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IN SITU AND REMOTE SENSING ESTIMATED PRIMARY
PRODUCTION IN THE SOUTHERN CALIFORNIA CURRENT
REGION, 1998-2002
J.C.A. CEPEDA-MORALES1 and G. GAXIOLA-CASTRO2
E-mail jcepeda_at_cicese.mx1 ggaxiola_at_cicese.mx2

ABSTRACT In situ and modeled water-column
primary production (PPeu) were determined from
seasonally 1998-2002 IMECOCAL surveys and
satellite data off Baja California. Behrenfeld
and Falkowski (1997) model (VGPM) was applied for
calculated PPeu, using PBopt obtained for the
southern California Current region from an
empirical relationship between surface
temperature (14.5C-23.0C) and in situ PB (Chl-a
normalized rate of C fixation). We used SeaWIFS
(Chl-a, EPAR, K490), and AVHRR (SST) imagery to
feed the VGPM model. Regional PBopt has a range
from 1.1 to 8.9 mgC (mgChla h)-1, with an
overall mean of 3.5 mgC (mgChla h)-1. PPeu
estimated from the VGPM model with in situ data
of Chl-a, PBopt and Zeu had a correlation
coefficient of 0.88 when was related with in situ
PPeu. However, when we used averaged monthly
satellite information, and the estimates of
global and the regional parameters (PBopt),
correlation coefficients diminished to 0.55 and
0.58 (plt0.05 n175), respectively. When we use
the global estimate of PBopt, PPeu was
overestimated (slope of 1.28) in relation with in
situ PPeu. Satellite Chl-a has the higher effect
on lowering the correlation coefficient between
in situ and modeled PPeu, with a difference of
0.37 in relation with PPeu modeled using in situ
Chl-a. PBopt estimated from the BF algorithm was
one standard deviation higher than the overall
regional mean. It is necessary to take account
these differences in the photosynthetic parameter
when the VGPM model is used to estimate regional
and local primary production from remote sensed
information. In order to show the spatial
variability of primary production from the VGPM
model and the regional PBopt, we separated the
area in two main latitudinal regions divided by
Line 113. In general, the southern region was
most productive, with higher values during summer
1999-2002.
DATA AND METHODS In situ primary production
data were collected from 19 surveys realized from
1998 to 2002 by the IMECOCAL program
(Investigaciones Mexicanas de la Corriente de
California) off Baja California. In situ PBopt
values were obtained as the maximum Chl-a
normalized rate of 14C fixation (PB P/Chl-a) in
the water column. Euphotic zone (Zeu) integrated
primary production (PPeu) was estimated from the
in situ experiments. Discrete values of Chl-a in
the water column was determined by the
fluorometric method, from where surface
chlorophyll (Chl-asup) and (Chl-aopt) were
obtained. From the CTD profiles, temperature data
(SST, Topt) were collected. Satellite chlorophyll
(Chl-asat) and K490 data were obtained from the
SeaWiFS program (DAAC, NASA). Monthly averaged
EPAR were kindly gave by Dr. R. Frouin from the
Scripps Institution of Oceanography. Satellite
SST were obtained from the AVHRR-NOAA,
PO.DAAC-NASA program. AVHRR imagery are monthly
composite data from January, 1998 to May, 2002,
with a resolution of 9x9 km. A regional empirical
equation was calculated from PBopt and SST data.
PPeu was calculated using the Behrenfeld and
Falkowski (1997) VGPM model, with different
estimates of PBopt.
Figure A shows the linear relationships between
in situ PPeu and modeled using monthy imagery
composites of Chl-asat, and in situ data of PBopt
and Zeu. The linear correlation coefficient was
lt0.37 units, related with PPeu calculated with in
situ surface Chl-a. When we compare the in situ
surface Chl-a with monthy composite imagery (B),
a very low correlation was found.
PPeu calculated from satellite data Chl-a, Zeu,
and regional PBopt estimated from the empirical
algorithm and SST from satellite data is shown in
the scatter A. In figure B, PBopt was estimated
by the BF global algorithm. In both cases
linear correlation coefficients were low (0.58,
and 0.55 respectively) but statistically
significant, with different slopes.
To identify how the photosynthetic parameter and
some variables affect primary productivity
estimations, we prove the effect on PPeu changing
PBopt, Zeu, and EPAR in the VGPM model. In the
first scatter (A), we use in situ data of
Chl-aopt, Zeu, and global BF PBopt. In this case
PPeu was overestimated, with a slope of 1.28, and
a higher rms value. For the figure B, global
PBopt was changed by the regional estimator, and
all the variables were the same. The slope of the
fitted line changed to 0.48, without a
significant difference in the linear correlation,
but a smaller data dispersion. In figure C, we
use in situ values of Chl-aopt and PBopt, but
Zeu was changed by the values estimated from K490
satellite data. Linear correlation coefficient
increase, and the slope is close to one, and the
data dispersion diminished. For draw figure D,
we calculated PPeu removing the averaged monthly
satellite EPAR from the VGPM model, keeping in
situ values of Chl-aopt, PBopt, and Zeu. We did
not see any changes in the correlation
coefficient, either in the data dispersion, but
with a better slope .
