Sabine Remmele

IntCal04 terrestrial radiocarbon age calibration, 0-26 cal kyr BP.

A new calibration curve for the conversion of radiocarbon ages to calibrated (cal) ages has been constructed and internationally ratified to replace IntCal98, which extended from 0-24 cal kyr BP (Before Present, 0 cal BP = AD 1950). The new calibration data set for terrestrial samples extends from 0-26 cal kyr BP, but with much higher resolution beyond 11.4 cal kyr BP than IntCal98. Dendrochronologically-dated tree-ring samples cover the period from 0-12.4 cal kyr BP. Beyond the end of the tree rings, data from marine records (corals and foraminifera) are converted to the atmospheric equivalent with a site-specific marine reservoir correction to provide terrestrial calibration from 12.4-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a coherent statistical approach based on a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The tree-ring data sets, sources of uncertainty, and regional offsets are discussed here. The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed in brief, but details are presented in Hughen et al. (this issue a). We do not make a recommendation for calibration beyond 26 cal kyr BP at this time; however, potential calibration data sets are compared in another paper (van der Plicht et al., this issue).

Marine04 marine radiocarbon age calibration, 0-26 cal kyr BP

New radiocarbon calibration curves, IntCal04 and Marine04, have been constructed and internationally rati- fied to replace the terrestrial and marine components of IntCal98. The new calibration data sets extend an additional 2000 yr, from 0-26 cal kyr BP (Before Present, 0 cal BP = AD 1950), and provide much higher resolution, greater precision, and more detailed structure than IntCal98. For the Marine04 curve, dendrochronologically-dated tree-ring samples, converted with a box diffusion model to marine mixed-layer ages, cover the period from 0-10.5 cal kyr BP. Beyond 10.5 cal kyr BP, high-res- olution marine data become available from foraminifera in varved sediments and U/Th-dated corals. The marine records are corrected with site-specific 14C reservoir age information to provide a single global marine mixed-layer calibration from 10.5-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed here. The tree-ring data sets, sources of uncertainty, and regional offsets are presented in detail in a companion paper by Reimer et al. (this issue). ABSTRACT. New radiocarbon calibration curves, IntCal04 and Marine04, have been constructed and internationally rati- fied to replace the terrestrial and marine components of IntCal98. The new calibration data sets extend an additional 2000 yr, from 0-26 cal kyr BP (Before Present, 0 cal BP = AD 1950), and provide much higher resolution, greater precision, and more detailed structure than IntCal98. For the Marine04 curve, dendrochronologically-dated tree-ring samples, converted with a box diffusion model to marine mixed-layer ages, cover the period from 0-10.5 cal kyr BP. Beyond 10.5 cal kyr BP, high-res- olution marine data become available from foraminifera in varved sediments and U/Th-dated corals. The marine records are corrected with site-specific 14C reservoir age information to provide a single global marine mixed-layer calibration from 10.5-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed here. The tree-ring data sets, sources of uncertainty, and regional offsets are presented in detail in a companion paper by Reimer et al. (this issue).

The 12,460-year Hohenheim Oak and Pine Tree-Ring Chronology from Central Europe-A Unique Annual Record for Radiocarbon Calibration and Paleoenvironment Reconstructions

