Deglacial change of Antarctic Bottom Water in transient simulations

Abstract

The deglacial change of Antarctic Bottom Water (AABW) since the Last Glacial Maximum (LGM) was investigated using transient simulations of climate evolution forced by individual deglacial forcings. The TraCE21k simulation faithfully reproduces the ∼500 m deepening of the cell interface between AABW and North Atlantic Deep Water (NADW) and suggests an approximate 1.5 Sv (1 Sv 106 m3 s−1) weakening in the deep Atlantic AABW from the LGM to the modern state. The deglacial Atlantic AABW change is approximately the combined impacts of increasing greenhouse gases and retreating ice sheets. The Southern Ocean sea-ice melting induced by deglacial warming serves as a major controlling factor for both AABW intensity and geometry. Increased surface buoyancy flux associated with reduced brine release leads to a suppressed deep convection over the Weddell Sea and reduced AABW, while the retreat of permanent sea ice favors a deepening of the cell interface. The buoyancy change in the Southern Ocean may also have modulated the deglacial NADW change from an adiabatic overturning perspective.摘要本文利用气候瞬变模拟试验TraCE21k分析了末次冰消期南极底层水 (Antarctic Bottom Water, AABW) 的演变特征及物理机制. TraCE21k的全强迫试验复现了观测记录里现代大西洋AABW相对于冰期时变薄的特征, 其强迫敏感性试验进一步指出冰期-现代AABW的差异主要由大气温室气体的升高及大陆冰川的退缩二者共同驱动. 冰消期气候强迫下海洋和大气温度升高, 南大洋海冰逐渐消融, 后者直接调控了AABW强度和形态的演变. 本文还从绝热翻转环流的观点出发, 认为冰消期南大洋的气候变化潜在影响了北大西洋深层水的演变.