Distribution of some planktonic foraminifera species in deep-sea cores from the red sea and their relation to eustatic sea-level changes

Distribution patterns of planktonic foraminifera in four sediment cores from the Red Sea are studied. The most common species are Globigerinoides ruber, G. sacculifer, Globigerinella siphonifera and Orbulina universa. G. ruber and G. sacculifer show opposite trends of distribution in the sediment cores. Abundance of the foraminifera during the glacial periods suggests that the connection of the Red Sea to the Indian ocean was not completely interrupted and the salinity conditions were not extreme.However, higher salinities appear to have existed in the northern Red Sea, where most of the planktonic foraminifera that occur in the southern Red Sea are absent. It is inferred that the salinity in the southern Red Sea during the glacial period was less than 50%, whereas higher salinity might have existed in the north where the influence of the Indian Ocean was minimal.     

Variation in test diameter of Orbulina universa in the paleoclimatology of the late Quaternary of the Gulf of Mexico

Previous workers have shown that the mean diameter of the test of the planktonic foraminifer Orbulina universa d'Orbigny in Recent sediments of the Indian Ocean is related to water mass distribution and Late Quaternary paleoclimatic variation. In three Late Quaternary deep-sea cores from the Gulf of Mexico, studied here, variation in mean size of O. universa shows an inconsistent relationship with paleoclimatic changes. In two cores (K 97 and TR 126—29), mean size is significantly cross-correlated with paleoclimatic curves derived from principal-component analyses of planktonic foraminiferal frequencies (r₀ = +0.46 and +0.37, respectively). In the third core (K 129), the variatilon in mean size is unrelated in a statistical basis to the paleoclimatic trends (r₀ = +0.16). Oxygen-isotope records are statistically cross-related with the mean size of O. universa in K 97 (r₀ = +0.51) but not in K 129 (r₀ = +0.30).However, despite the occurrence of statistically significant relations in some cases and a general similarity in the trends, the mean diameter of O. universa and the paleoclimatic curves are very different in detail and magnitude. These inconsistencies preclude the use of the mean size of O. universa as a paleoclimatic index in Late Quaternary sequences from the Gulf of Mexico.     

Radiolaria as a reflection of environmental conditions in the eastern and southern sectors of the Indian Ocean: A new statistical approach

Cluster analysis and species abundance plots of radiolarian abundance counts from core tops from the eastern Indian Ocean between 12° S and 31° S, and the southern Indian Ocean between 31° S and 62.5° S, demonstrate the existence of environmentally-related provinces supporting distinct taxa assemblages. These provinces are closely associated with currents in the eastern sector of the Indian Ocean and with fronts in the southern sector.The radiolarian assemblages correlate strongly with salinity-normalised total alkalinity (NTA) at the sea-surface, with temperature, salinity, and density from the sea-surface to 300 m, and with dissolved oxygen and nitrate and phosphate concentrations from the sea-surface to 100 m. Palaeo-reconstructions of these parameters at the sea-surface have been made for six Last Glacial Maximum (LGM) samples from five eastern Indian Ocean cores. The LGM sea-surface temperature estimates are comparable with those based on planktonic foraminiferal counts of the same samples obtained by other researchers. The reconstructions show that, since the LGM, density increased markedly along the Western Australian coast south of 20° S but changed little further from the Western Australian coast. By contrast, phosphate concentrations were marginally lower than modern values along the Western Australian coast south of 20° S but more than twice modern values in the other LGM samples.The utility of various regression and calibration techniques is discussed. It is concluded that, probably due to the effects of differences in radiolarian habitat, ocean currents, and/or environmental gradients, only one method, weighted averaging — partial least squares, is reliable in a study area of this size and complexity. If other methods are to be used, the study area must be partitioned into at least two separate regions with the major split between the eastern and southern sectors of the Indian Ocean.     

