Foehn jets over the Larsen C Ice Shelf, Antarctica Elvidge, Andrew D.; Renfrew, Ian A.; King, John C. ...
Quarterly journal of the Royal Meteorological Society,
April 2015 Part A, Letnik:
141, Številka:
688
Journal Article
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Previously unknown foehn jets have been identified to the east of the Antarctic Peninsula (AP) above the Larsen C Ice Shelf. These jets have major implications for the east coast of the AP, a region ...of rapid climatic warming and where two large sections of ice shelf have collapsed in recent years.
During three foehn events across the AP, leeside warming and drying is seen in new aircraft observations and simulated well by the Met Office Unified Model (MetUM) at ∼1.5 km grid spacing. In case A, weak southwesterly flow and an elevated upwind inversion characterise a highly nonlinear flow regime with upwind flow blocking. In case C strong northwesterly winds characterise a relatively linear case with little upwind flow blocking. Case B resides somewhere between the two in flow regime linearity.
The foehn jets – apparent in aircraft observations where available and MetUM simulations of all three cases – are mesoscale features (up to 60 km in width) originating from the mouths of leeside inlets. Through back trajectory analysis they are identified as a type of gap flow. In cases A and B the jets are distinct, being strongly accelerated relative to the background flow, and confined to low levels above the Larsen C Ice Shelf. They resemble the ‘shallow foehn’ of the Alps. Case C resembles a case of ‘deep foehn’, with the jets less distinct. The foehn jets are considerably cooler and moister relative to adjacent regions of calmer foehn air. This is due to a dampened foehn effect in the jet regions: in case A the jets have lower upwind source regions, and in the more linear case C there is less diabatic warming and precipitation along jet trajectories due to the reduced orographic uplift across the mountain passes.
The structure of lee‐side warming during foehn events is investigated as a function of cross‐barrier flow regime linearity. Two contrasting cases of westerly flow over the Antarctic Peninsula (AP) ...are considered – one highly nonlinear, the other relatively linear. Westerly flow impinging on the AP provides one of the best natural laboratories in the world for the study of foehn, owing to its maritime setting and the Larsen C Ice Shelf (LCIS) providing an expansive, homogeneous and smooth surface on its east side. Numerical simulations with the Met Office Unified Model (at 1.5 km grid size) and aircraft observations are utilized. In case A, relatively weak southwesterly cross‐Peninsula flow and an elevated upwind inversion dictate a highly nonlinear foehn event, with mountain wave breaking observed. The consequent strongly accelerated downslope flow leads to high‐amplitude warming and ice‐shelf melt in the immediate lee of the AP. However this foehn warming diminishes rapidly downwind due to upward ascent of the foehn flow via a hydraulic jump. In case C, strong northwesterly winds dictate a relatively linear flow regime. There is no hydraulic jump and strong foehn winds are able to flow at low levels across the entire ice shelf, mechanically mixing the near‐surface flow, preventing the development of a strong surface inversion and delivering large fluxes of sensible heat to the ice shelf. Consequently, in case C ice‐melt rates are considerably greater over the LCIS as a whole than in case A. Our results imply that although nonlinear foehn events cause intense warming in the immediate lee of mountains, linear foehn events will commonly cause more extensive lee‐side warming and, over an ice surface, higher melt rates. This has major implications for the AP, where recent east‐coast warming has led to the collapse of two ice shelves immediately north of the LCIS.
Oncogene amplification on extrachromosomal DNA (ecDNA) is a common event, driving aggressive tumor growth, drug resistance and shorter survival. Currently, the impact of nonchromosomal oncogene ...inheritance-random identity by descent-is poorly understood. Also unclear is the impact of ecDNA on somatic variation and selection. Here integrating theoretical models of random segregation, unbiased image analysis, CRISPR-based ecDNA tagging with live-cell imaging and CRISPR-C, we demonstrate that random ecDNA inheritance results in extensive intratumoral ecDNA copy number heterogeneity and rapid adaptation to metabolic stress and targeted treatment. Observed ecDNAs benefit host cell survival or growth and can change within a single cell cycle. ecDNA inheritance can predict, a priori, some of the aggressive features of ecDNA-containing cancers. These properties are facilitated by the ability of ecDNA to rapidly adapt genomes in a way that is not possible through chromosomal oncogene amplification. These results show how the nonchromosomal random inheritance pattern of ecDNA contributes to poor outcomes for patients with cancer.
