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Int. J. of Marine Science 2012, Vol.2, No.7, 51
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Figure 4
The sea surface height balance: annual sum of negative
and positive sea surface height anomalies in time series.
Figure 5
Examples of balance between positive and negative sea
surface height in a year cycle.
Note: A: 1998; B: 2002
When the total annual balance of cyclonic to
anticyclonic eddies is positive (Figure 4A), the
correlation between kinetic energy of eddies and
chlorophyll concentration is positive as well, showing
that cyclonic eddies dominated throughout the year
(reflected by the total negative balance of sea surface
height anomalies), so chlorophyll values were higher
than normal. In the case of the year with dominating
anticyclonic eddies the situation is reversed, the
balance is positive, so the kinetic energy of eddies and
chlorophyll concentration is negatively related,
showing that anticyclonic eddies dominated
throughout the year (Figure 4B); the chlorophyll values
were less than normal.
The balance between positive and negative sea surface
heights might be also partly driven by the general
switch between anticyclonic circulations dominating
the Arabian Sea during summer monsoon to a cyclonic
one, in winter. Interannually, the pronouncement of
mesoscale sea surface height anomalies as well as the
ratio of cyclonic-to-anticyclonic eddies could
markedly depend on how strong or weak the latest
monsoon was. Further development of this hypothesis
and its testing might contributes to the understanding of
the sign switch in the kinetic energy-chlorophyll
relationship.
As far as the interannual variability is concerned, the
time series and their statistical analysis does not allow
us to vote for the concept of rising productivity of the
Arabian Sea reported earlier (Goes et al., 2005). It
seems that in a given time range, we are dealing with a
balanced pelagic ecosystem exhibiting no pronounced
interannual trends (as far as the chlorophyll-
a
tend to
be used as the indicator of productivity) underlined by
the absence of interannual trends in variations of the
kinetic energy of eddies-partly driving the chlorophyll
variations. Moreover, we analyzed interannual changes
in chlorophyll-
a
over the whole Arabian Sea
subdivided into 61 2-degree regions. For each region,
remotely sensed chlorophyll-
a
, sea surface temperature,
and wind speed time series were retrieved, from
appropriate databases (Piontkovski and Claereboudt,
2012). The spatial and temporal trend analysis showed
physical-biological oscillations with dominant periods
of 12 and 6 months (reflecting the seasonality of
monsoonal winds) with a globally warming trend but
no overall increase in chlorophyll over the past 12
years (1997~2009).
Overall, the evaluated relationship between the sea
surface height anomalies, kinetic energy, and
chlorophyll concentration contributes to our
understanding of the mechanism mediating mesoscale