SIBER SPIS sept 2011.pdf - IMBER

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SIBER Science Plan and Implementation Strategy Comparative AS and BoB process studies should also include assessments of the benthos, benthic biogeochemical processes and fluxes, and benthic-pelagic coupling, across margins, OMZs and seasons. Existing mooring locations at key biogeochemical locations in the AS should be targeted as process study focal points. Two such sites are India’s time series station in the AS (17ºN 68ºE) at the core of the OMZ (see detailed description below) and the long-term Indo-German time series station (16ºN 60ºE) located within the upwelling zone off Oman. Known as the WAST site in the literature (Rixen et al., 1996), sediment trap observations dating back to 1986 were suspended in 1999, but were resumed again in November 2007 (Fig. 24). These sites should be maintained much like BATS and HOT for long-term measurements. They would also be appropriate sites for deployment of benthic landers in order to investigate benthic processes. Furthermore, deployment of sediment traps, benthic landers and time series samplers (e.g. cameras) below and in shelf/slope areas impacted by low OMZ waters would also be very valuable. Similar moorings should also be deployed in the central BoB for making physical and biogeochemical measurements. Both the central AS and BoB regions are currently targeted for deployment of moored instrumentation by IndOOS/RAMA (Fig. 24) and Indian investigators. Process studies could leverage on-going time series efforts as well as planned IndOOS/RAMA mooring array deployment activities. Moorings at these locations can potentially be deployed with biogeochemical sensors like those discussed above (see also Appendix IV). The IO Argo float program can also provide a physical context for carrying out comparative process studies in the AS and the BoB. The density of Argo floats in the IO is now sufficient to provide broad-scale characterization of physical variability on seasonal to interannual time scales; indeed the data density in the IO is now sufficient to allow for performing objective analyses on a weekly basis (cf., Gaillard et al., 2009). Differentiation between the two regions’ stratification conditions can be characterized, as well as their response to climate-related variability (e.g. IOD and ENSO). Any comparative process study of the AS and the BoB should start with a focused comparative analysis of the physical characteristics of the two basins. This analysis could be augmented with the deployment of Argo floats with oxygen and optical sensors, focusing in particular on deployments in the OMZ in the AS and a comparable location in the central OMZ waters of the BoB. A comparative study of the AS and the BoB could be augmented with surface measurements from ships of opportunity. Potential routes include ferry services between Chennai and Port Blair, between Kolkatta and Port Blair, and between Lakshwadeep and Kochi. Glider surveys should also be carried out, focusing on the coastal OMZ in the AS and a comparable location in the BoB, e.g. off Visakhapatnam or on the IndOOS repeat XBT line in the BoB (Fig. 24). Deployment of only two gliders, one in each basin, would provide crucial information on subsurface processes including the OMZ, the deep chlorophyll maximum and subsurface productivity. For such glider deployments, data handling, storage and distribution issues need to be worked out to make these data widely available to the oceanographic community in a timely manner. CPR surveys should also be motivated. As discussed below, efforts are already underway to establish routine surveys from India to Oman. A comparable transect should also be considered for the BoB. The ongoing WAIMOS monitoring program along the coast of western Australia provides further opportunity for initiating an international SIBER process study. WAIMOS efforts focus on shore-based and remote observations using satellites, CODAR (Coastal Ocean Dynamics Applications Radar) and glider technologies along with high-resolution coastal modeling (OFAM/ BLUELink), but ship time is limited. Establishing an offshore international time series station and process study would provide an ideal complement to these coastally-oriented observations, as well as endpoints for onshore-offshore transects and sustained measurements of the oceanic end-member properties. The maintenance of an international time series/monitoring 62
SIBER Science Plan and Implementation Strategy station could also provide much-needed ship time to support the WAIMOS coastal monitoring network. A study of at least five years duration is recommended. Relevant questions have been primarily defined in Theme 1, but quantification of the seasonality of chlorophyll distributions and primary production, as well as temporal and spatial distributions of nutrients and nutrient limitations (Theme 4) should also be targeted. Targeted process studies should also be motivated at specific sites and times that focus on the general scientific questions identified in Themes 4-6. One obvious potential study would be the hypothesized iron limitation or co-limitation and/or potential grazing control of phytoplankton production in the AS during the SWM in coastal and open ocean waters (Theme 4). In addition to basic measurements of hydrography, optics, nutrients, dissolved organics, etc., such investigations might include a suite of core measurements: ●● Phytoplankton biomass and composition (Chla, HPLC pigments, flow cytometry and microscopy) ●● Size-fractionated primary production ( 14C uptake) ●● Growth rates of different phytoplankton functional groups (dilution, pigment labeling) ●● Phytoplankton physiological indicators (e.g. fast repetition rate fluorometry) ●● Community metabolism (O2 production and consumption, net auto-/heterotrophy) ●● Micro- and mesozooplankton grazing (dilution, gut fluorescence, experimental) ●● Export flux (sediment traps, thorium deficit) ●● Bioassay experiments to assess limitation by Fe, Si and N ●● Stable isotope measurements These studies should embrace new technologies and instruments like gliders (discussed above) and also the moving vessel profiler (MVP), a versatile sampling platform with CTD, fluorometer, optical plankton counter, etc., that can be efficiently deployed from a moving vessel at full speed. Such an instrument can undertake high-resolution gridded surveys of mesoscale variability around specific experimental sites or investigate fine-scale distributional patterns associated with targeted features like filaments and eddies. Process studies are potentially important for investigating specific regions and processes. However, in general, they should play a relatively minor role in the investigation of the effects of climate change and anthropogenic impacts on the IO and its marginal seas. Rather, in this context, the role of monitoring should be emphasized along with leveraging of existing infrastructure to orchestrate long-term biogeochemical and ecosystem observations. Ben t h i c st u d i e s Benthic biogeochemical processes and benthic-pelagic coupling have important roles in global bioelement cycles and as controls on ocean productivity and climate, but have received only limited focus as part of JGOFS and other previous coordinated research programs in the IO. By including benthic process studies, and linking these to parallel pelagic studies, the SIBER program intends to address these previous shortcomings in a basin where benthic processes are particularly significant. The IO, and especially the AS and BoB, exhibit extreme monsoondriven variability in productivity (i.e. benthic food supply) and mid-water oxygen depletion that creates the largest expanse of reducing margin sediments (and associated suboxic benthic processes and fluxes) on earth. Moreover, major contrasts exist in both productivity and oxygen depletion between the AS and BoB, and both of these, as well as benthic biogeochemical processes, are subject to climate change and other anthropogenic impacts. Common sets of systematic in situ and shipboard studies are needed that will include: ●● Assessments of benthic microbial and faunal communities and sediment geochemistry 63
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