The Arctic and North Atlantic underwent significant climactic changes since the Last Glacial Maximum (25,000 years before present (1950 AD); ka BP), but offsets in the timing of events between the two regions are poorly constrained due to age model uncertainties that arise from changing radiocarbon reservoir ages. Here, we use a relatively high-resolution, multi-proxy stable isotope and sedimentologic dataset from Eastern Fram Strait (ODP Leg 162 Site 986) marine sediments to constrain the timing of Svalbard/Barents Sea Ice Sheet decay and infer deglacial reservoir ages over the last 30 ka. We use magnetic susceptibility, inorganic and organic carbon, foraminiferal assemblage counts, planktonic foraminiferal isotopes, and iceberg-rafted debris proxies to infer glaciomarine and paleoclimactic processes in Eastern Fram Strait. Significant negative Neogloboquadrina pachyderma (sinistral) δ18O episodes from background levels at 18.8 ka (-3.0 /) and 20.4 ka (-0.8 /) (on a radiocarbon-based age model) are shown to indicate meltwater discharge events from the Svalbard/Barents Sea Ice Sheet during the early glacial termination (21-14.7 ka). To allow for direct comparison between the timing of Eastern Fram Strait meltwater events and North Atlantic climate changes, the ODP Site 986 age model is correlated to the well-dated Greenland Ice Sheet Project 2 (GISP2) ice core δ18O record. The refined age model suggests that 16.0 and 18.1 ka are more realistic estimates for the meltwater events, inferring surface ocean reservoir age shifts of 1750 ± 1050 years in Eastern Fram Strait during the early glacial termination. Trends in reservoir ages throughout the last deglaciation mirror Nordic Sea deep ocean circulation changes and previously reported trends in the sub-polar North Atlantic; however, reservoir ages appear to be greater in Eastern Fram Strait. We hypothesize that processes affecting the distribution of reservoir ages in the North Atlantic and Arctic (e.g. sea ice cover, meltwater input, and ocean circulation) may have resulted in larger reservoir ages in polar regimes than in sub-polar ones during the last deglaciation, analogous to contemporary distributions. In contrast to previous radiocarbon age model-based studies in the Nordic Seas that predict a significant meltwater event at ~19 ka, these findings show that rapid Svalbard/Barents Sea Ice Sheet decay began at 16 ka and suggest that uncertainty on the order of thousands of years may exist in previous paleoclimate studies with radiocarbon-based age models from the deglacial Nordic Seas and Arctic.

During the last deglaciation (ca. 24-10 ka thousand years ago (ka)), the North American Laurentide Ice Sheet (LIS) was a major source of meltwater to the Arctic Ocean, North Atlantic Ocean, and the Gulf of Mexico (GOM), and it is hypothesized that meltwater routing played an important role in regulating Late Quaternary millennial-scale climate variability, via its influence on Atlantic Meridional Overturning Circulation (AMOC). For example, the meltwater routing hypothesis predicts that a rerouting of meltwater from the GOM to the North Atlantic and/or Arctic Oceans resulted in a decrease of North Atlantic Deep Water (NADW) formation and subsequent cooling in the northern North Atlantic region, at the onset of the Younger Dryas (ca. 13 ka). The GOM was an important outlet for meltwater that likely originated from the southern margin of the LIS. Northern GOM sediments document episodic LIS meltwater input via the Mississippi River throughout the last deglaciation, and further study may provide insight to the evolution of LIS deglaciation and the hydrological response of meltwater flux to the marine depositional environment of GOM. Here, a multi-proxy geochemical study, based on marine sediments from Orca Basin, in northern GOM, aims to 1) reconstruct high-resolution records of deglacial (ca. 24-10 ka) LIS melting history to assess linkage between meltwater input to the GOM and deglacial climate change; 2) investigate the relationship between marine-based records of meltwater input and terrestrial evidence for continental deglaciation to reconstruct LIS drainage patterns within the Mississippi River watershed; and 3) reconstruct the redox state of Orca Basin sediments to evaluate the potential role of turbidity flows as a means of meltwater transport into the northern GOM. All data for this study is from core MD02-2550, a 9.09 m long giant box core, recovered from 2248 m water depth from the Orca Basin, approximately 300 km southwest of the modern Mississippi River delta. High sedimentation rates (45 cm/thousand years (kyr)) and 0.5 to 2 cm sampling resolution allow for sub-centennial sampling resolution. An anoxic hypersaline brine lake currently occupies the bottom 200 m of Orca Basin; yet, visible laminations and color changes that suggest episodic suboxic to anoxic sedimentary conditions during deglaciation, possibly related to LIS meltwater input and/or local biologic productivity. In chapter one, paired d18O and Mg/Ca-sea-surface temperature (SST) analyses on two varieties of the surface-dwelling planktic foraminifera Globigerinoides ruber (G. ruber; (white and pink, separately)) are used to reconstruct deglacial changes in GOM seawater d18O (d18Osw). Once corrected for global ice volume, the ice volume-corrected d18Osw (d18Oivc-sw) record is primarily influenced by LIS meltwater. d18Oivc-sw records document negative excursions at ca. 19-18.2, 17.5-16.2, 15.3-14.8, and 13.7-13 ka, interpreted as four LIS melting events, followed by the cessation of meltwater at the onset of the Younger Dryas (12.9 ka). Additionally, LIS melting at ca. 17.5 ka suggests that enhanced seasonality in the North Atlantic produced mild summers sufficient for ice sheet retreat during the Mystery Interval (17.5-14.5 ka) despite extremely cold winters. Because of the inherent difficulties in quantifying meltwater flux using d18Oivc-sw data, foraminiferal (G. ruber) Ba/Ca data are generated in chapter two to assess the influence of LIS meltwater on GOM salinity (a function of meltwater flux) during deglaciation. Ba concentrations in the Mississippi River are elevated relative to GOM seawater and are negatively correlated to sea-surface salinity. Because foraminiferal Ba/Ca (Ba/Caforam) exhibits a predictable relationship to the Ba/Ca of seawater (Ba/Casw), it may be used to calculate changes in salinity arising from deglacial variations in Mississippi River discharge. A complicating factor for Ba/Ca-based salinity interpretations is that Ba concentrations vary spatially throughout the Mississippi River watershed. For example, modern Missouri and Upper Mississippi River Ba concentrations (633 and 436 nM, respectively) are higher than that of the Ohio River (253 nM). Thus, GOM Ba/Ca variability could reflect changes in total Mississippi River input and/or shifts in the dominant region of LIS melting. Applying the modern spatial variability of Ba, we can gain insights into the pattern of ice retreat along the southern margin of the LIS during the last deglaciation. d18Oivc-sw and Ba/Ca results suggest that meltwater, originating from the Great Lakes region, entered the GOM at ca. 19.0 ka and may have contributed to global sea level rise. A melting event at ca. 17.5 ka coincided with Lake Erie Lobe retreat and may have preconditioned the North Atlantic for AMOC instability during the Mystery Interval (ca. 17.5-14.5 ka). Elevated GOM Ba/Ca (ca. 15.6 to 14.0 ka) suggests greater meltwater input from the Ba-rich Missouri and Upper Mississippi River watershed during the second half of the Mystery Interval (ca. 16.1-14.5 ka), when wet climate conditions prevailed in the southwestern United States and Central America. Overall, Ba/Ca and d18Oivc-sw data suggest large variations in the delivery of meltwater to the Mississippi River and GOM during the last deglaciation. In chapter three, a suite of redox sensitive trace metals (Mo, Re, U, Mn) from bulk sediment samples are analyzed to reconstruct the redox state of Orca Basin sediments, from the Last Glacial Maximum through the early Holocene (24-7 ka). Variations in the redox state of Orca Basin sediments during deglaciation may be due to changes in local biologic productivity, sediment transport, and/or regional/global physical oceanography. Laminated sediments enriched with authigenic Mo, Re, and U, suggest suboxic to anoxic conditions coincident with high total organic carbon fluxes and LIS meltwater input at ~17.0 ka. Low authigenic trace element concentrations, high quantities of terrigenous material, and abundant Cretaceous-age nannofossils in a 19-cm homogenous interval indicate a turbidite in Orca Basin at ca. 14.4 ka. This stratigraphic unit correlates with evidence from Pigmy Basin, and the Louisiana Shelf, suggesting increased meltwater flux may reflect LIS contribution to Meltwater pulse 1a (MWP-1a) sea level rise. Trace element records coupled with analyses of Orca Basin sedimentary structures will likely improve understanding of deglacial water column stratification, how meltwater entered the GOM (i.e. as a buoyant cap or at depth via sediment-laden hyperpycnal plumes), and the affects of glacial meltwater on marine biologic productivity.

