Coupled radiocarbon and neodymium isotopes: Improved reconstructions of deep-ocean circulation change

由于温室气体（如二氧化碳）进入大气层而导致的气候变化是人类在21世纪及以后面临的最重大和最紧迫的挑战之一。多年来，科学家们一直在开发海洋-大气系统的模型，目的是预测二氧化碳排放量的增加将如何影响我们的气候。然而，在有信心地预测未来的气候行为之前，不仅需要调查过去的气候行为，而且还需要调查CO2如何在各种天然水库之间移动。利用主要来自海洋沉积物的信息，气候科学家已经确定，在过去的几百万年里，地球的气候经历了巨大的变化，从类似于今天的温暖条件到“冰川”条件，当时北方的大部分地区都被冰覆盖。这些冰川-间冰期循环是通过入射太阳辐射变化的外部强迫和温室气体CO2大气浓度变化引起的内部反馈引起的。虽然我们知道二氧化碳对过去的气候变化很重要，但我们仍然不知道二氧化碳水平是如何变化的，也不知道为什么会变化。气候科学家使用宇宙辐射在高层大气中产生的放射性碳（14 C）来了解二氧化碳如何以及何时在深海（千年时间尺度上地球最大的二氧化碳储存库）和大气之间转移。作为深海通风的代表，14 C是非常有用的，但它的解释是具有挑战性的。这种有价值的代理的效用可以大大提高了一个合适的“染料示踪剂”，可以揭示源和混合的深水质量，这两者都可以影响14 C数据的解释。在这里，我们建议采用新开发的和潜在的非常强大的示踪剂的水团来源和循环，钕（Nd）同位素。最近的一项开创性研究表明，底栖有孔虫是过去海水Nd同位素组成的有用档案，这代表了进一步开发的非常有前途的途径。我们的目标是进行必要的研究，以充分证明这种示踪剂的有效性，特别是当与14 C结合时。在初步调查之后，将进行两个案例研究，将联合收割机这一令人兴奋的新示踪剂与两个深海沉积物岩心的14 C数据结合起来。我们的目标是利用这些数据来了解在过去的2万年里，14 C（以及二氧化碳）是如何在大气和深海之间移动的，以及这是如何受到深海循环模式的影响的。

Climate change resulting from the introduction of greenhouse gases (e.g. carbon dioxide, CO2) into the atmosphere is one of the most significant and pressing challenges facing mankind in the 21st century and beyond. For years, scientists have been developing models of the ocean-atmosphere system, with the aim of predicting how increased CO2 emissions will affect our climate. Before future climatic behaviour can be predicted with any confidence, however, it is necessary to investigate not only how the climate has behaved in the past but also how CO2 has moved between the various natural reservoirs. Using information primarily derived from marine sediments, climate scientists have ascertained that for the last few million years the Earth's climate has undergone dramatic changes, from warm conditions similar to the present day to 'glacial' conditions, when much of the northern hemisphere was covered with ice. These glacial-interglacial cycles are brought about through external forcing by variations in incident solar radiation combined with internal feedbacks due to changes in the atmospheric concentration of the greenhouse gas CO2. Although CO2 is known to be important for past climate change, we still do not know exactly how or why CO2 levels have changed as they have. Climate scientists use radiocarbon (14C), which is produced in the upper atmosphere by cosmic radiation, to understand how and when CO2 has been transferred between the deep ocean, which is the Earth's largest reservoir of CO2 on millennial timescales, and the atmosphere. As a proxy for deep ocean ventilation 14C is incredibly useful but its interpretation is challenging. The utility of this valuable proxy can be greatly enhanced by a suitable 'dye tracer' that can reveal the sourcing and mixing of deep-water masses, both of which can impact the interpretation of 14C data. Here we propose to employ a newly-developed and potentially very powerful tracer of water mass sourcing and circulation, neodymium (Nd) isotopes. A recent pioneering study has demonstrated that benthic foraminifera are a useful archive of past seawater Nd isotope composition, and that this represents a very promising avenue for further development. We aim to conduct the necessary research to fully demonstrate just how effective this tracer can be, particularly when combined with 14C. An initial investigation will be followed by two case studies that will combine this exciting new tracer with 14C data from two deep-sea sediment cores. We aim to use these data to understand how 14C (and hence CO2) has moved between the atmosphere and the deep oceans over the last 20,000 years, and how this has been influenced by deep ocean circulatory patterns.