Deep-sea Ostracod Research Articles

Relationship between Modern Deep-Sea Ostracods and Water Mass Structure in East Antarctica

This study investigated the relationship between the distribution of modern ostracod biofacies and environmental factors in Lützow–Holm Bay, off Cape Darnley, and off Totten Glacier in East Antarctica. We collected study samples from water depths of 219 to 987 m by the 61st Japanese Antarctic Research Expedition. Nineteen species belonging to 13 genera and 47 species belonging to 31 genera of ostracods were found in three samples from Lützow–Holm Bay and ten samples from off Totten Glacier, respectively. We found no ostracods in the samples off Cape Darnley. Q-mode cluster analysis reveals four ostracod biofacies (A to D). Antarctiloxoconcha frigida (Neale, 1967) and Australicythere polylyca (Müller, 1908) were common under the influence of cold water in the upper bathyal zone (biofacies A to C). The genus Krithe was the most abundant taxon in biofacies D with low dissolved oxygen and high-water temperature (0.38°C, 34.66, and 5.0 ml/L, respectively), indicating the presence of warm deep seawater, i.e., modified Circumpolar Deep Water. Thus, we have checked the relationships between the ostracod assemblages and the environmental parameters analyzed in Lützow–Holm Bay and off Totten Glacier, and so strengthened the previous ostracod and environmental data.

Thoughts on the Late Paleozoic-Early Mesozoic records of deep-sea ostracods

The nature and timing of mechanisms and events that shaped the deep-sea biodiversity are still debated. The present contribution provides an analysis and discussion of the distribution of off-shelf ostracods in the Late Paleozoic-Early Mesozoic. A taxonomic revision introduces Kozuria gen. nov. to accommodate Triassic species of Acanthoscapha, traditionally seen as Devonian-Carboniferous holdover archetypal of the Middle Triassic deep-sea of the western Tethys. The taxonomic composition as well as the temporal and geographic distribution of Permian and Triassic off-shelf assemblages are summarized and discussed in the light of climatic and biotic events. This analysis illustrates the Triassic uniformization of the composition of off-shelf assemblages and two possible periods of offshore migration in the late Permian (Changhsingian) and Middle Triassic (Anisian).

Review of the history of the deep-sea ostracod genera Abyssocythere Benson and Dutoitella Dingle, and their responses to Cretaceous - Cenozoic oceanic water-mass changes

Abyssocythere and Dutoitella are extant benthic bathyal ostracod genera that evolved during Coniacian to Santonian/Campanian time from shallow-water progenitors around southeastern Africa. Their Late Cretaceous development was primarily in the South Atlantic, but during the Palaeogene they spread to the Indian and Pacific oceans. The establishment of the psychrosphere (late Eocene-mid-Oligocene) flushed populations of each genus from their central Atlantic cradles into the Pacific, presumably through the Panama Seaway, so that contemporaneous centres of evolution developed disjunct clades: A. trinidadensis and D. praesuhmi. The psychrospheric oceanic event defined temporal thermophyllic and cryophyllic populations of the two genera. Three Neogene ocean events appear to have affected several regionally-confined species, inter alia one of which entailed a counterflow migration of A. atlantica from the eastern Pacific back into the central Atlantic during the mid-Miocene. Modern distributions of Abyssocythere and Dutoitella are disjunct: in the Atlantic both genera occur south of approximately 40 degrees N (Dutoitella), and equatorial areas (Abyssocythere); in the Indian Ocean both are confined to the southern part; and in the Pacific, Abyssocythere is restricted to central and north-eastern areas, and Dutoitella to the west and northwest. Neither genus evolved species that were more than para-cosmopolitan: A. diagrenona (South Atlantic-Indian; Eocene-Oligocene), A. trinidadensis complex (central Atlantic-NW Pacific; Oligocene-Miocene), D. crassinodosa complex (South Atlantic-Indian; Eocene), and D. praesuhmi (north and central Atlantic-central Pacific; Oligocene-Miocene).

