MIS 5期以来南极威德尔海生产力演化及其古海洋意义

Productivity evolution in the antarctic Weddell Sea and its paleoceanographic implication since MIS 5

南大洋有关大气二氧化碳分压(pCO_(2))冰期旋回机制的最新假说表明,冰期南极带生产力降低指示的深部流通状况减弱对CO_(2)的封存,以及亚南极带生产力升高对CO_(2)的固定能够圆满解释冰期大气pCO_(2)的降低。显然,测试该假说合理性的关键是验证冰期旋回中南极带与亚南极带呈“镜像”关系的生产力演化特征。通过沉积物岩芯中生源蛋白石含量重建了MIS 5期以来南极威德尔海(南极带)生产力演化。结果显示,南极威德尔海生产力呈现暖期(MIS 5和3期)高、冷期(MIS 4和2期)低的冰期旋回特征以及总体降低的长期演化趋势。联合该生产力记录与搜集的南大洋其他海区多个生产力记录,确证了南极带与亚南极带“镜像”的生产力演化模式。进一步,通过该生产力记录与其潜在环境影响因素的对比,发现西风带经向移动和海冰张缩通过影响深部流通状况,进而控制深部营养物进入表层的可利用性,最终驱动MIS 5期以来威德尔海生产力演化的冰期旋回和长期趋势。南极威德尔海的深部流通状况对CO_(2)的“收押”与释放很可能贡献了MIS 5期以来大气pCO_(2)演化的冰期旋回和长期趋势。该研究确证了上述南大洋有关大气pCO_(2)冰期旋回机制假说的合理性,表明南大洋在全球气候演化中扮演重要角色。

The latest hypothesis on the mechanism of glacial/interglacial variation in atmospheric partial pressure of carbon dioxide(pCO_(2-atm))in the Southern Ocean suggests that the decrease of pCO_(2-atm)during glaciation can be satisfactorily explained by CO_(2)sequestration via the reduced deep ventilation indicated by the decrease in the Antarctic zone productivity,and the CO_(2)fixation by the increase in the subantarctic zone productivity.Obviously,verifying the mirror-image relation between productivity evolution in the Antarctic zone and the subantarctic zone in glacial cycles is the key to examine this hypothesis.The productivity evolution in the Weddell Sea(in Antarctic Zone)since MIS 5 was reconstructed based on the biogenic opal content from sediment cores.The results indicate that the productivity in the Weddell Sea showed glacial-interglacial variations,with high productivity during warm periods(MIS 5 and 3)and low productivity during cold periods(MIS 4 and 2),and a long-term decreasing trend was also observed.By combining our productivity records with those of other areas in the Southern Ocean,the mirror-image model of productivity evolution in the Antarctic and subantarctic zones was confirmed.Furthermore,comparison between the productivity records and potential environmental influence factors indicated that the meridional movement of Westerlies as well as the expansion and retreat of sea ice controlled the nutrient availability from deep water into surface by affecting deep convection,and ultimately drove glacial-interglacial and long-term variations of productivity in the Weddell Sea since MIS 5.The sequestration and release of CO_(2)due to variation of deep convection in the Weddell Sea probably contributed to the long-term trend and glacial-interglacial cycles of pCO_(2-atm)since MIS 5.This research confirms that the above hypothesis about the mechanism for glacial-interglacial pCO_(2-atm)cycles in the Southern Ocean is reasonable,indicating that the Southern Ocean plays an important role in global climate evolution.