G02_09

Sedimentary organic carbon ¹⁴C age and D¹⁴CTOC variations in a 200-yr core from Santa Barbara Basin: Anthropogenic and climatic influences

Li H¹,  Chang H¹, Shen T¹

¹Department of geosciences, National Taiwan University, Taipei, Taiwan

We have done 210Pb dating, varve counting, AMS ¹⁴C dating and scanning XRF and acid (0.5N HCl) leachate elemental (ALE) contents on a 51-cm core from the depo-center of Santa Barbara Basin (SBB). The core contains a depositional history during 1815-2011 CE. A total of 89 AMS ¹⁴C measurements on samples from 66 horizons show apparent ¹⁴C ages between 500 and 4000 yr BP. Among these AMS dates, 78 TOC ¹⁴C dates from 62 horizons provide high-resolution D¹⁴C variations ranging from -64.3‰ to -383.8‰. The ¹⁴CTOC is influenced by the input of terrigenous sediments, changes in ocean circulation, biological input and carbon remineralization as well as anthropogenic impacts. Three strong old ¹⁴CTOC excursions at 1964~69, 1884~87 and 1819~21 CE caused by some unusual events (e.g., oil spill and extraction, flood event and earthquake). The D¹⁴CTOC shifts in three zones were mainly caused by changes in fossil carbon emission from the seafloor and the atmospheric nuclear bomb ¹⁴C input. On interannual scales, variations of D¹⁴CTOC correspond to ENSO and PDO effects. During the La Niña period (and cold PDO phase), stronger upwelling and northerly California Current bring nutrient-enriched water into SBB and lead to higher productivity. The organic carbon and carbonate enriched sediment layers contain lower scanning XRF K and Ti but higher ALE with higher D¹⁴CTOC during La Niña period. During the El Niño period, the phenomena are opposite. Spectrum analyses of the SOI and the D¹⁴CTOC and their comparison support our scenarios.