Date: Thu, 02 Apr 1998 04:59 GMT
March 31, 1998 AESOPS Mooring Recovery and Benthic Processes Cruise Report 3: From the Antarctic Polar Front to Lyttelton When the plankton net was removed from the wire at 16:30 (NZT) on March 30 at our last regular station, many of us gathered around Cindy Lee, who was in charge of this memorable event, clapping and cheering the successful conclusion of both AESOPS and the U.S. JGOFS Process Study field program. (Note: the time series field program continues.) For Bob Anderson, who has led AESOPS since its earliest days, this was a moment of triumph. We will stop the ship just before the Chatham Rise and do a final hydrocast for Roger Francois's N-15 project. We hope to arrive in Lyttelton early on April 3, depending on the weather, five days earlier than planned. The U.S. JGOFS field program began nine years ago, late March 1989, at 38 deg N, 21 deg W north of Madeira Island in the North Atlantic. I was chief scientist on that kick off cruise; only 3 science party onboard R/V Atlantis II; Steve Manganini and Rick Krishfield were with me. We are enormously touched to have witnessed history in the making. Here in the Southern Ocean, the high winds and rough seas make work challenging, regardless of whether we are south or north of the APFZ. Winds of less than 40 knots are regarded as cooperative. Up to 45 knots, we can still get in-situ pumping, plankton towing and gravity cores. Over 45 knots with a big swell, the decks are closed. In the 60-knot winds we have encountered occasionally, R/V Palmer's fate depends on the skill of the bridge. During the Arabian Sea study in 1995, the highest wind speed measured by Bob Weller's air-sea interaction buoy was about 36.5 knots during the summer monsoon. We are talking about a sea story. The weather worsened as we left 60 deg S after recovering the optical moorings and the M-3 trap mooring and completing all the benthic, coring and other sampling planned. At the benthic sampling site between M-2 and M-3, where the SeaBeam chart produced during the AESOPS survey cruise showed promising topography, the sea was extremely rough. We managed to take cores except piston cores, and Fred Sayles's group collected excellent pore water and sediment samples with the WHIMP. The weather moves quickly in the Southern Ocean. When we struggled to the M-2 location at 57 deg S, 170 deg W, the wind calmed down to the low 20's and blue sky opened to the north. The satellite images show low pressure areas marching along south of us and a high close to the northeast. How come this calm sea? Mooring master Chris Moser agreed to gamble on this apparent gift. Halfway through the recovery of the M-2 mooring, we found we were cheated. The sea quickly built up to the level at which the fan tail is usually secured. The mooring team found that the last section of the mooring was missing when the lower IRS trap smashed against the transom coming in. The wire had parted some time earlier just below that trap. Daylight was diminishing. Chris and Captain Borkowsky did quick calculations based upon Mardi Bowles's recovery time log, and R/V Palmer followed the direction of the sea. In 20 minutes, the bridge spotted the flotation of the missing section, and we recovered the rest. This part of the mooring included a beautiful deep flux sample set. In a way, we won the game from King Neptune this time. As soon as the soaking wet mooring team turned in, we had to close the wave-washed fan tail for that night. We stayed at M-2 for three days after the recovery. The decks were closed for about half this time, but onboard laboratory work proceeded as much as possible. We pushed the benthic and coring programs through little by little. The third try with the multicore brought us beautiful cores from this critical station. By March 24, the weather situation had grown difficult, with winds in the low 60's and boiling waves. The ship could not proceed northward to M-1 station; we were just hovering with the sea. WeFax and other information indicated that the weather system to the north was even worse. We took a gamble and returned south for about 100 nautical miles to the benthic station half way between M-2 and M-3 at 58 deg 30'S. Bob Anderson and I reasoned that this station could be in a zone where the front oscillated south and north during glacial and interglacial periods. A long piston core record was desirable to investigate this environmental fluctuation through the Pleistocene and Holocene, and we did not have one from this station. Going back seemed better than sitting at M-2 and waiting for the weather to turn. We ran back for 36 hours. The wind eased off near this benthic station, and we thought we had won the first inning. But halfway through the piston core deployment, the sea took off. No matter how the bridge tried, the ship pitched harder. At about 3500 m, the wire stress gauge jumped violently and we lost most of the piston corer. We lost the second inning. Pete Kalk and Bob Anderson and their coring team did not give up. They gathered spare parts and the spare 2-ton "bomb" and constructed a "giant gravity corer" with hopes that it would penetrate to the glacial sequence and return. Since we lost the piston mechanism, holding 8 m of a heavy core with the core catcher and top valve alone sounded like too wishful a thought. This make-shift corer did not retain the upper part of the core, and we thought the third inning was lost. As a final effort, the coring group tried a gravity core