Cytoplasmic innate immune receptors are important therapeutic targets for diseases associated with overproduction of proinflammatory cytokines. One cytoplasmic receptor complex, the Nlrp3 ...inflammasome, responds to an extensive array of molecules associated with cellular stress. Under normal conditions, Nlrp3 is autorepressed, but in the presence of its ligands, it oligomerizes, recruits apoptosis-associated speck-like protein containing a caspase recruitment domain (Asc), and triggers caspase 1 activation and the maturation of proinflammatory cytokines such as IL-1β and IL-18. Because ischemic tissue injury provides a potential source for Nlrp3 ligands, our study compared and contrasted the effects of renal ischemia in wild-type mice and mice deficient in components of the Nlrp3 inflammasome (Nlrp3(-/-) and Asc(-/-) mice). To examine the role of the inflammasome in renal ischemia-reperfusion injury (IRI) we also tested its downstream targets caspase 1, IL-1β, and IL-18. Both Nlrp3 and Asc were highly expressed in renal tubular epithelium of humans and mice, and the absence of Nlrp3, but not Asc or the downstream inflammasome targets, dramatically protected from kidney IRI. We conclude that Nlrp3 contributes to renal IRI by a direct effect on renal tubular epithelium and that this effect is independent of inflammasome-induced proinflammatory cytokine production.
We investigated clinical and pathologic features of breast cancers (BC) in an unselected series of patients diagnosed in a tertiary care hospital serving a diverse population. We focused on ...triple-negative (Tneg) tumours (oestrogen receptor (ER), progesterone receptor (PR) and HER2 negative), which are associated with poor prognosis.
We identified female patients with invasive BC diagnosed between 1998 and 2006, with data available on tumor grade, stage, ER, PR and HER2 status, and patient age, body mass index (BMI) and self-identified racial/ethnic group. We determined associations between patient and tumour characteristics using contingency tables and multivariate logistic regression.
415 cases were identified. Patients were racially and ethnically diverse (born in 44 countries, 36% white, 43% black, 10% Hispanic and 11% other). 47% were obese (BMI > 30 kg/m2). 72% of tumours were ER+ and/or PR+, 20% were Tneg and 13% were HER2+. The odds of having a Tneg tumour were 3-fold higher (95% CI 1.6, 5.5; p = 0.0001) in black compared with white women. Tneg tumours were equally common in black women diagnosed before and after age 50 (31% vs 29%; p = NS), and who were obese and non-obese (29% vs 31%; p = NS). Considering all patients, as BMI increased, the proportion of Tneg tumours decreased (p = 0.08).
Black women of diverse background have 3-fold more Tneg tumours than non-black women, regardless of age and BMI. Other factors must determine tumour subtype. The higher prevalence of Tneg tumours in black women in all age and weight categories likely contributes to black women's unfavorable breast cancer prognosis.
Although preoperative radiation followed by wide local excision yields excellent local control in soft tissue sarcomas, the risk of wound complications is reported to be higher compared with the ...incidence in patients who were administered postoperative radiation therapy. Vacuum (vac)-assisted closure may improve wound healing, but it is unknown whether vac-assisted closure during soft tissue sarcoma resection may reduce the risk of wound complications or impair local disease control.
(1) Does the use of a wound vac application at the time of soft tissue sarcoma resection reduce the risk of developing wound complications after lower extremity sarcoma resection? (2) Is vac-assisted closure associated with an increased risk of local relapse?
From 2000 to 2016, 312 patients with stage I to III soft tissue sarcomas were treated. Of these, 123 were treated with preoperative radiation ± chemotherapy followed by limb-sparing resection based on tumor location, size, grade, histology, and patient age. There was a minimum followup of 12 months. Radiation was delivered generally based on tumor size, grade, superficial versus deep nature, and proximity to neurovascular structures. Chemotherapy was administered in patients < 70 years old with high-grade tumors and tumors > 5 cm. Patient, demographic, and treatment variables, including incisional vac application and wound outcomes, were retrospectively evaluated. Incisional vac-assisted closure took place at the time of primary resection in 32% (46 of 123) of patients. Vac-assisted closure was considered when there was a concern for risk of external contamination such as instances in which fixation of adhesives would be difficult or regions where there was a high risk of contamination. Vac-assisted closure may have also been used in instances with increased wound tension at closure or with heightened concern for shearing on the wound such as buttock wounds. Ten patients were lost to followup, two in the vac group and eight in the non-vac group. Potential factors associated with wound complications were evaluated using Fisher's exact test for univariate analysis and logistic regression for multivariate analysis. Local recurrence-free survival was evaluated using the Kaplan-Meier estimate.
