Organic pyrolysis data from eastern Baffin Bay, sediment core AMD14-204C

Radiocarbon dating of Arctic marine sediment is often challenging due to the low availability of calcareous fossils. Consequently, bulk organic matter dating has at times been used to establish sediment core chronologies. Yet, radiocarbon dates based on bulk organic matter often appear to deviate vastly from dates based on fossils, mainly caused by input of carbon from other sources, including terrigenous organic matter. In this study, we aim to examine the link between the composition of the bulk organic matter and the age offsets between the bulk radiocarbon dates and those obtained from calcareous foraminiferal tests. All samples are taken from the marine sediment core AMD14-204C from offshore Upernavik (eastern Baffin Bay). The radiocarbon dates for bulk organic matter are on average ~3000 years older than the radiocarbon dates based on foraminifera, but with changing age offsets throughout the record. To investigate the cause of this age offset and its variations over time, we applied X-ray Fluorescence analysis, stable isotopes, organic pyrolysis and microscopic organic petrology to examine the distribution and characterization of the organic matter. The results show that the older organic matter includes clastic input of reworked sedimentary rocks potentially originating from West Greenland and/or the Canadian Arctic Archipelago. Changes in the input of contemporary marine algal produced organic matter versus both terrigenous input and reworked ancient organic matter appear to control the age offsets between the bulk and foraminifera dates. Low Hydrogen Index and low δ13Corg together with high Oxygen Index, indicative of high influence of terrigenous organic matter, seem to correspond to samples with the largest age offsets; 1000-2000 years greater than in other samples. To examine the cause of the variations in the age offsets, a new quantification of the autochthonous organic matter as a fraction of the TOC was calculated. This shows that samples with the largest age offsets contained the lowest fraction (as low as ~12 %) of autochthonous organic matter in the TOC.

北极海洋沉积物的放射性碳定年（Radiocarbon dating）往往具有挑战性，原因在于钙质化石的可获得性较低。因此，整体有机质定年（bulk organic matter dating）有时被用于建立沉积物岩心年代序列。然而，基于整体有机质的放射性碳定年结果往往与基于化石的定年结果存在显著偏差，这主要是由其他来源（包括陆源有机质（terrigenous organic matter））的碳输入所致。本研究旨在探讨整体有机质的组成与整体放射性碳定年结果和钙质有孔虫壳体（calcareous foraminiferal tests）定年结果之间的年龄偏移量之间的关联。所有样本均取自乌佩纳维克近海（巴芬湾东部）的海洋沉积物岩心AMD14-204C。整体有机质的放射性碳定年结果平均比基于有孔虫的定年结果老约3000年，但在整个记录中年龄偏移量存在变化。为探究这种年龄偏移及其随时间变化的原因，我们采用X射线荧光分析（X-ray Fluorescence analysis）、稳定同位素分析、有机热解和显微有机岩石学（microscopic organic petrology）等方法，研究有机质的分布与特征。结果表明，较老的有机质包含来自西格陵兰和/或加拿大北极群岛的再加工沉积岩碎屑输入。现代海洋藻类产生的有机质输入量与陆源输入及再加工古老有机质输入量之间的变化，似乎控制着整体有机质定年与有孔虫定年之间的年龄偏移量。低氢指数（Hydrogen Index）、低δ¹³Corg值以及高氧指数（Oxygen Index）——这些指标表明陆源有机质的影响较强——似乎与年龄偏移量最大的样本相对应；其偏移量比其他样本大1000-2000年。为探究年龄偏移变化的原因，我们计算了原地有机质（autochthonous organic matter）占总有机碳（TOC）的比例，这是一种新的量化方法。结果显示，年龄偏移量最大的样本中，原地有机质占总有机碳的比例最低（低至约12%）。