Quaternary equatorial Atlantic deep-sea ostracodes: evidence for a distinct tropical fauna in the deep sea

AbstractLow-latitude, deep-sea faunas remain poorly understood and described. Here, we systematically describe Quaternary deep-sea ostracodes from the Ocean Drilling Program (ODP) Site 925 (Ceara Rise; 4°12.2'N, 43°29.3′W; 3040 m water depth) in the equatorial Atlantic Ocean. Twenty-six genera and 52 species were examined and illustrated with high-resolution scanning electron microscopy images. Six new species are described herein:Pseudocythere spinae,Hemiparacytheridea zarikiani,Pedicythere canis,Xylocythere denticulata,Paracytherois obtusa, andPoseidonamicus sculptus. The results show that deep-sea ostracodes have a tropical faunal element that is distinctive from higher latitude ostracodes, and that is globally distributed in low latitudes. This tropical faunal component is possibly a Tethyan legacy of a fauna that was widely distributed in tropical and extratropical latitudes in deep waters during greenhouse conditions in the Cretaceous and early Cenozoic. Global cooling thereafter shrank its distribution, limiting it to tropical latitudes, perhaps with the relatively warm uppermost bathyal area acting as the source or refuge of this faunal component. Because similar present-day biogeographic patterns (i.e., presence and wide distribution of tropical deep-sea fauna) are known in other deep-sea benthic groups, this scenario might be applicable to the deep-sea benthos more broadly.UUID:http://zoobank.org/552d4cb2-c0db-463a-ae3f-b2efcc0985df.

BATHYAL OSTRACODS FROM THE UPPER PLEISTOCENE OF THE RIO GRANDE CONE, PELOTAS BASIN, BRAZIL

Quaternary deep-sea ostracods supply invaluable data for the understanding of both hydrological and sedimentary processes in the continental slope. A huge portion of western South Atlantic bathyal regions is still poorly explored with respect to deep-sea ostracod research. This article contributes to the study of the assemblage ostracod of the Upper Pleistocene of five piston cores recovered in the Cone of Rio Grande, Pelotas Basin, Brazil. Taxonomic analysis revealed 21 species belonging to 13 genera: Cytherella, Macropyxis, Argilloecia, Paracytherois, Cytheropteron, Rimacytheropteron, Eucytherura, Loxoconchidea, Xestoleberis, Apatihowella, Henryhowella, Poseidonamicus and Krithe. The assemblages are quite similar to those registered in southwestern Brazilian bathyal regions. A taxon left in open nomenclature is probably a new genus and species. Eucytherura fossapunctata nov. sp. is here described.

Six new Krithe from the Kuril-Kamchatka Trench, with the first insight into phylogeography of deep-sea ostracods

Hadal depths are one of the least explored ecosystems on the planet, with little data on biodiversity and even less on phylogegraphy of its inhabitants, especially of meiofaunal groups. Ostracods are an important component of meiofaunal communities, but with less than a dozen species described from the world’s ocean trenches. Therefore, six species we describe from the Kuril-Kamchatka Trench greatly contribute to our knowledge of the hadal ostracod fauna. The new species belong to the genus Krithe Brady, Crosskey a Robertson, 1874, one of the most common ostracod genera from the continental slopes to abyss. Most of the 150 named species are fossil or subrecent, and described from shells only. Our discovery brings the list of species with known soft parts to 11, and provides further insights into morphology of these small ostracods. Our analysis shows that sexual dimorphism in the sixth leg should be excluded from the generic diagnosis. A relatively high abundance and wide distribution of the new species allowed us to study phylogeny (including estimation of the divergence time), genetic diversity, and phylogeography, providing the first such data for ostracods and one of the rare ones for all meiofaunal hadal (but also general deep-sea) groups. We use three genetic markers: mitochondrial cytochrome oxidase I (COI), internal transcribed spaces (ITS), and 18S rRNA; COI and ITS contained enough variability for the molecular phylogeny, and the former one for the population genetics and phylogeography analyses. Molecular clock analysis suggests that the most recent common ancestor (MRCA) of the six species lived 13 million years ago, supporting previously published estimates that the hadal fauna is relatively young. A high haplotype diversity coupled with a low nucleotide diversity are indicative of a rapid population expansion from a small effective population size. This is also supported with negative, statistically significant, values of Tajima’s D and Fu’s tests. Bayesian Skyline Plot places the time of expansion in the last interglacial period (120,000 years ago) and corresponds to the influx of cold, nutrient rich waters of the Oyashio current. The isolation by distance model is rejected, and almost non-existent population structuring is supported by a combination of low Fst values, and often a higher number of mutational changes between haplotypes sampled at the same locality than between those from different localities.