Planktonic foraminifera from the eastern Indian Ocean: distribution and ecology in relation to the Western Pacific Warm Pool (WPWP)

Faunal assemblages, principal component (PCA), canonical correspondence (CCA), and factor analysis are applied to planktonic foraminifera from 57 core-top samples from the eastern Indian Ocean. The foraminiferal lysocline occurs at 2400 m north of 15°S where carbonate dissolution is induced by the Java upwelling system, and occurs deeper south of 15°S where carbonate dissolution is characteristic of the oligotrophic regions in the Indian Ocean. Dissolution effects, the February standing stock at the time of collection of the plankton-tow material, and different production rates explain the different foraminiferal assemblages found between plankton-tow and core-top samples. Core-top samples are differentiated by PCA into four groups — Upwelling, Western Pacific Warm Pool (WPWP), Transitional, and Southern — that are related to environmental variables (temperature, salinity and nutrients); all environmental variables follow a strong latitudinal component as indicated by the CCA analysis. Similarly, three assemblages are recognized by factor analysis: Factor 1 (dominated by Globigerinoides sacculifer, G. ruber, Globigerinita glutinata and Globorotalia cultrata), factor 2 (dominated by Globigerina bulloides and Globorotalia inflata) and factor 3 (dominated by Neogloboquadrina dutertrei) explain more than 92% of the variance, and are related to sea-surface temperature, thermocline depth and nutrient levels. The seasonal influence of the Java upwelling system supplies nutrients, phyto- and zooplankton to the oligotrophic eastern Indian Ocean (factor 1). South of 24°S, a deep chlorophyll maximum, a deep euphotic zone, a deep thermocline, SSTs below 22°C, and brief upwelling pulses seem to explain factors 2 and 3. The ratio of G. sacculifer and N. dutertrei, two mutually excluding species, appears to indicate the southern boundary of the WPWP. This ratio is applied to core Fr10/95-11 to demonstrate past shifts of the southern boundary of the WPWP.     

Changes in quaternary oceanographic bottom conditions as documented by foraminifera in sediment cores from the slope of the exmouth plateau (off Western Australia)

Benthonic foraminifera from 15 surface- and 70 core-sediment samples (three cores) from the Western Australian continental margin (Exmouth Plateau) were quantitatively investigated. As far as possible, the occurrences of the species were correlated with the recent oceanographic conditions especially as related to water depths. The sampled sites are separated from the Australian Shelf by the Montebello Trough so that the taphocoenoses cannot become adulterated by foraminifera from the shelf. Only 1% or less of the foraminifera are benthonic species. The benthonic foraminiferal faunas of the surface sediment samples from 3800 to 1700 m are composed of about the same deep-water species as described from southeastern Indian Ocean basins by Corliss (1979a). They differ from one another only because different species dominate the faunas dependent on different water depth and/or water mass. Above 1700 m the character of the benthonic foraminiferal fauna is slowly changing from abyssal to bathyal. Downcore the benthonic foraminifera show marked changes in abundance patterns, which partly parallel the changes which can be observed with the “cool” and “warm” indicating planktonic foraminifera, partly show regular phase displacement with these changes. The different abundances of the same species in a core from, for instance, 3000 m or from 2000 m water depth, respectively, prevent a direct correlation between the cores. It also proved impossible to correlate the changes in the frequency patterns of certain species to certain paleo-oceanographic conditions. Examples for this are given.     

Planktonic foraminifera of the northern Indian Ocean: Distribution and preservation in surface sediments

In the northern Indian Ocean, planktonic foraminiferal tests accumulate in a wide variety of surface-water environments and depositional settings. This variability enables us to isolate the effects that surface-water ecology and differential dissolution have on the distribution of planktonic foraminifera from 251 geographically widespread surface sediment samples.Foraminiferal abundance varies from 0 to > 10⁴ whole foraminifera in the greater than 150 μm fraction per gram dry sediment. Values < 10 characterize the three deep basins of the equatorial Indian Ocean and the western Bay of Bengal. Foraminiferal tests are most abundant on carbonate covered Ninety-East and Carlsberg Ridges. Absolute abundance patterns are mainly controlled by non-ecological processes. Variations in dissolution resistant species (RSP) with water depth reveal that the foraminiferal lysocline (FL) varies regionally. The FL is deepest (3,800 m) in the equatorial region, rises abruptly to 3,300 m in the Arabian Sea, and varies from 2,600 m to near 2,000 m moving northward in the Bay of Bengal. Deep samples with anomalously low RSP (< 30%) suggest redeposition.Systematic geographic and depth-related variation is observed for the 17 most abundant foraminiferal species. Dissolution resistant species (G. menardii, G. tumida, G. dutertrei, P. obliquiloculata) generally exhibit a rapid and continuous increase in relative abundance at and below the FL. Susceptible species (G. ruber, G. bulloides, G. glutinata, for example) exhibit a rapid and continuous decrease in relative abundance at and below the FL. Moderately susceptible species (G. conglobatus, G. aequilateralis, G. conglomerata, for example) rapidly increase in abundance at the FL and systematically decrease with depth below the FL.Principal components analysis (PCA) of faunal data from minimally dissolved (< 30% RSP) samples reveals important ecologically related species intercorrelations. The major biogeographic gradient is the negative covarying relationship between aG. bulloides-G. glutinata species pair and a grouping ofG. sacculifer, G. conglobatus, G. aequilateralis, andG. ruber. PCA of all samples demonstrates how differential dissolution alters this and other species relationships. Species groupings that incorporateG. ruber, G. menardii, andG. dutertrei are particularly affected by dissolution.Comparison of average faunal data from minimally dissolved samples in the northern Indian Ocean with similar samples from other tropical regions suggests varying environmental factors produce distinct faunas within the tropical ocean. For example,G. bulloides, G. falconensis, andG. hexagona are significantly more abundant in northern Indian Ocean surface sediments while such species asG. ruber, G. sacculifer, G. dutertrei, andP. obliquiloculata dominate in other tropical regions.     

