Collaborative Research: Provenance of Alkenones & Holocene Temperature Evolution of the NW Atlantic

合作研究：烯酮的来源

• 批准号: 2022462
• 负责人: Elisabeth Sikes
• 金额: $ 42.84万
• 依托单位: Rutgers University New Brunswick
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-12-01 至 2023-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2022462&HistoricalAwards=false
• 关键词: Collaborative; Research; Provenance; Alkenones; &amp

This project will produce a set of 12 new sea-surface temperature reconstructions along the western North Atlantic to examine the accuracy of alkenone-based ocean temperature records. Temperature data over the past several thousand years show a mismatch between land-, sea-, and climate model-based estimates. Climate models suggest that temperature remained relatively unchanged, while land-based records shows slight warming. Oddly, sea surface temperatures show 4-6°C cooling over the same period of time. But concerns exist about how well these records reflect temperature conditions in the region. Alkenones are produced by algae which may be biased by the temperature of the season when algae are most abundant. They can also be carried to the North Atlantic from elsewhere by ocean currents and reflect temperature conditions of those regions. This study will attempt to resolve these issues by examination of alkenones collected directly in the water column throughout the year and comparing these to alkenones deposited on the seafloor nearby. Hydrogen isotope ratios and radiocarbon data will provide a test of how much material is transported from different sources. Alkenone temperature data will be compared to other temperature proxies (e.g. Mg/Ca of foraminifera) in the region. The project creates significant learning opportunities for middle and high school teachers who will team with scientists in the classroom to develop climate-based curricular instruction and participate in shipboard research during sediment coring operations. It will also provide significant support for undergraduate students and an early career postdoctoral student. The global composite of Holocene temperature proxy records indicates 0.5-1°C of cooling over the last 8,000 years, driven largely by a 2°C cooling in northern hemisphere marine records. Transient climate simulations, however, show no such cooling, and continental temperature records in eastern North America and Europe indicate slight warming. This “Holocene Conundrum” is one of the most prominent unmet challenges facing the climate science community. The northern hemisphere trend is largely driven by 4-6°C cooling in three alkenone SST records from the NW Atlantic. To determine whether this data-model mismatch indicates a gap in understanding of the climate system, these anomalous proxy records must be examined in the context of the factors influencing alkenone deposition in NW Atlantic slopewaters and compared to other SST proxies in the same locations for which samples are not available and analyses are presently lacking. Both deficiencies will be addressed in this research by measuring hydrogen isotope values and radiocarbon ages of alkenones, along with Mg/Ca ratios in planktonic foraminifera, from sediment cores and archived sediment trap samples collected in 2004-2007 in the NW Atlantic slopewater region. Alkenone SST records can be biased by lateral transport of slow-sinking alkenones via surface and abyssal currents, or by seasonal production, both potential causes for the data-model mismatch. This project will take advantage of the large hydrogen isotope gradient in NW Atlantic surface waters to ascertain alkenone synthetic provenance by measuring 2H/1H ratios in alkenones. Provenance will be further assessed by measuring alkenone 14C ages to determine the extent of pre-aging during advection. Comparison of alkenone temperatures and 14C ages to fast-sinking, foraminiferal Mg/Ca temperatures and calcite 14C ages, across a series of locations and depths, with seasonal resolution, will allow for the full characterization of advective or seasonal biasing in either proxy relative to in situ and satellite SSTs. Having established the impact of these potential biases, a robust re-assessment of NW Atlantic Holocene SSTs will be made via 12 new reconstructions (6 each from the two independent proxies) from 6 planned coring sites on depth transects east of New Jersey and Nova Scotia, allowing a possible solution to the “Holocene conundrum”.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

该项目将沿北大西洋西部进行一组 12 个新的海面温度重建，以检查过去数千年基于烯酮的海洋温度记录的准确性，这些数据显示陆地、海洋和海洋之间的不匹配。基于气候模型的估计。气候模型表明温度相对保持不变，而陆地记录显示同期海面温度略有变暖，但人们对这些变化的程度存在担忧。记录反映了温度条件烯酮是由藻类产生的，可能会受到藻类最丰富季节的温度的影响，它们也可以通过洋流从其他地方带到北大西洋，并反映这些地区的温度条件。通过检查全年直接在水体中收集的烯酮并将其与沉积在附近海底的烯酮进行比较来解决这些问题将提供对有多少物质从不同的地方运输的测试。烯酮温度数据将与该地区的其他温度指标（例如有孔虫的镁/钙）进行比较，该项目为初中和高中教师创造了重要的学习机会，他们将与课堂上的科学家合作开发基于气候的课程。它还将为本科生和早期职业博士后学生提供重要支持。全新世温度代理记录的全球综合数据表明，整个新世温度下降了 0.5-1°C。过去 8,000 年，主要是由北半球海洋记录中的 2°C 降温推动的，然而，瞬态气候模拟显示没有这种降温，而北美东部的大陆温度记录表明欧洲略有变暖，这一“全新世难题”就是其中之一。气候科学界面临的最突出的未解决挑战主要是由西北大西洋的三个烯酮海温记录中 4-6°C 的降温驱动的。不匹配表明对气候系统的理解存在差距，这些异常代理记录必须在影响西北大西洋斜坡水域烯酮沉积的因素的背景下进行检查，并与相同地点的其他海表温度代理进行比较，但无法获得样本且分析尚未完成。本研究将通过测量沉积物岩心和浮游有孔虫中的氢同位素值和烯酮的放射性碳年龄以及浮游有孔虫中的镁/钙比来解决目前缺乏的两个缺陷。 2004-2007 年在大西洋西北部坡水区收集的沉积物捕集样本存档可能会因表面和深海流缓慢下沉的烯酮的横向传输或季节性生产而产生偏差，这都是数据模型不匹配的潜在原因。该项目将利用西北大西洋表层水中较大的氢同位素梯度，通过测量 2H/1H 比率来确定烯酮的合成来源。将通过测量烯酮 14C 年龄来进一步评估烯酮的来源，以确定平流过程中的提前老化程度，以及一系列地点的快速下沉、有孔虫 Mg/Ca 温度和方解石 14C 年龄。具有季节分辨率的深度和深度将允许对任一代理相对于原位和卫星海表温度的平流或季节偏差进行全面表征。为了消除这些潜在偏差的影响，将通过新泽西州和新斯科舍省以东深度横断面的 6 个计划取芯点的 12 个新重建（两个独立代理各 6 个）对西北大西洋全新世海表温度进行强有力的重新评估，从而允许“全新世难题”的可能解决方案。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。