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

该项目将制作一套12个新的北大西洋西部海面温度重建，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，海面温度在同一时间段内降温4-6摄氏度。但人们担心，这些记录在多大程度上反映了该地区的气温状况。烯酮是由藻类产生的，这可能会受到藻类最丰富的季节温度的影响。它们也可以被洋流从其他地方带到北大西洋，反映这些地区的温度状况。这项研究将试图通过检查全年直接在水柱中收集的烷烃并将这些与沉积在附近海底的烷烃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提供对从不同来源运输多少材料的测试。烯烃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，他们将在课堂上与科学家合作，开发基于气候的课程教学，并在沉积物取心操作期间参与船上研究。它还将为本科生和早期职业博士后提供重要支持。全新世温度代理记录的全球合成表明，在过去的8000年里，气温下降了0.5-1摄氏度，主要是由北半球海洋记录中2摄氏度的降温推动的。然而，短暂的气候模拟显示没有这种降温，北美东部和欧洲大陆的温度记录表明略有变暖。这一“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。北半球的趋势在很大程度上是由西北大西洋记录的3个烯酮SST中4-6℃的降温推动的。为了确定这种数据模型不匹配是否表明对气候系统的理解存在差距，必须结合影响西北大西洋斜坡面的烯烃沉积的因素来审查这些异常的替代记录，并将其与同一地点的其他SST替代记录进行比较，因为这些地点没有样本，目前也缺乏分析。这项研究将通过测量2004-2007年收集的西北大西洋斜坡水域沉积岩心和沉积物圈闭样品中的烷酮的氢同位素值和放射性碳年龄以及浮游有孔虫中的镁/钙比来解决这两个不足之处。通过表层洋流和深海洋流对缓慢下沉的烯烃的侧向输送，或季节性生产，可能会对烯酮SST记录产生偏差，这两种因素都可能导致数据与模型的不匹配。该项目将利用大西洋西北部表层水中氢同位素的大梯度，通过测量烯酮中的2H/1H比率来确定烯酮的合成来源。将通过测量烯酮14C年龄来进一步评估物源，以确定平流过程中预老化的程度。将一系列地点和深度的烯烃温度和14C年龄与快速下沉、有孔虫的镁/钙温度和方解石14C年龄进行比较，并具有季节性分辨率，将能够充分表征相对于原地和卫星SSTs的平流或季节性偏差。在确定了这些潜在偏差的影响后，将通过12个新的重建(两个独立代理各6个)对西北大西洋全新世SST进行强有力的重新评估，这些重建来自新泽西州以东和新斯科舍省东部深度横断面上的6个计划取心地点，从而可能解决“全新世难题”。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.