Ocean-atmosphere radiocarbon age differences

The difference between the 14C age of the atmospheric and marine carbon reservoirs varies spatially in the ocean due to local and global ocean circulation. Although this is well known, most paleoceanographic studies assume a fixed age difference between the atmosphere and ocean even at times when ocean circulation and ocean reservoir ages are known to have changed dramatically. The ability to obtain well-constrained surface and deep radiocarbon ages in the marine sediment record is compromised by bioturbation and other stratigraphic issues. In our work we employ distinct, identified tephra layers from volcanic eruptions in New Zealand as instantaneous time markers. In terrestrial sediments, the tephras' ages have been firmly established using numerous radiocarbon ages from within-tephra and adjacent plant remains. Working in collaboration with Tom Guilderson (Lawrence Livermore National Laboratory), we are dating foraminifera from above and below the tephras in marine sediments and can determine the marine reservoir age (and the relative ventilation of deep water masses in the past) by comparing the 14C ages of coeval marine carbonate to terrestrial organic carbon. Our results indicate that surface and deep reservoir ages in the Southern Ocean and southwest Pacific increased by as much as ~3500 yrs years, which is 2-5 times more than previously assumed possible with glacial to interglacial changes in ocean circulation. This has important implications for glacial carbon cycling and far reaching consequences for determining leads and lags between terrestrial (ice core) and ocean records of climate change. I was chief scientist on an NSF-funded coring cruise on the R/V Roger Revelle in March 2005. On this month long cruise we obtained 37 cores which are the basis for our present work continuing this study.

Map of ship's track

We had a cruise in March 2005 to collect cores from many different depths so that we could reconstruct the ages of deep water around New Zealand in the past. See weblog of the cruise (link) for details of our cruise.

Ash Layers in the Core

What we were looking for in our cores were ash layers from th volcanoes on New Zealand's North Island that we could use as stratigraphic markers (like a golden spike) to correlate our many cores.
Sampling the Core

After selecting the core we would collect samples from them

Picking Forams

After washing away the fine mud, we select foraminfera of single species of our 
14C analyses.
New Zealand Forams

Some of the forams we find in the sediments around New Zealand.