Ranking of dissolution susceptibility of planktonic foraminifera at high latitudes of the South Atlantic Ocean

Surface-sediment samples from the Maurice Ewing Bank (eastern Falkland Plateau), South Atlantic Ocean, have been analyzed to rank dissolution susceptibility of cool water planktonic foraminiferal species. A dissolution index is formulated from quantitative analyses of sedimentological properties (CaCO₃ content, frequency of planktonic foraminiferal fragments, radiolarians, mineral grains, and ratio of a dissolution-tolerant to a dissolution-susceptible planktonic foraminiferal species). This index is used to assess degrees of dissolution in the samples. Quantified differences in relative abundance of species between the two dissolution regimes (less prominent and stronger dissolution) formed the basis for differentiation. The species were ranked in the following order, from most resistant to least resistant: sinistrally coiled variety ofNeogloboquadrina pachyderma (antarctic variety of this species),Globorotalia inflata, G. truncatulinoides, Globigerina bulloides andGlobigerinita glutinata (a tie), dextralN. pachyderma (subantarctic variety),Globigerinita uvula, andGlobigerina quinqueloba. Fragmentation (frequency of damaged tests) increases with increasing dissolution in tolerant species, but not in susceptible species. This may be because susceptible species are completely dissolved under intense dissolution, whereas tolerant species, although damaged, remain and increase in abundance.     

Oxygen and carbon isotope studies in recent foraminifera from the southwest Indian ocean

Eighteen species of planktonic foraminifera have been analyzed for their oxygen and carbon isotopic composition in five Recent samples of deep-sea sediment from the southwest Indian Ocean; one sample of glacial age and one mid-Holocene sample were also studied. On the basis of oxygen isotopic composition three groups are recognized. Species in the first group (Globigerinoides ruber, G. sacculifer and G. conglobatus; G. Globigerina rubescens and Globigerinita glutinata) calcity in the near-surface Tropical Water, so that the oxygen isotopic composition of their test carbonate may be used to indicate surface temperature. Species in the second group (Pulleniatina obliquiloculata, Neogloboquadrina dutertrei, Orbulina universa, Globigerinella siphonifera and Sphaeroidinella dehiscens) are associated with the sub-surface high-salinity Subtropical Water, so that their oxygen isotope composition indicates trends in the temperature of this water mass. The third group (the species of Globorotalia) calcity in the deeper Central Water. The average oxygen isotopic composition of each Globorotalia species is more or less constant over the range studied and does not reflect the surface temperature trend.The carbon isotopic composition of three species (Globigerina rubescens, Globigerinoides ruber and Globigerinita glutinata indicate departure from isotopic equilibrium by at least 3%₀. Among the remaining species the variation of carbon isotopic composition with depth (where depth is inferred from the temperature estimated from oxygen isotopic composition) implies that N. dutertrei, P. obliquiloculata and G. siphonifera occupy the shallow subsurface oxygen minimum, while the deeper-dwelling globorotaliids approach the deeper oxygen minimum. Hence it is possible, despite scatter among the data, to discern the pattern of oxygen content with depth in the overlying water masses from an examination of oxygen and carbon isotopic composition among foraminiferal species in the sediment. This promises to be an exciting new tool for palaeo-oceanographic investigations.     

Comparison of seasonal flux variations of planktonic foraminifera in sediment traps on both sides of the Ryukyu Islands,Japan

