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Int. J. of Marine Science 2012, Vol.2, No.7, 51
-
56
http://ijms.sophiapublisher.com
51
Research Report Open Access
Mesoscale Eddies of Arabian Sea: Physical-biological Interactions
S.A. Piontkovski
1
, N.P. Nezlin
2
1. Sultan Qaboos University, CAMS, P.O. 34, Al-Khod 123, Sultanate of Oman
2. Southern California Coastal Water Research Project, 3535 Harbor Blvd., Costa Mesa, CA 92626, USA
Corresponding author email: spiontkovski@gmail.com;
Authors
International Journal of Marine Science, 2012, Vol.2, No.7 doi: 10.5376/ijms.2012.02.0007
Received: 01 Sep., 2012
Accepted: 06 Oct., 2012
Published: 06 Nov., 2012
Copyright:
©
2012 Piontkovski et al., This is an open access article published under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:
Piontkovski et al., 2012, Mesoscale Eddies of Arabian Sea: Physical-biological Interactions, International Journal of Marine Science, Vol.2, No.7 51
-
56 (doi:
10.5376/ijms. 2012.02.0007)
Abstract
Satellite derived (SeaWIFS, TOPEX/Poseidon) products for chlorophyll-
a
concentration, sea surface heights, and
calculated kinetic energy of eddies were employed, to analyze physical-biological coupling from 1997 to 2008. It was shown that, when
cyclonic eddies dominated throughout the year, the chlorophyll-
a
concentration was positively related to the kinetic energy of eddies.
For the other years, when the total annual balance of negative to positive sea surface heights was dominated by anticyclonic eddies, the
correlation was negative. The evaluated switch contributes a useful detail to the understanding of the mechanism mediating variability
of the chlorophyll-
a
in regions with vigorous eddy fields.
Keywords
Mesoscale eddies; Arabian Sea; Chlorophyll-
a
; Remote sensing
Background
The mesoscale variability in the ocean spans the
spatial-temporal scale of motion from tens to hundreds
of km and tens to hundreds of days. Eddies with a
diameter of about 200 km and sea surface height
anomalies of up to 25 cm contribute the majority of
mesoscale variability to the World Ocean
(Chelton et
al., 2007). The kinetic energy is one of the major
characteristics of moving eddies, which is linked to sea
surface topography. The ring-shaped negative sea
surface height anomalies are used to be interpreted as
cyclonic eddies (with counter-clockwise rotation in the
northern hemisphere) in which the vertical component
of current speed is directed upward injecting nutrients
into the upper mixed layer (McGillicuddy et al., 1999).
Positive sea surface height anomalies reflect the
anticyclonic eddies with the downward motion
resulting in a depleted concentration of nutrients in
surface layers. The western Arabian Sea has a vigorous
field of mesoscale eddies (Fisher et al., 2002). The
kinetic energy of these eddies could exceed the mean
kinetic energy of the oceanic current flows (Flagg and
Kim, 1998). Eddies could markedly influence the heat
balance of waters, as well as the variation of biological
productivity in the region (Banse and Piontkovski, 2006).
The era of remote sensing enabled one to estimate
typical dimensions of mesoscale eddies in the western
Arabian Sea, as well as to track their propagation and
lifetime (Tang et al., 2002). However, an actual
mechanism and quantitative relationships underlying
physical-biological coupling are yet to be understood.
We were aimed at evaluating the relationship between
the energetic characteristics of eddies and
chlorophyll-
a
concentration.
1 Results and Discussion
Weekly time series of chlorophyll-
a
allowed us to
analyze the seasonal cycle on the scale of the western
Arabian Sea (Figure 1)
This cycle was bimodal, with two maxima corresponding
to February and September. In comparing two modes,
the summer peak tended to dominate in 80% of cases.
The summer peak used to be wider compared to the
winter peak and the variability of the summer peak (in
terms of interannual variability) is pronounced greater
than the variability of the winter peak. On average, the
chlorophyll concentration during the summer peak as
much as 2.5 times exceeded the background
concentrations featuring the off-peak months. In case
of the winter peak the difference between the modal
and background concentration is about double.