Basic HTML Version
International Journal of Marine Science 2013, Vol.3, No.18, 145-150
http://ijms.sophiapublisher.com
149
warming phase was observed between October
through mid-December. Thus off the Masirah region,
the bandwidth of warming/cooling is about 3 months.
This region experienced increased summer warming
coupled with reduced winter cooling during the study
period. The difference in the mean annual SSTs at
Muscat and Masirah showed a clear declining trend
with a maximum difference of about 1.13
℃
during
the 1960s to a minimum (0.33
℃
) in 1991. The SST
difference, after 1991, gradually increased and was
nearly constant around 0.5
℃
with the Muscat region
being warmer. The Sea of Oman, exhibited nearly
unimodal SST distribution with only one prominent
peak in SST occurring during summer (May-September)
and a prominent low in winter (January-March).
However, a mild cooling due to local upwelling during
August-September interrupted the unimodal character
of SST in the Sea of Oman. The SST distribution off
Masirah exhibited bi-modal distribution with alternating
and shorter warming and cooling periods. Sarma et al
(2013) showed that a large shift in the SST regime
appeared to have occurred after the 1983~1984 El Nino.
The increase in negative SST anomaly in the western
Arabian Sea reduce the southwest monsoon rainfall
over India (Shukla, 1975). Izumo et al (2008) made a
similar conclusion that increasing SST along
Somalia-Oman may result in increased rainfall along
India, thus the study of SSTA off Oman has regional
significance The El Nino years and La Nina years
have good correlation with SST peaks and lows
respectively (Sarma et al., 2013), particularly when
the ENSO epochs were stronger. The range of
intra-annual variance (0.11 to 0.88) noticed off
Masirah could be associated with intra-seasonal
variability in summer monsoon forcing and the
upwelling intensity. The SST off Muscat was always
higher and the variability is centered on winter
monsoon as well as the meso-scale eddy activity. The
long-term (decadal) signal of SST indicated a decline
in standard deviation off Masirah while it marginally
increased off Muscat. The monthly distribution of
variance shows that SST variability off Muscat and off
Masirah are impacted different monsoonal forcing viz.,
southwest and northeast monsoons respectively while
the ENSO influence is seen at both locations. The Sea
of Oman and the western Arabian Sea off Masirah
showed statistically significant increase in mean
temperature with higher increase in the Sea of Oman.
The variability is fairly constant in Sea of Oman while
it is declining off Masirah after 1981~1991. The
decadal signal of SST in both areas indicates a regime
shift in the SST towards warmer ocean surface. The
monthly distribution of variance observed at the study
locations showed distinct nature of seasonal forcing
that these locations experience during a year. The
Muscat region showed low variance (<0.2
℃
) during
most part of the year except during spring-summer
transition (April) and during summer-fall transition
(September). During winter (December~March) the
SST variance gradually increased in early winter and
was lowest during peak winter (0.11
℃
) off Muscat.
Large SSH anomalies are associated with increased
incidences of harmful algal blooms (HABs) in this
region that resulted in fish mortality during post-1990
(Al-Gheilani et al., 2011; Al-Hashmi et al., 2012;
Sarma et al., 2013). The changes in SSH anomaly
could be due to warming/cooling, seasonal wind
variability or meso-scale eddy activity. These processes
are capable of inducing the upwelling of nutrients that
enhances productivity of the region and causes blooms.
The algal blooms during the post-1990s resulted in
fish mortality, disruption of desalination plants in
Oman (Al-Hashmi et al., 2012; Al-Gheilani et al.,
2011). The intense weather systems noticed during
this decade (2000~2010) also appear to be the
consequence of the increasing in the SST. The
influence of El Nino-Southern Oscillation (ENSO) is
evident on the distribution of mean annual SSTs of
Muscat and Masirah. The El Nino years and La Nina
years have strong correlation with SST peaks and lows
respectively, particularly when the ENSO epochs are
strong (Sarma et al., 2013). The frequency of harmful
algal bloom (HAB) events in the Sea of Oman and in
the western Arabian Sea, along the east coast of Oman,
increased rapidly.(Sarma et al., 2013). The lowest
number of HAB events (2) was observed in 1991
gradually increased to six by 1994. Algal blooms
increased from two to seven between 1995 and 2002
but a rapid reduction in HAB events was observed
until 2004. Between 2006 and 2010, the number of
HAB events increased dramatically from three to
fourteen. The increase in the frequency of cyclones
(Sarma, 2011), harmful algal blooms (Sarma et al.,
2013), unseasonal rains (Sarma, 2012) and meso-scale
eddies (Piontkovski et al., 2012) during the present