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The Laurentide Ice Sheet (LIS) was the largest ice sheet during the last glacial period. An accurate representation of its behavior during the last deglaciation is critical to understanding its influence on and response to a changing climate. We use 10Be dating and Bayesian modeling to track the recession of the southwest sector of the Labrador Dome of the LIS along an ~500-km-long transect west of Lake Superior during the last deglaciation. This transect reflects terrestrial ice-margin retreat and crosses multiple moraine sets, with the southwestern part of the transect deglaciated by ca. 19 ka and the northeastern part deglaciated by ca. 10 ka. The predominant behavior of the ice margin during this interval is near-constant retreat with retreat rates varying between ~59 m/a and 38 m/a. The moraine sets mark standstills and/or readvances that in total constitute only ~17% of the retreat interval. The spatial and temporal pattern of ice-margin retreat tracked here differs from existing reconstructions that are based on using isochrons to define ice-margin positions. Acknowledging the uncertainties associated with the modeled ages of ice-margin retreat, we suggest that the overall retreat pattern is consistent with forcing by a gradual increase in Northern Hemisphere, high-latitude summer insolation. The pattern of ice-margin retreat is inconsistent with Greenland ice-core temperature records, and thus these records may not be suitable to drive models of the LIS. [ABSTRACT FROM AUTHOR]

A key challenge facing the mental health field is connecting children and families to services when symptoms first appear. Multiple barriers inhibit timely access to treatment, and interventions to resolve barriers to care are not common among health and social care organisations. To address this research‐to‐practice gap this study undertook a scoping review of the empirical literature aimed at identifying key factors in the social ecology of families which influence family engagement with child and adolescent mental health services, then identifying and describing models of intervention designed to help facilitate access to care. Forty studies published between 1 January 2000 and 28 February 2019 were reviewed. Key factors associated with child and adolescent mental health service engagement included family attitudes towards mental illness and help seeking, the flexibility and availability of needed services, community attitudes and stigma surrounding mental illness and mental health treatment, and the degree of coordination and integration across systems of health and social care. Models of intervention to facilitate engagement with mental health services included family outreach, telephone and digital health strategies, and integrated care approaches. Empirical support is strongest for family outreach and integrated care, although telephone and digital health strategies are underexplored with children and families and a potentially promising avenue for future research. To support family engagement with child and adolescent mental health services health and social care organisations should be prepared to identify barriers in their local practice settings and integrate efficacious engagement approaches into their continuum of available services. [ABSTRACT FROM AUTHOR]

The article explores that atmospheric greenhouse gas concentrations are thought to have synchronized global temperatures during Pleistocene glacial–interglacial cycles, and their impact relative to changes in high-latitude insolation and ice-sheet extent. It mentions the use of tropical glacial fluctuations to assess the timing of low-latitude temperature changes relative to global climate forcings. It informs how tropical warming was influenced by rising high-latitude insolation.

Background: There are no FDA-approved pharmacotherapies for cannabis use disorders (CUD), despite the evaluation of numerous medications. Notably, chronic dosing of oral naltrexone decreases self-administration of cannabis in human laboratory studies.Objectives: To test the feasibility of long-acting injectable naltrexone for the treatment of CUD, while obtaining preliminary safety and efficacy data.Methods: Twelve adult participants (seven male) meeting DSM-IV-TR criteria for cannabis dependence enrolled into an 8-week, open-label pilot study conducted at an academic treatment research clinic. They received 380 mg intramuscular injections of long-acting naltrexone on study day 1 and at the start of study week 5. Outcome measures included percentages of study completers and participants who received the second injection, frequency of adverse events (AEs), and cannabis consumption measured by average daily grams, dollars, and using days per week as measured by timeline follow-back and urine oral delta-9-tetrahydrocannabinol (THC) concentrations.Results: Of the 12 participants enrolled in the study, 9 completed the study and 6 received the second injection. There were no severe AEs but an unexpected AE led to the addition of supportive medications to the protocol. Number of cannabis use days per week significantly decreased over the course of the study (p = .001). Creatinine-corrected urine THC concentrations and average daily cannabis use per study week in grams and in dollars did not decrease over the course of the study.Conclusions: Long-acting injectable naltrexone is a feasible intervention for CUD worthy of further study in a placebo-controlled, double-blinded randomized clinical trial. [ABSTRACT FROM AUTHOR]

The Nipigon channels, located to the west and northwest of Lake Nipigon, Ontario, are thought to have enabled the eastward drainage of meltwater from glacial Lake Agassiz during the last deglaciation. Here we present the first direct ages of flood deposits in two of these channels using 10Be surface exposure dating. Five 10Be ages of a coarse-grained deposit near the Roaring River in the Kaiashk channel complex indicate deglaciation and cessation of water flow by ∼11 070 ± 430 years. To test for inherited nuclides in boulder samples, we also measured the 10Be concentrations of the undersides of two boulders at the Roaring River site. Five 10Be ages of boulders atop a large bedform near Mundell Lake in the Pillar channel complex indicate deglaciation and cessation of water flow by ∼10 770 ± 240 years. Two 10Be ages of nearby bedrock are slightly younger (10 340 ± 260 and 9860 ± 270 years). The 10Be ages from the two sites are statistically indistinguishable and indicate that Laurentide Ice Sheet recession occurred rapidly in the region. We used clast diameters and channel dimensions at the Mundell Lake site to estimate paleodischarge and evaluate the possibility that meltwater drainage influenced climate conditions. We estimate a large maximum discharge of 119 000-159 000 m3·s−1 at the site. However, the timing of meltwater discharge at both Roaring River and Mundell Lake is not contemporaneous with abrupt climate events. [ABSTRACT FROM AUTHOR]

