Credit: NASA

Nature 447, 577–580 (2007) Ocean mixing plays a crucial role in global climate because it is linked to the ocean's capacity to store and transport heat from the tropics to cooler regions. Tropical cyclones are thought to be important drivers of ocean mixing and heat transport, but until now their relative importance has been uncertain.

Ryan Shriver and Matthew Huber of Purdue University in Indiana now present substantive evidence that tropical cyclones have a significant role in mixing the ocean's uppermost layers. Using more data and longer sampling periods than previous studies, the researchers compared ocean temperatures before and after the passing of tropical cyclones to estimate the effect of these events on vertical mixing. Shriver and Purdue say that up to 15% of peak ocean heat transport can be linked to vertical mixing driven by tropical cyclones. Their estimate that cyclones account for 0.26 petawatts per year of ocean heat transport is significantly smaller than earlier calculations.

More surprisingly, the results show that cyclone-induced heat transport increases substantially with higher sea surface temperatures, suggesting that climate change could alter ocean circulation and heat transport. Climate models could be improved by including the effect of sea surface temperature on cyclone-driven ocean mixing.