The Neutrally Buoyant Sediment Trap A new tool for “Twilight Zone” exploration
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The Neutrally Buoyant Sediment Trap A new tool for “Twilight Zone” exploration James Valdes and Ken Buesseler, Woods Hole Oceanographic Institution Paper Number OS26A-10 NBST - A NEW WAY TO CATCH THE RAIN INTRODUCTION LOGO NBST BALLAST CONSIDERATIONS _ WORKSHEET DEPTH RECORDS, 150, 300, 500 dB – HOTS & K2 NBST– II CONCLUSIONS, OBSERVATIONS and RECOMMENDATIONS RECOVERY AIDS Ballastprep July /August2005 NBST depth weight traps 1-5 traps 6-10 equal brine x 5 w t_cac W T_DRY W T_W ET density temp salinity setA setB AW 1.04940 11 * A 150 1216.4 841.9 847.4 55.0 314.1 33.7 38.7 1.02740 2.6274 33.5876 # 313.6 300 1236.7 831.2 836.6 A + 6 52.3 347.8 0 1.02847 3.2902 34.0135 ^ +34.2 500 1254.8 820.2 825.6 49.6 379.6 31.8 36.5 1.02956 3.1702 34.1956 12 B 150 1207.2 829.8 836.0 55.0 316.2 -33.2 38.1 * # 315 300 1227.0 818.2 825.3 A + 6 52.3 349.4 0.0 ^ + 34.4 500 1244.2 807.9 814.2 49.6 380.4 31.0 35.6 13 * C 150 959.8 814.1 803.4 55.0 90.7 -33.7 -38.7 # 89.7 300 979.9 803.4 792.7 B + 10 52.3 124.2 0.0 ^ 34.4 500 997.5 792.5 781.8 49.6 155.4 31.2 35.8 14 * D 150 1050.7 833.4 822.5 55.0 162.3 -33.1 -38 # 161.2 300 1070.4 822.7 811.8 B + 11 52.3 195.4 0 ^ + 34.2 500 1087.6 811.9 801.1 49.6 226.1 30.7 35.2 15 E 150 1018.7 832.8 823.1 55.0 130.9 -33.7 -38.7 * # 130.2 300 1038.9 822 812.4 B + 10 52.3 164.6 0 ************************ ^ 34.4 500 1056.7 811 801.4 49.6 196.1 31.5 36.2 ADD Lg W asher externally 16 F 150 1219.1 843.9 827.1 55.0 320.2 -34.2 -39.3 +23gm WW # 320.1 300 1239.8 833.1 816.2 A + 17 52.3 354.4 0 *********************** * ^ 34.3 500 1258.3 822.1 805.3 49.6 386.6 32.2 37 17 G 150 1016.4 837.8 843.3 55.0 118.1 -30.4 -34.9 # 118.2 300 1033.3 826.9 832.5 A + 5 52.3 148.5 0.0 * ^ 30.3 500 1056.1 815.9 821.5 49.6 185.1 36.6 42.0 W ashers Jul-04 Jul-05 W W =AW -(Vol *D EN ) W W = A W *((D wash-D w)/D w ash) W W = Vol (D en1 -D en2) AW = W W/K /K W W =AW * 1.1494 1.1496 K= (D wash-D w )/D wash D w ash=7.9 AW = W W *.86997 B allastfor300 dB +/-external w eightchange 1. Profiling ALACEs and Other Advances in Autonomous Subsurface Floats, Davis et all Journal of Atmospheric and Oceanic technology:Vol.18,No.6,pp.982-983 We have recently developed and deployed for the first time in support of a major field experiment (VERTIGO) an improved sediment trap that is designed around a neutrally buoyant float (1). Since ocean particles sink slowly (10's-100's m/day) relative to ocean currents (km/day) it becomes extremely difficult to collect particles from a fixed or slowly moving platform. The NBST drifts with the currents, thus eliminating most of the hydrodynamic effects which can lead to particle sorting and flux biases. Our NBST opens up a new window to study more accurately the rain of particles out of the upper ocean, in the ocean’s “twilight zone”. The NBST is autonomous, it incorporates a dedicated controller (u-processor) which oversees all aspects of the mission from the deployment to the recovery. Over the term of it’s deployment (3 - 5 days nom.) the instrument actively monitors it’s depth and adjusts it’s displacement to maintain the pre- programmed depth, +/- 10 dB. At the conclusion of the mission a motorized pin is retracted closing the covers on the PITS style sample tubes prior to it’s returning to the surface. Once on the surface a suite of recovery aids facilitates it’s relocation and recovery. Instrument ballasting is crucial to the success of the mission. The hull assembly is weighed under pressure to determine it’s buoyancy and compressibility. All of the external components, including the brine NBST illuminated by ship’s spotlight at recovery. ADD PICTURE OF ENDCAP HERE End cap picture here HOTS -second deploym ent(alldepths) 0 1000 2000 3000 4000 5000 6000 7000 1 12 23 34 45 56 67 78 89 100 111 122 133 144 155 166 177 188 199 210 221 232 243 254 265 Tim e -30 m in /tic D ep th (c K2 -second deploym ent(alldepths) 0 1000 2000 3000 4000 5000 6000 1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106 113 120 127 134 141 148 155 162 169 176 183 190 197 204 211 218 225 232 239 246 253 Tim e -30 m in / tic D epth (cB ) In order to accurately set the operating depth the instruments overall mass, displacement and compressibility must be quantified. A worksheet was developed which details the necessary weight to be added for the various depths and trap assemblies for each instrument and