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South China Sea Deep:
In-situ observation of bottom flows and sediment dynamics in northeastern South China Sea

Overview

In 2010, the Natural Science Foundation of China (NSFC) funded an 200 million Yuan (~ 30 millions USD) initiative named "South China Sea Deep" - an interdisciplinary research project to study the tectonics, sedimentology and sediment transport, and biogeochemical cycling. PCMSC scientists were invited by colleagues in Tongji University (Shanghai, China) to collaborate on a proposal for studying the deep water sediment dynamics and sediment transport in the northeastern South China Sea. The proposal, "In-situ observation of bottom flows and sediment dynamics in northeastern South China Sea", has been funded for 4 years (2012-2015). A reimbursable agreement is being developed to fund the participation of PCMSC scientists and staff.

PCMSC is invited to participate this project because of our world-renowned research on sediment dynamics and proven expertise in designing and implementing field experiment for sediment dynamic studies from the continental shelves and slopes to submarine canyons. Participation of this project is deemed beneficial to PCMSC in multiple ways:

  1. Since the HEBBLE program more than 30 years ago, this project is one of only few studies on deep-water sedimentation and sediment dynamics in the entire world that are not conducted by oil industry, whose data are understandably always propriety. Any data and discovery from this project will be at the forefront of deep-water marine geology research for the region, and probably for the world.
  2. This project will strengthen our future capabilities in marine (deep-water) geology and geophysics research.
  3. Our participation of this project will likely to lead future collaborations with expanded research scope.

 

Maps of study location, read caption that follows and click for a larger version of the maps.

Above: A, Sites in South China Sea where the USGS deepwater tripod and about a dozen moorings will collect data to shed light on sediment movement and accumulation on the seafloor. Red dots, sites of instrumented platforms. Green triangles, sites of Ocean Drilling Program (ODP) boreholes. Long-dashed yellow line, hypothesized route of deep contour-following current entering from the Pacific Ocean. Short-dashed yellow line, hypothesized alternative route of deep current from the Pacific. B, Seismic-reflection profile along line ab on map, showing sediment layers in an apparent contourite (deposited by contour currents). Simplified drawings indicate where scientists intend to place the tripod (TJ-A-2) and several moorings (TJ-A-1, TJ-A-3, TJ-A-4). C, Enlarged map of line cd, showing sites (red dots) where groups of moorings will be placed along the axis of a submarine canyon (Formosa Canyon). [larger version]

Start/End Dates

10/1/11 to 9/30/15

Location

China

Investigators

  • Xu, Jingping, Oceanographer, Project Chief
  • Rosenbauer, Bob, Geochemist
  • Tate, George, Geologist

Objectives

Through in-situ observation of sediment and oceanographic parameters by deep-water mooring and tripod deployments at several key locations, and water column profiling along the transects, as well as sediment and water sampling, the study tries to better understand the following processes that control the bottom circulations and sediment dynamics:

  1. the property and temporal and spatial distribution of bottom ocean currents in the study area;
  2. characterization and distribution of bottom nepheloid layer;
  3. sedimentation and resuspension in the bottom boundary layer;
  4. turbidity currents and their triggering mechanisms;
  5. sources and transport pathways of bottom sediment that formed the subject high-sedimentation-rate deposit.

The results from this study, when combined with the analyses and interpretation of existing high-resolution sediment cores, are expected to help understanding the evolution of ocean bottom circulation since the last glacial maximum (LGM), and its control on the formation of the subject high-sedimentation-rate deposit.

Approach

For the past 4 decades PCMSC has been at the forefront of sediment dynamics research and had the world-renowned expertise in designing and implementing field experiment for sediment dynamic studies from the continental shelves and slopes to submarine canyons. In this project, we apply this expertise to the northeastern South China Sea where bottom boundary layer studies in deep ocean have never been done before. A decade of fast economic growth has afforded China to substantially increase her investment in ocean science research. A successful collaboration in this pilot project can conceivably extend PCMSC's participation to international projects and strengthen its ocean research capability.

Photo of the tripod at the Santa Cruz Wharf. Photo of the new FAT developed and designed in Santa Cruz, California by the Pacific Coastal and Marine Science Center.

Above: New USGS deepwater tripod, called the free-ascending tripod, or FAT. A, Sitting on the Santa Cruz Municipal Wharf in Santa Cruz, California, [larger version] and B, suspended from a crane before being lowered into water [larger version]. Some of the instruments mounted on the tripod have been labeled. USGS photographs taken February 6, 2013, by George Tate.

Task

Bottom Boundary Layers in South China Sea Deep

Read about the Free-Ascending Tripod (FAT) in this Sound Waves article:

"Deep-Sea Instrument Tripod Passes Test in Monterey Bay, California—Next Stop is South China Sea," http://soundwaves.usgs.gov/2013/08/fieldwork2.html

In 2012-2013, PCMSC staff designed, fabricated, and tested the deep-water Free-Ascending Tripod (FAT) that will be deployed in late 2013. Two identical tripods (including frame, flotation, and releasing mechanism, but without most instruments) were made; one tripod as a backup. The tripods are co-owned by PCMSC and Tongji University.

The study area is located at the northeastern South China Sea, at 2000-3000 m water depth. Five of the 6 observing stations are roughly along the 2500 m contour; and one station is located at the head of the Formosa submarine canyon at 700 m water depth. A mooring equipped with sediment traps, RCM current meters, transmissometers, temperature/salinity sensors, and dissolved oxygen sensors will be deployed at each of the six locations. In addition, a tripod instrumented with ADCP, ADV, transmissometers, LISST, and bottom photography is deployed in each of the two focus transits. The first focus transit is across the body of a high-sedimentation-rate sediment deposit where ODP-1144 was collected in 1999. The other focus transit is along the Formosa Canyon. In addition, CTD casts and water samples will be collected at all mooring stations and along one or two transects. Limited by the number of instruments and the equipment, not all stations are occupied at the same time.

Cooperator

State Key Laboratory of Marine Geology, Tongji University, China/POC: Liu, Zhifei

 

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