Radiolarian biogeography in surface sediments of the eastern Indian Ocean

We analyzed recurrent groups of Radiolaria in 74 core top samples from a transect through the eastern Indian Ocean in order to supplement our previous results from the western Indian Ocean (Johnson and Nigrini, 1980). We now identify six distinct recurrent groups and nine radiolarian assemblages in the combined data set of 120 samples; this extended sample coverage has led to several re-interpretations of the oceanographic significance of the radiolarian distribution patterns. Assemblage boundaries closely reflect the presence of major oceanographic fronts and surface currents including the South Equatorial Divergence, Subtropical Gyre, Subtropical Convergence, and Antarctic Convergence. At least four major aspects of the assemblages in the eastern transect are notably different from those in the western transect, leading to a marked east-west asymmetry in faunal distribution patterns across the Indian Ocean. The assemblage formerly associated with strong upwelling near the Arabian Peninsula is present throughout the Bay of Bengal as well, and is interpreted to reflect high salinity and low oxygen in the subsurface waters of the Indian Ocean north of the Equator. A new assemblage has been identified associated with the westward-flowing Pacific water into the eastern Indian Ocean in low latitudes, and may be a potential stratigraphic and paleoclimatic marker for times of low sea level when this westward near-surface flow was shut off (i.e., glacial maxima). An extensive region in the core of the subtropical gyre between 25°S and 35°S is relatively barren of Radiolaria, yet is marked by a characteristic assemblage distributed asymmetrically, perhaps reflecting the lack of a strong boundary current off the west coast of Australia. Assemblage boundaries in the vicinity of the eastward circumpolar flow are not strictly zonal, and may indicate significant deviations from the mean eastward flow as a necessary condition for conservation of potential vorticity when the flow encounters topographic irregularities.     

Extraordinary capture of a Randall's snapper Randallichthys filamentosus in the temperate south‐eastern Indian Ocean and its molecular phylogenetic relationship within the Etelinae

The capture of a rarely encountered Randall's snapper Randallichthys filamentosus (female, 587 mm fork length) from the upper continental slope (c. 350 m) off the south coast of Western Australia (c. 34·5° S; 122·5° E) in January 2014 represents its first record from the temperate Indian Ocean and a southern range extension. This record suggests that spawning of this predominantly tropical species may probably be occurring in the eastern Indian Ocean, considering the extensive, and unlikely, distance the progeny would have otherwise travelled from its typical distribution in the western and central Pacific Ocean.     

Benthic foraminiferal distributions in Chilean fjords: 47°S to 54°S

Surface sediment samples collected from the fjord region of southern Chile (47° to 54° South) were analyzed for benthic foraminifera. A total of 175 species were identified including agglutinated and calcareous benthic taxa. Hierarchical cluster analysis of the foraminiferal data resulted in the recognition of three distinct biofacies: inner-fjord, intermediate fjord and channel, and oceanic biofacies, geographically controlled by relative position between the Pacific Ocean and fjord heads. Similarity percentage (SIMPER) analysis identified key taxa in the definition of the biofacies that include Globocassidulina rossensis, Cassidulina laevigata and Bulimina notovata. Principal components analysis resulted in two principal components representing sediment size, and bottom water temperature and salinity.Regional distributions are strongly controlled by the oceanographic conditions influenced from the Pacific in the west and the glacial/freshwater input from the east. Localized distributions of foraminifera are controlled by conditions influenced by the physiography of the individual fjords and channels. The distribution of Chilean fjord foraminifera and their environmental associations are consistent with results from other temperate to high latitude fjord foraminiferal studies.     

