390 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
Temperature and mineral dust variability recorded in two low-accumulation Alpine ice cores over the last millennium
No full textAmong ice core drilling sites in the European Alps, Colle Gnifetti (CG) is the only non-temperate glacier to offer climate records dating back at least 1000 years. This unique long-term archive is the result of an exceptionally low net accumulation driven by wind erosion and rapid annual layer thinning. However, the full exploitation of the CG time series has been hampered by considerable dating uncertainties and the seasonal summer bias in snow preservation. Using a new core drilled in 2013 we extend annual layer counting, for the first time at CG, over the last 1000 years and add additional constraints to the resulting age scale from radiocarbon dating. Based on this improved age scale, and using a multi-core approach with a neighbouring ice core, we explore the time series of stable water isotopes and the mineral dust proxies Ca2+ and insoluble particles. Also in our latest ice core we face the already known limitation to the quantitative use of the stable isotope variability based on a high and potentially non-stationary isotope/temperature sensitivity at CG. Decadal trends in Ca2+ reveal substantial agreement with instrumental temperature and are explored here as a potential site-specific supplement to the isotope-based temperature reconstruction. The observed coupling between temperature and Ca2+ trends likely results from snow preservation effects and the advection of dust-rich air masses coinciding with warm temperatures. We find that if calibrated against instrumental data, the Ca2+-based temperature reconstruction is in robust agreement with the latest proxy-based summer temperature reconstruction, including a "Little Ice Age" cold period as well as a medieval climate anomaly. Part of the medieval climate period around AD 1100-1200 clearly stands out through an increased occurrence of dust events, potentially resulting from a relative increase in meridional flow and/or dry conditions over the Mediterranean
Twin Ice Cores from Greenland Reveal History of Climate Change, More
No full textTwo projects conducted from 1989 to 1993 collected parallel ice cores—just 30 km apart— from the central part of the Greenland ice sheet. Each core is more than 3 km deep and extends back 110,000 years. In short, the ice cores tell a clear story: humans came of age agriculturally and industrially during the most stable climatic regime recorded in the cores. Change—large, rapid, and global—is more characteristic of the Earth\u27s climate than is stasis
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
Ground-penetrating radar reveals ice thickness and undisturbed englacial layers at Kilimanjaro's Northern Ice Field
No full textAlthough its Holocene glacier history is still subject to debate, the ongoing iconic decline of Kilimanjaro's largest remaining ice body, the Northern Ice Field (NIF), has been documented extensively based on surface and photogrammetric measurements. The study presented here adds, for the first time, ground-penetrating radar (GPR) data at centre frequencies of 100 and 200 MHz to investigate bed topography, ice thickness and internal stratigraphy at NIF. The direct comparison of the GPR signal to the visible glacier stratigraphy at NIF's vertical walls is used to validate ice thickness and reveals that the major internal reflections seen by GPR can be associated with dust layers. Internal reflections can be traced consistently within our 200 MHz profiles, indicating an uninterrupted, spatially coherent internal layering within NIF's central flat area. We show that, at least for the upper 30 m, it is possible to follow isochrone layers between two former NIF ice core drilling sites and a sampling site on NIF's vertical wall. As a result, these isochrone layers provide constraints for future attempts at linking age-depth information obtained from multiple locations at NIF. The GPR profiles reveal an ice thickness ranging between (6.1 ± 0.5) and (53.5 ± 1.0) m. Combining these data with a very high resolution digital elevation model we spatially extrapolate ice thickness and give an estimate of the total ice volume remaining at NIF's southern portion as (12.0 ± 0.3) × 106 m3
Possible Icelandic Tephra Found in European Colle Gnifetti Glacier
No full textVolcanic ash (tephra) provides unique time markers (isochrons) that are often used as an independent age-control tool for stratigraphic correlations of paleoclimate archives from ice cores. However, little credence has been given to the notion of finding tephra in ice cores collected in the European Alps because of the relatively large distance from volcanic sources and the presumed nature of regional atmospheric circulation patterns. We filtered particles from melted ice core drilling chips gathered roughly every meter during a 2013 drilling operation at Colle Gnifetti glacier in the Swiss-Italian Alps (45°55.74′N, 7°52.58′E, 4450 m asl). One filter, preliminarily dated to the nineteenth century by annual layer counting, contained a group of six visually similar tephra particles. Analyzing their chemistry using a scanning electron microscope equipped with an energy-dispersive x-ray spectrometer established that the six particles were volcanic in origin and are very similar in composition (a distinctive geochemical signature), pointing to a single volcanic eruption source. We proposed that one of several massive nineteenth century Eastern Icelandic eruptions is a potential source given eruption timing, size, tephra dispersion area, and similarities in chemical composition. This first finding of tephra in an Alpine ice core contributes to a regional tephrochronological framework that can be adapted for future correlation among different paleoclimate sequences
