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OsmoSamplers: In Situ Long-term Continuous Osmotic Water Samplers |
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The osmotic pump technology is being adapted to develop long-term electronics-free osmotic samplers. OsmoSamplers essentially consist of an osmotic pump connected to a long section of small-bore sample tubing, minimizing sample smearing. OsmoSamplers built for a 13 month deployments displacing about 16 mL/h, pull sample into a 304 m (1000') long 0.8 mm ID tube with a total volume of about 152 ml. After recovery, the tubing is sealed and cut into 300 1-m sections, each with an 0.5 ml volume, representing an approximate 1.3-day time period. Theoretical calculations show that with this configuration, diffusion within the tube will have minimum impact on peak smearing and sample integrity. Laboratory experiments show that sample interfaces remain within a 1-m section of tubing even after 4 months of sampling. To insure that no sample is lost during recovery (e.g., due to degassing), mechanical valves isolate the sample tubing during deployment and recovery. OsmoSamplers have been built and deployed in Monterey Bay, in ODP boreholes off of the North Barbados Ridge and on the Juan de Fuca ridge, and at newly formed vents on Loihi. The samplers have been tested in holes with temperatures up to 70ºC.
Figure 1: 3 month OsmoSampler for deployment in 7.6 cm ROV-drilled boreholes. The T-handle (not shown) is rotated to seal the sampler into its hole, and the lever arm operates a valve to isolate the sample coil to prevent degassing upon recovery. (Jannasch, 1996)
Figure 2: One of four OsmoSamplers being deployed into sealed (CORK'ed) ODP boreholes on the Flank of the Juan de Fuca Ridge in August 1996. The samplers are 3 m long and 7.6 cm diameter and have a 2.5 cm ID for the thermistor string to pass through. The samplers pull in 10 ml per week, up to 2500 ml in five years. This work, in collaboration with Geoff Wheat (NURP) and Miriam Kastner (SIO), was funded by JOI. The samplers are expected to be recovered and analyzed in 2000.
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