chlorophyll (Chl) and temperature (T) time-series were run though a net production
algorithm, and a multiple regression was generated for POC as dependent variable
with the Chl, T, and BUI series as independent variables. The resulting relationship
suggests that POC flux was greater from late 1999 through 2006 than in 1996 through
1998 (Fig. 14.28). These shifts in POC flux (if they did occur) may have had some
effects on benthic fauna, and they appear to correspond crudely to variations in some
of the climate oscillation indices (Smith et al. 2009; in regard to climatic variation
indices see Chapter 16).
Fig. 14.28 Solid lines: sediment-trap POC flux (50 m above bottom) at Station M.
Dashed line: multiple regression model of the data (solid lines) based on satellite
chlorophyll (200 km radius), temperature and upwelling indices as independent
variables.
(^) (After Smith et al. 2006.)
Smith et al. (2001) converted sediment community oxygen consumption (SCOC)
rates to measures of organic-carbon oxidation using an assumed respiratory quotient
of 0.85 (CO 2 produced per O 2 consumed), appropriate to a mixture of carbohydrate
and lipid. Like supply, these consumption rates cycle strongly with season (Fig.
14.27c), being greatest in summer–fall, and lowest in winter, with a mean of roughly
10 mg C m−2 d−1. Like most ecological time-series, this one is not long enough to
fully establish relationships. It appears that summer peaks in SCOC were higher in
two of three years with greater POC flux, 1991 and 1993 but not in 1994, than in
years with lower flux, 1992, 1995, 1996. A major conclusion from the seasonal series
is that response to greater input is rapid, even immediate; organic matter is
metabolized soon after it arrives at the seafloor.
(^) On annual average, more organic matter appears to have been consumed than was
supplied, roughly 180% more, the discrepancy being greater when supply was
smaller, since consumption remained more constant than supply (Fig. 14.27).
Moreover, Smith et al. (2001) point out that the discrepancy should be assumed to be
even greater to account for the roughly 9% of supply that is eventually sequestered
deep in the sediment. That proportion sequestered is highly variable worldwide.
Reimers et al. (1992) give a general average as 13% of supply for the organic carbon