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Supplement to Challenges and progress in drilling offshore buried glacigenic deposits
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TILL J.J. HANEBUTH*, MARUM – Center for Marine Environmental Sciences, University of Bremen, Germany;
email: thanebuth@marum.de.
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MICHELE REBESCO, OGS (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale), Sgonico (TS), Italy.
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ROGER URGELES, CSIC (Institut de Ciències del Mar), Barcelona, Spain.
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RENATA G. LUCCHI, OGS (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale), Sgonico (TS), Italy.
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TIM FREUDENTHAL, MARUM – Center for Marine Environmental Sciences, University of Bremen, Germany.
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*
Currently at: Geology and Geophysics Department, Woods Hole Oceanographic Institution, MA, U.S.A.
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High latitudes are a fundamental player in the Earth’s climate system with regard to ice-sheet history
and interaction with global ocean circulation. Polar regions are, however, significantly under-investigated
and knowledge gaps exist in proximity to the formerly ice-covered regions. The physical characteristics of
glacial tills and proximal glacigenic marine deposits, with a highly consolidated, cohesive matrix and lithic clast inclusions, hinder successful sediment coring. Deep penetration of these deposits by conventional
piston and gravity coring, commonly used on multi-purpose research vessels, is very limited. Drill ships,
in contrast, allow for deep drilling, but are prohibitively expensive. An alternative with penetration depths
≤ 100 m are multi-barrel seafloor drill rigs deployed from conventional research vessels.
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In July to August 2013, a scientific expedition drilled two > 35-m long boreholes through tills and
glacigenic sediments in the Kveithola Trough (western Barents Sea; drill rig MeBo), that hosted icestreams during glacial times. Bathymetric and sub-bottom depositional structures indicate episodic icestream retreat during the climate warming after the last glacial maximum, resulting in successive transversal ridges (grounding-zone wedges, GZWs). Despite high stiffness of the glacigenic deposits forming the
GZWs and, thus, considerable sediment adhesion on the drill string that implied a reduced sediment recovery, the target base of the GZW was reached. The experience shows that obtaining marine sediment
cores and borehole logs in glacial sediments is technologically challenging. However, the scientific value
of drilling into such deposits is worth the effort. The sediment cores will allow for the very first time to
reconstruct the sedimentary processes and history of a GZW.
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Scientific demand to drill into glacigenic depositional successions
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The dynamics of ice sheets affect sea level, ocean circulation, heat transport, albedo, water-mass
characteristics, and marine productivity. For this reason it is extremely important to improve our
knowledge on the extent, timing, and mode of decline of past ice-sheets, which is required for reliable icesheet stability modeling. Notably, the past-extent, characteristics and behavior of marine-based ice-sheets
are inherently different and not as well understood as terrestrial ice-sheets [Carlson and Winsor, 2012].
However, obtaining adequate core recovery from the sedimentary units left by marine-based ice sheets is
difficult using the conventional technology available on most research ships (gravity/piston coring). Core
sampling of modern till deposits is prohibitive due to overlying moving ice. Borehole sampling of this ma1
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terial on ice-free present-day shelves is feasible, though drilling without a riser system is inherently difficult [De Santis et al., 2013].
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The development of new models of fast flowing ice streams, based on the analysis of sedimentary
records of erosion and deposition of former ice streams, is the main objective of the initiative NICE
STREAMS (Neogene ice streams and sedimentary processes on high-latitude continental margins), incorporated into the International Polar Year as Activity # 367. Within this initiative, and as a result of an international cooperation between several European institutions, the CORIBAR expedition targeted glacial
bedforms and meltwater deposits of the Kveithola Trough system with deep coring to reconstruct the
chronology of the deglaciation stages of the western Svalbard/Barents-Sea Ice Sheet.
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The CORIBAR expedition
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The CORIBAR expedition was recently carried out on board the German research vessel MARIA S.
MERIAN (cruise MSM-30, July 16 to August 15, 2013). The cruise aimed at drilling 70-m long sedimentary sequences through GZWs [Dowdeswell and Fugelli, 2012], made of glacigenic sediments, using the
MARUM-owned seafloor drill rig MeBo (Meeresboden-Bohrgerät). The paleo-ice stream depositional
system of the Kveithola Trough in the western Barents Sea was selected (Figure 1) because both catchment area and ice-stream extent were relatively small; therefore they were likely to have been sensitive to
changes in regional climate and sea level. Data collection in the area included 246 m of sediment cores,
including those collected at the five MeBo drilling sites, as well as 2,850 km of multibeam seafloor data
and PARASOUND sediment-acoustic profiles.
