Formation and Age of Raised Marine Beaches, Northern Scott Coast, Antarctica

The stability of the West Antarctic Ice Sheet (WAIS) is a key problem because of its potential effect on global sea level and climate. Some geologic evidence suggests that the ice sheet has collapsed in the past, which, if correct, implies that future disintegration is possible. Isolation of the mechanism(s) that have affected WAIS behavior since the last glacial maximum (LGM) may yield information about factors that control it today. Previous studies have indicated thatrecession of the WAIS from the LGM position occurred in the middle to late Holocene. However, the data come fiom points too far south to assess accurately the timing and cause of the early phase of deglaciation. Reconstruction of ice retreat in the Ross Sea Embayment since the LGM relies heavily on the development of relative sea-level curves from raised beaches. In turn, the accuracy of these curves depends on the manner in which the beaches fornl and in which organic material is incorporated. The present study has two main objectives. The first is to determine the processes that formed beaches now uplifted along the northern Scott Coast. The second is to obtain radiocarbon samples, which will determine the ages of the raised beaches, and aid in relative sea-level interpretations. My results suggest that stonn waves formed most beaches in the study areas. Moreover, nearly every wave-formed beach ridge is a single-storm deposit. These conclusions, at least for the southern part of the field area, support the idea that Holocene sea-ice extent was less than it is today. This is in agreement with glacial geologic and faunal proxies that suggest that temperatures were generally warmer and sea ice was less extensive during the mid-to-late Holocene. The radiocarbon data fiom this study have led to the first identification of pre- Holocene beach deposits along the coast of the Ross Sea. Every sample recovered from Cape Ross predates the last glacial maximum, and additional old samples come fiom Spike Cape and Inexpressible Island. There are two hypotheses to explain the pre- Holocene material. One is that Holocene beach sediments overlie a core of preserved older deposits. The other is that the entire set of beaches predates the last glacial maximum and that Holocene deposits are absent. It is not possible to distinguish conclusively between these two hypotheses at this time. However, these new data show that undated beaches along the Antarctic coast can no longer be assumed to be Holocene in age. Moreover, the presence of older beach deposits complicates the process of reconstructing Holocene relative sea-level curves and reaffirms the need for detailed dating and stratigraphic analysis of beach ridges