Abstract
We report profiles of concentrations and radiocarbon contents of suspended particulate organic carbon (POC susp) and sedimentary organic carbon from an abyssal site (Stn M) in the northeast (NE) Pacific collected in September 1994 (a period of very high flux of particulate carbon in the deep sea) and June 1995, as well as from stations on the continental rise and slope off the coast of California in June 1995. We show that during a period of anomalously high sinking POC flux to the deep sea (September 1994), Δ 14C of suspended POC did not decrease detectably between 85 and 1600 m depth. This is in contrast to depth profiles during low and moderate fluxes of sinking POC at this station where Δ 14C-POC susp decreased 50–60‰ in this depth range. One explanation for the constant Δ 14C values of POC susp between 85 and 1600 m is that large quantities of sinking POC could continuously release labile, 14C-enriched POC susp during biological and chemical alteration of the sinking POC. The radiocarbon evidence further suggests that resuspension of organic carbon from the sediment surface, either locally or laterally transported from the slope to the deep sea, is likely, but is probably limited to depths within a few hundred meters of the bottom. Sorption of ‘old’ DOC by suspended particulate matter in the water column is also possible, especially at shallower depths (<3500 m), though proof of this mechanism cannot be demonstrated at this time.
Highlights
Primary productivity in the euphotic zone (0—200 m depth) is the process that initiates the transport of organic carbon from the surface to the deep ocean
Bomb C is useful in studies of carbon transfer between the surface and deep ocean because it serves as a transient tracer
We report that the C signatures and concentrations of POC samples from the water column at the foot of the rise (3800 m depth) were similar to those at
Summary
Primary productivity in the euphotic zone (0—200 m depth) is the process that initiates the transport of organic carbon from the surface to the deep ocean. We wanted to test the hypothesis (Jahnke et al, 1990; Reimers et al, 1992) that inferred organic matter export off the continental shelf and upper slope from especially high organic carbon fluxes to the seafloor off the continental slope and rise off central California They suggested that Stn M may be affected by similar lateral processes, but by events that occurred less frequently and with lower intensity. We report that the carbon isotopic signature of the POC from the rise and upper slope regions of the California coast reflects the same signature as that at the abyssal ocean site, Stn M, during June 1995 This similarity suggests that a common mechanism may be responsible for different oceanic trheegimlaersg,etwdoepptohssgibrialidtiieens tofowf hPicOhCarelateraCl observed at these transport of resuspended SOC (sedimentary organic carbon) from the shelf and slope to the abyssal plain, or sorption or biological utilization of ‘old’ DOC onto suspended particulate matter
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