Sea surface temperature reconstruction based on alkenones of sediment core M35003-4

Evidence for abrupt climate changes on millennial and shorter timescales is widespread in marine and terrestrial climate records (Dansgard et al., 1993, doi:10.1038/364218a0; Bond et al., 1993, doi:10.1038/365143a0; Charles et al., 1996, doi:10.1016/0012-821X(96)00083-0, Bard et al., 1997, doi:10.1038/385707a0). Rapid reorganization of ocean circulation is considered to exert some control over these changes (Broecker et al., 1985, doi:10.1038/315021a0), as are shifts in the concentrations of atmospheric greenhouse gases (Broecker, 1994, doi:10.1038/372421a0). The response of the climate system to these two influences is fundamentally different: slowing of thermohaline overturn in the North Atlantic Ocean is expected to decrease northward heat transport by the ocean and to induce warming of the tropical Atlantic (Crowley, 1992, doi:10.1029/92PA01058; Manabe and Stouffer, 1997, doi:10.1029/96PA03932), whereas atmospheric greenhouse forcing should cause roughly synchronous global temperature changes (Manabe et al., 1991, doi:10.1175/1520-0442(1991)004<0785:TROACO>2.0.CO;2). So these two mechanisms of climate change should be distinguishable by the timing of surface-water temperature variations relative to changes in deep-water circulation. Here we present a high-temporal-resolution record of sea surface temperatures from the western tropical North Atlantic Ocean which spans the past 29,000 years, derived from measurements of temperature-sensitive alkenone unsaturation in sedimentary organic matter. We find significant warming is documented for Heinrich event H1 (16,900-15,400 calendar years bp) and the Younger Dryas event (12,900-11,600 cal. yr bp), which were periods of intense cooling in the northern North Atlantic. Temperature changes in the tropical and high-latitude North Atlantic are out of phase, suggesting that the thermohaline circulation was the important trigger for these rapid climate changes.

千年尺度及更短时间尺度上的气候突变证据，在海洋与陆地气候记录中广泛存在（Dansgard等，1993，doi:10.1038/364218a0；Bond等，1993，doi:10.1038/365143a0；Charles等，1996，doi:10.1016/0012-821X(96)00083-0；Bard等，1997，doi:10.1038/385707a0）。海洋环流的快速重组被认为对这类气候突变具有一定调控作用（Broecker等，1985，doi:10.1038/315021a0），大气温室气体浓度变化同样如此（Broecker，1994，doi:10.1038/372421a0）。气候系统对这两类驱动因素的响应存在本质差异：北大西洋温盐环流翻转（thermohaline overturn）的减缓，将削弱海洋向北的热输送，并引发热带大西洋海域升温（Crowley，1992，doi:10.1029/92PA01058；Manabe与Stouffer，1997，doi:10.1029/96PA03932）；而大气温室气体强迫则应引发大致同步的全球温度变化（Manabe等，1991，doi:10.1175/1520-0442(1991)004<0785:TROACO>2.0.CO;2）。因此，相较于深水环流变化，可通过表层水温变化的时序特征区分这两类气候变化驱动机制。本研究基于沉积有机质中对温度敏感的烯酮（alkenone）不饱和度测定结果，构建了一套覆盖过去29000年的热带北大西洋西部海域海表温度高时间分辨率记录。研究发现，海因里希事件H1（Heinrich event H1，距今16900~15400日历年）与新仙女木事件（Younger Dryas event，距今12900~11600日历年）这两个对应北大西洋北部强烈降温的时段，均记录了显著的升温现象。热带与高纬度北大西洋的温度变化存在相位差，表明温盐环流（thermohaline circulation）是这类气候突变的关键触发因素。