Date: Wed, 04 Mar 1998 07:12 GMT
March 4, 1998 AESOPS Mooring Recovery and Benthic Processes Cruise Report 1: Ross Sea Shelf Stations R/V Nathaniel B. Palmer left the ice pier at McMurdo Station the evening of 2/24, about 18 hours earlier than planned, to escape the ice buildup that accompanied rising winds and the bitter cold of -16 deg C. The ship cut through 7/10 to 9/10 ice almost all the way to Mooring Station 7, located at roughly 76 deg 50'S, 178 deg W. The ship's high capability and the outstanding skill of her officers and crew were well proved during this 36-hour transit. For most of the way, we were surrounded by icebergs, ranging from the size of city blocks to several hundred meters in diameter, all fresh cut and shining under the light that slanted through bright gold holes in the gray sky. At one point, the bridge counted 43 icebergs in sight. NBP 98-02, the last cruise of the last field program of U.S. JGOFS, started with a grand show in the spectacular theater of the Antarctic. Twenty-nine scientific party and 7 ASA staff are all in high sprits to tackle the enormous tasks to be completed during this 43-day cruise. I plan to submit three or four cruise reports before we get into Lyttelton by April 8. Unlike the AESOPS process cruises, however, we are all in the data collection stage, and we are not able to announce useful discoveries instantly. So please bear with us for not sending headlines such as " Green Fire" with our cruise report. We have successfully completed our sampling in the Ross Sea with two benthic stations near Station Orca (Mooring Station 7 a & b) and one near Station Sei (Mooring Station 6) in the northern Ross Sea. Both were about 600 m deep. Four gravity cores were taken from MS-7 and MS-6, and three multicores (8 sub-cores each) were recovered from MS-7. The bottom at MS-6 was packed sand and silt, and the gravity core did not penetrate much.The facilities for processing or pre-processing sediment and pore water samples onboard NBP are impressive. Sediment geochemistry laboratories from Georgia Tech, LDEO and WHOI have set up impressive laboratories on the ship as if they moved all of their facilities aboard. These benthic process groups are working night and day to extract, cut, squeeze and centrifuge the Ross Sea sediments. Groups from LDEO, WHOI and other institutions collected Ross Sea Shelf waters from deep and shallow CTD rosette casts for thorium decay series, N-15, trace metals, chlorophyll and other measurements. Large-volume in-situ pumping operations are also humming along under the command of Charlotte Meredith and Linda King. They have already made seven successful casts to collect trace metals and suspended particles in shelf waters, passing 250 to 700 liters of water through Nuclepore and GFF filters for trace metals and other programs. Shallow horizontal net tows collected a considerable mass of plankton for biochemical and radiochemical studies for Cindy Lee and Roger Francois programs. The standing crop on the Ross Sea Shelf is so high at this time that there are more than enough samples to work with. We have recovered three sediment trap moorings (including current meters and transmissometer), and all five traps worked as programmed. Two moorings were deployed about 2 nautical miles apart at Station Orca (MS-7a and b). Those two mooring were relatively short and deployed anchor first, as is the preferred procedure for ice-covered waters. The moment of landing at the ocean floor was marked by the P-code GPS. When we arrived, both sites were covered by 7/10 to 9/10 ice with a number of pressure ridges. Winds were around 15 knots and air temperature was about -10 deg C. Several icebergs passed slowly right over the mooring sites. Captain Joe Borkowski carefully judged the direction of the winds and currents, broke an oval-shaped pond in the ice about 300 m long and 200 wide with the longer axis parallel to the direction the sea was moving, and positioned the ship at the lee-side foci to release the mooring. The top cluster of yellow floats on the mooring popped to the surface right beside the ship in a few minutes among the chunks of finely crushed sea ice. Chris Moser, mooring master, and his ASA/OSU/UW/WHOI joint recovery team retrieved each mooring in about an hour and a half. The mooring recovery at MS-6 was free of sea ice, but the wind was blowing nearly 38 knots, the temperature was -5 deg C, and the snow was spitting. The mooring team's professionalism and the ship's extraordinary maneuvering skill ensured that all the components of the mooring made it onboard in spite of the weather. The heated fantail of NBP increases the safety of trap recoveries enormously. The "orange zone watch," Tom Gann and Dennis Root, received most of the rush of freezing waves through the open stern. They were the true heroes of the day. Trap samples were carefully inspected by Cindy Lee and Charlotte Meredith skillfully went through pre-processing of 85 export flux samples from the Ross Sea, each of these representing 8.5 to 34 days of the year. We can report a preliminary observation of export flux at the Ross Sea stations that some of you may find useful. The year-round time-series export flux record at the three Ross Sea stations shows a clear bell-curve maximum from April to June, late fall to early winter. The export flux of organic matter is very large, although we have to take the shallowness of the traps into account. Export flux was minimal during November and December at all stations. The apparent ratio of the summer minimum to the early winter maximum exceeds 1 to 15.This sort of late fall-early winter (late polar afternoon-evening) flux maximum has been found in many high-latitude trap stations in the northern hemisphere, including the Barents Sea and the Bering Sea. The seasonal contrast of the maximum to the minimum flux in the Ross Sea is outstanding. These observations support the hypothesis that in high-latitude marginal seas the grazers cannot consume all the primary production before they die or become disabled at the onset of winter. As a result, the raw phytoplankon material is deposited on the shelf bottom. One would be curious on the fate of those enormous fluff; while the most of the organic carbon must be quickly removed or consumed to maintain a steady state. We arrived early this morning (3/4) at Mooring Station 5, our first deep station. In addition to our pumping, coring and mooring recovery activity, Bob Anderson and Pete Kalk will deploy a piston corer and the Fred Sayles and his group will use WHIMP (Woods Hole Interstitial Marine Probe) in order to collect pore water in the deep sediment in situ for the first time on this cruise. We will keep you posted. We have a privilege of Margaret Bowles participation to this cruise. She is the editor of JGOFS News. She will be reporting for the JGOFS News primarily. In the long run, her first hand experience of a JGOFS cruise will help her to intermediate tax payers and us scientists what we have been accomplishing by coming all the way to the Southern Ocean in order to understand the global change. On behalf of the science team onboard R/V Nathaniel B. Palmer Susumu Honjo, Chief Scientist