Stable isotope record during the past 1 Myr of ODP Site 162-980 in the subpolar North Atlantic

Benthic foraminiferal carbon isotope records from a suite of drill sites in the North Atlantic are used to trace variations in the relative strengths of Lower North Atlantic Deep Water (LNADW), Upper North Atlantic Deep Water (UNADW), and Southern Ocean Water (SOW) over the past 1 Myr. During glacial intervals, significant increases in intermediate-to-deep delta13C gradients (commonly reaching >1.2 per mil ) are consistent with changes in deep water circulation and associated chemical stratification. Bathymetric delta13C gradients covary with benthic foraminiferal delta18O and covary inversely with Vostok CO2, in agreement with chemical stratification as a driver of atmospheric CO2 changes. Three deep circulation indices based on delta13C show a phasing similar to North Atlantic sea surface temperatures, consistent with a Northern Hemisphere control of NADW/SOW variations. However, lags in the precession band indicate that factors other than deep water circulation control ice volume variations at least in this band.

本研究采用北大西洋多站位钻探获取的底栖有孔虫碳同位素记录，追溯了过去1百万年间北大西洋下层深层水（Lower North Atlantic Deep Water, LNADW）、北大西洋上层深层水（Upper North Atlantic Deep Water, UNADW）与南大洋水（Southern Ocean Water, SOW）的相对强度演化特征。冰期时段内，中层-深层δ¹³C梯度显著升高（通常可达1.2‰以上），这与深层水环流及伴随的化学层结变化相一致。水深相关的δ¹³C梯度与底栖有孔虫δ¹⁸O呈现协同变化特征，且与沃斯托克冰芯二氧化碳记录呈负相关，这符合化学层结驱动大气二氧化碳浓度变化的理论认知。基于δ¹³C构建的三项深层环流指数，其相位变化与北大西洋海表温度相似，表明北大西洋深层水/南大洋水的变化受北半球过程调控。不过，岁差波段的滞后性特征表明，至少在该波段范围内，除深层水环流外的其他因素调控了冰量变化。