Background and aims Cannabis-dependent participants with depressive disorder are less likely to achieve abstinence with venlafaxine-XR (VEN-XR) treatment. Individuals on VEN-XR reported more severe withdrawal, despite not reducing their smoking behavior. We hypothesized that withdrawal-like symptoms, likely medication side effects, led to continued marijuana smoking in this group. Methods We conducted a secondary analysis using Marijuana Withdrawal Checklist (MWC) scores and urine THC to test whether severity of withdrawal-like symptoms mediates the relationship between VEN-XR treatment and continued marijuana smoking. We included 103 participants (VEN-XR = 51, Placebo = 52). Marijuana use was dichotomized into smoking (THC > 100 ng/ml) and non-smoking (THC ≤ 100 ng/ml) weeks. MWC scores were obtained weekly. We used three models in a regression based mediation analysis. Results The estimated risk of smoking marijuana was greater for individuals on VEN-XR in weeks 7–9, even when controlling for MWC scores (week 7 Risk Difference (RD) = 0.11, p = 0.034; week 8 RD = 0.20, p = 0.014), and higher scores mediated this effect. In weeks 10 and 11, the estimated effect was stronger (week 10 RD = 0.03, p = 0.380; week 11 RD = 0.07, p = 0.504), and worse withdrawal-like symptoms more fully accounted for continued marijuana smoking in the VEN-XR group, according to the models. Conclusions Individuals treated with VEN-XR had more severe withdrawal-like symptoms, which mediated their continued marijuana smoking. Noradrenergic agents, such as VEN-XR, may negatively impact treatment outcomes in cannabis-dependent patients attempting to reduce or stop their use. [ABSTRACT FROM AUTHOR]

Glaciers on the world's highest tropical mountains are among the most sensitive components of the cryosphere, yet the climatic controls that influence their fluctuations are not fully understood. Here we present the first 10Be ages of glacial moraines in Africa and use these to assess the climatic conditions that influenced past tropical glacial extents. We applied 10Be surface exposure dating to determine the ages of quartz-rich boulders atop moraines in the Rwenzori Mountains (~1°N, 30°E), located on the border of Uganda and the Democratic Republic of Congo. The 10Be ages document expanded glaciers ca. 23.4 and 20.1 ka, indicating that glaciers in equatorial East Africa advanced during the global Last Glacial Maximum (ca. 26-19.5 ka). A comparison of these moraine ages with regional paleoclimate records indicates that Rwenzori glaciers expanded contemporaneously with dry and cold conditions. Recession from the moraines occurred after ca. 20.1 ka, similar in timing to a rise in air temperature documented in East African lake records. Our results suggest that, on millennial time scales, past fluctuations of Rwenzori glaciers were strongly influenced by air temperature. [ABSTRACT FROM AUTHOR]

Abstract: The Greenland Ice Sheet is a major component of the Arctic cryosphere and the magnitude of its response to future climate changes remains uncertain. Longer-term records of climate near the ice sheet margin provide information about natural climate variability and can be used to understand the causes of past changes in the Greenland Ice Sheet. As a proxy for Holocene climate near the ice sheet margin, we reconstruct the fluctuations of Bregne ice cap in the Scoresby Sund region of central east Greenland. Bregne is a small ice cap (2.5 km2 in area) and responds sensitively to summer temperatures. We employ a multi-proxy approach to reconstruct the ice cap fluctuations using geomorphic mapping, 10Be ages of boulders and bedrock and lake sediment records. Past extents of Bregne ice cap are marked by moraines and registered by sediments in downvalley lakes. 10Be ages of bedrock and boulders outboard of the moraines indicate that Bregne ice cap was within ∼250 m of its present-day limit by at least 10.7 ka. Multi-proxy data from sediments in Two Move lake, located downvalley from Bregne ice cap, indicate that the ice cap likely completely disappeared during early and middle Holocene time. Increasing magnetic susceptibility and percent clastic material from ∼6.5 to ∼1.9 cal ka BP in Two Move lake sediments suggest progressively colder conditions and increased snow accumulation on the highlands west of the lake. Laminated silt deposited at ∼2.6 cal ka BP and ∼1.9 cal ka BP to present registers the onset and persistence of Bregne ice cap during the late Holocene. 10Be ages of boulders on an unweathered, unvegetated moraine in the Bregne ice cap forefield range from 0.74 to 9.60 ka. The youngest 10Be age (0.74 ka) likely represents the age of the moraine whereas older ages may be due to 10Be inherited from prior periods of exposure. This late Holocene moraine marks the second largest advance of the ice cap since deglaciation of the region at the end of the last ice age. The oldest moraine in the forefield dates to ≤2.6 cal ka BP. The fluctuations of Bregne ice cap were likely influenced by Northern Hemisphere summer insolation throughout the Holocene and abrupt late Holocene cold events. [Copyright &y& Elsevier]

The temporal and spatial patterns of late Holocene climate conditions provide valuable information for testing hypothesized mechanisms of recent climate changes. As a proxy for late Holocene climate in the southern tropics, we present a 10Be chronology of moraines deposited by Qori Kalis, an outlet glacier of Quelccaya Ice Cap in Peru. The Qori Kalis moraines are located downflow from the Quelccaya ice cores and provide the first glacial extent record that can be compared directly to annually resolved tropical ice core records. Qori Kalis advanced to its late Holocene maximum extent prior to 520 ± 60 yr before CE 2009, when Quelccaya ice core net accumulation values were at or below their late Holocene average. Subsequent glacial retreat between ~520 and 330 yr before CE 2009 coincides with the highest net accumulation values of the ~1800-yr-long ice core record. Therefore, we suggest that temperature, rather than net accumulation, was the primary driver of these glacial fluctuations. Comparison of the late Holocene fluctuations of Qori Kalis glacier with glaciers in the southern tropical Andes, Patagonian Andes, Switzerland, Alaska and New Zealand suggests globally synchronous, centennial-scale cold events. [ABSTRACT FROM AUTHOR]

The last glacial-interglacial transition (ca. 18--11 ka) was interrupted by abrupt climate events that differed in each hemisphere. During the Antarctic Cold Reversal (ca. 14.5--12.9 ka), the Southern Hemisphere high and mid latitudes cooled, while the Northern Hemisphere warmed. The pattern of change then reversed during the Younger Dryas (ca. 12.9--11.7 ka), which was characterized by cold conditions in much of the Northern Hemisphere. Well-dated paleoclimate records serve to reveal the possible mechanisms for these events. Here we present a reconstruction of the late glacial fl uctuations of Quelccaya Ice Cap, located in the southern tropics, based on 38 new radiocarbon ages. Quelccaya was retreating from its Last Glacial Maximum (ca. 21 ka) extent by ca. 17.2 ka, and was located upvalley from its late glacial moraines by 13.6--12.8 ka. Quelccaya experienced a signifi cant readvance that culminated at 12.5--12.4 ka, and then receded several kilometers to near, or within, its late Holocene extent by ca. 11.6 ka. This record provides the most detailed evidence yet of glacier fl uctuations in the southern tropics during late glacial time. [ABSTRACT FROM AUTHOR]

