The modern values of R are quantified by the
14 C dating
of carbonates (mollusk shells, corals) of known ages from
the historic collections of museums (Bard 1988; Siani et al.
2000; Tisnérat-Laborde et al. 2010) and, for older ages than
those of these collections, by subtracting the
14 C age of a
marine organism from that of the atmospheric calibration
record at the same absolute age (Reimer et al. 2013). The
mean value of R is about 300–400 years in the subtropical
sea surface, and it may be some 1100 years around the
Antarctic continent. Values of approximately 700 years were
δ
δ
Fig. 4.6 a Variations in the
atmospheric
14 C content (Δ
14
C in
‰) (triangle) and grey scale (line)
in marine varved sediments from
the Cariaco Basin as a function of
calendar ages by varve counting
(Hughen et al. 1998; Reimer et al.
2013). b Variations of d
18
O
trapped in CO 2 air bubbles in the
Greenland ice core GISP2 sites in
Greenland (line) and in the Byrd
ice core in Antarctica (diamond)
as a function of synchronized
time from analyses of CH 4
concentrations in the two sites
(Blunier et al. 1998)
60
M. Paterne et al.