Ocean is an essential component of the earth system and plays a crucial role in the climate change and climate variability. My research goal is to understand how the ocean affects the global climate in three different ways, the physical, chemical and biological ways. I am particularly interested in the diapycnal mixing in the deep ocean and its roles in controlling the meridional overturning circulation and the vertical transports of carbon as well as nutrients. To better understand the diapycnal mixing in the ocean, we also need to know the processes that can supply energy to the ocean mixing. These processes mainly include internal tides, near-inertial oscillation and mesoscale eddies. Although many studies on internal tides have been done in the past decades, the roles of inertial oscillation and particularly mesoscale eddies have not been intensively investigated. During my study at Columbia University, I have primarily been focusing on the roles of mesoscale eddies on the deep ocean dynamics, particularly on ocean mixing, based on a large data set obtained over the East Pacific Rise. I have found that the mesoscale eddies can affect deep ocean processesin nearly all frequency bands, including the general circulation, low-frequency flows, internal waves and ocean mixing.