Wednesday, 26 November 2008

Anchors Aweigh!

Leg 2 of Cruise 3 of the ASCLME survey aboard the R/V Fridtjof Nansen gave NOAA’s Pacific Marine Environmental Laboratory (PMEL) in Seattle, Washington the opportunity to deploy two ATLAS moorings in the western Indian Ocean. The first mooring was installed at a nominal location of 8°S, 55°E on 21 November 2008 and the second at 12°S, 55°E on 22 November 2008. These moorings are part of the Research Moored Array of African-Asian-Australian Monsoon Analysis and Prediction (RAMA), which is a multi-national effort to provide key oceanographic and marine meteorological data sets for monsoon research and forecasting. The goal is to span the Indian Ocean with an array of 46 such moorings between 15°N to 25°S. The cruise also provided the opportunity to deploy 4 Argo floats along the cruise track between the moorings. These are first PMEL Argo floats in the Indian Ocean and they fill a significant hole in Argo data coverage.

PMEL had never deployed an ATLAS mooring from the Nansen, so there was an element of suspense as to how the difficult and time consuming the operations might be. However, the surprises in store for us were all pleasant. Both deployments proceeded flawlessly, and in each case it took less than 5 hours from the time the buoy was placed in the water until the time the anchor was dropped. These successful operations were the result of a great team effort involving Mooring Technician Steve Kunze from PMEL who supervised the deployments; Chief Bosun Helge Dahl and his crew who masterfully carried out the work on deck; Captain Kjell Sandøy and his officers who were superb at maneuvering the ship in changing winds and currents; Data and Information Consultant Lucy Scott who applied her GIS skills to map echo sounder data during our pre-deployment bathymetry surveys; Chief Acoustician Tore Mørk who provided Lucy the ship’s log files during the surveys; and all the scientists who eagerly pitched in to help out on deck.

ATLAS moorings were developed at PMEL in the early 1980s and have been updated over the years with improved sensors, materials, and design. The mooring consists of a 2.8 m donut shaped float on which is mounted a 4 m high tower for meteorological measurements. The upper 700 m of the mooring line is plastic jacketed steel cable to protect against shark bite and to provide a conductor for electronic transmission of subsurface data to the CPU on the surface float. Below the steel cable is 3-4 km of nylon rope attached to a 3 metric ton anchor made of old railroad car wheels. Just above the anchor is an acoustic release that when triggered will detach from the anchor for easy recovery of all the instruments and mooring line.

ATLAS moorings measure surface wind speed and direction, air temperature, relative humidity, solar radiation, rain rate, sea surface temperature and conductivity, temperature and conductivity at several depths in the upper 500 m, and ocean velocity at 10 m depth in the surface mixed layer. Data are transmitted to shore in real-time via NOAA’s polar weather satellites and are available to researchers and operational centers world wide. You can view and download these data at
http://www.pmel.noaa.gov/tao/disdel/disdel.html







Thanks to ASCLME and the R/V Dr Fridtjof Nansen, RAMA has increased from 20 to 22 moorings and the array is now nearly 50% complete (See Rama figure below). Also in place is a fruitful partnership between PMEL and ASCLME for interdisciplinary studies in ocean circulation, climate variability, and large marine ecosystems of the western Indian Ocean. This is oceanography at its best! Schematic of RAMA as of November 2008. Solid symbols indicate those sites occupied so far. Color coding indicates national support, with year of first involvement shown in the upper right box. Open symbols indicate sites that are not yet instrumented.

Plate captions:
Top: First ATLAS bouy going over the side
Middle: Steven Kunze, Tommy Bornman & Ryan Palmer attaching temperature sensors to the mooring line
Bottom: Acoustic release ready for deployment
Left: The ATLAS succesfully deployed
Right: Steven Kunze and Mike McPhaden deploying an ARGO float

Text by: Mike McPhaden, NOAA/PMEL
Photos by: Lucy Scott, Isabelle Ansorge & Tommy Bornman

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