The history of the Arctic Ocean during the Cenozoic era (0-65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from >400 m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm 'greenhouse' world, during the late Palaeocene and early Eocene epochs, to a colder 'icehouse' world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent ∼14 Myr, we find sedimentation rates of 1-2 cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice (∼3.2 Myr ago) and East Antarctic ice (∼14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (∼45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at ∼49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (∼55 Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change. © 2006 Nature Publishing Group

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The future conditions of Arctic sea ice and marine ecosystems are of interest not only to climate scientists, but also to economic and governmental bodies. However, the lack of widespread, year-long biogeochemical observations remains an obstacle to understanding the complicated variability of the Arctic marine biological pump. Here we show an early winter maximum of sinking biogenic flux in the western Arctic Ocean and illustrate the importance of shelf-break eddies to biological pumping from wide shelves to adjacent deep basins using a combination of year-long mooring observations and three-dimensional numerical modelling. The sinking flux trapped in the present study included considerable fresh organic material with soft tissues and was an order of magnitude larger than previous estimates. We predict that further reductions in sea ice will promote the entry of Pacific-origin biological species into the Arctic basin and accelerate biogeochemical cycles connecting the Arctic and subarctic oceans.

A fixed-point observation station was set up in the northern Chukchi Sea during autumn 2013, and for about 2 weeks conductivity-temperature-depth (CTD)/water samplings (6 h) and microstructure turbulence measurements (2 to 3 times a day) were performed. This enabled us to estimate vertical nutrient fluxes and the impact of different types of turbulent mixing on biological activity. There have been no such fixed-point observations in this region, where incoming low-salinity water from the Pacific Ocean, river water, and sea-ice meltwater promote a strong pycnocline (halocline) that stabilizes the water column. Previous studies have suggested that because of the strong pycnocline, wind-induced ocean mixing could not change the stratification to impact biological activity. However, the present study indicates that a combined effect of an uplifted pycnocline accompanied by wind-induced inertial motion and turbulent mixing caused by intense gale-force winds (>10 m s 21 ) did result in increases in upward nutrient fluxes, primary productivity, and phytoplankton biomass, particularly large phytoplankton such as diatoms. Convective mixing associated with internal waves around the pycnocline also increased the upward nutrient fluxes and might have an impact on biological activity there. For diatom production at the fixed-point observation station, it was essential that silicate was supplied from a subsurface silicate maximum, a new feature that we identified during autumn in the northern Chukchi Sea. Water mass distributions obtained from wide-area observations suggest that the subsurface silicate maximum water was possibly derived from the ventilated halocline in the Canada Basin.

Warming of high northern latitudes in the Pliocene (5.33–2.58 Myr ago) has been linked to the closure of the Central American Seaway and intensification of North Atlantic Deep Water. Subsequent cooling in the late Pliocene may be related to the effects of freshwater input from the Arctic Ocean via the Bering Strait, disrupting North Atlantic Deep Water formation and enhancing sea ice formation. However, the timing of Arctic freshening has not been defined. Here we present neodymium and lead isotope records of detrital sediment from the Bering Sea for the past 4.3 million years. Isotopic data suggest the presence of Alaskan glaciers as far back as 4.2 Myr ago, while diatom and C37:4 alkenone records show a long-term trend towards colder and fresher water in the Bering Sea beginning with the M2 glaciation (3.3 Myr ago). We argue that the introduction of low-salinity Bering Sea water to the Arctic Ocean by 3.3 Myr ago preconditioned the climate system for global cooling.