Evidence for ice-free summers in the late Miocene central Arctic Ocean

Ruediger Stein,Laura Jensen,Wilfried Jokat,Achim Kopf,Kirsten Fahl,Michael Schreck,Jens Matthiessen,Michael Kaminski,Gerrit Lohmann,Matthias Forwick,Gregor Knorr,Catalina Gebhardt,Frank Niessen

doi:10.1038/ncomms11148

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.

Highlights

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
Records of past climate and sea-ice conditions going beyond instrumental records and representing times of different boundary conditions are of major value: such records can be used to assess the sensitivity of the Earth‘s climate system to changes of different forcing parameters, for example, level of CO2, and to test the reliability of climate models by evaluating their simulations for conditions very different from the modern climate
Polarstern Expedition PS87 was scheduled for August–September 2014 to explore the Lomonosov Ridge area (Fig. 2) with the objective of collecting seismic data and sediment cores to reconstruct the short- and long-term climate history and the tectonic evolution of the central Arctic Ocean[17]

Summary

Introduction

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. Understanding the processes controlling Arctic sea-ice variability is of overall interest and significance[8,9] In this context, records of past climate and sea-ice conditions going beyond instrumental records and representing times of different boundary conditions are of major value: such records can be used to assess the sensitivity of the Earth‘s climate system to changes of different forcing parameters, for example, level of CO2, and to test the reliability of climate models by evaluating their simulations for conditions very different from the modern climate. The ability to (semi-)quantitatively reconstruct paleo-sea-ice distributions has been significantly improved by a biomarker approach based on the determination of a highly branched isoprenoid (HBI) with 25 carbons (C25 HBI monoene 1⁄4 IP25)[10] This biomarker is only biosynthesized by specific diatoms living in the Arctic ice[11] and appears to be a specific, sensitive and stable proxy for Arctic sea ice in sedimentary sections representing Pliocene to Pleistocene times[12,13]. These data suggest that the PIP25 index seems to be a promising proxy for more semi-quantitative estimates of the present and past sea-ice extent, certainly further groundtruth data are needed (see Methods for some more details)[8,16]

Methods

Results

Conclusion