Isotopic and distributional evidence of a planktonic habit for the foraminiferal genusStreptochilus Bro¨nnimann and Resig, 1971

Oxygen and carbon isotope analyses show that the biserial foraminiferal genusStreptochilus, which was originally described from pelagic sediments on the Eauripik Rise and Ontong Java Plateau, lived deep in the upper water column within the oxygen minimum layer. The species ofStreptochilus average from 4 to 19% of the foraminiferal assemblages in which benthic forms compose less than 1 or 2%. Specimens ofStreptochilus are selectively dissolved when in contact with the bottom water mass. Their rapid evolutionary turnover of less than a few million years and their wide areal distribution in the equatorial Indo-Pacific are indicative of planktonic foraminifera. Aside from usefulness of the species ofStreptochilus as stratigraphic indices, these Neogene biserial planktonic foraminifera are potential indices of paleoceanographic stratification.     

Spatial Variations in Microbial Community Composition in Surface Seawater from the Ultra-Oligotrophic Center to Rim of the South Pacific Gyre

Surface seawater in the South Pacific Gyre (SPG) is one of the cleanest oceanic environments on earth, and the photosynthetic primary production is extremely low. Despite the ecological significance of the largest aquatic desert on our planet, microbial community composition in the ultra-oligotrophic seawater remain largely unknown. In this study, we collected surface seawater along a southern transect of the SPG during the Integrated Ocean Drilling Program (IODP) Expedition 329. Samples from four distinct sites (Sites U1368, U1369, U1370 and U1371) were examined, representing ∼5400 kilometers of transect line from the gyre heart to the edge area. Real-time PCR analysis showed 16S rRNA gene abundance in the gyre seawater, ranging from 5.96×10⁵ to 2.55×10⁶ copies ml⁻¹ for Bacteria and 1.17×10³ to 1.90×10⁴ copies ml⁻¹ for Archaea. The results obtained by statistic analyses of 16S rRNA gene clone libraries revealed the community composition in the southern SPG area: diversity richness estimators in the gyre center (Sites U1368 & U1369) are generally lower than those at sites in the gyre edge (Sites U1370 & U1371) and their community structures are clearly distinguishable. Phylogenetic analysis showed the predominance of Proteobacteria (especially Alphaproteobacteria) and Cyanobacteria in bacterial 16S rRNA gene clone libraries, whereas phylotypes of Betaproteobacteria were only detected in the central gyre. Archaeal 16S rRNA genes in the clone libraries were predominated by the sequences of Marine Group II within the Euryarchaeota, and the Crenarchaeota sequences were rarely detected, which is consistent with the real-time PCR data (only 9.9 to 22.1 copies ml⁻¹). We also performed cultivation of heterotrophic microbes onboard, resulting in 18.9% of phylogenetically distinct bacterial isolates at least at the species level. Our results suggest that the distribution and diversity of microbial communities in the SPG surface seawater are closely related to the ultra-oligotrophic oceanographic features in the Pacific Ocean.     

Living planktonic foraminifera in the Fram Strait (Arctic): absence of diel vertical migration during the midnight sun

The timing of vertical migration in planktonic foraminifera (ex. ontogenetic, diel) is still an open debate. This work aims to investigate the diel vertical migration (DVM) of Neogloboquadrina pachyderma (N. pachyderma) and Turborotalita quinqueloba (T. quinqueloba) in the Arctic during the midnight sun. N. pachyderma and T. quinqueloba dominate the total assemblage in the cold Polar Water and warmer North Atlantic Water masses, respectively. Foraminifera were collected at several depths along the Fram Strait. Afterwards sampling was performed at the same station for 24 h at continuous and discrete time intervals. Results show no evidence of planktonic foraminifera DVM since there was no significant variability in the abundance and size distribution during the 24-h collection period. This finding provides information to improve the interpretation of foraminifera in paleoclimatic works. This is especially relevant in the Fram Strait as paleoclimatic studies in this region are fundamental to investigating the history of the Atlantic water inflow into the Arctic Ocean.     