Deep-sea ostracod faunal dynamics in a marginal sea: biotic response to oxygen variability and mid-Pleistocene global changes

AbstractDeep-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, andAcanthocythereisare 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)Krithespp., known for their low-oxygen tolerance, substantially increase under moderate oxygen depletion. At the end of the MPT,Krithedominance diminishes and is replaced byRobertsonites hanaiiandPropontocyprisspp. after the MBE. The post-MBE assemblage, characterized byR. 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-swimmingPropontocyprisspp. 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.

Preliminary report on deep-sea benthic and pelago-benthic ostracods (subclass Myodocopa) of the North-Western Pacific with a description of a new genus Bathyconchoecetta

The diverse deep-water ostracod fauna of the subclass Myodocopa in the North-Western Pacific includes about 52 benthic and pelago-benthic species and has a high degree of endemism, whereas the deep-water zone of the Far East seas is inhabited by an impoverished Pacific fauna of ostracods. The deep-sea ostracod fauna in a basin of the Sea of Okhotsk is poorer (16 species) than that in the North-Western Pacific because this sea is separated from the oceanic waters by the Kuril Ridge. The ostracod fauna of the Sea of Japan do not include any typical deep-water species compared to ostracod fauna of the adjacent regions. The ostracod fauna of the deep-sea zone in the North-Western Pacific consists mainly of pelago-benthic species of the subfamily Bathyconchoeciinae (Halocyprida). This paper presents descriptions of the Bathyconchoecetta gen. nov. and two new species of this subfamily.

Quaternary deep-sea ostracods from the north-western Pacific Ocean: global biogeography and Drake-Passage, Tethyan, Central American and Arctic pathways

Twelve genera and 19 species of deep-sea ostracods from the Shatsky Rise, north-western Pacific, were examined and illustrated for taxonomy. Three new species, Cytheropteron nasutum sp. nov., Poseidonamicus shatskyensis sp. nov. and Legitimocythere stellae sp. nov., are described. Based on these Shatsky Rise ostracods and a comprehensive literature survey of synonyms, we discuss global biogeography and possible migration pathways of deep-sea species. The four possible deep-water pathways connecting the Atlantic and Pacific Oceans are: the Drake Passage (Southern Ocean), established by 30 Ma; the Tethys Seaway, which had closed by 19–14 Ma; the Central American Seaway, which had closed by 3 Ma; and the Arctic Ocean Seaway via the Bering Strait, which opened about 4.8–7.4 Ma, and via the Fram Strait, which opened between 10 and 20 Ma. The Drake Passage is likely the major pathway. We argue that the Arctic was an important pathway for some deep-sea species before the mid-Pleistocene. Most deep-sea organisms have poor fossil records, and thus the rich fossil record of deep-sea ostracods is an ideal model system for the study of deep-time biogeography of deep-sea organisms. It may well be that other deep-sea organisms had similar palaeobiogeographical histories and patterns.http://zoobank.org/urn:lsid:zoobank.org:pub:3B70B7E5-04E0-4FF7-91EF-88CE1B199C8D

