A. Davies, A.E.S. Kemp, J. Pike, Nature 460 (2009), Late Cretaceous seasonal ocean variability from the Arctic

Nature 460, 254-258 (9 July 2009); doi: 10.1038/nature08141; received 15 September 2008, accepted 13 May 2009.

Late Cretaceous seasonal ocean variability from the Arctic

Andrew Davies^*,**, Alan E. S. Kemp (National Oceanography Centre Southampton, School of Ocean and Earth Science, University of Southampton, Southampton, SO14 3ZH, U.K.) and Jennifer Pike (School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3YE, U.K.)

Abstract

The modern Arctic Ocean is regarded as a barometer of global change and amplifier of global warming¹ and therefore records of past Arctic change are critical for palaeoclimate reconstruction. Little is known of the state of the Arctic Ocean in the greenhouse period of the Late Cretaceous epoch (65–99 million years ago), yet records from such times may yield important clues to Arctic Ocean behaviour in near-future warmer climates. Here we present a seasonally resolved Cretaceous sedimentary record from the Alpha ridge of the Arctic Ocean. This palaeo-sediment trap provides new insight into the workings of the Cretaceous marine biological carbon pump. Seasonal primary production was dominated by diatom algae but was not related to upwelling as was previously hypothesized². Rather, production occurred within a stratified water column, involving specially adapted species in blooms resembling those of the modern North Pacific subtropical gyre³, or those indicated for the Mediterranean sapropels⁴. With increased CO₂ levels and warming currently driving increased stratification in the global ocean⁵, this style of production that is adapted to stratification may become more widespread. Our evidence for seasonal diatom production and flux testify to an ice-free summer, but thin accumulations of terrigenous sediment within the diatom ooze are consistent with the presence of intermittent sea ice in the winter, supporting a wide body of evidence for low temperatures in the Late Cretaceous Arctic Ocean^{6, 7, 8}, rather than recent suggestions of a 15 °C mean annual temperature at this time⁹.

*Correspondence and requests for materials should be addressed to A.E.S.K. (e-mail: aesk@noc.soton.ac.uk).
**Present address: Neftex Petroleum Consultants Ltd, 97 Milton Park, Abingdon, OX14 4RY, U.K.

Link to abstract: http://www.nature.com/nature/journal/v460/n7252/full/nature08141.html