Liu Chang

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  • Preprint
    Geochemical evidence for initiation of the modern Mekong delta in the southwestern South China Sea after 8 Ma
    ( 2017-01) Liu, Chang ; Clift, Peter D. ; Murray, Richard W. ; Blusztajn, Jerzy S. ; Ireland, Thomas ; Wan, Shiming ; Ding, Weiwei
    Sedimentary records in the southwestern South China Sea reflect the evolving erosion and drainage systems that have operated in Southeast Asia during the Neogene. Analyses of the chemistry and clay mineral composition of sediments from International Ocean Discovery Program (IODP) Site U1433 allow us to examine these processes over the last 17 Ma. Sediment older than 8 Ma was deposited relatively slowly. Sr and Nd isotopes indicate a variable provenance with sequences of less and more altered material accompanied by strong changes in the proportion of smectite. Sediment flux was probably from Indochina, as well as from a more primitive volcanic source, most likely the Palawan ophiolite and/or Luzon. Sediments younger than 8 Ma show a more stable Sr and Nd isotope character, indicating sources close to those seen in the modern Mekong River, although with some influx from smaller rivers draining the Indochina margin especially from 4–8 Ma. Our data are consistent with seismic estimates for an onset to the Mekong in its present location after 8 Ma, following an avulsion from the Gulf of Thailand.
  • Preprint
    Connectivity of the bay scallop (Argopecten irradians) in Buzzards Bay, Massachusetts, U.S.A.
    ( 2015-06) Liu, Chang ; Cowles, Geoffrey W. ; Churchill, James H. ; Stokesbury, Kevin D. E.
    The harvest of bay scallops (Argopecten irradians) from Buzzards Bay, Massachusetts, USA undergoes large interannual fluctuations, varying by more than an order of magnitude in successive years. To investigate the extent to which these fluctuations may be due to yearly variations in the transport of scallop larvae from spawning areas to suitable juvenile habitat (settlement zones), a high-resolution hydrodynamic model was used to drive an individual-based model of scallop larval transport. Model results revealed that scallop spawning in Buzzards Bay occurs during a time when nearshore bay currents were principally directed up-bay in response to a persistent southwesterly sea breeze. This nearshore flow results in substantial transport of larvae from lower-bay spawning areas to settlement zones further up-bay. Averaged over the entire bay, the spawning-to-settlement zone connectivity exhibits little interannual variation. However, connectivities between individual spawning and settlement zones vary by up to an order of magnitude. The model results identified spawning areas that have the greatest probability of transporting larvae to juvenile habitat. Because managers may aim to increase scallop populations either locally or broadly, the high-connectivity spawning areas were divided into: 1) high larval retention and relatively little larval transport to adjoining settlement areas, 2) both significant larval retention and transport to more distant settlement areas, and 3) little larval retention but significant transport to distant settlement areas.