Abstract: Although Greenland ice core records register relatively stable Holocene climate conditions, the lower elevation margins of the Greenland Ice Sheet (GrIS) experienced significant Holocene fluctuations. These fluctuations include ice sheet recession during the Holocene Thermal Maximum (9–5 ka) and advance during the Little Ice Age (LIA; ∼A.D. 1350–1880). Determining the extent and timing of these fluctuations is important for understanding the response of the GrIS to interglacial climate conditions both warmer and colder than at present and for developing accurate ice sheet models. Sets of moraines marking past extents of the southwestern GrIS margin occur in the Kangerlussuaq region. We focus on the Ørkendalen moraines, a prominent moraine set located within 2 km of the modern ice margin and just outboard of the LIA moraines. We present the first 10Be ages of the Ørkendalen moraines indicating they were deposited at 6.8 ± 0.3 ka. The geomorphic relationship between the Ørkendalen and LIA moraines indicates that the ice sheet margin was inboard of its Ørkendalen extent between ∼6.8 ka and the culmination of the LIA. The age of the Ørkendalen moraines provides an important constraint on the extent of the southwestern GrIS during the middle Holocene. [Copyright &y& Elsevier]

Abstract: Objective: Numerous studies have implicated the hippocampus and prefrontal cortex in schizophrenia. However, precisely which subregions of the hippocampus and prefrontal cortex are abnormal remain unknown. Our study goal was to investigate the structure of the anterior hippocampus, posterior hippocampus, dorsolateral prefrontal cortex (DLPFC), and orbitofrontal cortex (OFC) simultaneously in thirty-eight patients with schizophrenia and twenty-nine controls to determine which of these subregions are abnormal in schizophrenia. As an exploratory study goal, we investigated the relation of neurocognition to brain structure in schizophrenia patients. Method: We generated detailed structural magnetic resonance imaging data and compared hippocampal and prefrontal subregional structural brain volumes between schizophrenia and control groups. We obtained a neurocognitive test battery in schizophrenia patients and studied the association of abnormal brain structures to neurocognition. Results: Structural brain abnormalities were pinpointed to the left anterior hippocampus and left OFC in schizophrenia patients, which were both significantly reduced in volume. The DLPFC and posterior hippocampus, though numerically decreased in volume, were not significantly decreased. Anterior hippocampal volumes were more strongly associated with OFC volumes in schizophrenia patients compared to controls. By contrast, DLPFC volume was unrelated to anterior or posterior hippocampal volume. Both the anterior hippocampus and OFC were independently related to cognitive abnormalities common in schizophrenia, including indices of verbal, language, and executive functions. The DLPFC and posterior hippocampal volumes were unrelated to cognitive measures. Conclusions: These findings highlight related abnormalities of the anterior hippocampus and OFC in schizophrenia, which may shed light on the pathophysiology of the disorder. [Copyright &y& Elsevier]

Abstract: This paper is the first to summarize research on fluctuations of local glaciers in Greenland (e.g. ice caps and mountain glaciers independent of the Greenland Ice Sheet) during latest Pleistocene and Holocene time. In contrast to the extensive data available for fluctuations of the Greenland Ice Sheet, surprisingly little data exist to constrain local glacier extents. Much of the available research was conducted prior to wide-spread use of AMS radiocarbon dating and the advent of surface-exposure and luminescence dating. Although there is a paucity of data, generally similar patterns of local glacier fluctuations are observed in all regions of Greenland and likely reflect changes in paleoclimate, which must have influenced at least the margins of the Inland Ice. Absolute-age data for late-glacial and early Holocene advances of local glaciers are reported from only two locations: Disko (island) and the Scoresby Sund region. Subsequent to late-glacial or early Holocene time, most local glaciers were smaller than at present or may have disappeared completely during the Holocene Thermal Maximum. In general, local glacier advances that occurred during Historical time (1200–1940 AD) are the most extensive since late-glacial or early Holocene time. Historical documents and more recent aerial photographs provide useful information about local glacier fluctuations during the last ∼100 yrs. In all but one area (North Greenland), local glaciers are currently receding from Historical extents. [Copyright &y& Elsevier]

Abstract: Introduction: Numerous studies point to an association between childhood trauma and the later development of psychotic illness. However, little is known about the prevalence of childhood trauma and its relationship to attenuated positive and other symptoms in individuals at heightened clinical risk for psychosis. Method: Thirty clinical high-risk patients (83% male, 43% Caucasian, and with a mean age of 19) were ascertained from the New York metropolitan area and evaluated for prodromal and affective symptoms, and queried regarding experiences of childhood trauma and abuse. Results: Ninety-seven percent endorsed at least one general trauma experience, 83% reported physical abuse, 67% emotional abuse, and 27% sexual abuse. As hypothesized, total trauma exposure was positively associated with severity of attenuated positive symptoms (in particular grandiosity), an effect primarily accounted for by ethnic minority participants, who reported greater exposure to trauma. Trauma exposure was related to affective symptoms only in the Caucasian subgroup. Conclusions: Childhood trauma was commonly self-reported, especially among clinical high-risk patients from ethnic minorities, for whom trauma was related to positive symptoms. Future areas of research include an evaluation of potential mechanisms for this relationship, including neuroendocrine and subcortical dopaminergic function. [Copyright &y& Elsevier]

Abstract: Thirty-eight new cosmogenic (10Be) exposure ages from the Scoresby Sund region of east Greenland indicate that prominent moraine sets deposited by mountain glaciers date from 780 to 310yr, approximately during the Little Ice Age, from 11 660 to 10 630yr, at the end of the Younger Dryas cold interval or during Preboreal time, and from 13 010 to 11 630yr, during lateglacial time. Equilibrium line altitudes (ELAs) interpreted from lateglacial to Early Holocene moraines indicate summertime cooling between ∼3.9 and 6.6°C relative to today''s value, much less than the extreme Younger Dryas cooling registered by Greenland ice cores (mean-annual temperatures of ∼15°C colder than today''s value). This apparent discrepancy between paleotemperature records supports the contention that Younger Dryas cooling was primarily a wintertime phenomenon. 10Be ages of lateglacial and Holocene moraines show that mountain glaciers during the Little Ice Age were more extensive than at any other time since the Early Holocene Epoch. In addition, 10Be ages of lateglacial moraines show extensive reworking of boulders with cosmogenic nuclides inherited from prior periods of exposure, consistent with our geomorphic observations and cosmogenic-exposure dating studies in other Arctic regions. [Copyright &y& Elsevier]

