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

在过去的几十年里，北极变暖的速度大约是整个北半球的两倍，这与过去十年中北极海冰的大量退缩和变薄有关。与北极变暖和海冰覆盖减少相关的是北冰洋表层和深海环流的重组，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后冰期，类似于未来几十年提出的情景。全新世早期到中期的海冰最小值，10？六千年前的气候变化通常归因于太阳强迫的变化。然而，在海冰覆盖最小时期，提供北极上层水柱分层信息的记录很少。正常的古海洋学水体分层代用物不能用于北极；重建水柱水文需要不同的方法。拟议的研究有可能大大提高我们对从全新世早期到中全新世海冰最小期的过去北极水柱水文的认识，并为北冰洋未来条件的情景发展提供信息。该项目将通过支持博士研究生的培训来促进劳动力发展。开发的技术将通过一个正式的研讨会主动转让给国际科学界。近年来，二次离子质谱（SIMS）、激光烧蚀电感耦合等离子体质谱(laser-ablation电感耦合等离子体质谱（ICP-MS）和同位素比值质谱（IRMS）的联合应用创新表明，可以从化石有孔虫的单个壳中提取丰富的水柱分层环境信息。Neogloboquadrina pachyderma (sninistral) (Nps)，在北极表面附近生长其腔室（原生方解石），随后通过水柱下沉，在亚混合层深度的薄钙化腔室周围增加了厚厚的方解石外壳。因此，每个单独的Nps壳含有来自具有明显不同物理性质的水的化学和同位素带。一般为寒冷的低盐度表层混合层和温暖的地下盐斜。壳内变异性可以用原位分析方法测量。主要研究人员（pi）建议应用多仪器方法来量化从北冰洋一系列箱芯样品中获得的Nps壳中的壳内地球化学。他们计划将SIMS在5个ìm-sized域的壳内ä18O和ä13C测量结果与使用激光烧蚀ICP-MS对相同Nps壳进行的Mg/Ca（代表温度）、Ba/Ca（代表河流径流或融水排放）和Na/Ca（代表盐度）的分析结合起来。创新的SIMS超小域同位素分析方法是在过去几年中由PI Kozdon开发的，并在PI Spero实验室进行了校准。SIMS（点测量）和激光烧蚀数据（通过方解石层的深度剖面）都可以与有孔虫壳中明确的区域相关联，这些区域反映了样品的特定阶段。个体发育（时间标记）。每一项测量都可以被分配到一个一般的水深范围，这个水深范围与Nps在其自身发育过程中通过水柱迁移时方解石添加的深度有关。因此，所提出的分析方法提供了一个前所未有的机会，可以从沉积组合中Nps的单个壳中重建地表和盐斜层之间的过去水柱分层。这种创新的多仪器方法将应用于来自北冰洋~50个14c年代的盒芯顶样品的中全新世和晚全新世Nps壳。这些岩心将主要从美国的岩心库中精心挑选，使用以下标准：(1)覆盖北冰洋，重点关注对水团分层变化敏感的关键区域；(2)现有的14C年代，尽管一些岩心仍需要确定年代。

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.