COMPREHENSIVE CALIBRATION OF CRITICAL PALEOCEANOGRAPHIC PROXIES

人类只直接记录了很小范围内的气候信息。从冰芯和沉积物岩心等档案中获得的古气候记录，可以证明地球上可能有更大范围的气候变化，以及气候系统内的气候阈值。如果我们要准确地预测未来的气候，评估这些气候的范围和导致它们的机制是至关重要的。这样的古气候研究完全依赖于替代物的应用。过去我们不能直接测量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。这些指标的开发和校准对古气候至关重要。但这种校准有时会滞后于它们的应用，导致对过去的不确定重建。这里提出的工作旨在解决这一问题，明确侧重于古海洋学关键指标的校准。该提案汇集了来自不同化学专业的研究人员，但他们在代理校准工作方面都有很好的记录。虽然这些研究人员中的每一位也都将替代物应用于古气候问题，但这并不是古气候的提议，而是专注于理解用作古替代物的化学物种的现代水柱和上层沉积物行为。我们将了解将最终沉积物组成与气候变量联系起来的地球化学，并评估这些联系的限制，以避免不适当地应用替代物。我们将专注于有限数量的代理，每个代理都有明显(并且在大多数情况下，证明)提供关于过去的重要信息的潜力。如果准确校准，这些指标将提供有关过去海洋环流的模式和速度的信息，以及过去生物生产力的组成、通量和营养利用的信息(设定了大气中碳的去除)。因此，它们有巨大的潜力告诉我们海洋在过去气候中的作用，包括通过热量和碳的运输。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项新的重大国际研究方案的核心，该方案调查了微量元素和同位素的海洋循环--地球物理轨道系统。这里建议在南大西洋进行一次研究巡航，以便为替代校准工作收集水柱和沉积物样本。这次巡航将成为GEOTRACES计划的英国组成部分。尽管在这项提案中只为关键古代用品的校准寻求资金，但研究巡航将成为广泛的其他生物地球化学研究的平台。这类工作可能包括评估海洋边缘具有重要生物意义的金属通量、深水区的化学物质运输，以及对低尘埃的南大西洋表层水域的微量营养素供应的控制。我们将确保，尽管我们目前参与了GEOTRACES方案，但在邮轮上实现了尽可能广泛的此类研究，使其成为国际上范围广泛的地球化学家的重要研究邮轮。

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.