Description: Observations across both the West Antarctic and Antarctic Peninsula ice sheets over recent decades have confirmed that the region is warming and undergoing major and potentially rapid changes as a result. These changes have manifest in the form of significant ice-sheet thinning and retreat, and in dramatic short-lived events such as ice-shelf collapses. The longer-term backdrop to this recent change is vital information for our understanding of future ice and climate evolution, and for wider knowledge of ice-sheet function and sensitivity. Providing context on geological timescales, such records can be obtained from two main sources: (1) from ice cores extracted from the ice sheet interiors and (2) from continuous marine sedimentary sequences recovered from the sea floor surrounding the Antarctic continent. Whilst ice cores provide a very high-resolution archive of palaeo-climate, they offer data over only a relatively short window of time (〈1 million years) and provide little information on how the ice and oceans were changing at the ice sheet periphery. By contrast, sediments derived from the Antarctic continent have discharged continuously to the continental slope and deeper ocean over millions of years, and are sensitive recorders of both ice sheet an oceanographic variability. Repeated continental margin-derived turbidity currents, in combination with the activity of along-slope currents, have led to the accumulation of large hemi-pelagic depositional bodies, termed sediment drifts that are, today, oriented orthogonal to the continental margin and record continuous sedimentation on the continental rise since at least the Miocene. Along the Antarctic Peninsula Pacific margin, a chain of twelve large sediment drifts separated out by channels eroded by turbidity currents provide unique archives of environmental changes in Antarctica‘s ice sheets and the Southern Ocean. IODP proposal 732FULL2 aims to recover drill cores extending back into the Pliocene from the crests of a number of the drifts, as well as from the top of the Belgica trough mouth fan, during a future leg to the region. Two further sites will recover older strata that can be accessed at relatively shallow depth by drilling through eroded drift flanks where the overburden is particularly thin. However, before recovering sequences from these bodies, a full understanding of their geometry, internal architecture, age and stratigraphic evolution is required. We present preliminary results from recent Natural Environment Research Council (UKIODP Programme) funded site survey cruise JR298 that obtained high-resolution multichannel seismic (MCS) reflection data over the proposed drill sites and adjacent working areas. A first look at the seismic data from several of the drilling targets will be presented, and some initial interpretations regarding the (i) sedimentary processes that operated during the formation and evolution of the drifts and fan, and (ii) links between depositional systems on the continental rise, palaeo-ice-sheet dynamics and past oceanographic processes within the datasets will be discussed. Further geophysical analyses, in combination with marine sediment cores retrieved from the proposed sites, will aim to shed light upon continental margin sediment delivery, Antarctic ice-sheet history and stability, and Antarctic margin palae-oceanography that form the key scientific objectives of the planned drilling campaign.

Description: Scientific drilling continues to advance knowledge of Antarctica’s role in the climate system and the evolution of its ice sheets. Since 1972, seven DSDP, ODP, and IODP expeditions to Antarctic waters have documented cooling of Antarctic climate since the early Eocene; inception of large-scale glaciation at the start of the Oligocene; ice-sheet expansion and relative stabilization in the middle Miocene; fluctuations of the ice margins in the Pliocene; and high-resolution details of Holocene climate. Geological drilling by land- and ice-based projects such as ANDRILL has provided shoreward evidence of ice and climate behaviour complimentary to the ship-based drilling. The scientific significance of the sediment cores collected on these expeditions has grown as the problem of global warming has become more apparent, and the cores continue to be analysed with the development of new techniques, such as biomarker temperature estimates and geochemical sediment provenance. However, these existing sedimentary records do not cover all of the Cenozoic and the core locations are geographically restricted. Antarctic marine sediments hold further records of ice sheet dynamics and warm climates of the past that form analogues for high-CO2 greenhouse scenarios of the next centuries. Several proposals to collect these records are in the IODP review system, for regions where the ice sheets are sensitive to warming and for time periods when the ice response to warm climates is not well known. A workshop is being held at IODP in College Station, Texas, in May 2016 to: (1) Produce an integrated overview of how IODP drilling can advance understanding of Antarctic ice sheet retreat (and hence sea level rise) under warm climates; (2) Examine existing sediment cores that revealed Antarctica’s past marine glaciological history; and (3) Establish best practices for assessing ice and weather to conduct safe drilling operations in Antarctic waters. Here we review the highlights and outcomes of this workshop, and look to the future of scientific drilling around Antarctica.

