ALBERT

Description: As the planet cooled from peak warmth in the early Cenozoic, extensive Northern Hemisphere ice sheets developed by 2.6 Ma ago, leading to changes in the circulation of both the atmosphere and oceans. From not, vert, similar2.6 to not, vert, similar1.0 Ma ago, ice sheets came and went about every 41 ka, in pace with cycles in the tilt of Earth’s axis, but for the past 700 ka, glacial cycles have been longer, lasting not, vert, similar100 ka, separated by brief, warm interglaciations, when sea level and ice volumes were close to present. The cause of the shift from 41 ka to 100 ka glacial cycles is still debated. During the penultimate interglaciation, not, vert, similar130 to not, vert, similar120 ka ago, solar energy in summer in the Arctic was greater than at any time subsequently. As a consequence, Arctic summers were not, vert, similar5 °C warmer than at present, and almost all glaciers melted completely except for the Greenland Ice Sheet, and even it was reduced in size substantially from its present extent. With the loss of land ice, sea level was about 5 m higher than present, with the extra melt coming from both Greenland and Antarctica as well as small glaciers. The Last Glacial Maximum (LGM) peaked not, vert, similar21 ka ago, when mean annual temperatures over parts of the Arctic were as much as 20 °C lower than at present. Ice recession was well underway 16 ka ago, and most of the Northern Hemisphere ice sheets had melted by 6 ka ago. Solar energy reached a summer maximum (9% higher than at present) not, vert, similar11 ka ago and has been decreasing since then, primarily in response to the precession of the equinoxes. The extra energy elevated early Holocene summer temperatures throughout the Arctic 1–3 °C above 20th century averages, enough to completely melt many small glaciers throughout the Arctic, although the Greenland Ice Sheet was only slightly smaller than at present. Early Holocene summer sea ice limits were substantially smaller than their 20th century average, and the flow of Atlantic water into the Arctic Ocean was substantially greater. As summer solar energy decreased in the second half of the Holocene, glaciers re-established or advanced, sea ice expanded, and the flow of warm Atlantic water into the Arctic Ocean diminished. Late Holocene cooling reached its nadir during the Little Ice Age (about 1250–1850 AD), when sun-blocking volcanic eruptions and perhaps other causes added to the orbital cooling, allowing most Arctic glaciers to reach their maximum Holocene extent. During the warming of the past century, glaciers have receded throughout the Arctic, terrestrial ecosystems have advanced northward, and perennial Arctic Ocean sea ice has diminished. Here we review the proxies that allow reconstruction of Quaternary climates and the feedbacks that amplify climate change across the Arctic. We provide an overview of the evolution of climate from the hot-house of the early Cenozoic through its transition to the ice-house of the Quaternary, with special emphasis on the anomalous warmth of the middle Pliocene, early Quaternary warm times, the Mid Pleistocene transition, warm interglaciations of marine isotope stages 11, 5e, and 1, the stage 3 interstadial, and the peak cold of the last glacial maximum.

Description: This issue is the final synthesis report by QUEEN (Quaternary Environments of the Eurasian North), an à la carte programme of the ESF (European Science Foundation) Standing Committee for Life and Environmental Sciences (LESC), supported through funds from Denmark, Finland, Germany, Norway, Sweden, Switzerland and the United Kingdom. In addition to several national projects, the European Union project Ice Sheets and Climate in the Eurasian Arctic (Eurasian Ice Sheets) formed part of the program during the period 1998 to 2000. Support from many Russian institutions and individual researchers was essential for organizing the numerous expeditions into remote areas of the northernmost Eurasia and the adjacent Arctic Ocean. QUEEN was initially suggested in 1995 when several research groups of western European and Russian scientists studying the Quaternary in remote and poorly known regions of the Eurasian North decided that they could improve the scope and depth of their investigations through international coordination and cooperation. By that time several of the European groups had already acquired substantial experience in collaborative studies of Quaternary processes and sedimentation history along the polar North Atlantic margins through a similar project, PONAM (Elverhøi et al., 1998), and by working on a bilateral basis with their Russian colleagues.QUEEN was launched in 1996 for a 5-yr period and ended in 2002 after an extension for another 2 yr. The ESF-based funding for QUEEN allowed to conduct annual workshops for discussing the spectacular new observations from areas which had been largely inaccessible in earlier, political more troublesome times, and to jointly plan and coordinate field work for each successive year. A particular emphasis was on bringing numerous young researchers from Russia together with their western partners for scientific exchange within an international framework. Three of the workshops have yielded collections of papers summarizing the growing wealth of new data from the QUEEN area, which extends rom Norway to the shores of the Laptev Sea. This volume is the last collection of papers aiming at the final synthesis based on presentations given at the Sixth QUEEN workshop in Spiez, Switzerland.Preceding volumes published by Larsen et al. (1999) after the initial QUEEN workshop in Strasbourg, France and by Thiede et al. (2001) after workshops in Øystese, Norway and Lund, Sweden hosted a number of specialized studies in specific crucial areas. In July 2003 QUEEN results were also presented during a special symposium at the XVI. INQUA Congress in Reno (USA). Numerous expedition reports and detailed descriptions of QUEEN results are also spread throughout the scientific literature. However, the mentioned comprehensive volumes presented our results as a whole and should be considered as the main legacy of QUEEN, a full member of the international IGBP Core Project PAGES (Past Global Changes).