The Last Glacial Termination Denton, G. H.; Anderson, R. F.; Toggweiler, J. R. ...
Science (American Association for the Advancement of Science),
06/2010, Letnik:
328, Številka:
5986
Journal Article
Recenzirano
A major puzzle of paleoclimatology is why, after a long interval of cooling climate, each late Quaternary ice age ended with a relatively short warming leg called a termination. We here offer a ...comprehensive hypothesis of how Earth emerged from the last global ice age. A prerequisite was the growth of very large Northern Hemisphere ice sheets, whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation. The Southern Hemisphere westerlies shifted poleward during each northern stadial, producing pulses of ocean upwelling and warming that together accounted for much of the termination in the Southern Ocean and Antarctica. Rising atmospheric CO₂ during southern upwelling pulses augmented warming during the last termination in both polar hemispheres.
Twenty one differences between CME‐driven geomagnetic storms and CIR‐driven geomagnetic storms are tabulated. (CME‐driven includes driving by CME sheaths, by magnetic clouds, and by ejecta; ...CIR‐driven includes driving by the associated recurring high‐speed streams.) These differences involve the bow shock, the magnetosheath, the radiation belts, the ring current, the aurora, the Earth's plasma sheet, magnetospheric convection, ULF pulsations, spacecraft charging in the magnetosphere, and the saturation of the polar cap potential. CME‐driven storms are brief, have denser plasma sheets, have strong ring currents and Dst, have solar energetic particle events, and can produce great auroras and dangerous geomagnetically induced currents; CIR‐driven storms are of longer duration, have hotter plasmas and stronger spacecraft charging, and produce high fluxes of relativistic electrons. Further, the magnetosphere is more likely to be preconditioned with dense plasmas prior to CIR‐driven storms than it is prior to CME‐driven storms. CME‐driven storms pose more of a problem for Earth‐based electrical systems; CIR‐driven storms pose more of a problem for space‐based assets.
Ice Age Terminations Cheng, Hai; Edwards, R. Lawrence; Broecker, Wallace S ...
Science (American Association for the Advancement of Science),
10/2009, Letnik:
326, Številka:
5950
Journal Article
Recenzirano
²³⁰Th-dated oxygen isotope records of stalagmites from Sanbao Cave, China, characterize Asian Monsoon (AM) precipitation through the ends of the third- and fourthmost recent ice ages. As a result, AM ...records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments, establishing the timing and sequence of major events. In all four cases, observations are consistent with a classic Northern Hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets. Meltwater and icebergs entering the North Atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon, causing increases in atmospheric CO₂ and Antarctic temperatures that drive the termination in the Southern Hemisphere. Increasing CO₂ and summer insolation drive recession of northern ice sheets, with probable positive feedbacks between sea level and CO₂.
Here we report a palladium‐catalysed difunctionalisation of unsaturated C−C bonds with acid chlorides. Formally, the C−COCl bond of an acid chloride is cleaved and added, with complete atom economy, ...across either strained alkenes or a tethered alkyne to generate new acid chlorides. The transformation does not require exogenous carbon monoxide, operates under mild conditions, shows a good functional group tolerance, and gives the isolated products with excellent stereoselectivity. The intermolecular reaction tolerates both aryl‐ and alkenyl‐substituted acid chlorides and is successful when carboxylic acids are transformed to the acid chloride in situ. The reaction also shows an example of temperature‐dependent stereodivergence which, together with plausible mechanistic pathways, is investigated by DFT calculations. Moreover, we show that benzofurans can be formed in an intramolecular variant of the reaction. Finally, derivatisation of the products from the intermolecular reaction provides a highly stereoselective approach for the synthesis of tetrasubstituted cyclopentanes.
Using a catalytic system comprised of Pd and Xantphos, acid chlorides can be added across strained alkenes or tethered alkynes to form two new C−C bonds via formal C−COCl cleavage. This reaction allows for a dicarbofunctionalisation in which an acid chloride group is retained in the product. DFT studies are used to rationalise a plausible pathway, while product derivatisation highlights the synthetic utility of the method.