Description: Changes observed in the West Antarctic Ice Sheet (WAIS) and Antarctic Peninsula Ice Sheet (APIS) over recent decades include thinning and break up of ice shelves, glacier flow acceleration and grounding line retreat. How rapidly and how far these ice sheets will retreat in a warmer climate, however, remains uncertain. For example, it remains unclear whether or not the marine-based WAIS “collapsed” during Quaternary interglacial periods, including the last one, contributing more than 3 m to global sea-level rise. Continuous long-term records of ice sheet change with precise chronology are needed in order to answer these questions. On the Antarctic continental shelf, sedimentary records are interrupted by numerous unconformities resulting from glacial erosion, good core recovery has only been achieved from platforms sited on sea ice or ice shelves, and establishing reliable chronologies has proved challenging. In contrast, sediment drifts on the upper continental rise around Antarctica contain expanded, continuous successions dominated by muddy lithologies from which good recovery can be achieved using standard scientific ocean drilling methods. Ocean Drilling Program (ODP) Leg 178 demonstrated that sediment drifts west of the Antarctic Peninsula contain a rich high-resolution archive of Southern Ocean paleoceanography and APIS history that extends back to at least the late Miocene. The potential of existing ODP cores from the drifts is, however, compromised by incomplete composite sections and lack of precise chronological control. An International Ocean Discovery Program proposal (732-Full2) for future drilling on these drifts has been scientifically approved and is with the JOIDES Resolution Facilities Board for scheduling. The main aims of the proposal are to obtain continuous, high-resolution records from sites on sediment drifts off both the Antarctic Peninsula and West Antarctica (southern Bellingshausen Sea). The challenges will then be achieving good chronological control using a range of established and novel techniques and interpreting what facies variations indicate in terms of changes in the ice sheets. During a 2015 research cruise on RRS James Clark Ross (JR298) we obtained additional site survey data around the proposed sites including high-resolution multichannel seismic reflection data, piston cores and box cores. We will present results from this cruise and interpret them in terms of sedimentary processes that operated during the development of the drifts, and links between depositional systems on the continental rise, paleoice-sheet dynamics and paleoceanographic processes.

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.

Description: Lack of foraminiferal carbonate in marine sediments deposited at high latitudes results in traditional oxygen isotope stratigraphy not playing a central role in Quaternary age control for a large portion of the globe. This limitation has affected the interpretation of Quaternary sediment drifts off the Antarctic Peninsula in a region critical for documenting past instability of the West Antarctic Ice Sheet (WAIS) and Antarctic Peninsula Ice Sheet (APIS). Here we use piston cores recovered from these sediment drifts in 2015 during cruise JR298 of the RRS James Clark Ross to test the usefulness for age control of relative paleointensity (RPI) data augmented by scant d18O data. Thermomagnetic and magnetic hysteresis data, as well as isothermal remanent magnetization (IRM) acquisition curves, indicate the presence of prevalent magnetite and subordinate oxidized magnetite ("maghemite") in the cored sediments. The magnetite is likely detrital. Maghemite is an authigenic mineral, associated with surface oxidation of magnetite grains, which occurs preferentially in the oxic zone of the uppermost sediments, and buried oxic zones deposited during prior interglacial climate stages. Low concentrations of labile organic matter apparently led to arrested pore-water sulfate reduction explaining oxic zone burial and downcore survival of the reactive maghemite coatings. At some sites, maghemitization has a debilitating effect on RPI proxies whereas at other sites maghemite is less evident and RPI proxies can be adequately matched to the RPI reference template. Published RPI data at ODP Site 1101, located on Drift 4, can be adequately correlated to contemporary RPI templates, probably as a result of disappearance (dissolution) of maghemite at sediment depths 〉~10m.

Description: The Miocene Climatic Optimum (MCO; ~16.9 to 14.7 Ma) provides an outstanding opportunity to investigate climate-carbon cycle dynamics during a geologically recent interval of global warmth. We present benthic stable oxygen (d18O) and carbon (d13C) isotope records (5-12 kyr time resolution) spanning the late early to middle Miocene interval (18 to 13 Ma) at Integrated Ocean Drilling Program (IODP) Site U1335 (eastern equatorial Pacific Ocean). The U1335 stable isotope series track the onset and development of the MCO as well as the transitional climatic phase culminating with global cooling and expansion of the East Antarctic ice-sheet at ~13.8 Ma. We integrate these new data with published stable isotope, geomagnetic polarity and X-ray fluorescence (XRF) scanner-derived carbonate records from IODP Sites U1335, U1336, U1337 and U1338 on a consistent, astronomically-tuned timescale. Benthic isotope and XRF scanner-derived CaCO3 records depict prominent 100 kyr variability with 400 kyr cyclicity additionally imprinted on d13C and CaCO3 records, pointing to a tight coupling between the marine carbon cycle and climate variations. Our inter-site comparison further indicates that the lysocline behaved in highly dynamic manner throughout the MCO, with 〉75% carbonate loss occurring at paleo-depths ranging from ~3.4 to ~4 km in the eastern equatorial Pacific Ocean. Carbonate dissolution maxima coincide with warm phases (d18O minima) and d13C decreases, implying that climate-carbon cycle feedbacks fundamentally differed from the late Pleistocene glacial-interglacial pattern, where dissolution maxima correspond to d13C maxima and d18O minima. Carbonate dissolution cycles during the MCO were, thus, more similar to Paleogene hyperthermal patterns.