Susan Ivy

AMS radiocarbon dating and varve chronology of Lake Soppensee: 6000 to 12000 14C years BP

For the extension of the radiocarbon calibration curve beyond 10000 14C y BP, laminated sediment from Lake Soppensee (central Switzerland) was dated. The radiocarbon time scale was obtained using accelerator mass spectrometry (AMS) dating of terrestrial macrofossils selected from the Soppensee sediment. Because of an unlaminated sediment section during the Younger Dryas (10000–11000 14C y BP), the absolute time scale, based on counting annual layers (varves), had to be corrected for missing varves. The Soppensee radiocarbon-verve chronology covers the time period from 6000 to 12000 14C y BP on the radiocarbon time scale and 7000 to 13000 calendar y BP on the absolute time scale. The good agreement with the tree ring curve in the interval from 7000 to 11450 cal y BP (cal y indicates calendar year) proves the annual character of the laminations. The ash layer of the Vasset/Killian Tephra (Massif Central, France) is dated at 8230±140 14C y BP and 9407±44 cal y BP. The boundaries of the Younger Dryas biozone are placed at 10986±69 cal y BP (Younger Dryas/Preboreal) and 1212±86 cal y BP (Alleröd/Younger Dryas) on the absolute time scale. The absolute age of the Laacher See Tephra layer, dated with the radiocarbon method at 10 800 to 11200 14C y BP, is estimated at 12350 ± 135 cal y BP. The oldest radiocarbon age of 14190±120 14C y BP was obtained on macrofossils of pioneer vegetation which were found in the lowermost part of the sediment profile. For the late Glacial, the offset between the radiocarbon (10000–12000 14C y BP) and the absolute time scale (11400–13000 cal y BP) in the Soppensee chronology is not greater than 1000 years, which differs from the trend of the U/Th-radiocarbon curve derived from corals.

The Influence of CaCO3 Dissolution on Core Top Radiocarbon Ages for Deep-Sea Sediments

Radiocarbon ages on CaCO3 from deep-sea cores offer constraints on the nature of the CaCO3 dissolution process. The idea is that the toll taken by dissolution on grains within the core top bioturbation zone should be in proportion to their time of residence in this zone. If so, dissolution would shift the mass distribution in favor of younger grains, thereby reducing the mean radiocarbon age for the grain ensemble. We have searched in vain for evidence supporting the existence of such an age reduction. Instead, we find that for water depths of more than 4 km in the tropical Pacific the radiocarbon age increases with the extent of dissolution. We can find no satisfactory steady state explanation and are forced to conclude that this increase must be the result of chemical erosion. The idea is that during the Holocene the rate of dissolution of CaCO3 has exceeded the rain rate of CaCO3. In this circumstance, bioturbation exhumes CaCO3 from the underlying glacial sediment and mixes it with CaCO3 raining from the sea surface.

A Search for an Early Holocene CACO3 Preservation Event

The CO2 record for air bubbles from the Byrd Station ice core suggest a drawdown in the ocean-atmosphere carbon reservoir during the early Holocene. Such a drawdown would require a corresponding increase in the CO3= ion concentration in the deep sea. We report here the results of a search in Atlantic sediments for evidence that the lysocline showed a corresponding deepening. While both the pteropod and the calcite preservation records we have obtained are consistent with expectation, they are not conclusive.

AMS 14C age determinations of tissue, bone and grass samples from the Ötztal ice man

14 C ages of samples from the Otztal Ice Man, found on the Hauslabjoch in the Tyrolean Alps in September 1991, were determined using accelerator mass spectrometry (AMS). Uncalibrated 14 C ages of 4555 ± 34 bp, 4560 ± 65 bp and 4535 ± 60 bp were measured on tissue (mean of four samples), bone and grass, respectively, from the Ice Man. The mean of all of our measurements is 4550 ± 27 bp.

Radiocarbon Dating of Fourteen Dead Sea Scrolls

The name Dead Sea Scrolls refers to some 1200 manuscripts found in caves in the hills on the western shore of the Dead Sea during the last 45 years. They range in size from small fragments to complete books from the holy scriptures (the Old Testament). The manuscripts also include uncanonized sectarian books, letters and commercial documents, written on papyrus and parchment. In only a few cases, direct information on the date of writing was found in the scrolls. In all other cases, the dating is based on indirect archaeological and paleographical evidence. To check this evidence, radiocarbon ages of 14 selected scrolls were determined using accelerator mass spectrometry. The calibrated radiocarbon ages agree well, except in one case, with the paleographic estimates or the specific dates noted on the scrolls.