Variations in the fluxes of planktonic foraminifera were analyzed based on sediment trap data collected over a period of 10 months, from October 1994 to August 1995, at stations JAST01 and JAST02, located on both sides of the Ryukyu Islands, Japan. Station JAST01 (latitude 27°23′N, longitude 126°44′E) was deployed at a depth of 1000 m in the Okinawa Trough, East China Sea, along the flow axis of the Kuroshio Current, west of the islands, whereas station JAST02 (latitude 25°4′N, longitude 127°34′E) was deployed at a depth of 3000 m in the Ryukyu Trench, along the western margin of the northwest Pacific, east of the Islands. The total planktonic foraminiferal fluxes (TFFs) in the eastern station were high in winter, when the surface-water column was vertically well mixed. In contrast, the TFF peaks did not show significant seasonality in the western station, but values fluctuated with the northwest–southeast oscillation of the Kuroshio axis. Among the 36 planktonic foraminiferal species identified in the trap samples, Globigerina bulloides, Globigerinita glutinata, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, Globigerinoides ruber, Globigerinoides sacculifer and Globigerina falconensis exhibited a greater shell flux. On both sides of the Ryukyu Island Arc, the fluxes of G. ruber and G. sacculifer increased synchronously with the seasonal warming of surface waters, whereas that of G. falconensis increased during winter, when the water column was vertically well mixed as a result of the NW monsoon. In contrast to these species, which exhibited similar seasonal flux variation patterns at both stations, the species G. bulloides, G. glutinata, N. dutertrei, and P. obliquiloculata displayed different flux variations on both sides of the islands. These fluxes seem to be regulated by phytoplankton productivity, which is controlled by the vertical structure of the water column on the eastern Ryukyu Trench side and by the oscillation of the Kuroshio axis on the western Okinawa Trough side. Lateral transport of suspended planktonic foraminiferal shells to the Okinawa Trough might exist, but is not prominent enough to wipe out the original features of the planktonic foraminiferal flux. The species G. falconensis is an indicator of winter mixing on both sides of the Ryukyu Islands, and may possibly be used as a proxy to trace the intensity of the paleo-winter monsoon.     

Application paléoécologique de la méthode d'analyse factorielle en composantes principales: interprétation des microfaunes de foraminifères planctoniques quaternaires en méditerranée. II. Étude des espèces de méditerranée orientale

The principal component analysis method is applied to the study of associations of different Pleistocene and Holocene planktonic Foraminifera in five cores from the eastern Mediterranean. Comparison of the fossil foraminiferal distribution with the distribution of living species leads to grouping of the fossil microfauna on the basis of paleoecological controls. Factor 1 is interpreted as representing thermal control. We recognize as warm-water species Globigerinoides trilobus, Globigerinoides trilobus sacculifer, Orbulina universa, Globigerinella siphonifera, Globigerinoides ruber. Cold-water species are Globigerina pachyderma, Globorotalia scitula, Globigerina quinqueloba, Globigerinita glutinata. Species considered to be of intermediate character are Globigerina bulloides, Globorotalia inflata and Globorotalia truncatulinoides. Factor 2 also leads to the grouping of these last species and may reflect the contributing influence of productivity phenomena. A quadratic liaison interpreted as the “Guttman effect” relates factors 1 and 2. Factor 3 introduces complications resulting from apparently sporadic, irregular events affecting the distribution of certain species, notably Globoratalia inflata, Globorotalia truncatulinoides and Globigerina dutertrei.     

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.     

