2,669 research outputs found
On the timing and mechanism of millennial-scale climate variability during the last glacial cycle
No full textThe demonstration that natural climate variability during the last glacial cycle shifted rapidly between remarkable extremes has dramatically revised the understanding of climate change. To further advance our understanding, research continues into the timings, geographic distribution, and nature of the millennial-scale climate extremes, and into the mechanisms for intra-
and inter-hemispheric transmission of variability through the climate/ocean system. Complementing the traditional definition of the timings of millennial-scale climate variability from ice-core d18O records, we here further narrow down the temporal constraints by determining statistically significant anomalies in the major ion series of the GISP2 ice core. This exercise offers an objective definition of the timing of climatic anomalies in Northern Hemisphere palaeoclimate proxy records of the last 110,000 years that significantly improves the potential for inter-calibration of ‘ice-core tuned’ chronostratigraphies. We then present a process-oriented synthesis of proxy records from the Northern Hemisphere. This leads to a conclusion that the Dansgaard-Oeschger (D-O) style fluctuations in these records are (virtually) in phase, since all fall within a clear (atmospheric) pattern of concerted relative dominance shifts between polar/westerly dominated winter-type conditions and tropical/monsoon dominated summer-type conditions. Finally, we speculate on a monsoon-related mechanism that could help explain the anomalously long duration of D-O interstadials 12, 8, and 1, which coincided with cooling trends in Antarctic records
Holocene climate variability in the eastern Mediterranean, and the end of the Bronze Age
No full textHolocene atmosphere-ocean interactions: records from Greenland and the Aegean Sea
No full textWe compare paleoclimate proxy records from central Greenland and the Aegean Sea to offer new insights into the causes, timing, and mechanisms of Holocene atmosphere-ocean interactions. A direct atmospheric link is revealed between Aegean sea surface temperature (SST) and high-latitude climate. The major Holocene events in our proxies of Aegean SST and winter/spring intensity of the Siberian High (GISP2 K+ record) follow an 2300 year spacing, recognised also in the D14C record and in worldwide Holocene glacier advance phases, suggesting a solar modulation of climate.
We argue that the primary atmospheric response involved decadal-centennial fluctuations in the meridional pressure gradient, driving Aegean SST events via changes in the strength, duration, and/or frequency of northerly polar/continental air outbreaks over the basin. The observed natural variability should be accounted for in predictions of future climate change, and our timeframe for the Aegean climate events in addition provides an independent chronostratigraphic argument to Middle Eastern archaeological studies
Holocene climate variability (abstract of paper presented at AGU Fall Meeting, San Francisco, 8-12 Dec 2003)
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A New Multielement Method for LA-ICP-MS Data Acquisition from Glacier Ice Cores
No full textTo answer pressing new research questions about the rate and timing of abrupt climate transitions, a robust system for ultrahigh-resolution sampling of glacier ice is needed. Here, we present a multielement method of LA-ICP-MS analysis wherein an array of chemical elements is simultaneously measured from the same ablation area. Although multielement techniques are commonplace for high-concentration materials, prior to the development of this method, all LA-ICP-MS analyses of glacier ice involved a single element per ablation pass or spot. This new method, developed using the LA-ICP-MS system at the W. M. Keck Laser Ice Facility at the University of Maine Climate Change Institute, has already been used to shed light on our flawed understanding of natural levels of Pb in Earth's atmosphere
Ice core derived changes in Black Carbon concentrations, 15th ETH-Conference on Combustion Generated Nanoparticles, Zurich, Switzerland, 26.-29.6.2011
No full textSimple drag prediction strategies for an Autonomous Underwater Vehicle’s hull shape
No full textThe range of an AUV is dictated by its finite energy source and minimising the energy consumption is required to maximise its endurance. One option to extend the endurance is by obtaining the optimum hydrodynamic hull shape with balancing the trade-off between computational cost and fluid dynamic fidelity. An AUV hull form has been optimised to obtain low resistance hull. Hydrodynamic optimisation of hull form has been carried out by employing five parametric geometry models with a streamlined constraint. Three Genetic Algorithm optimisation procedures are applied by three simple drag predictions which are based on the potential flow method. The results highlight the effectiveness of considering the proposed hull shape optimisation procedure for the early stage of AUV hull desig
