Global Ocean Vertical Heat Flux and Its Bidecadal Change
Xinfeng Liang1,2, Carl I Wunsch1,3, Patrick Heimbach1,4, Gaël Forget1, Rui M Ponte5 and Christopher G Piecuch6, (1)Massachusetts Institute of Technology, Cambridge, MA, United States, (2)University of South Florida, St. Petersburg, FL, United States, (3)Harvard University, Cambridge, MA, United States, (4)University of Texas at Austin, Austin, TX, United States, (5)Atmospheric and Environmental Research, Lexington, MA, United States, (6)Atmospheric and Environmental Research Lexington, Lexington, MA, United States
Abstract:
Using a dynamically consistent state estimate, the vertical redistribution of heat within the ocean is investigated over a 20-year period (1992-2011). The 20-year mean vertical heat flux shows strong variations both horizontally and vertically, consistent with the ocean being a dynamically active and spatially complex heat exchanger. Between mixing and advection, the two processes determining the vertical heat transport in the deep ocean, advection plays a more important role in setting the spatial patterns of vertical heat exchange. The global integral of vertical heat flux shows an upward heat transport in the deep ocean, suggesting an abyssal cooling trend over 1992-2011. These results support the inference that the near-surface thermal properties of the ocean are a consequence, at least in part, of internal redistribution of heat, some of which must reflect water that has undergone long trajectories since last exposure to the atmosphere.
Analysis of linear trends in the bidecadal vertical heat flux provides dynamical insights into the global ocean heat content change. Preliminary results show that above 1500 m more heat is transported downward during 2002‑2011 than 1992-2001. The spatial pattern of the vertical heat flux change shows consistent features with previous studies, such as more downward heat transport in the tropical Pacific and the North Atlantic during the last decade. Whereas the spatial pattern of vertical heat flux change is closely related to the advection change, its global integral is largely determined by the change in mixing, indicating a crucial role of ocean mixing in explaining the long-term change of ocean vertical heat exchange. Near the surface, the change of the vertical diffusive heat flux shows similar spatial pattern to the air-sea heat flux change, suggesting a close relationship between upper ocean mixing and air-sea heat exchange.
