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，对全球气候条件有重要的控制作用。在过去的冰期(冷)和间冰期(暖)之间，大气中的二氧化碳浓度下降了80-100ppm，而在冰期内，二氧化碳浓度的变化最高可达60ppm。古气候学家感兴趣的是导致二氧化碳这些巨大变化的控制和过程。已提出的一种解释这些变化很大一部分的机制是海洋生物泵，在这种泵中，地表水生物生产力的变化导致大气中或多或少地产生二氧化碳，并将其储存在深海中。最近对海洋生物泵作用的调查主要集中在南大洋的南极和亚南极水域。然而，尽管一些气候模型表明，南大洋的变化可能解释了过去大气中二氧化碳的所有变化，但来自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上一个冰川周期(从131,000年前到今天)的变化，更好地了解控制过去和未来大气二氧化碳变化的机制和过程。这将主要通过分析分布在北太平洋的一系列沉积物岩芯中的硅藻--单细胞硅藻--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样品。然而，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过去变化的关键信息。这反过来将使我们能够深入了解过去131,000年来北太平洋生物泵的空间和时间变化，以及该泵在长期和短期时间尺度上改变全球大气二氧化碳浓度方面可能发挥的作用。通过将这项研究的结果与其他可能在类似时间尺度上控制大气二氧化碳浓度的机制相结合，如南大洋生物泵和陆地生物圈，将对影响全球气候的较长、冰川-间冰期和较短的千年时间尺度的内部机制有更详细的了解。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必要的框架，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.