THE CORRELATION OF THE MEDIEVAL EUROPEAN STATE AND LAW IN THE DOCTRINE OF P.A. KROPOTKIN
No full textThe actual task of Russian state studies and jurisprudence remains the opposition to the ideological and theoretical constructions of Russian classical anarchism. Purpose: to establish the most significant features and disadvantages of P.A. Kropotkin’s interpretation of the correlation of state and law on the example of Medieval Europe. When writing the article, the author applies interdisciplinary and class approaches. General scientific and specific scientific methods are used: historical, problem-theoretical, formal-logical, textual. Materials: monuments of law, other historical sources, foreign and national historiography. The analysis shows that P.A. Kropotkin’s works are characterised not only by a pronounced anti-exploitation pathos, but also by an equally pronounced tendentiousness. Results: aprioriism, anti-statism and antilegism, radical localism, Eurocentrism, diffusionism, cyclism and catastrophism, clothed in the form of postulates, predetermined P.A. Kropotkin’s one-sided interpretations of the interaction of the medieval European state with positive and customary law. In the first case, it took a purely causative form, and in the second, it was predominantly conflictual. These are the key flaws of P.A. Kropotkin’s correlation concept
Analysis of Historical and Projected Future Climate of Mali, West African Sahel
No full textThe West African country of Mali experienced devastating drought from the late 1960s to the mid 1980s, followed by partial rainfall recovery that remains below pre-1960s climatology. Here, we examine the historical and projected temperature and rainfall variability across the Malian Sahel in an effort to assist future planning for food security. Particular emphasis is placed on clarifying the teleconnection between sea-surface temperatures (SST) expressed by the Atlantic Multidecadal Oscillation (AMO) and the West African monsoon (WAM). Using gridded observations and reanalysis, we show that cool/wet (1950-1967) and warm/dry (1980-1997) end-member climates over Mali correspond to warm and cool phases of the AMO, respectively, with associated atmospheric patterns consistent with negative (slow winds, shallow poleward pressure gradient) and positive (fast winds, steep poleward gradient) modes of the North Atlantic Oscillation (NAO). These opposing climate regimes (AMO-warm/NAO-negative and AMO-cool/NAO-positive) are coupled to strength of the Sahara Low and latitudinal position of the Intertropical Convergence Zone (ITCZ), thereby accounting for changes in strength of the WAM. A case is made that multi-decade North Atlantic SST variability arises naturally from volcanic forcing and resultant changes in strength and position of the westerly winds. However, greenhouse-gas warming, stratospheric ozone depletion, and Arctic sea-ice loss is likely modifying the system behavior. In an examination of CMIP5 general circulation model (GCM) output for Mali, we find that temperature and precipitation in historical simulations fail to validate against observations, and notably do not show multi-decade variability. Atmospheric circulation across the North Atlantic is furthermore anomalously strong in CMIP5 due to an unrealistically steep pressure gradient between Azores and Iceland. These shortcomings undermine the fidelity and meaning of CMIP5 future rainfall projections across the western Sahel. We conclude here that downscale studies should target reanalysis, and investigate extreme years (e.g., cool/wet or hot/dry) as future climate analogs rather than depend on CMIP5. In all from this work, we suggest five plausible future climate scenarios for 2030-2050: 1) standard CMIP5 projection of 2 °C warming with slight rainfall decline; 2) Warming > 1 °C with rainfall remaining at present norm, or increasingly slightly due to poleward displacement of the ITCZ; 3) Warming > 1 °C with diminished rainfall or drought from southward displacement of the ITCZ; 4) Warming > 1 °C with onset of severe drought arising from renewal of high volcanic activity, and subsequent development of strong NAO-positive circulation and cool-AMO sea-surface temperature distribution; 5) Abrupt climate shift in response to collapse of summer Arctic sea ice, wherein any of the scenarios above could develop within a decade
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