Samuel Kelley

Supplemental material, Supplementary_PDF_for_HOL for Assessing ice margin fluctuations on differing timescales: Chronological constraints from Sermeq Kujatdleq and Nordenskiöld Gletscher, central West Greenland by Samuel E Kelley, Jason P Briner and Sandy L O'Hara in The Holocene

Understanding of the pre-development, baseline denudation rates that deliver sediment to the Great Barrier Reef (GBR) has been elusive. Cosmogenic 10Be in sediment is a useful integrator of denudation rates and sediment yields averaged over large spatial and temporal scales. This study presents 10Be data from 71 sites across 11 catchments draining to the GBR: representing 80% of the GBR catchment area and provide background sediment yields for the region. Modern, short-term, sediment yields derived from suspended load concentrations are compared to the 10Be data to calculate an Accelerated Erosion Factor (AEF) that highlights denudation "hot-spots" where sediment yields have increased over the long-term background values. The AEF results show that 58% basins have higher modern sediment yields than long-term yields. The AEF is considered a useful approach to help prioritise on-ground investments in remediation and the additional measured empirical data in this paper will help support future predictive models.

Abstract The duration and intensity of the early Holocene freshening events has been explained by subglacial outburst(s) from Lake Agassiz, the collapse of a Laurentide Ice Sheet ‘saddle’ overlying Hudson Bay, and/or a combination of the two events. Our field evidence provides new radiocarbon ages and geomorphologic observations to assess the deglacial history of this important region, allowing for revision of the sequence of events. We show that the collapse of the Hudson Bay Ice Saddle in southwestern Hudson Bay occurred between 8.57 ± 0.28 ka BP and 8.11 ± 0.19 ka BP. This event was preceded by at least one subglacial-drainage event through numerous newly-mapped subglacial channels onshore of southwestern Hudson Bay. Lake Agassiz may have experienced multiple subglacial drainage events prior to the final HBIS collapse, accounting for the timing discrepancies in freshwater cooling observed in the North Atlantic. Importantly, this new work links the chronology of events on the southwest (land-based) side of the HBIS to the northeast (marine-based) side of the ice sheet. Additionally, this work provides a potential analog for the behaviour of other ice sheets whose beds lie well below sea level, such as the West Antarctic Ice Sheet, during periods of warming climate.

The observational record of ice margin position reveals asynchrony in both the timing and magnitude of Greenland Ice Sheet (GrIS) margin fluctuations and illustrates the complex reactions of ice sheets to climatic perturbations. In this study, we reconstruct the timing and pattern of middle- and late-Holocene GrIS margin fluctuations at two locations, ~190 km apart, in central West Greenland using radiocarbon-dated sediment cores from proglacial-threshold lakes. Our results demonstrate that deglaciation occurs at both sites during the early Holocene, with the ice sheet remaining in a smaller-than-present ice margin configuration until ~500 years ago when it readvanced into lake catchments at both sites. At our northern site, Sermeq Kujatdleq, the late-Holocene advance of the GrIS approached maximum position during the past 280 years, with the culmination of the advance occurring at AD 1992–1994, and modern retreat was underway by AD 1998–2001. In contrast, field and observational ev...

Abstract Reconstructions of past ice-flow provide useful insights into the long-term behaviour of past ice sheets and help to understand how glaciated landscapes are shaped. Here, we present reconstruction of a 10-phase ice-flow history from southwestern Hudson Bay in northeastern Manitoba (Canada), a dynamic region situated between two major ice dispersal centres of the Laurentide Ice Sheet. We utilize a diverse geologic dataset including 1900 field-based erosional indicators, 12 streamlined-landform flowsets, esker and meltwater corridor orientations, 103 till-fabrics analyses, and 1344 till-clast lithology counts. Our reconstruction suggests that both pre-MIS 2 and MIS 2 glaciations followed similar growth patterns, where ice advanced into study area from ice centered to the east (probably in northern Quebec), followed by a switch in ice-flow direction indicating flow from the Keewatin ice centre to the northwest and north. The cause for this switch in ice-flow orientation is uncertain, but the youngest switch may relate to retreat of ice during MIS 3 that then left space for Keewatin-sourced ice to advance over the study area. While modelling experiments indicate widespread cold-based conditions in the study area during the last glacial cycle, uniformly relict landscapes are not common. Instead, the glaciated landscape is palimpsest and commonly fragmented, forming a subglacial bed mosaic of erosional and depositional assemblages that record both shifting ice-flow direction through time and shifting subglacial conditions. Each assemblage formed, or modified, during times of dynamic (warm-based) ice, and later preserved under conditions below or close to the pressure melting point (slow and sluggish, or cold-based).

