Evidence of Recent Warming in the Okinawa Region, Subtropical Northwestern Pacific, from an Oxygen Isotope Record of a Cave-Dwelling Marine Micro-Bivalve
“…Kitamura et al (2013) estimated that a mean annual surface water temperature was about 1°C higher than during the Medieval Warm Period (900-1100 AD) and the Middle Holocene Climatic Optimum (9-5.5 ka BP) and that the recent warming is likely exceptional during the past 7000 years around Okinawa Islands, based on δ 18 O of micro-bivalve from a submarine cave. Matsushima (1984) reported that tropical molluscan species, which are presently living south of Kyushu (~30°N) including Rhinoclavis kochi, Barbatia fusca, Saccostrea mordax, Periglypta chemnitzi, Dendostrea paulucciae, and Meropesta capillacea that migrated tõ 36°N 6.5-5.0 ka BP, indicating timing of the enhancement and northward expansion of the Kuroshio Current.…”
The Kuroshio Current is a major western boundary current controlled by the North Pacific Gyre. It brings warm subtropical waters from the Indo-Pacific Warm Pool to Japan exerting a major control on Asian climate. The Tsushima Current is a Kuroshio offshoot transporting warm water into the Japan Sea. Various proxies are used to determine the paleohistory of these currents. Sedimentological proxies such as reefs, bedforms, sediment source and sorting reveal paleocurrent strength and latitude. Proxies such as coral and mollusc assemblages reveal past shelfal current activity. Microfossil assemblages and organic/inorganic geochemical analyses determine paleo-sea surface temperature and salinity histories. Transportation of tropical palynomorphs and migrations of Indo-Pacific species to Japanese waters also reveal paleocurrent activity. The stratigraphic distribution of these proxies suggests the Kuroshio Current reached its present latitude (35°N) by~3 Ma when temperatures were 1 to 2°C lower than present. At this time a weak Tsushima Current broke through Tsushima Strait entering the Japan Sea. Similar oceanic conditions persisted until~2 Ma when crustal stretching deepened the Tsushima Strait allowing inflow during every interglacial. The onset of stronger interglacial/glacial cycles~1 Ma was associated with increased North Pacific Gyre and Kuroshio Current intensity. This triggered Ryukyu Reef expansion when reefs reached their present latitude (~31°N), thereafter the reef front advanced (~31°N) and retreated (~25°N) with each cycle. Foraminiferal proxy data suggests eastward deflection of the Kuroshio Current from its present path at 24°N into the Pacific Ocean due to East Taiwan Channel restriction during the Last Glacial Maximum. Subsequently Kuroshio flow resumed its present trajectory during the Holocene. Ocean modeling and geochemical proxies show that the Kuroshio Current path may have been similar during glacials and interglacials, however the glacial mode of this current remains controversial. Paleohistorical studies form important analogues for current behavior with future climate change, however, there are insufficient studies at present in the region that may be used for this purpose. Modeling of the response of the Kuroshio Current to future global warming reveals that current velocity may increase by up to 0.3 m/sec associated with a northward migration of the Kuroshio Extension.
“…Kitamura et al (2013) estimated that a mean annual surface water temperature was about 1°C higher than during the Medieval Warm Period (900-1100 AD) and the Middle Holocene Climatic Optimum (9-5.5 ka BP) and that the recent warming is likely exceptional during the past 7000 years around Okinawa Islands, based on δ 18 O of micro-bivalve from a submarine cave. Matsushima (1984) reported that tropical molluscan species, which are presently living south of Kyushu (~30°N) including Rhinoclavis kochi, Barbatia fusca, Saccostrea mordax, Periglypta chemnitzi, Dendostrea paulucciae, and Meropesta capillacea that migrated tõ 36°N 6.5-5.0 ka BP, indicating timing of the enhancement and northward expansion of the Kuroshio Current.…”
The Kuroshio Current is a major western boundary current controlled by the North Pacific Gyre. It brings warm subtropical waters from the Indo-Pacific Warm Pool to Japan exerting a major control on Asian climate. The Tsushima Current is a Kuroshio offshoot transporting warm water into the Japan Sea. Various proxies are used to determine the paleohistory of these currents. Sedimentological proxies such as reefs, bedforms, sediment source and sorting reveal paleocurrent strength and latitude. Proxies such as coral and mollusc assemblages reveal past shelfal current activity. Microfossil assemblages and organic/inorganic geochemical analyses determine paleo-sea surface temperature and salinity histories. Transportation of tropical palynomorphs and migrations of Indo-Pacific species to Japanese waters also reveal paleocurrent activity. The stratigraphic distribution of these proxies suggests the Kuroshio Current reached its present latitude (35°N) by~3 Ma when temperatures were 1 to 2°C lower than present. At this time a weak Tsushima Current broke through Tsushima Strait entering the Japan Sea. Similar oceanic conditions persisted until~2 Ma when crustal stretching deepened the Tsushima Strait allowing inflow during every interglacial. The onset of stronger interglacial/glacial cycles~1 Ma was associated with increased North Pacific Gyre and Kuroshio Current intensity. This triggered Ryukyu Reef expansion when reefs reached their present latitude (~31°N), thereafter the reef front advanced (~31°N) and retreated (~25°N) with each cycle. Foraminiferal proxy data suggests eastward deflection of the Kuroshio Current from its present path at 24°N into the Pacific Ocean due to East Taiwan Channel restriction during the Last Glacial Maximum. Subsequently Kuroshio flow resumed its present trajectory during the Holocene. Ocean modeling and geochemical proxies show that the Kuroshio Current path may have been similar during glacials and interglacials, however the glacial mode of this current remains controversial. Paleohistorical studies form important analogues for current behavior with future climate change, however, there are insufficient studies at present in the region that may be used for this purpose. Modeling of the response of the Kuroshio Current to future global warming reveals that current velocity may increase by up to 0.3 m/sec associated with a northward migration of the Kuroshio Extension.