Pleistocene deep-sea ostracods from the Oki Ridge, Sea of Japan (IODP Site U1426) and condition of the intermediate water

AbstractThe Sea of Japan (also termed the East Sea) has a circulation system isolated from the Pacific Ocean and East China Sea. The East Asian winter monsoon drives the circulation system and cools the Tsushima Warm Current (TWC) to form the Japan Sea Intermediate–Proper Water (JSIPW). The intermediate water conveys oxygen to deep-sea floors, which is available for benthic animals. During the Pliocene (3.5–2.8 Ma), Temperate Intermediate Water (TIW) was formed under the weak winter monsoon, and extinct ostracod TIW taxa were found. Little is known about early Pleistocene intermediate water and the extinction mode of benthic ostracods. We studied radiolarians and ostracods from deep-sea sediments between 2.0 and 1.3 Ma (Marine Oxygen Isotope Stage [MIS] 77 to MIS 41) at Integrated Ocean Drilling Program Site U1426, Sea of Japan. The ostracod faunas contained TIW and JSIPW taxa. The radiolarian subtropical-water taxa and the JSIPW ostracods indicate a small influx of the TWC and the JSIPW. The TIW occasionally expanded to the middle bathyal zone. By analogy with the relationship between the modern JSIPW and winter monsoon, weak winter monsoon possibly caused gentle temperature gradients in the water column and the expansion of the TIW. The JSIPW taxa expanded their ranges into the deep sea during interglacial periods.

Taxonomy and climatic zonation of the Late Quaternary bathyal ostracods from the Campos Basin, Brazil

This work represents a new contribution to the knowledge on deep-sea ostracods from the western South Atlantic Ocean based on the core GL77 drilled in the Campos Basin (40°02′50″W; 21°12′22″S), 1287m water depth. Radiocarbon dating and oxygen isotopic analyses in planktonic foraminifera indicate that the 275cm interval studied of this core comprises the marine isotope stages 1, 2 and 3 (approximately 45kyr). Forty ostracode species were identified, yet 19 of them are kept in open nomenclature due to either the absence of adult individuals or poor preservation. Thirteen of those species have been recorded previously in the Brazilian continental margin: Bythocypris kyamos, B. affinis, Cytheropteron inornatum, C. perlaria, K. coimbrai, K. morkhoveni, K. sinuosa, K. trinidadensis, Macrocypris adrecta, Microcythere dubia, M. cronini, Poseidonamicus pintoi and Saida ionia. A new Trachyleberididae species, Ambocythere circumporus nov. sp. is proposed, and Cobanocythere? dubia is reassigned to the genus Microcythere. The stratigraphic distribution of the species in the core GL77 was compared to other studies on deep-sea assemblages carried out in the western Atlantic Ocean. The general species diversity pattern is a significant reduction during the Last Glacial Maximum (LGM) followed by conspicuous changes in Holocene assemblages caused by the appearance of species absent in the Pleistocene. The species Bythocypris kyamos, Cytheropteron perlaria and Saida ionia are restricted to the Marine Isotope Stage (MIS) 1. Poseidonamicus pintoi and Australoecia sp. are predominant and almost exclusive to the MIS 2 and 3. These data indicate the possibility of elaboration of an ostracod-based paleoclimatic zonation for the Quaternary of the south/southeast Brazilian margin.

