Reconstruction of paleotemperatures in the Northwest Pacific over the past 3,000 years from δ¹⁸O values of the micro-bivalvia Carditella iejimensis found in a submarine cave

Keywords: submarine-cave sediments; Okinawa Islands; late Holocene; palaeoclimatology; micro-bivalve; oxygen isotope ratio

Abstract: We measured the δ¹⁸O values of the whole shells of the cavernicolous micro-bivalvia Carditella iejimensis obtained from sediments within a submarine cave (31 m water depth) at Ie Island (Okinawa Island, Japan) in the subtropical Northwest Pacific. Our results show no significant millennial-scale trend in the δ¹⁸O record, implying that both springtime temperature and the δ¹⁸O of sea water at 30 m depth around the Okinawa Islands have been stable for the past 3,000 years at values similar to those of today. Moreover, we found one exceptionally light δ¹⁸O value from specimens spanning the past 250 years. The δ¹⁸O derived temperature represents a departure of 2.1°C from the average value for the past 250 years, being equal to the departure recorded during unusually high temperatures in the spring of 1998. This finding may imply that such high springtime sea surface temperature has been a rare event over the past 3,000 years.