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

北大西洋次极区千年尺度的气候变率被认为是整个全新世海洋、冰芯和陆地档案中普遍存在的共同特征，主要由大西洋经向翻转环流（AMOC）的变化驱动。北大西洋强烈的海洋-大气耦合意味着与延长的北大西洋涛动（NAO）正（负）相相关的更强（或更弱）的西风带可能在过去一千年中增强了AMOC。我们打算首次证明，在过去一千年中提出的AMOC的大气强迫是整个全新世持续存在的潜在机制。通过北大西洋海流（NAC）向北的热量纬向转移，AMOC变率在欧洲（和全球）气候变率的调节中起着重要作用，并且人们对主要由大气强迫驱动的亚极环流（SPG）动力学的重要性有了新的认识，该动力学影响NAC的盐度，从而影响AMOC的强度。以苏纳特湖（Loch Sunart）为代表的苏格兰峡湾环境很好地捕捉了这种变化，加上该地点最近的温度年代学进展，为全新世期间区域陆地-海洋相互作用的年代学提供了一个独特的机会。从苏格兰西北部的苏纳特湖（Loch Sunart）恢复的22.5m长的岩心（MD04-2832）的盐度、温度和环流的高分辨率（0.3 cm/yr）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期间，MD04-2832代用物响应了大气环流的一次重大重组4、SPG动力学和AMOC变率。然而，这些记录中可用的时间控制限制了我们严格测试这些大规模北半球天气气候变化的相对时间的能力。本提案的目的是建立MD04-2832的低温地层学，以支持这些全新世海洋气候大规模变化的精确时间，并促进与格陵兰冰芯和其他地方记录的大气环流代用物的比较。如果目前对较强西风带的理解是正确的，那么我们假设来自苏格兰西部的海洋代理记录将与格陵兰冰芯推断的大气环流的大规模变化同步。至关重要的是，考虑到现有年龄控制的不确定性，毯层等时线是解决这个时间问题的关键，苏格兰和爱尔兰的陆地环境中已知了大量全新世毯层。

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.