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Final Report Summary - ARCTIC GEO-HAZARDS (Arctic Geo-hazards, Geo-fluids and Climate Change)

Arctic Geohazards

Researcher and Author: Rieka Harders,

Introduction to the Project
This project aimed at filling a fundamental gap in the understanding of Arctic geosystems with respect to submarine slope stability. Due to the impending exploration and use of the continental margins of the Arctic Ocean by industrialized countries this topic requires urgent attention. Present-day state-of-the-art knowledge indicates that the predicted increment in temperature due to climate change might lead to hydro-geological modifications that could alter the stability of sediments covering the continental slopes of Arctic margins.
Numerous submarine landslides from the North Atlantic have been dated to Pleistocene - Holocene age, which was interpreted to indicate that occurred most frequently during Northern Hemisphere Glaciation (NHG) or deglaciation respectively (Maslin et al. (2004), Owen et al. (2007), Lee (2009), and Leynaud et al. (2009). Changing sea levels during glaciation and deglaciation come together with enhanced erosive processes due to glacier build up and decline and thus have been directly linked to produce the highest sediment rates along arctic margins and thus precondition submarine slopes for failure. This project was designed to investigate slope stability especially detecting weak layers. At this type of margin weak layers might occur by alternation of glacigenic debris flows produced during high glacials and plumites, contourites or hemipelagic deposited during interstadials and deglacials. Sediment shear stresses along these weak layers may critically be reduced by rising pore pressures by different processes, so that sliding along these layers may be induced by earthquakes related to isostatic rebound.
Different model scenarios should test slope failures to help understand past failures and evaluate the potential for future events in similar regions related to changing climate. However recent analysis of well-dated slide events from the North Atlantic has reopened the debate on the validity of the assumption that large submarine slides are directly related to sea level changes and high sediment accumulation rates occurring preferably during high glacials or deglacials (Urlaub et al. 2013).

A major endeavor of this project is to investigate a little known region of the poorly surveyed Arctic margins, where the origin and nature of deep sediment record under the slope and deep basin are inadequately known. During our investigations we discovered large volumes of reworked sediments in the deeper records, older than 2.58Ma, formed before Northern Hemisphere Glaciation. We had to undertake the reprocessing of seismic data to improve the deep resolution to discover unexpected several giant submarine landslides –unknown to that date- from before and at the beginning of the last Northern Hemisphere Glaciation (NHG). Our unexpected findings challenge previous conceptual models of slide generation and the fundaments on our early hypotheses. We found, contrary to former conventional wisdom, that there is no link in the volume and frequency of submarine slides to sea-level changes at glaciation or deglaciation times. Thus the often called relevance of the analysis of young sediments and hydro-geological system does not seem to be able to play the previously envisioned fundamental role..

Summary of Results and Conclusions
We re-processed about 1000km of multichannel seismic reflection data along the Svalbard continental margin and deep basin. Reprocessing revealed giant Mass Transport Deposits (MTDs) that extend into the deep-water basin bounded by Knipovich ridge. These newly discovered MTDs exceed in size slope failures of younger high-glacial times, that had been considered to be frequent and assumed to be the largest MTDs in the region offshore Svalbard, because the giant failures in the deeper record had not been detected. The internal seismic structure of the giant MTDs shows a chaotic to sub parallel character, indicating disintegration but also cohesive sliding/ slumping on a large scale with over-pressures, expressed by diapiric structures. The images show up to 1km thick MTDs, that can be correlated N-S along slope for about 300km. The MTDs run up basement ridges in the west towards the Knipovich ridge supporting a catastrophic failure. Taken in conjunction to other recent findings in the area –that have discovered similar structures where we have no data- indicate that the volume of some MTDs may be twice as large as recent previous estimates (Safronova et al., 2017). There exist similar MTDs in other Arctic regions (Hjelstuen et al., 2007 & 2015), and we interpret that the processes leading to giant slope failures discovered along the margin have not yet been described in the literature.

Seismostratigraphy and correlation to ODP site 986 permited to date the MTDs to Plio- early Pleistocene age of 2.7 to 2.3Ma. It has been suggested before by Butt et al. (2000) that the up to 60% sand contenting clayey sediments are most likely of fluviatil to glacio-fluviatil origin. During that time glaciers did not reach the shelf edge. From 2.7 to 1Ma there were no fast flowing ice streams delivering vast amounts of sediments to the shelf edge, causing the later deposited GDFs in the region, which nowadays built the trough mouth fans (Knies et al., 2009). We think the found MTDs represent one single, large, catastrophic mass movement event more than 1Ma before onset of high glaciation in the region. We hypothesize that the material consists of sediment mixtures from glacial erosion of the hinterland and was later washed out and transported by glacial meltwater rivers crossing the flat area of the (during that time) emerged Barents Sea. It is interesting to note that the Norway and Svalbard basins contain several giant MTDs that occurred between Pliocene age at 2.7 Ma to 2.3Ma, but in the intervening Lofoten Basin giant MTDs are younger than ~1 Ma. We hypothesize that giant MTDs are not exclusively related to high glaciation nor to deglaciation episodes but occur also on a even larger scale right before NHG..

Knies J., Matthiessen, J., Vogt, C., Laberg, J.S., Hjelstuen, B.O., Smelror, M., Larsen, E., Andreassen, K., Eidvin, T. & Vorren, T.O. (2009) The plio-pleistocene glaciation of the barents sea-svalbard region: a new model based on revised chronostratigraphy. Quatern. Sci. Rev., 28, 812–829.

Lee, H.J., 2009. Timing and occurrence of large submarine landslides on the Atlantic
Ocean Margin. Marine Geology 264, 53e64.

Leynaud, D., Mienert, J. & Vanneste, M., 2009. Submarine mass movements on glaciated and non-glaciated European continental margins: a review of triggering mechanisms and preconditions to failure. Mar. Pet. Geol., 26, 618–632.

Maslin, M., Owen, M., Day, S., Long, D., 2004. Linking continental-slope failures and climate change: testing the clathrate gun hypothesis. Geology 32, 53-56.

Owen, M., Day, S., Maslin, M., 2007. Late Pleistocene submarine mass movements:
occurrence and causes. Quaternary Science Reviews 26, 958-978.

Urlaub, M., Talling P.J., Masson, D.G., 2013. Timing and frequency of large submarine landslides: implications for understanding triggers and future geohazard, Quaternary Science Reviews 72, 63-82.

Safronova, P. A., Laberg, J. S, Andreassen, K., Shlykova, V., Vorren T. O. , Chernikov, S., 2017. Late Pliocene–early Pleistocene deep-sea basin sedimentation at high-latitudes:mega-scale submarine slides of the north-western Barents Sea margin prior to the shelf-edge glaciations, Basin Research 29 (Suppl. 1), 537–555, doi: 10.1111/bre.12161

Hjelstuen, B.O., Eldholm, O. & Faleide, J.I., 2007. Recurrent pleistocene mega-failures on the SW Barents Sea margin. Earth Planet. Sci. Lett., 258, 605–618.

Hjelstuen, B.O. and Andreassen, E.V. (2015) North Atlantic ocean deep-water processes and depositional environments: a study of the Cenozoic Norway basin. Mar. Pet. Geol., 59, 429–441.

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