SIBER SPIS sept 2011.pdf - IMBER

SIBER
Science Plan and Implementation Strategy
the IOD, reveal standard depths of the thermocline and nutracline (Fig. 11). The SCTR is
depressed at intraseasonal and interannual time scales in association with MJO and IOD
activity. Recent studies suggest a clear impact of the MJO and IOD on the region’s upper
ocean chlorophyll concentration, with the IOD acting to significantly reduce biological response
to MJO events due to an anomalously deepened thermocline and nutracline (Resplandy et al.,
2009; Vialard et al., 2009).
Co r e q u e s t i o ns
The Southern Tropical Indian Ocean (STIO):
1) How do local and remote forcing mechanisms and the Indonesian Throughflow
combine to prescribe the physical environment that in turn drives variability in the
biological distributions, primary productivity and export flux of the southern tropical
IO
The ITF connects the Pacific and Indian Ocean basins providing an estimated input to the
IO of ~10Sv (Gordon and Fine, 1996; McCreary et al., 2007). This influences water mass
properties of the IO through heat and freshwater exchange; indeed, it has been suggested
that ITF waters propagate across the STIO and into the AS via the Somali Current during the
SWM (Song et al., 2004). Exchange and transport of nutrients, plankton and even juvenile fish
via the ITF could fundamentally influence biogeochemical and ecological variability, especially
in the southeastern IO, but the extent of this impact is unknown. What is the total nutrient
flux contributed by the ITF directly to the IO, how do ITF dynamics contribute to nutrient
fluxes regionally, and how are these nutrients subsequently distributed More specifically, do
these inputs influence the biogeochemical properties of the South Equatorial Current (SEC)
and the Leeuwin Current (LC Fig. 2) (Feng et al., 2009) and what are the dominant scales
of temporal variability of this nutrient input The LC and its attendant mesoscale features
clearly contribute significantly to the spatio-temporal variability of chemical, biological and
ecological distributions off NW Australia (Hanson et al., 2007; Muhling et al., 2007; Pearce et
al., 2006), but further studies are needed. Regional hydrological processes result in differential
phasing of phytoplankton seasonal cycles throughout the Indonesian archipelago (Kinkade
et al., 1997) while the influence of Indo-Pacific exchanges that occur in the ITF is manifested
in the distribution of plankton concentration, planktonic foraminifera and fish (Martinez et
al., 1998; Ovenden et al., 2002). What are the underlying mechanisms Is passive east to
west transport primarily responsible Are there meridional speciation gradients across the
ITF passage Do organisms take advantage of subtle circulations beyond the ITF’s zonal
transport in determining their distribution patterns How are these patterns altered in response
to perturbations associated with the IOD and MJO How significantly do freshwater inputs
from the Indonesian archipelago affect regional ecosystem and biogeochemical variability
How do the ITF and its fluctuations affect nutrient concentrations and ecosystem processes of
the Kimberley and the NW shelf of Australia
Local wind curl and the ITF fundamentally prescribe thermocline depth within the SCTR, with
modulations imposed by westward propagating Rossby waves. However, more knowledge
of the interaction of these mechanisms is needed, especially to reveal how they collectively
generate associated biogeochemical variability. Finally, as vast areas of the STIO are
remote from the terrigenous dust sources of the IO they are likely to be influenced by the
availability of dissolved Fe. Indeed, independently derived results from a coupled physicalbiogeochemical
modeling study and remote-sensing based distributions of phytoplankton
physiological state suggest that Fe limitation affects much of the STIO, particularly in the west
(Behrenfeld et al., 2009; Wiggert et al., 2006). What is the magnitude of primary production
in the SCTR and how significantly does it contribute to higher trophic levels How prominent
and widespread is Fe limitation and how does this affect the accumulation of phytoplankton
biomass that supports these higher trophic levels What contribution does the SCTR make
toward supporting commercially significant fisheries In general, what role does the SCTR
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