Subglacial drainage processes at a High Arctic polythermal valley glacier

Peer reviewedPublisher PD

Mixing theory for culture and harvest in bioreactors of human mesenchymal stem cells on microcarriers

The use of human mesenchymal stem cells (hMSCs) in regenerative medicine is a potential major advance for the treatment of many medical conditions, especially with the use of allogeneic therapies where the cells from a single donor can be used to treat ailments in many patients. Such cells must be grown attached to surfaces and for large scale production, it is shown that stirred bioreactors containing ~200 μm particles (microcarriers) can provide such a surface. It is also shown that the just suspended condition, agitator speed NJS, provides a satisfactory condition for cell growth by minimizing the specific energy dissipation rate, εT, in the bioreactor whilst still meeting the oxygen demand of the cells. For the cells to be used for therapeutic purposes, they must be detached from the microcarriers before being cryopreserved. A strategy based on a short period (~7 min) of very high εT, based on theories of secondary nucleation, is effective at removing >99% cells. Once removed, the cells are smaller than the Kolmogorov scale of turbulence and hence not damaged. This approach is shown to be successful for culture and detachment in 4 types of stirred bioreactors from 15 mL to 5 L

Seasonal variations in Greenland Ice Sheet motion : Inland extent and behaviour at higher elevations

Peer reviewedPreprin

Diatoms of the Northeastern Gulf of Mexico: Light and Electron Microscope Observations of Sulcatonitzschia, a new Genus of Nitzschioid Diatoms (Bacillariales: Bacillariaceae) with a Transverse Sulcus

During a systematic investigation of phytoplankton assemblages in the northeastern Gulf of Mexico (GOM) in the aftermath of the Deepwater Horizon blowout we encountered a population of diatoms morphologically similar to Nitzschia ossiformis (Taylor) Simonsen located about 75 km offshore and concentrated at a depth of 60—120 meters. The density of individuals in the population was sufficient to make detailed observations using light and electron microscopy. Our specimens were frequently united into short ribbon—like colonies. This, plus features of the fine structure of valve (biseriate striae, raphe canal without pores and flush with the valve surface) suggest the GOM population is more closely related to Fragilariopsis than to Nitzschia sensu stricto. The presence of a unique feature, described here for the first time, a transverse sulcus in the exterior surface of one of the poles, coupled with the characteristic shape of the valve, suggest our taxon cannot be accommodated in Fragilariopsis, or any other genus hitherto known within the family Bacillariaceae. We, therefore, propose a new genus, Sulcatonitzschia for this diatom and any other nitzschioid diatom with a transverse sulcus, with a new species, Sulcatonitzschia novossiformis as the generitype. Published descriptions suggest that some populations identified as Nitzschia ossiformis may be conspecific with S. novossiformis, but the type of N. ossiformis as delineated by Taylor is not. Examination of the fine structure of the valves is necessary to resolve these relationships

Modelling the transfer of supraglacial meltwater to the bed of Leverett Glacier, Southwest Greenland

This is the final version of the article. Available from EGU via the DOI in this record.Meltwater delivered to the bed of the Greenland Ice Sheet is a driver of variable ice-motion through changes in effective pressure and enhanced basal lubrication. Ice surface velocities have been shown to respond rapidly both to meltwater production at the surface and to drainage of supraglacial lakes, suggesting efficient transfer of meltwater from the supraglacial to subglacial hydrological systems. Although considerable effort is currently being directed towards improved modelling of the controlling surface and basal processes, modelling the temporal and spatial evolution of the transfer of melt to the bed has received less attention. Here we present the results of spatially distributed modelling for prediction of moulins and lake drainages on the Leverett Glacier in Southwest Greenland. The model is run for the 2009 and 2010 ablation seasons, and for future increased melt scenarios. The temporal pattern of modelled lake drainages are qualitatively comparable with those documented from analyses of repeat satellite imagery. The modelled timings and locations of delivery of meltwater to the bed also match well with observed temporal and spatial patterns of ice surface speed-ups. This is particularly true for the lower catchment ( < 1000 m a.s.l.) where both the model and observations indicate that the development of moulins is the main mechanism for the transfer of surface meltwater to the bed. At higher elevations (e.g. 1250-1500 m a.s.l.) the development and drainage of supraglacial lakes becomes increasingly important. At these higher elevations, the delay between modelled melt generation and subsequent delivery of melt to the bed matches the observ ed delay between the peak air temperatures and subsequent velocity speed-ups, while the instantaneous transfer of melt to the bed in a control simulation does not. Although both moulins and lake drainages are predicted to increase in number for future warmer climate scenarios, the lake drainages play an increasingly important role in both expanding the area over which melt accesses the bed and in enabling a greater proportion of surface melt to reach the bed.We acknowledge the College of Physical Sciences, University of Aberdeen, the Leverhulme Trust through a Study Abroad Studentship and the Swedish Radiation Safety Authority, for funding awarded to C. Clason. Data collection was supported by the UK Natural Environment Research Council (through a studentship to I. Bartholomew and grants to P. Nienow and D. Mair) and the Edinburgh University Moss Centenary Scholarship (I. Bartholomew)

