The earliest part of the Holocene, from 11.5k to 7k (k = 1000 years before present), is a critical transition period between the relatively cold last deglaciation and the warm middle Holocene. It is marked by more pronounced seasonality and reduced greenhouse gases (GHGs) than the present state, as well as by the presence of the Laurentide Ice Sheet (LIS) and glacial meltwater perturbation. This paper performs experiments under pre-industrial and different early-Holocene regimes with AWI-ESM (Alfred Wegener Institute–Earth System Model), a state-of-the-art climate model with unstructured mesh and varying resolutions, to examine the sensitivity of the simulated Atlantic meridional overturning circulation (AMOC) to early-Holocene insolation, GHGs, topography (including properties of the ice sheet), and glacial meltwater perturbation. In the experiments with early-Holocene Earth orbital parameters and GHGs applied, the AWI-ESM simulation shows a JJA (June–July–August) warming and DJF (December–January–February) cooling over the mid and high latitudes compared with pre-industrial conditions, with amplification over the continents. The presence of the LIS leads to an additional regional cooling over the North America. We also simulate the meltwater event around 8.2k. Big discrepancies are found in the oceanic responses to different locations and magnitudes of freshwater discharge. Our experiments, which compare the effects of freshwater release evenly across the Labrador Sea to a more precise injection along the western boundary of the North Atlantic (the coastal region of LIS), show significant differences in the ocean circulation response, as the former produces a major decline of the AMOC and the latter yields no obvious effect on the strength of the thermohaline circulation. Furthermore, proglacial drainage of Lakes Agassiz and Ojibway leads to a fast spin-down of the AMOC, followed, however, by a gradual recovery. Most hosing experiments lead to a warming over the Nordic Sea and Barents Sea of varying magnitudes, because of an enhanced inflow from lower latitudes and a northward displacement of the North Atlantic deep convection. These processes exist in both of our high- and low-resolution experiments, but with some local discrepancies such as (1) the hosing-induced subpolar warming is much less pronounced in the high-resolution simulations; (2) LIS coastal melting in the high-resolution model leads to a slight decrease in the AMOC; and (3) the convection formation site in the low- and high-resolution experiments differs, in the former mainly over northeastern North Atlantic Ocean, but in the latter over a very shallow subpolar region along the northern edge of the North Atlantic Ocean. In conclusion, we find that our simulations capture spatially heterogeneous responses of the early-Holocene climate.

中文翻译：

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在 AWI-ESM 中使用不同强迫和分辨率的早期全新世模拟

全新世的最早部分，从 11.5k 到 7k（k = 1000 年之前），是相对寒冷的末次冰消期和温暖的中全新世之间的关键过渡期。它的特点是比现在更明显的季节性和温室气体 (GHG) 减少，以及劳伦泰德冰盖 (LIS) 和冰川融水扰动的存在。本文使用 AWI-ESM（阿尔弗雷德韦格纳研究所 - 地球系统模型）在工业化前和不同的全新世早期制度下进行实验，这是一种具有非结构化网格和不同分辨率的最先进的气候模型，以检查模拟的大西洋经向翻转环流 (AMOC) 到全新世早期日照、温室气体、地形（包括冰盖的特性）和冰川融水扰动。在应用全新世早期地球轨道参数和 GHG 的实验中，AWI-ESM 模拟显示，与之前相比，中高纬度地区出现 JJA（6 月至 7 月至 8 月）变暖和 DJF（12 月至 1 月至 2 月）降温。工业条件，在各大洲放大。LIS 的存在导致北美上空的额外区域降温。我们还模拟了 8.2k 左右的融水事件。海洋对不同位置和淡水排放量的反应存在很大差异。我们的实验将拉布拉多海均匀释放淡水的影响与沿北大西洋西部边界（LIS 沿海地区）的更精确注入的影响进行了比较，结果表明海洋环流响应存在显着差异，前者使AMOC大幅下降，后者对温盐环流强度无明显影响。此外，Agassiz 湖和 Ojibway 湖的冰川前排水导致 AMOC 快速减速，但随后逐渐恢复。大多数软管实验导致北欧海和巴伦支海出现不同程度的变暖，这是因为来自低纬度的流入量增加和北大西洋深层对流向北位移。这些过程存在于我们的高分辨率和低分辨率实验中，但存在一些局部差异，例如 (1) 软管引起的次极地变暖在高分辨率模拟中不那么明显；(2) 高分辨率模型中的LIS海岸融化导致AMOC略有下降；(3) 低分辨率和高分辨率实验的对流形成地点不同，前者主要在北大西洋东北部，而后者主要在北大西洋北部边缘的一个非常浅的次极区。总之，我们发现我们的模拟捕获了早期全新世气候的空间异质响应。