been a focus of research for over a century, and yet we have only a generalised picture of its extent and internal geometry. This is a remarkable situation compared to knowledge of the larger former ice sheets of North America and Fennoscandia. The central tenet of this thesis is that the glacial landform record has been neglected as a source of spatial information, hindering our attempts to reconstruct the characteristics of the ice sheet. This motivated systematic mapping of glacial landforms (subglacial bedforms, moraines, eskers, and meltwater channels) for the whole of Britain, yielding the first consistent and countrywide glacial maps. Mapping was achieved primarily using a high resolution (5 m horizontal) digital elevation model to visualise the landscape. Over 60,000 features were identified and mapped, greatly expanding the known distribution and pattern of glacial landforms. Analysis of the landform data permitted a country-wide reconstruction of the pattern of ice sheet retreat. A database of just over 400 dates, compiled from the literature, was used to arrange the pattern of retreat in time. This exercise highlighted various incompatibilities between the presently available dates. Examination of landform patterns enabled the elucidation of some pre-deglacial configurations of ice divides and flow geometry, including ice streams. This revealed the existence of both transient (migrating) and persistent ice divides. In contrast to other and larger palaeo-ice sheets, the majority of flow evidence in Britain exhibits a particularly close association with topography, indicative of an ice sheet thickness comparable with the amplitude of subglacial relief. The retreat pattern, flow geometries and divide configurations that have been identified from this research provide a set of evidence-based constraints at ice sheet scale for future numerical ice sheet modelling experiments.

New Zealand fills a large geographic gap in the global glacial record, with landforms and near-surface deposits preserving a remarkable footprint of Quaternary glaciation. As one of the few land masses in the Southern Hemisphere, the record of glacial geomorphology is of great importance for research into the natural behaviour of the Earth’s climate system. This thesis presents a 3D simulation of the New Zealand Southern Alps glaciers at the Last Glacial Maximum (LGM, c. 30 to 18 ka) in an attempt to constrain glacial geometry of that period. To achieve this, the REVOLTA (Reconstruction of Volume and Topography Automation) model was developed, a Python script tool for ArcGISTM that requires just a DEM of glacier bed conditions and the down-valley extent of glaciation as initial inputs. Ice thickness is initially estimated at points along an automatically generated centreline network based on the perfect-plasticity rheology assumption, taking into account a valley side drag component of the force balance equation. Distributed ice thickness is subsequently interpolated using a glaciologically correct algorithm. Results indicate a total LGM ice volume of 6771.9 km3, in good correspondence of previous studies using a climate-driven ice dynamics approach. Combined with an estimate of contemporary ice volume (50.67 km3), this result reinforces the notion that New Zealand has lost almost the entirety (99.25 %) of its glacial ice since the LGM, although this volume has contributed to just 17.02 mm of global sea level rise. Analysis of the LGM distributed ice thickness output shows a large number of nunataks and exposed ridges in the central Mt. Cook and northern regions, with a localised icefield in the Fiordland area. LGM Equilibrium Line Altitudes (ELAs) automatically calculated using the Accumulation Area Ratio (AAR) method reveals an average lowering of 1074 m from present, with those to the west of main divide 461m lower than those to the east on average. LGM climatic conditions were estimated using the ELAs and scaled versions of contemporary temperature and precipitation distributions, suggesting a temperature reduction of between 5.6°C to 10.3°C and precipitation change of +4.3 % to +100.4% from present. When considering these new estimates in conjunction with critically evaluated previous evidence, an average LGM cooling of 6.5 °C to 8°C is proposed, a refinement on the wide range of previously published values. Importantly, there is large spatial variability between catchments, with eastern regions experiencing significantly greater cooling and greater precipitation increases (or less decrease) than their western counterparts. Increased westerly circulation and reduced sea level altering the relative position of the orographic barrier is a suggested potential mechanism for the predicted precipitation pattern changes, whilst increased southerly flow bringing cool air up the east coast is a possible cause of the temperature change differential predicted. The proportion of precipitation falling as snow or rain was also found to be an important factor when considering New Zealand LGM conditions, with up to 50% estimated to be falling as rain at the LGM ELA, with a strong east-west differential. Input dataset generation for REVOLTA resulted in several important research outcomes. A DEM approximating LGM bed conditions was created, using a variety of novel techniques to modify the existing DEM. These included the estimation of contemporary ice thickness distribution using the VOLTA (Volume and Topography Automation) model for removal from the DEM, merging offshore and lake bathymetry and considering Holocene in-fill sediments. Furthermore, an in-depth review of the most up to date literature and datasets regarding the lateral extent of LGM glaciation was also carried out, generating an updated ‘outline’ of LGM glaciation.

No description available.

