Submarine Landslides along the Siberian part of Lomonosov Ridge: Triggering Mechanisms, Timing and Significance

Abstract:

During PolarsternExpedition PS87, numerous slide scars and mass-transport deposits were discovered along the Siberian part of Lomonosov Ridge between about 81°N and 84°N. Swath-bathymetry data indicate that different processes probably triggered slope failures and that failures occurred at various times. On top of the southern Lomonosov Ridge at water depths between 800 and 1000 m we mapped SE-NW oriented, streamlined landforms over long distances. These features are interpreted to be glacial lineations that formed beneath grounded ice sheets and ice streams. Similar unidirectional bed forms have also been identified on the East Siberian continental margin where they were related to large and coherent ice masses („East Siberian Chukchi Ice Sheet – ESCIS“). The orientations of the lineations identified in this study are similar to those on the East Siberian continental margin, suggesting that the ESCIS extended further north than originally proposed. The load and erosional behaviour of this extended ice sheet/shelf that probably occurred during major Quaternary glaciations (MIS 6 or older, i.e. MIS 12 and 16?), may have caused physical conditions that triggered the landslides on this part of Lomonosov Ridge.

Although the single landslides with sediment volumes of 2 to 20 km³ are relatively small in comparison to well-studied megaslides (e.g., the Storrega Slide off Norway: 2400-3200 km³), in sum probably >1000 km³of sediment were redistributed and transported down-slope. The widespread dimension of such processes was not known yet, and its discovery has certainly to be considered in re-calculation of Arctic Ocean sedimentary and organic-carbon budgets.

Along the steep and 100-500 metres high headwalls of the escarpments, younger sediments have been removed and led to exhumation of Miocene to early Quaternary sediments close to the seafloor. Some of these sediments were studied in more detail. Here, we can show for the first time that the mid/late Miocene central Arctic Ocean was relatively warm (4-7°C) and ice-free during summer, but sea ice occurred during spring and autumn/winter. A comparison of our proxy data with Miocene climate simulations seems to favour relatively high late Miocene atmospheric CO₂ concentrations.