Antarctic meltwater slows down global warming by more than a decade

A new study published in Nature used climate models to explore the effects of meltwater from the Antarctic ice sheets and ice shelves on global surface temperature under a warming climate. The study found that the increasing meltwater decreases the surface salinity of the Southern Ocean and thus increases the near-surface stratification, which in turn reduces the upwelling of local warm deep water mass, known as Circumpolar Deep Water (CDW). The meltwater-induced surface cooling further enhances drying of the Southern Hemisphere and increases the formation of Antarctic sea ice. Additionally, due to the reduced upwelling of CDW, ocean heat accumulates below the surface and is redirected toward the Antarctic coast leading to further ice-sheet and ice-shelf melting. The study concluded that Antarctic meltwater could slow down global warming by more than a decade.

Figures 5b and c from Bronselaer et al. (2018): Schematic of the meltwater-induced Southern Ocean subsurface warming, shown as a zonal-mean cross-section. In the pre-industrial state (b), isopycnals (black lines) are tilted towards the ocean surface by westerly winds (black circles, directed out of the page), away from the continental shelf, with an upward heat flux transporting heat from the warm CDW (orange water) towards the cooler surface (blue water), as shown by the red arrow. In the perturbed state (c), meltwater from the Antarctic Ice Sheet freshens the surface (blue), depressing isopycnals (solid to dashed black lines) so that isopycnal mixing transports heat towards the continent rather than towards the ocean surface (red arrow), leading to coastal warming at depth around the shelf and cooling at the surface.

Bronselaer, B., Winton, M., Griffies, S. M., Hurlin, W. J., Rodgers, K. B., Sergienko, O. V., … & Russell, J. L. (2018). Change in future climate due to Antarctic meltwater. Nature, https://doi.org/10.1038/s41586-018-0712-z.

https://www.nature.com/articles/s41586-018-0712-z

 

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