Abstract
The underwater light field in the Bellingshausen and Admundsen Seas was characterised using data collected during the R/V Polarstern cruise ANT XI/3, from 12.1.94 to 27.3.94. The euphotic zone varied from 24 to 100 m depth. Spectral diffuse vertical attenuation coefficients (Κd(λ))were determined for 12 narrow wavebands as well as for photosynthetically available radiation (PAR, 400-700 nm): Κd(490) ranged from 0.03 to 0.26 m-1; Κd(550) from 0.04 to 0.17 m-1; Κd(683) from 0.04 to 0.17 m-1; and Κd(PAR) varied from 0.02 to 0.25 m-1. Κd(λ) for wavelengths centred at 412 nm, 443 nm, 465 nm, 490 nm, 510 nm, 520 nm and 550 nm were significantly correlated with chlorophyll concentration (ranging from 0.1 to 6 mg m-3). The vertical attenuation coefficients for 340 nm and 380 nm ranged from 0.10 to 0.69 m-1 and from 0.05 to 0.34 m-1, respectively, and were also highly correlated with chlorophyll concentrations. These Κd values indicate that the 1% penetration depth may reach maxima of 46 m and 92 m for 340 nm and 380 nm, respectively. The spectral radiance reflectances (Rr(λ)) for 443 nm, 510 nm and 550 nm were less than 0.01 sr-1. Rr(λ) for 665 nm and 683 nm increased with depth up to 0.2 sr-1 because of chlorophyll fluorescence. Using a model that predicts downward irradiances by taking into account the attenuation by water and absorption by chlorophyll, we show that chlorophyll fluorescence has a significant influence on the red downward irradiance (Ed (633, 665, 683)) in deeper layers. The ability of the phytoplankton population to influence the light environment by autofluorescence and absorption processes depends on the light conditions and on the photoacclimation of the cells, represented by the in vivo cross section absorption coefficient of chlorophyll (a*). The obtained mean chlorophyll-specific light attenuation coefficients of phytoplankton in situ (kc) are higher than the in vivo absorption coefficient of chlorophyll, more than to be excepted from the scattering, a* (λ), m2 mg chl-1, decreased due to packaging effect with increasing chlorophyll concentrations.
Original language | English |
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Pages (from-to) | 41-56 |
Number of pages | 16 |
Journal | Hydrobiologia |
Volume | 344 |
Issue number | 1-3 |
DOIs | |
State | Published - 1 Jan 1997 |
Externally published | Yes |
Keywords
- Antarctica
- Chlorophyll absorption
- Natural fluorescence
- Spectral water transparency
- UV-A
- Underwater light field
ASJC Scopus subject areas
- Aquatic Science