with an elongated tube. This returned a 2-m core, and the bottom section may have reached to the last glacial sequence. A draw. The time ran out, and we thought we had lost the game. While the corers were cleaning the giant gravity corer, however, they found that the 2-m sediment sample in the inner pipe was from a glacial era. We won after all. We see an apparent but very abrupt change in the sediments at the M-2 station (60 degrees S, 140 degrees W) compared to those farther south, although it will take more detailed analysis to substantiate these impression. This change seems to start at the station between M-2 and M-3 described above. The color of the trapped particles was much darker than we found farther south and similar to samples we are used to seeing from other parts of the ocean. Lots of Foraminifera were concentrated at the bottom of trap bottles from M-2. White color and fluffy fluff material on the top of the multicores that was a hallmark of the sediment on the south, were not found at all at M-2 and barely recognized at the station between M2 and 3. But the surface millimeter preserved a variety of planktonic Foraminifera, radiolarians and larger diatoms. However, this change may be seasonal. On the other hand, Flip Floerich and Bill Martin has found that the manganese redox depth in a cores was deep, more than 1.5 m and pore water nitrate concentration stays as high as 45 mcromoles below a few centimeters at all stations regardless the front location except in the Ross Sea. Although these are preliminary findings. Carbonate chemistry at M-1 And 2 has to wait to hear the preliminary result of WHIMP sample analysis by Fred Sayles and Joanne Goudreau. When we arrived at the M-1 mooring station at 53 deg S, 174.43 deg W on the evening of March 27, the sea was still high, but the most intense storm had moved to the northeast. We did not know what to expect at M-1; this was the trap array that had been hit by the CTD rosette cage lowered by R/V Revelle on Dec. 7 during AESOPS APFZ Process Cruise 1. Everyone was relieved when Rick Krishfield and Kathryn Brooksforce heard a normal response from the release more than 5,000 m deep at the mooring anchor. The ship's keel transponder, wired to deck units in the dry lab by Rick and Paul Olsgaard, worked outstandingly. With triangulation from four separate points using P-codes, Rick and Kathryn pinned down the location of the release within 10 m. That was an excellent start. After the accident with the CTD rosette in December, a little more than 1,100 m of the 5,440-m mooring came to the surface and was brought aboard R/V Revelle. We calculated that the rest of the mooring had only 80 lb. positive buoyancy. This small net buoyancy out of 1100 lb. total remaining with the damaged mooring would diminish when the mooring comes close to the surface by pressure difference and it would need 400 lb. for the mooring to come all the way to the surface by itself. Steve Manganini, mooring master of the deployment cruise, and Chris Moser, who assumed Steve's responsibilities during this recovery cruise, spent many weeks working on a recovery plan, advised by other mooring experts at WHOI. As a result, we had come with a recovery plan with sets of choices depending on what we found. Because our modeling efforts indicated that the chances of the mooring floating all the way to the surface were very low, we were well prepared for a grappling operation "in the air" that nobody has tried previously as far as we know of. But we had to find the mooring first. Thus the finding and fixing of the release was very good news. To our surprise, the anchor had moved approximately 1.5 km to the northeast from the original location. As we reconstruct it, R/V Revelle must have lifted the entire M-1 mooring with her CTD wire, carried it while drifting for about a mile and dropped the lower part of the mooring at the position in which we found it. Although the entire weight of M-1 exceeded 5,000 lb., the net weight balanced by the buoyancy was about 1,000 lb. and Revelle's CTD wire could hold this extra weight until M-1's wire parted. We sent the release command during the evening of March 27. With their usual skill, the bridge kept the ship within 25 to 50 m of the release location for several hours. We monitored the distance of the release throughout its ascent and were delighted that the initial ascending speed, 32 m per minute, was faster than we anticipated. As the mooring rose to 3800 m, the speed slowed down at about 8 m/minute. We estimated that the last dangling wire from the mooring lifted from the sea floor, completely suspended, at about 2:30 on the morning of March 28. When the release reached about 1,200 m, the ascending speed became less than 1 m per minute and drifting accelerated to almost 20 cm per second to north-west. After the release ascended to 2,000 m below the surface, the SIMRAD 3.5 sounder provided images of parts of the mooring. Paul and Marty Fleisher were able to confirm the ascending speed from this instrument. The chasing of the hovering mooring was not easy. Rick and Kathryn followed the kiting mooring with no string attached through the long night and made innumerable acoustic triangulation to keep track of its position. Cindy Lee, Linda King, Mardi Bowles, Sara Stillman and Mindy Kayl took turns helping to record the mooring depths. Early in the afternoon on March 28, Chris and I concluded that the mooring had stopped ascending at about 1200 m and was drifting fast toward