Surface exposure dating, using in situ produced cosmogenic 10Be, is applied to determine the time since deglaciation of bedrock surfaces in the Grimsel Pass region. Nine 10Be dates from bedrock surfaces corrected for cover by snow are minimum ages for deglaciation of the pass. Four 10Be dates from surfaces below 2500 meters above sea level (m a.s.l.) on Nägelisgrätli, east of Grimsel Pass, yield ages that range from about 14 000 to 11 300 years. Three 10Be dates from locations above 2600 m a.s.l. on Nägelisgrätli are between about 11 700 and 10 400 years. Two 10Be dates from locations at 2560 m a.s.l. below Juchlistock are about 12 100 and 11 000 years. The geographical distribution of 10Be dates on Nägelisgrätli either may show the timing of progressive deglaciation of Grimsel Pass or may reflect differences in subglacial erosion of bedrock in the pass region. All dates are discussed in the context of deglaciation of the late Würmian Alpine ice cap and deglaciation from Last Glacial Maximum (LGM) ice extents in other regions. [ABSTRACT FROM AUTHOR]

Focuses on the late Cenozoic stability of the East Antarctic Ice Sheet in southern Victoria Land, Antarctica. Sedimentology of Victoria drift; Distribution of radiocarbon dates; Composition of the Victorian drift.

Introduction: Frailty is conventionally diagnosed using clinical tests and self-reported assessments. However, digital health technologies (DHTs), such as wearable accelerometers, can capture physical activity and gait during daily life, enabling more objective assessments. In this study, we assess the feasibility of deploying DHTs in community-dwelling older individuals, and investigate the relationship between digital measurements of physical activity and gait in naturalistic environments and participants' frailty status, as measured by conventional assessments. Methods: Fried Frailty Score (FFS) was used to classify fifty healthy individuals as non-frail (FFS = 0, n/female = 21/11, mean ± SD age: 71.10 ± 3.59 years), pre-frail (FFS = 1–2, n/female = 23/9, age: 73.74 ± 5.52 years), or frail (FFS = 3+, n/female = 6/6, age: 70.70 ± 6.53 years). Participants wore wrist-worn and lumbar-worn GENEActiv accelerometers (Activinsights Ltd., Kimbolton, UK) during three in-laboratory visits, and at-home for 2 weeks, to measure physical activity and gait. After this period, they completed a comfort and usability questionnaire. Compliant days at-home were defined as follows: those with ≥18 h of wear time, for the wrist-worn accelerometer, and those with ≥1 detected walking bout, for the lumbar-worn accelerometer. For each at-home measurement, a group analysis was performed using a linear regression model followed by ANOVA, to investigate the effect of frailty on physical activity and gait. Correlation between at-home digital measurements and conventional in-laboratory assessments was also investigated. Results: Participants were highly compliant in wearing the accelerometers, as 94% indicated willingness to wear the wrist device, and 66% the lumbar device, for at least 1 week. Time spent in sedentary activity and time spent in moderate activity as measured from the wrist device, as well as average gait speed and its 95th percentile from the lumbar device were significantly different between frailty groups. Moderate correlations between digital measurements and self-reported physical activity were found. Conclusions: This work highlights the feasibility of deploying DHTs in studies involving older individuals. The potential of digital measurements in distinguishing frailty phenotypes, while unobtrusively collecting unbiased data, thus minimizing participants' travels to sites, will be further assessed in a follow-up study. [ABSTRACT FROM AUTHOR]

Warming following the Last Glacial Maximum was interrupted by abrupt, millennial-scale climate reversals. Registered in high-latitude proxy records, these reversals were apparently anti-phased between hemispheres. Although the signals of these late-glacial (~15-11 ka) climate events are found far beyond the poles, the thermal footprint of these events around the globe remains enigmatic. This is particularly true in low-latitude regions, where terrestrial temperature records are relatively rare. Here we present a beryllium-10 chronology of glacier fluctuations from the equatorial Rwenzori Mountains, Uganda, which elucidates the timing and magnitude of deglacial warming in tropical Africa during late-glacial time. In the Bujuku valley, a suite of moraines that mark the maximum late-glacial ice extent in the valley date to ~15-14 ka. Up valley from these deposits, a lateral moraine dated to ~11.8 ka marks the last preserved late-glacial ice margin. In the Nyamugasani valley, beryllium-10 ages suggest a similar pattern of glacier fluctuations. Expanded glacier conditions are marked by perched boulders on bedrock dated to ~14 ka. After ~12 ka, glacier retreat was punctuated by stillstands or readvances until ~11.2 ka. In both the Bujuku and Nyamugasani valleys, ice apparently retreated rapidly during the earliest Holocene. Overall, the chronology indicates that glaciers in the Rwenzori were more extensive during the southern hemisphere Antarctic Cold Reversal (ACR; ~14.7-13.0 ka) than during the northern hemisphere Younger Dryas (YD; ~12.9-11.7 ka), yet the moraine sequence does not necessarily align with the timing of either late-glacial event. The Rwenzori data are similar to chronologies reported from the South American tropics, where expanded glaciers during the ACR are recognized across the region. This similarity suggests that glaciers across the tropics responded to a common forcing during late-glacial time, most likely temperature. Potential mechanisms to induce such change include radiative greenhouse-gas forcing and tropical ocean dynamics. [ABSTRACT FROM AUTHOR]

The article looks into the chronology and mechanisms of Younger Dryas cold event and related climate change events. In the report by Robert P. Ackert Jr. and colleagues entitled "Patagonian Glacier Response during the Late Glacial-Holocene Transition," published within the issue, Ackert et al suggest that Younger Dryas advanced during the early Holocene as a result of changes in southern westerly wind circulation. To determine the chronology of Younger Dryas events, radiocarbon or surface-exposure dating of past glacial extents is used. However, results may differ using these approaches which might be because both may yield accurate ages of different stratigraphic levels or offsets may result from uncertainties associated with dating techniques.