Abstract Tracing indicator minerals and geochemical pathfinders in glacial sediments back to their up-ice source is a common mineral exploration approach in prospective, formerly glaciated regions. In this study, we utilize surface and subsurface data from the Lac de Gras area of the Northwest Territories to develop a three-dimensional understanding of till compositional anomalies emanating from two known kimberlite pipes, DO-18 and DO-27. Specifically, this study examines the three-dimensional shape of dispersal trains as defined by geochemical pathfinder elements and kimberlite indicator minerals shed from a pair of kimberlite pipes within a till cover of variable thickness. From our ninety-four reverse circulation boreholes (n = 251 till samples), and other publicly-available geologic datasets, we have reconstructed bedrock topography, till thickness, and the subsurface geometry of two dispersal trains. Utilizing our three-dimensional dataset, we have documented the role of basal topography in creating dispersal patterns with contrasting geometries from two adjacent kimberlites, as well as in the preferential preservation of older till units. The combination of field observations of ice-flow indicators and till compositional data demonstrates that features produced by multiple ice flows are preserved in both the erosional and depositional records in this region. Three-dimensional dispersion patterns of kimberlite indicators reflect the effect of shifting ice-flow direction with respect to slope aspect of bedrock topography in governing compositional variability within glacial drift. Our findings suggest that surficial data do not capture the full extent of dispersion patterns even in areas of relatively thin and discontinuous till cover.

The impact of the Laurentide Ice Sheet (LIS) deglaciation on Northern Hemisphere early Holocene climate can be evaluated only once a detailed chronology of ice history and sea-level change is established. Foxe Peninsula is ideally situated on the northern boundary of Hudson Strait, and preserves a chronostratigraphy that provides important glaciological insights regarding changes in ice-sheet position and relative sea level before and after the 8.2 ka cooling event. We utilized a combination of radiocarbon ages, adjusted with a new locally derived ΔR, and terrestrial in-situ cosmogenic nuclide (TCN) exposure ages to develop a chronology for early-Holocene events in the northern Hudson Strait. A marine limit at 192 m a.s.l., dated at 8.1–7.9 cal. ka BP, provides the timing of deglaciation following the 8.2 ka event, confirming that ice persisted at least north of Hudson Bay until then. A moraine complex and esker morphosequence, the Foxe Moraine, relates to glaciomarine outwash deltas and beaches at 160 m a.s.l., and is tightly dated at 7.6 cal. ka BP with a combination of shell dates and exposure ages on boulders. The final rapid collapse of Foxe Peninsula ice occurred by 7.1–6.9 cal. ka BP (radiocarbon dates and TCN depth profile age on an outwash delta), which supports the hypothesis that LIS melting contributed to the contemporaneous global sea-level rise known as the Catastrophic Rise Event 3 (CRE-3).

... step down in the marine limit at AvaInlet,MarkhamBay,to60mto72m,orabouthalfofthat measured40kmfartherseaward.Thissuggeststhatanywest-ward extension of ... GeoscienceProject study area was included in a glacialland-forms map produced by Kleman and Jansson (1996). ...

ABSTRACT The termination of the last ice age featured a major reconfiguration of Earth's climate and cryosphere, yet the underlying causes of these massive changes continue to be debated. Documenting the spatial and temporal variations of atmospheric temperature during deglaciation can help discriminate among potential drivers. Here, we present a 10Be surface-exposure chronology and glaciological reconstruction of ice recession following the Last Glacial Maximum (LGM) in the Rakaia valley, Southern Alps of New Zealand. Innermost LGM moraines at Big Ben have an age of 17,840 ± 240 yrs, whereas ice-marginal moraines or ice-molded bedrock surfaces at distances up-valley from Big Ben of 12.5 km (Lake Coleridge), ˜25 km (Castle Hill), ˜28 km (Double Hill), ˜43 km (Prospect Hill), and ˜58 km (Reischek knob) have ages of 17,020 ± 70 yrs, 17,100 ± 110 yrs, 16,960 ± 370 yrs, 16,250 ± 340 yrs, and 15,660 ± 160 yrs, respectively. These results indicate extensive recession of the Rakaia glacier, which we attribute primarily to the effects of climatic warming. In conjunction with geomorphological maps and a glaciological reconstruction for the Rakaia valley, we use our chronology to infer timing and magnitude of past atmospheric temperature changes. Compared to an overall temperature rise of ˜4.65 °C between the end of the LGM and the start of the Holocene, the glacier recession between ˜17,840 and ˜15,660 yrs ago is attributable to a net temperature increase of ˜4.0 °C (from ‑6.25 to ‑2.25 °C), accounting for ˜86% of the overall warming. Approximately 3.75 °C (˜70%) of the warming occurred between ˜17,840 and ˜16,250 yrs ago, with a further 0.75 °C (˜16%) increase between ˜16,250 and ˜15,660 yrs ago. A sustained southward shift of the Subtropical Front (STF) south of Australia between ˜17,800 and ˜16,000 yrs ago coincides with the warming over the Rakaia valley, and suggests a close link between Southern Ocean frontal boundary positions and southern mid-latitude climate. Most of the deglacial warming in the Southern Alps occurred during the early part of Heinrich Stadial 1 (HS1) of the North Atlantic region. Because the STF is associated with the position of the westerly wind belt, our findings support the concept that a southward shift of Earth's wind belts accompanied the early part of HS1 cooling in the North Atlantic, leading to warming and deglaciation in southern middle latitudes.

Determining the areal extent and the cause of climate fluctuations during the late Quaternary remains a major issue in quaternary geology. This is especially well elucidated in the Southern Hemisphere, where terrestrial records are rare outside of the high latitudes. The South Island of New Zealand is noteworthy, because of the well-preserved moraine sequences located there. This provides records of