Collaborative Research: Partitioning early Holocene Laurentide v. Antarctic ice melt from high-resolution reconstruction of sea-level rise and glacial isostatic adjustment modeling

合作研究：从海平面上升的高分辨率重建和冰川均衡调整模型中划分全新世早期的劳伦泰德诉南极冰融化

• 批准号: 1502753
• 负责人: Brad Rosenheim
• 金额: $ 14.44万
• 依托单位: University of South Florida
• 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 2018-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1502753&HistoricalAwards=false
• 关键词: Collaborative; Research; Partitioning; early; Holocene

Sea-level rise is a defining issue for the future of densely populated low-lying coastal regions. Within this context, the fate of the remaining large ice sheets is arguably the primary concern. Therefore, numerous studies over the past few decades have focused on the retreat of ice sheets during the end of the last ice age, 20,000 to 7,000 years ago. The North American and Antarctic continents collectively account for up to 80% of total ice melt, but the amount and timing of their contributions is not well known. Resolving this is important because the location of meltwater input is likely to have major implications for ocean-atmosphere circulation across the globe. The period between 12,000 and 7,000 years ago that witnessed about half (the last ~60 m) of the total sea-level rise is particularly poorly studied, despite the fact that the Earth's climate was roughly comparable to that of the present-day. Thus, this time interval could serve as a useful analog for the future. The present project will reconstruct the rate of sea-level rise in the Mississippi Delta during this period with unprecedented resolution. Combining this new record with state-of-the art computer models of ice sheets and the solid earth, it will be possible to calculate the relative contribution of North American v. Antarctic ice sheets to global sea-level rise during this time interval. The project will support a postdoctoral scholar as well as undergraduate students, and also contain numerous outreach activities. This includes instruction and field demonstrations at a New Orleans urban farm that educates local youth leaders on sustainable food production. Educational materials will be provided for high school teachers throughout Florida and for an exhibit on sea-level rise in the Tampa Bay-St. Petersburg area. Finally, all new sea-level data will be publicly released through the NOAA-WDC Paleoclimatology database.Uncertainty about the meltwater contribution from different ice sheets during the last deglaciation is particularly well reflected by the sea-level history during the early Holocene, where recent end-member estimates of the Laurentide Ice Sheet (LIS) contribution to global sea-level rise between 11 and 7 ka vary from ~20 to 30 m sea-level equivalent. This difference corresponds to about 1.5 times the volume of the present-day Greenland Ice Sheet. Possibly even larger uncertainties exist about the retreat history of the Antarctic Ice Sheet (AIS). Ice-sheet volumes during this time window are equally poorly constrained. The Mississippi Delta is uniquely suited to produce a highly detailed early Holocene relative sea-level (RSL) record, extending to ~9.5 ka and possibly older. Wherever conventional approaches (AMS 14C dating of plant macrofossils extracted from basal peat) are not feasible, ramped pyrolysis 14C dating of brackish wetland paleosols, a novel geochronological technique, will be used to obtain sea-level index points of sufficiently high resolution. The new early Holocene RSL record will be combined with a synthesis of lower resolution records from across the globe, with the primary goal to determine the rate of RSL rise and its spatial variability from 7 to 10 ka. Glacial isostatic adjustment modeling that considers a large suite of ice-sheet histories will be used to correct RSL records for viscoelastic and rotational effects. The residual signal should provide new information on the contribution from the LIS and AIS to early Holocene sea-level rise, due to their distinctly different sea-level fingerprints. Specific questions that the work will answer include: (1) Was the early Holocene sea-level rise predominantly smooth or was it punctuated by distinct sea-level jumps akin to (and possibly larger than) those around the 8.5 to 8.2 ka time window? and (2) What was the relative contribution of the LIS v. AIS to early Holocene sea-level rise, in particular during the time interval from ~9.5 to 8 ka?

海平面上升是人口稠密的低洼沿海地区未来的一个决定性问题。在这种背景下，剩余大冰盖的命运可以说是最令人担忧的。因此，过去几十年的许多研究都集中在20，000至7，000年前的最后一个冰河时代结束时冰盖的退缩。北美和南极大陆总共占冰融化总量的80%，但其贡献的数量和时间尚不清楚。解决这个问题很重要，因为融水输入的位置可能对整个地球仪的海洋-大气环流产生重大影响。12，000年至7，000年前的这段时间见证了海平面上升的一半（最后60米），尽管地球的气候与现在大致相当，但研究得特别少。因此，这个时间间隔可以作为未来的有用模拟。本项目将以前所未有的分辨率重建这一时期密西西比三角洲海平面上升的速度。将这一新记录与冰盖和固体地球的最先进计算机模型相结合，将有可能计算出这一时间间隔内北美冰盖与南极冰盖对全球海平面上升的相对贡献。该项目将支持一名博士后学者和本科生，还包括许多外联活动。这包括在新奥尔良的一个城市农场进行指导和实地示范，教育当地青年领袖可持续粮食生产。将为整个佛罗里达的高中教师提供教育材料，并为坦帕湾-圣彼得堡地区的海平面上升展览提供教育材料。最后，所有新的海平面数据将通过NOAA-WDC古气候数据库公开发布。末次冰消期间不同冰盖融水贡献的不确定性特别好地反映在全新世早期的海平面历史中，其中，最近对劳伦泰德冰盖（LIS）在11 - 7 ka之间对全球海平面上升的贡献的端元估计在~20 - 30 m海平面之间变化-水平相当。这一差异相当于现今格陵兰冰盖体积的1.5倍。关于南极冰盖（AIS）的退缩历史可能存在更大的不确定性。在这段时间内，冰盖的体积同样受到很差的限制。密西西比三角洲是唯一适合于产生一个非常详细的早全新世相对海平面（RSL）记录，延伸到~9.5万年，可能更老。传统的方法（AMS 14 C测年的植物大化石提取的基底泥炭）是不可行的，斜坡热解14 C测年的半咸水湿地古土壤，一种新的地质年代学技术，将被用来获得足够高的分辨率海平面指数点。新的全新世早期RSL记录将与来自地球仪的低分辨率记录的合成相结合，主要目标是确定RSL上升的速率及其从7到10 ka的空间变异性。冰川均衡调整模型，考虑了一个大套冰盖的历史将被用来纠正RSL记录的粘弹性和旋转效应。由于LIS和AIS具有明显不同的海平面指纹，因此残留信号应提供有关LIS和AIS对全新世早期海平面上升贡献的新信息。具体的问题，这项工作将回答包括：（1）是早期全新世海平面上升主要是平稳的，或者是由明显的海平面跳跃类似（可能更大）周围的8.5至8.2万年的时间窗口？（2）LIS和AIS对全新世早期海平面上升的相对贡献是什么，特别是在~9.5 ~ 8 ka的时间间隔内？