364 research outputs found
Rapid temperature rise may have triggered glacier surges all over Svalbard
Observational and geomorphological records suggest that most glaciers on Svalbard reached their maximum Little Ice Age extents by means of surging. Furthermore, it seems to have happened within just a few decades, suggesting that the rapid concurrent changes in climate might have triggered this widespread surging. The specific precipitation and temperature range of Svalbard seems optimal for glacier surges, and areas with a climatic trend toward the same range may therefore exhibit more glacier surging in the future. This is important, as surges contribute significantly to overall melt and sea-level rise when they occur, and the potential for it to spread is essential to study further. To understand the phenomenon better, five glaciers in Bolterdalen and Foxdalen on Svalbard were studied in depth. Observational, geomorphological, photogrammetric, and ground penetrating radar data indicate that four out of five glaciers seemed to have surged between 1896 and 1936. On average, they lost 81%±7% of their volumes between 1936 and 2019, twice as much as the one glacier that did not show signs of surging. In addition, the glacier Scott Turnerbreen lost 90.4%±5.4 of its volume in the same interval, in a previously undescribed kind of surge where it did not terminate in stagnation directly, but instead continued to advance for many years. This surge and post-surge advance phase occurred over between 22 and 47 years, making it the longest dynamically driven advance ever recorded on Svalbard. The results indicate that climate change-triggered surging may expedite subsequent melt by multiple times, highlighting the immense need to study the phenomenon further and include it in future ice-loss projections
Ross Ice Shelf in situ radio-frequency ice attenuation
We have measured the in situ average electric field attenuation length for
radio-frequency signals broadcast vertically through the Ross Ice Shelf. We
chose a location, Moore Embayment, south of Minna Bluff, known for its high
reflectivity at the ice-sea interface. We confirmed specular reflection and
used the return pulses to measure the average attenuation length from 75-1250
MHz over the round-trip distance of 1155 m. We find the average electric field
attenuation length to vary from 500 m at 75 MHz to 300 m at 1250 MHz, with an
experimental uncertainty of 55 to 15 m. We discuss the implications for
neutrino telescopes that use the radio technique and include the Ross Ice Shelf
as part of their sensitive volume.Comment: 6 pages, 7 figures, Fig. 7 updated and minor text changes made since
the published versio
The dual approach to optimal control in the coefficients of nonlocal nonlinear diffusion
We derive the dual variational principle (principle of minimal complementary
energy) for the nonlocal nonlinear scalar diffusion problem, which may be
viewed as the nonlocal version of the -Laplacian operator. We establish
existence and uniqueness of solutions (two-point fluxes) as well as their
quantitative stability, which holds uniformly with respect to the small
parameter (nonlocal horizon) characterizing the nonlocality of the problem. We
then focus on the nonlocal analogue of the classical optimal control in the
coefficient problem associated with the dual variational principle, which may
be interpreted as that of optimally distributing a limited amount of
conductivity in order to minimize the complementary energy. We show that this
nonlocal optimal control problem -converges to its local counterpart,
when the nonlocal horizon vanishes.Comment: 37 pages, 0 figure
Manual and Electroacupuncture for Labour Pain: Study Design of a Longitudinal Randomized Controlled Trial
Introduction. Results from previous studies on acupuncture for labour pain are contradictory and lack important information on methodology. However, studies indicate that acupuncture has a positive effect on women's experiences of labour pain. The aim of the present study was to evaluate the efficacy of two different acupuncture stimulations, manual or electrical stimulation, compared with standard care in the relief of labour pain as the primary outcome. This paper will present in-depth information on the design of the study, following the CONSORT and STRICTA recommendations. Methods. The study was designed as a randomized controlled trial based on western medical theories. Nulliparous women with normal pregnancies admitted to the delivery ward after a spontaneous onset of labour were randomly allocated into one of three groups: manual acupuncture, electroacupuncture, or standard care. Sample size calculation gave 101 women in each group, including a total of 303 women. A Visual Analogue Scale was used for assessing pain every 30 minutes for five hours and thereafter every hour until birth. Questionnaires were distributed before treatment, directly after the birth, and at one day and two months postpartum. Blood samples were collected before and after the first treatment. This trial is registered at ClinicalTrials.gov: NCT01197950
