Response Mechanism Of Atlantic Meridional Overturning Circulation To Precession And Obliquity Forcing Under Different Climatic Backgrounds

The Atlantic Meridional Overturning Circulation(AMOC)is an important component of the climate system,of which change in the strength can affect meridional heat distribution between the northern and southern hemisphere.Proxy records show that changes in Atlantic Ocean circulation during the Late Pleistocene is associated with precession and obliquity cycle,but the physical mechanism remains unclear.Here we use a fully coupled climate model to investigate dynamics associated with AMOC changes in precession and obliquity band under glacial-interglacial climate conditions.Our results show that :1.Pre-industrial(PI): the decrease in precession(obliquity)can effectively weaken(strengthen)the AMOC during warm interglacial periods.The combined effects of low and high-latitude hydrological processes and high latitude sea ice finally lead to an obvious weakening of vertical mixing and AMOC.The response of AMOC to the decrease of obliquity mainly depends on the salting out process caused by high latitude sea ice melting and the relative action between high latitude hydrological processes,and finally leads to the significant enhancement of vertical mixing and AMOC strength;2.Last Glacial Maximum(LGM): The response of AMOC is similar to that of PI period when decreasing obliquity and precession,but it is dependent on climate background ——the response of PI period is more sensitive than that of LGM period;The dependence of AMOC on climate background is mainly reflected in high latitude hydrological process(more significant in the PI period)and sea ice response process(more significant in the LGM period);3.Regulation effect: The response of AMOC to the decrease of precession(obliquity)is modulated by obliquity(precession).When the precession is reduced under the conditions of low obliquity and high obliquity,there is little difference in AMOC response in the PI period,and the weakening degree of AMOC under low obliquity is stronger than that under high obliquity in the LGM period;When the obliquity is reduced under the conditions of low precession and high precession,there is little difference in AMOC response in the PI period.In the LGM period,AMOC increases under high precession,but decreases under low precession.Overall,our results provide an understanding of governing mechanism for precessionally-induced and obliquity-induced AMOC change under glacial-interglacial climatic backgrounds,shedding light on our interpretation of precessional and obliquity periodicity in reconstructed ocean circulation changes during the Pleistocene.