Biostratigraphy, magnetostratigraphy, granulometry, isotopes and clay mineral composition of ODP Site 188-1165

During Ocean Drilling Program Leg 188 to Prydz Bay, East Antarctica, several of the shipboard scientists formed the High-Resolution Integrated Stratigraphy Committee (HiRISC). The committee was established in order to furnish an integrated data set from the Pliocene portion of Site 1165 as a contribution to the ongoing debate about Pliocene climate and climate evolution in Antarctica. The proxies determined in our various laboratories were the following: magnetostratigraphy and magnetic properties, grain-size distributions (granulometry), near-ultraviolet, visible, and near-infrared spectrophotometry, calcium carbonate content, characteristics of foraminifer, diatom, and radiolarian content, clay mineral composition, and stable isotopes. In addition to the HiRISC samples, other data sets contained in this report are subsets of much larger data sets. We included these subsets in order to provide the reader with a convenient integrated data set of Pliocene-Pleistocene strata from the East Antarctic continental margin. The data are presented in the form of 14 graphs (in addition to the site map). Text and figure captions guide the reader to the original data sets. Some preliminary interpretations are given at the end of the manuscript.

P-wave velocities and applied bed thickness and velocity changes for synthetic seismograms, ODP Leg 188 and Leg 119 sites

Synthetic seismograms provide a crucial link between lithologic variations within a drill hole and reflectors on seismic profiles crossing the site. In essence, they provide a ground-truth for the interpretation of seismic data. Using a combination of core and logging data, we created synthetic seismograms for Ocean Drilling Program Sites 1165 and 1166, drilled during Leg 188, and Site 742, drilled during Leg 119, all in Prydz Bay, Antarctica. Results from Site 1165 suggest that coring penetrated a target reflector initially thought to represent the onset of drift sedimentation, but the lithologic change across the boundary does not show a change from predrift to drift sediments. The origin of a shallow reflector packet in the seismic line across Site 1166 and a line connecting Sites 1166 and 742 was resolved into its constituent sources, as this reflector occurs in a region of large-scale, narrowly spaced impedance changes. Furthermore, Site 1166 was situated in a fluvio-deltaic system with widely variable geology, and bed thickness changes were estimated between the site and both seismic lines.

Ice-rafted debris in ODP Holes 177-1090D and 188-1165B

Constraining the nature of Antarctic Ice Sheet (AIS) response to major past climate changes may provide a window onto future ice response and rates of sea level rise. One approach to tracking AIS dynamics, and differentiating whole system versus potentially heterogeneous ice sheet sector changes, is to integrate multiple climate proxies for a specific time slice across widely distributed locations. This study presents new iceberg-rafted debris (IRD) data across the interval that includes Marine Isotope Stage 31 (MIS 31: 1.081-1.062 Ma, a span of ~19 kyr; Lisiecki and Raymo, 2005), which lies on the cusp of the mid-Brunhes climate transition (as glacial cycles shifted from ~41,000 yr to ~100,000 yr duration). Two sites are studied - distal Ocean Drilling Program (ODP) Leg 177 Site 1090 (Site 1090) in the eastern subantarctic sector of the South Atlantic Ocean, and proximal ODP Leg 188 Site 1165 (Site 1165), near Prydz Bay, in the Indian Ocean sector of the Antarctic margin. At each of these sites, MIS 31 is marked by the presence of the Jaramillo Subchron (0.988-1.072 Ma; Lourens et al., 2004) which provides a time-marker to correlate these two sites with relative precision. At both sites, records of multiple climate proxies are available to aid in interpretation. The presence of IRD in sediments from our study areas, which include garnets indicating a likely East Antarctic Ice Sheet (EAIS) origin, supports the conclusion that although the EAIS apparently withdrew significantly over MIS 31 in the Prydz Bay region and other sectors, some sectors of the EAIS must still have maintained marine margins capable of launching icebergs even through the warmest intervals. Thus, the EAIS did not respond in complete synchrony even to major climate changes such as MIS 31. Further, the record at Site 1090 (supported by records from other subantarctic locations) indicates that the glacial MIS 32 should be reduced to no more than a stadial, and the warm interval of Antarctic ice retreat that includes MIS 31 should be expanded to MIS 33-31. This revised warm interval lasted about 52 kyr, in line with several other interglacials in the benthic d18O records stack of Lisiecki and Raymo (2005), including the super-interglacials MIS 11 (duration of 50 kyr) and MIS 5 (duration of 59 kyr). The record from Antarctica-proximal Site 1165, when interpreted in accord with the record from ANDRILL-1B, indicates that in these southern high latitude sectors, ice sheet retreat and the effects of warming lasted longer than at Site 1090, perhaps until MIS 27. In the current interpretations of the age models of the proximal sites, ice sheet retreat began relatively slowly, and was not really evident until the start of MIS 31. In another somewhat more speculative interpretation, ice sheet retreat began noticeably with MIS 33, and accelerated during MIS 31. Ice sheet inertia (the lag-times in the large-scale responses of major ice sheets to a forcing) likely plays an important part in the timing and scale of these events in vulnerable sectors of the AIS.