Abstract For the first time, we present a decadal-scale stable isotope record (δ 18 O, δ 13 C) of 67 speleothem calcite samples coming from an artificial tunnel network located in Graz, Austria. Stable isotope data are interpreted with the help of time series (TS) analysis of mean air temperatures (MAT) and mean annual precipitations (MAP) that have been monitored and recorded in a neighbouring meteorological station. Speleothem records have proved to be very useful in reconstructing changes of environmental conditions. For studied stalagmites, which grew between 1945 and 2018, the δ 18 O values average −18.64‰ and range from −23‰ to −17‰ (VPDB, Vienna Pee Dee Belemnite), suggesting variable climatic conditions. The δ 18 O values of calcite increase along the growth axis and are correlated with high temporal resolution MAT, MAP and weighted mean annual δ 18 O of precipitations. For the same time interval, while the temperature TS show an increasing trend, with a steeper gradient since the 1980s, the precipitation TS presents a weak decreasing tendency. Increase in the δ 13 C values of speleothems from −33‰ to −24‰ (VPDB) is correlated with increasing temperature and drought, associated CO 2 degassing and soil erosion over the tunnel system.

ABSTRACT This paper summarizes the hydrological variability in eastern California (central Sierra Nevada) for the past 3000 yr based on three distinct paleoclimate proxies, δ 18 O, total inorganic carbon (TIC), and magnetic susceptibility (chi). These proxies, which are recorded in lake sediments of Pyramid Lake and Walker Lake, Nevada, and Mono Lake and Owens Lake, California, indicate lake-level changes that are mostly due to variations in Sierra Nevada snowpack and rainfall. We evaluated lake-level changes in the four Great Basin lake systems with regard to sediment-core locations and lake-basin morphologies, to the extent that these two factors influence the paleoclimate proxy records. We documented the strengths and weaknesses of each proxy and argue that a systematic study of all three proxies together significantly enhances our ability to characterize the regional pattern, chronology, and resolution of hydrological variability. We used paleomagnetic secular variation (PSV) to develop paleomagnetic chronostratigraphies for all four lakes. We previously published PSV records for three of the lakes (Mono, Owens, Pyramid) and developed a new PSV record herein for Walker Lake. We show that our PSV chronostratigraphies are almost identical to previously established radiocarbon-based chronologies, but that there are differences of 20–200 yr in individual age records. In addition, we used eight of the PSV inclination features to provide isochrons that permit exacting correlations between lake records. We also evaluated the temporal resolution of our proxies. Most can document decadal-scale variability over the past 1000 yr, multidecadal-scale variability for the past 2000 yr, and centennial-scale variability between 2000 and 3000 yr ago. Comparisons among our proxies show a strong coherence in the pattern of lake-level variability for all four lakes. Pyramid Lake and Walker Lake have the longest and highest-resolution records. The δ 18 O and TIC records yield the same pattern of lake-level variability; however, TIC may allow a somewhat higher-frequency resolution. It is not clear, however, which proxy best estimates the absolute amplitude of lake-level variability. Chi is the only available proxy that records lake-level variability in all four lakes prior to 2000 yr ago, and it shows consistent evidence of a large multicentennial period of drought. TIC, chi, and δ 18 O are integrative proxies in that they display the cumulative record of hydrologic variability in each lake basin. Tree-ring estimations of hydrological variability, by contrast, are incremental proxies that estimate annual variability. We compared our integrated proxies with tree-ring incremental proxies and found a strong correspondence among the two groups of proxies if the tree-ring proxies are smoothed to decadal or multidecadal averages. Together, these results indicate a common pattern of wet/dry variability in California (Sierra Nevada snowpack/rainfall) extending from a few years (notable only in the tree-ring data) to perhaps 1000 yr. Notable hydrologic variability has occurred at all time scales and should continue into the future.

ABSTRACT Global warming and ice melting in the “tripolar” regions, namely, Antarctica, the Arctic, and the Tibetan Plateau, might lead to a reorganization of the global climate system. Understanding the dynamic links between the “tripolar” environments and the Earth climate system is crucial to improving our capability to project future climate variability. “Tripolar” changes have influenced the onset and evolution of the Asian paleomonsoon system through various atmospheric and/or oceanic mechanisms. Here, we summarize previously reported Asian paleomonsoon variations that can be linked to “tripolar” environmental changes, from tectonic to millennial time scales, and explore linkages between the “tripolar” regions and global climate changes.

Abstract The existing controversy regarding the climatic response to given changes in the geomagnetic field intensity (e.g. climate cooling or warming in periods of geomagnetic field strengthening) raises scepticism about the existence of any relationship between both variables. The main shortcomings of the recent understanding of the geomagnetic field–climate relationship are the expectations for: (i) its universal character over the globe; and (ii) the zonal homogeneity of this relationship. This paper offers a new conceptual framework aimed at resolving the existing controversy and explaining the mechanism for the appearance of geomagnetic footprints on climatic records. We show that particles trapped in the Earth's radiation belts are subject to geomagnetic lensing in the parts of their trajectories closest to the surface, being focused or defocused at different regions over the world. The irregularly distributed ionization, created in such a way near the tropopause, activates various ion–molecular reactionships which affect the atmospheric composition there. Thus, the regional changes in the ozone and water vapour are furthermore projected onto the surface temperature and pressure. Consequently, the geomagnetic field–climate relationship is not a rigid but, rather, a flexible one because it is mediated by the near-tropopause ionization, ozone and humidity, with each of them being subject to the other's influence.

Abstract High-elevation tropical glaciers provide records of past climate from which current changes can be assessed. Comparisons among three ice-core records from tropical mountains on opposite sides of the Pacific Ocean reveal how climatic events are linked through large-scale processes such as El Niño–Southern Oscillation. Two distinctive trans-Pacific events in the mid-fourteenth and late-eighteenth centuries are distinguished by elevated aerosol concentrations in cores from the Peruvian Andes and the Tibetan Himalaya. Today aerosol sources for these areas are enhanced by droughts accompanying El Niños. In both locations, large-scale atmospheric circulation supports aerosol transport from likely source regions. Oxygen isotopic ratios from the ice cores are significantly linked with tropical Pacific sea-surface temperatures, especially in the NIÑO3.4 region. The arid periods in the fourteenth and eighteenth centuries reflect droughts that were possibly connected to strong and/or persistent El Niño conditions and Intertropical Convergence Zone migration. These ‘black swans’ are contemporaneous with climate-related population disruptions. Recent warming, particularly at high elevations, is posing a threat to tropical glaciers, many of which have been retreating at unprecedented rates over the last several thousand years. The diminishing ice in these alpine regions endangers water resources for populations in South Asia and South America.