50 mab (Fig. 14.27a & b) showed strong seasonal cycling. The POC time sequences
at the two depths were very close, confirming that very little is consumed from
sinking organic matter below 2000 m. Rates at 50 mab were about 10% higher than
those at 600 mab, which can be attributed to lateral particle transport close to the
bottom. Maxima in POC flux followed, with a lag of 2–3 months (relatively
immediately), the seasonal highs in expected coastal upwelling based on crude
estimates (Bakun indices) of the regional, upwelling-favorable winds. In addition to
seasonal cycling, there was variability in total annual flux (Table 14.2; sampling gaps
do not allow updating after 1997–1998). POC flux correlated somewhat (Spearman
rank correlation = 0.3, P < 0.001) with strength of upwelling (Bakun index; BUI) 20
to 60 days earlier, and upwelling strength varies considerably between years.
Fig. 14.27 (a and b) Time-series of particulate organic carbon flux into traps at 600
and 50 m above bottom (at 4100 m) 220 km west of Point Conception, California,
USA (Station M). (c) Sediment community oxygen consumption at the same station.
Left-hand scale is implied organic carbon metabolized if respiratory quotient is 0.85.
(After Smith et al. 2001.)