Glacial extent on Campbell Island at the last glacial maximum

Abstract

Campbell Island, New Zealand’s southernmost island, is located approximately 700 km south of the South Island at 52.33˚S, 169.09˚E. In February 2009, the R/V Polaris II (Otago University’s research vessel) travelled to Campbell Island to conduct a high-frequency seismic survey and collect sediment cores to find evidence of the Last Glacial Maximum (LGM). Campbell Island is an important site for understanding the LGM and its termination because it is situated in the mid latitudes and is therefore more sensitive to small climatic variations than sites located at extreme high and low latitudes.

A detailed high-frequency seismic survey was conducted using electro-acoustic (Boomer) sub-bottom imaging, Teledyne Benthos C3D interferometric side-scan sonar and CHIRP in Perseverance Harbour, Northeast Harbour and off the more sheltered east coast of Campbell Island. The survey was designed to target possible glacial features that are beneath present-day sea level. The survey revealed that within the harbours, U-shaped valleys have been filled with flat lying sediment with modern marine transgressional sediments at the entrance of each harbour. Six piston cores were recovered from key sites within the harbours.

Whole-core physical properties (P-wave velocity, magnetic susceptibility, resistivity, gamma-ray density and colour reflectance) of the piston cores were determined by a GEOTEK MSCL (multisensory core logger). The measured properties were used to identify variations within and between the cores and to tie the seismic data to the sedimentary record. Paleomagnetic analyses of U-channel subsamples of five of the six piston cores were conducted to establish chronological constraints. Rock magnetic experiments (determinations of temperature dependant magnetic susceptibility, isothermal remanent magnetisation and anhysteretic remanent magnetisation) were performed on selected discrete samples to determine changes in the magnetic mineralogy with depth.

Preliminary results suggest glaciers did not extend beyond the mouths of the present day harbours. Sub-aerially eroded channels on the eastern shelf have been identified to depths of ~160 m beneath present-day sea level. The sub-aerially eroded channels can be traced from the harbours to the edge of the survey and have been in filled with longshore drift sediment, during the current highstand of sea level.