The combined oak and pine tree-ring chronologies of Hohenheim University are the backbone of the Holocene radiocarbon calibration for central Europe. Here, we present the revised Holocene oak chronology (HOC) and the Preboreal pine chronology (PPC) with respect to revisions, critical links, and extensions. Since 1998, the HOC has been strengthened by new trees starting at 10,429 BP (8480 BC). Oaks affected by cockchafer have been identified and discarded from the chro- nology. The formerly floating PPC has been cross-matched dendrochronologically to the absolutely dated oak chronology, which revealed a difference of only 8 yr to the published 14C wiggle-match position used for IntCal98. The 2 parts of the PPC, which were linked tentatively at 11,250 BP, have been revised and strengthened by new trees, which enabled us to link both parts of the PPC dendrochronologically. Including the 8-yr shift of the oak-pine link, the older part of the PPC (pre-11,250 BP) needs to be shifted 70 yr to older ages with respect to the published data (Spurk 1998). The southern German part of the PPC now covers 2103 yr from 11,993-9891 BP (10,044-7942 BC). In addition, the PPC was extended significantly by new pine chronologies from other regions. A pine chronology from Avenches and Zurich, Switzerland, and another from the Younger Dryas forest of Cottbus, eastern Germany, could be crossdated and dendrochronologically matched to the PPC. The abso- lutely dated tree-ring chronology now extends back to 12,410 cal BP (10,461 BC). Therefore, the tree-ring-based 14C calibra- tion now reaches back into the Central Younger Dryas. With respect to the Younger Dryas-Preboreal transition identified in the ring width of our pines at 11,590 BP, the absolute tree-ring chronology now covers the entire Holocene and 820 yr of the Younger Dryas. THE NEW HOLOCENE OAK CHRONOLOGY (HOC) The long tree-ring chronologies of the Hohenheim laboratory are based on sub-fossil trees found in Quaternary deposits of the large rivers of central Europe (Becker 1982; Friedrich et al. 1999). We sampled mainly oaks (Quercus robur L.; Q. petraea M.) and pines (Pinus sylvestris L.) exposed in gravel pits of southern Germany. Both genera form resistant heartwood, which helps preservation in anaerobic conditions over thousands of years. The trees are remnants of former riparian forests which were eroded and buried by fluvial activity. They are rarely found in situ, but the good condi- tion of most of the trunks, with traces of branches and roots, shows that they did not drift over long distances but were quickly buried in sediment. Therefore, the stands of the trees can be localized to the lower terraces of the rivers. The sites where subfossil oaks were found are shown in Figure 1. They are located along the south- ern German river valleys Rhine, Main, Danube, and tributaries and from the eastern German river valleys Spree, Saale, and Elster. The individual ages of the subfossil oaks are surprisingly short. The mean age of all sampled oaks is only 176 yr, with a maximum age of 575 yr. Some 97% of all trees were younger than 300 yr (Fig- ure 2). This fact is related to the regular occurrence of floods connected with extensive erosion, which often disturbed riparian forests. On the other hand, the good growing conditions on the flood- plains, especially after the mid-Holocene, allowed large annual growth increments resulting in huge, but young, trees with a stem diameter of more than 1 m. Most of those trees were killed long before their potential biological age through erosion, or they collapsed under their own weight. ABSTRACT. The combined oak and pine tree-ring chronologies of Hohenheim University are the backbone of the Holocene radiocarbon calibration for central Europe. Here, we present the revised Holocene oak chronology (HOC) and the Preboreal pine chronology (PPC) with respect to revisions, critical links, and extensions. Since 1998, the HOC has been strengthened by new trees starting at 10,429 BP (8480 BC). Oaks affected by cockchafer have been identified and discarded from the chro- nology. The formerly floating PPC has been cross-matched dendrochronologically to the absolutely dated oak chronology, which revealed a difference of only 8 yr to the published 14C wiggle-match position used for IntCal98. The 2 parts of the PPC, which were linked tentatively at 11,250 BP, have been revised and strengthened by new trees, which enabled us to link both parts of the PPC dendrochronologically. Including the 8-yr shift of the oak-pine link, the older part of the PPC (pre-11,250 BP) needs to be shifted 70 yr to older ages with respect to the published data (Spurk 1998). The southern German part of the PPC now covers 2103 yr from 11,993-9891 BP (10,044-7942 BC). In addition, the PPC was extended significantly by new pine chronologies from other regions. A pine chronology from Avenches and Zurich, Switzerland, and another from the Younger Dryas forest of Cottbus, eastern Germany, could be crossdated and dendrochronologically matched to the PPC. The abso- lutely dated tree-ring chronology now extends back to 12,410 cal BP (10,461 BC). Therefore, the tree-ring-based 14C calibra- tion now reaches back into the Central Younger Dryas. With respect to the Younger Dryas-Preboreal transition identified in the ring width of our pines at 11,590 BP, the absolute tree-ring chronology now covers the entire Holocene and 820 yr of the Younger Dryas. THE NEW HOLOCENE OAK CHRONOLOGY (HOC) The long tree-ring chronologies of the Hohenheim laboratory are based on sub-fossil trees found in Quaternary deposits of the large rivers of central Europe (Becker 1982; Friedrich et al. 1999). We sampled mainly oaks (Quercus robur L.; Q. petraea M.) and pines (Pinus sylvestris L.) exposed in gravel pits of southern Germany. Both genera form resistant heartwood, which helps preservation in anaerobic conditions over thousands of years. The trees are remnants of former riparian forests which were eroded and buried by fluvial activity. They are rarely found in situ, but the good condi- tion of most of the trunks, with traces of branches and roots, shows that they did not drift over long distances but were quickly buried in sediment. Therefore, the stands of the trees can be localized to the lower terraces of the rivers. The sites where subfossil oaks were found are shown in Figure 1. They are located along the south- ern German river valleys Rhine, Main, Danube, and tributaries and from the eastern German river valleys Spree, Saale, and Elster. The individual ages of the subfossil oaks are surprisingly short. The mean age of all sampled oaks is only 176 yr, with a maximum age of 575 yr. Some 97% of all trees were younger than 300 yr (Fig- ure 2). This fact is related to the regular occurrence of floods connected with extensive erosion, which often disturbed riparian forests. On the other hand, the good growing conditions on the flood- plains, especially after the mid-Holocene, allowed large annual growth increments resulting in huge, but young, trees with a stem diameter of more than 1 m. Most of those trees were killed long before their potential biological age through erosion, or they collapsed under their own weight.