Climatic change drives dynamic source–sink relationships in marine species with high dispersal potential

While there is now strong evidence that many factors can shape dispersal, the mechanisms influencing connectivity patterns are species‐specific and remain largely unknown for many species with a high dispersal potential. The rock lobsters Jasus tristani and Jasus paulensis have a long pelagic larval duration (up to 20 months) and inhabit seamounts and islands in the southern Atlantic and Indian Oceans, respectively. We used a multidisciplinary approach to assess the genetic relationships between J. tristani and J. paulensis, investigate historic and contemporary gene flow, and inform fisheries management. Using 17,256 neutral single nucleotide polymorphisms we found low but significant genetic differentiation. We show that patterns of connectivity changed over time in accordance with climatic fluctuations. Historic migration estimates showed stronger connectivity from the Indian to the Atlantic Ocean (influenced by the Agulhas Leakage). In contrast, the individual‐based model coupled with contemporary migration estimates inferred from genetic data showed stronger inter‐ocean connectivity in the opposite direction from the Atlantic to the Indian Ocean driven by the Subtropical Front. We suggest that the J. tristani and J. paulensis historical distribution might have extended further north (when water temperatures were lower) resulting in larval dispersal between the ocean basis being more influenced by the Agulhas Leakage than the Subtropical Front. As water temperatures in the region increase in accordance with anthropogenic climate change, a southern shift in the distribution range of J. tristani and J. paulensis could further reduce larval transport from the Indian to the Atlantic Ocean, adding complexity to fisheries management.     

The development of planktonic biogeography in the Southern Ocean during the Cenozoic

