Upwelling: closing the conveyor belt cycle

As mentioned in earlier posts, upwelling describes the process of ocean deep water changing its density and rising to the top. Global upwelling is not only necessary to close the conveyor belt system, but also essential for most marine life on earth.

Major upwelling areas around the world

http://oceanservice.noaa.gov/education/kits/currents/media/supp_cur04a.html

Upwelling may occur either in the open ocean or on the coast. In both cases, upwelling is induced by wind stress on the upper ocean layer, referred to as Ekman transport [info box, Price et al., 1987]. 

Wind pushes away water which needs to be replaced immediately. During an upwelling event, the water replacing the blown away surface water is ocean deep water. So, cold bottom water is forced to the top of the ocean. Once in contact with the atmosphere and surrounding water masses, it will change its temperature/salinity/density characteristics and become part of the warmer surface currents.

The upwelling phenomenon may be especially strong on coast lines (Figueroa & Moffat, 2012), due to the coriolis force [see post on Deep Water Formation]. 

Depending on the direction of the wind and the earth “spinning away from the water” an especially large “hole” is left behind to be filled with cold bottom water. Hence, most large upwelling areas are close to the world’s coastlines.

http://www.nwfsc.noaa.gov/research/divisions/fe/estuarine/oeip/db-coastal-upwelling-index.cfm

Why is the process of upwelling so important for our marine life:

Cold ocean bottom water is known to be high in oxygen and nutrient content (see info box), while warm surface waters often lack this richness. Now imagine yourself on a hot summer day, when suddenly someone hands you a wonderful cold and fresh drink! That’s what it must be like as a marine living being in the (sub)tropics during an upwelling event. In other words, marine life explodes. The large excess in nutrients and oxygen lead to excessive algal blooms with in turn activate the whole food chain !

(Widman & Smith, 2003; Gruber et al., 2011; Chavez & Messie, 2009; broader information also available at: Edyvane, 1999; Cheung et al., 2009;

http://wordquests.info/cgi/ice2-for.cgi?file=/hsphere/local/home/scribejo/wordquests.info/htm/L-Gk-plankton-phyto-zooPt2.htm&HIGHLIGHT=japan

[All of the above named processes are well described in van Aken (2007) The OceanicThermohaline Circulation, An Introduction. Atmospheric and Oceanic SciencesLibrary, Vol. 39 or Talley et al. (2011) Descriptive Physical Oceanography: An Introduction, 6.Ed.]