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The purpose of this web page is to introduce MITESS and briefly describe our ongoing trace metal time series efforts at BATS and HOT.
We developed MITESS (Moored In-situ Trace Element Serial Sampler, figure 1a) to allow for high-frequency upper-ocean time-series sampling for trace metals. This data effort is directed at understanding the variability of trace metals with respect to fluxes from the atmosphere, physical processes (mixed layer and seasonal thermocline development, mesoscale eddies, and vertical mixing), and biogeochemical activity. The sampler was originally developed with funding from the ONR, and our time series efforts near BATS (Bermuda Testbed Mooring, BTM, (Dickey et al., 1998, Deep-Sea Res. I 45:771-794) and HOT (HALE-ALOHA, D.M. Karl] are now supported by the NSF Chemical Oceanography program. In addition, a spin-off product of the development effort is ATE (Automated Trace Element sampler, figure 1b), a single-sample module of MITESS that allows personnel at BATS and HOT (and a newly-established time-series station in the Cariaco Basin) to collect uncontaminated mixed-layer trace metal samples.
MITESS was first deployed in testing on the BTM beginning in 1995 and has been on all subsequent deployments. The sampling interval reached sub-weekly resolution beginning in 1997. MITESS was deployed continuously at HALE-ALOHA from June 1997-Jan. 2000, when the mooring was discontinued. It is now deployed on the MOSEAN mooring at the same site, with near-weekly sample resolution.
MITESS is documented in the paper: Bell, J., J. Betts, and E. Boyle (2002) MITESS: A Moored In-situ Trace Element Serial Sampler for Deep-Sea Moorings, Deep-Sea Research I: 49:2103-2118.
Figure 1a: MITESS mooring assembly.
Figure 1b: ATE surface sampler, showing IR communication device .
Figure 1c: Samples collected with MITESS at the Bermuda Testbed Mooring (BTM) 1995-2000
This description is abbreviated to allow for an understanding of the operation and reliability of the sampler. Further information is available.
The instrument consists of a colony of independent sampling modules. Each sample module is designed to function independently during deployment, so failure of any one module does not affect others. For trace metal cleanliness, the exterior of the unit is constructed from ultra-high molecular weight (UHMW) polyethylene. Before being deployed, each unit is programmed for the sampling time. We communicate with a fully sealed unit by infrared transmission through the UHMW body. A timer-controlled highly-geared motor opens trace metal clean polyethylene (or teflon) bottles filled with dilute (1N) high-purity hydrochloric acid. Upon opening, the low density dilute acid is replaced by denser seawater. Complete replacement occurs within a few minutes. The timer then reverses the motor, closing and sealing the bottle until recovery. Samples are preserved by diffusion of 1N acid retained in a teflon diffusion chamber inside the bottle, acidifying the sample to pH of 2.5 within a day. The current data set is based on these unfiltered mildly acidified samples. Avoiding filtration simplifies the instrument, minimizes contamination, and as discussed in more detail in the appendix at the end of the text of the proposal, may best represent biologically-available metal. Filtered and ultrafiltered samples are obtained during mooring deployments for comparison with these unfiltered samples. Ongoing testing-and-development efforts are directed at enabling reliable filtered sample collection with MITESS.
In addition to the trace metal modules, MITESS is deployed with a WaDaR temperature recorder which records T to better than 0.01°C every ten minutes. This data allows us to evaluate the position of MITESS with respect to the thermal structure recorded by other T recorders on the moorings.
Trace metal integrity
The trace metal reliability of the device has been tested in two ways:
(1) Collecting samples in vertical profile for Pb and Fe, comparing these to profiles collected in other ways, and demonstrating "oceanographic consistency" (see figure 2)
(2) Comparing samples collected by MITESS and ATE with samples collected by previously demonstrated trace metal sampling methods.
These tests show that MITESS and ATE collect uncontaminated trace metal samples.
Figure 2: Pb and Fe profiles ("total dissolvable") in the upper 1000 m near Bermuda. May 1997 data obtained with MITESS. Note Fe minimum at 200 m, resulting from increases in mixed layer Fe as the seasonal thermocline develops. Data of J. Wu and E.A. Boyle
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This web page was last modified on Aug. 31, 2004.