Latest Cretaceous/Paleocene deep-sea ostracode fauna at IODP Site U1407 (western North Atlantic) with special reference to the Cretaceous/Paleogene boundary and the Latest Danian Event

Abstract During the Paleocene, the marine plankton community recovered its diversity after a severe diversity loss at the Cretaceous/Paleogene (K/Pg) boundary. In general, changes in Paleocene deep-sea ostracode faunas are poorly understood. It is still unclear how the deep-sea ostracode faunas changed during compelling events such as the K/Pg boundary (66.04 Ma) and the Latest Danian Event (LDE: ~ 62.18 Ma), a transient Paleocene warming event. In this report, we describe a study on the latest Cretaceous–Late Paleocene ostracodes from Integrated Ocean Drilling Program Site U1407, off Newfoundland, in the northwestern Atlantic. Thirty-six ostracode taxa were obtained from 202 discrete samples that were collected from the interval between 66.3 and 57.3 Ma. Near the K/Pg boundary, 8% (2 of 25) of the Maastrichtian taxa became extinct. The extinction rate is estimated to be at most 0.12 E MSY − 1 , which is equal to extinction rate of 12% per one million years and is in the same range as the background-level extinction rate. Comparing the extinction rates between different ocean basins such as Maud Rise and Blake Nose, the ostracode extinction at the K/Pg boundary displays striking geographical heterogeneity. Between the Maastrichtian and Danian, the ostracode faunas change from a biofacies dominated by shallow bathyal taxa to one dominated by deep bathyal taxa. During the LDE, ostracode faunas display an increase in their benthic ostracode accumulation rates and taxonomic diversity as well as an increase in the relative abundance of Krithe crassicaudata simultaneously with a decline in carbonate content. A similar change is commonly documented in fauna from the northeastern Atlantic during the Paleocene–Eocene Thermal Maximum (PETM; 56.0 Ma). In contrast to the PETM fauna, an extinction event is not recognized. Near the Danian/Selandian boundary, the ostracodes show an increase in export productivity. After the Danian, the ostracodes form a community that appears to tolerate warm and acidified water. Export productivity remains high during the Selandian and Thanetian.

Vertical distribution of living ostracods in deep-sea sediments, North Atlantic Ocean

The depth distribution of living specimens of deep-sea benthic ostracods (small crustaceans with calcareous shells that are preserved as microfossils) in sediments is poorly understood, despite the importance of this aspect of basic ostracod biology for paleoecologic and paleoceanographic interpretations. Here, we investigated living benthic ostracod specimens from deep-sea multiple core samples, to reveal their depths distributions within sediment cores. The results showed shallow distribution and low population density of living deep-sea benthic ostracods (which are mostly composed of Podocopa). The living specimens are concentrated in the top 1cm of the sediment, hence deep-sea benthic ostracods are either epifauna or shallow infauna. This observation is consistent with the information from shallow-water species. We also confirmed shallow infaunal (0.5–2cm) and very shallow infaunal (0–1cm) habitats of the deep-sea ostracod genera Krithe and Argilloecia, respectively.

Early Pleistocene deep–sea ostracode assemblages and the marine environment in the Sea of Japan

Early Pleistocene deep–sea ostracode assemblages and the marine environment in the Sea of Japan

Late Quaternary deep-sea ostracod taxonomy of the eastern North Atlantic Ocean

Abstract. Taxonomic revision and re-evaluation of the eastern North Atlantic deep-sea ostracods are conducted based on late Quaternary sediments from Ocean Drilling Program (ODP) Hole 982A, Rockall Plateau, eastern North Atlantic. Twenty-one genera and 51 species were examined and (re-)illustrated with high-resolution scanning electron microscopy images. Six new species are described: Polycope lunaris, Argilloecia labri, Bythoceratina nuda, Cytheropteron colesoabyssorum, Cytheropteron colesopunctatum and Cytheropteron paramediotumidum. Excellent fossil ostracod preservation in this sediment core enabled us to provide a robust taxonomic baseline of the eastern North Atlantic deep-sea ostracods for application to palaeoceanographical, palaeoecological and biogeographical studies.