Meltwater reaching the base of the snowpack may either infiltrate the underlying stratum, run off, or refreeze, forming a basal ice layer. Frozen ground underneath a melting snowpack constrains infiltration promoting runoff and refreezing. Compositional changes in chemistry take place for each of these flowpaths as a result of phase change, contact between meltwater and soil, and mixing between meltwater and soil water. Meltwater ion concentrations and infiltration rate into frozen soils both decline rapidly as snowmelt progresses. Their temporal association is highly non-linear and the covariance must be compensated for in order to use time-averaged values to calculate chemical infiltration over a melt event. This temporal covariance is termed �enhanced infiltration� and represents the additional ion load that infiltrates due to the timing of high meltwater ion concentration and infiltration rate. Both theoretical and experimental assessments of the impact of enhanced infiltration showed that it causes a greater ion load to infiltrate leading to relative dilute runoff water. Sensitivity analysis showed that the magnitude of enhanced infiltration is governed by initial snow water equivalent, average melt rate, and meltwater ion concentration factor. Based on alterations in water chemistry due to various effects, including enhanced infiltration, three major flowpaths could be distinguished: overland flow, organic interflow, and mineral interflow. Laboratory experiments were carried out in a temperature-controlled environment to identify compositional changes in water from these flowpaths. Samples of meltwater, runoff, and interflow were filtered and analyzed for major anions and cations. Chemical signatures for each flowpath were determined by normalizing runoff and interflow concentrations using meltwater concentrations. Results showed that changes in ion concentrations were most significant for H⁺, NO₃^�, NH₄⁺, Mg²⁺, and Ca²⁺. Repeated flushes of meltwater through each interflowpath caused a washout of ions. In the field, samples of soil water and ponding water were collected daily from a Rocky Mountain hillslope during snowmelt. Their normalized chemical compositions were compared to the laboratory-identified signatures to evaluate the flowpath. The majority of the flowpaths sampled had chemical signatures, which indicated mineral interflow, only 10% showed unmixed organic interflow.

Meltwater reaching the base of the snowpack may either infiltrate the underlying stratum, run off, or refreeze, forming a basal ice layer. Frozen ground underneath a melting snowpack constrains infiltration promoting runoff and refreezing. Compositional changes in chemistry take place for each of these flowpaths as a result of phase change, contact between meltwater and soil, and mixing between meltwater and soil water. Meltwater ion concentrations and infiltration rate into frozen soils both decline rapidly as snowmelt progresses. Their temporal association is highly non-linear and the covariance must be compensated for in order to use time-averaged values to calculate chemical infiltration over a melt event. This temporal covariance is termed �enhanced infiltration� and represents the additional ion load that infiltrates due to the timing of high meltwater ion concentration and infiltration rate. Both theoretical and experimental assessments of the impact of enhanced infiltration showed that it causes a greater ion load to infiltrate leading to relative dilute runoff water. Sensitivity analysis showed that the magnitude of enhanced infiltration is governed by initial snow water equivalent, average melt rate, and meltwater ion concentration factor. Based on alterations in water chemistry due to various effects, including enhanced infiltration, three major flowpaths could be distinguished: overland flow, organic interflow, and mineral interflow. Laboratory experiments were carried out in a temperature-controlled environment to identify compositional changes in water from these flowpaths. Samples of meltwater, runoff, and interflow were filtered and analyzed for major anions and cations. Chemical signatures for each flowpath were determined by normalizing runoff and interflow concentrations using meltwater concentrations. Results showed that changes in ion concentrations were most significant for H⁺, NO₃^�, NH₄⁺, Mg²⁺, and Ca²⁺. Repeated flushes of meltwater through each interflowpath caused a washout of ions. In the field, samples of soil water and ponding water were collected daily from a Rocky Mountain hillslope during snowmelt. Their normalized chemical compositions were compared to the laboratory-identified signatures to evaluate the flowpath. The majority of the flowpaths sampled had chemical signatures, which indicated mineral interflow, only 10% showed unmixed organic interflow.

