Beyond pH and temperature: thermodynamic constraints imposed by global warming and ocean acidification on mid-water respiration by marine animals

No abstracts are to be cited without prior reference to the author.

The rising levels of anthropogenic carbon dioxide in the atmosphere are responsible for several aspects of climate change. They contribute to an enhanced atmospheric greenhouse effect leading to a warmer world and are causing a slow but inexorable acidification of the world ocean. While these effects are well known to scientists and are becoming known to the general public on a daily basis, there are secondary effects which have until recently not been considered. As the surface ocean slowly warms, less oxygen is dissolved in the down-welled waters. Meanwhile, uptake of some 1.2 million tons of CO2 per hour on average, not only drives down the sea surface pH, but adds to the pre-formed CO2 burden of deep waters. As organic matter decays at depth, this amplifies the ambient partial pressure of carbon dioxide. Combined, these effects of lower oxygen concentration and increased carbon dioxide partial pressure lead to a dramatic decrease in the thermodynamic respiration capacity of the mid-waters. Areas of already low oxygen concentration will be the first to be impacted. Sub-oxic and anoxic conditions will not only expand laterally, but vertically as well. These expanding sub-oxic zones will present an ever increasing challenge to the diurnal vertical migration of zooplankton. Where these areas intersect the coast and the continental shelf, the so called 'dead zones' will expand greatly impacting the life histories of multi-cellular organisms.