Diversity of planktonic foraminifer fauna found in 18 deep-sea cores from the North Atlantic

Greenland stadial/interstadial cycles are known to affect the North Atlantic's hydrography and overturning circulation and to cause ecological changes on land (e.g., vegetation). Hardly any information, directly expressed as diversity indices, however, exists on the impacts of these millennial-scale variations on the marine flora and fauna. We calculated three diversity indices (species richness, Shannon diversity index, Hurlbert's probability of interspecific encounter) for the planktonic foraminifer fauna found in 18 deep-sea cores covering a time span back to 60 ka. Clear differences in diversity response to the abrupt climate change can be observed and some records can be grouped accordingly. Core SO82-05 from the southern section of the subpolar gyre, the cores along the British margin and core MD04-2845 in the Bay of Biscay show two modes of diversity distribution, with reduced diversity (uneven fauna) during cold phases and the reverse (even fauna) during warm phases. Along the Iberian margin high species diversity prevailed throughout most of the glacial period. The exceptions were the Heinrich stadials when the fauna abruptly shifted from an even to an uneven or less even fauna. Diversity changes were often abrupt, but revealed a high resilience of the planktonic foraminifer faunas. The subtropical gyre waters seem to buffer the climatic effects of the Heinrich events and Greenland Stadials allowing for a quick recovery of the fauna after such an event. The current work clearly shows that planktonic foraminifer faunas quickly adapt to climate change, albeit with a reduced diversity.

已知格林兰冰阶/间冰阶旋回（Greenland stadial/interstadial cycles）可对北大西洋水文状况与翻转环流产生影响，并引发陆地生态系统（如植被）的改变。然而，目前鲜有以多样性指数形式直接表征的研究数据，用以阐明这类千年尺度气候波动对海洋动植物群落的影响。本研究针对18根覆盖距今6万年时间跨度的深海岩芯中的浮游有孔虫（planktonic foraminifer）群落，计算了三类多样性指数：物种丰富度（species richness）、香农多样性指数（Shannon diversity index）以及赫尔伯特种间相遇概率（Hurlbert's probability of interspecific encounter）。研究发现，浮游有孔虫群落多样性对突发性气候变化的响应存在显著差异，据此可将部分岩芯记录进行归类。其中，副极地环流圈南部海域的SO82-05岩芯、不列颠边缘海域的岩芯以及比斯开湾的MD04-2845岩芯，呈现出两种多样性分布模式：冷期阶段群落多样性降低（群落结构不均一），暖期阶段则反之（群落结构均一）。伊比利亚边缘海域的岩芯记录显示，冰期绝大多数时段内物种丰富度始终处于较高水平，仅海因里希冰阶（Heinrich stadials）时期，浮游有孔虫群落发生突发性转变，从结构均一的群落变为结构不均一或相对不均一的群落。多样性变化往往具有突发性，但同时揭示出浮游有孔虫群落具备较强的恢复弹性。副热带环流圈水域似乎能够缓冲海因里希事件（Heinrich events）与格林兰冰阶带来的气候影响，使得该区域的浮游有孔虫群落在极端气候事件后可快速恢复。本研究明确证实，浮游有孔虫群落能够快速适应气候变化，尽管此时群落多样性往往有所降低。