Synchronizing the WAIS Divide Ice Core with GICC05 from 39-43 ka BP using High-resolution 10Be Measurements during Laschamp Geomagnetic Excursion

The production of cosmogenic ¹⁰Be in the atmosphere is affected mainlyby variations in solar activity and geomagnetic field strength; within 1-2 year after production, ¹⁰Be is deposited onto the Earth's surface, in polar regions ending up in the glacial ice. The concentrations of ¹⁰Be in polar ice samples are also affected by atmospheric mixing and deposition effects, but these local effects operate on a different timescale than primary cosmic ray effects. Since these effects operate on a global scale, the concentration of ¹⁰Be in polar ice cores can be used as a chronological marker that can be recognized in both hemispheres. High-resolution ¹⁰Be records in ice cores have previously been used to synchronize ice cores from Greenland and East Antarctica during the Laschamp geomagnetic minimum (39-43 ka BP) on the GICC05 timescale. The West Antarctic Ice Sheet (WAIS) Divide core, WDC, is a 3405 m deep ice core with a bottom age of ~68 ka BP. Its timescale, WD2014, is based on a combination of annual layer counting, chronological markers, ¹⁰Be-¹⁴C synchronization and synchronization of the methane record with the U,Th-dated Hulu Cave d¹⁸O record. Our goal is to obtain a continuous ¹⁰Be record in WDC to obtain a direct ice-to-ice synchronization of WDC to other ice cores. Here, we present ¹⁰Be measurements in 280 ice samples from 2935-3015 m depth in WDC, corresponding to ages of 39-43 ka BP, with decadal resolution. Comparison of the WDC ¹⁰Be data with other ice core ¹⁰Be records shows that the WD2014 timescale at 40-42.5 ka BP is ~210 yr older than the GICC05 timescale, consistent within errors with estimates of 250-270 yr by Buizert et al. (Clim. Past 11, 153-173, 2015) and with the synchronization based on volcanic markers (Buizert et al., Nature 563, 681-685, 2018). This implies that in general the conclusions of the timing of the bipolar seesaw of the WAIS Divide project Members (Nature 520, 661-665, 2015) are valid; We will further constrain the timing of the bipolar seesaw once we further extend our ¹⁰Be dataset.