Much of Greenland experienced summers warmer than present in parts of the early to middle Holocene, during a precession-driven positive anomaly in summer insolation. However, the magnitude of that warmth remains poorly known, and its timing and spatial pattern are uncertain. Here we describe the first quantitative Holocene palaeotemperature reconstruction from central East Greenland based upon insect (chironomid) assemblages preserved in lake sediments. We postulate that landscapes like our study site, characterized by minimal soil and vegetation development through the Holocene and thus little influenced by some important secondary gradients, are especially well suited to the use of chironomids to reconstruct Holocene temperatures. The inferred timing of warmth at our study site near Scoresby Sund agrees well with other nearby evidence, including glacial geological reconstructions and temperatures inferred from precipitation isotopes at Renland ice cap, supporting the use of chironomids to reconstruct temperatures at this site. We infer highest temperatures from c. 10 to 5.5 ka, followed by gradual cooling after 5.5 ka and progressively colder and less productive conditions after 3.5 ka. Models based upon two independent training sets yield similar inferred temperature trends, and suggest an average summer temperature anomaly from c. 10 to 5.5 ka of 3 to 4 °C relative to the preindustrial last millennium. The estimated overall rate of Neoglacial cooling averaged over the period from 5.5 to 0.5 ka was 0.6 to 0.8 °C per thousand years, more than twice the rate previously estimated for the Arctic as a whole. Given strong apparent spatial variability in Holocene climate around the Arctic, and the utility of palaeoclimate data for improving climate and ice-sheet models, it should be a priority to further quantify past temperature changes around the margins of the Greenland Ice Sheet, where few quantitative reconstructions exist and future warming will affect global sea level. [ABSTRACT FROM AUTHOR]

Deciphering the climate changes that influenced the glacial fluctuations of the last millennium requires documenting the spatial and temporal patterns of these glacial events. Here, we estimate the change in equilibrium line altitudes (ELAs) between the most prominent glacial advance of the last millennium and the present for four alpine glaciers located in different climatic regimes along the Andes. For each glacier, we reconstruct scenarios of climatic conditions (temperature and precipitation anomalies) that accommodate the observed ELA changes. We focus on the following glaciers: an alpine glacier in the Cordillera Vilcanota (13°S), Tapado glacier (30°S), Cipreses glacier (34°S), and Tranquilo glacier (47°S). Our results show that the range of possible temperature and precipitation anomalies that accommodate the observed ELA changes overlap significantly at three of the four sites (i.e. Vilcanota, Cipreses, and Tranquilo). Only Tapado glacier exhibits a set of climate anomalies that differs from the other three sites. Assuming no change in precipitation, the estimated ELA changes require a cooling of at least 0.7°C in the Cordillera Vilcanota, 1.0°C at Tapado glacier, 0.6°C at Cipreses glacier, and 0.7°C at Tranquilo glacier. Conversely, assuming no change in temperature, the estimated ELA changes are explained by increases in precipitation exceeding 0.52 m yr-1 (64% of the annual precipitation) in the Cordillera Vilcanota, 0.3 1 m yr-1 (89%) at Tapado glacier, 0.22 m yr-1 (27%) at Cipreses glacier, and 0.3 m yr-1 (27%) at Tranquilo glacier. By mapping the ELA changes and modeling the potential climate forcing across diverse climate settings, we aim to contribute toward documenting the spatial variability of climate conditions during the last millennium, a key step to decipher the mechanisms underlying the glacial fluctuation that occurred during this period. [ABSTRACT FROM AUTHOR]

Both modern anthropogenic emissions of mercury (Hg), primarily from artisanal and small-scale gold mining (ASGM), and preindustrial anthropogenic emissions from mining are thought to have a large impact on present-day atmospheric Hg deposition. We study the spatial distribution of Hg and its depositional history over the past ∼400 years in sediment cores from lakes located regionally proximal (∼90-150 km) to the largest ASGM in Peru and distal (>400 km) to major preindustrial mining centers. Total Hg concentrations in surface sediments from fourteen takes are typical of remote regions (10-115 ng g-1). Hg fluxes in cores from four lakes demonstrate preindustrial Hg deposition in southeastern Peru was spatially variable and at least an order of magnitude lower than previously reported fluxes in lakes located closer to mining centers. Average modern (A.D. 2000-2011) Hg fluxes in these cores are 3.4-6.9 μg m-2 a-1, compared to average preindustrial (A.D. 1800-1850) fluxes of 0.8-2.5 μg m-2 a-1. Modern Hg fluxes determined from the four lakes are on average 3.3 (±1.5) times greater than their preindustrial fluxes, similar to those determined in other remote lakes around the world. This agreement suggests that Hg emissions from ASGM are likely not significantly deposited in nearby down-wind regions. [ABSTRACT FROM AUTHOR]

Abstract: The Greenland Ice Sheet is undergoing dynamic changes that will have global implications if they continue into the future. In this regard, an understanding of how the ice sheet responded to past climate changes affords a baseline for anticipating future behavior. Small, independent ice caps adjacent to the Greenland Ice Sheet (hereinafter called “local ice caps”) are sensitive indicators of the response of Greenland ice-marginal zones to climate change. Therefore, we reconstructed late Holocene ice-marginal fluctuations of the local Istorvet ice cap in east Greenland, using radiocarbon dates of subfossil plants, 10Be dates of surface boulders, and analyses of sediment cores from both threshold and control lakes. During the last termination, the Istorvet ice cap had retreated close to its maximum Holocene position by ∼11,730 cal yr BP. Radiocarbon dates of subfossil plants exposed by recent recession of the ice margin indicate that the Istorvet cap was smaller than at present from AD 200 to AD 1025. Sediments from a threshold lake show no glacial input until the ice cap advanced to within 365 m of its Holocene maximum position by ∼AD 1150. Thereafter the ice cap remained at or close to this position until at least AD 1660. The timing of this, the most extensive of the Holocene, expansion is similar to that recorded at some glaciers in the Alps and in southern Alaska. However, in contrast to these other regions, the expansion in east Greenland at AD 1150 appears to have been very close to, if not at, a maximum Holocene value. Comparison of the Istorvet ice-cap fluctuations with Holocene glacier extents in Southern Hemisphere middle-to-high latitude locations on the Antarctic Peninsula and in the Andes and the Southern Alps suggests an out-of-phase relationship. If correct, this pattern supports the hypothesis that a bipolar see-saw of oceanic and/or atmospheric circulation during the Holocene produced asynchronous glacier response at some localities in the two polar hemispheres. [Copyright &y& Elsevier]