A size analysis of planktic foraminifera from the Arabian Sea

Planktic foraminiferal faunas from different environments in the Arabian Sea were size fractionated using 14 sieves with meshes between 100 and 710 μm, to assess the effect of the sieve mesh size cut off level on the faunal composition and to determine the size frequency distribution of individual species. Nine samples from a plankton pump and a towed net, a sediment trap, a box-core and a piston core were selected, to cover living and settling flux faunas as well as fossil faunas from the sediment. In living faunas, most species show an exponential size frequency distribution, with highest numbers in the finest interval of the size spectrum. In sediment trap and core samples, individual species size frequency distributions may consist of: (1) an exponential distribution of relatively small pre-adult specimens; (2) a Gaussian-shaped distribution of larger specimens, which may be classified as adult or terminal; or (3) a combination of both. The distributions are separated using a best fit technique. The composition of the total planktic foraminiferal fauna strongly changes along the size spectrum. Dominant taxa in >355 μm fractions are Orbulina universa, Globorotalia menardii, Globorotalia tumida, Globigerinella siphonifera and Globigerinoides sacculifer, in 125–355 μm fractions Globigerina bulloides, Globigerinoides ruber, Neogloboquadrina dutertrei and Globigerinita glutinata, and in <125 μm fractions Dentigloborotalia anfracta, Tenuitella compressa, Tenuitella iota, Turborotalita quinqueloba and the immature specimens of larger species. Consequently, the choice of the sieve mesh size strongly determines the percent composition of the assemblage and in turn the paleoceanographic interpretations based on these counts. Species richness and the Shannon diversity increase with decreasing sieve mesh size, while equitability generally decreases with decreasing size. In the water column approximately 60% of the fauna (>100 μm) is present in the 100–125 μm fraction and 1–6% is larger than 250 μm. In samples representing a settling flux (sediment trap and sediment samples) 29–57% of the fauna is present in the 100–125 μm fraction, while 6–23% is larger than 250 μm. Size frequency distributions of the dextral Neogloboquadrina complex (= Neogloboquadrina dutertrei and Neogloboquadrina pachyderma + P–D intergrades) show a bimodal pattern; a smaller peak reflecting dextral Neogloboquadrina pachyderma, and a larger peak of adult Neogloboquadrina dutertrei. By applying a best fit technique to the data, the two species may be separated from each other. In size fractions larger than 150 μm most species have reached the adult stage of ontogeny and we recommend this mesh size for standard faunal analysis. In addition, sieve mesh sizes of 125 and 250 μm have to be used to obtain a reliable estimate of the abundance of small and large species, respectively.     

Linkages between surface and deep circulations in the southern Japan Sea during the last 27,000 years: Evidence from planktic foraminiferal assemblages and stable isotope records

We analyzed planktic foraminiferal assemblages, oxygen and carbon isotope records, and the presence or absence of laminations to reconstruct the paleoenvironments of the southern Japan Sea since the last glacial period. Data were collected from two well-dated cores. One core (water depth 999 m) included thinly laminated mud layers, the other (water depth 283 m) contained nonlaminated sediments. Tephrochronology and accelerator mass spectrometry ¹⁴C dating of 14 horizons revealed that the two cores contained continuous records of the last 27 cal kyr. A total of 13 planktic foraminiferal species belonging to six genera were identified in down-core samples. The typical indicators of the Tsushima Current water, Globigerinoides ruber, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, Globigerinoides tenellus, and Globigerinita glutinata occurred since 9.3 cal kyr BP. Neogloboquadrina incompta, which was the dominant species in the Tsushima Current region of the modern Japan Sea, first occurred at 8.2 cal kyr BP and dominated the assemblage since 7.3 cal kyr BP. These results clearly indicate that the warm Tsushima Current started to inflow into the Japan Sea at 9.3 cal kyr BP, and the modern surface conditions in the southern Japan Sea were essentially established at 7.3 cal kyr BP. Our data and comparison of the presence or absence of laminated sediments in three locations from the southern Japan Sea suggest that deep circulation during the deglacial period was weaker than that at present. In addition, deep circulation in the modern Japan Sea, which supplies oxygen-rich water to the entire basin, started probably in association with the first inflow of the Tsushima Current beginning at 9.3 cal kyr BP.     

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.     

Calcite dissolution and the modification of planktonic foraminiferal assemblages

The results of an in situ experiment in the Panama Basin allow us to determine the way in which planktonic foraminiferal assemblages are modified by calcite dissolution. Pre-weighed planktonic foraminiferal samples of known species composition were attached to a deep-sea mooring at various water depths between 665 m and 3791 m for a period of 123 days. Weight loss due to dissolution during this period ranged from less than 5% for the shallowest samples to slightly over 30% for the deepest samples. In terms of change in foraminiferal number, this is equivalent to decreases of between 1% and 26%. Only in the samples placed at the two deepest levels (3769 m and 3791 m) was there a significant loss in the total number of foraminifera. The magnitude of change in the abundance of individual species in early related to their different susceptibilities to dissolution. Species such as Hastigerina pelagica, Globigerinella aequilateralis and Candeina nitida, which are very susceptible to dissolution, exhibited the largest decreases in frequency percentage while the more resistent species (Sphaeroidinella dehiscens, Pulleniatina obliquiloculata and Globorotalia truncatulinoides) had minimal changes. From these results a solution-susceptibility ranking for planktonic foraminifera is established that is quite similar to those derived from previous laboratory experiments and sea-floor studies.     