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The Kveithola system consists of a ~100-km long, 12-km wide E-W trending 300-m deep glacial
trough [Bjarnadóttir et al., 2013]. Inside the trough, forward motion of the paleo-ice stream produced parallel mega-scale lineations that are overlain by GZWs [Rebesco et al., 2011]. The dynamic mechanism
and timing of emplacement of these GZWs are of primary scientific interest as they document an episodic
retreat of the paleo-ice stream with interposed periods of ice-sheet stillstand after the last glacial maximum. Moreover, GZWs represent a key morphological element responsible for ice-shelf stabilization because they counteract collapses induced by ice-sheet thinning and sea-level rise [Dowdeswell and Fugelli,
2012].
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The reconstruction of the glacial history of the Kveithola Trough included the study of its Trough
Mouth Fan (TMF) developed off the shelf edge (Vorren et al., 1998). This fan is composed of a succession of hemipelagic sediments deposited during warm interglacial periods; gravity-transported glacigenic
debrites originated from sediment dumping over the shelf edge by the paleo-ice stream during glacial
maxima; and fine-grained laminated sediments supplied by turbid subglacial meltwaters (plumites) released at the ice-stream front during the deglaciation [Lucchi et al., 2013].
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First deployment of a shipboard-operating seafloor drill rig in a high-latitude environment
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During the CORIBAR expedition, we deployed the seafloor drill rig MeBo for the first time in the
Arctic region to gain experience in high-latitude drilling and to obtain unique sedimentary records from
GZW and plumite successions documenting a rapidly-retreating fast-moving ice system. MeBo drilling is
conducted with a stationary platform on the seabed, mandatory for optimal control on the drilling process
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(Freudenthal and Wefer, 2013). A special umbilical is used for lowering the 10 tons device to the seabed
and for remote control. Standard H-size wire line core barrels and drill rods for drilling down to 70 m below seafloor are stored on two magazines on the drill rig. An autonomous spectral gamma ray probe
serves for borehole logging.
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We were able to deploy the MeBo at five sites: three sites located in the Kveithola trough having the
target to drill across the GZWs, and two sites along the TMF to recover older units including glacigenic
debrites (i.e., mass-transport deposits made of unsorted glacially-derived sediments dumped over the shelf
edge by the paleo-ice stream during glacial maxima).
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Characteristics of grounding-zone wedges and glacigenic debrites
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The results document sediment-dynamic and paleo-environmental aspects of the Kveithola paleo-icestream and associated TMF from the last glacial maximum through the deglaciation and interglacial stages. The dataset provide evidence for an ice stream that reached the shelf edge carving a glacial trough and
delivering substantial amounts of sediment to the slope in the form of glacigenic diamicton and plumites.
The ice stream retreated in at least four different stages recorded as a succession of GZWs. Glacial landforms and deposits have been subsequently draped by 15 m of post-glacial muds interbedded with icerafted debris, and up to 20-m thick contourite drifts in the inner area of the Kveithola Trough.
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The CORIBAR expedition provided the first long-recovery sedimentary record of a GZW. At Site
GeoB17601-6 (Figure 1), MeBo cored through a 15-m thick glacimarine sediment drape, fully penetrated
the 15-m thick glacigenic sediments of the GZW, and drilled 11 m into the underlying basal tills. Borehole
gamma-ray logging highlighted major depositional discontinuities and lithological changes, particularly
evident at the base of the GZW, at the contact with the underlying deformation till. Along the upper clayrich succession (GZW, glacimarine sediment drape), major changes in log data likely relate to the sediment consolidation state resulting from the loading history (or lack of) by the ice stream.
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Indeed, despite potential drilling disturbance, the shear strength (measured with a pocket penetrometer at the base of the recovered sections) is relatively low in the glacimarine sediment drape (> 12 kPa) and
increases suddenly within the clays of the GZW with values up to 52 kPa. Below the GZW, a diamicton
with cobbles and pebbles within a stiff clayey matrix has shear strengths even up to 100 kPa, likely indicative of basal deformation tills. The core, though not analyzed yet, will provide the first age constraints on
the timing of GZW formation.
