juvenile Cape hake (Merluccius capensis) offshore from
their typical inshore habitat, subjecting them to heavy mortalities from predation by larger hake and from commercial
trawling (Hamukuaya et al., 1998). Lobsters (Jasus lalandii)
were trapped by low-oxygen waters advecting onshore that
caused a “walkout” and mass mortality (Cockroft, 2001).
Today, there are a number of isolated ocean basins that
are hypoxic/anoxic due to restricted water circulation
combined with high primary production in surface
waters. Among them are the permanently anoxic Black
Sea and Cariaco Basin and several smaller basins along
the California, USA, coast (Santa Monica, Santa
Barbara, San Pedro, San Nicolas basins) that are
reoxygenated periodically (Berelson, 1991). Some deep
fjords that are permanently anoxic, such as the
Framvaren, Norway, have a similar biogeochemistry to
oceanic anoxic basins (Skei, 1983). But, most fjords have
some seasonal deepwater renewal, which keeps them
from being anoxic all year.
In the case of the Black Sea, anoxic conditions occur
beneath 100–200 m of oxygenated surface waters in the
open sea area. The restricted connection with the Mediterranean Sea, strong stratification, and geomorphology
make the Black Sea a sink for nutrients and other materials
(Richards, 1965; McQuatters-Gollop et al., 2008). The
persistent anoxic basin in the open Black Sea is the largest
naturally occurring anoxic area on earth. It covers about
75 % of the basin’s area and is distinct from and not related
Anoxia, Hypoxia, And Dead Zones, Figure 2 General global distribution of oxygen minimum zones (60 mmol/L). (a) Colors indicate
oxygen concentrations at the depth of minimum oxygen. (b) Depth of the 60 mmol/L isoline in meters (From Keeling et al., 2010).
22
ANOXIA, HYPOXIA, AND DEAD ZONES
their typical inshore habitat, subjecting them to heavy mortalities from predation by larger hake and from commercial
trawling (Hamukuaya et al., 1998). Lobsters (Jasus lalandii)
were trapped by low-oxygen waters advecting onshore that
caused a “walkout” and mass mortality (Cockroft, 2001).
Today, there are a number of isolated ocean basins that
are hypoxic/anoxic due to restricted water circulation
combined with high primary production in surface
waters. Among them are the permanently anoxic Black
Sea and Cariaco Basin and several smaller basins along
the California, USA, coast (Santa Monica, Santa
Barbara, San Pedro, San Nicolas basins) that are
reoxygenated periodically (Berelson, 1991). Some deep
fjords that are permanently anoxic, such as the
Framvaren, Norway, have a similar biogeochemistry to
oceanic anoxic basins (Skei, 1983). But, most fjords have
some seasonal deepwater renewal, which keeps them
from being anoxic all year.
In the case of the Black Sea, anoxic conditions occur
beneath 100–200 m of oxygenated surface waters in the
open sea area. The restricted connection with the Mediterranean Sea, strong stratification, and geomorphology
make the Black Sea a sink for nutrients and other materials
(Richards, 1965; McQuatters-Gollop et al., 2008). The
persistent anoxic basin in the open Black Sea is the largest
naturally occurring anoxic area on earth. It covers about
75 % of the basin’s area and is distinct from and not related
Anoxia, Hypoxia, And Dead Zones, Figure 2 General global distribution of oxygen minimum zones (60 mmol/L). (a) Colors indicate
oxygen concentrations at the depth of minimum oxygen. (b) Depth of the 60 mmol/L isoline in meters (From Keeling et al., 2010).
22
ANOXIA, HYPOXIA, AND DEAD ZONES