Implications of bio‐optical modeling of phytoplankton photosynthesis in Antarctic waters: Further evidence of no light limitation in the Bransfield Strait

Abstract

During the cruise ECOANTAR 94 photosynthesis versus irradiance relationships, phytoplankton spectral absorption, quantum yield of carbon fixation, and water column light regime were determined in the eastern Bransfield Strait and surrounding areas of the Weddell Sea and Weddell-Scotia Confluence, to determine if photosynthesis is light limited in these areas. There were no significant differences in the light-saturated chlorophyll-specific rate of photosynthesis (P ), light-limited slope (␣ B ), light saturation parameter (E kPAR ), and the maximum quantum yield B m ( m ) between surface and subsurface water for several water masses in the area, which indicates that the photosynthetic response in the upper mixed layer was uniform. There were also no significant differences between the spectral light saturation parameter (E kPUR ) and the mean absorbed irradiance by phytoplankton in the upper mixed layer (E umlPUR ). These similarities suggest that phytoplankton photosynthesis was not light limited in this Antarctic region during the cruise period. This was also affirmed by the fact that the average operational quantum yield of the water column (0.03 mol C [mol photons] Ϫ1 ) was half of the mean maximum quantum yield (0.06 mol C [mol photons] Ϫ1 ). Primary production is underestimated by 24% when broadband models are compared with spectral ones. These results have important implications for the modeling of carbon flows in the Southern Ocean.

Phytoplankton production in the North Water Polynya: size-fractions and carbon fluxes, April to July 1998

“…Large phytoplankton exhibit higher quantum yield than small phytoplankton when nutrients are replete (Sathyendranath et al 1999), which could explain why large phytoplankton were less light-dependent than small phytoplankton in the NOW. Figueiras et al (1999) also observed a lack of light limitation when the phytoplankton community was dominated by large diatoms and Phaeocystis in the Weddell Sea in summer.…”

Response of Antarctic phytoplankton to solar UVR exposure: inhibition and recovery of photosynthesis in coastal and pelagic assemblages

“…Horizontal bars are SE of measurements erature values, maximum photosynthetic rates in the absence of inhibition (P B s ) were high for the WSC (Figueiras et al 1999) and near or somewhat below averages for the Palmer Station region (Moline et al 1998). Furthermore, nutrient limitation (e.g.…”

Dissolved and suspended organic carbon in the Atlantic sector of the Southern Ocean. Stock dynamics in upper ocean waters

“…3). This is also the reason behind the relatively high PP ( ment with those found in most studies in the area (Bracher et al 1999 and references there in, Figueiras et al 1999, Park et al 1999). Bacterial production rates (BHP : Table 3) showed the same latitudinal trend as PP rates, representing < 4% of PP in all the study regions.…”

“…A 24 h average EPUR(z) was considered to remove from PP estimates the short time variability caused by clouds. Therefore D = 24 h. For more details see Figueiras et al (1999).…”

“…Hansell (BBSR, Bermuda). We obtained an average concentration of 45.1 ± 0.7 µM C (n = 50) for the 'deep ocean' reference material (Sargasso Sea deep water, 2600 m) and 0.4 ± 0.7 µM C (n = 44) for the 'blank' ) rates were calculated according to Figueiras et al (1999), taking into account the spectral irradiance (using Eq. 3) because of the absence of light inhibition: (3) where D is daylength, P m B is the chl-specific light-saturated rate of photosynthesis (mg C mg -1 chl h -1 ), and…”