Holocene Upper Atlantic Temperature Trend: AMOC Variability or Anomalous Heat Uptake

在过去的11,000年中，大西洋经向海洋环流（AMOC）是否以及如何发生变化尚不确定。然而，AMOC影响热量，盐度和营养物质的分布，其强度的变化可以影响全球气候，并产生生态影响。最初的数据表明，热带大西洋，在大约1000米的水深，从大约11,000年到5,000年前冷却。其他证据也暗示这段时间该地区也有类似的降温。AMOC强度的变化影响热量在深海内的分布，并可能导致观察到的冷却趋势。深海的温度也受到表层沃茨沉入深海的区域的温度变化的影响。这些地表温度可能会因全球温度变化或高纬度地区气候变化而变化。G.风、海冰分布）。本研究的目的是生成数据以确认观察到的冷却趋势，并评估该趋势是由于流向这些站点的高纬度沃茨的冷却还是由于AMOC的变化，还是由于这两种机制。确定这种冷却的原因对理解全新世气候和变化具有重要意义。初步结果表明，在北大西洋热带地区西部，南极中层水（AAIW）占主导地位的深度（约950米），全新世早期至中期出现了冷却现象。这种冷却开始于大约11 kyBP，并在接近现代的底层水温（BWT）达到顶峰，大约7 - 5 kyBP。 解释这种冷却的假设包括：（1）大西洋经向翻转环流（AMOC）的加强是对北大西洋冰消淡水输入减少的响应，或者（2）一个或多个源沃茨的冷却。研究人员将通过在现代AAIW深度内的几个浅热带站点重建BWT来确认这种冷却，并使用AAIW和北方源沃茨内其他亚热带站点的测量结果来测试替代假设。来自北大西洋、南大西洋和热带大西洋的一套海洋沉积物岩心，水深从300米到1100米不等，将用于重建温度变化的空间格局，并帮助区分温度趋势的两个可能原因，即流向热带大西洋的沃茨的高纬度冷却，或在此期间AMOC的加强。由于模型模拟无法预测这些地点在这段时间内的冷却，确认和理解这种冷却的原因可能有助于确定模型或模型设置可以改进的地方。该奖项反映了NSF的法定使命，并被认为值得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来支持。

Whether and how the Atlantic Meridional Ocean Circulation (AMOC) has changed during the last 11,000 years is uncertain. Yet, the AMOC influences the distribution of heat, salinity, and nutrients, and variations in its strength can affect global climate, with ecological impacts. Initial data suggest the tropical Atlantic, at about 1000 meters water depth, cooled from approximately 11,000 to 5,000 years ago. Other evidence also hints similar cooling in this region during this time. Changes in the strength of the AMOC influence how heat is distributed within the deep ocean and may have caused the observed cooling trend. Temperature of the deep ocean is also affected by temperature changes in the regions where surface waters sink into the deep ocean. These surface temperatures may change due to global temperature change or due to regional climate changes at high latitudes (e. g. winds, sea ice distribution). The goal of this study is to generate data to confirm the observed cooling trend and to assess whether the trend is due to cooling of high latitude waters flowing to these sites or to changes in AMOC, or to both of these mechanisms. Identifying the cause of this cooling has important implications for understanding Holocene climate and variability. A post-doctoral scientist will participate in this project.Initial results suggest an early – middle Holocene cooling in the western tropical north Atlantic, at a depth (about 950 m) where Antarctic Intermediate Water (AAIW) is the dominant water mass. This cooling began at approximately 11 kyBP and culminated in near-modern bottom water temperatures (BWT) by about 7-5 kyBP. Hypotheses to explain this cooling include (1) a strengthening Atlantic Meridional Overturning Circulation (AMOC) in response to a decrease in the input of deglacial freshwater to the North Atlantic, or (2) cooling in one or more of the source waters to the site. Researchers will confirm this cooling by reconstructing BWT at several shallow tropical sites within modern AAIW depths, and test the alternative hypotheses with measurements from other subtropical sites within AAIW and northern source waters. A suite of marine sediment cores from the north, south, and tropical Atlantic, and ranging from 300 to 1100 meters water depth will be used to reconstruct the spatial pattern of temperature change and help distinguish between the two likely causes of the temperature trend, a high-latitude cooling in waters flowing to the tropical Atlantic, or a strengthening of the AMOC during this time period. As model simulations do not predict a cooling at these sites over this time period, confirming and understanding the cause of this cooling may help identify where models or model set-up can be improved.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.