It has long been known that mountain glaciers and continental ice sheets around the globe reached their respective maximum extent at different times during the last glacial cycle, often well before ...the global Last Glacial Maximum (LGM; c. 23–19ka), which is formally defined by peaks in global sea-level and marine oxygen isotope records. However, there is increasing evidence from around the world that it was not only mountain glaciers which were asynchronous with the global LGM but also some regions of the large continental glaciers. The Barents–Kara Ice Sheet in northern Eurasia together with a majority of ice masses throughout Asia and Australasia reached their maximum early in the last glacial cycle, a few thousand years before the global LGM period. The East Antarctic Ice Sheet also reached its maximum extent several millennia before the global LGM. In numerous mountainous regions at high-, mid- and low-latitudes across the world, glaciers reached their maximum extent before Marine Isotope Stage (MIS) 2, in MIS 5, 4 and 3. This is in contrast to most sectors of the Laurentide Ice Sheet, the Cordilleran Ice Sheet, the SE sector of the Fennoscandinavian Ice Sheet and the Alpine Ice Sheet in central Europe, which appear to have reached their maximum close to the global LGM in MIS 2. The diachronous maximum extents of both mountain glaciers and continental ice sheets during the last glacial cycle, means that the term and acronym Last Glacial Maximum (LGM) has limited chronostratigraphical meaning when correlating glacial deposits and landforms.
The Last Glacial Maximum (LGM) is widely used to refer to the episode when global ice volume last reached its maximum and associated sea levels were at their lowest. However, the boundaries of the ...interval are ill-defined and the term and acronym have no formal stratigraphical basis. This is despite a previous proposal to define it as a chronozone in the marine records on the basis of oxygen isotopes and sea levels, spanning the interval 23–19 or 24–18 ka and centred on 21 ka. In terrestrial records the LGM is poorly represented since many sequences show a diachronous response to global climate changes during the last glacial cycle. For example, glaciers and ice sheets reached their maximum extents at widely differing times in different places. In fact, most terrestrial records display spatial variation in response to global climate fluctuations, and changes recorded on land are often diachronous, asynchronous or both, leading to difficulties in global correlation. However, variations in the global hydrological system during glacial cycles are recorded by atmospheric dust flux and this provides a signal of terrestrial changes. Whilst regional dust accumulation is recorded in loess deposits, global dust flux is best recorded in high-resolution polar ice-core records, providing an opportunity to define the LGM on land and establish a clear stratigraphical basis for its definition. On this basis, one option is to define the global LGM as an event between the top (end) of Greenland Interstadial 3 and the base (onset) of Greenland Interstadial 2, spanning the interval 27.540–23.340 ka (Greenland Stadial 3). This corresponds closely to the peak dust concentration in both the Greenland and Antarctic ice cores and to records of the global sea-level minima. This suggests that this definition includes not just the coldest and driest part of the last glacial cycle but also the peak in global ice volume. The later part of the LGM event is marked by Heinrich Event 2, which reflects the onset of the collapse of the Laurentide at c. 24 ka, together with other ice sheets in the North Atlantic region. A longer and later span for the LGM may be desirable, although defining this in chronostratigraphical terms is problematic. Whichever formal definition is chosen, this requires the contribution of the wider Quaternary community.
Annual balances of eight alpine glaciers were slightly negative for 1961–90 and highly negative for 1991–2018. We explain this by changes in positive degree-day sums and summer temperatures ...extrapolated to the median altitudes of the glaciers. We test a new way of calculating degree-day sums that performs better than the traditional method which used daily mean temperatures. Annual degree-day sums are highly correlated with May–September temperatures as suggested in 1866 by Karl von Sonklar. We find moderate correlations between annual balances and degree-day sums, and with May–September temperatures. Calculated degree-day factors for the eight glaciers cover the reported range for snow and ice ablation, while the temperature sensitivity of annual balance is from −0.4 to −1.0 m w.e. for a +1°C temperature change. We accurately predict mean balances for 1991–2018 using May–September temperatures in regression models calibrated for 1961–90. May–September temperatures in the Alps have already increased ~+3°C since 1880 and, if temperatures continue to rise, these glaciers will shrink rapidly. As annual balances are already negative for present-day temperatures, these glaciers will not be ‘safe’ under the further temperature increase permitted by the Paris Agreement.