Tropical glaciers have retreated alongside warming temperatures over the past century, yet the way in which these trends fit into a long-term geological context is largely unclear. Here, we present reconstructions of Holocene glacier extents relative to today from the Quelccaya ice cap (Peru) and the Rwenzori Mountains (Uganda) based on measurements of in situ 14C and 10Be from recently exposed bedrock. Ice-extent histories are similar at both sites and suggest that ice was generally smaller than today during the first half of the Holocene and larger than today for most, if not all, of the past several millennia. The similar glaciation history in South America and Africa suggests that large-scale warming followed by cooling of the tropics during the late Holocene primarily drove ice extent, rather than regional changes in precipitation. Our results also imply that recent tropical ice retreat is anomalous in a multimillennial context. [ABSTRACT FROM AUTHOR]

Abstract: Patterns that maintain and generate biodiversity of macro‐organisms in the Neotropics are widely discussed in the scientific literature, yet the spatial ecology of micro‐organisms is largely unknown. The unique character of the tropical Andes and adjacent Amazon lowlands generates a wide gradient of environmental conditions to advance our understanding of what drives community assembly and diversity processes. We analysed the distribution patterns of benthic diatoms (unicellular siliceous algae) as a model group of microbial passive dispersers, including predictors that describe limnological and geo‐climatic gradients for a total of 113 waterbodies (0–28°S and 58–80°W), including lakes and streams. Complementary multivariate statistical analyses were performed to correlate (1) community composition and (2) diatom species richness with environmental and spatial factors to infer niche‐based and dispersal‐based assembly processes, respectively. Results showed that two gradients structured both diatom assemblages and waterbodies, namely climate and landscape configuration. Variance partitioning revealed that broadscale spatial variables (distance‐based Moran's Eigenvectors) outperformed the two environmental components (limnological and geo‐climatic), suggesting dispersal‐assembled communities. However, diatom assemblages were structured by geo‐climatic (regional) factors in certain lakes in the northern and central Andes, although their effects were partially manifested via local variables after the geographical distances were factored out. In a similar way, climatic and topographic structuring homogenized lake and stream communities within ecoregions, as indicated by the strong overlap between the two community types and the weak correlation between biota and limnological variables. Notably, a significant increase in diatom species richness was related to increased water connectivity, interpreted to indicate that a decrease in the remoteness of the system increase species number. Synthesis. We emphasize the strength of macroecological gradients (landscape configuration and climatic factors) in affecting both diatom diversity and community composition in the South American tropics. In this context, our results and the commonalities of ecoregion patterning with groups of macro‐organisms (vegetation) suggest the need to integrate microbial ecology into a macroecology framework to unravel mechanisms behind diversity gradients. [ABSTRACT FROM AUTHOR]

Projections of future rates of mass loss from the Greenland Ice Sheet are highly uncertain because its sensitivity to warming is unclear. Geologic reconstructions of Quaternary interglacials can illustrate how the ice sheet responded during past warm periods, providing insights into ice sheet behavior and important tests for data-model comparisons. However, paleoclimate records from Greenland are limited: Early Holocene peak warmth has been quantified at only a few sites, and terrestrial sedimentary records of prior interglacials are exceptionally rare due to glacial erosion during the last glacial period. Here, we discuss findings from a lacustrine archive that records both the Holocene and the Last Interglacial (LIG) from Greenland, allowing for direct comparison between two interglacials. Sedimentary chironomid assemblages indicate peak July temperatures 4.0 to 7.0 ±C warmer than modern during the Early Holocene maximum in summer insolation. Chaoborus and chironomids in LIG sediments indicate July temperatures at least 5.5 to 8.5 ±C warmer than modern. These estimates indicate pronounced warming in northwest Greenland during both interglacials. This helps explain dramatic ice sheet thinning at Camp Century in northwest Greenland during the Early Holocene and, for the LIG, aligns with controversial estimates of Eemianwarming from ice core data retrieved in northern Greenland. Converging geologic evidence for strong LIG warming is challenging to reconcile with inferred Greenland Ice Sheet extent during the LIG, and the two appear incompatible in many models of ice sheet evolution. An increase in LIG snowfall could help resolve this problem, pointing to the need for hydroclimate reconstructions from the region. [ABSTRACT FROM AUTHOR]

Elucidating the timing and regional extent of abrupt climate events during the last glacial-interglacial transition (∼18–11.5 ka) is critical for identifying spatial patterns and mechanisms responsible for large-magnitude climate events. The record of climate change in the Southern Hemisphere during this time period, however, remains scarce and unevenly distributed. We present new geomorphic, chronological, and equilibrium line altitude (ELA) data from a climatically sensitive mountain glacier at Monte San Lorenzo (47°S), Central Patagonia. Twenty-four new cosmogenic 10 Be exposure ages from moraines provide a comprehensive glacial record in the mid-latitudes of South America, which constrain the timing, spatial extent and magnitude of glacial fluctuations during the Antarctic Cold Reversal (ACR, ∼14.5–12.9 ka). Río Tranquilo glacier advanced and reached a maximum extent at 13.9 ± 0.7 ka. Three additional inboard moraines afford statistically similar ages, indicating repeated glacier expansions or marginal fluctuations over the ACR. Our record represents the northernmost robust evidence of glacial fluctuations during the ACR in southern South America, documenting not only the timing of the ACR maximum, but also the sequence of glacier changes within this climate event. Based on ELA reconstructions, we estimate a cooling of >1.6–1.8 °C at the peak of the ACR. The Río Tranquilo record along with existing glacial reconstructions from New Zealand (43°S) and paleovegetation records from northwestern (41°S) and central-west (45°S) Patagonia, suggest an uniform trans-Pacific glacier-climate response to an ACR trigger across the southern mid-latitudes. We posit that the equatorial migration of the southern westerly winds provides an adequate mechanism to propagate a common ACR signal across the Southern Hemisphere. [ABSTRACT FROM AUTHOR]

