Changes in the North Pacific Ocean biological pump over the last glacial-interglacial cycle

二氧化碳（CO2）是一种主要的温室气体，对全球气候条件具有重要的控制作用。在过去的冰期（寒冷）和间冰期（温暖）之间，大气中的二氧化碳浓度下降了80-100 ppm，而在冰期内，浓度变化高达60 ppm。古气候学家感兴趣的是导致这些二氧化碳变化的控制和过程。有人提出的一种机制可以解释这些变化的很大一部分，即海洋生物泵，在这种机制中，表层水生物生产力的变化导致更多或更少的大气CO2从大气中被抽出并储存在深海中。最近对海洋生物泵作用的调查集中在南大洋的南极和亚南极沃茨。然而，虽然一些气候模型表明南大洋的变化可以解释过去大气中二氧化碳的所有变化，但海洋沉积物岩心和其他气候模型的证据表明，南大洋实际上只能解释观测到的二氧化碳变化的一部分。因此，有必要研究生物泵在其他地方的作用。拟议研究金范围内的研究旨在通过调查北太平洋生物泵在最后一个冰川周期（从131，000年前到今天）的变化，更好地了解控制过去和未来可能发生的大气CO2变化的机制和过程。这将主要通过分析遍布北太平洋的一系列沉积物岩心中硅藻、单细胞硅质藻类的同位素组成来实现。硅藻同位素分析是一项相对较新的技术，尚未广泛应用于许多海洋样品，特别是南大洋以外的海洋样品。不过，这些分析的结果将提供关于北太平洋地表水生物生产力、营养物质利用和水柱稳定性变化的关键信息。反过来，这将使人们能够深入了解过去131，000年来北太平洋生物泵的时空变化，以及泵在长期和短期内改变全球大气CO2浓度的可能作用。通过将这项研究的结果与其他机制相结合，这些机制也可能在类似的时间尺度上控制大气中的CO2浓度，例如南大洋生物泵和陆地生物圈，将更详细地了解影响全球气候的内部机制。这些信息对试图了解过去全球气候变化的古海洋学家和古气候学家都很有价值。此外，这项研究将为开发更准确的气候模型提供一个基本框架，以调查过去和未来的气候变化情景。

Carbon dioxide (CO2) is a major greenhouse gas which exerts a significant control on global climatic conditions. Between past glacial (cold) and interglacial (warm) periods atmospheric concentrations of CO2 decreased by 80-100 ppm while within glacial periods concentrations varied by up to 60 ppm. Of interest to palaeoclimatologists are the controls and processes which result in these large changes in CO2. One mechanism which has been proposed to explain a large proportion of these changes is the marine biological pump in which variations in surface water biological productivity lead to greater or lower amounts of atmospheric CO2 being draw down out of the atmosphere and stored within the deep ocean. Recent investigations into the role of the marine biological pump have focused on the Antarctic and Subantarctic waters of the Southern Ocean. However, while some climate models suggest that changes in the Southern Ocean may explain all of the past changes in atmospheric CO2, evidence from marine sediment cores and other climate models suggest that the Southern Ocean is actually only able to explain a proportion of the observed CO2 changes. As such, there is a need to examine the role of the biological pump in other locations. The research within the proposed fellowship aims to develop a better understanding of the mechanisms and processes which controlled past and potentially future changes in atmospheric CO2 by investigating changes in the North Pacific Ocean biological pump over the last glacial cycle (from 131,000 years ago to the current day). This will primarily be achieved by analysing the isotopic composition of diatoms, unicellular siliceous algae, within a series of sediment cores spread across the North Pacific Ocean. Analysis of diatom isotopes is a comparatively novel technique and has not yet been widely applied to many marine samples, particularly outside of the Southern Ocean. Results from these analyses, though, will provide key information on past changes in surface water biological productivity, nutrient utilisation and changes in the stability of the water column in the North Pacific Ocean. This, in turn, will enable an insight into the spatial and temporal changes in the North Pacific Ocean biological pump over the last 131,000 years and the possible role of the pump in changing global atmospheric concentrations of CO2 over both long and short timescales. By combining the results of this research with other mechanisms which may also control atmospheric concentrations of CO2 over similar timescales, such as the Southern Ocean biological pump and the terrestrial biosphere, a more detailed understanding will be obtained with regards to the internal mechanisms that influence the global climate over long, glacial-interglacial, and shorter, millennial, timescales. This information will be valuable both to palaeoceanographers and palaeoclimatologists attempting to understand past global climatic changes. In addition, the research will provide an essential framework for the development of more accurate climate models to investigate both past and future climate change scenarios.