SIBER SPIS sept 2011.pdf - IMBER

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SIBER Science Plan and Implementation Strategy These sites include, for example, 16°S 55°E; 80°S 67°E in the Seychelles-Chagos Thermocline Ridge (SCTR) region and in the subduction zone in the SE tropical IO (97°E 26°S). These are regions of biogeochemical interest where additional measurements would enhance the planned physical and air-sea flux measurements. Site selection for biogeochemical sensors is informed by remotely sensed chlorophyll variability. An animation of this variability (provided by Pete Strutton at http://www.imber. info/SIBER_downloads.html) shows climatological monthly chlorophyll with the eight RAMA Flux Reference Sites plotted as black circles. These animations show that the AS and BoB Flux Reference Sites are crucial locations for deploying biogeochemical sensors on RAMA moorings. These locations will also potentially have the further benefit of nearby sediment trap moorings (Prasanna Kumar, personal communication). At the western SCTR site (8°S 67°E) some interesting phytoplankton iron-stress indications are suggested by biogeochemical model results (Wiggert et al., 2006) and MODIS-obtained chlfluorescence, as recently reported in Behrenfeld et al. (2009). Moreover, the site is influenced by the IOD, with the subsurface biological response being difficult to perceive with remote sensing platforms, thus making moored in situ observations a paramount need (Vialard et al., 2009). 30°N 20°N June 2010 10°N 0° 10°S 20°S 30°S 40°E 60°E 80°E 100°E 120°E Surface mooring Acoustic Doppler Current Profiler (ACDP) Flux Reference Site Solid = Existing Deep ocean mooring Open = Planned Japan (2000) India (2000) USA/India (2004) USA/Indonesia (2006) USA/France (2007) China/Indonesia (2007) USA/ASCLME (2008) Fi g u r e A4.1 Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA). Note that the filled symbols represent assets deployed as of June 2010. Reproduced with permission from McPhaden et al. (2009) 90
SIBER Science Plan and Implementation Strategy The site off SW Indonesia (5°S 95°E) would be the flux site most strongly impacted by the IOD, with the eastern tropical IO undergoing significant biogeochemical alteration during these events. A recent analysis of satellite-observed interannual chlorophyll variability, combined with ocean color based estimates of net primary production (NPP), reveals that the eastern IO from the equator down to ~ 8°S realizes significant enhancement of phytoplankton biomass (Wiggert et al., 2009). The NPP estimates show that local production rates can attain up to a 100% increase, with an overall regional increase of >40% recorded during the 1997/98 IOD. The time series of climatological chlorophyll is plotted for each of the eight Flux Reference Sites in Fig. A4.2 (note that the y scale on the two plots is different). The upper panel shows the four western sites and the lower panel is the four eastern sites. The western sites are of general interest due to their high biological variability. By contrast, the eastern sites have much lower variability but are interesting for the reasons discussed above. In addition, while productivity appears low and invariant at the eastern sites in the monthly climatological maps, model results (Jerry Wiggert, personal communication) suggest that these sites should experience short-term pulses of physical and biological variability that are not revealed by these coarse resolution (monthly) climatologies. Higher temporal resolution measurements are required to validate these results. In addition, one interesting aspect of the 26°S 97°E mooring is that numerous eddies come off the Leeuwin Current and the mooring might be able to capture the biogeochemical impact of these. Research is currently being carried out at Oregon State University (USA) focusing on these features, i.e. satellite analyses of the sea surface temperature and chlorophyll anomalies associated with these eddies (see animation provided by Pete Gaube and Dudley Chelton at http://www.imber.info/SIBER_downloads.html). Given the preceding discussion, it is difficult to prioritize the RAMA Flux Reference Sites for chl (mg m-3) 1 0.8 0.6 0.4 0.2 0 0,2 16°S 55°E EQ 55°E 15°N 65°E 8°S 67°E J F M A M J J A S O N D chl (mg m-3) 0,1 0 EQ 80°E 15N 90°E 5°S 95°E 26°S 97°E Fi g u r e A4.2 Time series of climatological chlorophyll plotted for each of the eight Flux Reference Sites. Note that the y scale on the two plots is different. The upper panel shows the four western sites and the lower panel the four eastern sites. 91
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