The Role of Historical Context in Understanding Past Climate, Pollution and Health Data in Trans-disciplinary Studies: Reply to Comments on More et al., 2017
No full textUnderstanding the context from which evidence emerges is of paramount importance in reaching robust conclusions in scientific inquiries. This is as true of the present as it is of the past. In a trans-disciplinary study such as More et al. (2017, https://doi.org/10.1002/2017GH000064) and many others appearing in this and similar journals, a proper analysis of context demands the use of historical evidence. This includes demographic, epidemiological, and socio-economic data—common in many studies of the impact of anthropogenic pollution on human health—and, as in this specific case, also geoarchaeological evidence. These records anchor climate and pollution data in the geographic and human circumstances of history, without which we lose a fundamental understanding of the data itself. This article addresses Hinkley (2018, https://doi.org/10.1002/2018GH000105) by highlighting the importance of context, focusing on the historical and archaeological evidence, and then discussing atmospheric deposition and circulation in the specific region of our study. Since many of the assertions in Bindler (2018, https://doi.org/10.1002/2018GH000135) are congruent with our findings and directly contradict Hinkley (2018), this reply refers to Bindler (2018), whenever appropriate, and indicates where our evidence diverges
Review of Science in the snow: fifty years of international collaboration through the Scientific Committee on Antarctic Research, by David W.H. Walton & Peter D. Clarkson
No full textD. Walton and P. Clarkson present a history of the last 50 years of international collaborations stimulated by the presence and flexibility inherent in the Scientific Committee on Antarctic Research (SCAR) in their new book Science in the snow. As aptly portrayed in the acknowledgements that precede the book, SCAR has been both an important umbrella for drawing attention to the Antarctic and a virtual and real (meeting rooms to pubs) venue for Antarctic scientists to discuss their scientific findings, their experiences, and their dreams for understanding a place that - with the exception of the impact of iconic expeditions of the early explorers - was barely on the world’s collective mind until about 50 years ago.(Published: 3 September 2012)Citation: Polar Research 2012, 31, 19275, http://dx.doi.org/10.3402/polar.v31i0.1927
Paleoclimatic Variability Inferred from the Spectral Analysis of Greenland and Antarctic Ice-Core Data
No full textPaleoclimate variations occur at various time scales, between a few centuries for the Heinrich events and several hundreds of millenia for the glacial to interglacial variations. The recent ice cores from Greenland (Greenland Ice Core Project and Greenland Ice Sheet Project 2) and Antarctica (Vostok) span at least one glacial oscillation and provide many opportunities to investigate climate variations with a very fine resolution. The joint study of cores from both hemispheres allows us to distinguish between the sources of variability and helps to propose mechanisms of variations for the different time scales involved. The climate proxies we analyze are inferred from δ18O and δD for temperature and chemical species (such as calcium) for the joint behavior of the major ions in the atmosphere, which yield an estimate of the polar circulation index. Those data provide time series of climatic variables from which we extract the information on the dynamics of the underlying system. We used several independent spectral analysis techniques, to reduce the possibility of spurious results. Those methods encompass the multitaper spectral analysis, singular-spectrum analysis, maximum entropy method, principal component analysis, minimum bias spectral estimates, and digital filter reconstructions. Our results show some differences between the two hemispheres in the slow variability associated with the astronomical forcing. Common features found in the three ice-core records occur on shorter periods, between 1 and 7 kyr. The Holocene also shows recurrent common patterns between Greenland and Antarctica. We propose and discuss mechanisms to explain such behavior
Rövid távú koraholocén (8200 év) klímafluktuációk vegetációra gyakorolt hatása a Déli-Kárpátok Retyezát hegységben
No full textA holocén a negyedidőszak utolsó interglaciális szakasza, mely ~11 600 évvel ezelőtt1 kezdődött és napjainkban is tart (Mayewski, P. A. et al. 2004). Kimutatható, hogy a holocén korai szakasza (11 600-7000 évek között) instabil, éghajlati változásokban gazdagabb, mint a holocén későbbi része (Magny, M. et al. 2007). A rövidebb időszakot, rendszerint pár száz évet felölelő klímaingadozások (rapid climate change events, RCC) a holocén egészében kimutathatók, és kb. 6000 évtől gyakoriságuk növekszik (Mayewski, P. A. et al. 2004). Különös jelentőséggel bír a 8200 évvel ezelőtt bekövetkezett, rövid ideig tartó klímakilengés, mely az egyetlen, ami a grönlandi jégfúrások oxigénizotóp-arány görbéjében (δ18O) is markáns csökkenésként (1. ábra) jelentkezik (Rasmussen, S. O. et al. 2006, Rasmussen, S. O. et al. 2007, Tinner, W.–Lotter, A. F. 2001, Weninger, B. et al. 2006, Vinther, B. M. et al. 2006, Thomas, E. R. et al. 2007, Young, N. E. et al. 2012)
- …
