(^) Wenzhöfer and Glud (2002) have compared DOU between areas of high surface
production (e.g. the West African upwelling zone) with that in oligotrophic central
waters. On bottoms 1 km deep, the difference is a factor of four; at 3 km it is a factor
of two. Overhead production is a major determinant of deep-sea biological activity,
but less organic matter reaches the bottom when it must traverse more water to get
down. It is not surprising to find that reflected in SCOC results; they simply agree
with trap flux, macrofauna abundance, and so on.
Food Supply Relative to Metabolism
(^) Once TOU and DOU can be measured, the obvious question is: to what extent does it
compare with supply rates of organic matter descending to the seafloor? Answering is
complicated by the seasonal cycling of both supply and consumption. So, a sufficient
comparison requires a time-series of considerable length and at least seasonal
resolution. K.L. Smith and colleagues (Baldwin et al. 1998; Smith et al. 2009) have
obtained such a time-series in a study of Station “M” on an abyssal plain at 4100 m
depth, 220 km west of Point Conception, California. From 1989 to 1998, they made
36 cruises at roughly seasonal intervals. Additional bursts of sampling have been
made through 2010. At each visit they retrieved and replaced conical sediment traps
(baffled openings were 0.25 m^2 ) moored at 600 and at 50 m above the bottom (mab).
The traps collected downward particle flux in a series of cups filled with preservative
and automatically changed every 10 days. The cup-changing mechanisms sometimes
jammed, so some data were lost, but intervals in the series are complete. Cruise
participants also made a series of benthic observations, most prominently sediment
oxygen-consumption rates over two days with canisters on landers. Other studies were
conducted as well, including camera sled photography, trawls for megafauna, and
submersible dives.
(^) Supply rates of particulate organic carbon (POC) measured by traps at both 600 and