The oxygen isotope composition of planktonic foraminifera from the Guaymas Basin,Gulf of California: Seasonal,annual, and interspecies variability

Sediment trap samples collected over a seven-year period (February 1991–October 1997) from Guaymas Basin in the Gulf of California were used to study the oxygen isotope composition of five species of planktonic foraminifera, Globigerinoides ruber (white), Globigerina bulloides, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, and Globorotalia menardii. The δ¹⁸O data were analyzed for temporal and interspecies variability and were compared to local hydrography to evaluate the use of each species in reconstructing past oceanographic applications. The two surface dwelling species, G. ruber and G. bulloides displayed the lowest δ¹⁸O values (～ 0.0 to ? 5.0‰), while δ¹⁸O values for the thermocline dwelling N. dutertrei, P. obliquiloculata, and G. menardii were higher (～ 0.0 to ? 2.0‰). The δ¹⁸O of G. ruber most accurately records measured sea surface temperatures (SSTs) throughout the year. G. bulloides δ¹⁸O tracks SSTs during the winter–spring upwelling period but for the remainder of the year records slightly colder, subsurface temperatures. The difference between the δ¹⁸O of the surface dwelling species, G. ruber and G. bulloides, and that of the thermocline dwelling species, N. dutertrei, P. obliquiloculata, and G. menardii, was used to estimate the surface to thermocline temperature gradient. During the winter these δ¹⁸O differences are small (～ 0.50‰) reflecting a well-mixed water column. These interspecies δ¹⁸O differences increase during the summer (～ 1.90‰) in response to the strong thermal stratification that exists at this time of year.     

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.     

Fluxes and isotopic composition of planktonic foraminifera off Hainan Island,northern South China Sea: Implications for paleoceanographic studies

Planktonic foraminifera collected from a sediment trap deployed off Hainan in the northwestern South China Sea (SCS-NW) between July 2012 and April 2013 were studied to evaluate their seasonal variability and ecology as well as to infer the factors controlling their shell fluxes. The total planktonic foraminifera flux, as well as the fluxes of the dominant species (Globigerinoides ruber, Globigerinoides sacculifer and Neogloboquadrina dutertrei), showed three distinct maxima during SW-monsoon in August 2012, the SW-NE intermonsoon in October 2012 and the NE-monsoon in December 2012–February 2013. These periods were characterized by upwelling, aerosol fallout, and intense wind mixing, respectively, from which the foraminiferal assemblages benefitted, as indicated by the close correlation between wind speed, sea surface temperature (SST), chlorophyll a concentration (Chl-a), δ¹⁸O of G. ruber and the shell fluxes. The correlation also suggests that temperature and food availability might have been the primary drivers of the observed changes in foraminiferal abundance. The offset between the SST deduced from flux-weighted of G. ruber δ¹⁸O and annual mean SST is only ∼0.3 °C, much lower than ∼5.2 °C between the summer and winter temperature, indicating a balanced seasonality bias in the shell flux. The linear regression between the satellite-derived sea surface temperature and G. ruber δ¹⁸O reveals the strong potential of this species, at least in the studied region, as an ecological indicator for past oceanic environments.     

