Collaborative Research: Evolution of Arctic Water Column Hydrography during the Holocene Based on a Novel Instrumentation Combination

在过去几十年中，北极变暖的速度大约是整个北方的两倍，这与过去十年中北极海冰覆盖面积的大幅退缩和变薄有关。与北极变暖和海冰覆盖减少有关的是北冰洋表层和深水环流的重组，但对相关过程的了解有限。全新世早期到中期提供了一个类似于季节性无冰北冰洋的冰后期模拟，类似于未来几十年提出的情景。这早中期全新世海冰最小，10？六千年前，通常归因于太阳强迫的变化。然而，记录提供的资料，北极上层水柱分层期间的海冰覆盖最小的事件是稀疏的。正常的古海洋学代理水团分层不能在北极应用，需要不同的方法来重建水柱水文。拟议的研究有可能大大提高我们对过去北极水柱水文的了解，从早到中全新世海冰最小值，并为北冰洋未来条件的情景发展提供信息。该项目将通过支持培训一名博士生，促进劳动力发展。 开发的技术将通过一个正式讲习班主动转让给国际科学界。 二次离子质谱（西姆斯），激光烧蚀电感耦合等离子体质谱（激光烧蚀ICP-MS）和同位素比质谱（IRMS）的组合使用的最新创新表明，丰富的环境信息的水柱分层可以从化石有孔虫的单个外壳提取。Neogloboquadrina pachyderma（左）（NPS），增长其腔室（个体发育方解石）附近的北极表面，并随后通过水柱下沉，在那里它添加了一个厚厚的方解石外壳周围的稀薄的钙化室在亚混合层深度。因此，每一个单独的核粒子壳包含化学和同位素分带从沃茨具有明显不同的物理性质？低盐度表层混合层总体较冷，次表层盐跃层总体较暖。壳内变异性可以用原位分析方法测量。主要研究人员（PI）建议采用多仪器的方法来量化壳内的地球化学NPS壳从整个北冰洋的boxcore样品阵列。他们计划将西姆斯在5微米大小的区域中进行的壳内Δ 18 O和Δ 13 C测量与通过激光消融ICP-MS对相同Nps壳进行的Mg/Ca（温度代理），Ba/Ca（河流径流或融水排放代理）和Na/Ca（盐度代理）分析相结合。创新的西姆斯超小域同位素分析方法是由PI Kozdon在过去几年中开发的，并在PI Spero的实验室中校准。西姆斯（现场测量）和激光烧蚀数据（通过方解石层的深度剖面）可以相关的有孔虫壳，反映了一个特定的阶段，在标本定义明确的域？个体发育（？时间标记？）。每一个测量可以被分配到一个一般的水深范围，这是有关的深度方解石除了NPS迁移通过水柱在其个体发育。因此，建议的分析方法提供了一个前所未有的机会，重建过去的水柱分层之间的表面和盐跃层从个人壳的NPS沉积组合。这种创新的多仪器方法将适用于中全新世和晚全新世NPS壳~50 14 C-定年盒芯样品从北冰洋。核心将被仔细挑选，主要来自美国核心存储库，使用以下标准：（I）北冰洋的良好覆盖，重点关注对水团分层变化敏感的关键区域，（II）现有的14 C日期，尽管一些核心仍需要日期。

During the past few decades, the Arctic has warmed approximately twice as rapidly as the entire northern hemisphere, associated with substantial retreat and thinning of the Arctic sea-ice cover during the past decade. Associated with the Arctic warming and waning sea-ice cover is a reorganization of the surface and deep-water circulation of the Arctic Ocean, but understanding of the associated processes is limited. The early to mid-Holocene provides a post-glacial analogue of a seasonally ice-free Arctic Ocean, similar to scenarios that have been proposed for the next several decades. This early-mid Holocene sea ice minimum, 10?6 thousand years ago, is often attributed to changes in solar forcing. However, records providing information on upper Arctic water column stratification during episodes of minimum sea ice cover are sparse. The normal paleoceanographic proxies for water mass stratification cannot be applied in the Arctic; different approaches are required to reconstruct water column hydrography. The proposed research has the potential to greatly improve our knowledge of past Arctic water column hydrography from the early to mid-Holocene sea ice minimum and inform scenario development of future conditions in the Arctic Ocean. The project will contribute to workforce development through support for the training of a PhD student. The technology developed will be proactively transferred to the international science community through a formal workshop. Recent innovations in the combined use of secondary ion mass spectrometry (SIMS), laser-ablation inductively coupled plasma mass spectrometry (laser-ablation ICP-MS) and Isotope ratio mass spectrometry (IRMS) have shown that a wealth of environmental information about water column stratification can be extracted from single shells of fossil foraminifera. Neogloboquadrina pachyderma (sinistral) (Nps), grows its chambers (ontogenetic calcite) near the Arctic surface, and subsequently sinks through the water column where it adds a thick calcite crust around the thinly calcified chambers at sub-mixed layer depths. Thus, each individual Nps shell contains chemical and isotopic zonation from waters with distinctly different physical properties ? the generally cold low salinity surface mixed layer and warmer subsurface halocline. Intrashell variability can be measured with in situ analytical approaches. The principal investigators (PIs) propose to apply a multi-instrument approach to quantify intrashell geochemistry in Nps shells obtained from an array of boxcore samples across the Arctic Ocean. They plan to combine intrashell ä18O and ä13C measurements in 5 ìm-sized domains by SIMS with analyses of Mg/Ca (proxy for temperature), Ba/Ca (proxy for river runoff or meltwater discharge), and Na/Ca (proxy for salinity) by laser-ablation ICP-MS on the same Nps shells. The innovative SIMS ultra-small domain isotope analytical approach was developed within the last few years by PI Kozdon, and calibrated in the lab of PI Spero. Both SIMS (spot-measurements) and laser-ablation data (depth profiles through the calcite layers) can be correlated to well defined domains in the foraminiferal shells that reflect a specific stage in the specimens? ontogenetic development (?time-markers?). Each of the measurements can be assigned to a general water depth range that is related to the depth of calcite addition as Nps migrates through the water column during its ontogenetic development. Thus, the proposed analytical approach provides an unprecedented opportunity to reconstruct past water column stratification between the surface and halocline from individual shells of Nps in sedimentary assemblages. This innovative multi-instrument approach will be applied to mid-Holocene and late Holocene Nps shells from ~50 14C-dated box-coretop samples from the Arctic Ocean. The cores will be carefully selected, mainly from U.S. core repositories, using the following criteria: (I) good coverage of the Arctic Ocean with a focus on key-areas sensitive to changes in water mass stratification and (II) existing 14C dates, although some of the cores will still need to be dated.