Compensating change in the Indo-Pacific MOC in response to the Atlantic MOC slowdown

The climate model simulations forced with increasing anthropogenic greenhouse gases consistently project a robust decline of the Atlantic Meridional Overturning Circulation (MOC) and a strengthening of the Southern Hemisphere westerly winds, which may in turn result in an increase in the Southern Ocean MOC. In a research article recently accepted in the Journal of Physical Oceanography, a team of scientists from California Institute of Technology and Scripps Institution of Oceanography carried out a series of ocean and climate model experiments to show that the future declines of the Atlantic MOC and associated northward ocean heat transport may be compensated by the slowdown of the Indo-Pacific MOC. This allows the Southern Ocean MOC to evolve independently of the AMOC slowdown, over timescales up to many decades. Due to the compensation of MOC changes between the Atlantic and Indo-Pacific Oceans, the southward transport of ocean heat from the Indo-Pacific Oceans to the Southern Ocean will decrease across 30^oS (i.e., heat loss in the Southern Ocean), compensating the reduced northward ocean heat transport to the Atlantic Ocean across 30^oS (i.e., heat gain in the Southern Ocean). This study highlights the importance of inter-ocean heat exchange in shaping the global heat budget and regional distribution in the response to the increasing anthropocentric greenhouse gases.

Figure 1 from Sun et al. (2020). Two-dimensional (depth-latitude) schematic of the global meridional ocean overturning circulation, adapted from Talley (2013). Colors represent different water masses and their abbreviations are shown to the right of the figure. Changes in color along pathways indicates water mass transformation. Volume transports are given by the various T terms. The dotted line represents the southern boundary of the basins. The small vertical arrows close to the surface indicate surface buoyancy gain (pink) and loss (blue).

Sun, S., Thompson, A. F., and Eisenman, I. (2020). Transient overturning compensation between Atlantic and Indo-Pacific basins. J. Phys. Oceanogr., https://doi.org/10.1175/JPO-D-20-0060.1.

Lee, S.-K., Lumpkin, R., Baringer, M. O., Meinen, C. S., Goes, M., Dong, S., Lopez, H. and Yeager, S. G. (2019). Global meridional overturning circulation inferred from a data-constrained ocean & sea-ice model. Geophysical Research Letters, 45, https://doi.org/10.1029/2018GL080940.

Lumpkin, R., and Speer, K. (2007). Global ocean meridional overturning. J. Phys. Oceanogr., 37(10), 2550–2562. https://doi.org/10.1175/JPO3130.1.

Talley, L. D. (2013). Closure of the global overturning circulation through the Indian, Pacific, and Southern Oceans: Schematics and transports. Oceanography, 26(1), 80–97. https://doi.org/10.5670/oceanog.2013.07.