SIBER SPIS sept 2011.pdf - IMBER

SIBER
Science Plan and Implementation Strategy
this oligotrophic region needs further exploration. Similarly, the biogeochemical impact of the
LC’s anomalous (small) planktonic ecosystem structure remains elusive, as does the impact
of variability in the LC system on the transport of larvae. Finally, a better understanding of the
climate-induced fluctuations associated with the ENSO and Southern Oscillation Index modes
on the transport of biogeochemical and ecological properties of the LC is needed.
3) How do the mechanisms that cause mesoscale eddies vary between the AS and
BoB
Due to the influence of the strong and seasonally reversing monsoon winds, the AS and
BoB are highly energetic systems which generate numerous mesoscale eddies. The primary
mechanisms that generate these eddies and how these differ between the AS and the BoB
is not yet known. Further, the impact of these eddies on the biogeochemical properties of
coastal waters, ventilation of subsurface waters and distribution of the oxygen minimum
zones, warrants examination. Do these eddies impact regional biodiversity by influencing
biogeochemical properties which in turn force shifts in planktonic species composition such
as Noctiluca and/or Trichodesmium dominance in the northwestern AS (Parab et al., 2006),
and thus also higher trophic levels Are sub-mesoscale chlorophyll features and filaments
ecologically important for higher trophic levels Does eddy-induced production and/or vertical
mixing play a role in determining the intensities and distribution of the oxygen minimum zones
in the AS and the BoB
Th e m e 2: Va r i ab i l i t y o f t h e e q u a t o r i a l z o n e, s o u t h e r n t r o p i cs
a n d i n d o n es i a n t h r o u g h f l o w a n d t h e i r i m p a c ts o n e c o l o g i c a l
p r o c e s s e s a n d b i o g e o c h e m i c a l c y c l i n g
How do the unique physical dynamics of the equatorial zone of the IO impact ecological
processes and biogeochemical cycling
Ba c k g r o u n d
There is a striking contrast between equatorial biological distributions in the IO and those in
the Pacific and Atlantic Oceans. The IO typically exhibits elevated chlorophyll concentrations
in the west and highly oligotrophic conditions in the east (Fig. 2, b o t t o m p a n e l s) that result
from the westward shoaling of the thermocline and nutracline. While the physical processes
of the equatorial IO have been comprehensively investigated (see below), the associated
biogeochemical and ecological spatio-temporal variability has not, and there are few examples
of either observational or modeling efforts (Hanson et al., 2007; Resplandy et al., 2009; Waite
et al., 2007; Wiggert et al., 2006). Given the equatorial IO’s atypical, dynamic and fluctuating
physical environment, does this lead to unique adaptations and/or species complements
within the marine ecosystems If so, do these in turn lead to subtle contrasts in attendant
biogeochemical variability in comparison to the other oceans The fundamental overarching
question here is: what physical forcing mechanisms are responsible for the observed variability
in biogeochemical processes and ecosystems in equatorial IO waters and the southern
tropics
Beyond seasonal monsoon dynamics that extends southward to ~10°S, the equatorial and
southern regions of the IO are fundamentally affected by additional physical processes on
intraseasonal to interannual time scales. Within the equatorial band, eastward propagating
Wyrtki Jets occur semi-annually during intermonsoon periods, developing primarily as a result
of equatorial westerlies (Han et al., 1999; Wyrtki, 1973). The main impact of these jets on
biogeochemical distributions is to depress the thermocline/nutracline in the eastern side of
the basin upon their arrival in May and November. The equatorial wind regime precludes
development of tropical instability waves and the associated biological responses that are
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