Modeling Atmospheric ¹⁴C Influences and ¹⁴C Ages of Marine Samples to 10,000 BC

Abstract

INTRODUCTIONThe detailed radiocarbon age vs, calibrated (cal) age studies of tree rings reported in this Calibration Issue provide a unique data set for precise 14C age calibration of materials formed in isotopic equilibrium with atmospheric CO2. The situation is more complex for organisms formed in other reservoirs, such as lakes and oceans. Here the initial specific 14C activity may differ from that of the contemporaneous atmosphere. The measured remaining 14C activity of samples formed in such reservoirs not only reflects 14C decay (related to sample age) but also the reservoir '4C activity. As the measured sample 14C activity figures into the calculation of a conventional 14C age (Stuiver & Polach 1977), apparent 14C age differences occur when contemporaneously grown samples of different reservoirs are dated.A correction for the apparent age anomaly is possible when the reservoir-atmosphere offset in specific 14C activity is known. The offset (e.g.,14C age of marine sample -14C age of atmospheric sample) is expressed as a reservoir 14C age, R(t), which need not be constant with time. When constant, however, the reservoir sample 14C age, A, can be reconciled with the atmospheric one by deducting R(t) from A. Similar reservoir age corrections would be possible for a variable R(t), but complications arise because information on R time dependency usually is lacking. However, R(t) can be accounted for in the world oceans by using a marine calibration curve derived from carbon reservoir modeling (Stuiver, Pearson & Braziunas 1986). In these calculations, atmospheric 14C change is attributed to solar-and geomagnetic-induced 14C production change. Climate-induced changes in global carbon reservoirs, which may repartition 14C among reservoirs, are not accounted for in these calculations.Measuring a marine calibration curve is complicated because most marine samples lack the continuity and fine structure of tree rings. The 234U/23°Th dating of corals (Bard et al. 1993) provides a good cal age equivalent, but measuring errors in the 234U/230Th ratio and 14C accelerator mass spectrometry (AMS) determinations are such that the (bi)decadal chronological detail achieved for tree rings is not possible. Such detail, however, can be realized by calculating the response of the world oceans to tree-ring derived atmospheric 14C changes.The long-term trend of the 14C age vs. cal age curve for the world oceans parallels that of the atmosphere. Short-term (century) variations, however, are smoothed in the oceans. Thus, whereas a constant, R, could be used for long-term variations, the shorter-term variations cannot be accounted for in this manner. Use of constant, R, and the atmospheric calibration curve assumes that the features of the marine and atmospheric curves are identical. The consequences of the constant R approach are obvious when the cal ages of a marine and atmospheric sample with identical (reservoir-corrected) 14C age + standard deviation are evaluated. Calibration of both vs. the atmospheric curve yields identical re...

East Asian monsoon climate during the Late Pleistocene: high-resolution sediment records from the South China Sea

“…Hence the 775-year periodicity may be a harmonics of the 1500-year cycle. The 102=84-year periodicities may possibly reflect the Gleissberg cycle of solar activity, frequently described in ultrahigh-resolution records such as tree-ring 1 14 C and the GISP2 ice core (Stuiver and Braziunas, 1993;Grootes and Stuiver, 1997).…”

“…D distilled water. b A 400-yr correction is applied for the reservoir age of sea water, although its precise age range is unknown in the South China Sea (Stuiver and Braziunas, 1993). c Foraminiferal tests with 80% of size fraction 150-315 µm.…”

“…For the calculation of accumulation rates we converted the 14 C ages into calendar ages, which implied two major unknowns: (1) changes in the 14 C-reservoir effect of the surface water in the SCS; and (2) the differential 14 C-production rates in the atmosphere during the last glacial cycle (Duplessy et al, 1989;Stuiver and Braziunas, 1993;Laj et al, 1996;Völker et al, 1998). The 14 C ages of dissolved CO 2 in surface-water samples from the SCS (unpublished data) show a post-bomb age of 750 years.…”

“…In our approach, 14 C dates of the last 11,000 years were converted into calendar ages, based on the calibration technique of Stuiver and Braziunas (1993) and taking into account a minor additional reservoir age for the western Pacific (140 š 45 yr; i.e. a total of 540 yr).…”

Holocene megathermal abrupt environmental changes derived from 14C dating of a coral reef at Leizhou Peninsula, South China Sea

“…CRA's of the coral reef samples were converted to calendar ages using a calibration that incorporates variations of the 14 C concentration in the atmosphere and the marine reservoir effect [8][9][10][11]. This effect was estimated for the South China Sea to be DR ¼ À17 AE 17 14 C years [12] and was input to the calibration program Oxcal [13].…”