1. University of Victoria, School of Earth & Ocean Sciences, E‐hut 112, 3800 Finnerty Road, Victoria, British Columbia V8P 5C2, Canada.
2. Naval Research Laboratory, Stennis Space Center, Mississippi 39526.
3. University of Victoria, School of Earth & Ocean Sciences, E‐hut 112, 3800 Finnerty Road, Victoria, British Columbia V8P 5C2, Canada, and Geological Survey of Canada, Pacific Geoscience Centre, Sidney, British Columbia, Canada.
4. Geological Survey of Canada, Pacific Geoscience Centre, Sidney, British Columbia, Canada.