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，在过去的十年中，北极的北半球速度和北极海冰覆盖率变薄的速度迅速两倍。 IS是北极海的深水循环的重组，但对相关过程的理解是有限的。几十年d重建水有可能大大提高我们对底层水柱的知识，从地球到中新世海洋中期，并为北极海洋中的未来状况提供了信息。通过正式的研讨会。在北极表面附近，随后将水柱降低，它会在子混合层depther上添加厚的甲壳。主要研究者（PIS）提出了一种多功能仪器方法，以量化从北极海洋中的一系列盒核样品获得的S壳中，他们计划将Intrashellä18O和13c测量结合使用。 mg/ca（温度的代理），BA/CA（河流径流或融化液排放）在同一NPS壳上的激光施加ICP-MS。 PI KOZDON F PI SPERO。可以分配给与方向的一般水深度范围，该范围与NPS的内部发育中的NPS相关 - 仪器方法将从北极海洋中的〜50 14C盒子式样品中应用于北极海洋中的中世，主要是从美国核心存储库中选择的。钥匙方面对水质量分层的变化敏感，（ii）现有的14c日期仍需要日期。