Study area located at southern region of
California Current off Baja California. IMECOCAL
grid survey program is shown over a imagery of
PPeu estimated for April, 1998.
VGPM model (Behrenfeld y Falkowski, 1997)
RESULTS AND DISCUSSION
In situ PBopt (mgC mgChl-a h-1) was showed
together with the parameters estimated with
regional (red dots) and global (yellow dots)
algorithms (scatter A). Both empirical equations
(BF, and our algorithm) have similar patterns,
but with difference of the BF equation higher
than one standard deviation (?1.6) of the overall
regional mean (3.5 mgC mgChl-a h-1) (figure B).
This pattern between measured versus modeled
PBopt has been also reported by Behrenfeld et al.
(2002) for Atlantic Ocean waters. The continuos
line represent the value of the regional ovearll
mean, with dashed lines as one standard deviation
interval.
In situ PBopt values had a range from 1.0 mgC
(mgChl-a h)-1 to 9.0 mgC (mgChl-a h)-1. About
76 of the data were between 2.5 and 5.0 mgC
(mgChl-a h)-1, with an overall mean of 3.5 mgC
(mgChl-a h)-1 (s.d. 1.67). We had a wide
dispersion of this parameter for each year, with
the tendency to increase during summer. This
pattern was mainly evident for 1999, 2000, and
2001.
In situ water-column integrated PPeu values had a
range from 8.0 mgC m-2 h-1 (October, 1998) to 240
mgC m-2 h-1 (October, 1999). A higher percentage
of the data (77.5) had a range between 20 mgC
m-2 h-1 to 80 mgC m-2 h-1, with a overall mean of
59 mgC m-2 h-1 (equivalent to 0.71 gC m-2 d-1).
Regional empirical relation between SST and PBopt
was fitted by equation 1. The full circles
indicate the median of PBopt for each SST
interval (0.5 oC). The bars correspond to one
standard deviation. Dashed contours show the
standard error of the estimations, and the solid
lines is the best fit.
Using remote sensed information (Chl-a, EPAR,
Zeu) monthly PPeu was calculated with the VGPM
model and regional PBopt algorithm. Figure A
shows the overall mean (1998-2002) of the PPeu
(mgC m-2 d-1) estimated. The line contours
represent PPeu values along the study area. Main
features with high primary productivity (gt400 mgC
m-2 d-1) are the Ensenada Front and the inshore
waters. In the figure B, standard deviations of
the overall mean is shown.
PBopt -0.0012418 T 4 0.062177 T 3 - 0.93274
T 2 2.5485 T 27.066 (1)
A Hovmuller diagram for each variable (SST, EPAR,
Chl-a, and Zeu) was done following a latitudinal
section parallel to the coast (100 km). Figure A
shows latitudinal changes of SST. Figure B
represent the temporal variability of EPAR.
Figure C describe the Chl-a patterns along the
transect, with a characteristic feature of the
Ensenada Front, and two main events with high
pigment concentrations during 1998, and 2002
years. Figure D show strong temporal and
latitudinal changes in the euphotic zone (Zeu).
Following Kahru and Mitchell (2000) we divided
the area in four regions northern and southern of
28?N. A first band from inshore to 100 km, and a
second band from 100 km to 300 km offshore.
Temporal variability of monthly PPeu anomalies
(monthly value minus overall mean) show higher
values for the inshore southern (below 28N)
waters, without apparent differences at both
offshore regions. During the El Niño 1997-98 were
calculated the lower PPeu values, with a more
evident effect at inshore waters of the southern
region. Higher anomalies were calculated during
summer, with values gt1.0 gC m-2 d-1 for
1999-2002.
PPeu was modeled from the VGPM model with monthly
imagery of EPAR and in situ Chl-aopt, PBopt, and
Zeu. Figure A shows a significant correlation
(r0.88, pgt0.05) between PPeu in situ vs PPeu
modeled. In the scatter B, Chl-aopt was replaced
by surface in situ Chl-a. The linear tendency is
maintained but the correlation down 0.10 (r
0.78, pgt0.05) and data dispersion increased, with
a higher root mean square (rms) value.
REFERENCES Behrenfeld, M., and P. Falkowski.
(1997). Photosynthetic rates derived from
satellite-based chlorophyll concentration.
Limnol. Oceanogr. 42. 1-20. Behrenfeld, M., E.
Marañon, D. Sieguel, and S. Hooker (2002).
Photoacclimation and nutrient-based model of
light-saturated photosynthesis for quantifying
oceanic primary production. Mar. Ecol. Prog.
Ser. 228 103-117.     Kahru, M., and G. Mitchell
(2000). Influence of the 1997-98 El Niño on the
surface chlorophyll in the California Current.
Geophys. Res. Letters. 27 2937-2940.