Spatial and temporal variability and size fractionation of chlorophyll a in the tropical and subtropical Pacific Ocean
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Spatial and temporal variability and size fractionation of chlorophyll a in the tropical and subtropical Pacific Ocean ZHANG Dongsheng1 , WANG Chunsheng1∗ , LIU Zhensheng1 , XU Xuewei1 , WANG Xiaogu1 , ZHOU Yadong1 1
Laboratory of Marine Ecosystem and Biogeochemistry, State Oceanic Administration, Hangzhou 310012, China
Received 14 February 2011; accepted 15 November 2011 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2012
Abstract The spatial and temporal variability and size fractionation of chlorophyll a (Chl a) were investigated in the tropical and subtropical Pacific Ocean during four survey cruises from 2005 to 2009. The surface Chl a (S-Chl a) concentration ranged from 0.002 to 0.497 mg/m3 and was obviously higher in the eastern Pacific than in the western and central Pacific. The vertical distribution of Chl a displayed a single peak pattern, and the maximum Chl a layer (MCL) was observed at a shallower depth in the eastern Pacific than in the western Pacific. All three size fractions of Chl a measurements in the surface water showed a similar distribution to total Chl a and were found in higher concentrations in the eastern Pacific than in the western and central Pacific. Picoplankton dominated the phytoplankton in the surveyed tropical and subtropical Pacific Ocean. Furthermore, pico-Chl a (0.2–2 µm) accounted for a larger percentage of the total Chl a in the central Pacific than it did in the western Pacific and eastern Pacific. In the western Pacific, there seemed to be a latitudinal variability in the phytoplankton community composition where small-sized phytoplankton (WSPL (Table 2). The sizefractionated Chl a results suggest that the contribution of the picoplankton (0.2–2 µm) to the total phytoplankton biomass predominated in the entire tropical and subtropical Pacific Ocean. However, the size fraction compositions were different among the western Pacific, central Pacific and eastern Pacific. The aver-
ZHANG Dongsheng et al. Acta Oceanol. Sin., 2012, Vol. 31, No. 3, P. 120-131
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Fig.6. Distribution of Chl a (mg/m3 ) along the western Pacific (a) and the eastern Pacific (b) transects. Table 2. Size-fractionated Chl a (mg/m3 ) and the percentage of total Chl a in the tropical and subtropical Pacific Surface lines∗
Micro-plankton (>20 µm) Average Chl a Percentage 0.010±0.010 14.2% 0.004±0.006 4.2% 0.025±0.020 12.0%
WSPL CTPL ETPL CTD stations∗∗ DY20-WP5 DY20-WP6 DY20-WP7 DY20-EP1 DY20-EP2 DY21-WP5 DY21-WP6 DY21-WP7 DY21-EP1 DY21-EP2 Notes: * average value of
Nano-plankton (2–20 µm) Average Chl a Percentage 0.017±0.005 27.40% 0.014±0.009 15.8% 0.041±0.023 20.5%
0.003 4.88% 0.022 32.94% 0.004 4.81% 0.020 22.71% 0.003 3.87% 0.017 21.72% 0.008 9.46% 0.021 17.36% 0.004 6.85% 0.014 18.78% 0.003 5.59% 0.016 26.10% 0.000 0.00% 0.021 27.80% 0.001 1.18% 0.014 17.22% 0.006 8.35% 0.015 17.66% 0.005 10.30% 0.010 19.43% cruises DY20 and DY21; ** average value of depths.
age percentage of pico-Chl a (0.2–2 µm) to the total Chl a was 80.0% in the CTPL, which was higher than that in the ETPL (67.5
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