The Late Devonian and Mississippian record the transition from Greenhouse into a cooler global climate punctuated by glaciations. Evidence for glaciation in the latest Devonian is primarily derived from diamictites deposits in South America. The event was broadly coincident with eustatic changes and mass extinction associated with the Hangenberg Crisis. To understand the record of glaciation in more detail a stratigraphic, palynostratigraphic and chemostratigraphic field-study has been undertaken near Lake Titicaca, Bolivia. Three primary sections were measured; Chaguaya, Villa Molino and CR5. These record a 1.1 km thick Devonian-Carboniferous (D/C) boundary interval. Glacigenic strata are represented by the Cumaná Formation, dated to within the lepidophyta-nitidus (LN) miospore zone. Additional sections were measured along a strike-parallel topographic ridgeline, which revealed that the Cumaná Formation consists of a single, preserved advance of glacigenic strata into a marine shelfal environment. It is associated with incised palaeo-relief, which is >7 km in length and 110 m deep. The D/C boundary in the study area is defined on the loss of Retispora lepidophyta and a collapse in marine phytoplankton diversity during initial post-glacial transgression. Hence, palynological extinctions represent a proxy for the D/C boundary in South America that is tied to wider palaeoclimatic and glacioeustatic changes. A 2 ‰ positive carbon isotope excursion is associated with palynological extinctions at the D/C boundary. Palynofacies were unable to quantify the marine vs. terrestrial ratio of preserved organic matter as amorphous organic matter was preferentially lost during standard palynological processing techniques. However the excursion is likely related to a reduction in the supply of terrestrial and marine organic matter at a time of environmental stress. These combined results provide a high-palaeolatitude glacial perspective on debates regarding mass-extinction, eustatic and environmental change around the D/C boundary. The glacigenic Cumaná Formation is interpreted to represent the glacioeustatic control sea-level falls observed globally at the D/C boundary.

Sea level is an excellent proxy for past climate change as it represents the combined impact of changing temperatures and ice volumes through time. Reconstructing a record of global ice volume change is complex as the growth and loss of high volume ice sheets results in a spatially varying pattern of sea-level change. This is known as glacial isostatic adjustment (GIA) and means that all past sea-level indicators are effectively relative sea level (RSL) indicators. Each indicator is relative to a particular position on the Earth’s crust and requires a GIA correction to reconstruct global mean sea level (GMSL). Generating a GIA correction requires an appropriate ice volume and distribution history. As no field-constrained global ice history exists beyond the last glacial maximum we create five different global ice-loading histories to investigate a range of potential ice volume and dispersal scenarios through the last interglacial. Within this thesis we develop a methodology for inclusion of coral taxon depth-habitat relationships in the uncertainties associated with fossil coral reconstructed relative sea levels. We test our ice histories against the coral dataset, and find the best matches to the coral dataset come from ice histories that contain a longer interglacial and / or reduced ice volume through the interglacial than is currently found in many continuous records of sea level. We model the GIA response of the Hanish and Camarinal Sills, and Rosh Hanikra on the Israeli coast to determine how two continuous RSL curves, for the Red Sea and Gibraltar respectively, and the temporally discrete RSL indicators relate to GMSL. Our analysis reveals sensitivities that may be used to constrain the evolution of a past Eurasian ice sheet.

The Loch Lomond Stadial (LLS) refers to the abrupt return to severe cold conditions that occurred in Britain, between 12.9 and 11.7 ka, subsequent to the retreat of the last (Late Devensian) British-Irish Ice Sheet. This period has long been associated with the regrowth of glaciers in upland areas of Britain and left a wealth of geomorphological evidence in the landform record. However, previous research on these glaciers has largely comprised localised case studies, producing a fragmented and spatially inconsistent dataset. This thesis draws together the published geomorphological evidence for Loch Lomond Stadial glaciation to build a coherent picture of the extent, style and dynamics of glaciation during the stadial. Geomorphological mapping of glacial landforms associated with this period is compiled from the published literature to create a map and geographic information systems database of over 95,000 features. The evidence used to produce this map is critically assessed in the most comprehensive review of the Loch Lomond Stadial to date and is used to identify conceptual themes, common to the geomorphology in multiple sub-regions within Scotland, England and Wales. Persisting uncertainties, particularly regarding the extent and timing of Loch Lomond Stadial glaciation, are discussed and recommendations of future research to address these are made. Building on this review, the glacial geomorphological map is then used to construct five glacial landsystem models which reflect the style of Loch Lomond Stadial glaciation; the cirque/niche glacier landsystem, the alpine icefield landsystem, the lowland piedmont lobe landsystem, the plateau icefield landsystem and the ice cap landsystem. Use of these models to classify the Loch Lomond Stadial glacial geomorphology reveals the spatial distribution of each landsystem. Three styles of glacier retreat are represented by the glacial geomorphology. It is demonstrated that both landsystem and retreat style reflect the combined importance of pre-existing topography and palaeoclimate. Given the paucity of dating constraints on Loch Lomond Stadial landforms, the thesis pilots the use of a relative dating technique using soil chronosequences to differentiate between Loch Lomond Stadial and older moraines in the English Lake District. The results of this study highlight the potential of this technique to discriminate between Loch Lomond Stadial and pre-Loch Lomond Stadial moraines in Britain, although further work is required.