Electromagnetic ion cyclotron (EMIC) waves can act as a loss process for both ring current ions and radiation belt electrons, and the spatial and temporal characteristics of these waves are important ...for quantifying their effects on energetic particles. Here we utilize observations from multiple spacecraft to constrain the azimuthal and radial dimensions as well as the duration of an EMIC wave event occurring on the nightside of the inner magnetosphere on 7 July 2013. These combined observations reveal waves limited to a narrow radial extent but persisting ~10+ hr and spanning ~12 hr in local time. The solar wind conditions, geomagnetic activity, and plasma environment are also examined to better understand the conditions under which persistent nightside EMIC waves can occur. Relativistic electron phase space density profiles during this event reveal local minima concurrent with the wave activity, consistent with EMIC‐driven scattering and loss of radiation belt electrons.
Plain Language Summary
Various oscillating electric and magnetic fields, or waves, can interact with high‐energy particles in near‐Earth space and cause a change in the particles' energy and/or direction of motion. Where and when these waves occur can have a significant impact on how they interact with particles. Here we combine measurements from multiple spacecraft around the Earth to study one specific wave mode. While these waves are often thought to be localized and of short durations, we observe an event on 7 July 2013 where waves persist for over 10 hr and span the entire nightside of the Earth. We explore the dynamics of the Earth's magnetic field, in response to activity on the Sun, to better understand what causes these widespread, long‐lasting waves. Changes in the energetic particle environment around the Earth are also presented to examine the effects of these waves. Events like these have the potential to cause significant effects in the particle populations around the Earth.
Key Points
Sustained, azimuthally extended EMIC waves are observed spanning the nightside of the inner magnetosphere on 7 July 2013
Wave structure lies at the inner edge of the plasma sheet overlaping the outer plasmasphere and plumes following enhanced Kp activity
Local minima in phase space density are observed concurrent with wave activity, consistent with EMIC‐driven MeV electron scattering
We present observations of the radiation belts from the Helium Oxygen Proton Electron and Magnetic Electron Ion Spectrometer particle detectors on the Van Allen Probes satellites that illustrate the ...energy dependence and L shell dependence of radiation belt enhancements and decays. We survey events in 2013 and analyze an event on 1 March in more detail. The observations show the following: (a) at all L shells, lower energy electrons are enhanced more often than higher energies; (b) events that fill the slot region are more common at lower energies; (c) enhancements of electrons in the inner zone are more common at lower energies; and (d) even when events do not fully fill the slot region, enhancements at lower energies tend to extend to lower L shells than higher energies. During enhancement events the outer zone extends to lower L shells at lower energies while being confined to higher L shells at higher energies. The inner zone shows the opposite with an outer boundary at higher L shells for lower energies. Both boundaries are nearly straight in log(energy) versus L shell space. At energies below a few 100 keV, radiation belt electron penetration through the slot region into the inner zone is commonplace, but the number and frequency of “slot filling” events decreases with increasing energy. The inner zone is enhanced only at energies that penetrate through the slot. Energy‐ and L shell‐dependent losses (that are consistent with whistler hiss interactions) return the belts to more quiescent conditions.
