COMPREHENSIVE CALIBRATION OF CRITICAL PALEOCEANOGRAPHIC PROXIES

人类只直接记录了一小部分气候信息。地球气候可能存在的更大范围的证据，以及气候系统中的阈值，来自于来自冰和沉积物岩心等档案的古气候记录。如果我们要准确地预测未来的气候，那么评估这些气候的范围和造成它们的机制是至关重要的。这种古气候研究完全依赖于代用指标的应用。我们无法直接测量过去的海洋环流等环境变量，但我们可以在古档案中找到这些变量的化学替代物。这些代用指标的开发和校准对古气候研究至关重要。但这种校准有时会滞后于其应用，导致对过去的不确定重建。这里提出的工作旨在解决这个问题，明确侧重于校准的关键代理古海洋学。该提案汇集了具有各种化学专业的研究人员，但他们都在代理校准工作方面有着良好的记录。虽然这些研究人员也适用于代理古气候问题，这不是一个古气候的建议，但重点是了解现代水柱和上层沉积物行为的化学物种作为古代理。我们将了解将最终沉积物成分与气候变量联系起来的地球化学，并评估这些联系的局限性，以便代理不被不适当地应用。我们将集中讨论数量有限的代理，其中每一个都有明确的（在大多数情况下，已经证明）潜力提供有关过去的重要信息。这些代理，如果准确校准，将提供有关过去海洋环流的模式和速率，以及过去生物生产力的组成，通量和营养利用（确定大气中碳的去除）的信息。因此，它们具有巨大的潜力，可以让我们了解海洋在过去气候中的作用，包括热量和碳的输送。这里提出的代理校准工作将使这一潜力得到更好和更准确的实现。这一提议的地球化学重点也是一个新的国际研究方案的核心，该方案调查海洋微量元素和同位素的循环- GEOTRACES。在此提议在南大西洋进行一次研究航行，以便收集水柱和沉积物样本，用于代用品校准工作。这次航行将成为GEOTRACES计划的一个英国组成部分。虽然在本提案中只为校准关键的古代用指标寻求资金，但研究航行将成为广泛开展其他地球化学研究的平台。这类工作可包括评估海洋边缘具有生物重要性的金属通量、深水区的化学迁移以及对低尘南大西洋表层沃茨微量营养素供应的控制。我们将确保，通过我们目前参与的GEOTRACES方案，在航行中进行尽可能广泛的研究，使这次航行成为国际上众多地球化学家的重要研究航行。

Humans have directly recorded information about only a narrow range of climate. Evidence for a much larger range of possible Earth climate, and for thresholds within the climate system, come from paleoclimate records derived from archives such as ice and sediment cores. Assessing the range of such climates and the mechanisms that caused them is of fundamental importance if we are to accurately predict future climate. Such paleoclimate work relies absolutely on the application of proxies. We cannot measure environmental variables such as ocean circulation directly for past times, but we can find chemical proxies for these variables in paleo-archives. Development and calibration of these proxies is critical to paleoclimate. But such calibration can sometimes lag behind their application, leading to uncertain reconstructions of the past. The work proposed here seeks to address this issue with an explicit focus on calibration of critical proxies for paleoceanography. The proposal brings together researchers with a variety of chemical specialities, but all with a strong track record for proxy calibration work. Although each of these researcher also applies proxies to paleoclimate questions, this is not a paleoclimate proposal, but is focused on understanding the modern water-column and upper-sediment behaviour of chemical-species used as paleoproxies. We will understand the geochemistry that links the final sediment composition to climate variables, and assess the limitations on these links so that proxies are not applied inappropriately. We will focus on a limited number of proxies, each of which has clear (and, in most cases, demonstrated) potential to provide important information about the past. These proxies, if accurately calibrated, will provide information about the pattern and rate of past ocean circulation, and about the composition, flux and nutrient utilisation of past biological productivity (which sets the removal of carbon from the atmosphere). They therefore have tremendous potential to inform us about the role of the oceans in past climate, both through the transport of heat and carbon. The proxy calibration work proposed here will allow that potential to be better and more accurately realized. The geochemical focus of this proposal is also central to a major new international research programme investigating the marine cycling of trace elements and isotopes - GEOTRACES. A research cruise in the South Atlantic is proposed here to allow collection of water-column and sediment samples for the proxy calibration work. This cruise will form a UK component of the GEOTRACES programme. Although funds are only sought for the calibration of critical paleoproxies in this proposal, the research cruise will be a platform for a wide range of other biogeochemical research. Such work might include assessment of biologically significant metal fluxes at ocean margins, chemical transport in deep-water masses, and the controls on micronutrient supply to the surface waters of the low-dust South Atlantic. We will ensure, though our existing involvement in the GEOTRACES programme, that the widest possible range of such research is achieved on the cruise, making this an important research cruise for a wide range of geochemists internationally.