Natural Gamma Radiation-derived K, U and Th contents of marine sediments obtained during IODP Expeditions 359, 360, 361, 362 and 363 with DV JOIDES Resolution

During International Ocean Discovery Program (IODP) expeditions, shipboard-generated data provide the first insights into the cored sequences. The natural gamma radiation (NGR) of the recovered material, for example, is routinely measured on the ocean drilling research vessel DV JOIDES Resolution. At present, only total NGR counts are readily available as shipboard data, although full NGR spectra (counts as a function of gamma-ray energy level) are produced and archived. These spectra contain unexploited information, as one can estimate the sedimentary contents of potassium (K), thorium (Th), and uranium (U) from the characteristic gamma-ray energies of isotopes in the 40K, 232Th, and 238U radioactive decay series. Dunlea et al. [2013] quantified K, Th and U contents in sediment from the South Pacific Gyre by integrating counts over specific energy levels of the NGR spectrum. However, the algorithm used in their study is unavailable to the wider scientific community due to commercial proprietary reasons. Here, we present a new MATLAB algorithm for the quantification of NGR spectra that is transparent and accessible to future NGR users. We demonstrate the algorithm’s performance by comparing its results to shore-based inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma-emission spectrometry (ICP-ES), and quantitative wavelength-dispersive X-ray fluorescence (XRF) analyses. Samples for these comparisons come from eleven sites (U1341, U1343, U1366, U1367, U1368, U1369, U1414, U1428, U1429, U1430, U1463) cored in two oceans during five expeditions. In short, our algorithm rapidly produces detailed high-quality information on sediment properties during IODP expeditions at no extra cost. Data for IODP Expeditions 317, 318, 320-324, 327, 329, 330, 334, 336, 339-342, 344-346, 349-356 can be found at http://dx.doi.org/10.1594/IEDA/100668. The Vocatio Foundation provided funding through a scholarship to David De Vleeschouwer, laureate in the 2016 promotion. This work also benefited from funding through European Research Council (ERC) Consolidator grant “EARTHSEQUENCING” (grant agreement 617462), awarded to Heiko Pälike.

在国际大洋发现计划（International Ocean Discovery Program, IODP）科考航次中，船载采集的数据可为岩心序列提供初步认知。例如，回收沉积物的自然伽马辐射（natural gamma radiation, NGR）通常在大洋钻探研究船“乔迪斯·决心号”（DV JOIDES Resolution）上开展常规测定。目前，公开可获取的船载数据仅为总自然伽马计数，尽管完整的自然伽马能谱（伽马计数随伽马射线能级的分布曲线）已被生成并归档。这类能谱蕴含尚未得到利用的关键信息：通过40K、232Th与238U放射性衰变链中同位素的特征伽马射线能级，可估算沉积物中钾（K）、钍（Th）及铀（U）的含量。
Dunlea等人[2013]通过对自然伽马能谱特定能级下的计数进行积分，量化了南太平洋环流区沉积物中的K、Th、U含量。但受商业专有性限制，其研究使用的算法无法向更广泛的科研群体开放。为此，本文提出一款全新的MATLAB算法用于NGR能谱定量分析，该算法透明开源，可供后续所有NGR使用者获取。
我们通过将该算法的计算结果与岸基电感耦合等离子体质谱法（inductively coupled plasma-mass spectrometry, ICP-MS）、电感耦合等离子体发射光谱法（inductively coupled plasma-emission spectrometry, ICP-ES）及定量波长色散X射线荧光光谱法（quantitative wavelength-dispersive X-ray fluorescence, XRF）的分析结果进行比对，验证了算法的性能。用于性能验证的样品采自5个科考航次在两大洋钻取的11个站位（U1341、U1343、U1366、U1367、U1368、U1369、U1414、U1428、U1429、U1430、U1463）。
简言之，本算法可在无需额外投入的前提下，快速为IODP航次提供高精度的沉积物属性详细信息。IODP第317、318、320-324、327、329、330、334、336、339-342、344-346、349-356航次的相关数据可从http://dx.doi.org/10.1594/IEDA/100668获取。
本研究的经费由Vocatio基金会通过2016届获奖者David De Vleeschouwer的奖学金资助。本研究同时得益于欧洲研究理事会（European Research Council, ERC）巩固型资助项目“EARTHSEQUENCING”（资助协议编号：617462）的支持，该项目由Heiko Pälike主持。