Archaeoseismic Evidence of Surface Faulting in 1703 Norcia Earthquake (Central Italian Apennines, Mw 6.9)

We present the first evidence of surface rupture along the causative fault of the 14 January 1703 earthquake (Mw 6.9, Italian central Apennines). This event was sourced by the ~30 km-long, Norcia fault system, responsible for another catastrophic event in Roman times, besides several destructive earthquakes in the last millennium. A dozen paleoseismological excavations have already investigated the surface ruptures occurred during the Holocene along the Cascia-Mt Alvagnano segments, as well as along secondary splays close to the Medieval Norcia Walls. Remarkably, the master fault bounding the Norcia-Campi basins have never be proved to rupture at the surface. An antique limekiln that was improvidently set across the main fault scarp provides the amazing evidence of an abrupt offset in the 1703 earthquake, which likely occurred during a liming process of carbonate stones. Obviously, the limekiln became useless, and was progressively buried by slope debris. The amount of the offset and the kinematics indicators surveyed in the site allow the strengthening of our knowledge on the seismogenic potential of the Norcia fault system, on its geomorphic rule, and on its impact on the human activities.

Tropical volcanism enhanced the East Asian summer monsoon during the last millennium

Extreme East Asian summer monsoon (EASM) rainfall frequently induces floods that pose threats to millions of people across East Asia. The intensified EASM rainfall has been generally attributed to internal modes of climate variability, while external volcanic forcing has been suggested to suppress the EASM. In contrast to the hydrological weakening theory of volcanic eruptions, we present convergent empirical and modeling evidence for significant intensification of EASM rainfall in response to strong tropical volcanic eruptions. Our paleoclimate proxy analyses show a significantly increased EASM in the first summer after large tropical eruptions from 1470 AD to the present. The multi-proxy ensemble mean demonstrates that the occurrence of an El Niño in the first boreal winter after a volcanic eruption is necessary for the enhanced EASM. The results from the last-millennium climate model simulations show that a volcano-induced El Niño and the associated warm pool air-sea interaction intensify EASM precipitation, overwhelming volcanic-induced moisture deficiency. This work offers a new perspective on the intertwined relationship between external forcing and internal variability in the complex climate system and potential flood disasters resulting from tropical volcanic eruption.

Influence of long-term changes in solar irradiance forcing on the Southern Annular Mode

The Southern Annular Mode (SAM) is the leading mode of climate variability in the extratropical Southern Hemisphere, with major regional climate impacts. Observations, reconstructions, and historical climate simulations all show positive trends in the SAM since the 1960s; however, earlier trends in palaeoclimate SAM reconstructions cannot be reconciled with last millennium simulations. Here we investigate the sensitivity of the SAM to solar irradiance variations using simulations with a range of constant solar forcing values, and last millennium transient simulations with varying amplitude solar forcing scenarios. We find the mean SAM state can be significantly altered by solar irradiance changes, and that transient last millennium simulations using a high-amplitude solar scenario have an improved and significant agreement with proxy-based SAM reconstructions. Our findings suggest that the effects of solar forcing on high-latitude climate may not be adequately incorporated in most last millennium simulations, due to solar irradiance changes that are too small and/or the absence of interactive atmospheric chemistry in global climate models.

Investigating oxygen and carbon isotopic relationships in speleothem records over the last millennium using multiple isotope-enabled climate models

The incorporation of water isotopologues into the hydrology of general circulation models (GCMs) facilitates the comparison between modelled and measured proxy data in paleoclimate archives. However, the variability and drivers of measured and modelled water isotopologues, and indeed the diversity of their representation in different models are not well constrained. Improving our understanding of this variability in past and present climates will help to better constrain future climate change projections and decrease their range of uncertainty. Speleothems are a precisely datable paleoclimate archive and provide well preserved (semi-)continuous multivariate isotope time series in the lower and mid-latitudes, and are, therefore, well suited to assess climate and isotope variability on decadal and longer timescales. However, the relationship between speleothem oxygen and carbon isotopes to climate variables also depends on site-specific parameters, and their comparison to GCMs is not always straightforward. Here we compare speleothem oxygen and carbon isotopic signatures from the Speleothem Isotopes Synthesis and AnaLysis database version 2 (SISALv2) to the output of five different water-isotope-enabled GCMs (ECHAM5-wiso, GISS-E2-R, iCESM, iHadCM3, and isoGSM) over the last millennium (850–1850 common era, CE). We systematically evaluate differences and commonalities between the standardized model simulation outputs. The goal is to distinguish climatic drivers of variability for both modelled and measured isotopes. We find strong regional differences in the oxygen isotope signatures between models that can partly be attributed to differences in modelled temperatures. At low latitudes, precipitation amount is the dominant driver for water isotope variability, however, at cave locations the agreement between modelled temperature variability is higher than for precipitation variability. While modelled isotopic signatures at cave locations exhibited extreme events coinciding with changes in volcanic and solar forcing, such fingerprints are not apparent in the speleothem isotopes, and may be attributed to the lower temporal resolution of speleothem records compared to the events that are to be detected. Using spectral analysis, we can show that all models underestimate decadal and longer variability compared to speleothems, although to varying extent. We found that no model excels in all analyzed comparisons, although some perform better than the others in either mean or variability. Therefore, we advise a multi-model approach, whenever comparing proxy data to modelled data. Considering karst and cave internal processes through e.g. isotope-enabled karst models may alter the variability in speleothem isotopes and play an important role in determining the most appropriate model. By exploring new ways of analyzing the relationship between the oxygen and carbon isotopes, their variability, and co-variability across timescales, we provide methods that may serve as a baseline for future studies with different models using e.g. different isotopes, different climate archives, or time periods.

Humidity changes and possible forcing mechanisms over the last millennium in arid Central Asia

Hydroclimate changes have exerted a significant influence on the historical trajectory of ancient civilizations in arid Central Asia where the central routes of the Silk Road have been hosted. However, the climate changes at different time scales and their possible forcing mechanisms over the last millennium remain unclear due to low-resolution records. Here, we provide a continuous high-resolution humidity history in arid Central Asia over the past millennium based on the ~1.8-year high-resolution multiproxy records with good chronological control from Lake Dalongchi in the central Tianshan Mountains. Generally, the climate was dry during the Medieval Warm Period (MWP) and Current Warm Period (CWP), and wet during the Little Ice Age (LIA), which could be attributed to the influence of the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO). Furthermore, we find that the humidity oscillation was dramatic and unstable at multidecadal to century-scale, especially within the LIA. The continuous wavelet analysis and wavelet coherence show that the humidity oscillation is modulated by the Gleissberg cycle at the century-scale and by the quasi-regular period of El Niño-Southern Oscillation (ENSO) at the multidecadal scale. Our findings suggest that the effect of the solar cycle and the quasi-regular period of ENSO should be seriously evaluated for hydroclimate predictions and climate simulations in arid Central Asia in the future.