Benthic foraminiferal biodiversity response to changing Arctic palaeoclimate

Four sediment cores recovered from 1000 to 2500 m water depth in the Arctic Ocean, tracing the inflowing Atlantic water from Fram Strait, Yermak Plateau, northern Barents Sea continental slope as far as the Laptev Sea, have been analyzed for species richness and diversity. Samples were wet sieved after freeze-drying using a 63-µm sieve. Where possible at least 300 specimens were counted from the size fraction >63 µm, however, samples from deglacial periods are often affected by carbonate dissolution. In such samples foraminiferal numbers are low. Samples containing less than 40 specimens were excluded from statistical analyses. Because we are aware that specimen numbers <100 specimen are still critical for H analyses, core sections containing less than 100 specimens are highlighted in the figures. Here, we will characterize biodiversity trends by the two most widely used biodiversity measurements, the information function H (Buzas and Gibson, 1969) with its decomposition equation ln(S) and ln(E) (Buzas and Hayek, 1996), and the Fisher Alpha Index (Fisher, Corbett, and Williams, 1943). For spectral analysis the Fisher alpha record of core PS2837-5 was resampled at equally spaced 100-year intervals. For the spectral analysis, two methodes were used within the ANALYSERIES software package (Paillard et al., 1996): 1. The Blackman-Tuckey (1958) for its high confidence of the results; 2. The maximum entropy method (e.g. Haykin, 1983) for its high resolution. The cores reveal well-correlated biodiversity maxima and minima. Distinct periodicities of species richness variability of 1.57 kyr and 0.76 kyr characterize the Late Weichselian, and of 1.16 kyr and 0.54 kyr even more pronounced the Holocene. The biodiversity maxima/minima coincide with terrestrial and marine warm and cool events at high northern latitude. We suggest that either the physiology of most rare species is temperature sensitive, or sustained food supply increased the taxonomic richness during warmer intervals.本研究针对从北冰洋水深1000至2500米海域采集的4根沉积物岩芯展开分析，这些岩芯的序列可示踪从弗拉姆海峡（Fram Strait）、耶尔马克高原（Yermak Plateau）、巴伦支海北部大陆坡直至拉普捷夫海的大西洋水入侵路径，分析内容涵盖物种丰富度与生物多样性。样品经冷冻干燥后，采用孔径63微米的筛网进行湿筛处理。在条件允许的情况下，研究人员对粒径>63微米的组分至少计数300个标本；然而冰消期的样品常受碳酸盐溶蚀作用影响，此类样品中的有孔虫（foraminifera）个体数量偏低。标本数少于40个的样品被排除在统计分析之外。鉴于我们意识到标本数不足100个仍会对信息函数H的分析造成显著影响，因此图件中对标本数少于100个的岩芯段进行了标注突出。本研究采用两类最常用的生物多样性指标表征生物多样性变化趋势：其一为信息函数H（Buzas与Gibson, 1969），其分解公式为ln(S)与ln(E)（Buzas与Hayek, 1996）；其二为费希尔α多样性指数（Fisher Alpha Index，Fisher等, 1943）。针对频谱分析，本研究将岩芯PS2837-5的费希尔α多样性指数序列以等间距100年的步长进行重采样。本次频谱分析采用ANALYSERIES软件包（Paillard等, 1996）中的两种方法：1. 布莱克曼-图基法（Blackman-Tuckey, 1958），其分析结果置信度较高；2. 最大熵法（maximum entropy method，Haykin, 1983），其频谱分辨率更强。所有岩芯的生物多样性峰值与谷值均呈现出良好的相关性。晚威斯康星冰期（Late Weichselian）的物种丰富度变化存在1.57千年与0.76千年的显著周期，而全新世（Holocene）的该周期更为显著，分别为1.16千年与0.54千年。生物多样性的峰值与谷值与北半球高纬度地区的陆地与海洋冷暖事件相吻合。本研究提出两种推测：其一，多数稀有种的生理活动对温度敏感；其二，温暖时段持续的食物供给提升了分类群丰富度。