![]() |
||||||||||||||
Australia: The Land Where Time Began |
||||||||||||||
Hypoxia
by degrees - Establishing Definitions for Oceans that are Changing
Significant scientific and public attention has been drawn to a
marked increase in the incidence of low oxygen events that have been
occurring on continental shelves, coupled with expanding low oxygen
regions that have been observed in the ocean. A need for the
establishment of definition of terms that are widely used such as
“hypoxia” and “dead zones“ has resulted from the increasing levels and
distribution of regions that have low oxygen content. Units such as μMol
O2/kg for reporting as these terms are independent of
temperature, salinity and pressure, and are required for mass balances,
as well as for numerical models of transport by the oceans. For
historical reasons much of the dead zone occurrence reporting is in
units of volumetric concentration of ml O2/l or mg O2/l.
Reporting of the partial pressure of oxygen (pO2)
is required for direct measurements of the physiological state of marine
animals. The incorporation of temperature and salinity terms is
necessary and therefore accommodates changes brought about by climate
warming and the influence of the very large temperature range around the
world where there have been reports of an oxygen-limiting temperature
range. In this paper the authors1 examine the various
definitions that have been used and the boundaries that have been set,
then setting them in a common framework. They examine the large scale
ocean pO2 fields that are required for the pairing with CO2
data for examination of the combined impacts of global warming and the
acidification of the ocean. Shallow, coastal regions with low oxygen
concentrations are usually termed “dead zones”, usually caused by either
coastal eutrophication or the decomposition of organic matter, or by the
upwelling of water that is low in oxygen content. The authors1
point out that bathyal water, which has low oxygen levels, represents a
vast global pool of low oxygen water, and that deep water species are
well-adapted to these oxygen-poor waters, and that upwelling waters can
readily entrain these low oxygen waters which then contribute to coastal
hypoxia throughout the world, and may be characterised identically. In
this study the authors’1 examined the potential for the
expansion of those low oxygen waters onto continental shelves around the
world which may push the coastal waters past the limits for low oxygen
content to which the coastal species are adapted and beyond the point
which many coastal shallow water species can tolerate.
|
|
|||||||||||||
|
||||||||||||||
Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |