Enhanced long-term mixing of deep western-boundary currents in the north Pacific Ocean after Panama seaway closure

Closure of the Panama seaway significantly impacted global climate and environmental change with the development of modern oceanic circulation. It remains unclear as to the evolution of north Pacific western-boundary deep circulation after Panama seaway closure. Here, we summarize published Nd isotope data for the north Pacific and Atlantic, combined with amorphous Fe hydroxide (AFHs; a newly developed water-mass proxy) of Fe-Mn nodule from the western Pacific to investigate deep-current evolution since the late Miocene. Our results show a prominent deep-water mass change in the north Pacific at ~5 Ma, indicating the Panama seaway shoaling had disrupted the exchange of intermediate water masses between the Pacific and Atlantic. A decrease trend occurred in the western currents of the north Pacific since ~3 Ma, which contradicts with intensified Antarctic bottom water since ~3.4 Ma. This contradiction can be resolved by enhanced south-north mixing of deep western-boundary currents in the north Pacific.