The impact of glacier geometry on meltwater plume structure and submarine melt in Greenland fjords

Meltwater from the Greenland Ice Sheet often drains subglacially into fjords, driving upwelling plumes at glacier termini. Ocean models and observations of submarine termini suggest that plumes enhance melt and undercutting, leading to calving and potential glacier destabilization. Here we systematically evaluate how simulated plume structure and submarine melt during summer months depends on realistic ranges of subglacial discharge, glacier depth, and ocean stratification from 12 Greenland fjords. Our results show that grounding line depth is a strong control on plume-induced submarine melt: deep glaciers produce warm, salty subsurface plumes that undercut termini, and shallow glaciers produce cold, fresh surface-trapped plumes that can overcut termini. Due to sustained upwelling velocities, plumes in cold, shallow fjords can induce equivalent depth-averaged melt rates compared to warm, deep fjords. These results detail a direct ocean-ice feedback that can affect the Greenland Ice Sheet

Elevation change of the Greenland Ice Sheet due to surface mass balance and firn processes, 1960–2014

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in The Cryosphere 9 (2015): 2009-2025, doi:10.5194/tc-9-2009-2015.Observed changes in the surface elevation of the Greenland Ice Sheet are caused by ice dynamics, basal elevation change, basal melt, surface mass balance (SMB) variability, and by compaction of the overlying firn. The last two contributions are quantified here using a firn model that includes compaction, meltwater percolation, and refreezing. The model is forced with surface mass fluxes and temperature from a regional climate model for the period 1960–2014. The model results agree with observations of surface density, density profiles from 62 firn cores, and altimetric observations from regions where ice-dynamical surface height changes are likely small. In areas with strong surface melt, the firn model overestimates density. We find that the firn layer in the high interior is generally thickening slowly (1–5 cm yr−1). In the percolation and ablation areas, firn and SMB processes account for a surface elevation lowering of up to 20–50 cm yr−1. Most of this firn-induced marginal thinning is caused by an increase in melt since the mid-1990s and partly compensated by an increase in the accumulation of fresh snow around most of the ice sheet. The total firn and ice volume change between 1980 and 2014 is estimated at −3295 ± 1030 km3 due to firn and SMB changes, corresponding to an ice-sheet average thinning of 1.96 ± 0.61 m. Most of this volume decrease occurred after 1995. The computed changes in surface elevation can be used to partition altimetrically observed volume change into surface mass balance and ice-dynamically related mass changes.P. Kuipers Munneke received financial support from the Netherlands Polar Programme (NPP) of the Netherlands Institute for Scientific Research (NWO). ECMWF at Reading (UK) is acknowledged for use of the Cray supercomputing system. The J. E. Box contribution is supported by Det Frie Forskningsråd grant 4002-00234 and Geocenter Denmark

Syndromic surveillance of potentially epidemic infectious diseases: Detection of a measles epidemic in two health centers in Gabon, Central Africa

Measles is a respiratory disease caused by the measles virus (MV) belonging to the Paramyxovirus family and the Morbillivirus genus. Due to a failure in maintaining immunization coverage in some countries, measles is a re-emerging disease in the human population, especially in Africa. The aim of this study was to describe a measles epidemic in Gabon. At first, a syndromic surveillance was set up. Blood samples from febrile patients with maculopapular rash were taken and sent to the measles reference center in Cameroon for laboratory confirmation. Between March and May 2016, 79 clinically suspected cases were reported including 82.3% (n=65) and 17.7% (n=14) in Oyem and Libreville, respectively. In total, 39.2% (n=31) of children were 11 months-old, 34.2% (n=27) were children aged 1 to 4 years, 11.4% (n=9) were older children from 5 to 9 years, 6.3% (n=5) of children were aged 10 to 15 years and 8.9% (n=7) were 15 years and older. 53.3% (16/30) were laboratory confirmed. This measles outbreak reiterates the importance of maintaining a high level of vaccine coverage in Gabon for vaccine-preventable diseases, as well as the usefulness of a near-real-time surveillance system for the detection of infectious diseases

Direct Measurements of Meltwater Runoff on the Greenland Ice Sheet Surface

Meltwater runoff from the Greenland Ice Sheet surface influences surface mass balance (SMB), ice dynamics and global sea level rise, but is estimated with climate models and thus difficult to validate. We present a way to measure ice surface runoff directly, from hourly in situ supraglacial river discharge measurements and simultaneous high-resolution satellite/drone remote sensing of upstream fluvial catchment area. A first 72-hour trial for a 63.1 square kilometer moulin-terminating internally drained catchment (IDC) on Greenland's mid-elevation (1207-1381 meters above sea level) ablation zone is compared with melt and runoff simulations from HIRHAM5, MAR3.6.1 (Modele Atmospherique Regionale 3.6.1), RACMO2.3 (Regional Atmospheric Climate Model 2.3), MERRA-2 (Modern Era Retrospective-analysis for Research and Applications-2) and SEB climate/SMB models. Current models cannot reproduce peak discharges or timing of runoff entering moulins, but are improved using synthetic unit hydrograph theory (SUH). Retroactive SUH applications to two older field studies reproduces their findings, signifying that remotely sensed IDC area, shape, and river-length are useful for predicting delays in peak runoff delivery to moulins. Applying SUH to HIRHAM5, MAR3.6.1, RACMO2.3 gridded melt products for 799 surrounding IDCs suggests their terminal moulins receive lower peak discharges, less diurnal variability, and asynchronous runoff timing relative to climate/SMB model output alone. Conversely, large IDCs produce high moulin discharges, even at high elevations where melt rates are low. During this particular field experiment models overestimated runoff by plus 21 percent to plus 58 percent, linked to overestimated ablation and possible meltwater retention in bare, low-density ice. Direct measurements of ice surface runoff will improve climate/SMB models, and incorporating remotely sensed IDCs will aid coupling of surface mass balance with ice dynamics and subglacial systems

