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Radiocarbon (<sup>14</sup>C)

but features improved vacuum (four Cryotorr 8's) plus additional beam diagnostics and corrective steerers as compared to earlier systems.

Radiocarbon (14C), a rare isotope of carbon, is used to determine rates of exchange of carbon between the ocean, land and atmosphere. 14C is produced naturally in the upper atmosphere and was produced during thermonuclear bomb testing of the late 1950s and early 1960s. The equilibration time of 14CO2 between the atmosphere and ocean is quite long (~10 years), which makes 14C a tracer of water mass movement rather than gas exchange. The 14C "age" of the surface ocean DIC (where atmospheric CO2 has zero age) ranges from 620 14C years (-72‰) to 340 14C years (-40‰) in the equatorial and mid-gyre regions, respectively [Toggweiler et al., 1991; Druffel, 1987, 2001]. These old ages of surface DIC are primarily due to vertical and advective mixing of subsurface waters that have still older 14C ages due to isolation from the atmosphere. 14C in surface water DIC (dissolved inorganic carbon) of the eastern tropical Pacific is a particularly sensitive measure of the PDO phase, termed the background climate state [Rodgers et al. 2000]. SST anomalies (e.g. upwelling events) equilibrate with the atmosphere on the order of one month, but 14C is a proxy of longer time scale processes, e.g., ventilation of the thermocline in the tropical ocean.

The compact AMS particle accelerator from National Electrostatics Corporation (NEC 0.5MV 1.5SDH-2 AMS system) for measuring radiocarbon set up at the UCI Keck Carbon Cycle AMS Facility.

For a discussion of methods used to measure radiocarbon in environmental samples using accelerator mass spectrometry, go to the Keck Carbon Cycle AMS Laboratory at University of California Irvine http://www.ess.uci.edu/ams/ A helpful resource that describes how an AMS works is located at the AMS Laboratory in Adam Mickiewicz University, Poland http://www.radiocarbon.pl/machine2.htm.