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International Journal of Marine Science 2013, Vol.3, No.34, 267-277
http://ijms.sophiapublisher.com
275
Table 2 briefly explores the environmental relationships
with annual fish catch in the southern Benguela.
Chlorophyll shows a significant correlation at 1.5-3.5
yr lead (r=-0.65) in the period 1998-2008. Zonal
stress is correlated with annual fish catch at 1.5-2.5
yr lead (r=0.30), as is T at 0.5-1.5 yr lead (r=0.46)
over the period 1980-2008. Such memory is related
to the fishery response to cumulative environ-
mental stresses, and the lag between catch effort and
its management. Further analysis of fishery-
environment relationships may be found in Jury (2011,
2012).
Table 2 Cross
-
correlations between southern Benguela annual fish catch and environmental indices in the period 1980
-
2008 except
CHL 1998
-
2008
Lag (yr)
CHL
X
T
-
3.5
-
0.65
0.14
-
0.36
-
2.5
-
0.70
0.29
0.12
-
1.5
-
0.61
0.32
0.37
-
0.5
-
0.08
0.21
0.55
0.5
0.03
-
0.09
0.20
1.5
0.23
-
0.24
-
0.18
Note: Values significant above 95% confidence are bold (CHL>0.6, others>0.3). Negative lag refers to (Jul.-Jun.) environment
leading catch (Jan.-Dec.)
When the South Atlantic high pressure cell ridges
south of Africa, phytoplankton tend to bloom in St
Helena Bay. Analysis of the February-March 2008
period of unusual weather and chlorophyll reveals a
pattern of anomalous high pressure in the south
(Figure 9a) and offshore winds (Figure 9b). The
coastal zone north of 33°S exhibited an atmospheric
mixed layer height <400m, cyclonic wind vorticity
(curl) <-10
-4
s
-1
, and a solar radiation anomaly of +10
W/m
2
(not shown). CFS surface temperature
anomalies <-2.5
℃
were observed in St Helena Bay
during this period (Figure 9c). Along the coast to the
north, SODA 1-100 m temperatures were <8
℃
and
MODIS chlorophyll exceeded 10 mg/m
3
(Figure 9d).
4 Conclusions
The southern Benguela coastal upwelling zone is a
narrow, seasonal feature. This paper has considered a
variety of operational model-assimilated databases
and their ability to represent the coastal upwelling
(sections 3.1, 3.2). Reanalysis products that did a
‘better job’ of estimating the cross-shore slope of
isotherms were analyzed in detail (section 3.3). Here
the 30 km CFS reanalysis resolved a cool strip of SST,
albeit with a 1-2
℃
warm bias on the coast (cf. Figure
1c). The subsurface zonal overturning and longshore
current jet were adequately represented in the 50 km
SODA reanalysis and mean upwelling rates of 1-2
m/day (cf. Figure 3c) were consistent with Andrews
and Hutchings (1980) and Veitch et al (2010). A key
finding here is the ability of CFS and SODA reanalysis
Figure 9 Case study of offshore wind and high chlorophyll
event in February-March 2008: a) ECMWF surface air pressure
anomalies (hPa), b) CFS zonal wind anomalies (m/s) and
SODA wind stress, c) CFS surface temperature anomalies (
℃
),
and d) MODIS chlorophyll (mg/m
3
) and SODA 1-100 m
current vectors
Note: High pressure in a) and anticyclonic eddy in d) are
labeled