Holocene fluctuations in Arctic sea-ice cover: dinocyst-based reconstructions for the eastern Chukchi SeaThis article is one of a series of papers published in this Special Issue on the theme Polar Climate Stability Network .GEOTOP Publication 2008-0023.

• Published in: Canadian Journal of Earth Sciences
• Main Authors: McKay, J. L., de Vernal, A., Hillaire-Marcel, C., Not, C., Polyak, L., Darby, D.
• Other Authors: Hollings, P.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2008
• Subjects: General Earth and Planetary Sciences; Arctic; Arctic Ocean; Chukchi Sea; Chukchi; Sea ice
• Online Access: http://dx.doi.org/10.1139/e08-046; http://www.nrcresearchpress.com/doi/full-xml/10.1139/E08-046; http://www.nrcresearchpress.com/doi/pdf/10.1139/E08-046

Cores from site HLY0501-05 on the Alaskan margin in the eastern Chukchi Sea were analyzed for their geochemical (organic carbon, δ 13 C org , C org /N, and CaCO 3 ) and palynological (dinocyst, pollen, and spores) content to document oceanographic changes during the Holocene. The chronology of the cores was established from 210 Pb dating of near-surface sediments and 14 C dating of bivalve shells. The sediments span the last 9000 years, possibly more, but with a gap between the base of the trigger core and top of the piston core. Sedimentation rates are very high (∼156 cm/ka), allowing analyses with a decadal to centennial resolution. The data suggest a shift from a dominantly terrigenous to marine input from the early to late Holocene. Dinocyst assemblages are characterized by relatively high concentrations (600–7200 cysts/cm 3 ) and high species diversity, allowing the use of the modern analogue technique for the reconstruction of sea-ice cover, summer temperature, and salinity. Results indicate a decrease in sea-ice cover and a corresponding, albeit much smaller, increase in summer sea-surface temperature over the past 9000 years. Superimposed on these long-term trends are millennial-scale fluctuations characterized by periods of low sea-ice and high sea-surface temperature and salinity that appear quasi-cyclic with a frequency of about one every 2500–3000 years. The results of this study clearly show that sea-ice cover in the western Arctic Ocean has varied throughout the Holocene. More importantly, there have been times when sea-ice cover was less extensive than at the end of the 20th century.