Influence of boundary scavenging and sediment focusing on 234Th, 228Th and 210Pb fluxes in the Santa Barbara Basin

Abstract Sediment trap samples were collected from the Santa Barbara Basin to examine the flux of 234 Th, 228 Th and 210 Pb. Mean ratios of measured to predicted fluxes are 2, 10 and 21 for 234 Th, 228 Th and 210 Pb, respectively. Boundary scavenging may supply a portion of all three radionuclides. However, sediment focusing supplies additional 228 Th and 210 Pb but little 234 Th. Sediment temporarily deposited on the shelf around the basin contains little excess 234 Th due to its short half-life. 228 Th and 210 Pb fluxes to the sediments in the Santa Barbara Basin are several times greater than predicted from their supply in the overlying water column. These enhanced fluxes require lateral transport of 228 Th and 210 Pb to the basin through boundary scavenging and sediment focusing. 234 Th flux is poorly correlated with 228 Th and 210 Pb fluxes because individual radionuclide sources to the basin differ (i.e. water column production, boundary scavenging and/or sediment focusing). Correlations between 228 Th and 210 Pb fluxes are high due to the strong influence of sediment focusing on both radionuclides. There is a strong correlation between both the 228 Th and 210 Pb flux and total mass flux and lithogenic flux, but a weak correlation with the other major sediment components (e.g. organic carbon, carbonate and biogenic opal). In the Santa Barbara Basin, a large fraction of the total mass flux is lithogenic material (50–80%), hence the strong correlation between 228 Th and 210 Pb fluxes and both total mass and lithogenic fluxes. 234 Th flux is poorly correlated with total mass and major sediment component fluxes.

[1]  W. Moore,et al.  Comparison of 234Th, 228Th, and 210Pb fluxes with fluxes of major sediment components in the Guaymas Basin, Gulf of California , 1999 .

[2]  R. Thunell.  Particle fluxes in a coastal upwelling zone: sediment trap results from Santa Barbara Basin, California , 1998 .

[3]  D. Anderson,et al.  Sediment fluxes and varve formation in Santa Barbara Basin, offshore California , 1995 .

[4]  W. Moore,et al.  Elemental and isotopic fluxes in the Southern California Bight: A time‐series sediment trap study in the San Pedro Basin , 1994 .

[5]  W. Broecker,et al.  Transport and burial rates of 10Be and 231Pa in the pacific-ocean during the holocene period , 1992 .

[6]  W. Curry,et al.  Automated system to measure the carbonate concentration of sediments , 1990 .

[7]  P. Froelich,et al.  A simple method for the rapid determination of biogenic opal in pelagic marine sediments , 1989 .

[8]  K. Harada,et al.  Particulate removal of230Th and231Pa in the biologically productive northern North Pacific , 1989 .

[9]  T. Beasley,et al.  Profiles of dissolved and particulate thorium isotopes in the water column of coastal Southern California , 1987 .

[10]  W. Moore.  Radium isotope measurements using germanium detectors , 1984 .

[11]  D. Hammond,et al.  The fallout rate of PB‐210 on the western coast of the United States , 1983 .

[12]  R. Dunbar,et al.  A sediment trap intercomparison study in the Santa Barbara Basin , 1981 .

[13]  K. Bruland,et al.  Southern California inner basin sediment trap calibration , 1981 .

[14]  W. Moore,et al.  Fluxes of uranium and thorium series isotopes in the Santa Barbara Basin , 1981 .

[15]  R. Dunbar,et al.  Fecal pellet flux to modern bottom sediment of Santa Barbara Basin (California) based on sediment trapping , 1981 .

[16]  P. Froelich.  Analysis of organic carbon in marine sediments1 , 1980 .

[17]  W. Moore,et al.  Radium and thorium isotopes in the surface waters of the East Pacific and coastal Southern California , 1978 .

[18]  A. Soutar,et al.  Sedimentation and climatic patterns in the Santa Barbara Basin during the 19th and 20th centuries , 1977 .

[19]  S. Krishnaswami,et al.  210Pb/226Ra disequilibrium in the Santa Barbara Basin , 1975 .

[20]  D. Lal,et al.  GEOCHRONOLOGICAL STUDIES IN SANTA BARBARA BASIN: 55Fe AS A UNIQUE TRACER FOR PARTICULATE SETTLING , 1973 .

[21]  K. Emery,et al.  The Sea off Southern California: A Modern Habitat of Petroleum , 1961 .

[22]  K. Emery,et al.  Stratification in Recent Sediments of Santa Barbara Basin as Controlled by Organisms and Water Character , 1961, The Journal of Geology.

[23]  Winant,et al.  Surface Circulation in the Santa Barbara Channel , 1996 .

[24]  W. Broecker,et al.  Particulate fluxes of 230Th, 231Pa, and 10Be in the northeastern Pacific Ocean , 1993 .

[25]  Susumu Honjo,et al.  Large aperture time-series sediment traps; design objectives, construction and application , 1988 .

[26]  H. Sakai,et al.  The distribution of 230Th and 231Pa in the deep-sea surface sediments of the Pacific Ocean , 1986 .

[27]  K. Bruland,et al.  234Th:238U disequilibria within the California Current1: 234Th:238U disequilibria , 1985 .

[28]  P. Brewer,et al.  Removal of230Th and231Pa from the open ocean , 1983 .

[29]  O. Pilkey,et al.  Shelf sediment transport : process and pattern , 1972 .

[30]  Rama,et al.  234Th/238U ratios in the ocean , 1968 .

[31]  K. Emery,et al.  The relationships of sediments, life and water in a marine basin , 1961 .