THE MIDDLE MIOCENE CLIMATE SHIFT ON THE ROSS SEA CONTINENTAL SHELF: A FIRST ORDER TEST OF THE MARINE OXYGEN ISOTOPE RECORD

Evolution of the Antarctic cryosphere during the Miocene is well documented in the marine oxygen isotope record. The oxygen isotope curves indicate that Antarctica underwent dramatic cooling in the middle Miocene, which led to the development of the stable continental-scale glaciation present today. Estimates of timing and magnitude of the climate shift are readily available from proxies, however physical evidence from Antarctica has not been used to address the issue. For example, initial reports from DSDP leg 28, site 274 indicated a significant decrease in sedimentation during the middle Miocene however, Hayes and Frakes (1975) suggested sediment capture by a graben structure up slope as opposed to climate change as the mechanism. More recently, sedimentary sequences were correlated and mapped across the Ross Sea in ANTOSTRAT (1995), although this data has not been specifically applied to the middle Miocene shift. Given Antarctica's integral role in modern ocean circulation and climate, understanding how the Antarctic cryosphere developed is in many respects fundamental to understanding the development and evolution of Earth's modern climate. If the cooling and ice growth during the middle Miocene developed in the manner proposed by oxygen isotope data, then sedimentary features and volumes should be characteristic of such a shift. This study examines sediment yield and stratigraphy in the Ross Sea using published sediment isopach maps in combination with single and multi-channel seismic reflection data. Miocene sequences (RSS3-6), from the ANTOSTRAT Project indicate sediment volume and distribution shifting toward the shelf edge from early to middle Miocene. This shift is consistent with the stratal geometries expected from the transition from a temperate to polar climate. Our research will evaluate changes in sediment yield as well as stratal geometries identified in seismic data. Recognizing the changes in stratigraphy and sediment volume, provides means to directly test how the middle Miocene shift proceeded in the Ross Sea and can refine the interpretations of the deep-sea proxy records.