Biogeography of deep-sea wood fall, cold seep and hydrothermal vent Ostracoda (Crustacea), with the description of a new family and a taxonomic key to living Cytheroidea

Stimulated by finding a novel cytheroid ostracod in a piece of sunken wood retrieved from the sea-bed in the Kuril–Kamchatka Trench, we have reviewed all previously published data on ostracods from similarly ephemeral deep-sea habitats (wood falls, hydrothermal vents and cold seeps). These data are placed in the context of all data on living, deep-sea ostracods from other environments. We confirm previous authors׳ conclusions that faunas from these ephemeral habitats are similar at the generic level, and include elements common to shallow and deep habitats. However, at the species level, endemism varies from zero at cold seeps, to 35% in wood falls and 60% at hydrothermal vents, which is an indication of the relative longevity of these habitats. Non-endemic species occur also in oligotrophic, deep-sea sediments but not in shallow environments. This is in contradiction to previous assumptions that these ephemeral faunas share more species and with shallow habitats than genera with the oligotrophic, deep-sea sediments. We agree with previous authors that the dispersal strategy of wood fall, vent and seep ostracods includes hitchhiking and we propose that it also includes the ability to survive ingestion by larger, more motile animals. The homogeneity of the faunas from ephemeral habitats collected off the American continent is in stark contrast to the highly endemic fauna found in Northwestern Pacific. This suggests that the ostracods may have biogeographical patterns similar to those previously proposed for other groups of benthos. However, any proposal for a global biogeographical scheme for ostracod distributions will have to await far more comprehensive coverage from presently unstudied regions.Finally, we describe and name a novel species of ostracod from the wood fall collected at a depth of 5229m in the abyss east to the Kuril–Kamchatka Trench, Northwestern Pacific; erecting a new family Keysercytheridae fam. nov. and a new genus, Keysercythere gen. nov., to accommodate it, and name it, Keysercythere enricoi sp. nov. We present a preliminary key to all Cytheroidea families for which living representatives have been described.

Cenozoic bathyal and abyssal ostracods beneath the oligotrophic South Pacific Gyre (IODP Expedition 329 Sites U1367, U1368 and U1370)

This study reports on Paleocene through Pleistocene deep sea ostracod assemblages from carbonate sequences recovered at Integrated Ocean Drilling Program (IODP) Sites U1367, U1368, and U1370 during Expedition 329 to the South Pacific Gyre (SPG). The SPG has the lowest surface primary productivity in the world oceans, and the sedimentary system beneath it has the lowest rates of organic matter flux to the seafloor in the ocean. Results show that this oligotrophic oceanic environment supported abundant and diverse ostracod faunas during the Oligocene, and the middle Miocene suggesting that ostracods are capable of exploiting low levels of food availability in the deep ocean. The SPG records revealed ostracod assemblages following major global climatic transitions: the Cretaceous/Paleocene (~65.5Ma) and the Eocene/Oligocene (~33.5Ma) transitions, and the middle Miocene climatic optimum (~14Ma). The Danian ostracod assemblage is scarce and characterized by Paraphysocythere spp. and Anebocythereis hostizea. High faunal turnover by the early Oligocene gives rise to an assemblage predominantly characterized by typical lower bathyal and abyssal genera Krithe, Poseidonamicus, Argilloecia, and Cytheropteron that are indicative of cold, moderately oxygenated conditions and signal the cooling of the deep ocean after the E/O transition. An increase in abundance of robust epifaunal taxa Bradleya, Henryhowella, Dutoitella, Pennyella, and Rugocythereis, and a pronounced decrease Argilloecia and Cytheropteron characterize the middle Miocene and Pleistocene assemblages, and indicate the presence of more corrosive bottom waters and enhanced oligotrophic conditions in the SPG. However, low variability in the ostracod assemblage taxonomic composition and stratigraphic distribution at Sites U1367 and U1368 suggest that mostly stable paleoceanographic conditions existed in the South Pacific Gyre during the early to the late Oligocene and from the middle to late Miocene (U1368). Declines in ostracod abundances toward the top of the sedimentary sequences at these sites are synchronous with the late Oligocene warming and the late Miocene carbonate crash in the equatorial Pacific, but they seem to also overlap the time when the site locations subsided below the calcium carbonate compensation depth (CCD) as they moved away from the East Pacific Rise.