Revisions and extension of the Hohenheim oak and pine chronologies; new evidence about the timing of the Younger Dryas/ Preboreal transition.

Oak and pine samples housed at the Institute of Botany, University of Hohenheim, are the backbone of the early Holocene part of the radiocarbon calibration curve, published in 1993 (Becker 1993; Kromer and Becker 1993; Stuiver and Becker 1993; Vogel et al. 1993). Since then the chronologies have been revised. The revisions include 1) the discovery of 41 missing years in the oak chronology and 2) a shift of 54 yr for the oldest part back into the past. The oak chronology was also extended with new samples as far back as 10,429 BP (8480 BC). In addition, the formerly tentatively dated pine chronology (Becker 1993) has been rebuilt and shifted to an earlier date. It is now positioned by 14 C matching at 11,871-9900 BP (9922–7951 BC) with an uncertainty of ±20 yr (Kromer and Spurk 1998). With these new chronologies the 14 C calibration curve can now be corrected, eliminating the discrepancy in the dating of the Younger Dryas/Preboreal transition between the proxy data of the GRIP and GISP ice cores (Johnsen et al. 1992; Taylor et al. 1993), the varve chronology of Lake Gościąz (Goslar et al. 1995) and the pine chronology (Becker, Kromer and Trimborn 1991).

Late glacial 14C ages from a floating, 1382-ring pine chronology

We built a floating, 1382-ring pine chronology covering the radiocarbon age interval of 12,000 to 10,650 BP. Based on the strong rise of ∆14C at the onset of the Younger Dryas (YD) and wiggle-matching of the decadal-scale ∆14C fluc- tuations, we can anchor the floating chronology to the Cariaco varve chronology. We observe a marine reservoir correction higher than hitherto assumed for the Cariaco site, of up to 650 yr instead of 400 yr, for the full length of the comparison inter- val. The tree-ring ∆14C shows several strong fluctuations of short duration (a few decades) at 13,800; 13,600; and 13,350 cal BP. The amplitude of the strong ∆14C rise at the onset of the YD is about 40‰, whereas in the marine data set the signal appears stronger due to a re-adjustment of the marine mixed-layer ∆14C towards the atmospheric level.

A 1200-year multiproxy record of tree growth and summer temperature at the northern pine forest limit of Europe

Combining nine tree growth proxies from four sites, from the west coast of Norway to the Kola Peninsula of NW Russia, provides a well replicated (> 100 annual measurements per year) mean index of tree growth over the last 1200 years that represents the growth of much of the northern pine timberline forests of northern Fennoscandia. The simple mean of the nine series, z-scored over their common period, correlates strongly with mean June to August temperature averaged over this region (r = 0.81), allowing reconstructions of summer temperature based on regression and variance scaling. The reconstructions correlate significantly with gridded summer temperatures across the whole of Fennoscandia, extending north across Svalbard and south into Denmark. Uncertainty in the reconstructions is estimated by combining the uncertainty in mean tree growth with the uncertainty in the regression models. Over the last seven centuries the uncertainty is < 4.5% higher than in the 20th century, and reaches a maximum of 12% above recent levels during the 10th century. The results suggest that the 20th century was the warmest of the last 1200 years, but that it was not significantly different from the 11th century. The coldest century was the 17th. The impact of volcanic eruptions is clear, and a delayed recovery from pairs or multiple eruptions suggests the presence of some positive feedback mechanism. There is no clear and consistent link between northern Fennoscandian summer temperatures and solar forcing.

PRELIMINARY REPORT OF THE FIRST WORKSHOP OF THE INTCAL04 RADIOCARBON CALIBRATION/COMPARISON WORKING GROUP

The first meeting of the IntCal04 working group took place at Queens University Belfast from April 15 to 17, 2002. The participants are listed as co-authors of this report. The meeting considered criteria for the acceptance of data into the next official calibration dataset, the importance of including reliable estimates of uncertainty in both the radiocarbon ages and the cal ages, and potential methods for combining datasets. This preliminary report summarizes the criteria that were dis- cussed, but does not yet give specific recommendations for inclusion or exclusion of individual datasets.

Segments of atmospheric 14C change as derived from late glacial and early Holocene floating tree-ring series

We present results of (super 14) C dating of several tree-ring series from the Late Glacial and Early Holocene, analyzed at the Heidelberg University radiocarbon laboratory. Although these are floating series, they contribute high-resolution information about the variability of atmospheric (super 14) C during those periods.