After taking into consideration factors such as tumor size, location, age, and patient comorbidities, it was shown that patients who underwent vac-assisted closure were less likely to experience wound complications compared with patients who did not undergo vac-assisted closure (odds ratio, 0.129; 95% confidence interval CI, 0.041-0.398; p = 0.004). The local control incidence in the entire cohort was 98%. With the numbers available, Kaplan-Meier survivorship free from local recurrence did not differ between patients treated with or without the vac (100% 95% CI, 154.09-154.09 versus 96% 95% CI, 152.21-169.16; p = 0.211), respectively.
Vac-assisted closure at the time of resection of proximal lower extremity soft tissue sarcomas is associated with a lower risk of wound complications, and its use apparently did not compromise local control. We show that the use of vac-assisted closure may be worth considering in surgeons' attempts to reduce the risk of wound complications among patients with soft tissue sarcomas of the proximal lower extremities.
Level III, therapeutic study.
The Antarctic Peninsula is experiencing one of the fastest rates of regional climate change on Earth, resulting in the collapse of ice shelves, the retreat of glaciers and the exposure of new ...terrestrial habitat. In the nearby oceanic system, winter sea ice in the Bellingshausen and Amundsen seas has decreased in extent by 10% per decade, and shortened in seasonal duration. Surface waters have warmed by more than 1 K since the 1950s, and the Circumpolar Deep Water (CDW) of the Antarctic Circumpolar Current has also warmed. Of the changes observed in the marine ecosystem of the western Antarctic Peninsula (WAP) region to date, alterations in winter sea ice dynamics are the most likely to have had a direct impact on the marine fauna, principally through shifts in the extent and timing of habitat for ice-associated biota. Warming of seawater at depths below ca 100 m has yet to reach the levels that are biologically significant. Continued warming, or a change in the frequency of the flooding of CDW onto the WAP continental shelf may, however, induce sublethal effects that influence ecological interactions and hence food-web operation. The best evidence for recent changes in the ecosystem may come from organisms which record aspects of their population dynamics in their skeleton (such as molluscs or brachiopods) or where ecological interactions are preserved (such as in encrusting biota of hard substrata). In addition, a southwards shift of marine isotherms may induce a parallel migration of some taxa similar to that observed on land. The complexity of the Southern Ocean food web and the nonlinear nature of many interactions mean that predictions based on short-term studies of a small number of species are likely to be misleading.
Antarctic coastal surface winds affect ice‐sheet stability, sea ice, and local ecosystems. The strongest coastal winds are especially important due to the nonlinear relationship between wind speed ...and wind stress. We investigate the dynamics of extreme coastal winds using a simplified momentum budget calculated across the period 2010–2020 from the ERA5 reanalysis. The pressure‐gradient forcing term in the budget is decomposed into a large‐scale component and one associated with the temperature deficit layer. The role of budget terms across the coastal sector is compared for weak and strong winds. We then calculate composites of the top 100 easterly wind events across six east Antarctic coastal sectors, identifying terms responsible for the evolution of coastal extremes. A simple balance of terms exists offshore, dominated by large‐scale forcing, contrasting with the complex balance in the onshore sector where katabatic forcing is large. Large‐scale forcing explains 57% of offshore coastal wind‐speed variance overall, improving to 81% when budget terms associated with the temperature deficit layer and horizontal advection are included, with significant regional variation. The residual term plays an increasingly active role as wind speed increases. Extremes in all coastal sectors are associated with a synoptic‐scale transient dipole of pressure anomalies driving warm‐air advection. Although katabatic forcing is a very large term in magnitude, it is found to play a passive role, declining as wind speeds increase during extreme conditions. In some regions, an anomalous southerly component develops during extremes, which we attribute to an ageostrophic barrier wind. This research underscores the major role for large‐scale forcing in Antarctica's coastal winds, but also reveals a significant regional locally driven component. The results have implications for improving numerical model simulations of coastal easterlies and for studying their impacts on ocean circulation, sea ice, and ice‐shelf basal melt.
