Sediment Mixing in a Pockmark Field on the Chatham Rise, New Zealand – Implications for Paleoceanographic Reconstructions

Abstract:

Pockmarks ranging in size from approximately 1 m to 10 km on the southwestern flank of the Chatham Rise, New Zealand are believed to result from gas hydrate dissociation linked to sea-level changes during glacial-interglacial cycles [1]. Geophysical profiles (seismic and multi-beam) collected in the pockmark field in January and February 2013 on the Chatham Rise onboard the RV Sonne (SO226) suggested past and present gas migration in the sediments. With the overall objectives of constraining the timescales for the pockmark formation and describing their formation mechanisms, sediment coring (multi and piston cores) targeted the gas escape features.

Surface sediments were collected using a multi-corer at water depths ranging from ~500 to 1000 m. Solid phase ²¹⁰Pb (half-life = 22 y) and ¹⁴C (half-life = 5568 y) were measured in surface sediments (≤ 20 cm). Sediment mixing coefficients in the surface sediments calculated from excess ²¹⁰Pb profiles ranged from 3 – 8 cm² ky^-1. Excess ²¹⁰Pb penetration depths were ~ 8 cm in most cores. Generally, ¹⁴C profiles showed mixing depths similar to excess ²¹⁰Pb but were greater in some locations. Sediment mixing and its potential effects on paleoceanographic reconstructions at these sites will be presented.

[1] Davy et al. (2010) Geophys. Res. Lett. 37, L21309.