United States Antarctic Journal Report
US-China collaborative research program on particulate organic matter production and export in the Southern Indian Ocean
University of Maine, Orono, ME 04469
University of Southern Mississippi
Stennis Space Center, MS 39529
During the 1998-99 austral summer, a field-based Southern Ocean research program was initiated through a collaborative agreement between the United States agencies of the National Oceanic and Atmospheric Administration and the National Science Foundation, and the Chinese Arctic and Antarctic Administration (Beijing), the State Oceanic Administration (SOA) of China, and the Chinese Polar Research Institute (Shanghai). The primary scientific objectives of the collaboration are to measure the production and export (or flux) of particulate organic matter in the Indian Ocean Sector of the Southern Ocean, specifically within the region of Prydz Bay (figure 1). Such measurements are necessary to quantify the amount of atmospheric carbon that is removed to the interior ocean via biological processes, thus representing a potentially significant factor involved in global carbon cycling budgets. The present project is a first-time field collaboration between the United States and the Chinese to study carbon production and export dynamics in the Southern Ocean.
The Chinese polar research vessel the Xue Long ("Snow Dragon", 167 m length) has completed annual resupply cruises from Shanghai to the Chinese Zhongshan Station in Prydz Bay beginning in 1989 (figures 1 and 2 ). An important component of the annual cruises is the completion by Chinese scientists of a series of hydrographic and water sampling stations in Prydz Bay and immediately adjacent areas. The suite of scientific activities conducted include conductivity-temperature-depth (CTD) and Acoustic Doppler profiling, and measurements of primary productivity, dissolved nutrient concentrations, suspended mass of particulate organic carbon (POC), and zooplankton and phytoplankton biomass. Up to 37 such stations are completed annually between approximately 62o-69o S and 68o-108o E encompassing Prydz Bay and its adjacent Southern Indian Ocean Sector near the Antarctic continent (figure 1; Ning et al., 1993). In November 1998 we joined the Xue Long in Freemantle, Australia, transiting to Prydz Bay in order to participate in the 1998-99 station activities and to deploy a time-series sediment trap mooring in the deep waters north of Prydz Bay (figure 1). The subsurface, bottom tethered mooring deployed in 4000 m of water at 62o 28.63’ S, 72o 58.55’ E, consists of three, high resolution time-sequencing sediment traps placed at depths of 1400, 2400, and 3400 meters (m) and a current meter at 1380 m, (figures 1 and 3 ). The sediment traps are of the same design as those used in the recent U.S. Southern Ocean Global Ocean Flux Study in the Ross Sea, consisting of a large aperture (0.5 square meter opening) cone and a microprocessor-controlled, rotating carousel of sample cups (Honjo and Doherty, 1988). In the present study, sinking particulate samples are to be collected simultaneously by the three time-sequencing traps from December 1998 through December 1999 on a 17 day frequency from December 1998 through March 1999, a 40 day frequency from the end of March to late November 1999, and a 17 day frequency from the end of November through the end of December 1999. All sediment trap sample cups were filled with a 4% buffered (pH of 8.0) formalin/seawater solution prior to deployment in order to prevent bacterial oxidation of the particulate material. The acoustic current meter located at 1380 m on the mooring will record current speed in three directional vectors, tilt angle, and water temperature every five minutes over the approximate twelve month mooring deployment period.