Seaweeds are receiving increasing attention as third generation biofuels, which do not compete for land or freshwater with agricultural crops and have a high polysaccharide content. Seaweed growth is ...dependent on the presence of suitable physical and chemical conditions. The selection of cultivation sites with suitable characteristics is therefore essential for the successful establishment of European seaweed mariculture. The growth conditions of the site directly impact the biomass yield and composition of the crop, which in turn control the conversion efficiency of biomass to bioenergy. This review focuses on three European brown phaeophyte kelp species which may be suitable for large-scale offshore cultivation: Laminaria digitata, Saccharina latissima and Sacchoriza polyschides. It describes the known responses of each to a number of important physical and chemical parameters: temperature, salinity, water motion, nutrient concentrations, carbon dioxide/pH, light and ultra-violet radiation. It also reports density effects on their growth rate and what is known concerning the impact of disease and grazing. Conclusions are made on the conditions necessary for the optimal growth of each species for biofuel production. Where conditions are sub-optimal, this review has made recommendations for the most suitable species for a particular set of environmental conditions.
•We review the response of three brown seaweeds to various physico-chemical conditions.•This will aid site and species selection of seaweed cultivation for biofuel.•Laminaria digitata, Saccharina latissima and Sacchoriza polyschides were examined.•Differential tolerance will allow one species to be cultivated where another cannot.•A table highlights these tolerances and the ideal conditions for a cultivation site.
IMPORTANCE: Outcomes after exacerbations of chronic obstructive pulmonary disease (COPD) requiring acute noninvasive ventilation (NIV) are poor and there are few treatments to prevent hospital ...readmission and death. OBJECTIVE: To investigate the effect of home NIV plus oxygen on time to readmission or death in patients with persistent hypercapnia after an acute COPD exacerbation. DESIGN, SETTING, AND PARTICIPANTS: A randomized clinical trial of patients with persistent hypercapnia (Paco2 >53 mm Hg) 2 weeks to 4 weeks after resolution of respiratory acidemia, who were recruited from 13 UK centers between 2010 and 2015. Exclusion criteria included obesity (body mass index BMI >35), obstructive sleep apnea syndrome, or other causes of respiratory failure. Of 2021 patients screened, 124 were eligible. INTERVENTIONS: There were 59 patients randomized to home oxygen alone (median oxygen flow rate, 1.0 L/min interquartile range {IQR}, 0.5-2.0 L/min) and 57 patients to home oxygen plus home NIV (median oxygen flow rate, 1.0 L/min IQR, 0.5-1.5 L/min). The median home ventilator settings were an inspiratory positive airway pressure of 24 (IQR, 22-26) cm H2O, an expiratory positive airway pressure of 4 (IQR, 4-5) cm H2O, and a backup rate of 14 (IQR, 14-16) breaths/minute. MAIN OUTCOMES AND MEASURES: Time to readmission or death within 12 months adjusted for the number of previous COPD admissions, previous use of long-term oxygen, age, and BMI. RESULTS: A total of 116 patients (mean SD age of 67 10 years, 53% female, mean BMI of 21.6 IQR, 18.2-26.1, mean SD forced expiratory volume in the first second of expiration of 0.6 L 0.2 L, and mean SD Paco2 while breathing room air of 59 7 mm Hg) were randomized. Sixty-four patients (28 in home oxygen alone and 36 in home oxygen plus home NIV) completed the 12-month study period. The median time to readmission or death was 4.3 months (IQR, 1.3-13.8 months) in the home oxygen plus home NIV group vs 1.4 months (IQR, 0.5-3.9 months) in the home oxygen alone group, adjusted hazard ratio of 0.49 (95% CI, 0.31-0.77; P = .002). The 12-month risk of readmission or death was 63.4% in the home oxygen plus home NIV group vs 80.4% in the home oxygen alone group, absolute risk reduction of 17.0% (95% CI, 0.1%-34.0%). At 12 months, 16 patients had died in the home oxygen plus home NIV group vs 19 in the home oxygen alone group. CONCLUSIONS AND RELEVANCE: Among patients with persistent hypercapnia following an acute exacerbation of COPD, adding home noninvasive ventilation to home oxygen therapy prolonged the time to readmission or death within 12 months. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00990132
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