Was the deep Atlantic dominated by southern source waters during the LGM? A conservative view based on the oxygen isotopic ratio of benthic foraminifera

末次盛冰期期间，大西洋深海是否以南部源水为主？

• 批准号: 2306931
• 负责人: David Lund
• 金额: $ 45.2万
• 依托单位: University of Connecticut
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-06-01 至 2026-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2306931&HistoricalAwards=false
• 关键词: Was; deep; Atlantic; dominated; southern

The cause of glacial-interglacial atmospheric CO2 cycles remains one of the most important unresolved questions in the field of paleoclimatology. It has long been known that Earth’s ice sheets expand when atmospheric CO2 is low and shrink when CO2 rises. The underlying climate mechanisms that regulate CO2 levels however, remain unclear. One possibility is that changes in ocean circulation influence air-sea gas exchange. It has been hypothesized that expansion of deep waters from the Southern Ocean limited the release of carbon during the last ice age (~20,000 years ago). Reconstructing ocean circulation in the past is therefore essential to understanding what regulates atmospheric CO2 over long time periods. In this study, we will use a new method to reconstruct the ocean circulation using oxygen isotope analyses of microscopic fossils from marine sediment cores. Students from all levels, high school to undergraduate to graduate, will participate in this research.Earth’s climate during the LGM (Last Glacial Maximum ~20,000 years ago) was characterized by lower atmospheric CO2 levels, cooler surface temperatures, and lower global sea level. The Atlantic Ocean circulation was also likely marked by shoaling of deep waters that emanate from the North Atlantic and incursion of abyssal waters from the Southern Ocean. Our understanding of the circulation is based mainly on carbon isotope analyses of microfossils that suggest southern source waters replaced northern source waters in the North Atlantic. The image of southern source waters dominating the deep Atlantic has become a defining feature of the LGM, as familiar as well-known changes in pCO2, surface temperature, and sea level. More recently, however, results from neodymium isotopes imply the deep North Atlantic was influenced primarily by northern source waters, challenging the canonical view of the LGM circulation. The goal of the proposed work is to determine which of these two scenarios is most likely correct using oxygen isotopes as a circulation tracer. The oxygen isotopic composition of microfossils is conservative because it varies mainly as a function of temperature. Once the oxygen isotope ratio is set at the sea surface, it changes only through ocean circulation and mixing. The carbon isotope composition of microfossils, on the other hand, is non-conservative because it is also influenced by biological processes that compromise its utility as a circulation tracer. The proposed work will benefit the paleoclimate community by creating the first section for the LGM Atlantic based on a conservative water mass tracer. The oxygen isotope results will also facilitate validation of other circulation proxies and lead to improved model simulations of the ocean circulation and its role in the carbon cycle.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

冰川间 - 冰川大气二氧化碳循环的原因仍然是古气候学领域中最重要的未解决问题之一。早就知道，当二氧化碳升高时大气二氧化碳且收缩时，地球的冰片会扩大。但是，调节二氧化碳水平的潜在气候机制尚不清楚。一种可能性是海洋循环的变化会影响空气气体交换。据推测，从南大洋的深水扩张限制了最后一个冰河时代（约20，000年前）的碳的释放。因此，过去重建海洋循环对于了解长期时间内调节大气二氧化碳的方法至关重要。在这项研究中，我们将使用一种新方法使用来自海洋沉积物核心的微观化石的氧同位素分析来重建海洋循环。来自各个层次的学生，高中到本科毕业生，将参加这项研究。在LGM期间（最后一次冰川最多〜20，000年前）的气候，其特征是大气中的二氧化碳水平较低，表面温度较低，全球海平面较低。大西洋循环也很可能以从北大西洋散发出深水的浅滩标志，并从南大洋中吸入了深处的水域。我们对循环系统的理解主要基于微化石的碳同位素分析，这些化石表明南部源水域取代了北大西洋的北部源水域。占主导地域的南部源水域的图像已成为LGM的定义特征，如PCO2，表面温度和海平面的众所周知变化一样。然而，最近，北部北大西洋近代的新医生的结果受到北部源水域的影响，挑战了LGM循环的规范视图。提议的工作的目的是确定以氧同位素作为循环示踪剂的方式确定这两种情况中的哪种是正确的。微化石的氧同位素组成是保守的，因为它主要因温度而变化。一旦将氧同位素比设置在海面，仅通过海洋循环和混合而变化。另一方面，微化石的碳同位素组成是非保守的，因为它也受到损害其作为循环示踪剂效用的生物过程的影响。拟议的工作将通过基于保守的水质示踪剂为LGM大西洋创建第一部分，从而使古气候社区受益。氧同位素结果还将促进其他循环代理的验证，并导致对海洋循环的改进模型及其在碳周期中的作用。该奖项反映了NSF的法定任务，并通过使用基金会的知识分子优点和更广泛的影响审查标准来通过评估来诚实地支持支持。