Rapid dynamic activation of a marine-based Arctic ice cap

We use satellite observations to document rapid acceleration and ice loss from a formerly slow-flowing, marine-based sector of Austfonna, the largest ice cap in the Eurasian Arctic. During the past two decades, the sector ice discharge has increased 45-fold, the velocity regime has switched from predominantly slow (~ 101 m/yr) to fast (~ 103 m/yr) flow, and rates of ice thinning have exceeded 25 m/yr. At the time of widespread dynamic activation, parts of the terminus may have been near floatation. Subsequently, the imbalance has propagated 50 km inland to within 8 km of the ice cap summit. Our observations demonstrate the ability of slow-flowing ice to mobilize and quickly transmit the dynamic imbalance inland; a process that we show has initiated rapid ice loss to the ocean and redistribution of ice mass to locations more susceptible to melt, yet which remains poorly understood.This work was supported by the UK Natural Environment Research Council.This article was originally published in Geophysical Research Letters (M McMillan, A Shepherd, N Gourmelen, A Dehecq, A Leeson, A Ridout, T Flament, A Hogg, L Gilbert, T Benham, M van den Broeke, JA Dowdeswell, X Fettweis, B Noël, T Strozzi, Geophysical Research Letters 2014, 41, 8902–8909)

Musculoskeletal disorders among secondary school teachers in Douala, Cameroon: The effect of the practice of physical activities

IntroductionMusculoskeletal disorders (MSDs) represent an important threat to public health in both developed and developing countries, and are present in many occupational sectors including education. Regular practice of physical activity (PA) is known elicit preventive effects on the occurrence of MSDs.ObjectiveThis study aimed at determining the prevalence of MSDs and the preventive impact of PA on their occurrence among secondary school teachers.Participants and MethodsA cross-sectional study was conducted among 179 teachers in five government secondary schools in Douala, Cameroon. The Nordic and Ricci-Gagnon questionnaires were used to determine MSDs and to assess the level of PA, respectively.ResultsThe 12-month and 7-day prevalence of MSD (PMSD-12m and PMSD-7d) were 84.3% and 69.3%, respectively. The most affected body regions by MSDs were neck (PMSD-12m = 54.2%, PMSD-7d = 33.5%), lower back (PMSD-12m = 43%, PMSD-7d = 33%), and shoulders (PMSD-12m = 35%, PMSD-7d = 22.9%). Compared to female, males were protected against MSDs during the last 12 months (OR = 0.37; 95% CI 0.16–0.93; p = 0.04). The risk of MSDs during the last seven days was higher in teachers aged 30-40 years (OR = 2.86; 95% CI 1.14–7.14; p = 0.02) and 40-50 years (OR = 4.28; 95% CI 1.49–16.29; p = 0.008) than those under 30 years. This risk was tripled in inactive teachers (OR = 3.07; 95% CI 1.40–6.78; p = 0.005), compared to their active counterparts.ConclusionMSDs are prevalent among secondary school teachers and associated with aging, gender, and lower level of P

Mass balance of the Greenland Ice Sheet from 1992 to 2018

In recent decades, the Greenland Ice Sheet has been a major contributor to global sea-level rise1,2, and it is expected to be so in the future3. Although increases in glacier flow4–6 and surface melting7–9 have been driven by oceanic10–12 and atmospheric13,14 warming, the degree and trajectory of today’s imbalance remain uncertain. Here we compare and combine 26 individual satellite measurements of changes in the ice sheet’s volume, flow and gravitational potential to produce a reconciled estimate of its mass balance. Although the ice sheet was close to a state of balance in the 1990s, annual losses have risen since then, peaking at 335 ± 62 billion tonnes per year in 2011. In all, Greenland lost 3,800 ± 339 billion tonnes of ice between 1992 and 2018, causing the mean sea level to rise by 10.6 ± 0.9 millimetres. Using three regional climate models, we show that reduced surface mass balance has driven 1,971 ± 555 billion tonnes (52%) of the ice loss owing to increased meltwater runoff. The remaining 1,827 ± 538 billion tonnes (48%) of ice loss was due to increased glacier discharge, which rose from 41 ± 37 billion tonnes per year in the 1990s to 87 ± 25 billion tonnes per year since then. Between 2013 and 2017, the total rate of ice loss slowed to 217 ± 32 billion tonnes per year, on average, as atmospheric circulation favoured cooler conditions15 and as ocean temperatures fell at the terminus of Jakobshavn Isbræ16. Cumulative ice losses from Greenland as a whole have been close to the IPCC’s predicted rates for their high-end climate warming scenario17, which forecast an additional 50 to 120 millimetres of global sea-level rise by 2100 when compared to their central estimate