Holocene tephra constraints on the timing of millennial-scale variability in the subpolar North Atlantic

亚极地北大西洋千年尺度的气候变化被认为是整个全新世海洋、冰芯和陆地档案普遍存在的一个共同特征，主要是由大西洋子午线翻转环流(AMOC)的变化驱动的。北大西洋强烈的海-气耦合意味着更强(或更弱)的西风与延长的正(或负)北大西洋涛动(NAO)阶段有关，可能在过去的1000年里增强了AMOC。我们打算第一次证明，在过去千年中提出的大气强迫是一种在整个全新世持续存在的基本机制。通过北大西洋流(NAC)向北输送热量，AOC变率在欧洲(和全球)气候变率的调制中发挥着重要作用，人们开始认识到亚极涡旋(SPG)动力学的重要性，这种动力主要是由大气强迫驱动的，对NAC的盐度，从而对AMOC的强度。以苏纳特湖为代表的苏格兰Fjordic环境很好地捕捉到了这种变异性，加上该遗址最近的年代学进展，提供了一个独特的机会来支持全新世期间区域陆地-海洋相互作用的年代学。从苏纳特湖(苏格兰西北部)恢复的22.5米长的岩芯(MD04-2832)对盐度、温度和环流的高分辨率(0.3厘米/年)重建反映了东北大西洋水文和大尺度大气强迫的控制。例如，在5-6 KYR之间，MD04-2832代表对大气环流4、SPG动力学和AMOC变异性的重大重组作出反应。然而，这些记录中可用的时间控制限制了我们对这些北半球大规模天气气候变化的相对时间进行批判性测试的能力。这项提议的目的是建立MD04-2832的特弗拉地层学，以支持这些全新世海洋气候大规模变化的准确时间，并便于与格陵兰冰芯和其他地方记录的大气环流指标进行比较。如果目前对更强西风的理解是正确的，那么我们假设我们在苏格兰西部的海洋代理记录将与从格陵兰冰芯推断的大气环流的大范围变化同步。关键是，考虑到现有年龄控制的不确定性，Tephra等时线是解决这一年代学问题的关键，而相当数量的全新世Tephra是从苏格兰和爱尔兰的陆地环境中得知的。

Millennial-scale climate variability in the subpolar North Atlantic is thought to be a pervasive, common feature of marine, ice core and terrestrial archives throughout the Holocene, mainly driven by changes in the Atlantic Meridional Overturning Circulation (AMOC). Strong ocean-atmosphere coupling in the North Atlantic mean that stronger (or weaker) westerlies associated with a prolonged positive (or negative) North Atlantic Oscillation (NAO) phase may have enhanced AMOC during the last millennium. We intend to demonstrate for the first time that the proposed atmospheric forcing of AMOC during the past millennium is an underlying mechanism that persists throughout the Holocene. AMOC variability plays an important role in the modulation of European (and global) climate variability through the latitudinal transfer of heat northwards via the North Atlantic Current (NAC) and there is an emerging understanding of the importance of subpolar gyre (SPG) dynamics, primarily driven by atmospheric forcing, upon the salinity of the NAC and hence the strength of AMOC. The fjordic environments of Scotland, as represented by Loch Sunart, are well-placed to capture this variability, and together with recent tephrochronological advances at this site, present a unique opportunity to underpin the chronology of regional land-ocean interactions during the Holocene. High-resolution (0.3 cm/yr) reconstructions of salinity, temperature and circulation from a 22.5m long core (MD04-2832), recovered from Loch Sunart (NW Scotland), reflect the controls of both NE Atlantic hydrology and large-scale atmospheric forcing. For example, between 5-6 kyr, MD04-2832 proxies respond to a major reorganization in atmospheric circulation4, SPG dynamics and AMOC variability. The available chronological control in these records, however, limits our ability to critically test the relative timing of these large-scale northern hemisphere synoptic climate changes. The aim of this proposal is to establish a tephra stratigraphy for MD04-2832, to underpin the precise timing of these large-scale shifts in Holocene marine climate and facilitate a comparison with proxies of atmospheric circulation recorded in Greenland ice cores and elsewhere. If the current understanding of stronger westerlies associated with a prolonged positive NAO phase linked to enhanced AMOC via SPG dynamics is correct, then we hypothesize that our marine proxy records from the west of Scotland will synchronize with large-scale changes in atmospheric circulation inferred from Greenland ice cores. Critically, given the uncertainties of existing age-control, tephra isochrones are the key to solving this chronological problem and a significant number of Holocene tephra are known from terrestrial settings in Scotland and Ireland.