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International Journal of Marine Science 2013, Vol.3, No.34, 267-277
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to represent coastal structure and seasonal variability
in temperatures, winds and currents (cf. Figure 1c, 2c,
4d, 5d). Nonetheless many reanalysis products
under-represent features over the shelf: the 70 km
ECMWF meridional wind variability (Figure 2d) and
the 100 km GODAS temperature slope and longshore
current (Figure 4b, c), despite similar temporal data
assimilation cycles. These issues also plague the
CMIP-5 models (Taylor et al., 2012) used for climate
change projections.
In the statistical analysis (Table 1) many expected
links were found between the annual cycle of
meridional wind stress and longshore currents, and
between uplift, temperature, salinity and chlorophyll
in the St Helena Bay area. While west coast upwelling
is driven by meridional wind stress and shear, here the
zonal component of wind stress was found to
modulate shelf productivity as represented by
chlorophyll. A ~5 year cycle in these variables may
relate to expansion and contraction of the circumpolar
mid-latitude westerlies, an issue that deserves further
attention. Environmental relationships with a fisheries
index were briefly explored. Statistical evidence
suggests that higher catch follows a multi-year spell of
lower chlorophyll with onshore winds and warmer
waters (Table 2).
The CFS and SODA reanalysis adequately characterize
the coastal structure and seasonal fluctuations of
wind-forced upwelling. If skepticism in reanalysis can
be alleviated, detailed studies can proceed to evaluate
links between marine variability and the food web.
Further work is recommended to distinguish how the
southern annular mode influences anticyclonic ridging
south of Africa, and the process by which coastal
upwelling intensity and chlorophyll enrichment affect
the fishery.
Acknowledgements
The data suppliers are acknowledged: NCEP (CFS) and ECMWF reanalysis,
NASA (SeaWifs and MODIS), IRI Climate Library (SODA) and Climate
Explorer KNMI (data and analysis tool).
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