Interannual variations of D14CTOC and elemental contents in the laminated sediments of Santa Barbara Basin during the past 200 years

Hong-Chun Li, National Taiwan University, Department of Geosciences, Taipei, Taiwan, Yi-Wei Chang, Natioanl Taiwan University, Department of Geosciences, Taipei, Taiwan and William Berelson, University of Southern California, Earth Sciences, Los Angeles, United States
A 52-cm gravity core retrieved by the depo-center of Santa Barbara Basin (SBB) of California in 2012 has been dated by 210Pb dating method and lamination counting. The core contains depositional history since ~1815 C.E. with sedimentation rate of 0.25~0.29cm/yr. The core was X-ray radiographed on 0.2mm resolution by an Itrax-XRF Core Scanner, showing laminations and providing elemental content of bulk sediments. Acid (0.5N HCl) leachable Elements (ALEs) of the bulk sediments from 71 horizons have been measured by an ICP-OES. A total of 89 AMS 14C measurements on samples from 66 horizons, including animal cartilage, shells and total organic carbon (TOC) in the sediments. Among these AMS dates, 78 14C dates of TOC from 62 horizons show apparent 14C ages between 500 and 4000 yr BP with D14C values ranging from -64.3‰ to -383.8‰. Both organic and inorganic carbons in SBB have serious old carbon influences. The old carbon sources in SBB are the input of terrigenous sediments, the changes of ocean circulation, the biological input and the old carbon remineralization. These factors are affected by the changes of the sedimentary environment in the basin, and resulting in 14CTOC fluctuations. Three strong old 14CTOC excursions around 1964, 1884 and 1819 CE might indicate strong input of terrestrial sediments caused by natural hazards (e.g., earthquake or flooding). On multiple decadal scales, the D14CTOC changes are also related to remineralization of CH4 which is reduced from the old marine sediments in deeper layers and to the oxidation condition that is affected by vertical mixing of the water column. On interannual scales, variations of D14CTOC probably correspond to El Niño-Southern Oscillation (ENSO) effect. During the La Niña period, stronger upwelling and northerly current bring nutrient enriched water into SBB and lead to higher productivity. The organic and carbonate enriched sediments containing lower ALEs and lower XRF measured elements with higher D14CTOC form the light layer during La Niña period. During the El Nino period, the phenomena are opposite.