Compression and expansion index and void ratio of samples from Lomonosov Ridge and Yermak Plateau

With the coupled use of multibeam swath bathymetry, high-resolution subbottom profiling and sediment coring from icebreakers in the Arctic Ocean, there is a growing awareness of the prevalence of Quaternary ice-grounding events on many of the topographic highs found in present water depths of <1000 m. In some regions, such as the Lomonosov Ridge and Yermak Plateau, overconsolidated sediments sampled through either drilling or coring are found beneath seismically imaged unconformities of glacigenic origin. However, there exists no comprehensive analysis of the geotechnical properties of these sediments, or how their inferred stress state may be related to different glacigenic processes or types of ice-loading. Here we combine geophysical, stratigraphic and geotechnical measurements from the Lomonosov Ridge and Yermak Plateau and discuss the glacial geological implications of overconsolidated sediments. The degree of overconsolidation, determined from measurements of porosity and shear strength, is shown to result from consolidation and/or deformation below grounded ice and, with the exception of a single region on the Lomonosov Ridge, cannot be explained by erosion of overlying sediments. We demonstrate that the amount and depth of porosity loss associated with a middle Quaternary (~ 790-950 thousand years ago - ka) grounding on the Yermak Plateau is compatible with sediment consolidation under an ice sheet or ice rise. Conversely, geotechnical properties of sediments from beneath late Quaternary ice-groundings in both regions, independently dated to Marine Isotope Stage (MIS) 6, indicate a more transient event commensurate with a passing tabular iceberg calved from an ice shelf.

(Table 1) Strontium isotope ratios (87Sr/86Sr) of Neogloboquadrina pachyderma (sinistrally coiling) tests from ODP Hole 151-910A

The sediment sequence at Ocean Drilling Program (ODP) Site 910 (556 m water depth) on the Yermak Plateau in the Arctic Ocean features a remarkable "overconsolidated section" from ~19 to 70-95 m below sea floor (m bsf), marked by large increases in bulk density and sediment strength. The ODP Leg 151 Shipboard Scientific Party interpreted the overconsolidated section to be caused by (1) grounding of a marine-based ice sheet, derived from Svalbard and perhaps the Barents Sea ice sheet, and/or (2) coarser-grained glacial sedimentation, which allowed increased compaction. Here I present planktonic foraminiferal d18O data based on Neogloboquadrina pachyderma (sinistrally coiling) that date the termination of overconsolidation near the boundary between isotope stages 16 and 17 (ca. 660 ka). No evidence is found for coarser grained sedimentation, because lithic fragments >150 µm exhibit similar mean concentrations throughout the upper 24.5 m bsf. The overconsolidated section may reflect more extensive ice-sheet grounding prior to ca. 660 ka, suggesting a major change in state of the Svalbard ice sheets during the mid-Quaternary. Furthermore, continuous sedimentation since that time argues against a pervasive Arctic ice shelf impinged on the Yermak Plateau during the past 660 k.y. These findings suggest that Svalbard ice-sheet history was largely independent of circum-Arctic ice-sheet history during the middle to late Quaternary.

(Table T1) Correlation of the postglacial laminated unit between ODP Holes 178-1098A, 178-1098B and 178-1098C

The Antarctic Peninsula region is ideally suited to monitor how global change affects Antarctica because it is one of the most sensitive regions of the continent to rapid climate change. This has been clearly demonstrated by the recent break up of the Larsen A Ice Shelf. Drilling at Ocean Drilling Program Site 1098, Palmer Deep, western Antarctic Peninsula, recovered almost 50 m of sediments that record the paleoceanographic and paleoclimatic history of the region from the last glacial maximum through the rapid climate oscillations of deglaciation into the Holocene. This sedimentary section will provide a wealth of high-resolution paleoenvironmental data from Antarctica that will be useful for climate modelers and paleoceanographers alike. This data report presents the preliminary results of a high-resolution, microscale sediment fabric study of the postglacial sediments from Palmer Deep Site 1098. These sediments have previously been described as being annually laminated; however, this investigation shows that although the interpretation of this sequence as seasonal sediments is most likely correct, there are a number of features that indicate there is strong interannual variability affecting the laminations.