Reconstructions of Holocene lake water isotopic composition based upon subfossil aquatic organic material offer new insights into Arctic climate. We present quantitative estimates of warmth during the Holocene Thermal Maximum in northwest Greenland, inferred from oxygen isotopes of chironomid head capsules and aquatic moss preserved in lake sediments. δ 18 O values of chironomids from surface sediments of multiple Greenland lakes indicate that these subfossil remains record the δ 18 O values of the lake water in which they grow. Our lake water δ 18 O reconstruction is supported by downcore agreement with δ 18 O values in aquatic moss and chironomid remains. δ 18 O of both organic materials from Secret Lake decrease after 4 ka (ka = thousands of years ago) by 3‰ into the Neoglacial. We argue that lake water at Secret Lake primarily reflects precipitation δ 18 O values, which is strongly correlated with air temperature in NW Greenland, and that this signal is biased towards summer and early autumn conditions. Other factors may have influenced Secret Lake δ 18 O values through the Holocene, including evaporation of lake water and changing seasonality and source of precipitation. The maximum early Holocene summer and early autumn-biased temperature anomaly at Secret Lake is 2.5–4 °C warmer than present from 7.7 (the beginning of our record) to ∼6 ka. The maximum late Holocene cold anomaly (which includes the Little Ice Age) is 1.5–3 °C colder than present. These ranges of possible temperature anomalies reflect uncertainty in the δ 18 O – temperature relationship for precipitation at the study site through the Holocene. [ABSTRACT FROM AUTHOR]

We investigated the response of lake algal communities to changes in glacial meltwater from the Renland Ice Cap (Greenland) through the Holocene to assess whether influxes always elicit consistent responses or novel responses. We measured sedimentary algal pigments in two proximal lakes, snow-fed Raven and glacier- and snow-fed Bunny Lake, and diatom community structure and turnover in Bunny Lake. Diatom data were not available in Raven Lake. We also modeled lake-level change in Bunny Lake to identify how glacial meltwater may have altered diatom habitat availability through time. Through a series of glacier advances and retreats over the Holocene, the algal response in Bunny Lake was relatively constant until approximately 1015 yr BP, after which there were major changes in sedimentary algal remains. Algal pigment concentrations sharply declined, and diatom species richness increased. Diatom community structure underwent three reorganizations. Until 1015 yr BP, assemblages were dominated by Pinnularia braunii and Aulacoseira pffaffiana. However, approximately 1015-480 yr BP, these species declined and Tabellaria flocculosa and Hannaea arcus became a significant component of the assemblage. Approximately 440 yr BP, A. pfaffiana increased along with species indicating elevated nitrogen. In contrast, the algal pigment records from nearby snow-fed Raven Lake showed different and minimal change through time. Our results suggest that changes in the magnitude and composition of meltwater in our two study lakes were unique over the last 1000 yr BP and elicited a non-linear threshold response absent during other periods of glacier advance and retreat. Deciphering the degree to which glaciers structure algal communities over time has strong implications for lakes as glaciers continue to recede. [ABSTRACT FROM AUTHOR]

Improving the late Quaternary paleoclimate record through climate interpretations of low-latitude glacier length changes advances our understanding of past climate change events and the mechanisms for past, present, and future climate change. Paleotemperature reconstructions at low-latitude glaciers are uniquely fruitful because they can provide both site-specific information and enhanced understanding of regional-scale variations due to the structure of the tropical atmosphere. We produce Little Ice Age (LIA) and Younger Dryas (YD) paleoclimate reconstructions for the Huancané outlet glacier of the Quelccaya Ice Cap (QIC) and low-latitude southern hemisphere regional sea surface temperatures (SSTs) using a coupled ice-flow and energy balance model. We also model the effects of long-term changes in the summit temperature and precipitiation rate and the effects of interannual climate variability on the Huancané glacier length. We find temperature to be the dominant climate driver of glacier length change. Also, we find that interannual climate variability cannot adequately explain glacier advances inferred from the geomorphic record, necessitating that these features were formed during past colder climates. To constrain our LIA reconstruction, we incorporate the QIC ice core record, finding a LIA air temperature cooling at the ice cap of between ∼0.7 °C and ∼1.1 °C and ∼0.4 °C and regional SSTs cooling of ∼0.6 °C. For the YD paleoclimate reconstructions, we propose two limits on the precipitation rate, since the ice core record does not extend into the Pleistocene: 1) the precipitation rate scales with the Clausius-Clapeyron relationship (upper limit on cooling) and 2) the precipitation rate increases by 40% (lower limit on cooling), which is an increase about twice as great as the regional increases realized in GCM simulations for the period. The first limit requires ∼1.6 °C cooling in ice cap air temperatures and ∼0.9 °C cooling in SSTs, and the second limit requires ∼1.0 °C cooling in ice cap air temperatures and ∼0.5 °C cooling in SSTs. Our temperature reconstructions are in good agreement with the magnitude and trend of GCM simulations that incorporate the forcing mechanisms hypothesized to have caused these climate change events. [ABSTRACT FROM AUTHOR]

Tropical mountain environments, such as the Rwenzori Mountains in equatorial Africa, are thought to be particularly sensitive to climate change. Ongoing warming in the Rwenzori is impacting local environments and communities through glacial retreat, fires, and flooding. Paleoclimate reconstructions from elsewhere in Africa suggest considerable warming accompanied glacier retreat during the last glacial termination, from ∼21 thousand years before present (ka) through the early to mid-Holocene. Quantifying these changes has been difficult but could help to assess future impacts in the Rwenzori. Here, we present a ∼21 thousand-year (kyr) temperature reconstruction based on the relative abundance of branched glycerol dialkyl glycerol tetraethers (brGDGTs) from Lake Mahoma (2,990 m above sea level; m asl) in the Rwenzori Mountains, Uganda. Our record, paired with existing Rwenzori glacial moraine 10Be exposure ages, suggests that deglacial warming and glacial retreat began by ∼20 ka and accelerated at ∼18–18.5 ka. The timing of the onset of rapid warming matches the timing of the post-glacial rise in radiative forcing from atmospheric greenhouse gases (GHGs) from Antarctic ice cores (Brook et al., 1996; Marcott et al., 2014; Monnin et al., 2004; Schilt et al., 2010). Our temperature reconstruction registers ∼4.9 °C warming from the Last Glacial Maximum (LGM) to the late Holocene. This increase is larger than the average ∼2-4 °C warming observed in records from lower elevation sites in tropical East Africa, but similar to that observed at other high-elevation sites in this region. The increased warming at higher elevations thus confirms that the temperature lapse rate steepened during the LGM over this region. Our results also indicate ∼3 °C of warming during the mid-Holocene relative to the late Holocene. This suggests that the freezing-level height rose above Rwenzori summit elevations at that time, likely causing complete deglaciation of the Rwenzori Mountains from ∼5 to 7 ka. The mid-Holocene is thus a potential analog for the glacial and environmental changes that these mountains are likely to experience in the coming decades. Overall, the timing and magnitude of temperature change observed in our record has important implications for climate model projections of future warming in tropical Africa. • We produce a 21 kyr temperature record from alpine Lake Mahoma, Uganda. • Rwenzori glaciers and vegetation are very sensitive to past temperature change. • ∼3 °C warming during middle Holocene caused complete deglaciation in Rwenzori. • Regional temperature records indicate a steeper tropical lapse rate during the LGM. • Tropical lapse rate shoaled and stabilized during the middle and late Holocene. [ABSTRACT FROM AUTHOR]