“…years BP was related to an intensification of the winter monsoon, although they reported no changes in temperatures or salinities during the past 2700 years. Yamamoto et al (2010) Kitamura et al (2013) confirmed that no changes have occurred in either sea-surface temperatures or salinities during the past 7000 years. These results are consistent with the findings of previous studies in the East China Sea (Jian et al, 2000;Ijiri et al, 2005;Sun et al, 2005;Lin et al, 2006;Kubota et al, 2010).…”
Section: Discussionmentioning
confidence: 66%
“…18 O and corresponding temperature values of Carditella iejimensis shells from cored samples (Kitamura et al, 2013). Bottom: On common scale Mg/Ca-derived SSTs and d…”
Section: Discussionmentioning
confidence: 99%
“…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). In addition, the history of sea level changes has been examined using both speleothems and changes in faunal assemblages preserved in cave sediments (Dorale et al, 2010;Tuccimei et al, 2010;van Hengstum and Scott, 2011, 2012, van Hengstum et al, 2011.…”
We examined the spatial distributions and 14 C ages of sessile marine organisms in the submarine cave Ginama at Okinawa, Japan. The cave is the northernmost and only known submarine cave with an air chamber in the northwestern Pacific region. The upper limit of living individuals of the coralline sponges Acanthocaetetes wellsi and the bivalve Pycnodonte taniguchii in the cave is located at a depth of approximately 10 m relative to the surface of the pool in the cave. Low temperatures and low salinities prevent these organisms from colonizing water depths shallower than 10 m. On the other hand, the upper limit of fossil individuals, dated between 5117 and 387 cal yr BP, is at a depth of 2.5 m, implying that at present the influence of fresh water on the cave pool is stronger than it has been at other times in the past 5000 years. This increase in the flux of fresh water may be explained by continuous cavern-forming activities such as dissolution.
“…This 40-m-long cave is known for its dark and oligotrophic environment (Omori et al 2010). The salinity (34.3, seasonal variation range unknown) and temperature (annual mean of ~24°C, with a seasonal variation range of 20–29°C) in the cave are similar to conditions outside at a similar water depth (i.e., 30 m) (salinity: ~35, with a seasonal variation range of 34.5–35.0; temperature: ~24°C, with a seasonal variation range of 20–29°C) (Yamamoto et al 2009b; Kitamura et al 2013; Chiu et al 2016). Figure 1 Location of sampling sites: A and B, location of Daidokutsu Cave; C, simplified cross section of Daidokutsu cave showing the position of core 06, core 19, and the surface-sediment sample IR1.…”
A submarine cave is a unique environment that is dark, food limited, semi-isolated from the outside, and sheltered from wave action. However, our knowledge of the long-term change in submarine-cave ecosystems remains limited. We document here the community-scale responses toward long-term change in a submarine cave, Daidokutsu in Okinawa in southern Japan. Using both metazoans (ostracods and bivalves) and protozoans (larger benthic foraminiferans) in two sediment cores obtained from the cave, we reconstruct the faunal and diversity changes of the past 7 Kyr. All taxonomic groups showed long-term, gradual linear change of faunal composition from predominantly open-water taxa to predominantly cave taxa, and ostracods showed short-term variability of species diversity. The long-term faunal trend probably reflects gradual isolation of the cave ecosystem due to coral reef development (i.e., development of the cave ceiling) during periods of the Holocene transgression and subsequent sea-level highstand. The short-term diversity changes show substantial similarity to centennial- to millennial-scale Holocene Asian monsoon variability. Ostracod species diversity peaks tend to correspond with periods of strong East Asian winter monsoons. The results indicate that limestone submarine-cave ecosystems, an important cryptic habitat, developed gradually during the Holocene and may be sensitive to rapid climate changes.
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