Differential dissolution of upper Cretaceous deep-sea benthonic foraminifers from the Angola Basin,South Atlantic Ocean

Material from the Deep Sea Drilling Project (DSDP) Site 527 from the Angola Basin, South Atlantic Ocean, has been analyzed to determine whether Upper Cretaceous benthonic foraminiferal taxa are differentially sensitive to calcite dissolution, and, if so, to rank their order of susceptibility. Two regimes of dissolution, established on the basis of the degree of planktonic foraminiferal fragmentation, representing stronger and less prominent dissolution within the section studied, were used as a framework for reference. A total of 60 calcareous and eight agglutinated benthonic foraminiferal taxa were identified at the species or genus level; of these, twenty-three calcareous and five agglutinated taxa were selected for the dissolution study. Relative abundance of each of the various taxa was tested statistically, using t-test, between dissolution regimes to assess the significance of the change induced by increased dissolution.Nuttallides truempyi andNeoeponides sp. intermediate form are interpreted as resistant to dissolution.Pullenia spp.,Alabamina sp. a,Anomalina sp. a,Praebulimina sp. fusiform, andNuttallinella sp. a are susceptible to dissolution. The majority of the taxa (16 in number) are unaffected by dissolution because they show no change between dissolution regimes. Among the agglutinated taxaGaudryina pyramidata is resistant to dissolution, whereas the remaining four taxa are unaffected by dissolution. At the level of superfamilies, one calcareous superfamily (Discorbacea) is resistant, two (Orbitoidacea and Cassidulinacea) are unaffected, and two (Nodosariacea and Buliminacea) are susceptible to dissolution.     

Standing stock,vertical distribution and flux of planktonic foraminifera in the Panama Basin

The relationships between planktonic foraminifera in the upper 2000 m of the water column and those in sediment traps and deep-sea sediments of the Panama Basin were investigated as part of the Composition, Flux and Transfer Experiments (CFATE) and the Sediment Trap Intercomparison Experiment (STIE) July–Dec. 1979. Planktonic foraminifera larger than 333 μm, sampled during the July–August trap deployment cruise, occurred most abundantly in the euphotic zone with maximal populations associated with the chlorophyll and primary production maxima both located in the upper thermocline just below the mixed layer. Juvenile abundances exceeded those of the >333 μm adults by 3–4 orders of magnitude and their depth distribution systematics indicated that most foraminifera reproduction occurs prior to sinking of the adults from the euphotic zone. Macroscopic aggregates and fecal pellets were identified as major carriers of smaller sized shells from the euphotic zone.During the July–August cruise, the species changed from an assemblage dominated byG. theyeri to one dominated byG. ruber; the liveG. theyeri population sank passively from the euphotic zone in early August with a mean settling speed of 150 m day^?1 while theG. ruber population grew in. The abundance of empty shells of all species in the upper 200 m varied by a factor of 40 during the deployment cruise and peaked on July 30, 1979. This variability was reflected in foraminifera collection rates of sediment traps deployed at 305 m for 24- and 6-h periods. The trap and watercolumn data were combined to calculate mean sinking speeds (>333 μm fraction) of several dominant foraminiferal species (G. ruber andG. theyeri, 500 m day^?1;G. dutertrei, 2000 m day^?1). Size and weight analysis of empty shells from plankton tows yielded values of empty shell density (calculated on a spherical basis using maximum shell dimension) ranging from 0.12 and 0.15 g cm^?3 (G. theyeri andG. ruber) to 0.60 g cm^?3 (G. dutertrei). These speeds and shell densities were found to be consistent with the laboratory sinking experiments of Berger and Piper (1972) and Fok-Pun and Komar (1983). It was concluded that shell fluxes through the water column may be calculated with reasonable accuracy using a modified version of the Bishop et al. (1977) settling model and empty shell size distribution data from pump and plankton tow collections. The Fok-Pun and Komar (1983) settling model is recommended for future modelling efforts but requires a more extensive set of measurements of each foraminiferal specimen to be made.The interpretation of foraminiferal flux profiles, based on the collections of sediment traps, plankton tows, and pumps deployed on time scales shorter than several days, must take into account the very short residence times of empty shells in the water column and short term temporal variability in empty shell production rates.Populations of >333 μm foraminifera sampled in Nov.–Dec. 1979 were reduced by a factor of six relative to the July–Aug. values. The cruise-to-cruise differences were due to reduced primary production and greater mixed layer depth.Planktonic foraminifera were well preserved in sediment traps deployed for 112 days at 665, 935 and 1770 m, although aragonitic pteropod shells were partially dissolved. The fluxes of many species into the 935 m trap could not be explained based on the standing stock data from the July–August cruise alone and it was noted that species fluxes during STIE were comparable to or exceeded maximal values measured by Thunell and Reynolds (1984) in bi-monthly time series traps deployed at the same location during the whole of 1980. The moored trap data could only be explained by higher mean foraminifera shell fluxes in the interval between trap deployment and recovery, consistent with the Bishop and Marra (1984) model of primary production and carbon flux at the STIE site.Primary differences between core top samples and trap samples, were explained by the loss from the sediments of dissolution prone species,G. theyeri andG. ruber leaving an assemblage dominated by the dissolution resistant species,G. dutertrei.     

