SIBER SPIS sept 2011.pdf - IMBER

SIBER
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