Sifan Gu
Published: 2018
Total Pages: 0
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Ocean circulation during the last deglaciation can help to improve the understanding of the mechanisms underlying the ocean circulation. However, previous model-data comparisons suffer from indirect comparison because both reconstruction and climate model have uncertainties. To meet this challenge, my PhD work contributes to the isotope enabled Community Earth System Model (iCESM) project by developing a Neodymium (Nd) model and a Protactinium (231Pa) and Thorium (230Th) in the ocean model of CESM. With the isotope enabled ocean model (iPOP2), I investigated two scientific questions: (1) Deglacial AAIW in the Atlantic. AAIW plays important roles in the global climate system and the global ocean nutrient and carbon cycles. However, neodymium isotopic composition ([epsilon]Nd) reconstructions from different locations from the tropical Atlantic, have led to a debate on the relationship between northward penetration of AAIW into the tropical Atlantic and AMOC variability during the last deglaciation. Our results suggest a coherent response of AAIW and AMOC: when AMOC weakens, the northward penetration and transport of AAIW decreases while its depth and thickness increase. Moreover, the inconsistency among different tropical Atlantic [epsilon]Nd reconstructions is reconciled by considering their corresponding core locations and depths, which were influenced by different water masses in the past. (2) Using 18Oc to reconstruct AMOC. 18Oc gradient can be used to reconstruct density gradient, therefore the AMOC strength. 18Oc from the Florida Straits has been used to reconstruct AMOC evolution during the last deglaciation but the strength of Florida current can also be influenced by surface wind stress. Our model simulation suggests that in the western boundary, the Florida current strength is dominated by AMOC through the last deglaciation, instead of surface wind. However, in the South Atlantic, the basin-wide 18Oc contrast is decoupled from density contrast through the deglaciation in the upper ocean because of the deglacial density contrast change is dominated by salinity, which is caused by the deglacial change of AAIW. Our model suggests that 18Oc contrast across the western boundary is a good indicator for AMOC strength and 18Oc contrast across the whole basin only works for the North Atlantic.