Key Points
Radiation belt dynamics are a strong function of energy and L shell
Events that fill the slot region are common at lower energies and rare at higher energies
During enhancement events different energies are enhanced in different spatial regions
Section Errors Corrections Abstract A random effects meta-analysis indicated that physical activity interventions with feedback provision were more effective than physical activity interventions ...without feedback (d = 0.73, 95% CI 0.09;1.37) A random effects meta-analysis indicated that physical activity interventions with feedback provision were more effective than physical activity interventions without feedback (d = 0.29, 95% CI 0.16;0.43) Data extraction and synthesis In addition, a meta-analysis was conducted if at least three studies using similar manipulations and reporting on the same outcome provided data on group means and standard deviations that could be used to calculate Cohen’s d 31 In addition, a meta-analysis was conducted if at least three studies using similar manipulations and reporting on the same outcome provided data on group means and standard deviations or standard errors that could be used to calculate Cohen’s d 31 Impact of feedback provision The meta-analysis yielded a statistically significant pooled effect size of Cohen’s d = 0.73, 95% CI 0.09; 1.37 (test for overall effect: Z = 2.23, p = 0.026; see Fig. 2). Correction Open access Published:23 February 2024 Correction: Impact of feedback generation and presentation on self-monitoring behaviors, dietary intake, physical activity, and weight: a systematic review and meta-analysis Rebecca A. Krukowski 1, Andrea H. Denton2 & Laura M. König3,4 International Journal of Behavioral Nutrition and Physical Activity volume 21, Article number: 20 (2024) Cite this article 431 Accesses 1 Altmetric Metrics details The Original Article was published on 04 January 2024 Correction: Int J Behav Nutr Phys Act 21, 3 (2024) https://doi.org/10.1186/s12966-023-01555-6 Following the publication of the original article 1, the authors reported they made an error in using two standard errors instead of standard deviations in their meta-analysis calculations. Section Errors Corrections Abstract A random effects meta-analysis indicated that physical activity interventions with feedback provision were more effective than physical activity interventions without feedback (d = 0.73, 95% CI 0.09;1.37) A random effects meta-analysis indicated that physical activity interventions with feedback provision were more effective than physical activity interventions without feedback (d = 0.29, 95% CI 0.16;0.43) Data extraction and synthesis In addition, a meta-analysis was conducted if at least three studies using similar manipulations and reporting on the same outcome provided data on group means and standard deviations that could be used to calculate Cohen’s d 31 In addition, a meta-analysis was conducted if at least three studies using similar manipulations and reporting on the same outcome provided data on group means and standard deviations or standard errors that could be used to calculate Cohen’s d 31 Impact of feedback provision The meta-analysis yielded a statistically significant pooled effect size of Cohen’s d = 0.73, 95% CI 0.09; 1.37 (test for overall effect: Z = 2.23, p = 0.026; see Fig. 2).
The termination of the last ice age featured a major reconfiguration of Earthʼs climate and cryosphere, yet the underlying causes of these massive changes continue to be debated. Documenting the ...spatial and temporal variations of atmospheric temperature during deglaciation can help discriminate among potential drivers. Here, we present a 10Be surface-exposure chronology and glaciological reconstruction of ice recession following the Last Glacial Maximum (LGM) in the Rakaia valley, Southern Alps of New Zealand. Innermost LGM moraines at Big Ben have an age of 17,840 ± 240 yrs, whereas ice-marginal moraines or ice-molded bedrock surfaces at distances up-valley from Big Ben of 12.5 km (Lake Coleridge), ∼25 km (Castle Hill), ∼28 km (Double Hill), ∼43 km (Prospect Hill), and ∼58 km (Reischek knob) have ages of 17,020 ± 70 yrs, 17,100 ± 110 yrs, 16,960 ± 370 yrs, 16,250 ± 340 yrs, and 15,660 ± 160 yrs, respectively. These results indicate extensive recession of the Rakaia glacier, which we attribute primarily to the effects of climatic warming. In conjunction with geomorphological maps and a glaciological reconstruction for the Rakaia valley, we use our chronology to infer timing and magnitude of past atmospheric temperature changes. Compared to an overall temperature rise of ∼4.65 °C between the end of the LGM and the start of the Holocene, the glacier recession between ∼17,840 and ∼15,660 yrs ago is attributable to a net temperature increase of ∼4.0 °C (from −6.25 to −2.25 °C), accounting for ∼86% of the overall warming. Approximately 3.75 °C (∼70%) of the warming occurred between ∼17,840 and ∼16,250 yrs ago, with a further 0.75 °C (∼16%) increase between ∼16,250 and ∼15,660 yrs ago. A sustained southward shift of the Subtropical Front (STF) south of Australia between ∼17,800 and ∼16,000 yrs ago coincides with the warming over the Rakaia valley, and suggests a close link between Southern Ocean frontal boundary positions and southern mid-latitude climate. Most of the deglacial warming in the Southern Alps occurred during the early part of Heinrich Stadial 1 (HS1) of the North Atlantic region. Because the STF is associated with the position of the westerly wind belt, our findings support the concept that a southward shift of Earthʼs wind belts accompanied the early part of HS1 cooling in the North Atlantic, leading to warming and deglaciation in southern middle latitudes.
