SIBER SPIS sept 2011.pdf - IMBER

SIBER
Science Plan and Implementation Strategy
within the equatorial and southern tropical IO during fall (Fig. 12). This develops as a result
of the combined weaker Wyrtki Jet and anomalous winds in the east that promote shoaling of
the eastern thermocline/nutracline. Analysis of a remote-sensing based production algorithm
indicates that carbon uptake can double (Murtugudde et al., 1999; Wiggert et al., 2009). How
does the altered physical environment of the IOD act to redistribute primary production, export
production and carbon flux throughout the IO and to what degree do IOD manifestations
modulate the influence of the higher frequency-mechanisms described above (e.g. the
MJO) Do the anomalous atmospheric forcings that stimulate IOD appearance also result in
pronounced change of atmospheric dust (and Fe) deposition patterns
During the 1997/98 IOD, there were also significant responses in the central AS and southern
BoB (Vinayachandran and Mathew, 2003; Wiggert et al., 2002) (Fi gs. 12 a n d 13). Moreover,
during this IOD catch per unit effort (CPUE) for the equatorial IO tuna fishery shifted eastward
(Marsac and Le Blanc, 1999; Menard et al., 2007) and there were catastrophic losses of coral
communities in western subtropical waters (Spencer et al., 2000). Is this diverse assortment
of ecosystem responses typical or is there significant variation in how IOD events alter
biogeochemical processes within the equator and STIO, or the other IO regions How do these
perturbations combine and propagate through the food web and influence apex predators such
as tuna Finally, what are the socio-economic impacts of the IOD Rainfall patterns around the
IO are significantly altered (Ashok et al., 2004; Meyers et al., 2007; Saji and Yamagata, 2003),
which must also modify patterns of runoff and nutrient loading in coastal waters of the IO rim
nations. Do these influence coastal fisheries or human health directly To what degree does
the IOD impact the intensity of coastal and open ocean OMZs and the unique biogeochemical
cycles and fluxes that are associated with them
Th e m e 3: Ph y s i c a l, b i o g e o c h e m i c a l a n d e c o l o g i c a l c o n t r a s t s
b e t w e e n t h e Ar a b i a n Se a a n d t h e Ba y o f Be n g a l
How do differences in natural and anthropogenic forcings impact the biogeochemical cycles
and ecosystem dynamics of the AS and the BoB
Ba c k g r o u n d
Although both the AS and the BoB are strongly influenced by the monsoons and are similar
in terms of size, latitude and proximity to the northern land boundary, they also have many
important physical, biogeochemical and ecological differences. These differences are
expressed, for example, in their response to global warming, which is much stronger in the AS
than in the BoB (Fig. 14), as well as in CO 2 emission. While the AS is clearly a net emitter of
CO 2 to the atmosphere (Goyet et al., 1998; Sarma et al., 1998), the BoB seems to be a sink in
winter and a weak source in summer (Fig. 5).
The most striking difference between the two basins is the impact of the monsoons. The
SWM winds are stronger over the AS, forming an intense atmospheric (Findlater) jet (Fig. 2,
u p p e r r i g ht) that drives vigorous upwelling along the coasts of Oman, Yemen and Somalia,
as indicated by high chlorophyll concentrations (Fig. 2, b o t t o m r i g ht). Surface circulation in
both basins reverses seasonally (Fig. 2, m i d d l e p a n e l s) but chlorophyll-rich filaments, jets
and eddies that extend offshore can be seen only in the western AS (Fig. 2, b o t t o m r i g ht).
Upwelling-favorable winds also blow northeast along the east coast of India during the SWM
(Fig. 2, u p p e r r i g ht), but they are much weaker and therefore do not generate such a strong
surface upwelling signature. In general, the SWM winds produce much higher levels of surface
kinetic energy in the AS compared to the BoB. Similarly, during the NEM the winds blow from
the northeast over the AS and the BoB. However, the winds reaching the AS from the Tibetan
Plateau are colder and dryer and impinge upon a less stratified and more saline surface water
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