末次冰消期北太平洋中深层水的突变及气候意义

Climate system has certain tipping points. Once human-being induced changes exceed these thresholds, the climate system will become unstable and likely turn into extreme and abrupt scenarios. The occurrence of the extreme and abrupt climate in the past was thought to be correlated to major shifting in the modes of the North Pacific intermediate and deep-water circulation. However, there is a controversy regarding the existence of the North Pacific Overturning Circulation. Here, we will systematically measure proxies for the circulation velocity, orientation and water masses property on sediment cores retrieved from the source region and downstream region of the North Pacific intermediate and deep-water circulation. Based on multi-dimension properties, we should be able to discriminate circulation modes and its transitional times. A sediment core in the Okinawa Trough was used to reconstruct the Western Boundary Current since the Last Glaciation Maximum. State-of-art statistical and modeling simulation will be implemented to unravel the transitional mechanism and reveal the coupling relationship between circulation modes of North Pacific intermediate-deep water and Western Boundary Current. Finally, we will be able to verify the existence of the North Pacific Overturning Circulation and the North Pacific-Atlantic seesaw, establishing the role of the North Pacific intermediate and deep-water circulation on global climate system.

气候系统存在一定的临界点，一旦人类活动所导致的变化突破气候临界点，将可能使气候系统产生极端、突变气候事件。为更好预测未来气候走向，需要对过去气候突变事件的驱动机制进行研究。已有研究显示过去极端、突变气候事件与北太平洋中、深层环流模态间切换具有很好对应。但北太平洋中、深洋流是否翻转产生径向翻转流还存在争议。本项目将系统测定和整合北太平洋中、深层水源区的鄂霍次克海到下游的南海柱状样中洋流的方向、强度、水团性质等替代性指标，确立末次盛冰期以来北太平洋中、深层水模态及其切换时间。利用冲绳海槽中部地区柱状样，重建末次盛冰期以来北太平洋西边界流强度演化历史。通过数理统计和古气候模拟，揭示末次盛冰期以来北太平洋中、深层水模态切换机制，探索中、深层水模态与西边界流之间的动态耦合关系，探讨末次冰消期北太平洋径向翻转流、北太平洋-北大西洋“跷跷板”效应的存在性，确立北太平洋中、深层水在全球气候系统中的地位。

气候系统存在一定的临界点，一旦人类活动所导致的变化突破气候临界点，将可能使气候系统产生极端、突变气候事件。为更好预测未来气候走向，需要对过去气候温暖和突变事件的驱动机制进行研究。本研究对冲绳海槽和北太平洋鄂霍茨克海的岩芯样品进行沉积物粒度、磁化率各向异性、XRF岩芯扫描以及长链烯酮标志物测试，揭示了冰消期北太平洋中深层水的影响深度并未超过2100m，太平洋深部由南极底层水所驱动。千年尺度气候突变时期，南极底层水以及南大洋上升流的强化可能是千年尺度气候和CO2变化的驱动机制。中全新世暖期，北太平洋浅层经向翻转环流的强化使得北太平洋东西向的温度梯度增加，调控北太平洋空间尺度的热量分配，且其周期震荡由1500年向870年转换，与北半球劳伦斯冰盖的消亡时间一致，暗示中全新世劳伦斯冰盖的消融可能是环北太平洋气候变化的重要临界点。

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