•Record of last deglaciation from the Rakaia valley, Southern Alps, New Zealand.•Extensive glacier recession between 17,840 and 15,660 yrs ago.•Atmospheric warming of 4 °C drove ice retreat.•Southern mid-latitude warming and glacier recession coeval with Heinrich Stadial 1.
Self-monitoring of dietary intake, physical activity, and weight is a key strategy in behavioral interventions, and some interventions provide self-monitoring feedback to facilitate goal setting and ...promote engagement. This systematic review aimed to evaluate whether feedback increases intervention effectiveness, and which forms of feedback presentation (e.g., personalized vs. not personalized) and generation (i.e., human vs. algorithm-generated) are most effective. To achieve this aim, 5 electronic databases (PubMed/MEDLINE, Web of Science, CINAHL, PsycINFO, and Google Scholar) were searched in April 2022 and yielded 694 unique records, out of which 24 articles reporting on 19 studies were included (with a total of 3261 participants). Two reviewers independently screened titles and abstracts and then full texts and categorized articles as eligible or excluded according to the pre-registered criteria (i.e., availability of full text, peer reviewed manuscript in English; adult participants in a randomized controlled trial that included both self-monitoring and feedback; comparisons of different forms of feedback or comparisons of feedback vs. no feedback; primary outcomes of diet, physical activity, self-monitoring behavior, and/or weight). All included studies were assessed for methodological quality independently by two reviewers using the revised Cochrane risk-of-bias tool for randomized studies (version 2). Ten studies compared feedback to no feedback, 5 compared human- vs. algorithm-generated feedback, and the remaining 4 studies compared formats of feedback presentation (e.g., frequency, richness). A random effects meta-analysis indicated that physical activity interventions with feedback provision were more effective than physical activity interventions without feedback (d = 0.73, 95% CI 0.09;1.37). No meta-analysis could be conducted for other comparisons due to heterogeneity of study designs and outcomes. There were mixed results regarding which form of feedback generation and presentation is superior. Limitations of the evidence included in this review were: lack of details about feedback provided, the brevity of most interventions, the exclusion of studies that did not isolate feedback when testing intervention packages, and the high risk of bias in many studies. This systematic review underlines the importance of including feedback in behavioral interventions; however, more research is needed to identify most effective forms of feedback generation and presentation to maximize intervention effectiveness.Trial registration (PROSPERO)CRD42022316206.
The properties of plasmaspheric drainage plumes are examined using cold‐plasma measurements in geosynchronous orbit. During high‐speed stream‐driven storms, 210 plume crossings are collected and ...statistically analyzed. Plumes that persist for 4 days are common, which was the duration of our search. Plumes weaken with age, becoming narrower in local time with plasma that becomes less dense. Cold‐plasma flow velocities are sunward in the plumes, with flow speeds decreasing as the storms progress. Plumes transfer typically 2 × 1026 ions/sec (1.2 ton/hr of protons) when they are young, and the rate of transport decreases with plume age. A total of approximately 2 × 1031 ions (34 tons of protons) are transported via plumes in the life of a storm. About half of the outer plasmasphere is drained in the first 20 hours of a storm. Large density fluctuations in the plumes indicate that the drainage plumes are lumpy, and large velocity fluctuations of the plasma flow indicate that the drainage plumes may be turbulent. Because of their persistence, drainage plumes are anticipated to be a regular feature of any ongoing geomagnetic storm.
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