Global Climate Change and Intensification of Coastal Ocean Upwelling

Equatorward upwelling-favorable winds have been observed to increase in strength in most EBUS.

“Moreover, equatorward upwelling-favorable winds were observed to be increasing their strength in most EBUS (Bakun, 1990;García-Reyes et al., 2015;Sydeman et al., 2014).”

The Bakun hypothesis initiated from the fact that trade winds in all four EBUS had increased from the mid-1900s to the 1980s.

“Briefly, the Bakun hypothesis initiated from the fact that trade winds in all four EBUS (Canary, California, Peru, and Benguela) had increased from the mid-1900s to the 1980s.”

It was proposed that upwelling in EBUS will be increasing during future global warming scenarios.

“It was therefore proposed that upwelling in EBUS will be increasing during future global warming scenarios.”

Bakun hypothesized that a global warming scenario with increased CO2 concentrations would reduce night-time cooling and increase daytime warming.

“In fact, the author hypothesized that a global warming scenario with increased CO 2 concentrations would reduce night-time cooling and increase daytime warming.”

Bakun (1990) did not consider stratification and other processes that might change thermocline depth such as coastal trapped waves.

“Bakun (1990) did not consider the stratification and other processes that might change the thermocline depth such as coastal trapped waves.”

Consequently, the temperature difference at land and sea would cause greater pressure gradients leading to intensified alongshore winds and enhanced upwelling.

“Consequently, the temperature difference at land and sea would cause greater pressure gradients leading to intensified alongshore winds and enhanced upwelling.”

Bakun (1990) hypothesized that upwelling favorable winds would intensify under global warming.

“In 1990, Bakun (1990) hypothesized that the upwelling favorable winds would intensify under global warming.”

This relationship is supported by findings of other authors that stratification and coastal trapped waves, which have not been considered by Bakun (1990), may have stronger effects on upwelling intensity and productivity in the Canary current upwelling system than wind stress.

“This relationship is supported by findings of other authors that the stratification and coastal trapped waves which have not been considered by Bakun (1990) may have stronger effects on the upwelling intensity (and productivity) in the Canary current upwelling system than the wind stress.”

Bakun (1990) presented evidence of a tendency for stronger upwelling in the Californian, Iberian, Moroccan and Peruvian areas during the period from 1945 to 1985.

“Bakun (1990) presented evidence of a tendency for stronger upwelling in the Californian, Iberian, Moroccan and Peruvian areas during the period from 1945 to 1985.”

Local thermodynamic arguments suggest that regional upwelling winds in eastern boundary upwelling systems may increase due to increased land-sea temperature contrast, as suggested by Bakun.

“In addition to these dynamical changes in the Hadley Cells, local thermodynamic arguments suggest that regional upwelling winds in the EBUS may increase due to increased land-sea temperature contrast as suggested by Bakun [11], often referred to as the Bakun Hypothesis (BH).”

Under global warming, continental temperatures will rise faster during local heating seasons than nearby ocean temperatures, steepening the cross-shore pressure gradients that drive upwelling-favorable winds.

“The BH suggests that under global warming, continental temperatures will rise faster during the local heating seasons than will temperatures in the nearby ocean, thereby steepening the cross-shore pressure gradients that drive upwelling-favorable winds (Fig. 1b, c).”

Intensified upwelling-favorable winds would lead to an increased upwelling rate, greater turbulence in the upper ocean, and swifter offshore transport of surface waters.

“Intensified upwelling-favorable winds [11] would lead to an increased upwelling rate, greater turbulence in the upper ocean, and swifter offshore transport of surface waters.”