Chronostratigraphy of the Larsen blue-ice area in northern Victoria Land, East Antarctica, and its implications for paleoclimate

Abstract

In blue-ice areas (BIAs), deep ice is directly exposed at the surface, allowing for the cost-effective collection of large-sized old-ice samples. However, chronostratigraphic studies on blue-ice areas are challenging owing to fold and fault structures. Here, we report on a surface transect of ice with an undisturbed horizontal stratigraphy from the Larsen BIA, northern Victoria Land, East Antarctica. Ice layers defined by dust bands and ground-penetrating radar (GPR) surveys indicate a monotonic increase in age along the ice flow direction on the downstream side, while the upstream ice exhibits a potential repetition of ages on scales of tens of meters, which result from a complicated fold structure. Stable water isotopes (delta O-18(ice), and delta H-2(ice)) and components of the occluded air (i.e., CO2, N2O, CH4, delta N-15-N-2, delta O-18(atm) (= delta O-18-O-2), delta O-2/N-2, delta Ar/N-2, Kr-81, and Kr-85) are analyzed for surface ice and shallow ice core samples. Correlating delta O-18(ice), delta O-18(atm) and CH4 records from the Larsen BIA with ice from previously drilled ice cores indicates that the gas age at various shallow vertical coring sites ranges between 9.2-23.4 kyr BP, while the ice age sampled from the surface ranges from 5.6 to 24.7 kyr BP. Absolute radiometric Kr-81 dating for the two vertical cores confirms ages within accept- able levels of analytical uncertainty. A tentative climate reconstruction suggests a large deglacial warming of 15 +/- 5 degrees C (1 sigma) and an increase in snow accumulation by a factor of 1.7-4.6 (from 24.3 to 10.6 kyr BP). Our study demonstrates that BIAs in northern Victoria Land may help to obtain high-quality records for paleoclimate and atmospheric greenhouse gas compositions through the last deglaciation, although in general climatic interpretation is complicated by the need for upstream flow corrections, evidence for strong surface sublimation during the last glacial period, and potential errors in the estimated gas age-ice age difference.