Description: It has been suggested that salinity increases in the subtropical gyre system may have pre-conditioned the North Atlantic Ocean for a rapid return to stronger overturning circulation and high-latitude warming following meltwater events during the Last Glacial period (Schmidt et al., 2006). Planktonic foraminifera oxygen isotopes (δ18O) measured on the surface dwelling Globigerinoides ruber show a positive gradient going from the Gulf Stream into the subtropical gyre during the Holocene as well as the Last Glacial Maximum (Keigwin, 2004). This gradient is due to decreasing temperatures, increasing salinity and a change from a summer to year round occurrence of G. ruber(Keigwin, 2004). During rapid climate oscillations between 54 and 46 ka of Marine Isotope Stage 3, including Heinrich ice-rafting event 5, this gradient may have been largely absent; G. ruber δ18O of ODP Site 1060 (subtropical gyre location) and ODP Site 1056 (Gulf Stream location) are virtually identical. Lower G. ruber δ18O that characterize the major warm DO interstadials 14 and 12 suggest a mainly summer occurrence of this species and indicate a more zonal and wider Gulf Stream influencing both ODP Sites. A large vertical δ18O gradient between shallow dwelling G. ruber and the deep dwelling species Globorotalia inflataat site 1056 is associated with strong summer stratification, supporting a Gulf Stream presence during these major interstadials. From about 51 ka until the end of Heinrich event 5 G. ruber δ18O is increased and the δ18O gradient between G. ruber and G. inflata is greatly reduced, suggesting a more year round occurrence of G. ruber and absence of summer stratification at site 1056, associated with subtropical gyre conditions. From this we infer that the Gulf Stream may have taken up a position nearer to the continental shelf during this cold period, where it may have been narrower with reduced transport.

Description: Late Miocene to Recent sediments offshore from the Antarctic Peninsula are predominantly lithogenic, having originated through glacial erosion. Sediments that accumulated during interglacial periods commonly have a greater biogenic component, but deposits in which this constitutes a substantial fraction are rare. Only a small fraction of the continental block is above sea level and even during interglacial periods temperatures are only warm enough to generate significant melt at low elevations for a few weeks each summer, so sediment input to the sea from surface runoff is minor. Sediment transport to the continental margin takes place mainly at the ice bed during glacial periods when the grounding line advances to the shelf edge. On the Pacific margin, downslope transport from the shelf edge region occurs mainly through gravitational mass transport processes. These processes are likely most active during glacial periods when rapid delivery of glacial sediment leads to instability on the uppermost slope and discharge of sediment-laden subglacial meltwater at the shelf edge grounding line initiates turbidity currents. The lack of obvious large slide scars along most of the relatively steep continental slope suggests that most individual failures are small in volume. Dendritic networks of small channels on the lower slope feed into large turbidity current channels that run out across the continental rise for hundreds of kilometres. Between the channels are giant sediment drifts, some with more than a kilometre of relief, which are composed predominantly of finely-bedded silt and clay layers. The drifts have been produced through entrainment of the fine-grained components of turbidity currents in the ambient bottom current that flows southwestward along the margin. Results from Ocean Drilling Program Leg 178 showed that these drifts contain high-resolution records of ice sheet and oceanographic changes, although unfortunately insufficient core material was recovered to generate continuous composite sections. During a 2015 research cruise on RRS James Clark Ross (JR298) we obtained new data over several of the drifts and channels, including high-resolution multichannel seismic reflection data, piston cores and box cores. We will present results from these new data, interpreting them in terms of sedimentary processes that operated during the development of the giant sediment drifts, and links between depositional systems on the continental rise, palaeo-ice-sheet dynamics and palaeoceanographic processes.