Meltwater reaching the base of the snowpack may either infiltrate the underlying stratum, run off, or refreeze, forming a basal ice layer. Frozen ground underneath a melting snowpack constrains infiltration promoting runoff and refreezing. Compositional changes in chemistry take place for each of these flowpaths as a result of phase change, contact between meltwater and soil, and mixing between meltwater and soil water. Meltwater ion concentrations and infiltration rate into frozen soils both decline rapidly as snowmelt progresses. Their temporal association is highly non-linear and the covariance must be compensated for in order to use time-averaged values to calculate chemical infiltration over a melt event. This temporal covariance is termed �enhanced infiltration� and represents the additional ion load that infiltrates due to the timing of high meltwater ion concentration and infiltration rate. Both theoretical and experimental assessments of the impact of enhanced infiltration showed that it causes a greater ion load to infiltrate leading to relative dilute runoff water. Sensitivity analysis showed that the magnitude of enhanced infiltration is governed by initial snow water equivalent, average melt rate, and meltwater ion concentration factor. Based on alterations in water chemistry due to various effects, including enhanced infiltration, three major flowpaths could be distinguished: overland flow, organic interflow, and mineral interflow. Laboratory experiments were carried out in a temperature-controlled environment to identify compositional changes in water from these flowpaths. Samples of meltwater, runoff, and interflow were filtered and analyzed for major anions and cations. Chemical signatures for each flowpath were determined by normalizing runoff and interflow concentrations using meltwater concentrations. Results showed that changes in ion concentrations were most significant for H+, NO3�, NH4+, Mg2+, and Ca2+. Repeated flushes of meltwater through each interflowpath caused a washout of ions. In the field, samples of soil water and ponding water were collected daily from a Rocky Mountain hillslope during snowmelt. Their normalized chemical compositions were compared to the laboratory-identified signatures to evaluate the flowpath. The majority of the flowpaths sampled had chemical signatures, which indicated mineral interflow, only 10% showed unmixed organic interflow.

The purpose of this research is to gain understanding of the occurrence and origin of streamlined forms in central British Columbia. More than 50,000 landforms, primarily drumlins and crag-and-tail ridges, were digitally mapped over an area covering five 1:250,000 NTS map sheets. Visual Basic programs were written to statistically analyze the streamlined forms database and to simulate site-scale, two-dimensional glacial erosion. Results show three principal ice and/or meltwater flow directions: southeast flows probably originating in the Skeena Mountains, northeast flows from the Coast Mountains and Quanchas Range, and west flows originating east of the Babine and Telkwa Ranges. Rat-tails and striae occur up to 1680 m elevation and record uphill flow to the west in these ranges. Streamlined forms were investigated at outcrop scale (e.g. rat-tails), landform scale (e.g. drumlins) and landscape scale (as defined by closed contours). On bedrock outcrops, cross-cutting striae are common and they both parallel and cross-cut rat-tails. Small rat-tails occur on, and parallel to, larger rat-tails but they do not cross-cut, suggesting a different origin than striae. Rat-tails are interpreted as being formed by subglacial meltwater flows, an interpretation supported by the glacial erosion model. Lowland streamlined forms (e.g. drumlins and crag-and-tails) are interpreted as either glacially-formed ridges subsequently shaped by meltwater floods or as being formed entirely by meltwater floods. This interpretation is largely based on the common occurrence of interconnecting hairpin furrows around these streamlined forms and on the demonstrated association of hairpin furrows with fluvial erosion. The results of topographic analysis indicate that an interconnecting system of valleys separates uplands that can be objectively defined by single (closed) contours. The aspect ratios of the uplands are highly correlated (L/W = 2.38, R2 = 0.89) with values that are similar to those reported for braid bars and erosional residuals thought to have been formed by glacial outburst floods. This upland/lowland landform assemblage may, in places, represent streamlined erosional residuals within braided channel networks formed, at least in part, by subglacial or glacial outburst floods.

