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

该项目将制作一套沿北大西洋西部沿着的12个新的海面温度重建图，以检查基于烯酮的海洋温度记录的准确性。过去几千年的温度数据显示，基于陆地、海洋和气候模型的估计值之间存在不匹配。气候模型表明，气温保持相对不变，而陆基记录显示略有变暖。奇怪的是，在同一时期，海面温度显示出4-6°C的冷却。但人们担心这些记录能否很好地反映该地区的温度状况。烯酮是由藻类产生的，其可能受到藻类最丰富季节的温度的影响。它们也可以被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。这项研究将试图通过检查全年直接在水柱中收集的烯酮并将其与附近海底沉积的烯酮进行比较来解决这些问题。氢同位素比率和放射性碳数据将检验有多少物质从不同来源迁移。烯酮温度数据将与该区域其他温度代用指标（例如有孔虫的Mg/Ca）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，他们将在课堂上与科学家合作，制定基于气候的课程教学，并在沉积物取芯作业期间参与船上研究。它还将为本科生和早期职业博士后学生提供重要支持。全新世温度代用记录的全球综合数据表明，在过去8,000年里，气温下降了0.5-1°C，这主要是由于北方海洋记录中气温下降了2°C。然而，瞬态气候模拟显示没有这种冷却，北美东部和欧洲的大陆温度记录显示略有变暖。这个“全新世难题”是气候科学界面临的最突出的未解决的挑战之一。北方的趋势主要是由来自西北大西洋的三个烯酮SST记录中的4-6°C冷却驱动的。为了确定这种数据模型不匹配是否表明气候系统的理解差距，这些异常的代理记录必须检查的背景下，影响烯酮沉积在西北大西洋slopewaters和其他SST代理在相同的位置，样品不可用，目前缺乏分析的因素进行比较。这两个不足之处将解决在这项研究中，通过测量氢同位素值和放射性碳年龄的烯酮，沿着镁/钙比在南极有孔虫，从沉积物岩心和存档的沉积物陷阱样品收集在2004-2007年在西北大西洋slopewater地区。烯酮SST记录可以通过表面和深海海流或季节性生产的缓慢下沉的烯酮的横向运输而产生偏差，这两种可能的原因是数据模型不匹配。该项目将利用西北大西洋表面沃茨氢同位素梯度大的优势，通过测量烯酮中的2 H/1H比率来确定烯酮合成来源。将通过测量烯酮14 C年龄进一步评估种源，以确定平流过程中的预老化程度。烯酮温度和14 C年龄的比较快速下沉，有孔虫的Mg/Ca温度和方解石14 C年龄，在一系列的位置和深度，与季节分辨率，将允许充分表征平流或季节性偏置在任何代理相对于原位和卫星SST。在确定了这些潜在偏差的影响后，将通过12个新的重建对西北大西洋全新世SST进行可靠的重新评估（两个独立代理中各6个）来自新泽西和新斯科舍省以东深度剖面上的6个计划取芯点，为“全新世难题”提供了可能的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知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.