11:45 AM - 12:00 PM
[MIS26-11] Reconstructing the environmental history of macroalgae by the use of dual carbon isotope tracers
Keywords:microalgae, radiocarbon, carbon stable isotope, Sanriku region, Oyashio, Tsugaru warm current
To test this hypothesis, we cultured U. Pinattifida sporophyte in Otsuchi Bay between November 2013 and April 2014 and examined variability in Δ14C among different pinnate blades formed during different periods. Our results indicated that the lower blades formed after the Oyashio water intrusion, which appeared to occur in early March as indicated by a marked shift in salinity and temperature, had significantly lower Δ14C values compared to the upper blades formed before the event. These results are consistent with our hypothesis and suggest a possibility that the blade-order-dependent Δ14C variability in a sporophyte can be used as a new tool to reconstruct the timing of the Oyashio intrusion event in Sanriku bays. Our results also showed that the carbon stable isotopic signature (δ13C) varied widely (range, 4.7‰) among the blades. Because this range in δ13C among blades largely exceeded the difference in δ13C-DIC between Tsugaru warm water and Oyashio water (0.22‰), it was considered that the variability in the δ13C of blades primarily reflected the variability in the extent of isotope fractionation, which was presumably related to changes in physiological state (growth rate) of the sporophyte. Furthermore, our data showed that there was a significant negative correlation between δ13C and Δ14C of the blades, suggesting that the growth rate of the sporophyte increased after the intrusion of Oyashio water. Dual carbon isotopic signatures of the blades of sporophyte could be potentially useful to reconstruct the timing of the Oyashio intrusion event and to examine physiological responses of macroalgae to this oceanographic event.