ALBERT

Description: The assassination of Julius Caesar in 44 BCE triggered a power struggle that ultimately ended the Roman Republic and, eventually, the Ptolemaic Kingdom, leading to the rise of the Roman Empire. Climate proxies and written documents indicate that this struggle occurred during a period of unusually inclement weather, famine, and disease in the Mediterranean region; historians have previously speculated that a large volcanic eruption of unknown origin was the most likely cause. Here we show using well-dated volcanic fallout records in six Arctic ice cores that one of the largest volcanic eruptions of the past 2,500 y occurred in early 43 BCE, with distinct geochemistry of tephra deposited during the event identifying the Okmok volcano in Alaska as the source. Climate proxy records show that 43 and 42 BCE were among the coldest years of recent millennia in the Northern Hemisphere at the start of one of the coldest decades. Earth system modeling suggests that radiative forcing from this massive, high-latitude eruption led to pronounced changes in hydroclimate, including seasonal temperatures in specific Mediterranean regions as much as 7 °C below normal during the 2 y period following the eruption and unusually wet conditions. While it is difficult to establish direct causal linkages to thinly documented historical events, the wet and very cold conditions from this massive eruption on the opposite side of Earth probably resulted in crop failures, famine, and disease, exacerbating social unrest and contributing to political realignments throughout the Mediterranean region at this critical juncture of Western civilization.

Description: Understanding the temporal variation of cosmic radiation and solar activity during the Holocene is essential for studies of the solar-terrestrial relationship. Cosmic-ray produced radionuclides, such as 10Be and 14C which are stored in polar ice cores and tree rings, offer the unique opportunity to reconstruct the history of cosmic radiation and solar activity over many millennia. Although records from different archives basically agree, they also show some deviations during certain periods. So far most reconstructions were based on only one single radionuclide record, which makes detection and correction of these deviations impossible. Here we combine different 10Be ice core records from Greenland and Antarctica with the global 14C tree ring record using principal component analysis. This approach is only possible due to a new high-resolution 10Be record from Dronning Maud Land obtained within the European Project for Ice Coring in Antarctica in Antarctica. The new cosmic radiation record enables us to derive total solar irradiance, which is then used as a proxy of solar activity to identify the solar imprint in an Asian climate record. Though generally the agreement between solar forcing and Asian climate is good, there are also periods without any coherence, pointing to other forcings like volcanoes and greenhouse gases and their corresponding feedbacks. The newly derived records have the potential to improve our understanding of the solar dynamics and to quantify the solar influence on climate.

Description: In the Eurasian Arctic, the archipelago of Severnaya Zemlya is the most eastern one which is covered by a considerable ice cap, giving the opportunity to study regional climate signals from the Holocene period. The Academii Nauk ice cap (Komsomolets Island) was chosen for drilling a deep ice core because it is the thickest and coldest ice cap on Severnaya Zemlya. A suitable drilling site was found at 80°31'N 94°49'E by the help of airborne radio-echo sounding data and SAR interferometry. The ice thickness was 724 m at this location. Drilling was carried out between 1999 and 2001 reaching bedrock. It was a joint project of the Alfred Wegener Institute (Germany), the Arctic and Antarctic Research Institute, and the Mining Institute (Russia, St.Petersburg both). An electromechanical ice core drill (KEMS-112M) was used, the same type as at Vostok Station, Antarctica. The paper presents the results of electrical conductivity measurements (DEP) of the whole ice core. Several zones with high conductivity were assumed to be caused by major volcanic eruptions. By help of catalogues of historical volcanic events we used these signals for core dating of the upper 245 meters. The time scale developed this way is in good agreement with horizons of enriched radioactivity caused by nuclear weapon tests in the early 1960's and by the Chernobyl accident. The d180 record fits almost perfectly to values published earlier by Klementev et al. for Akademii Nauk, however, we have no evidence for the age model used in this Russian paper. We found annual accumulation rates in the isotope record and in the electrical data indicating none-steady state conditions of this glacier in the past. Hence, the core ages are overestimated by flow models. There seems to be an age discordance in the deepest part of the core. For Akademii Nauk ice cap the isotope data indicate a climate warming since app. 1860 which is much higher than found at central Greenland (GRIP/GISP2), Devon lsland or Hans Tausen ice cap. REFERENCE Klementev, O.L.; Potapenko, V. Yu.; Savatyugin, L.M. & Nikolaev, V.l.: Studies of the intemal structure and thennal-hydrodynarnic state of Vavilov Glacier, Archipelago Sevemaya Zernlya. IAHS Publ. 208, 1991, p.49-59