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The Design Process, Evolution and Deployment of the Rapid-MOC Moorings in the Atlantic at 26.5ºN

The Design Process, Evolution and Deployment of the Rapid-MOC Moorings in the Atlantic at 26.5ºN Darren Rayner and Rob McLachlan National Oceanography Centre, Southampton. Introduction to the Rapid-MOC project.

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The Design Process, Evolution and Deployment of the Rapid-MOC Moorings in the Atlantic at 26.5ºN

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  1. The Design Process, Evolution and Deployment of the Rapid-MOC Moorings in the Atlantic at 26.5ºN Darren Rayner and Rob McLachlan National Oceanography Centre, Southampton

  2. Introduction to the Rapid-MOC project Project aim: To provide a 10 year time series of the strength and structure of the Atlantic Meridional Overturning Circulation Collaborative project between NOCS, RSMAS (University of Miami) and AOML (NOAA, Miami) Combines array of moorings across the Atlantic at 26 N, with winds from satellite scatterometry and the Florida Straits flow from a disused telephone cable between Florida and the Bahamas Mooring array first deployed in 2004 and serviced annually Array will continue to 2014 through funding of Rapid-WATCH project Evolving array design

  3. UK contribution currently consists of: • 21 moorings (9 of which “tall”) • 12 BPR landers • 2 Inverted Echosounders • US contribution currently consists of :- • 3 moorings (in WB sub-array) • 4 BPR landers (in WB sub-array) • Florida Straits Cable Introduction to the Rapid-MOC project 3 sub-arrays - Eastern Boundary (EB), Western Boundary (WB) and the Mid-Atlantic Ridge (MAR)

  4. Non-uniform drift in pressure sensor - looks exponential but detrending may remove signal we’re trying to detect 2nd year of drift more closely approximated to linear Difficult to join subsequent time-series due to pressure drift so now use overlapping time-series 1st year “tall” moorings deployed using a drop off mechanism Now use a lander tripod separate from the rest of the mooring and deployed for two years Bottom Pressure Recorders (BPRs)

  5. Example of 1st year mooring design • Main hold-up from single large steel sphere • Very little support/backup buoyancy used • Light anchor (900kg) • 3/16” diameter wire used throughout • 9 Microcat CTDs for 4700m of water column • BPR on drop-off mechanism

  6. Example of current mooring design • Staged top design with 2 steel spheres and • buoyancy above this too • Much more support/backup buoyancy • Heavier anchor (twice as heavy) • Mixture of 4 different wire diameters • (4mm, 5mm, 3/16” and 1/4”) • 16 Microcat CTDs • No BPR

  7. In-situ tension Reserve 3 x Trimsyns 50m depth 25kg 935kg 40m of 4mm wire 960kg MBL 24” Steel Sphere 90m depth Weakest Link 66kg 894kg 60m of 4mm wire 960kg MBL 37” Steel Sphere 150m depth 371kg 1129kg 630m of 5mm wire 1500kg MBL 8 x 17” glass 780m depth 543kg (at 2000m) 1271kg 3/16” wire 1814kg MBL Multi-stage top design • Top floats can be cut off and 24” SS will support the upper section • Weakest link is above main buoyancy • Assumes actual breaking load close to manufacturer’s stated minimum breaking load

  8. Design Process - Flowchart Previous experience Science requirements Site info Rough idea/sketch of mooring .csv text file of mooring design Database of materials Current profile Mooring package Adjust design • Outputs: • Backup buoyancy • Launch tension • Knockdown (max depths) • Stretch (min depths) • Required anchor weight • In-situ tension No Design OK? Working design Yes

  9. MAR1 - 2004 Backup buoyancy MAR1 - 2007

  10. Launch tension • Peak launch tension calculated from modelling • drag as the mooring falls to the seabed following • an anchor last deployment. • Design package gives warning if launch tension • is over 50% of breaking load • Heavier anchor = higher launch tension • WHOI safe anchor weight determined from • buoyancy, current profile and drag using: • Wet Anchor Weight = 1.5 x (VA + HA/0.6) • VA= vertical anchor load • HA = horizontal anchor load • Need to convert to dry anchor weight for • material being used

  11. Knockdown • Knockdown (Subduction) calculated from • mooring drag and current profile • Design package produces simple reference • plot • Aim to modify routines further to warn if • exceeds maximum operating depth • Instrument tilt can be calculated (routines • been modified to automatically do this)

  12. Summary • Brief intro into the Rapid-MOC project. • Discussed changes in the mooring designs • – BPR landers • – “tall” moorings • Example of MAR1 design from 1st year and present • Development of the multi-stage top design • Ran through the design process and gave example outputs from the design • package I use.

  13. THE END

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