Particulate organic carbon and nitrogen in the eastern pacific ocean

Abstract

Particulate organic carbon and nitrogen in sea water were measured in samples collected along a line 155°W; 50° N-15°S, during the cruise of R.V. “Hakuho-Maru” (KH-69-4). High concentrations of particulate matter were generally found at or near the sea surface; the concentrations decreased rapidly with depth. A consistent minimum was located in the depth range 150 to 250 m through the entire section sampled. The subsurface maximum layers roughly coincided with the chlorophyll maximum, but several irrregularities were noted. One of the most remarkable features of the vast stratum below 200 m depth was the presence of distinctively regional variation in concentration of particulate material through the entire section. In the section, we could define at least 6 large water parcels, vertically oriented, all with significantly different concentrations of both carbon and nitrogen. Variation in the deep water ranged from less than 5 μgC/l to more than 50 μgC/l. Correlation analysis between carbon concentration and apparent oxygen utilization (AOU) of ambient water for all samples showed that the carbon from particle-poor water parcels consistently decreased with increasing AOU, levelling to a practically constant low of around 5 to 10 μgC/l, whereas the carbon from particle-rich parcels was anomalously high (10 to 50 μgC/l) in the range of high AOU, and showed no consistent trend of convergence. The intergrated amount of particulate carbon in the total water column at each station was in the range 20 to 150 gC/m². More than 90% of this total amount was in the water column below 200 m depth, and the correlation of total amount of particulate material between the surface layer (0 to 200 m) and the water column below 200 m depth was highly significant. These observations are considered to indicate that the downward transport of these materials may be much quicker than so far estimated, at least in some localized areas.