Deep-sea Benthic Ostracodes from Multiple Core and Epibenthic Sledge Samples in Icelandic Waters

AbstractDeep-sea benthic Ostracoda (Crustacea) in Icelandic waters are poorly known. Here we report deep-sea ostracode assemblages from the multiple core (MUC) and the epibenthic sledge (EBS) samples collected from Icelandic waters by the first cruise of the IceAGE (Icelandic Marine Animals: Genetics and Ecology) project. Samples from shelf-edge and lower-bathyal working areas are examined. The results show (1) distinct MUC and EBS faunas due to the large difference in mesh size of MUC and EBS; and (2) distinct shelf-edge and lower-bathyal ostracode faunas. Such remarkable faunal turnover from shelf to bathyal depths is similar to the faunal turnovers reported from depth transects in the adjacent regions of the western North Atlantic Ocean, the Greenland Sea, and the North Sea, but, at the same time, there are certain differences in the faunal composition between the Icelandic waters and these adjacent regions. In addition, we illustrate many Icelandic deep-sea ostracode species with high-resolution scanning electron microscopy and composite all-in-focus stereomicroscopic images for the first time. These results provide important basic information on deep-sea ostracode research and biogeography of this important region connecting North Atlantic proper and Nordic Seas.

Quaternary deep-sea ostracode taxonomy of Ocean Drilling Program Site 980, eastern North Atlantic Ocean

Ocean Drilling Program (ODP) Holes 980 B and C, Feni Drift at the eastern slope of the Rockall Plateau, eastern North Atlantic, were examined for late Quaternary deep-sea ostracode taxonomy. Nineteen genera and 32 species were examined and (re-)illustrated with high-resolution scanning electron microscopy images. One new speciesCytheropteron paramassonin. sp. is described and one new nameEucytherura zehaliis proposed forEucytherura hazeliYasuhara et al., 2009. This study provides updated taxonomic information for deep-sea ostracode genera and species from the eastern North Atlantic, which is an important baseline for application of deep-sea ostracodes to paleoceanographical reconstructions and paleoecological studies in this region.

Calibration of past water temperature in the Sea of Japan based on Mg/Ca of ostracode shells of two shallow marine species in the genus Cytheropteron

Compared to Mg/Ca-temperature calibrations in deep-sea ostracodes and the use of these calibrations to understand past conditions, there have been few studies of shallow marine ostracode taxa. In the present study, Mg/Ca-temperature calibrations were constructed for two shallow marine ostracode species belonging to the genus Cytheropteron in the recent sediments of the Sea of Japan in order to reconstruct the past water temperature record in shallow sea areas. The Mg/Ca of adult Cytheropteron miurense and Cytheropteron sawanense shells from nine bottom sediment samples was positively correlated with the mean annual water temperature (WT) according to the following equation: WT (°C)=Mg/Ca of ostracode shell (mmol/mol)∗0.94–9.53. Comparison of the regression curves of Mg/Ca versus WT for six genera showed similar temperature sensitivity of Mg uptake in shells of Cytheropteron, Sarsicytheridea and the genus Krithe in most cases, but lower than those for genera Bythocypris and Loxoconcha and Xestoleberis hanaii. The regression equation was applied to Late Pliocene and the resulting past water temperatures were compared to modern oceanographic data from water depths of 50 to 150m in the Sea of Japan, which is the paleodepth estimated to encompass the habitat of ostracode assemblages. Decreasing variation in the obtained past WT with the increase in the number of fossil ostracode valves from one to four suggests that more than four ostracode valves are required to reconstruct the mean annual WT using the equation established with C. miurense and C. sawanense. Thus, the mean annual WT during the Late Pliocene based on analysis of four specimens ranged from 8.9 to 11.6°C, which is similar to or slightly lower than the WT observed today.