COSMOGENIC 10BE SURFACE EXPOSURE DATING OF LATE HOLOCENE MORAINES OF THE HOOKER GLACIER, SOUTHERN ALPS, NZ

While the Little Ice Age (LIA, c. 1250-1850 CE) and Medieval Climate Optimum (MCO, c. 750-1250 CE) are well recorded in paleoclimate records from Europe, it is not clear whether climate variations during this portion of the Late Holocene were global or regional in extent. Alpine glaciers like the Hooker Glacier, on the southern flank of Aoraki/Mt. Cook in New Zealand’s Southern Alps, and on the opposite side of the planet from the European records first used to identify the LIA and MCO, are sensitive monitors of atmospheric temperature. The Hooker Glacier is particularly well-suited for use in paleoclimate research because its relatively small size, steep incline, and large mass-balance gradient make it especially sensitive to temperature change, with a terminal response time of about five years (Mackintosh, et al., 2017).

We use a suite of ¹⁰Be surface exposure ages from well-preserved moraines of the Hooker Glacier to construct a chronology of moraine deposition tracing the retreat of the Hooker Glacier since about 1500 y.b.p. Since that time, the Hooker Glacier was at or near its maximum extent during the period of the European MCO. Moraines constructed during the European LIA are inboard of those constructed during the MCO and record progressively smaller glacier extents throughout the LIA. In contrast, European records of glacier extent (e.g. Holzhauser, et al., 2005) indicate that glaciers in the Alps occupied retracted positions during the MCO and readvanced beyond those positions during the LIA. ¹⁰Be surface exposure dating of moraines of the Hooker Glacier indicates that Late Holocene climate in New Zealand’s Southern Alps did not match the well-known European climate variations during the Medieval Climate Optimum and Little Ice Age. During the past century, the Hooker Glacier has undergone extensive recession from the positions it occupied during the European LIA, part of a global pattern of glacier recession in post-industrial time.