末次冰消期冲绳海槽中部表层和温跃层海水温度演化的脱耦现象

Decoupled Evolution of Surface and Thermocline Water Temperatures in Middle Okinawa Trough during Last Deglaciation

解读末次冰消期全球水文气候演变过程对于理解气候系统对内外强迫的响应具有重要意义.以冲绳海槽中部OKI02岩心为材料,通过浮游有孔虫Globigerinodes ruber和Pulleniatina obliquiloculata壳体Mg/Ca比值分别重建了19 ka BP以来海槽中部表层和温跃层海水温度(SST和TWT),结合浮游有孔虫群落组成变化重点恢复了末次冰消期(~18~11.7 ka BP)上层水体温度变化的特征和过程.结果显示SST在LGM显著偏低,末次冰消期表现为显著的千年尺度变化,清楚地记录了HS1、B/A、YD等快速气候波动事件. 19 ka BP以来重建的TWT整体呈明显的上升趋势,但波动频繁而剧烈,末次冰消期相对较低,未显示显著的千年尺度变化.对比北半球高纬和热带太平洋的记录发现,末次冰消期冲绳海槽中部SST开始上升的时间基本与前者相当,但明显滞后于热带西太平洋;冰消期其变化模式明显区别于热带西太平洋持续稳定的升温过程,而更类似于北半球高纬区的变化.与SST明显不同,海槽区温跃层的升温(~18 ka BP)明显早于北半球高纬变暖,却接近于热带西太平洋海表温度开始上升的时间;且TWT的上升和波动方式也更接近于热带太平洋海温的变化模式.对末次冰消期SST和TWT差异化演变的分析表明,AMOC对中低纬大气环流的影响可能通过东亚冬季风强度的变化控制了海槽区SST的演变,而热带太平洋ENSO过程则可能通过黑潮强度的变化决定了区域TWT的演化.末次冰消期冲绳海槽中部SST和TWT演化存在明显的脱耦现象,显示了其与高、低纬海洋和气候变化之间的密切联系.

Deciphering the evolution of global hydroclimate during the last deglaciation is of great significance for understanding the response of the climate system to the internal and external forces.Based on planktonic foraminiferal Globigerinodes ruber and Pulleniatina obliquiloculata shell Mg/Ca ratio obtained from core OKI02,we reconstructed a 19 000-year record of Sea Surface Temperature(SST) and Thermocline Water Temperature(TWT) to unveil the characteristics and process of upper water temperature in the Middle Okinawa Trough during the last deglaciation.The results imply that the SST was significantly low(about 23.7 ℃ on average) during the Last Glacial Maximum(LGM,about 19-18 ka BP),and was of obvious millennial-scale variation features during the last deglaciation.Heinrich Stadial 1(HS1),B?lling-Aller?d(B/A) and Younger Dryas(YD) events could be identified obviously in the record of SST.TWT shows a rising trend,with frequent and strong fluctuation since 19 ka BP.TWT is relatively low(about 20.3 ℃ on average) during the last deglaciation,without apparent significant millennial-scale changes.During the last deglaciation,the beginning time of SST rising in the Okinawa Trough was consistent with the SST record in high latitudes of the northern hemisphere,while lagged significantly behind SST record of the tropical western Pacific.Meanwhile,the SST change pattern in the Okinawa Trough was different from the continuous and stable warming process of the tropical western Pacific,but more similar to the climate change of the northern hemisphere high latitudes.In contrast,the warming time of TWT was earlier than that happened in the northern high latitudes but close to the tropical western Pacific.Moreover,the rising and fluctuating mode of TWT was different from the former and was more similar to the variation pattern of the tropical Pacific.The differentiated evolution of SST and TWT demonstrates that the influence of Atlantic Meridional Overturning Circulation(AMOC) on the atmospheric circulation may control the SST in the trough area through the changes of the East Asian winter monsoon.However,the tropical Pacific ENSO process probably plays an important role in the evolution of the regional TWT through the changes of the Kuroshio during the last deglaciation.The trend of the decoupling change in SST and TWT in the middle of the Okinawa Trough implies its intimate connection with high and low latitude oceans and climate change.