Date: Sun, 22 Mar 1998 01:36 GMT
March 18, 1998 AESOPS Mooring Recovery and Benthic Processes Cruise Report 2: Off Cape Adare to the Antarctic Polar Front Despite the weather for which the Antarctic Polar Frontal Zone is famous, we have not used as much of our stock of weather contingency time as one might expect. But Mother Nature has unveiled her real face for the last week or so. We are right in the middle of the high-low trough, sandbagged by the powerful weather parcels that run through every 12 to 18 hours. We have seen winds as high as 55 knots and waves up to 20-22 feet. Under these conditions, the sea surface is covered by streaks of foam and the wind roars as though innumerable freight trains were rushing by the ship to the dark horizon. Even the inquisitive albatrosses and prions that follow the ship disappear when the storms reach their height. The ship has been receiving new WeFax imagery since we were in the Ross Sea through the efforts of electronics technician Paul Olsgaard. Captain Borkowski and Paul are using all the information available on the weather systems to predict short-term, local changes as much as possible. Our crystal ball is murky at best, but we are starting to understand the local weather cycle ever so slightly. We have had to shut down all activity overnight twice so far and have changed the schedule numerous times to deploy relatively less motion-sensitive instruments overboard when the weather is bad. But we have completed some work under marginal conditions. For example, the recovery of M-3 began in acceptable sea conditions but ended in a 40-mile-an hour gale. We made it to home base successfully anyway. We are still great believers in R/V Palmer's horse shoes, which are prominently displayed on the bridge. They were a gift to Captain Borkowski from the mooring deployment team in the fall of 1996. The coring team, led by Bob Anderson, is achieving all it planned. Pete Kalk, Flip Froelich, Marty Fleisher, George Bouchard and Roseanne Schwartz prepare and lower the piston corer, the multicorer (with 8 subcores) and the gravity corer and process samples from them at any time of the day. Marine projects coordinator Jon Alberts is always at the winch side, talking to the bridge and directing two very able ASA marine technicians. The coring team has collected eight sets of these three types of cores successfully since we left the Ross Sea. Most of the piston cores exceeded 8 meters; the longest was 8.67 meters from benthic station 3/4 (62 deg S, 170 deg W). Although investigation of core materials takes time, we have some early news. Multicores from many of the northern stations have brought up a thick fluff layer from the water-sediment boundary. The most spectacular fluff layer was recovered from Benthic Station 3/4. The off-white fluff was as thick as 3 cm, although the upper boundary was less clear than the bottom one. The white sediment is a mat of opal fiber from the shells of Rhizosolenia species. Underlying the mat, we saw a few millimeters of a layer that appeared to be composed of fecal pellets clearly demarcated from the older sediment below. Cindy Lee, Linda King and Roger Francois have been collecting plankton for their organic chemistry and radiochemical studies. They noticed that net-collectable biomass increased after we crossed the Antarctic Circle early on March 4. Most of the material in the cod end was made up of Rhizosolenia fibers, which reflect the light as though zillions of white stars were embedded in them. Linda noticed a slight smell of Phaeocystis but we have not seen a bloom of these species so far. With the help of ASA marine science technician Marc Pomeroy, Cindy and I set up a dissecting microscope in the main lab to make preliminary observations of the plankton in the material from the plankton tows and the bottom fluff from the cores. We can keep the objects in the watch-glass in focus for several milliseconds while the ship negotiates the waves. We saw primarily the opal fiber of Rhizosolenia in the net material from tows at M- 5 and 4. In the material from mooring station 3, Cindy noticed abundant pteropods. Calanus were also seen, all fat and in higher growth stages. We saw large, occasionally very large, centric frustules as well, but we could not see pennate frustules under these conditions. Radiolarians were common and diversified. There were a few foraminifer tests in the fine mesh tow material; they appeared to be monospecific, N. pachyderma. Fluff under a dissecting microscope was even more intriguing. Opal fiber remains were considerably thinner than in the net material and broken into short pieces. Pteropod shells were broken and opaque. Large diatom frustules lost their glassy appearance and were often broken. The fluff materials appeared to contain significant organic matter; they were yellow-brown with a tint of green. There were abundant fecal pellets. The contents of the pellets suggests that something is eating the glass fiber! We could spend hours at the microscope enjoying the art work of nature at the southern end of the Pacific. Were there any coccolithophorids in the fluff? This question will only be answered after we get an on-shore laboratory report. We successfully recovered three time-series sediment trap moorings south of the Antarctic Polar Front along the 170 degree W transect. First was M-5, deployed in ice-covered conditions on Jack Dymond's deployment cruise in November 1996, then M-4 and M-3. Twelve PARFLUX sediment traps and 4 IRS sediment traps tended by Cindy Lee, Mike Peterson, Daniel Montlucon and Linda King (we all work together on mooring recovery) have been brought aboard from M-5, M-4 and M-3 since we moved out of the Ross Sea. The mooring team, led by Chris Moser, has done a spectacular job bringing these complex and very large moorings in safely from the high seas. A recovery starts with Kathryn Brooksforce talking acoustically to a distant release. Rick Krishfield puts the data into a computer, and