Marine radiocarbon (14C) dates are widely used for dating oceanic events and as tracers of ocean circulation, essential components for understanding ocean-climate interactions. Past ocean ventilation rates have been determined by the difference between radiocarbon ages of deep-water and surface-water reservoirs, but the apparent age of surface waters (currently ~400 years in the tropics and ~1,200 years in Antarctic waters) might not be constant through time, as has been assumed in radiocarbon chronologies and palaeoclimate studies. Here we present independent estimates of surface-water and deep-water reservoir ages in the New Zealand region since the last glacial period, using volcanic ejecta (tephras) deposited in both marine and terrestrial sediments as stratigraphic markers. Compared to present-day values, surface-reservoir ages from 11,900 14C years ago were twice as large (800 years) and during glacial times were five times as large (2,000 years), contradicting the assumption of constant surface age. Furthermore, the ages of glacial deepwater reservoirs were much older (3,000-5,000 years). The increase in surface-to-deep water age differences in the glacial Southern Ocean suggests that there was decreased ocean ventilation during this period.

Item Type:	Refereed Article
Research Division:	Earth Sciences
Research Group:	Geology
Research Field:	Geology not elsewhere classified
Objective Division:	Environment
Objective Group:	Other Environment
Objective Field:	Environment not elsewhere classified
UTAS Author:	Sikes, EL (Dr Sikes)
UTAS Author:	Samson, CR (Dr Catherine Samson)
UTAS Author:	Howard, W (Associate Professor William Howard)
ID Code:	19309
Year Published:	2000
Web of Science® Times Cited:	189
Deposited By:	IASOS
Deposited On:	2000-08-01
Last Modified:	2011-11-22
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