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

合作研究：基于新型仪器组合的全新世北极水柱水文演化

• 批准号: 1501526
• 负责人: Howard Spero
• 金额: $ 29.83万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-07-01 至 2020-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1501526&HistoricalAwards=false
• 关键词: Collaborative; Research; Evolution; Arctic; Water

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.

在过去的几十年中，在过去十年中，北极的温暖速度大约是整个北半球的两倍，与北半球的大量撤退和北极海冰覆盖率相关。与北极变暖和衰落的海冰覆盖相关的是对北极海洋的表面和深水循环的重组，但是对相关过程的理解是有限的。上世早期至中新世提供了冰期无冰的北极海洋的冰川类似物，类似于未来几十年中提出的情况。这种早期的全新世海冰最低限度为10？6000年前，通常归因于太阳能强迫的变化。但是，在最小海冰覆盖时发作期间提供有关上北极水柱分层的信息的记录很少。北极不能应用正常的水质量分层的古虫学代理。重建水柱水文需要不同的方法。拟议的研究有可能大大改善我们对过去北极水柱从早期到中新世海冰的最低限度的了解，并为北极海洋未来状况的情况开发。该项目将通过支持博士生的培训来为劳动力发展做出贡献。开发的技术将通过正式研讨会主动转移到国际科学界。二次离子质谱法（SIMS），激光燃烧的联合使用的最新创新是从单一的环境信息（IRMS）和同位素质谱（IRM）和同位素比率（IRMS）和同位素质谱（IRMS）中的创新，表明，关于水柱分层的大量环境信息可以从单壳中提取大量的环境信息。 Neogloboquadrina Pachyderma（Sinistral）（NPS）在北极表面附近生长其腔室（遗传学钙），然后通过水柱在水柱上下沉，在该水柱上增加了较厚的钙壳，在亚粘的层深度处较薄钙化的腔室。那是每个NPS壳都包含具有明显不同物理特性的水域的化学和同位素区吗？通常冷的低盐度表面混合层和较温暖的地下卤石。 Intrashell可变性可以通过原位分析方法来测量。主要研究人员（PIS）提出了采用多功能方法来量化Intrashell地球化学的NPS壳中，这些NPS壳从北极海洋中获得的一系列Boxcore样品获得。他们计划通过使用MG/CA（温度的代理），BA/CA（河流径流或融合河水放电的代理）和Na/ca（通过Laser-Ablation ICP-MS上的iCP-MS sells in Na/ca），通过MG/CA（河流径流或融合河流排放的代理），通过同一nps nps nps nps na/ca将Intrashellä18O和ä13c测量结合在5 `m大小的域中。 Pi Kozdon在过去几年内开发了创新的SIMS超小域同位素分析方法，并在Pi Spero的实验室中进行了校准。 SIMS（点测量）和激光燃烧数据（通过钙层的深度剖面）都可以与有孔虫壳中定义良好的域相关联，这些域反映了样品中特定阶段？个体发育（？时标？）。每个测量值都可以分配到一般的水深范围，该水深度与钙的添加深度有关，因为NPS在其个体发育过程中通过水柱迁移。这就是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NP的单个壳中重建表面和卤素之间的水柱分层。这种创新的多功能仪器方法将应用于北极海洋中〜50 14C的盒子式样品中的全新世和晚期NPS壳。将使用以下标准仔细选择核心，主要是从美国核心存储库中选择：（i）北极海洋的良好覆盖范围，重点是对水质量分层变化敏感的钥匙差异，（ii）现有的14C日期，尽管某些核心仍需要进行日期。