MERIDIONAL OVERTURNING VARIABILITY EXPERIMENT (MOVE)
Link to NOAA Strategic Plan: NOAA's Mission Goal 2: Understand Climate Variability and Change to Enhance Society's Ability to Plan and Respond
RESEARCH OBJECTIVES AND SPECIFIC PLANS TO ACHIEVE THEM
A present gap in the sustained ocean climate observing system are techniques and programs for monitoring the circulation and mass/heat/freshwater transports of major current systems, sometimes called “transport reference sites.” For broad-scale and deep-reaching circulations, a recently demonstrated method consists of fixed-point installations with moored and bottom-mounted instruments to obtain horizontally and vertically integrated measurements throughout the water column. The new MOVE project intends to maintain the developed elements of the first such system by taking over partial operation of a moored transport array in the Atlantic. This had been operated via the German CLIVAR program from 2000 to 2006 in the subtropical west Atlantic along 16N, in order to observe the transport fluctuations in the North Atlantic Deep Water layer.
With the new MOVE project, SIO/NOAA will operate the two geostrophic endpoint moorings between the western boundary and the Mid Atlantic Ridge (yielding dynamic height and bottom pressure differences), plus a small current meter mooring on the slope. This will be complemented on the eastern side of the Atlantic with a German-funded and operated mooring (near the Cape Verde islands). In the first years, the acquisitions for complete configuration of the moorings will take place, and the array will gradually be built up to its full implementation. In later years, routine operation will be achieved, and routine delivery of indicators about the state of the thermohaline overturning circulation at this latitude will be enabled.
RESEARCH ACCOMPLISHMENTS
A German cruise on R/V Merian was used in December 2006 to re-deploy the MOVE moorings. Due to the limited funding in Year 1, not all the required mooring hardware and sensors could be purchased. Therefore, the two new geostrophic (microcat) moorings that were deployed still use some German equipment and wire purchased with leftover German funds, and the current meter mooring on the continental slope carries entirely German equipment (current meter, flotation, acoustic release). Also the PIES that remained in the water were mainly German-supplied. Additionally, some of the flotation and microcats were leveraged from other relatable SIO research projects of Uwe Send.
The new MOVE project contributed 20 microcats, salaries for the mooring and cruise preparations, container shipments and travel of the three SIO participants in the German cruise. We also constructed new top float assemblies for the moorings, which carry new ARGOS beacons purchased (these activate after surfacing) plus recovery aids (FM radio and flasher). The joint SIO/IfM-Geomar cruise in December 2006 successfully recovered the previous MOVE moorings (plus a tomography system) and redeployed 2 microcat transport moorings, and 1 current meter mooring on the continental slope.
Problems were found with the existing PIES in the array, four of which were meant to be only visited and have data read out acoustically. All of them were found inoperative, i.e., they did not transmit data and were not acquiring data anymore. Since the release mechanism is powered separately, they could be recovered and diagnosed. A faulty battery configuration by the manufacturer had caused failure of the units one year prior to this cruise.
Because of this problem with the PIES, the April 07 NOAA NTAS cruise was used to redeploy PIES systems with corrected battery assemblies. Two new PIES purchased with NOAA funds were prepared and shipped to the NOAA Ship Ron Brown, and another three PIES were sent from Germany to complement the MOVE bottom pressure array for GRACE validation measurements. The two MOVE PIES were successfully deployed next to the microcat moorings (deployed in December), as well as two additional German PIES. The PIES are expected to operate for 4 years, and data will be retrieved each year on the NTAS cruises, when the moorings are serviced.
As such, we now have a rudimentary MOVE array operating again, with the two basic geostrophic endpoint moorings covering the North Atlantic Deep Water using microcats, plus PIES bottom pressure measurements, and a slope mooring. Next year, all the loaned equipment has to be returned and both sensors and mooring hardware must be supplied by NOAA’s support of MOVE. In the long run, the mooring coverage should be extended to the surface again, and dual PIES should be deployed at each mooring, to allow rotating the 4-year deployments with 2-year overlap—this would significantly reduce the long-term sensor drift in the bottom pressures and allow recognition of interannual variability.
Fig. 1
Total absolute transport of North Atlantic Deep Water layer from first 5 years of (German CLIVAR) project
Fig. 2
Preliminary (uncalibrated) internal (dynamic-height derived) meridional transport below 1200m relative to 5000db from the data recovered in December 2006
