AbstractSubmarine cave faunas remain poorly understood, and only a few stygobite podocopid ostracods are known. We describe an enigmatic submarine cave ostracod, Tabukicypris decoris gen. et sp. nov., from Holocene sediment cores taken from the Daidokutsu submarine cave off Ie Island, Okinawa, Japan. This species is endemic to the submarine cave environment. At least part of its enigmatic morphology, especially the distinct pore clusters in the anterior and posterior parts, is probably an adaptation to the submarine cave environment. There is no clear morphological evidence to indicate that Tabukicypris decoris is a 'living fossil'. The morphological characters of this stygobite indicate three possible origins of this species: from a deep-sea, interstitial or tropical open shallow-marine environment.http://zoobank.org/urn:lsid:zoobank.org:pub:25E37E49-C0A0-4A49-A8D8-E4AE9D85DB74Keywords: submarine caveOstracodaHoloceneOkinawaJapan AcknowledgementsWe thank David J. Horne, Thomas M. Cronin and an anonymous reviewer for valuable comments; Ryoichi Tabuki for providing surface sediments and information; Laura Wong for continuous support; HKU Electron Microscope Unit for technical support; Hayato Tanaka for giving advice on taxonomy; and Gene Hunt and Daniel Levin for depositing type and figured specimens. This study is supported by the Early Career Scheme of the Research Grants Council of Hong Kong (project code: HKU 709413P) and the Seed Funding Programme for Basic Research of the University of Hong Kong (project code: 201111159140) (to MY). Collaboration with KF was partly supported by the International Research Hub Project for Climate Change and Coral Reef/Island Dynamics of University of the Ryukyus.
Abstract Deep-sea benthic ostracod assemblages covering the last 2 Myr were investigated in Integrated Ocean Drilling Program Site U1426 (at 903 m water depth) in the southern Sea of Japan. Results show that (1) orbital-scale faunal variability has been influenced by eustatic sea-level fluctuations and oxygen variability and (2) secular-scale faunal transitions are likely associated with the mid-Brunhes event (MBE, ~0.43 Ma) and the onset of the Tsushima Warm Current (TWC, ~1.7 Ma). Krithe , Robertsonites , and Acanthocythereis are the three most abundant genera throughout the core, accounting for 78.5% of total specimens. Multiple-regression tree analysis indicated that the TWC, the MBE, and oxygen content are the significant controlling factors of ostracod dominance. Changes in assemblages exhibit decline and recovery patterns corresponding to orbital-scale cyclicity of sea-level changes. In the Sea of Japan marginal ocean setting, this cyclicity shows a close relationship with bottom-water oxygen variability since the onset of the TWC influx. The MBE amplified the influence of the TWC and oxygen variability to the deep-sea ecosystem through larger sea-level fluctuations. Acanthocythereis dunelmensis , a circumpolar species, dominates before the TWC onset. After the TWC onset and during the mid-Pleistocene transition (MPT, ~1.2–0.7 Ma) Krithe spp., known for their low-oxygen tolerance, substantially increase under moderate oxygen depletion. At the end of the MPT, Krithe dominance diminishes and is replaced by Robertsonites hanaii and Propontocypris spp. after the MBE. The post-MBE assemblage, characterized by R. hanaii , suggests a slightly warmer environment under the development of the TWC. In addition, the post-MBE high-amplitude climate system may have caused the increased abundance of active-swimming Propontocypris spp. due to their superior migration ability. Benthic ecosystems in marginal seas are sensitive and vulnerable to both short- and long-term climatic changes, and the MBE is suggested to be a global biotic event affecting benthic ecosystems substantially.
Abstract The East Asian summer monsoon (EASM) is a key component of the Asian Monsoon system affecting regional precipitation in East Asia and thus human culture, society, and development. Despite this, decadal‐ to centennial‐scale EASM dynamics remain poorly understood over the last millennium. Here we used high‐resolution benthic microfossil proxies to reconstruct EASM variability for the last 1,000 years from a brackish lake in South Korea. We compared this EASM record with Asian Monsoon proxy records from East China (i.e., continental proxy) and East Asian coasts (i.e., oceanic setting), and identified four pervasive EASM strengthening events at 1250, 1450, 1550, and 1900 CE and their deviation, likely related to land‐ocean temperature gradients. Our results indicate that data from the oceanic setting under the direct influence of the Pacific High are important in understanding the EASM dynamics over the last millennium. It is also noteworthy that EASM variability shows striking similarity to changes in the Atlantic meridional overturning circulation, implying the causal relationship.