the bridge maneuvers the ship for triangulation on the mooring. When the location of the mooring is clear on the screen, Kathryn or Rick sends the release signal. Within 20 minutes, the first cluster of yellow floats pops up near the ship. With outstanding skill, the bridge maneuvers the ship to bring the spar buoy and floats within reach along the aft starboard starboard side. With a mate on the helm, the captain pilots the ship from the starboard bridge wing. The deck team throws grappling hooks to snag the array, and Chris secures the top flotation cluster to the winch. All the mooring components bob and porpoise in the waves. Now the 3- to 5-hour battle starts. The teamwork is good enough for an America's Cup contender. Tom Gann and Dennis Root stand on the edge of the stern in mustang suits, tethered with life lines. They catch instruments, unbolt and rebolt shackles and direct the removal of components of the array from the fantail. Two ASA marine techs, Mindy Kayl, Jim Woods or Jesse Doren, control the stopper lines. Winch operator Larry Costello stays in tune with the progress of the deck works and adjusts the tension of the incoming line according to the waves, the wind and the weight of the instruments. His task requires lots of experience at sea. Jon Alberts signals ship's A-frame operator and communicates with the bridge. Captain Borowski and Chief Engineer Johnny Pierce are often in the aft control room advising the A-frame operator. Kathryn takes care of the current meters, transmissometers and acoustic releases. Rick and the IRS team move flotation and traps away. Our mooring master Chris stands in the middle and judges where the main pass of the line is and when to proceed with each step. He signals for action by hand like the maestro of a symphony. Mardi Bowles records the returning instruments and flotation and writes down times under the spray in the stern. Export fluxes on the southern side of the Antarctic Polar Front have stunned us all with their distinct white appearance from the opal particles. It is safe to say that nobody has ever seen such voluminous particle fluxes in the open ocean. We were alerted when the first 13-cup trap came on board with most of its large-capacity cups filled to the neck, and we immediately began to worry about overfilling of the smaller containers on the 21-cup traps. Some high-resolution traps were overfilled at the second cup (December). Some operated until after the 10th cup (February) and gave up. The deepest traps barely recorded the whole annual cycle of the flux. Thanks to John Billings who set the electronics, all the traps worked well mechanically and electronically, but we could not capture all of this enormous export flux in the Southern Ocean. However, we have enough samples to probe into the seasonality of this enormous opal flux. We should be cautious and note that this apparently huge export flux may be deceptive. If the silicon fiber is not compacted in the sampling bottle, its volume may be giving a false impression of the size of the flux. After each trap recovery, Cindy Lee, Chi Meredith and Roger Francois settle the sediment in the original sampling bottles for several minutes and measure the height of the sediment so that the variability of particle flux measured by PARFLUX traps over the 14 months from Nov. 28, 1996 to Jan. 27, 1998 can be observed. Chi preprocesses all the trap samples immediately. We have noticed that the period of the maximum flux occurs earlier in the more southerly stations. With regards to the seasonality, the maximum flux occurred at the Ross Sea stations during late January to late April with a sharp maximum from Feb. 4 to Feb. 21. In samples from the M-5 station at 66 deg S, the bell curve was about same as the ones from the Ross Sea but the sharp maximum occurred between Jan. 18 and Feb. 4. The large flux occurred from late December to late February (1997) at the M-4 station at 63 deg S. At the M-3 station at 60 deg S, the maximum flux period started as early as late November and lasted to mid April. At M-4 and M-3, the relatively large flux was maintained without any clear maximum; export continued throughout the austral summer. Roger Francois, assisted by Sara Stillman, and Linda King collect suspended particles on 30 cm Nuclepore filters from the underway sea-water system for their N-15 and organic compound analyses. Chi Meredith and Linda run large volume in-situ pumping for Jack Dymond's trace-metal programs and many others. The biomass remaining on the filter that is observable with bare eyes seems relatively small on this cruise. Suzanne O'Hara, who directs CTD operations and handles the data, noted that fluorescence in the upper ocean indicates a distribution of only 0.2 to 0.3 mg/m3 equivalent of chlorophyll-a. Lisa Maroney, our youngest science team menber, is analyzing total chlorophyll and its degradation products in upper water column; these numbers can be used to calibrate fluorometer profiles. One interpretation is that we arrived just at the beginning of the annual inter-bloom period as recorded in the time-series sediment trap record of the last year. I understand that the SeaWiFS imagery during the December 1997 process cruise aboard R/V Revelle showed a continuous green band, while only a few patches remained in the southern area during the March cruise. In the area south of 64 deg S, a cold water layer about 50 to 200 m thick develops from brine rejected from the low-salinity surface water. This layer is not heavy enough to settle to the bottom. It forms a cold dichothermal layer between 60 to 200 m deep; this feature is sustained year-round. The minimum temperature of the dichothermal layer at the M-5 station (66 deg S, 170 deg W) was -1.75 deg C, only 0.1 degrees higher than the potential freezing temperature of seawater, according to Suzanne's calculations. Claudia Guilivi is devoting herself to Autosal calibrations on this cruise, and Suzanne will produce more precise water-column