Risk of Subsequent Preeclampsia by Maternal Country of Birth: A Norwegian Population-Based Study
In this nationwide population-based study, we investigated the associations of preeclampsia in the first pregnancy with the risk of preeclampsia in the second pregnancy, by maternal country of birth using data from the Medical Birth Registry of Norway and Statistics Norway (1990â2016). The study population included 101,066 immigrant and 544,071 non-immigrant women. Maternal country of birth was categorized according to the seven super-regions of the Global Burden of Disease study (GBD). The associations between preeclampsia in the first pregnancy with preeclampsia in the second pregnancy were estimated using log-binomial regression models, using no preeclampsia in the first pregnancy as the reference. The associations were reported as adjusted risk ratios (RR) with 95% confidence intervals (CI), adjusted for chronic hypertension, year of first childbirth, and maternal age at first birth. Compared to those without preeclampsia in the first pregnancy, women with preeclampsia in the first pregnancy were associated with a considerably increased risk of preeclampsia in the second pregnancy in both immigrant (n = 250; 13.4% vs. 1.0%; adjusted RR 12.9 [95% CI: 11.2, 14.9]) and non-immigrant women (n = 2876; 14.6% vs. 1.5%; adjusted RR 9.5 [95% CI: 9.1, 10.0]). Immigrant women from Latin America and the Caribbean appeared to have the highest adjusted RR, followed by immigrant women from North Africa and the Middle East. A likelihood ratio test showed that the variation in adjusted RR across all immigrant and non-immigrant groups was statistically significant (p = 0.006). Our results suggest that the association between preeclampsia in the first pregnancy and preeclampsia in the second pregnancy might be increased in some groups of immigrant women compared with non-immigrant women in Norway.publishedVersio
Groundwater springs formed during glacial retreat are a large source of methane in the high Arctic
Permafrost and glaciers in the high Arctic form an impermeable âcryospheric capâ that traps a large reservoir of subsurface methane, preventing it from reaching the atmosphere. Cryospheric vulnerability to climate warming is making releases of this methane possible. On Svalbard, where air temperatures are rising more than two times faster than the average for the Arctic, glaciers are retreating and leaving behind exposed forefields that enable rapid methane escape. Here we document how methane-rich groundwater springs have formed in recently revealed forefields of 78 land-terminating glaciers across central Svalbard, bringing deep-seated methane gas to the surface. Waters collected from these springs during FebruaryâMay of 2021 and 2022 are supersaturated with methane up to 600,000 times greater than atmospheric equilibration. Spatial sampling reveals a geological dependency on the extent of methane supersaturation, with isotopic evidence of a thermogenic source. We estimate annual methane emissions from proglacial groundwaters to be up to 2.31âkt across the Svalbard archipelago. Further investigations into marine-terminating glaciers indicate future methane emission sources as these glaciers transition into fully land-based systems. Our findings reveal that climate-driven glacial retreat facilitates widespread release of methane, a positive feedback loop that is probably prevalent across other regions of the rapidly warming Arcti
Internal structure and significance of ice-marginal moraine in the Kebnekaise Mountains, northern Sweden
Despite a long history of glaciological research, the palaeo-environmental significance of moraine systems in the Kebnekaise Mountains, Sweden, has remained uncertain. These landforms offer the potential to elucidate glacier response prior to the period of direct monitoring and provide an insight into the ice-marginal processes operating at polythermal valley glaciers. This study set out to test existing interpretations of Scandinavian ice-marginal moraines, which invoke ice stagnation, pushing, stacking/dumping and push-deformation as important moraine forming processes. Moraines at IsfallsglaciÀren were investigated using ground-penetrating radar to document the internal structural characteristics of the landform assemblage. Radar surveys revealed a range of substrate composition and reflectors, indicating a debris- ice interface and bounding surfaces within the moraine. The moraine is demonstrated to contain both ice-rich and debris-rich zones, reflecting a complex depositional history and a polygenetic origin. As a consequence of glacier overriding, the morphology of these landforms provides a misleading indicator of glacial history. Traditional geochronological methods are unlikely to be effective on this type of land- form as the fresh surface may post-date the formation of the landform following reoccupation of the moraine rampart by the glacier. This research highlights that the interpretation of geochronological data sets from similar moraine systems should be undertaken with caution
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