The strongest winds in coastal Antarctica are important for ocean circulation and sea ice, but the role of local processes such as katabatic winds remains uncertain. We decompose the ERA5 momentum budget to show that composite‐mean extreme wind events in coastal Antarctica are predominantly associated with large‐scale forcing, indicated by the dark orange line. To explain short‐time‐scale variability more generally, other terms accounting for pooling of cold air and katabatic forcing are critical, especially for more moderate winds.
Carbohydrates and glycoproteins modulate key biological functions. However, experimental structure determination of sugar polymers is notoriously difficult. Computational approaches can aid in ...carbohydrate structure prediction, structure determination, and design. In this work, we developed a glycan-modeling algorithm, GlycanTreeModeler , that computationally builds glycans layer-by-layer, using adaptive kernel density estimates (KDE) of common glycan conformations derived from data in the Protein Data Bank (PDB) and from quantum mechanics (QM) calculations. GlycanTreeModeler was benchmarked on a test set of glycan structures of varying lengths, or “trees”. Structures predicted by GlycanTreeModeler agreed with native structures at high accuracy for both de novo modeling and experimental density-guided building. We employed these tools to design de novo glycan trees into a protein nanoparticle vaccine to shield regions of the scaffold from antibody recognition, and experimentally verified shielding. This work will inform glycoprotein model prediction, glycan masking, and further aid computational methods in experimental structure determination and refinement.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Recent ice shelf retreat on the east coast of the Antarctic Peninsula has been principally attributed to atmospherically driven melt. However, previous studies on the largest of these ice ...shelves—Larsen C—have struggled to reconcile atmospheric forcing with observed melt. This study provides the first comprehensive quantification and explanation of the atmospheric drivers of melt across Larsen C, using 31‐months' worth of observations from Cabinet Inlet, a 6‐month, high‐resolution atmospheric model simulation and a novel approach to ascertain the surface energy budget (SEB) regime. The dominant meteorological controls on melt are shown to be the occurrence, strength, and warmth of mountain winds called foehn. At Cabinet Inlet, foehn occurs 15% of the time and causes 45% of melt. The primary effect of foehn on the SEB is elevated turbulent heat fluxes. Under typical, warm foehn conditions, this means elevated surface heating and melting, the intensity of which increases as foehn wind speed increases. Less commonly—due to cooler‐than‐normal foehn winds and/or radiatively warmed ice—the relationship between wind speed and net surface heat flux reverses. This explains the seemingly contradictory results of previous studies. In the model, spatial variability in cumulative melt across Larsen C is largely explained by foehn, with melt maxima in inlets reflecting maxima in foehn wind strength. However, most accumulated melt (58%) occurs due to solar radiation in the absence of foehn. A broad north‐south gradient in melt is explained by the combined influence of foehn and non‐foehn conditions.
Plain Language Summary
The recent rapid retreat and collapse of ice shelves on the east coast of the Antarctic Peninsula is known to be primarily a result of enhanced surface melt due to climate warming and changing atmospheric circulation patterns. However, previous studies have struggled to reconcile observed melt patterns with meteorological conditions. Here we provide the first quantification and explanation of the atmospheric drivers of melt across Larsen C, the largest ice shelf on the Antarctic Peninsula. We find that variability in melt across Larsen C is primarily governed by mountain winds known as foehn, with melt maxima in ice shelf inlets coinciding with the strongest foehn winds. Foehn air is usually much warmer than the ice below, resulting in elevated heating and melting of the ice, the intensity of which increases with increasing wind speed. However, in rare cases where the foehn air is not significantly warmer than the ice, the relationship between melt and foehn wind speed reverses, which explains the seemingly contradictory results of previous studies. While foehn causes the highest melt rates, non‐foehn‐driven melt is more common and, via summertime solar heating, is responsible for most of the accumulation of melt across the ice shelf as a whole.
Key Points
Spatial variability and maxima in Larsen C melt are chiefly due to foehn‐driven sensible heating, though most melt is due to solar radiation
Low static stability reverses the usual positive correlation between melt and foehn wind speed, explaining conflicting results in previous studies
A high‐resolution atmospheric model capably reproduces melt patterns across Larsen C but has notable biases in the surface radiative fluxes
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