deployment. Trim weights (washers) are added externally to facilitate ballast adjustments at sea. The addition of a single 1/2 inch washer is equivalent to approximately 50 meters depth change in the ocean. ` The NBST exhibits a small surface profile. Incorporated into the design of the NBST are a number of recovery aids. Argos / GPS relocation beacon - A single antenna functions for both Argos and GPS, position data are embedded in the data stream of the Argos satellite transmitter. LED Flasher – this Depth records from deployments at HOTS and K2 are shown above. Note that in all cases the instruments settled at the intended depths. The NBST took no corrective action if within +/- 10 dB of the programmed depth. The K2 deployments utilized a modified launch algorithm which resulted in a larger overshoot at deployment in an effort to reach the neutral depth in a shorter period of time. The ballast was adjusted on the 500 meter K2 instrument to minimize the launch transient. The NBST has proven to be a cost effective, practical and reliable means of sampling particle flux in the twilight zone, there have been no instrument losses in the last 33 deployments. Multiple deployments at a single depth during K2 resulted in the NBSTs (3 ea.) surfacing within 100 meters of each other after 3+ days at depth ! These were several miles from the surface tethered PITs arrays. Additional deployments should be
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The Neutrally Buoyant Sediment Trap A new tool for “Twilight Zone” exploration James Valdes and Ken Buesseler, Woods Hole Oceanographic Institution Paper Number OS26A-10. - PowerPoint PPT Presentation
Transcript of The Neutrally Buoyant Sediment Trap A new tool for “Twilight Zone” exploration
The Neutrally Buoyant Sediment Trap A new tool for “Twilight Zone” exploration James Valdes and Ken Buesseler, Woods Hole Oceanographic Institution
Paper Number OS26A-10
NBST - A NEW WAY TO CATCH THE RAIN INTRODUCTION
LOGO
NBST BALLAST CONSIDERATIONS _ WORKSHEET DEPTH RECORDS, 150, 300, 500 dB – HOTS & K2
NBST– II
CONCLUSIONS, OBSERVATIONS and RECOMMENDATIONS
RECOVERY AIDS
Ballast prep July / August 2005
NBST depth weight traps 1-5 traps 6-10 equal brine x 5 wt_cac WT_DRY WT_WET density temp salinityset A set B AW 1.04940
11 * A 150 1216.4 841.9 847.4 55.0 314.1 33.7 38.7 1.02740 2.6274 33.5876# 313.6 300 1236.7 831.2 836.6 A + 6 52.3 347.8 0 1.02847 3.2902 34.0135^ +34.2 500 1254.8 820.2 825.6 49.6 379.6 31.8 36.5 1.02956 3.1702 34.1956
12 B 150 1207.2 829.8 836.0 55.0 316.2 -33.2 38.1* # 315 300 1227.0 818.2 825.3 A + 6 52.3 349.4 0.0 ^ + 34.4 500 1244.2 807.9 814.2 49.6 380.4 31.0 35.6
13 * C 150 959.8 814.1 803.4 55.0 90.7 -33.7 -38.7 # 89.7 300 979.9 803.4 792.7 B + 10 52.3 124.2 0.0 ^ 34.4 500 997.5 792.5 781.8 49.6 155.4 31.2 35.8
14 * D 150 1050.7 833.4 822.5 55.0 162.3 -33.1 -38# 161.2 300 1070.4 822.7 811.8 B + 11 52.3 195.4 0^ + 34.2 500 1087.6 811.9 801.1 49.6 226.1 30.7 35.2
15 E 150 1018.7 832.8 823.1 55.0 130.9 -33.7 -38.7* # 130.2 300 1038.9 822 812.4 B + 10 52.3 164.6 0 ************************^ 34.4 500 1056.7 811 801.4 49.6 196.1 31.5 36.2 ADD Lg Washer
externally 16 F 150 1219.1 843.9 827.1 55.0 320.2 -34.2 -39.3 +23gm WW# 320.1 300 1239.8 833.1 816.2 A + 17 52.3 354.4 0 ************************ ^ 34.3 500 1258.3 822.1 805.3 49.6 386.6 32.2 37
17 G 150 1016.4 837.8 843.3 55.0 118.1 -30.4 -34.9# 118.2 300 1033.3 826.9 832.5 A + 5 52.3 148.5 0.0* ^ 30.3 500 1056.1 815.9 821.5 49.6 185.1 36.6 42.0
Washers Jul-04 Jul-05 WW=AW-(Vol * DEN)WW= AW*((Dwash-Dw)/Dwash) WW= Vol (Den1 - Den2)AW= WW/K) / K WW=AW * 1.1494 1.1496 K= (Dwash-Dw)/Dwash
Dwash=7.9 AW= WW *.86997Ballast for 300 dB +/- external weight change
1. Profiling ALACEs and Other Advances in Autonomous Subsurface Floats, Davis et all Journal of Atmospheric and Oceanic technology:Vol.18,No.6,pp.982-983
We have recently developed and deployed for the first time in support of a major field experiment (VERTIGO) an improved sediment trap that is designed around a neutrally buoyant float (1). Since ocean particles sink slowly (10's-100's m/day) relative to ocean currents (km/day) it becomes extremely difficult to collect particles from a fixed or slowly moving platform. The NBST drifts with the currents, thus eliminating most of the hydrodynamic effects which can lead to particle sorting and flux biases. Our NBST opens up a new window to study more accurately the rain of particles out of the upper ocean, in the ocean’s “twilight zone”.