Deep-sea drilling at high latitudes of the Southern Hemispheres has provided almost the only available data to evaluate the biogeographic development of the planktonic biota in the Southern Ocean during the Cenozoic (65 m.y. to Present Day). Paleontological investigations on Deep Sea Drilling Project (DSDP) materials have shown that the development of Cenozoic planktonic biogeography of the Southern Ocean is intimately linked with the evolution of the Southern Ocean water masses themselves. During the Cenozoic, this has included the development of the Circum-Antarctic Current system as obstructing land masses moved apart, the refrigeration and later extensive glaciation of the continent, and the development of the Antarctic Convergence (Polar Front) with related oceanic upwelling.Almost all evolution of calcareous planktonic microfossils has occurred outside of the Antarctic—Subantarctic region followed by limited migration into these water masses. Virtually no endemism occurs amongst calcareous microfossil groups at these latitudes. In contrast, conspicuous and widespread evolution has occurred within the siliceous microfossil groups especially during the Neogene. Low diversity and differences in stratigraphic ranges of Antarctic calcareous microfossils makes them only broadly useful for correlation. Relatively higher diversities within the Subantarctic provide a firmer basis for more detailed correlation, although the ranges of fossils are often different than at lower latitudes because of different paleoceanographic and paleoclimatic controls. Within the Antarctic water mass south of the Antarctic Convergence, siliceous microfossilsbiostratigraphy, oxygen isotopic stratigraphy and magnetostratigraphy, provide the only firm basis for correlation with low-latitude sequences.Eocene (55-38 Ma) sediments contain abundant calcareous microfossils even closely adjacent to the continent. Antarctic calcareous planktonic microfossils of this age exhibit relative high diversity, although this is lower than assemblages of equivalent age at middle and low latitudes. Within the Subantarctic region, Eocene planktonic foraminifera exhibit strong affinities with those in the temperate regions. Biogeographic differences exist between various sectors of the Southern Ocean related to biogeographic isolation preceding the development of the Circum-Antarctic Current. Subantarctic calcareous nannofossil assemblages of Paleocene and Eocene age exhibit higher diversity than Oligocene and Neogene assemblages. Siliceous microfossils are poorly represented or at best poorly known.One of the most dramatic changes in Southern Ocean planktonic biogeography occurred near the Eocene/Oligocene boundary (38 Ma). Since then, Antarctic planktonic foraminiferal assemblages have exhibited distinct polar characteristics, marked in particular by low diversity, and this event thus reflects the initiation of the Antarctic faunal and floral provinces. Profound paleoceanographic changes at this time, which triggered the biogeographic crisis, appear to be related to the initiation of widespread Antarctic sea-ice formation, and rapid cooling of deep and intermediate waters, in turn associated with increased Antarctic glaciation. During the Oligocene, planktonic microfossil diversity was low in all groups throughout the world's oceans. In Antarctic waters, the early Oligocene foraminiferal fauna is monospecific (Subbotina angiporoides), while in the later Oligocene two species (S. angiporoides and Catapsydrax dissimilis) were recorded. Calcareous nannofossil assemblages are of low diversity compared with the Eocene. Subantarctic foraminiferal faunas of Oligocene age display much higher diversity than those in the Antarctic, but early and middle Oligoceae faunas still exhibit the lowest diversities for the entire Cenozoic. Siliceous assemblages remain relatively inconspicuous in most regions of the Southern Ocean.The Paleogene-Neogene transition (22 Ma) is marked by a major change in the global planktonic biogeography, i.e. modern patterns developed in which permanent, steep faunal and floral diversity gradients existed between tropical and polar regions; a gradient which has persisted even during the most severe glacial episodes. Oligocene assemblages of low diversity and almost cosmopolitan distribution were replaced by distinctive belts of planktonic assemblages arranged latitudinally from the tropics to the poles. The establishment of the steep planktonic diversity gradients and latitudinal provinces near the beginning of the Neogene almost certainly were linked to the development of the Circum-Antarctic Current in the late Oligocene which effectively separated high- and low-latitude planktonic assemblages. These fundamental global circulation and biogeographic patterns have persisted through the Neogene.During the Neogene (22 Ma to Present Day), Antarctic calcareous microfossil assemblages exhibit persistent low diversity and high dominance, while Subantarctic assemblages are of much greater diversity. The beginning of the Neogene (= beginning of Miocene) heralded the development of the high-latitude siliceous microfossil assemblages towards their present-day dominant role. Siliceous biogenec productivity began to increase. These changes were linked to the initial development and later intensification of circulation associated with the Antarctic Convergence and Antarctic Divergence. The Antarctic Convergence sharply separates dominantly siliceous assemblages to the south from calcareous assemblages to the north. Radiolarian assemblages became more endemic. Relatively warm early and middle Miocene conditions are reflected by slightly higher diversity of planktonic foraminifera and by the presence, in the northern Subantarctic, of conspicuous discoasters in early Miocene sediments. In Antarctic waters, calcareous nannofossils become unimportant as biogenic elements after the middle Miocene.The latest Miocene ( 5 m.y. ago) was marked by northward movement of the Antarctic Convergence, corresponding expansion of the Antarctic water mass, and low diversity of calcareous assemblages. Pliocene planktonic foraminifera seem to be largely monospecific in Antarctic and southern Subantarctic sequences. During the Quaternary, Antarctic waters reached a maximum northward expansion and exhibit highest siliceous biogenic productivity for the Cenozoic. In the Subantarctic, Quaternary foraminiferal diversities are much higher than in Pliocene sequences. Although calcareous nannofossil diversity may be high, only a few species are abundant. Large northward shifts of Antarctic and Subantarctic water masses have occurred during the Quaternary although no southward penetrations have occurred much beyond that of the present day. Several radiolarian and foraminiferal species disappeared or appeared at or close to a number of paleomagnetic reversals during the last 4 m.y. These faunal events, which provide valuable datums, do not seem to be associated with major climatic changes.     

A cladistic phylogeny of the family Patellidae (Mollusca: Gastropoda)

A phylogenetic hypothesis for the patellid limpets is reconstructed by cladistic analysis of morphological characters from 37 species, representing all but one of the living members of the family. Characters included in the analysis are derived from shell shape and microstructure, headfoot and pallial complex, radula and sperm. The species fall into four clades, providing the basis for a new phylogenetic classification into four monophyletic genera: Helcion (four species; southern Africa), Cymbula (eight species; southern Africa, eastern Atlantic, southern Indian Ocean), Scutellastra (17 species; southern and southwestern Africa, Australia, Indo-West Pacific, Eastern Pacific) and Patella (nine species; northeastern Atlantic and Mediterranean). The analysis suggests sister-group relationships between Helcion and Cymbula, and between Scutellastra and Patella. In combination with present-day patterns of geographical distribution, this phylogenetic hypothesis is used to discuss the historical biogeography of the Patellidae. Scutellastra may have originated in southern Africa and dispersed across the Pacific, or alternatively may be a primitively Tethyan group. Both Helcion and Cymbula appear to have originated in southern Africa, but three Cymbula species have dispersed respectively to northwest Africa, St Helena and the southern Indian Ocean. The patellids of the northeastern Atlantic form a single clade, Patella (including P. pellucida), which may have arrived by northward dispersal of an ancestor from southern Africa, or possibly by vicariance of a widespread ancestral Tethyan distribution. The known fossil record of patellids is too fragmentary to permit choice between these alternatives.     

