Sediment Trap Recovery Cruise - TTN-055

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Date: Fri, 12 Jan 1996 17:41:00 +0000 (GMT)

Believe it or not, there is another "last" JGOFS Arabian Sea cruise. Even though folks from the previous leg ran off with the charts, we still managed to find our way to the mooring sites. Steve Manganini, Chris Moser and the WHOI/OSU teams have once again shown their stuff by successfully recovering the moorings at sites 1-5. In spite of some pretty fuzzy wuzzles (challenging snarls), the recovery team (including Brooksforce, Billings, Peterson, Gann, Hart and Bogue) maintained high spirits and good humor throughout. They are a joy to work with. We are also lucky to have Susan Kadar with us. She was a much needed and experienced hand with plankton tows, CTDs, and trap processing. In all, we recovered a complete set of samples at each depth of deployment covering every time period over the last 6 months at trap stations 1 through 4. Combined with the results from the first trap recovery cruise, this gives us a year-long uninterrupted record. Redundancy of traps and trap types (see below) allowed this remarkable collection. Perhaps this redundancy is a lesson to consider in Southern Ocean planning. Results from the sediment traps show a clear pattern of seasonal flux and will help us greatly in linking surface water processes and benthic carbon fluxes. We are all enthusiastic about getting these samples back to the lab, and to tying in our results with those from the process cruises! The recovered moorings included 16 OSU/WHOI (OW) time-series sediment traps. The sample changers of all 16 of the OW traps functioned perfectly. All traps collected material through the beginning of the SW monsoon. As expected, fluxes were extremely high at that time. The cups were timed to advance more quickly during the high flux periods, but the peak flux was later than expected. Clogging occurred in 21-cup traps in the uppermost waters due to the extremely high influx of material at this time. This possibility had been forseen and "redundant" 13-cup MK7 traps with larger delivery spouts that did not clog had been placed just above the smaller-aperture traps. A total of 255 samples were returned to the surface. Collections from mooring 5 were sub-sampled for trace metals and nutrients immediately, and heights of sediment in the collection cups recorded for all mooring samples. Sediment heights provided an exciting first glimpse of flux patterns. The recovered moorings also included 8 UW/SKIO/SUNY (USS) arrays. The USS arrays held 4 traps each, 3 with swimmer exclusion (IRS) valves, and 1 open trap without a valve. Two of the USS IRS traps also had time-series carousels. A complete set of time-series samples was collected at each depth and site, with one or both of the IRS traps with carousels working perfectly on each array. Time-integrated IRS and open traps also collected samples at each depth and site for direct comparison and analysis of the contribution of swimmers. Swimmers were rampant in the shallow (ca. 500 m) open traps, and present in deeper open traps as well, whereas the exclusion valves were effective at minimizing visible swimmers in the IRS traps. The Hedges/Lee/Montlucon splitting team managed to work up a lather with more than 200 samples returned that were split, filtered and frozen on board. Initial surveilance of samples (height of material in the sample cups) shows a dramatic pulse-like delivery of material during the SW monsoon. Fluxes appear to be roughly 2-3 times those of the previous 6-month deployment. Agreement between duplicate 13- and 21-cup OW traps was excellent when comparison was possible. The USS traps showed a clear attenuation of material with depth and hint at a decrease in surface flux away from the coast. Both the OW and the USS traps show a single influx of material closest to the coast with multiple, but distinct, pulses further from land. Microscopic analysis by Misho Stirn and his crew, Adnan and Khamis, from Sultan Qaboos University indicated that smaller diatoms found in surface waters were not present in material collected by mid-depth traps, and even robust, larger diatoms were gone at deeper depths. Calcareous material apparently was well preserved, as expected. Mike R. was busy on the CTD with 20 casts completed. Suspended particles were collected at trap stations for Bob Bidigare for stable carbon isotope measurement, and for the organic geochemistry group (Wakeham/Hedges/Lee) for biochemical analyses. Roger Francois collected particles at trap stations and throughout the cruise for stable nitrogen isotope measurements of PON. He also collected seawater for nitrogen isotope analysis of nitrate, while samples were taken for Bidigare for carbon isotope analyses of DIC. Plankton was collected at each trap site and daily during transit to the Seychelles. Just after recovering the mooring at Station 4, we were treated to a Noctiluca bloom. It was great fun looking at all the symbiotic flagellates inside them. Plankton will be analyzed for species composition and abundance as well as chlorophyll biomass (Stirn). At the trap sites, plankton will also be analyzed for organic composition. Brenda Boleyn was a big help with the plankton tows and identifying creatures of the deep. Goldendale Middle School (WA) 7th-graders are getting a daily feed of ship position and weather data courtesy of marine-tech Neil Bogue who is also answering questions the students send over email. Some future oceanographers may result! Major inroads into training for the next international ping-pong championship were made during the steam south to the Seychelles, not to mention a visit from King Neptune. As usual, Captain Al and the crew of the Thompson have been outstanding. We continue to be impressed with their efficiency, competence and geniality. cindy lee is