A promising new technique uses the accumulated recoil Ar stable isotope ratios (19), but the current uncertainty in this dating method is also large (180 ka or 11% relative age, whichever is greater).
There is significant scientific interest in obtaining glacial ice dating beyond 800 ka, as such an archive would extend the ice core record further back in time, providing valuable constraints on the evolution of past climate, atmospheric composition, and the Antarctic ice sheet (20).
Because the ice stratigraphy is exposed laterally along the BIA surface, such ice records are often referred to as horizontal ice cores.
Determining the age of the ablating ice is the main difficulty in using BIAs for climate reconstructions (4).
Finally, in contrast to Kr dating of ice gave inconclusive results owing to ∼50% gas loss and substantial but poorly quantified (≥20%) contamination with modern air (35).
The single sample in that study was extracted by chainsaw from the surface of the Allan Hills BIA site in Antarctica, and the sample quality was compromised by “extensive fracturing of the highly strained ice” (ref. In addition, a reliable method for Kr radiometric dating of polar ice using air extracted from four ice samples from the Taylor Glacier blue ice area in Antarctica.
Stratigraphic matching of water-stable isotopes to the nearby Taylor Dome ice core (38) previously identified ice in the 11.5–65-ka age range at the glacier surface (10).
Here we present extensive dating of the near-surface ice using a combination of CH trapped in the ice).
We show that ice from the previous interglacial period (Marine Isotope Stage 5e, 130–115 ka before present) can be found in abundance near the surface of Taylor Glacier.
The ice at this site is heavily fractured to a depth of ∼3 m with sporadic cracks extending to 5 m, and consequently, we sampled ice in the 5–15-m depth range. Our study shows that ice from the previous interglacial period [Marine Isotope Stage (MIS) 5e, 130–115 ka B.
P.] can be found in abundance near the surface of the Taylor Glacier BIA. Along the lower ∼70 km of the glacier the surface mass balance is dominated by sublimation (37), causing outcropping of old ice.
Our method will enhance the scientific value of outcropping sites as archives of old ice needed for paleoclimatic reconstructions and can aid efforts to extend the ice core record further back in time. Krypton was extracted from the air bubbles in four ∼350-kg polar ice samples from Taylor Glacier in the Mc Murdo Dry Valleys, Antarctica, and dated using Atom Trap Trace Analysis (ATTA).
The Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 ± 2.5 ka.