Trincomalee Bay is situated on the northeast coast of Sri Lanka. This is the first study to report the recent ostracode assemblages in this bay. As a result, at least 36 ostracode taxa were identified from surface sediments in the bay. Many of them are typical tropical-water species that have been reported from inner bays and shallow marine areas around the coast of the Indo-Pacific region. We compared the species composition of ostracodes in the study area with that in adjacent seas. The result clearly showed that ostracode assemblages from Sri Lanka have strong connection with those along the coast of the Indian subcontinent. Moreover we evaluated the bottom environment in Trincomalee Bay on the basis of statistical analyses of ostracode assemblages combined with grain size, and total organic carbon (TOC) and total nitrogen (TN) contents. The results showed that the TOC content is related to grain size and is relatively high in the inner part of Inner Harbor and Koddiyar Bay, where fine-grained sediments are distributed. Four biofacies were recognized based on Q-mode cluster analysis using ostracode data for 36 taxa. Biofacies I is consistent with distributions of fine-grained sediments with moderate TOC contents (0.30%–0.49 %). Biofacies II is collected from relatively deep water areas with sediments of low TOC contents (0.22%–0.41 %) in InnerHarbor. Biofacies III and IVare characterized by euryhaline species and are influenced by fresh water and shallow depth with low TOC contents (0.14%–0.37%) in sediments. The ostracode distribution in Trincomalee Bay is depend on natural environmental factors such as water depth, grain-size, TOC contents of sediments, and water salinity.
Abstract The Sea of Japan is a marginal sea, connecting to adjacent seas by four shallow straits (water depths <130 m). Marginal seas are ideal for studying biotic responses to large‐scale environmental changes as they often are sensitive to glacial‐interglacial and stadial‐interstadial climatic cycles. However, only a limited number of studies cover time periods beyond the last two glacial‐interglacial cycles. Here we present a 700,000‐year record of benthic biotic response to paleoceanographic changes in the southern Sea of Japan, covering the past seven glacial‐interglacial cycles, based on ostracode assemblages at the Integrated Ocean Drilling Program (IODP) Site U1427. The results indicate that long‐term oxygen variability in the bottom water has been the major control impacting the marginal‐sea biota. Five local extirpation events were recognized as barren zones during glacial maxima immediately before terminations I, II, IV, V, and VII, which are probably caused by bottom‐water deoxygenation. Results of multivariate analyses indicated clear faunal cyclicity influenced by glacial‐interglacial oxygen variability with a succession from opportunistic species dominance through tolerant infauna dominance to barren zone during the deoxygenation processes and the opposite succession during the recovery processes. The Sea of Japan ostracode faunal composition showed distinct difference between the post‐MBE and pre‐MBE (Mid‐Brunhes Event) periods, indicating the MBE as a major disturbance event in marginal‐sea ecosystems. The MBE shortened the duration of the extirpation events, fostered dominance of warmer‐water species, and amplified the glacial‐interglacial faunal cyclicity. Our long‐term biotic response study clearly indicates that deep marginal sea ecosystems are dynamic and vulnerable to climate changes.
Abstract Aim Cenozoic dynamics of large‐scale species diversity patterns remain poorly understood, especially for the Western Pacific, in part, because of the paucity of well‐dated fossil records from the tropics. This article aims to reveal the spatiotemporal dynamics of species diversity in the Western Pacific through the Cenozoic, focusing on the tropical Indo‐Australian Archipelago ( IAA ) biodiversity hotspot. Location Tropical and north‐western Pacific Ocean. Methods We analysed well‐preserved fossil ostracodes from the tropical Western Pacific and combined their diversity data with other published data from the region to reconstruct Cenozoic dynamics of species diversity in the tropical and north‐western Pacific Ocean. We fitted generalized additive models to test for differences in richness over time and across geographical regions while accounting for sample‐size variation among samples. Results Low‐, mid‐ and high‐latitude regions all show a similar diversity trajectory: diversity is low in the Eocene and Oligocene, increases from the Early Miocene to the Plio‐Pleistocene but then declines to the present day. Present‐day high biodiversity in these regions was established during the Pliocene with a remarkable diversity increase at that time. Latitudinal diversity patterns are relatively flat and never show a simple decline from the tropics to higher latitudes. Main conclusions Western Pacific Cenozoic ostracodes exhibit a spatiotemporal pattern of species diversity that is inconsistent with the commonly reported and persistent pattern of declining diversity from the tropics to the extratropics. While this inconsistency could be interpreted as evidence that ostracodes are a contrarian clade, Atlantic ostracodes display a standard latitudinal species diversity gradient. Contrasting patterns between oceans suggest an important role for regional factors (e.g. plate tectonics and temporal geomorphological dynamics) in shaping the biodiversity of the Western Pacific.
'/%3e%3cuse xlink:href='%23a' transform='rotate(144 450 300)'/%3e%3cuse xlink:href='%23a' transform='rotate(216 450 300)'/%3e%3cuse xlink:href='%23a' transform='rotate(288 450 300)'/%3e%3c/svg%3e)