Seventeen of the anticipated 27 Chinese hydrographic and water sampling stations were completed during our participation in the Xue Long activities from late November 1998 to January 1999 in Prydz Bay ( stations shown in figure 1). The remaining stations were conducted in February following the break-up of the fairly heavy seasonal pack ice in Prydz Bay after our January departure from the ship. Supplied with 10 liter Niskin bottles from the United States Antarctic Program and our own SeaBird CTD and SeaTech transmissometer (25 centimeter beam path-length), we obtained beam attenuation and suspended particle mass (SPM) profiles from seven of the first seventeen Chinese hydrographic stations, and 0-200 m CTD profiles from ten of the 17 Chinese stations (figure 1). SPM values ranged from 0.2-0.8 milligrams/liter (mg/l) in the upper 50 m at all stations, with minimal values of <0.1 mg/l below 100 m at all stations. A subsurface SPM peak at 50 m was observed at several stations, and was assumed to be the result of a subsurface chlorophyll maximum. Confirmation of a 50 m chlorophyll maximum along with other pertinent water column data sets will be forthcoming from our Chinese colleagues following the Xue Long’s return to Shanghai in April 1999. The Chinese scientists with whom we worked to complete the suite of hydrographic/water sampling stations and deploy the mooring, were from the Second Institute of Oceanography (Hangzhou), Xiamen University (Xiamen), the First Institute of Oceanography (Qingdao), and the Marine Environmental Forecasting Center, (Beijing).
The near-future plans for the continuation of the research collaboration involves meetings in China during the fall of 1999 to share and discuss the 1998-1999 water column data sets and discuss plans for the 1999-2000 Prydz Bay expedition. Following the recovery of the 1998-1999 sediment trap samples in early 2000, sample splits will be provided to our Chinese colleagues for their use. We will complete a suite of geochemical and isotopic analyses according to JGOFS protocol and following the standard procedures detailed in Pilskaln and Paduan (1992) and Pilskaln et al. (1996). Our long range plan is to continue the collaborative Prydz Bay cruise activities with our Chinese colleagues and annually redeploy the sediment trap mooring for a period of several years. Recently initiated and planned field programs by the Australians and the Japanese in the Prydz Bay region offer great potential for a larger-scale, international collaborative research effort in this sector of the Southern Ocean.
The POC export/sediment trap project in Prydz Bay is supported by the National Science Foundation Office of Polar Programs grant # OPP-9726186 (to Pilskaln); support for Chinese ship-time and hydrographic station work is provided by the Chinese Arctic and Antarctic Administration and the State Oceanic Administration of China.References
Honjo, S. and K.W. Doherty. 1988. Large aperture time-series sediment traps: design objectives, construction and application. Deep-Sea Research, 35(1): 133-149.
Ning, X., Z. Liu, J. Shi, G. Zhu and M. Gong. 1993. Size-fractionated biomass and productivity of phytoplankton in Prydz Bay and the adjacent sector of the Southern Ocean during the austral summer 1990/1991. Korean Journal of Polar Research, 4(2): 17-28.
Pilskaln, C.H. and J.B. Paduan. 1992. Laboratory techniques for the handling and geochemical analysis of water column particulate and surface sediment samples. MBARI Technical Report #92-9: 22 p.
Pilskaln, C.H., J.B. Paduan, F.P. Chavez, R.Y. Anderson and W.M. Berelson. 1996. Carbon export and regeneration in the coastal upwelling system of Monterey Bay, central California. Journal of Marine Research, 54: 1149-1178.
Figure 1. Location of 1998-1999 Prydz Bay hydrographic and water sampling stations and sediment trap mooring site within the Indian Ocean Sector of the Southern Ocean. Chinese hydrographic and water sampling stations completed by early January 1999 are shown; those stations where suspended particle mass (SPM) profiles were completed are denoted by "*". Time-series sediment trap mooring site designated by large star.
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Figure 2. Photograph of the 167 meter-long Chinese polar research vessel Xue Long ("Snow Dragon") in heavy seasonal pack ice, Prydz Bay, 25 kilometers from the Chinese Zhongshan Station, December 1998.
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Figure 3. Schematic of subsurface sediment trap mooring deployed north of Prydz Bay in 4000 meters of water at 62o 28.63’ S, 72o 58.55’ E. Mooring deployed December 21, 1998 and will be recovered in early 2000 during the 1999-2000 Xue Long expedition to the Prydz Bay region.
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