Decadal-scale climate forcing of Alpine glacial hydrological systems

Available at https://rdcu.be/bxMf

Heterogeneous and rapid ice loss over the Patagonian Ice Fields revealed by CryoSat-2 swath radar altimetry

The Northern and Southern Patagonian Ice Fields (NPI and SPI) in South America are the largest bodies of ice in the Southern hemisphere outside of Antarctica and the largest contributors to eustatic sea level rise (SLR) in the world, per unit area. Here we exploit swath processed CryoSat-2 interferometric data to produce maps of surface elevation change at sub-kilometer spatial resolution over the Ice Fields for six glaciological years between April 2011 and March 2017. Mass balance is calculated independently for nine sub-regions, including six individual glaciers larger than 300 km². Overall, between 2011 and 2017 the Patagonian Ice Fields have lost mass at a combined rate of 21.29 ± 1.98 Gt a−¹, contributing 0.059 ± 0.005 mm a−¹ to SLR. We observe widespread thinning on the Ice Fields, particularly north of 49° S. However the pattern of surface elevation change is highly heterogeneous, partly reflecting the importance of dynamic processes on the Ice Fields. The Jorge Montt glacier (SPI), whose tidewater terminus is approaching floatation, retreated ~2.5 km during our study period and lost mass at the rate of 2.20 ± 0.38 Gt a−¹ (4.64 ± 0.80 mwe a−¹). In contrast with the general pattern of retreat and mass loss, Pio XI, the largest glacier in South America, is advancing and gaining mass at 0.67 ± 0.29 Gt a−¹ rate

Culture of human mesenchymal stem cells on microcarriers in a 5 l stirred-tank bioreactor

This article was published in the journal, Biotechnology Letters [© Springer Science+Business Media] and the definitive version is available at: http://dx.doi.org/10.1007/s10529-013-1211-9For the first time, fully functional human mesenchymal stem cells (hMSCs) have been cultured at the litre-scale on microcarriers in a stirred-tank 5 l bioreactor, (2.5 l working volume) and were harvested via a potentially scalable detachment protocol that allowed for the successful detachment of hMSCs from the cell-microcarrier suspension. Over 12 days, the dissolved O2 concentration was >45 % of saturation and the pH between 7.2 and 6.7 giving a maximum cell density in the 5 l bioreactor of 1.7 × 105 cells/ml; this represents >sixfold expansion of the hMSCs, equivalent to that achievable from 65 fully-confluent T-175 flasks. During this time, the average specific O2 uptake of the cells in the 5 l bioreactor was 8.1 fmol/cell h and, in all cases, the 5 l bioreactors outperformed the equivalent 100 ml spinner-flasks run in parallel with respect to cell yields and growth rates. In addition, yield coefficients, specific growth rates and doubling times were calculated for all systems. Neither the upstream nor downstream bioprocessing unit operations had a discernible effect on cell quality with the harvested cells retaining their immunophenotypic markers, key morphological features and differentiation capacity

A model for tidewater glacier undercutting by submarine melting

Dynamic change at the marine-terminating margins of the Greenland Ice Sheet may be initiated by the ocean, particularly where subglacial runoff drives vigorous ice-marginal plumes and rapid submarine melting. Here we model submarine melt-driven undercutting of tidewater glacier termini, simulating a process which is key to understanding ice-ocean coupling. Where runoff emerges from broad subglacial channels we find that undercutting has only a weak impact on local submarine melt rate but increases total ablation by submarine melting due to the larger submerged ice surface area. Thus, the impact of melting is determined not only by the melt rate magnitude but also by the slope of the ice-ocean interface. We suggest that the most severe undercutting occurs at the maximum height in the fjord reached by the plume, likely promoting calving of ice above. It remains unclear, however, whether undercutting proceeds sufficiently rapidly to influence calving at Greenland's fastest-flowing glaciers