profiles soon. Although this dichothermal layer exists farther north, the minimum temperature rises and the lower boundary with the intermediate water becomes blurred, while the abrupt thermocline at the upper boundary remains. The dichothermal layer completely disappeared at the M-3 station (60 deg S, 170 deg W). The dichothermal layer limits development of the mixed layer. Fluorometer profiles are showing that chlorophyll is only distributed in the mixed layer, which is thin. The chlorophyll maximum is slightly above the upper boundary of the dichothermal layer. The question is how this thin mixed layer can support an apparently very large productivity consistently for much of the year? The same question has been raised with regard to the Sea of Okhotsk, which has the archetype of the basin-wide dichothermal layer. The SeaBeam charts generated by Suzanne O'Hara during Bob Anderson's survey cruise in September 1996 are helping us tremendously. We are taking two sets of cores (piston, gravity and multicore) at stations carefully selected by Bob, Fred Sayles and Flip Froelich. They based their choices upon the detailed sea-floor topography obtained from the survey cruise, and their cores will maximize paleoceanographic interpretations and provide a very useful archive for the future. Whenever possible we take a course that will allow us to broaden the area surveyed by the SeaBeam in the Southern Ocean. We all appreciate Suzanne's great skill and efficiency in processing SeaBeam data. Supported by the successful coring program, Fred Sayles and the benthic processes group have achieved a lot so far, and they are all very excited to be in the middle of the silicate ocean. Flip Froelich and Marty Fleisher have found that the extraction of pore water from the extremely siliceous sediment is not easy by ordinary methods. Using their powerful centrifuge and squeezing the cores under pressure, they have successfully separated a large quantity of interstitial water from the sediments for detailed analyses of variouselements. For this group, this is the time to concentrate on extracting as much pore water as possible. Bill Martin, assisted by Zev Frankel, is making onboard thorium-234 observations. These indicate that the fluff-layer material we are observing has gotten to the bottom within the last few weeks. He did not find this short-lived tracer mixed in any sediments except the uppermost few centimeters. On a preliminary basis, it looks as though the mixing rate of sediment might be very small in this area. That is good news indeed for paleoproxy researchers in the Southern Ocean. Pore water samples for investigation of carbonate chemistry in sediments deeper than the carbonate compensation depth (CCD) must be extracted in situ. That sounds like "mission impossible." Fred Sayles and the WHIMP group have gotten their highly sophisticated in-situ benthic pore water extraction device working well. They can squeeze out interstitial water at a precision of 1.5 millimeters from cores while they are still at the bottom of the ocean. Cal Eck keeps the instrument in top condition. Fred and Joanne Goudreau run laboratory analyses around the clock. Fred now tends to believe that there are significant alkalinity fluxes in the deep water at the five stations they have recently completed. Most of the particles settling in this area appeared to be silica, but pteropod shells were sometimes abundant in the water column and fluff layer, as we have noted. The shells dissolve as soon as reach the bottom at these depths. If the pteropod shell flux is consistent and large, could they play a significant role in decreasing alkalinity in the surface water of a silicate ocean? Study of sediment trap material will be helpful to answer this question. The balance with CO2 is yet to be explored. Under the leadership of Dennis Root, the mooring team recovered 11 of the 12 bio-optical moorings deployed over an area approximately 60 by 60 miles around mooring station 3. We started with the southernmost mooring at 61 deg S, 170 deg W on March 13. We were unable to find that mooring after hours of acoustic interrogation and finally decided to drag for it. Captain Borkowski maneuvered the ship in a perfect "knotting" pattern, dragging 2 km of wire with grappling hooks over the area where the mooring was supposed to be. When this approach failed, we discontinued the recovery effort and continued on to pick up 11 other bio-optical moorings. We picked up one more on March 14 before bringing in sediment trap mooring 3. After half a day of weather holding, we recovered four more bio-optical moorings on March 15 and three to the east of 170 deg W on March 16. The next storm blew us north past the northernmost bio-optical mooring site. As soon as it was over, we picked it up on our way back to mooring station 3. Mardi Bowles is answering questions about JGOFS, AESOPS and this cruise as well as about R/V Palmer from students in Sue Cowles's class at Linn-Benton Community College in Oregon. The ship's e-mail and data communication systems are running flawlessly under the management of communication systems technician Paul Huckins. His contribution to the success of this cruise is not trivial. We strongly believe that the ability to communicate with the home laboratoy enhances onboard science significantly. For example, exchanges with Steve Manganini, the shore coordinator of the mooring project, provided crucial information needed to overcome a shortage of 9/16 wire aboard the ship that we learned about after the cruise began. We are now a little past the halfway point of this cruise. We are in good shape with regards to the work schedule and leaving for a benthic station between M-2 and M-3. We are very anxious to see how the export flux and bottom sediments change. Where is the boundary between the carbonate and silicate oceans? Best regards, Susumu Honjo, Chief Scientist On behalf of the science team onboard R/V Nathaniel B. Palmer at 60 deg S, 170 deg W