Thesis (Ph. D.)--Universität Zürich, 2007. / Added thesis t.p. Vita. Includes bibliographical references (p. 155-167).

Understanding how debris-covered glaciers respond to climate is necessary in order to evaluate future water resources and glacier flood hazard potential, and to make sense of the glacier chronology in mountain regions, In order achieve this, it is necessary to improve the current understanding of how surface debris affects glacier ablation rate, and to develop methods by which the ablation of debris-covered glaciers can be predicted under various climatic scenarios. This thesis develops a numerical surface energy balance model that uses simple meteorological data to calculate melt beneath a debris layer of given thickness and thermal characteristics. Field data from three contrasting sites demonstrate that the assumptions made within the model concerning the thermal properties of supraglacial debris are valid during most ablation conditions and that model performance is considerably better than previous models. Model results indicate that the effect of debris on melt rate is highly dependent on meteorological conditions. Under colder climates, thin debris can accelerate ice melt by extending the ablation period at both diurnal and seasonal scales. However, in milder mid- summer conditions, even a very thin debris cover inhibits melt rate compared to that of exposed ice. The new melt model is applied to produce the first quantified ablation gradients for debris- covered glaciers, and to model the evolution of ice surfaces under a debris layer of variable thickness. Modelled ablation gradients are qualitatively similar to hypothetical ones outlined previously, and quantitatively similar to those measured in the field. The ablation gradients are used to explore the factors affecting the response of debris-covered glaciers to climate change. Beneath a debris layer of variable thickness, the melt model produced ablation topography, as observed in the field, which underwent topographic inversion over time in response to debris redistribution. Debris thickness variability was found to cause calculated ablation rate to increase compared to that calculated using a mean debris thickness by one to two orders of magnitude, suggesting that melt calculations made on the basis of spatially averaged debris thickness may be inaccurate.

Mountain glaciers have influenced the surface of our planet throughout geologic time. These large reservoirs of water ice sculpt alpine landscapes, regulate downstream river flows, perturb climate-tectonic feedbacks, contribute to sea level change, and guide human migration and settlement patterns. Glaciers are especially relevant in modern times, acting as buffers which supply seasonal meltwater to densely populated downstream communities and support economies via hydropower generation. Anthropogenic warming is accelerating ice loss in most glacierized regions of the world. This has sparked concerns regarding water resources and natural hazards, and placed glaciers at the forefront of climate research. Here we provide new observations of glacier change in key mountain regions to quantify rates of ice loss, better understand climate drivers, and help establish a more unified framework for studying glacier change across timescales. In Chapter 1 we use seismic observations, numerical modeling, and geomorphic analysis to investigate a destructive glacial lake outburst flood (GLOF) which occurred in Bhutan. GLOFs are a substantial hazard for downstream communities in many vulnerable regions. Yet key aspects of GLOF dynamics remain difficult to quantify, as in situ measurements are scarce due to the unpredictability and remote source locations of these events. Here we apply cross-correlation based seismic analyses to track the evolution of the GLOF remotely (~100 km from the source region), use the seismic observations along with eyewitness reports and a downstream gauge station to constrain a numerical flood model, then assess geomorphic change and current state of the unstable lakes via satellite imagery. Coherent seismic energy is evident from 1 to 5 Hz beginning approximately 5 hours before the flood impacted Punakha village, which originated at the source lake and advanced down the valley during the GLOF duration. Our analysis highlights potential benefits of using real-time seismic monitoring to improve early warning systems. The next two chapters in this work focus on quantifying multi-decadal glacier ice loss in the Himalayas. Himalayan glaciers supply meltwater to densely populated catchments in South Asia, and regional observations of glacier change are needed to understand climate drivers and assess impacts on glacier-fed rivers. Here we utilize a set of digital elevation models derived from cold war–era spy satellite film and modern stereo satellite imagery to evaluate glacier responses to changing climate over the last four decades. In Chapter 2 we focus on the eastern Himalayas, centered on the Bhutan–China border. The wide range of glacier types allows