title: Evidence for ice-free summers in the late Miocene central Arctic Ocean.
abstract: Although the permanently to seasonally ice-covered Arctic Ocean is a unique and sensitive component in the Earth's climate system, the knowledge of its long-term climate history remains very limited due to the restricted number of pre-Quaternary sedimentary records. During Polarstern Expedition PS87/2014, we discovered multiple submarine landslides along Lomonosov Ridge. Removal of younger sediments from steep headwalls has led to exhumation of Miocene sediments close to the seafloor. Here we document the presence of IP25 as a proxy for spring sea-ice cover and alkenone-based summer sea-surface temperatures >4 °C that support a seasonal sea-ice cover with an ice-free summer season being predominant during the late Miocene in the central Arctic Ocean. A comparison of our proxy data with Miocene climate simulations seems to favour either relatively high late Miocene atmospheric CO2 concentrations and/or a weak sensitivity of the model to simulate the magnitude of high-latitude warming in a warmer than modern climate.
authors.affiliation: Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.|Department of Geosciences (FB5), University of Bremen, Klagenfurter Strasse 4, Bremen 28359, Germany.
authors.forename: Ruediger
authors.initials: R
authors.lastname: Stein
authors.affiliation: Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Fahl
authors.affiliation: Arctic Research Centre, Korea Polar Research Institute, 26 Songdomirae-ro, Yeonsu-gu, Incheon 406-840, Korea.
authors.forename: Michael
authors.initials: M
authors.lastname: Schreck
authors.affiliation: Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Gregor
authors.initials: G
authors.lastname: Knorr
authors.affiliation: Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Niessen
authors.affiliation: Institute of Geology, University of Tromsø-The Arctic University of Norway, P O Box 6050 Langnes, Tromsø 9037, Norway.
authors.forename: Matthias
authors.initials: M
authors.lastname: Forwick
authors.affiliation: Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Catalina
authors.initials: C
authors.lastname: Gebhardt
authors.affiliation: Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Laura
authors.initials: L
authors.lastname: Jensen
authors.affiliation: Geosciences Department, College of Petroleum Engineering &Geosciences, King Fahd University of Petroleum &Minerals, Dhahran 31261, Saudi Arabia.
authors.forename: Michael
authors.initials: M
authors.lastname: Kaminski
authors.affiliation: Department of Geosciences (FB5), University of Bremen, Klagenfurter Strasse 4, Bremen 28359, Germany.|MARUM-Center for Marine Environmental Sciences, University of Bremen, Leobener Strasse, Bremen 28359, Germany.
authors.forename: Achim
authors.initials: A
authors.lastname: Kopf
authors.affiliation: Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Matthiessen
authors.affiliation: Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.|Department of Geosciences (FB5), University of Bremen, Klagenfurter Strasse 4, Bremen 28359, Germany.
authors.forename: Wilfried
authors.initials: W
authors.lastname: Jokat
authors.affiliation: Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.|MARUM-Center for Marine Environmental Sciences, University of Bremen, Leobener Strasse, Bremen 28359, Germany.
authors.forename: Gerrit
authors.initials: G
authors.lastname: Lohmann