This thesis explores continental weathering patterns in glacial and non-glacial river catchments in Iceland and Greenland. Specific attention is placed on characterizing the relative iron (oxyhydr)oxide export rates of glacial and non-glacial catchments to the ocean. Total element concentration and iron stable isotope measurements indicate that chemical weathering differences do exist between glacial and non-glacial catchments. The differences appear primarily related to variations in soil formation and organic matter availability between the environments. Physical, rather than chemical, differences between glacial and non-glacial catchments however dominate the relative differences in (oxyhyr)oxide export rates. Glacial and non-glacial river sediments from otherwise analogous terrains contain about the same quantity of iron (oxyhyr)oxide on a weight normalized basis. This equates to glacial rivers exporting far more iron (oxyhyr)oxides on a discharge weighted basis, because glacial rivers contain far higher suspended sediment concentrations that non-glacial rivers. Existing research shows that organic carbon accumulation and burial in marine environments scale directly with iron (oxyhydr)oxide accumulation. This means that shifts in continental weathering over glacial-interglacial cycles drive further changes in marine carbon burial creating a global climate feedback loop.

The seismic stratigraphy and sedimentary architecture of the Canadian Beaufort Sea margin are investigated using a comprehensive grid of two-dimensional seismic reflection data. Three cross-shelf troughs, representing locations of former ice streams draining a 1000 km-long section of the Laurentide Ice Sheet (LIS), are examined: the Mackenzie, Amundsen Gulf and M'Clure Strait systems. These palaeo-ice streams operated during the last, Late Wisconsinan glacial maximum, as well as during a hitherto unknown number of earlier Quaternary glaciations. Their dynamics influenced past ice-sheet configuration and may have forced abrupt climate change through transport of ice and freshwater to the Arctic Ocean. The objectives of this work are to constrain the number of ice advances through each trough, to discuss the possible timing of these events, and to examine the impact of Quaternary glaciation on the continental shelf and slope. The implications of these data are discussed in relation to ice dynamics at the northwest LIS limit, the glacial history of the Canadian Beaufort Sea margin, and the geomorphological imprint of palaeo-ice streams. The number of Quaternary ice advances across the Canadian Beaufort Sea margin varies markedly between the Mackenzie Trough (two) and the Amundsen Gulf Trough (at least nine). The Mackenzie Trough was probably occupied by an ice stream during the Late Wisconsinan and either the Illinoian or Early Wisconsinan glaciation. The Amundsen Gulf ice stream was initiated earlier in the Quaternary. The architecture of the slope beyond the Mackenzie Trough reflects this comparatively short history of ice advance and lacks the progradational architecture and major glacialsedimentary depocentre that is characteristic of slopes seaward of high-latitude cross-shelf troughs. In contrast, trough-mouth fans ( of volumes -10,000 km.3 and -60,000 km3) are present beyond Amundsen Gulf and M'Clure Strait, respectively. The location of 75 High Arctic cross-shelf troughs is presented together with a synthesis of their key physiographic characteristics and available glacial-geological evidence of past occupation by ice streams. The dimensions and architecture of the three troughs on the Canadian Beaufort Sea margin are compared to those of other High Arctic troughs. The Amundsen Gulf and M'Clure Strait troughs were probably two of the most significant cross shelf troughs in the High Arctic, in terms of their dimensions and palaeo-drainage basin areas. A number of buried glacigenic landforms, including grounding-zone wedges and lateral moraines, are identified from the Canadian Beaufort Sea shelf, recording the former positions of still-stands or re-advances in the ice margin. The youngest sequence of sediment in the Amundsen Gulf Trough is interpreted to have been deposited by a subsidiary ice stream, the Anderson ice stream, subsequent to Late Wisconsinan ice retreat through the Amundsen Gulf. This provides evidence of dynamic ice-stream behaviour and the reorganisation of the north west sector of the LIS during the last de glaciation.

During the mid- to late Neogene (20 - 2.5 million years ago), episodic retreat of the Antarctic Ice Sheet (AIS) coincided with periods of higher-than-present atmospheric CO2, indicating ice sheet sensitivity to climatic conditions similar to those projected for the coming decades. Understanding Antarctic climate and vegetation during such a period of AIS retreat is crucial for our fundamental understanding of high latitude environments in warmer-than-present climate scenarios. This thesis presents a detailed geochemical study of sediments and plant fossils from the terrestrial Sirius Group of Oliver Bluffs, Transantarctic Mountains, located at 85 °S today and during the Neogene. Biomarker analysis of the sediments show strong evidence for a warmer Antarctica, where summer temperatures reached 5 °C. These relatively favourable conditions sup- ported a low diversity mixed vegetation. In contrast to the macrofossil record, there is geochemical evidence for conifers, suggesting that Antarctic vegetation was strongly controlled by local environmental variability. The warmer conditions are associated with a dynamic carbon cycle, evidenced by anomalously high and variable atmospheric 13C and possibly linked to atmospheric CO2 levels. Precipitation isotopes are reconstructed from plant compound isotope analysis of the fossils, and indicate markedly different hydrological cycling. This result is supported by climate modelling experiments which suggest that Antarctic hydrological cycling is most strongly governed by the extent of the ice sheet rather than by greenhouse gas radiative forcing. This thesis presents a new approach to exploring Antarctic climate and vegetation and provides important novel information on this crucial region of the world.