for the first mass balance comparison between clean, debris, and lake-terminating (calving) glaciers in the area. Measured glaciers show significant ice loss, with statistically similar mass balance values for both clean-ice and debris-covered glacier groups. Chapter 3 extends the same methodology to quantify glacier change across the entire Himalayan range during 1975–2000 and 2000–2016. We observe consistent ice loss along the entire 2000-km transect for both intervals and find a doubling of the average loss rate during 2000–2016 compared to 1975–2000. The similar magnitude and acceleration of ice loss across the Himalayas suggests a regionally coherent climate forcing, consistent with atmospheric warming and associated energy fluxes as the dominant drivers of glacier change. Chapter 4 investigates millennial-scale glacier changes during the Late Glacial period (15-11 ka). Here we present a high-precision beryllium-10 chronology and geomorphic map from a sequence of well-preserved moraines in the Nendaz valley of the western European Alps, with the goal to shed light on the timing and magnitude of glacier responses during an interval of dramatic natural climate variability. Our chronology brackets a coherent glacier recession through the Younger Dryas stadial into the early Holocene, similar to glacier records from the southern hemisphere and a new chronology from Arctic Norway. These results highlight a general agreement between mountain glacier changes and atmospheric greenhouse gas records during the Late Glacial. In Chapter 5 we use a numerical glacier model to simulate glacier change across a typical alpine region in the European Alps. Model results suggest that shorter observational timespans focused on modern periods (when glaciers are far from equilibrium and undergoing rapid change) exhibit greater spatial variability of mean annual ice thickness changes, compared to intervals which extend further back in time (to include decades when climate was more stable). The model agrees with multi-decadal satellite observations of glacier change, and clarifies the positive correlation between glacier disequilibrium and spatial variability of glacier mass balance. This relationship should be taken into account in regional glacier studies, particularly when analyzing recent spatial patterns of ice loss. Advances made in this work are of practical value for societies vulnerable to glacier change. This includes potential improvements to GLOF early warning systems via seismic monitoring, better constraints on glacier-sourced water scenarios in South Asia, strengthened understanding of long-term glacier responses to baseline natural climate variability, and a clarified relationship between glacier disequilibrium and spatial variability of ice loss. When placed within a global context, our observations highlight the correlation between regional mountain glacier change and greenhouse gas forcing through time.

Thesis advisor: Mark D. Behn / Ice sheet flow is strongly controlled by the conditions at the ice-bed interface. While these processes are hard to observe directly, comparisons between numerical modeling and ice surface observations can be used to indirectly infer subglacial processes. Specifically, seasonal summer speed up near the margin of the Greenland Ice Sheet (GIS) has been linked to the presence of subglacial water. For decades, the Glen flow law has been the most widely-accepted constitutive relation for modeling ice flow. However, while the Glen law captures the temperature-dependent, nonlinear viscosity of ice, it does not explicitly incorporate ice grain size, which has been shown in laboratory experiments to influence ice rheology. To compensate for the lack of explicit grain size dependence, ice sheet models often utilize an “enhancement factor” that modifies the flow law to better match observations, but does not provide insight into the physical processes at play. Using a grain size sensitive rheology that incorporates grain size evolution due to dynamic recrystallization and grain growth, I model the effects of seasonal variations of subglacial hydrology in a 2-D vertical cross-section of ice flow on both annual and inter-annual timescales. The presence of subglacial water reduces the frictional coupling between the ice and the bed. Here I simulate the presence of water at the ice-bed interface during the melt season using patches of free-slip and explore a range of patch sizes and geometries to investigate their role in modulating ice surface velocities and grain size within the ice. I compare modeled winter and summer surface velocities to observations taken on the western margin of the GIS and find that realistic surface velocities are achievable using agrain size sensitive flow law without the introduction of an enhancement factor. Further, the grain size of the internal ice responds on an inter-annual timescale to these seasonal forcings at the bed, potentially leading to long-term changes in surface velocities. / Thesis (MS) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.