penetration (Fig. 14.25b, from electrode profiles). Where less organic matter is
supplied to the sediment to support respiration, the oxygen can diffuse farther into the
sediment. Beneath oligotrophic waters and at great depth, oxygen can diffuse down 8
cm or even 20 cm (Wenzhöfer et al. 2001). The difference is clearly related to
organic-matter availability, that is, to biological oxygen demand. However, the depth
of oxygen penetration is strongly variable, even on local scales, as close together as
separate probe drops can be made (Fig. 14.26). In a rich coastal site, Sagami Bay at
1450 m, the variation in O 2 penetration was from 0.2 to 1.2 cm. This local patchiness
is due to local concentrations of organic matter (food), to stirring along the trails of
megafauna; to nearby presence or not of burrowers; to bacterial mat present or absent
– all resulting in substantial variation in microbial activity on a scale of centimeters.
Similar variation occurs in all seabeds.
Fig. 14.25 (a) Global assemblage of DOU (open squares) and TOU (closed squares)
results versus depth. Log–log plots with regression equations. (b) Oxygen penetration
into sediment vs. water column depth.
(^) (After Glud 2008.)
Fig. 14.26 Three sample profiles (the extremes and a median example) of [O 2 ] versus
depth in the sediment of Sagami Bay, Honshu, Japan, at 1450 m water depth. Jgrad
values are flux rates calculated from the slope of the upper profile. Implied oxygen-
consumption rates of the sediment community are on the lower abscissa. Similar local
variations of the flux and depths of penetration of oxygen are typical.
(^) (After Berg et al. 2009.)