Abstract: The statistical distributions of cosmogenic nuclide measurements from moraine boulders contain previously unused information on moraine ages, and they help determine whether moraine degradation or inheritance is more important on individual moraines. Here, we present a method for extracting this information by fitting geomorphic process models to observed exposure ages from single moraines. We also apply this method to 94 10Be apparent exposure ages from 11 moraines reported in four published studies. Our models represent 10Be accumulation in boulders that are exhumed over time by slope processes (moraine degradation), and the delivery of boulders with preexisting 10Be inventories to moraines (inheritance). For now, we neglect boulder erosion and snow cover, which are likely second-order processes. Given a highly scattered data set, we establish which model yields the better fit to the data, and estimate the age of the moraine from the better model fit. The process represented by the better-fitting model is probably responsible for most of the scatter among the apparent ages. Our methods should help resolve controversies in exposure dating; we reexamine the conclusions from two published studies based on our model fits. [Copyright &y& Elsevier]

Abstract: We use a simple model to analyse the relationship between ice core temperature proxy data and global ice volume/eustatic sea-level data over the last glacial cycle (LGC). By allowing the temperature forcing to be a mix of Greenlandic and Antarctic signals we optimise the proportion of this mixing to fit sea-level data. We find that sea-level forcing is best represented by a mix of Antarctic and Greenlandic temperature signals through the whole glacial cycle. We suggest that a distinct bipolar switch occurs which links eustatic sea-level more closely with the Antarctic-like variability during the glacial period (MIS 4, 3 and 2) and more closely to the Greenland-like variability during the last termination (TI) and the interglacial periods (Holocene and MIS 5). This switch may be caused by the spatio-temporal distribution of ice sheet collapse perhaps linked to glacial to interglacial changes in deep water distribution in the ocean, which in turn drive changes in pole-ward heat and moisture transport. [Copyright &y& Elsevier]

Shrinking glaciers, melting permafrost, and reduced sea ice all indicate rapid contraction of the Arctic cryosphere in response to present-day climate warming, a trajectory that is expected to continue, if not accelerate. The reaction of the Arctic cryosphere to past periods of climate variation can afford insight into its present and future behavior. Here, we examine a ∼12,000 year record of glacier fluctuations and meltwater variation associated with the Renland Ice Cap, East Greenland, that extends from the early Holocene thermal optimum through the cooling of the Little Ice Age to present. Sediment records from glacially fed lakes indicate rapid early Holocene deglaciation, with ice extent likely slightly smaller than at present by ∼9500 yr BP. Glacial activity resulted in occasional deposition of rock flour in the studied lakes in the early Holocene until at least ∼7500 yr BP. Rock flour is absent for much of the period ∼7000-4000 yr BP, suggesting ice extent generally was smaller than at present. However, thin layers of blue-gray clay throughout this period may indicate millennial-scale ice expansions, with Renland Ice Cap briefly reaching extents during cold phases that may have been similar to today. Glacial sediment deposition occurred again in the late Holocene at ∼3200–3400 yr BP and was followed by a brief glacial episode at ∼1340 yr BP and then a major event beginning shortly after ∼1050 yr BP. We infer that rock flour deposition in the lakes in the last millennium corresponds with advance of Renland glaciers to their Little Ice Age positions, marked by a fresh, gray drift limit. Radiocarbon dates of in situ plant remains adjacent to the present ice cap indicate a short relatively warm period ∼500 yr ago, when ice was within its AD 2011 limit, followed by glacier readvance. The general pattern of ice fluctuations in Renland is similar to that at other ice caps in the region, but also has important differences, including the preservation of a possible mid-Holocene record at times when lower-elevation ice caps in the Scoresby Sund region may have been absent. This finding reinforces the concept that examination of multiple geographic and geomorphologic settings is necessary for a full understanding of ice variations in a region. • Sediments from glacially fed lakes constrain the Holocene history of Renland Ice Cap. • Ice extent was similar to or smaller than at present by ∼10,000 yr BP. • Millennial-scale glacier fluctuations occurred throughout the Holocene. • Examination of multiple geographic settings is necessary for a full understanding of ice variations in a region. [ABSTRACT FROM AUTHOR]

To put recent Greenland Ice Sheet (GrIS) ice loss into a longer-term context, we must understand its behavior during late-glacial and Early Holocene warming. Previous results seem to suggest that there is a large contrast in the timing of deglaciation between South and Southeast Greenland. However, because of lack of available data, in particular in Southeast Greenland, it is difficult to assess how the ice sheet responded to major late-glacial and Early Holocene climate changes. In this study, we use 41 new 10Be ages to constrain the deglaciation chronology in 12 new locations from the coast to the present ice margin in South and Southeast Greenland. We find that South Greenland (south of 61.5°N) deglaciated between ∼14.8 and 11.9 ka, whereas Southeast Greenland (61.5°N to 68.2°N) deglaciated between ∼11.4 and 11.3 ka. The deglaciation of the coastal, low-intermediate topography in South Greenland coincides with increased air surface temperatures during the Bølling-Allerød with fjords continuing to deglaciate into the Early Holocene. In contrast, the ice sheet persisted at the coast until the late-glacial and Early Holocene in Southeast Greenland, likely because of increased precipitation in the high alpine topography and fjord geometry and bathymetry (e.g. width of fjords and presence of sills). This multi-phased deglaciation demonstrates a contrasting response of the southern GrIS to changes in climate and variations in topographic setting, and that the spatial deglaciation of the GrIS was complex and likely did not respond to a single external climate forcing. • Deglaciation began in South Greenland by 14.8 ka coeval with rising air temperature. • Warm Atlantic water likely drove deglaciation during the Younger Dryas. • Ice retreated from Southeast Greenland coast by 11.3 ka when air temperatures rose. • Evidence of a Neoglacial advance occurs in Southeast Greenland by ∼1.9 ka. • Local climate, topography and fjord geometry/bathymetry likely mediated ice retreat. [ABSTRACT FROM AUTHOR]