The NBST is autonomous, it incorporates a dedicated controller (u-processor) which oversees all aspects of the mission from the deployment to the recovery.
Over the term of it’s deployment (3 - 5 days nom.) the instrument actively monitors it’s depth and adjusts it’s displacement to maintain the pre-programmed depth, +/- 10 dB. At the conclusion of the mission a motorized pin is retracted closing the covers on the PITS style sample tubes prior to it’s returning to the surface. Once on the surface a suite of recovery aids facilitates it’s relocation and recovery.
Instrument ballasting is crucial to the success of the mission. The hull assembly is weighed under pressure to determine it’s buoyancy and compressibility. All of the external components, including the brine solution, must be characterized when calculating the weight to be added to send to instrument to the desired depth.
There are 5 polycarbonate sample tubes per instrument (4.75 id x 23.0 Inches) with an approximate 5:1 aspect ratio. These incorporate an internal baffle and a “Clap Trap” closure mechanism.
Night recoveries – with a known GPS position and the flasher -were nearly routine. Most instruments were recovered within an hour of their reaching the surface. We were able to monitor the satellite uplink transmission with a shipboard RDF. Once within range, a nominal 5 – 8 miles, we could decode the embedded GPS position to quickly close on the instrument at the surface.
NBST illuminated by ship’s spotlight at recovery.
ADD PICTURE OF ENDCAP HERE
End cap picture here
HOTS - second deployment (all depths)
0
1000
2000
3000
4000
5000
6000
7000
1 12 23 34 45 56 67 78 89 100 111 122 133 144 155 166 177 188 199 210 221 232 243 254 265
Time - 30 min / tic
Dep
th (
cB
)
K2 - second deployment (all depths)
0
1000
2000
3000
4000
5000
6000
1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106 113 120 127 134 141 148 155 162 169 176 183 190 197 204 211 218 225 232 239 246 253
Time - 30 min / tic
Dep
th (
cB)In order to accurately set the operating depth the instruments
overall mass, displacement and compressibility must be quantified. A worksheet was developed which details the necessary weight to be added for the various depths and trap assemblies for each instrument and deployment. Trim weights (washers) are added externally to facilitate ballast adjustments at sea. The addition of a single 1/2 inch washer is equivalent to approximately 50 meters depth change in the ocean.
`
The NBST exhibits a small surface profile. Incorporated into the design of the NBST are a number of recovery aids.
Argos / GPS relocation beacon - A single antenna functions for both Argos and GPS, position data are embedded in the data stream of the Argos satellite transmitter.
LED Flasher – this low power flasher is visible at up to 3 miles under ideal conditions.
Painted top cap – enhances visibility during daytime recovery.
Depth records from deployments at HOTS and K2 are shown above. Note that in all cases the instruments settled at the intended depths. The NBST took no corrective action if within +/- 10 dB of the programmed depth. The K2 deployments utilized a modified launch algorithm which resulted in a larger overshoot at deployment in an effort to reach the neutral depth in a shorter period of time. The ballast was adjusted on the 500 meter K2 instrument to minimize the launch transient.
The NBST has proven to be a cost effective, practical and reliable means of sampling particle flux in the twilight zone, there have been no instrument losses in the last 33 deployments.
Multiple deployments at a single depth during K2 resulted in the NBSTs (3 ea.) surfacing within 100 meters of each other after 3+ days at depth ! These were several miles from the surface tethered PITs arrays.
Additional deployments should be made under a variety of sea states and particle flux conditions to quantify the collection characteristics of the NBST.
