TRACE ELEMENT ANALYSIS OF TWO HOLOCENE BIVALVE TAXA, CYRENODONAX FORMOSANA AND POTAMOCORBULA AMURENSIS, AS PROXIES FOR TEMPERATURE AND PRODUCTIVITY IN THE PEARL RIVER DELTA, CHINA

Recent studies have shown an escalation of parasite prevalence among bivalve hosts in shallow marine, lagoonal, and estuarine settings concurrent with sea-level rise. For example, parasite prevalence was significantly higher during the first 300 years of sea level rise, significantly lower during maximum regression, and indistinguishable in other stages of sea-level rise and delta progradation than at any other time during the 9600 year record provided in a drill core taken from the Pearl River delta, China (Huntley et al, 2014). Sea level rise alone is likely not the cause of this pattern as eustatic cycles co-vary with a variety of biotic and abiotic variables. Biotic factors, such as host abundance, richness, and community structure, have been ruled out as drivers of this pattern. However, the roles of abiotic factors remain largely untested. Here we present the initial results testing the roles of temperature and productivity events/nutrient availability via trace element concentrations preserved within bivalve growth increments. 60 bivalve individuals (30 C. formosana and 30 P. amurensis) were selected from eight temporal bins from a 9,600 yr Holocene record from a drill core situated in the Pearl River delta. These were sectioned along the axis of maximum growth and analyzed using laser ablation inductively coupled mass spectrometry (LA-ICP-MS). Individual spots, 40um in diameter and spaced every 100um were analyzed across growth from the umbo to the ventral margin for a total of 4,070 analyses. Instrument calibrations were performed using NIST SRM 610 and 612 glass references materials. Sr:Ca, Mg:Ca, Li:Ca, Li:Mg, and U:Ca values were used as proxies for temperature and Ba:Ca was used as a proxy for productivity events/nutrient availability. Proxy data were pooled by temporal bin and characterized by median, 75^th percentile, and skewness values to characterize temporal trends. Preliminary results of our study indicate our data agree with literature that trace element ratios are reliable indicators of temporal environmental change in aragonitic bivalves. However, further analyses and data processing are needed.