SIBER SPIS sept 2011.pdf - IMBER

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<strong>SIBER</strong> Science Plan and Implementation Strategy basic variables, derived quantities, such as latent and sensible heat, net surface radiation, penetrative shortwave radiation, mixed-layer depth, ocean density, and dynamic height (the baroclinic component of sea level) can be computed. Thus, the mooring-based measurements can provide an excellent atmospheric and physical oceanographic observational foundation for carrying out a wide variety of biogeochemical and ecological studies. Indian Ocean Integrated Observing System 30°N 20°N WAST NEAST ASEA BoB 10°N WBC 0° WBC 10°S 20°S 30°S ITF WBC EBC 40°E 60°E 80°E 100°E 120°E Surface mooring Flux Reference Site ADCP Frequently repeated XBT lines High resolution XBT and flux lines Carbon lines Long-term sediment trap sites Deep equatorial currents Real-time and near real-time tide gauge network (20 stations in operation, ~24 planned) 3°x3° Argo profiling float array 5°x 5° drift floating buoy array Fi g u r e 24 The integrated observing system with basin-scale observations by moorings, Argo floats, XBT lines, surface-drifters and tide gauges; as well as boundary arrays to observe boundary currents off Africa (WBC), in the Arabian Sea (ASEA) and Bay of Bengal (BoB), the Indonesian Throughflow (ITF), off Australia (EBC) and deep equatorial currents. Figure modified and reproduced with permission from International CLIVAR Project Office, 2006. 58
<strong>SIBER</strong> Science Plan and Implementation Strategy The mooring array is intended to cover the major regions of ocean–atmosphere interaction in the tropical IO, namely: the AS, the BoB, the equatorial waveguide, where wind-forced intraseasonal and semi-annual current variations are prominent; the eastern and western index regions of the IO SST Dipole mode (10°N–10°S, 50–70°E; 0–10°S, 90–110°E); the thermocline ridge between 5°S and 12°S in the STIO, where wind-induced upwelling and Rossby waves in the thermocline affect SST; and the southwestern tropical IO, where ocean dynamics and air– sea interaction affect cyclone formation (Xie et al., 2002). The bulk of the array is concentrated in the area 15°N–16°S, 55–90°E (Fig. 24). Thus, the mooring array will be ideally situated to study the equatorial biogeochemical and ecological impacts of phenomena such as the IOD, MJO and Wyrtki Jets. The transmission of data to shore in real-time mode is required for monitoring evolving climatic conditions, oceanic and atmospheric model-data assimilation and analyses, weather, climate and ocean forecasting, and forecast verification. Real-time transmission also allows for accelerated scientific analysis of the observations and provides backup in case moorings are lost. A variety of biological and chemical sensors can now be deployed for extended periods on moorings, and transmission of real-time observations is potentially feasible. These sensors/ observations include in situ light transmission and spectral optical characteristics, chlorophyll fluorescence, oxygen, carbon, pH and nutrient concentrations, and acoustic measurements of zooplankton and potentially even fish. A major challenge here is integrating these biological and chemical sensors into existing moorings along with the physical sensors due to power constraints and other physical limitations. There are already precedents for simultaneous deployment of fluorescence and optical sensors on NOAA/ATLAS buoys (Chavez et al., 2000; Kuwahara et al., 2003; Subramaniam et al., 2003) in the Atlantic, Pacific and, most recently, Indian Oceans. In the system described by Subramaniam et al. (2003) that was deployed in the tropical Atlantic, the package also included an independent telemetry system that transmitted the data via the Argo network on a daily basis. Although biofouling eventually degrades data return, anti-fouling capabilities are continually evolving (Chavez et al., 2000), with extended deployments (6-12 months) featuring high-quality measurements becoming a more realistic expectation. Thus, while the servicing schedule may be longer than the length of the highestquality data from these sensors, the measurements still have great value. Efforts are currently underway to deploy biogeochemical sensors on more RAMA moorings. Specific plans and priorities for these are described in detail in Appendix IV. The ongoing Argo program in the IO is a continuation of the exploratory float measurements made during the WOCE (World Ocean Circulation Experiment). Argo is designed to obtain global 3° coverage of temperature and salinity profiles every 10 days. The data from the Argo program are highly complementary with satellite altimetry data (also sampled at 10-day intervals) for research applications and operational oceanography and the floats can be deployed with a limited suite of biological and/or chemical sensors. Specifically, Argo-compatible sensors for measuring chlorophyll and CDOM fluorescence, particle backscatter, downwelling irradiance, and oxygen concentration are available. An additional proven application of the Argo floats is to equip them with transmissometers. These so-called “Carbon Explorers” were used during the SOFEX cruises to measure the downward flux of carbon (Bishop et al., 2004). The IO to 40°S requires 450 floats to meet the Argo network design criterion of one float per 3°×3° latitude/ longitude, with 125 deployments per year needed to maintain this coverage. Deployment of these floats is ongoing and a limited number have onboard oxygen sensors, but many more with this capability can and should be deployed. Such float deployments provide a tremendous leveraging opportunity for making combined physical, biological and chemical measurements over broad scales in the IO. The potential for obtaining information about oxygen distributions is particularly valuable. At present, open ocean oxygen concentration distributions are notably under sampled throughout the IO (cf. Stramma et al., 2008), particularly in equatorial and southern hemisphere waters. 59
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