Recognizing the effect of modern and paleo bottom currents across deep-marine basins: insights from sedimentological and geophysical data across the Western Gap and Josephine Seamount (NE Atlantic)

We present geophysical and sedimentological data acquired during the 59^th cruise of the P/V Akademik Ioffe (September – October 2021) from the eastern North Atlantic. Two sediment cores AI-59022 and AI-59027 were recovered southwest of the Western Gap entrance sill (water depth 4872 m) and from the western slope of the Josephine seamount (water depth 3282 m), respectively.  The collected data is valuable for reconstructions of the Pleistocene to Holocene sedimentary record and recognizing the influence of near-bottom currents on sediment deposition in the study areas.

Using high-resolution sub-bottom profiling, sediment waves (up to 50 m in amplitude) were found southwest of the entrance sill of the Western Gap. The presence of ripples and scours north of this sill also indicate elevated bottom current velocities in the gap which is in agreement with direct current velocity measurements (30 cm/s). Given that temperatures of <2 °C, which are characteristic of the AABW (Morozov et al., 2010), were recorded by CTD profiling near the seafloor, it is possible that AABW has played a significant role in shaping the sedimentary and morphological features in the Western Gap.

On the western slope of the Josephine seamount, a contourite drift intercalated with mixed features was identified, characterized by multiple, continuous sub-parallel reflections.  High-resolution sub-bottom profiling has also allowed us to identify a distinct erosional furrow at 1410 m (water depth). The depth of this feature corresponds to the present depth of the Mediterranean Outflow Water and may be related to the erosive passage of MOW currents.

The sponge species Pheronema carpenter was also observed on the western slope of the Josephine seamount. This species is typically associated with areas of high productivity, and possibly with regions of enhanced bottom tidal currents which promote the resuspension of organic matter. Thus, the presence of this sponge indicates elevated near-bottom hydrodynamic activity in the Josephine seamount area.

The dataset across the western slope of the Josephine seamount was supported by an IO RAS state assignment (№0128-2021-0012), whereas the study in the Western Gap was financed by RFBR (№20-08-00246).