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1; 50, 50, 15; 0, 100, 18.5; 0, 100 and 19; 75, 25. Pigments were detected with the diode-array absorbance signal set at 440 nm. Identification was made by comparing
retention time and spectral characteristics with those of commercial pigment standards
14
International Agency for C determinations, Denmark and a rich prochlorophyte
sample collected at the deep chlorophyll maximum from the Mexican Pacific Ocean 19852.2 N, 113811.99W during the USA METOX01 cruise for the DvChl a.
Quantification was done with the pigment response factor HPLC peak area pigment mass obtained with the commercial pigment standards according to Mantoura and
Repeta 1997. Nitrate and dissolved oxygen were measured according to Strickland and Parson 1972, sulfide by the iodometric method Clesceri et al., 1989, and temperature
and salinity with a Kahlsico salinometer model 140.
3. Results
3.1. Physical and chemical conditions Using the physical and chemical variables Fig. 1, three zones can be distinguished:
i a surface mixed layer upper 12 m with the highest temperature 32.58C and
21
dissolved oxygen . 6 ml l , and relatively low nitrate concentration lower than 0.4
21
mg at l ; ii an intermediate layer with temperature between 32.5 and 298C,
21
decreasing dissolved oxygen from 6.6 to 1.0 ml l and stable nitrate concentration
21
0.4–0.42 mg at l ; and iii a bottom layer with temperature decreasing to 228C, very
21
low or undetectable dissolved oxygen , 1.0 ml l , and increasing nitrate and H S
2
concentration. In this last layer, irradiance was between 4 and 10 of the incident irradiance at the surface [Fig. 1B].
3.2. Pigments Peridinin and fucoxanthin, pigment signatures of dinoflagellates Jeffrey, 1974 and of
diatoms Liaaen-Jensen, 1985; Wright and Jeffrey, 1987 had a low concentration in the mixed layer, a slight increase between 12 and 19 m, and a sharp increase at 21 m [Fig.
2C]. A second increase of peridinin occurs at the bottom. Zeaxanthin concentration, an indicator of cyanobacteria and prochlorophyte abundance Guillard et al., 1985;
Goericke and Repeta, 1993 is relatively low and homogeneous in the upper 20-m layer
21
[Fig. 2B; values , 0.2 mg l and decreases in the bottom layer. The general
phytoplankton biomass signature, the Chl a, closely matches the variation of the peridinin and fucoxanthin [Fig. 2A], suggesting that diatoms and dinoflagellates are the
main contributor to the phytoplankton biomass. To corroborate this, the contribution of the different phytoplankton groups to the Chl a was calculated by using a multiple linear
regression analysis between diagnostic pigment peridinin, fucoxanthin and zeaxanthin and Chl a profile data Barlow et al., 1993; Bustillos-Guzman et al., 1995. We found
dinoflagellates, diatoms, and cyanobacteria contributed 73, 17 and 6 to Chl a.
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Fig. 2. Vertical variation of pigment concentration in Bahia Concepcion, Gulf of California: A chlorophyll a; B zeaxanthin; C fucoxanthin and peridinin.
3.3. Unidentified pigments At least six chlorophyll-like pigments Chl-like and one carotenoid were recorded.
The Chl-like pigments eluted between the diadinoxanthin and Chl b and the carotenoid eluted after the Chl a Fig. 3. The first three Chl-like pigments, eluting after the
diadinoxanthin, have the same absorption spectrum form: a soret blue and a red Qy maximum at 476 nm and 658 nm with a soret:red ratio r of 3.68 [Fig. 4A]. The other
Chl-like pigments have a soret at 444 nm, a Qy at 660 nm, and an r of 4.94 [Fig. 4B].
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Fig. 3. Typical chromatogram 440 nm from highly pigmented A and normal samples B. Peak identification: 1, chlorophyll c
1 and c2; 2, peridinin; 3, fucoxanthin-like pigment; 4, diadinoxanthin; 5–11, unknown chlorophyll-like pigments; 12, chlorophyll b; 13, chlorophyll a; 14, unknown carotene; 15, unknown
pigment; 16, b-carotene; 17, fucoxanthin; 18, zeaxanthin; 19 and 20, unknown pigments. X-axis units are min. Y-axis units are milliabsorbance units.
The carotenoid has maximum absorbance at 450 nm and 476 nm with a 450 476 ratio of 1.15 [Fig. 4C]. Because we do not have the response factor for these unknown
pigments, the response factor of Chl b and pheophytin b were used to quantify the first and second group of Chl-like pigments, and that of b-carotene for the carotene because
their spectra match closely. Pheophytin b was prepared according to Jeffrey 1997 to obtain its response factor. The vertical distribution shows Chl-like pigments start
increasing below 19-m depth, peaking at 25 m, and then decreasing [Fig. 5A and B]. The carotenoid pigment also increases together with the Chl-like pigments but peaked at
23 m [Fig. 5C]. All Chl-like pigments show the same quantitative variation with depth.
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Fig. 4. Vertical variation of chlorophyll-like pigments in Bahia Concepcion, Gulf of California: A pigments 5, 6 and 7; B pigments 9, 10 and 11; C carotenoid 14.
4. Discussion
