Potential of submarine-cave sediments and oxygen isotope composition of cavernicolous micro-bivalve as a late Holocene paleoenvironmental record

Abstract

A sediment layer (43 cm thick) and surface sediments (5 cm thick) in a submarine limestone cave (31 m water depth) on the fore-reef slope of Ie Island, off Okinawa mainland, Japan, were examined by visual, mineralogical and geochemical means. Oxygen isotope analysis was performed on the cavernicolous micro-bivalve Carditella iejimensis from both cored sediments and surface sediments, and the water temperature within the cave was recorded for nearly one year. These data show that: (1) water temperature within the cave is equal to that at 30 m deep in the open sea; (2) the biotic and non-biotic environments within the cave have persisted for the past 2000 years; (3) mud-size carbonate detritus is a major constituent of the submarine-cave deposit, and may have come mainly from the suspended carbonate mud produced on the emergent Holocene reef flat over the past two millennia; (4) the δ 18 O-derived temperature (T δ 18 O ) of C. iejimensis suggests that the species grows between April and July; (5) the T δ 18 O of C. iejimensis from cored sediments implies that there were two warmer intervals, at AD 340 ± 40 and AD 1000 ± 40, which correspond to the Roman Warm Period and Medieval Warm Period, respectively. These suggest that submarine-cave sediments provide unique information for Holocene reef development. In addition, oxygen isotope records of cavernicolous C. iejimensis are a useful tool to reconstruct century-scale climatic variability for the Okinawa Islands during the Holocene.

Reconstruction of paleotemperatures in the Northwest Pacific over the past 3000 years from δ18O values of the micro-bivalvia Carditella iejimensis found in a submarine cave

“…There remains an ongoing debate concerning the variability of late Holocene SST estimates for the area around the Okinawa Trough and the Ryukyu Islands. Kitamura et al (2007a) measured the oxygen isotope compositions of the micro-bivalve Carditella iejimensis obtained from surface sediments (5 cm thick) within a submarine cave named Daidokutsu (31 m water depth) at Ie Island (26°43′N, 127°50′E), Japan, located ca. 10 km west of the Okinawa Island ( Fig.…”

“…Although the temporal resolution and duration of this proxy are not comparable to those derived from corals, it represents a thermometer at a fixed observation point that provides data in addition to coral records. Based on T δ 18 O from C. iejimensis obtained from cored sediments, Kitamura et al (2007a) identified two relatively warm intervals over the past 2000 years; at AD 340± 40 and AD 1000 ± 40, corresponding to the Roman Warm Period and the Medieval Warm Period, respectively.…”

“…To further assess and extend Kitamura et al's (2007a) study, the present study involved additional δ 18 O measurements of whole shells obtained from the surface and cored sediments from the cave. This work was undertaken for two reasons; first, to address the paucity of data in the previous study (Kitamura et al, 2007a) obtained from individuals with shell heights ranging from 1.4 to 2.1 mm, and second, to address the fact that the low abundance of C. iejimensis (accumulation rates b 0.02/cm 2 /yr) meant that Kitamura et al (2007a) measured only 13 individuals from cored sediments that cover the past 2000 years.…”

Possible Cavern-Forming Activity at Millennial Time Scales and its Impact on Variations in Submarine Cave Environments and Habitat Availability, Okinawa, Japan

“…A number of workers have recently used archival materials from submarine caves to reconstruct environmental changes during the late Quaternary (Antonioli et al, 2001;Kitamura et al, 2007, Yamamoto et al, 2008, 2009a. For example, oxygen-isotopic compositions of coralline sponges and micro-bivalves from submarine caves have been studied as proxies for palaeotemperature (Böhm et al, 2000;Haase-Schramm et al, 2003;Yamamoto et al, 2008Yamamoto et al, , 2009bYamamoto et al, , 2010Kitamura et al, 2013).…”

“…Many submarine limestone caves occur on the islands (Hayami and Kase, 1993). However, previous studies of changes in the communities of submarines caves have only considered millennial-scale variations in the species compositions of bivalves (Kitamura et al, 2007;Yamamoto et al, 2009a) and algal symbiont-bearing large benthic foraminifers (Omori et al, 2010) in Daidokutsu submarine cave (water depth, 29 m) at Ie Island, Okinawa (Fig. 1a).…”