Marine Geology Near the southernmost point of the cruise on the LR towards Greenland, a Kastenlot (PS87/023)

was retrieved at a slope location on the Amundsen Sea side of the ridge. The PARASOUND record (Fig. 10.2.2) is strongly affected by secondary noise created from breaking sea-ice by the hull of the vessel. At the coring location (Fig. 10.2.2) the profile exhibits an acoustic sub-bottom penetration of about 40 m into pelagic sediments. Acoustic stratigraphy suggests three different units. The uppermost unit (1) is about 13 m thick and has strong reflectors overlying a featureless almost transparent unit, which is about 20 m thick. This is underlain by a unit with more distinct reflectors similar in geometry to those of unit 1 but showing weaker reflectors.

Towards both lateral ends of the profile, debris-flow deposits lens out, which cover most of unit 1 sediments draped by a thin veneer of pelagic deposits. The coring location is not covered by debris flows (Fig. 10.2.2).

Core PS87/040 (KAL) was retrieved from an intra-basin of the central LR relatively close to the North Pole. The PARASOUND profile (Fig. 10.2.3) shows the coring location between the time markers 22:20 UTC and 03:50 UTC towards the eastern end of the basin. The record is well stratified and has two acoustic units, an upper one with strong reflectors and a lower one with weaker reflections. The relative sedimentation rate at the eastern (left and shallower) end of the profile is about 20% lower than at the right and deeper end. This suggests that the basin is affected by lateral sediment transport and sediment focussing into the basin possibly related to gravity induced re-deposition and/or currents.

Fig. 10.2.3: PARASOUND example from the central Lomonosov Ridge. Position of coring location PS87/040 is between the time markers 22:20 and 03:50 UTC. The black and white bars at system.

10.2 Sediment Echosounding using PARASOUND

Fig. 10.2.4: PARASOUND example from the central Lomonosov Ridge. Position of coring location PS79/287 is close to the time marker 23:30 UTC. The black and white bars at the bottom give lateral

distance in km. The depth has been determined by the PARASOUND system.

Along a PARASOUND profile across the LR at about 84° N, the sediments appear mostly well stratified and drape sub-bottom topographies (Fig. 10.2.4). Here the acoustic stratigraphy is less distinct compared to the profiles described above. Stronger reflectors in the upper 15 m thickness are underlain by a transitional zone of 5 m and then followed by weaker reflectors.

The location of core PS87/070 was selected between the time marks of 23:30 and 23:40 UTC.

The left end of the profile is characterized by slump hummocks covered by pelagic sediments.

Along a PARASOUND profile across the LR at about 83° N, the sediments exhibit slide scars in places near the crest of the LR (Fig. 10.2.5). Between coring stations PS87/079 /080 and /083, which were selected along the profile, about 200 m thick packages of a formerly well-stratified pelagic drape were removed and re-deposited onto the slope of the Amundsen Basin (left of time mark 21:20 UTC in Fig. 10.2.5). Coring location PS87/079 was selected at about 1,400 m water depth on the undisturbed part of the profile. Cores PS87/080-1 to /080-4 as well as cores PS87/083-1 to /083-3 were selected along the slide scar between about 1,480 m and 1,560 m water depth (Fig. 10.2.5).

At the southern end of the LR on the Siberian side (about 81°N), near a sill encouraging water-mass exchange between the Amundsen and Makarov basins, coring site PS87/109 was selected in about 1,350 m water depth at time mark 15:20 UTC (Fig. 10.2.6). The PARASOUND profile exhibits a hemi-pelagic drape on a mount of the LR. Again, the acoustic stratigraphy consists of an upper unit with stronger reflections to a sediment depth of about 11 m underlain but well-stratified sediments forming weaker reflectors. Lateral sedimentation rates decrease towards deeper water suggesting stronger winnowing towards the sill below 1,300 m of water (Fig. 10.2.6).

10. Marine Geology

Fig. 10.2.5: PARASOUND example from the central Lomonosov Ridge. Positions of coring locations are described in text. The black and white bars at the bottom give lateral distance (1 km per bar). The

depth has been determined by the PARASOUND system.

Fig. 10.2.6: PARASOUND example from the southern Lomonosov Ridge (Siberian side). Position of coring location PS87/109 is at the time marker 15:20 UTC. The black and white bars at the bottom

give lateral distance in km. The depth has been determined by the PARASOUND system.

10.2 Sediment Echosounding using PARASOUND

On the Gakkel Ridge coring station PS87/110 was selected in one of the small deep basins, which characterize the ridge between 83° and 84° north. The position of the core is slightly above the deepest spot of the basin in 5,100 m water depth at the 12:00 time mark (Fig.

10.2.7). The echo character of the sediments in the basin is somewhat diffuse probably as a result of interfingering of bottom and side echoes. However, some stratification in the upper 20 m of the sedimentary record is visible at the coring site.

Fig. 10.2.7: PARASOUND example from the southern end of the Gakkel Ridge (Siberian side).

Position of coring location PS87/110 is close to the time marker 12:00 UTC. The black and white bars at the bottom give lateral distance in km. The depth has been determined by the PARASOUND

system.

For the time after the cruise it is expected that major results can be achieved with respect to correlating the acoustic (PARASOUND) stratigraphy of PS87 with those of previous Polarstern cruises in the same area. This will allow to transfer existing age models from cores of previous cruisis into the PS87 sediment-echosounding records. Consequently this will aid to constrain the interpretation of spacial and temporal facies changes in the central Arctic Ocean. In particular, this will become important for the shallower parts of the LR, where hints were noted in the PARASOUND data, which will confirm and modify the view that ice has grounded on the LR in places, eroded older strata, and formed diamicton (e.g. Jakobsson et al. 2014).

Data Management

For the entire period of data acquisition five different types of data files were stored on hard disc:

- PHF data in ASD format - PHF data in PS3 format - SLF data in ASD format - SLF data in PS3 format

- Navigation and Auxiliary data (60s intervals) in ASCI format - ATLAS PARASTORE 3 settings in XML files

10. Marine Geology