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.

我们的气候一直是由地球绕太阳轨道的复杂但数学上可确定的变化来决定的。这些变化解释了过去270万年冰期-间冰期震荡的地质记录，每一次震荡都代表着略有不同的轨道结构。这些振荡被称为海洋同位素阶段：在过去的100万年中有28个被识别出来。发生在77万年前的海洋同位素阶段（MIS） 19具有重要意义，原因有二。首先，其最温暖间隔的轨道结构与今天的间冰期几乎相同——两者都具有低偏心轨道。因此，MIS 19的研究为了解人类如何影响我们的现代气候和预测其自然持续时间提供了一个基线。其次，在过去的260万年里，地球磁场最显著的反转发生在MIS 19。这种反转是早-中更新世边界的主要指南，并且与MIS 19相关的反转和气候信号都可以精确地在全球范围内识别该边界。已经选择了五个地点来阐明MIS 19，两个在日本，一个在北大西洋北部、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，并包含大量的古气候信号。此外，日本遗址是早-中更新世边界的全球参考剖面，意大利遗址可能是其辅助层型。然而，尽管这种主要由浮游生物组成的微化石群通常被用于过去广泛的海洋条件下的定量古环境重建，但尚未对甲藻囊进行过研究。MIS 19具有独特的全球气候特征，从消冰中断开始，早期上升到完全间冰期条件，冰川开始，最后是三到四次以气候状态快速变化为标志的冷暖振荡。完全间冰期的细微振荡是由低纬度轨道谐波驱动的。冰川开始代表了全球冰量增加时跨越的一个阈值，随后的高振幅振荡反映了高纬度地区融水对大西洋经向翻转环流的破坏，从而激活了热两极跷跷板。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，可能被低纬度季风动力在区域上放大。通过应用鞭毛藻囊作为一种强大的气候代理，对MIS 19及其运行机制的精确理解将有助于总体评估气候系统的哪些特征对低偏心轨道配置敏感。该研究还将使MIS 19成为全球早-中更新世边界定位的工具。