Smith H J, Fischer H, Wahlen M, Mastroianni D, Deck B
Scripps Institution of Oceanography, University of California San Diego, La Jolla 92093-0220, USA.
Nature. 1999 Jul 15;400(6741):248-50. doi: 10.1038/22291.
The most conspicuous feature of the record of past climate contained in polar ice is the rapid warming which occurs after long intervals of gradual cooling. During the last four transitions from glacial to interglacial conditions, over which such abrupt warmings occur, ice records indicate that the CO2 concentration of the atmosphere increased by roughly 80 to 100 parts per million by volume. But the causes of the atmospheric CO2 concentration increases are unclear. Here we present the stable-carbon-isotope composition (delta 13 CO2) of CO2 extracted from air trapped in ice at Taylor Dome, Antarctica, from the Last Glacial Maximum to the onset of Holocene times. The global carbon cycle is shown to have operated in two distinct primary modes on the timescale of thousands of years, one when climate was changing relatively slowly and another when warming was rapid, each with a characteristic average stable-carbon-isotope composition of the net CO2 exchanged by the atmosphere with the land and oceans. delta 13 CO2 increased between 16.5 and 9 thousand years ago by slightly more than would be estimated to be caused by the physical effects of a 5 degrees C rise in global average sea surface temperature driving a CO2 efflux from the ocean, but our data do not allow specific causes to be constrained.
极地冰中保存的过去气候记录最显著的特征是，在经历长时间的逐渐冷却之后会出现快速变暖。在过去四次从冰川期向间冰期的转变过程中，均出现了这种突然变暖的情况，冰芯记录表明，大气中二氧化碳的体积浓度增加了约80至100 ppm（百万分之一）。但是大气中二氧化碳浓度增加的原因尚不清楚。在此，我们展示了从南极泰勒穹顶冰芯中捕获的空气里提取的二氧化碳的稳定碳同位素组成（δ¹³CO₂），时间跨度从末次盛冰期到全新世开始。结果表明，全球碳循环在数千年的时间尺度上以两种不同的主要模式运行，一种是气候相对缓慢变化时的模式，另一种是快速变暖时的模式，每种模式下大气与陆地和海洋交换的净二氧化碳都有其特征性的平均稳定碳同位素组成。在距今16500年至9000年期间，δ¹³CO₂的增加幅度略高于全球平均海表温度升高5℃导致海洋二氧化碳排放的物理效应所预计的增加幅度，但我们的数据无法确定具体原因。
