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的复杂但数学上可确定的变化的影响。这些变化解释了过去270万年来冰川-间冰期振荡的地质记录，每一次都代表着略微不同的轨道配置。这些振荡被标记为海洋同位素阶段：在过去的100万年中，有28个被确认。海洋同位素阶段（MIS）19发生在77万年前，有两个原因。首先，它最温暖时期的轨道结构与今天的间冰期几乎相同-两者都具有低离心率轨道的特征。因此，对MIS 19的研究提供了一个基线，以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。其次，过去260万年来地球磁场最显著的逆转发生在MIS 19内。这种反转是早-中更新世界线的主要标志，这种反转和与MIS 19相关的气候信号都使全球能够精确地识别这一界线。选择了五个地点来阐明MIS 19，两个在日本，一个在北大西洋北方、北大西洋东部和意大利。每个站点都具有高度的时间分辨率，并包含许多古气候信号。此外，日本站点是早-中更新世边界的全球参考剖面，意大利站点可能是其辅助层型。然而，没有一个建议的部分已被研究的甲藻孢囊，即使这主要是浮游微体化石群通常用于定量古环境重建在过去的海洋条件下的范围很广。MIS 19有一个独特的全球气候特征，开始于冰川消退的中断，早期上升到完全的间冰期条件，冰川的开始，最后是三到四个温暖和寒冷的振荡，标志着气候状态的快速变化。在整个间冰期条件下的微妙振荡是由低纬度轨道谐波驱动的。冰川初期是一个阈值跨越全球冰量的增加，随后的高振幅振荡反映了高纬度融水对大西洋纬向翻转环流的破坏，从而激活了热双极跷跷板。太平洋和南极-地中海站点之间的信号的一致性表明热带辐合带的影响，可能通过低纬度季风动力学在区域上放大。通过应用甲藻孢囊作为强有力的气候代用指标，对MIS 19及其运行机制的深入了解将有助于普遍评估气候系统的哪些特征对低偏心率轨道配置敏感。这项研究还将使MIS 19成为全球定位早-中更新世边界的工具。