Description: Research campaigns over the last decade have yielded a growing stream of data that highlight the dynamic nature of Arctic cryosphere and climate change over a range of time scales. As a consequence, rather than seeing the Arctic as a near static environment in which large scale changes occur slowly, we now view the Arctic as a system that is typified by frequent, large and abrupt changes. The traditional focus on end members in the system - glacial versus interglacial periods - has been replaced by a new interest in understanding the patterns and causes of such dynamic change. Instead of interpreting changes almost exclusively as near linear responses to external forcing (e.g. orbitally-forced climate change), research is now concentrated on the importance of strong feedback mechanisms that in our palaeo-archives often border on chaotic behaviour. The last decade of research has revealed the importance of on-off switching of ice streams, strong feedbacks between sea level and ice sheets, spatial and temporal changes in ice shelves and perennial sea ice, as well as alterations in ice sheet dynamics caused by shifting centres of mass in multi-dome ice sheets. Recent advances in dating techniques and modelling have improved our understanding of leads and lags that exist in different Arctic systems, on their interactions and the driving mechanisms of change. Future Arctic research challenges include further emphases on rapid transitions and untangling the feedback mechanisms as well as the time scales they operate on.

Description: To better understand Pleistocene climatic changes in the Arctic, integrated palaeoenvironmental and palaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologic age control are required, not least for correlation to extra-Arctic records. In this paper we discuss, from an Arctic perspective, methods and correlation tools that are commonly used to date Arctic Pleistocene marine and terrestrial events. We review the state of the art of Arctic geochronology, with focus on factors that affect the possibility and quality of dating, and support this overview by examples of application of modern dating methods to Arctic terrestrial and marine sequences. Event stratigraphy and numerical ages are important tools used in the Arctic to correlate fragmented terrestrial records and to establish regional stratigraphic schemes. Age control is commonly provided by radiocarbon, luminescence or cosmogenic exposure ages. Arctic Ocean deep-sea sediment successions can be correlated over large distances based on geochemical and physical property proxies for sediment composition, patterns in palaeomagnetic records and, increasingly, biostratigraphic data. Many of these proxies reveal cyclical patterns that provide a basis for astronomical tuning. Recent advances in dating technology, calibration and age modelling allow for measuring smaller quantities of material and to more precisely date previously undatable material (i.e. foraminifera for C-14, and single-grain luminescence). However, for much of the Pleistocene there are still limits to the resolution of most dating methods. Consequently improving the accuracy and precision (analytical and geological uncertainty) of dating methods through technological advances and better understanding of processes are important tasks for the future. Another challenge is to better integrate marine and terrestrial records, which could be aided by targeting continental shelf and lake records, exploring proxies that occur in both settings, and by creating joint research networks that promote collaboration between marine and terrestrial geologists and modellers.

Description: Terrestrial and marine geological archives in the Arctic contain information on environmental change through Quaternary interglacial–glacial cycles. The Arctic Palaeoclimate and its Extremes (APEX) scientific network aims to better understand the magnitude and frequency of past Arctic climate variability, with focus on the “extreme” versus the “normal” conditions of the climate system. One important motivation for studying the amplitude of past natural environmental changes in the Arctic is to better understand the role of this region in a global perspective and provide base-line conditions against which to explore potential future changes in Arctic climate under scenarios of global warming. In this review we identify several areas that are distinct to the present programme and highlight some recent advances presented in this special issue concerning Arctic palaeo-records and natural variability, including spatial and temporal variability of the Greenland Ice Sheet, Arctic Ocean sediment stratigraphy, past ice shelves and marginal marine ice sheets, and the Cenozoic history of Arctic Ocean sea ice in general and Holocene oscillations in sea ice concentrations in particular. The combined sea ice data suggest that the seasonal Arctic sea ice cover was strongly reduced during most of the early Holocene and there appear to have been periods of ice free summers in the central Arctic Ocean. This has important consequences for our understanding of the recent trend of declining sea ice, and calls for further research on causal links between Arctic climate and sea ice.

Description: While there are numerous hypotheses concerning glacialeinterglacial environmental and climatic regime shifts in the Arctic Ocean, a holistic view on the Northern Hemisphere’s late Quaternary ice-sheet extent and their impact on ocean and sea-ice dynamics remains to be established. Here we aim to provide a step in this direction by presenting an overview of Arctic Ocean glacial history, based on the present state-of-the-art knowledge gained from field work and chronological studies, and with a specific focus on ice-sheet extent and environmental conditions during the Last Glacial Maximum (LGM). The maximum Quaternary extension of ice sheets is discussed and compared to LGM. We bring together recent results from the circum-Arctic continental margins and the deep central basin; extent of ice sheets and ice streams bordering the Arctic Ocean as well as evidence for ice shelves extending into the central deep basin. Discrepancies between new results and published LGM ice-sheet reconstructions in the high Arctic are highlighted and outstanding questions are identified. Finally, we address the ability to simulate the Arctic Ocean ice sheet complexes and their dynamics, including ice streams and ice shelves, using presently available ice-sheet models. Our review shows that while we are able to firmly reject some of the earlier hypotheses formulated to describe Arctic Ocean glacial conditions, we still lack information from key areas to compile the holistic Arctic Ocean glacial history.