Coastal upwelling and the development of hypoxic dead zones are not removed from the effects that climate change is having on the Earthís dynamic climate systems.  In fact, it has become increasingly evident that in light of climate change they may be inextricably linked.  The relevance of climate change in considering the development and implications of hypoxic dead zones was only first suggested in 1990 by Andrew Bakun.  The important insight he made almost 20 years ago was that the increase of atmospheric stocks of CO₂ and other greenhouse gases could lead to increased coastal upwelling.  If increased greenhouse gas emissions forced increases in temperature, the continents would warm, increasing the onshore-offshore atmospheric pressure gradients.  This would then result in stronger winds and accelerated upwelling (Bakun, 1990).  Bakun even suggested that the cooling of the ocean surface inherent in upwelling could couple with this process, creating a local positive feedback by increasing atmospheric pressure gradients further (Bakun 1990).  Intensified upwelling means more nutrient rich deep-water coming up to the surface, which Bakun posited would lead to increased primary production that would not by any necessity contribute to greater populations of commercial fish.  Instead ìincreased organic production might cause large areas of these systems to become anoxic at depth,î (Bakun, 1990, p201).

Since then, the link between climate change and coastal upwelling (and thus, dead zones) is being more rigorously looked at.  The nature of that link and its implications are clearer and more frightening.

Much of what Bakun and others has suspected has come to fruition, and some things are worse.  Anoxia has not been limited to deeper waters.  The increased rate of water renewal due to stronger upwelling prevents herbaceous zooplankton from maintaining populations.  Phytoplankton populations, already benefiting from the nutrient-rich waters provided by the intensified upwelling systems, now grow unchecked by their traditional predator; herbaceous zooplankton (Bakun, 2004).  This, as Bakun observed in the dead-zone along the Namib Desert, ìprovides an opportunity for massive buildup of phytoplankton biomass, much of which may sink unutilized onto the sea floor, resulting in thick accumulations of deposited unoxidized organic matter,î (Bakun, 2004, p1015-1016).  Much of this ends up in anoxic deep waters, where this mass decomposes, producing H₂S and CH₄, which rise through the depths in the form of effervescent eruptions.

So whereís the anoxia?  Well, H₂S, aside from being extremely poisonous, has the ìeffect of stripping the dissolved oxygen from the water column as it moves upward through it,î (Bakun, 2004, p1016).  Anoxia caused by such means is blamed for, ìthe loss of 80% of the regional stock of Cape hake (Merluccius capensis), normally the basis for Namibia's most valuable fishery,î (Bakun, 2004, p1016).

The diagram below illustrates the chemical and biological dynamics of a coastal upwelling zone under conditions of moderate and intensified upwelling (the diagram also illustrates a scenario stipulating a healthy sardine population; see Solutions):