Mid-Pleistocene paleoceanography during a low-eccentricity climate cycle

低偏心率气候周期期间更新世中期的古海洋学

• 批准号: RGPIN-2022-05456
• 负责人: Head, Martin
• 金额: $ 2.66万
• 依托单位: Brock University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=751144
• 关键词: Mid; Pleistocene; paleoceanography; during; low

Our climate has always been paced by complex but mathematically determinable changes in Earth's orbit around the Sun. These changes explain a geological record of glacial-interglacial oscillations during the past 2.7 million years, each representing a slightly different orbital configuration. The oscillations are labelled marine isotope stages: 28 are recognized in the past 1 million years. Marine Isotope Stage (MIS) 19, occurring 770,000 years ago, is significant for two reasons. Firstly, the orbital configuration of its warmest interval was almost identical to that of today's interglacial -- both feature low eccentricity orbits. The study of MIS 19 therefore provides a baseline to understand how humans have affected our modern climate and to predict its natural duration. Secondly, the most significant reversal of Earth's magnetic field in the past 2.6 million years occurred within MIS 19. This reversal is the primary guide to the Early-Middle Pleistocene boundary, and both the reversal and the climatic signals associated with MIS 19 allow precise global recognition of this boundary. Five sites have been selected to elucidate MIS 19, two in Japan, and one in the northern North Atlantic, eastern North Atlantic, and Italy. Each site is highly time-resolved and contains numerous paleoclimatic signals. Moreover, the Japanese site is the global reference section for the Early-Middle Pleistocene boundary and the Italian site is potentially its auxiliary stratotype. However, none of the proposed sections has been studied for dinoflagellate cysts even though this largely planktonic microfossil group is used commonly for quantitative paleoenvironmental reconstructions across a wide range of past oceanographic conditions. MIS 19 has a distinctive global climate signature beginning with an interruption of deglaciation, an early rise to full interglacial conditions, the inception of glaciation, and finally three or four warm and cold oscillations marked by rapid shifts in the climate state. Subtle oscillations during full interglacial conditions were driven by low-latitude orbital harmonics. Glacial inception represents a threshold crossed as global ice volume increased, and the subsequent high-amplitude oscillations reflect disruptions to the Atlantic meridional overturning circulation by meltwater at high latitudes, thereby activating the thermal bipolar seesaw. The coherence of signals between Pacific and Atlantic-Mediterranean sites suggests the influence of the Intertropical Convergence Zone, perhaps amplified regionally by low-latitude monsoon dynamics. A refined understanding of MIS 19 and the mechanisms then operating, facilitated by the application of dinoflagellate cysts as a powerful climate proxy, will help assess generally which features of the climate system are sensitive to low-eccentricity orbital configurations. This research will also sharpen MIS 19 as an instrument for locating the Early-Middle Pleistocene boundary globally.

我们的气候一直受到地球绕太阳轨道复杂但在数学上可以确定的变化的影响。这些变化解释了过去270万年来冰川-间冰川振荡的地质记录，每一次都代表了略有不同的轨道配置。这种振荡被标记为海洋同位素阶段：在过去100万年中发现了28个阶段。发生在77万年前的海洋同位素阶段(MIS19)意义重大，有两个原因。首先，其最热时期的轨道构型与今天的间冰期几乎相同--两者都具有低偏心轨道。因此，对MIS19的研究为了解人类如何影响我们的现代气候并预测其自然持续时间提供了一个基线。其次，过去260万年来最显著的地球磁场反转发生在MIS19内。这种反转是早-中更新世界线的主要指南，与MIS19相关的反转和气候信号都允许全球对这一边界进行精确识别。已经选择了五个地点来阐明MIS19，其中两个在日本，一个在北大西洋北部、北大西洋东部和意大利。每个地点都具有高度的时间分辨率，并包含大量的古气候信号。此外，日本遗址是早-中更新世界线的全球参考剖面，而意大利遗址可能是其辅助层型。然而，没有一个拟议的剖面对甲藻包囊进行研究，尽管这一主要是浮游微化石的组通常用于定量重建过去各种海洋条件下的古环境。管理信息系统19具有独特的全球气候特征，首先是冰川消融的中断，然后是提前升至完全间冰期状态，然后是冰川作用的开始，最后是以气候状态快速变化为标志的三到四次冷暖振荡。全间冰期条件下的微小振荡是由低纬轨道谐波驱动的。冰川起始代表着随着全球冰量增加而跨过的门槛，随后的高幅度振荡反映了高纬度融水对大西洋经向翻转环流的干扰，从而激活了热两极拉锯。太平洋和大西洋-地中海站点之间信号的一致性表明热带辐合带的影响，可能是低纬季风动力在区域内放大了这一影响。通过应用甲藻包囊作为强大的气候指标，进一步了解MIS19和当时的运行机制，将有助于从总体上评估气候系统的哪些特征对低偏心率轨道构型敏感。这项研究还将加强MIS19作为确定全球早-中更新世界线的工具。