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The future of deep drilling in polar regions from research vessels
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As expected, the glacigenic deposits were a challenge for drilling. With the attempt to get a bestpossible recovery, average recovery rates were 84 % for continental slope deposits, 72 % for the Holocene
drape, and 23 % for the drilled diamicton (GZW 43 %; basal till 9 %). Valuable experience was collected
for MeBo drilling during the CORIBAR expedition by testing different types of drill bits, core catchers
and controlling drill parameters. Core-catcher strength proved to be critical in the soft Holocene drape.
Typically we worked with flush rates of 10-15 l/m, torque values below 200 Nm and penetration rates of
about 0.25 cm/s in these extremely soft deposits. Glacigenic diamictons and slope deposits, of cohesive
and plastic clayey matrix were very sticky and hampered rotation of the drilling string. This was especially
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the case for basal tills as indicated by high torque values of >350 Nm despite of increased flushing rates of
~25 l/min. A slight reduction in flushing rate from 22-23 l/min to <20 l/min resulted in a core recovery increase from 31 to 55 % within the GZW indicating that the amount of flush water is a critical parameter
for core recovery rates in the glacial deposits. Glacigenic debrites on the continental slope were sticky and
had similar consistency as GZW tills inside the trough. We allowed torque values up to 600 Nm by keeping the flush water rate below 25 l/min and reached recovery rates > 80%.
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Our core recovery for the diamictons is comparable to previous ODP expeditions, but significantly
higher for the firm to stiff GZW sediments. Average recovery in ODP drilling in Antarctica was 10.1 %
(subglacial till in Leg 178 shelf-transect sites) and 7.9 % (subglacial and proximal diamicton in Leg 188
Site 1166). IODP Exp. 341 had a recovery rate of 24 % for diamictons deposited from suspension settling,
gravity flows, and ice rafting (Site U1421). With the SHALDRILL technology, recovery was 40 % for an
80-cm thick diamicton (2nd leg), but 0 % in preceding attempts during the 1st leg. Only the ANDRILL
project, deploying full drill-hole cementation and circulation muds, achieved a recovery of 98 %. Using
MeBo with further flush-water reduction would likely improve core recovery in the stiff to hard (likely
highly consolidated) basal tills. as well. We are, thus, optimistic that further technical experience will help
improving recovery rates and sediment quality in polar environments.
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MARUM is currently developing the second MeBo generation with a drilling capacity of 200 m below seafloor. MeBo200 will supplement the several hundred meters deep drillings performed from drill
ships such as RV JOIDES RESOLUTION and RV CHIKYU.
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Acknowledgements
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The CORIBAR team members: A. Camerlenghi and A. Caburlotto (OGS), T. Hörner (AWI, Bremerhaven), H. Lantzsch and A. Özmaral (MARUM, Bremen), J. Llopart (CSIC, Barcelona), L.S. Nicolaisen
(GEUS, Copenhagen), K. Andreassen and G. Osti (UiTromsø), A. Sabbatini (UNIVPM, Ancona). CORIBAR is funded by the Italian PNRA, Spanish “Ministerio Economia y Competitividad”, Danish Carlsberg
Foundation and Dansk Center for Havforskning, Norwegian Statoil ASA, and MARUM incentive. CORIBAR is embedded into the international NICESTREAM project.
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Fig. 1: PARASOUND profile through a grounding-zone wedge in the Kveithola Trough with MeBo Site
GeoB17601-6. Logs and lithological information are converted to time using a 1500m/s sound-speed velocity. The vertical scale is the same for the PARASOUND profile and the logs/lithology plots. Borehole
logs and sediment samples: natural -ray of Uranium (U) and Potassium (K), shear strength (SS) measurements (pocket penetrometer), natural Gamma Ray (GR), sediment recovery (blue dots), lithology from
barrel core catchers (colored bars). Physical drilling parameters: Drill-head torque (DT), flush rate
(FR), penetration rate (PR). Right bottom inset shows location of Kveithola Trough (star). Left top shows
multibeam bathymetry with location of PARASOUND and MeBo borehole.
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