Molecular evidence for an independent origin of modern triserial planktonic foraminifera from benthic ancestors

Gallitellia vivans is the only Recent representative of the triserial planktonic foraminiferal family Guembelitriidae. The origin and evolution of this interesting albeit poorly known family are enigmatic. To elucidate the phylogenetic relationships between G. vivans and other planktonic foraminifera, we sequenced the small subunit ribosomal DNA (SSU rDNA) for comparison to our extensive database of planktonic and benthic species. Our analyses suggest that G. vivans represents a separate lineage of planktonic foraminifera, which branches close to the benthic rotaliids Stainforthia and Virgulinella. Both genera resemble Gallitellia in general morphological appearance, having elongate triserial tests at least in their early ontogenic stages. The divergence time of G. vivans is estimated at ca. 18 Ma (early Miocene), suggesting an origin independent from the Cretaceous and Paleogene triserial planktonic foraminifera. Our study thus indicates that modern triserial planktonic foraminifera are not related to the Cretaceous–Paleogene triserial species, and that the sporadic occurrences in the fossil record are not the result of poor preservation, but reflect multiple transitions from benthic to planktonic mode of life.     

Spatial and temporal variability of surface water in the Kuroshio source region, Pacific Ocean, over the past 21,000 years: evidence from planktonic foraminifera

The Kuroshio Current is the major western boundary current of the North Pacific Ocean and has had a large impact on surface water character and climate change in the northwestern Pacific region. The Kuroshio Current becomes a distinctive surface flow in the Ryukyu Arc region after diverging from the North Equatorial Current and passing through the Okinawa Trough. Therefore, the Ryukyu Arc area can be called the Kuroshio source region. We reconstructed post-21-ka time–space changes in surface water masses in the Ryukyu Arc region using 15 piston cores which were dated by planktonic δ¹⁸O stratigraphy and AMS ¹⁴C ages. Our analysis utilized spatial and temporal changes in planktonic foraminiferal assemblages which were classified into the Kuroshio, Subtropical, Coastal, and Cold water groups on the basis of modern faunal distributions in the study region. These results indicate that the Kuroshio Current and adjacent surface water masses experienced major changes during: (1) the Last Glacial Maximum (LGM), and (2) the so-called Pulleniatina minimum event (PME) from 4,500 to 3,000 yr BP. The Kuroshio LGM event corresponds to severe global cooling and is marked by decreases in planktonic δ¹⁸O values and estimated sea-surface temperature (SST) with the dominance of the Cold water group of planktonic foraminifera. Cooling within the Kuroshio source region was enhanced during the LGM event because the Kuroshio Current was forced eastward due to the formation of a land bridge between Taiwan and the southern Ryukyu Arc which prohibited its flow into the Okinawa Trough. Except for the severe reduction and disappearance of the Pulleniatina group, no clear cooling signal was identified during the PME based on δ¹⁸O values, estimated SST values and variations in the composition of planktonic foraminiferal faunas. The PME assemblages are marked by high abundances of Neogloboquadrina dutertrei, a distinctive Kuroshio type species, along with other species assigned to the Coastal and Central water groups. Subtle ecological differences exist between Pulleniatina obliquiloculata and N. dutertrei; i.e. P. obliquiloculata exhibits lower rates of reproduction under conditions of lower primary productivity in the central Equatorial Pacific Ocean. El Niño-like conditions in the Equatorial Pacific Ocean result in lower rates of surface transport in the Kuroshio Current. In turn, this response triggers lower rates of primary productivity in central equatorial surface waters as well as in the upstream Kuroshio source region, ultimately resulting in a lower abundance of P. obliquiloculata. Thus, we interpret the PME as a possible proxy signal of El Niño-like conditions and enhancement of the El Niño Southern Oscillation climate system after the PME in the tropical and sub-tropical Pacific Ocean.     

