Date: Wed, 29 Apr 1998 08:48:41 -0400 X-Sender: eadie@glerl.noaa.gov Mime-Version: 1.0 To: eegle-pi@wings.glerl.noaa.gov From: "Brian J. Eadie" Subject: Lagrangian traps At the end of March we launched 2 drifting sequencing traps with attached transmissometers in the plume off St Joseph (see original message below for details). A brief report follows: After several adventures we retrieved them on April 16. The traps were launched in waters with approximately 3 mg/L TSM and were scheduled to have 2 day collection intervals for the first 10 days, then 3 day intervals since I assumed that mass fluxes would decline. We haven't yet calibrated the transmissometer data, but the recorded voltages (TSM) showed that the system passed through some turbidity fronts. The immediate message is in the very low trap mass fluxs, ranging from near zero to a maximum of 0.2 g/m2/day. In contrast, 1996 traps moored within the plume region reached fluxes of several hundred g/m2/day. The message is that after a few weeks (plume began March 9, traps began April 2), the materials remaining in the satellite observable plume are small particles with low settling velocities. A ballpark estimate of the settling velocity range, based on the trap and TSM data, is 0 - 0.1 m/d. This is certainly consistent with the long-lived offshore features that we observed this year in the satellite images and is clearly important as the resuspension residual in the euphotic zone. In an effort to encourage "interdisciplinariness (new word)" I encourage others to e-mail preliminary results and/or inspirations. Best --------------------------------------- Prior message This morning Andy Winkelman launched our two (satellite tracked) drifters, each equiped with a (10 bottle, 8" diameter) sequencing trap and a transmissometer (from CCIW). The drifters were deployed from the Laurentian; 1 in 25m total depth and 1 in 50m, west and northwest of Benton Harbor, respectively (within the visible plume). The instruments are at 5m below the surface and the traps are sampling at 2 day intervals for 10 days, then at 3 day intervals for 15 days. We hope that they last without grounding for the entire deployment, and plan to retrieve them after 00:05 on April 27 from the Laurentian (if possible) as part of the sediment cruise. We hope to get mass and constituent fluxes, ensemble settling velocities and changes in the plume materials settling out as the system relaxes from the event. Is there any interest in Th ? - we will measure carbon, nutrients, chlorophyll and mass > and < 60um. Don't know sample sizes, but guess 100s of mg per for the 20 samples. Anyone else interested in sub-samples ?? Poisoned with HgCl2 @ 500 mg/l concentration. ---------------------------------------------------------------------------- ------- Brian J. Eadie, PhD NOAA - Great Lakes Environmental Research Laboratory 2205 Commonwealth Blvd Ann Arbor, MI 48105 - 2945 NEW (12/07) 734 -741-2281 (voice) -2055 (fax) ---------------------------------------------------------------------------- -----