Environmental Engineering Reference
In-Depth Information
Figure 3.
Vertical profiles of hydrographic and optical properties and particle distributions
during CAR-74 (16 Jan 02). (a) potential temperature, θ, salinity, S, and density, σ
θ
; (b) chloro-
phyll fluorescence and light scattering presented as beam attenuation coefficient; (c) suspended
particulate organic carbon and nitrogen (POC, PON) and particle's elemental ratio (C:N). Bro-
ken horizontal line denotes O
2
/H
2
S interface. Dotted vertical line represents Redfield C:N ratio
(6.6).
plankton cells. Light scattering is uniformly high in the mixed layer, attenuates
rapidly with depth, but typically exhibits several subsurface peaks, such as
those between 50 and 100 m, at 140-160 m and 270-315 m observed on 16
Jan 02 (Fig. 3b). Without exception, light scattering layers have been found
within the redoxcline, very close to the O
2
/H
2
S interface, and they seem to
coincide with prokaryotic abundance peak(s) (n = 17 of 17 cruises). Unlike
deep light scattering layers in the Black Sea [39,8], these do not appear to
be attributable to anoxygenic photoautotrophs. The Cariaco's redoxcline is at
least 150 m deeper than the Black Sea's and downwelling irradiance attenuates
dramatically, with the 0.01% I
0
isolume typically positioned at
<
100 m (Fig.
2b). Turbidity-driven light scattering below 450 m is typically uniformly low,
but may increase towards the seafloor, suggesting increasing abundances of
fine, suspended particles.
In the open ocean, concentrations of suspended organic matter (POC/PON)
typically attenuate more or less as a power function of depth and primary
production, reflecting depth-dependent consumption, solubilization, reminer-
alization and transport of surface-produced organic matter [7,41,65]. Vertical