the northeast at 25 cm/sec. It was time to be aggressive. The mooring team lowered a grappling wire with 3,000 m of 9/16" wire, three 200 lb. hooks and a 500 lb. depressor weight. Over a period of at least five hours under 40-knot winds, R/V Palmer made precise knotting patterns around the suspended mooring. Kathryn continued to keep track of the location of the release as Chris worked with the captain on the bridge. After times of knotting maneuvering, we found the distance between the ship and the release had become constant. We caught it! However, no mooring was remained on the grappling hooks when they were brought on deck. As soon as we started to range on the release again, we found that it was ascending again rapidly. At 20:30 we concluded that the release was at 160 m, suggesting that some flotation might be on the surface. Captain Borkowski turned on powerful searchlights from the bridge to scan the waves and slowly maneuvered the ship in the direction the shipboard ADCP indicated. About 45 minutes later, Captain Borkowski spotted an almost submerged float bobbing in a pitch-black sea with breaking waves under the starboard searchlight. This was the second time he succeeded in spotting flotation under rough conditions. He brought the ship around, and the mooring team successfully grabbed the cluster. It was dangerous. The waves crashed at knee height on the fan tail, and Tom and Dennis could not see the next wave that hitting the stern. The returning lines were snarled in various clumps. Chris and Jon Alberts did a great job orchestrating the recovery. We found out why the mooring ascended to the surface on its own. The line had parted below the middle trap of the array and the long sections of wire above and below it. The remaining portion of the array, with two traps and a current meter, had more buoyancy as a result. Sadly enough, the deepest sediment trap did not work. The IRS trap array above it came in upside down, and the samples were lost. A bitter result after the long fight we waged. This round King Neptune won. He badly wanted a titanium sediment trap with possibly a great set of samples as the sacrifice for letting us work in this part of the ocean. The weather improved overnight. The wind dropped to around 30 knots. We finished up all the benthic and other sampling, including piston coring. Invincible Bob, Pete and coring team made up a complete new piston core and deployed it. We left the memorable M-1 station last evening for Lyttelton, having used only three days of our weather contingency. The end of the U.S. JGOFS field program is an occasion to celebrate. But it will only be a happy occasion if we have a chance to analyze, discuss and publish all the results. If we do not get funding to complete the AESOPS and other JGOFS synthesis, our efforts would be in vain. Synthesis is not just satellite imagery and numerical modeling. A lot of useful and basic information on the global ocean flux comes from dedicated laboratory work. We U.S. JGOFS investigators and the funding agencies must do all we can to maximize the taxpayers' investment in ocean research to allow us to do the field phase of JGOFS. Over the years since U.S. JGOFS was conceived in 1984, new philosophies have emerged in ocean science. The fences between ocean physics, chemistry and biology have been disappearing. The term "biogeochemical cycles" well indicates the arrival of the new era. We now deal with the glacial past and the present and try to predict the future; thus we gain the freedom to think over the time and space without the disciplinary boundaries. On this cruise, every scientist is strongly interested in paleoproxies as a key to understanding what might happen in the future. We have developed an enormous amount of technology for JGOFS during the last decade. Microprocessor-controlled time-series sample collectors such as sediment trap moorings which work as a syschronized one array no matter how many are deployed and sophisticated bio-optical mooring array are only a couple of examples. Multicoring and WHIMP deployments have opened new approaches to understanding processes at the seafloor surface and in the sediments. The continuos high precision meteorological upper ocean data from ASI buoys have accelerated our understanding of the ocean fluxes. Those field technologies are as important and useful as satellite remote sensing and ocean modeling. After the end of the U.S. JGOFS field program, what will we do with the treasures we have obtained? We have a lot of homework to do. Thank you for reading our cruise reports. We will see you in Knoxville in June. Susumu Honjo, Chief Scientist On behalf of the science team onboard R/V Nathaniel B. Palmer (Appendix) Event Summary; R/V N. B. Palmer 98-02, McMurdo, Antarctica to Lyttelton, New Zealand. February 24 to April 3, 1998. Water Column: CTD: 16 lowering including 7 to the sea floor. In situ large volume pumping: 32 lowering. Underway suspended particles collection for N-15: >90 on 30 cm GFF/Nytex filters Net towing: 14 events. Underway pCO2 for Taro Takahashi by Suzane O'hara Moorings: All 7 time series, synchronized trap moorings were recovered. Two ice covered. One damaged mooring. Recovered 26 sediment traps. One lost from M-1. Eleven optical moorings were recovered. One mooring did not exist. WHIMP: WHIMP was lowered to the sea-floor 11 times. All satisfactory. Coring: Gravity cores: 21 Muticores: 17 lowering. Gained 120 subcores. Piston cores: 10 recovered. Average length; 8 m.