Foraminifera and coccolithophorid assemblage changes in the Panama Basin during the last deglaciation: Response to sea-surface productivity induced by a transient climate change

The responses of community assemblages of planktonic and benthonic foraminifera and coccolithophorids to transient climate change are explored for the uppermost 2 m of cores ODP677B (1.2°N; 83.74°W, 3461 m) and TR163-38 (1.34°S; 81.58°W, 2200 m), for the last ∼ 40 ka. Results suggest that the deglaciation interval was a time of increased productivity and a major reorganization of planktonic trophic webs. The succession in dominance between the planktonic foraminifera species Globorotalia inflata, Globigerina bulloides, and Neogloboquadrina pachyderma denote four periods of oceanographic change: (1) advection (24-20 ka), (2) strong upwelling (20-15 ka), (3) weak upwelling (14-8 ka) and (4) oligotrophy (8 ka to present). Strong upwelling for the deglaciation interval is supported by the low Florisphaera profunda/other coccolithophorids ratio and the high percentage abundance of Gephyrocapsa oceanica. Benthonic foraminifera assemblage changes are different in both cores and suggest significant regional variations in surface productivity and/or oxygen content at the seafloor, and a decoupling between surface productivity and export production to the seafloor. This decoupling is evidenced by the inverse relationship between the percentage abundance of infaunal benthonic foraminifera and the percentage abundance of N. pachyderma. The terrigenous input of the Colombian Pacific rivers, particularly the San Juan River, is suggested as a possible mechanism. Finally, the Globorotalia cultrata/Neogloboquadrina dutertrei ratio is used to reconstruct the past influence of the Costa Rica Dome-Panama Bight and cold tongue upwelling systems in the Panama Basin. A northern influence is suggested for the late Holocene (after 5 ka) and the last glacial (before 20 ka), whereas a southern influence is suggested for the 20-5 ka interval. There is a correspondence between our reconstructed northern and southern influences and previously proposed positions of the Intertropical Convergence Zone (ITCZ) after the Last Glacial Maximum (LGM).     

Magnesium and strontium compositions of recent symbiont-bearing benthic foraminifera

Minor and trace elements in foraminiferal carbonates are potential paleo-proxies of climate, nutrient and seawater composition. There are very few reports of trace element composition of symbiont-bearing, larger foraminifera that are known to be important constituents of shallow-marine, modern and ancient carbonates. In this paper we examine the range of variation in Mg and Sr content of Recent species of these foraminifera from a lagoon of Lakshadweep Atoll (Indian Ocean) and Akajima Islands, Japan. Two hyaline species, Amphistegina lessonii and Neorotalia calcar,and two porcellaneous species, Amphisorus hemprichii and Marginopora vertebralis were collected live from Lakshadweep islands. Mg / Ca in these foraminifera is of an order of magnitude higher than the values reported for planktonic and symbiont-free benthic foraminifera. The Sr / Ca values are, however, comparable with the reported values in other foraminiferal taxa and they are found to vary within a narrow range. Electron-probe micro-analysis of three symbiont-bearing benthic species indicates spatial heterogeneity of high orders in Mg / Ca composition in all the species. The annual variation in temperature and pH of the lagoon water cannot explain the observed amplitude of the compositional variation. The photosynthesis and respiration of the symbionts and host foraminifera are possibly the major cause of compositional heterogeneity in individual tests, as has also been recently postulated for symbiont-bearing planktonic foraminiferal species. It highlights the need to isolate biological factors and necessitates species-specific paleotemperature scale in paleoclimatic analysis. We also analyzed δ¹⁸O, δ¹³C, Ca, Mg and Sr in carefully dissected chambers of a reef-dwelling, porcellaneous benthic foraminifer, Marginopora kudakajimaensis, collected live in four seasons. A moderate positive correlation is observed between Mg / Ca and temperature. However, large inter- and intra-test variation in Mg limits the precision of Mg / Ca as palaeotemperature proxy. The Sr / Ca of the test calcite is unrelated to temperature of the sea water. The δ¹³C of M. kudakajimaensis does not correlate with δ¹⁸O, Mg / Ca or Sr / Ca.