The relationship between upwelling and wind-further reading
Productivity and wind speed
Productivity and wind speed have a dome-shaped relationship (see image below) where weak wind does not stimulate much upwelling of nutrients to stimulate phytoplankton growth. In contrast, with very strong wind, mixing is turbulent and nutrients are pushed out of the system too quickly to be used. However, there is an “optimal environmental window” where wind speed is just right to promote phytoplankton growth and fish productivity (5-6 metres per second for fish and 10-12 metres per second for phytoplankton on the Bonney Coast of south-eastern Australia). Research performed at the University of Tasmania and CSIRO has shown that the Bonney Upwelling is a low-wind system, with average wind speed of just 3 metres per second, which is much less than optimal.
The optimal environmental window describes the parabolic relationship between wind speed and productivity. Low wind leads to low upwelling with few new nutrients to stimulate productivity. High winds cause too much turbulence and push nutrients offshore too quickly to be used within the system. There is an optimum wind speed of 5-6 metres per second for fish and 10-12 metres per second for phytoplankton (Image: adapted from Cury & Roy 1989).
Biological (phytoplankton and fish) productivity is dependent upon the direction, timing, persistence, and strength of the wind in addition to other background environmental conditions (such as ocean currents and the depth of the surface mixed layer). Wind strength is expected to increase with climate change, which means that upwelling is likely to increase in strength along the Bonney Coast. As the Bonney Upwelling is a low-wind system, a rise of 2-3 times the present wind speed may enhance productivity (if all other environmental conditions stay the same). However, there are many aspects of the ocean that might be affected by climate change that may lessen the effects of increased wind speed on productivity (such as changes in currents or a deeper mixed layer). Additionally, the interactions between fish and other marine organisms are not well understood, making their response to changing environmental conditions difficult to predict.
Upwelling winds are expected to increase with climate change. As the Bonney is a low-wind system, increases in wind speed of up to 2-3 times the present wind speed are likely to increase phytoplankton productivity. However, biological interactions make the impacts on fish and other marine organisms difficult to predict (Image: taken from Nieblas et al. 2008).
Source Information:
This section was supplied by Anne-Elise Nieblas.
Cury P, Roy C (1989) Optimal environmental window and pelagic fish recruitment success in upwelling areas. Can J Fish Aquat Sci 46:670-680
Bakun A (1990) Global climate change and intensification of coastal ocean upwelling. Science 247:198-201