Recent abyssal benthic foraminiferal biofacies of the eastern equatorial Indian Ocean

Study of Recent abyssal benthic foraminifera from core-top samples in the eastern equatorial Indian Ocean has identified distinctive faunas whose distribution patterns reflect the major hydrographic features of the region. Above 3800 m, Indian Deep Water (IDW) is characterized by a diverse and evenly-distributed biofacies to whichGlobocassidulina subglobosa, Pyrgo spp.,Uvigerina peregrina, andEggerella bradyi are the major contributors.Nuttalides umbonifera andEpistominella exigua are associated with Indian Bottom Water (IBW) below 3800 m. Within the IBW fauna,N. umbonifera andE. exigua are characteristic of two biofacies with independent distribution patterns.Nuttalides umbonifera systematically increases in abundance with increasing water depth. TheE. exigua biofacies reaches its greatest abundance in sediments on the eastern flank of the Ninetyeast Ridge and in the Wharton-Cocos Basin. The hydrographic transition between IDW and IBW coincides with the level of transition from waters supersaturated to waters undersaturated with respect to calcite and with the depth of the lysocline. Carbonate saturation levels, possibly combined with the effects of selective dissolution on the benthic foraminiferal populations, best explain the change in faunas across the IDW/IBW boundary and the bathymetric distribution pattern ofN. umbonifera. The distribution of theE. exigua fauna cannot be explained with this model.Epistominella exigua is associated with the colder, more oxygenated IBW of the Wharton-Cocos Basin. The distribution of this biofacies on the eastern flank of the Ninetyeast Ridge agrees well with the calculated bathymetric position of the northward flowing deep boundary current which aerates the eastern basins of the Indian Ocean.     

Patterns of crystal organization and calcite twin formation in planktonic,rotaliid, foraminifera shells and spines

The foraminiferal order Rotaliida represents one third of the extant genera of foraminifers. The shells of these organisms are extensively used to decipher characteristics of marine ecosystems and global climate events.It was shown that shell calcite of benthic Rotaliida is twinned. We extend our previous work on microstructure and texture characterization of benthic Rotaliida and investigate shell calcite organization for planktonic rotaliid species. Based on results gained from electron backscattered diffraction (EBSD) and field emission electron microscopy (FESEM) imaging of chemically etched/fixed shell surfaces we show for the planktonic species Globigerinoides sacculifer, Pulleniatina obliquiloculata, Orbulina universa (belonging to the two main planktonic, the globigerinid and globorotaliid, clades): very extensive 60°-{0 0 1}-twinning of the calcite and describe a new and specific microstructure for the twinned crystals. We address twin and crystal morphology development from nucleation within a biopolymer template (POS) to outermost shell surfaces. We demonstrate that the calcite of the investigated planktonic Rotaliida forms through competitive growth. We complement the structural knowledge gained on the clade 1 and clade 2 species with EBSD results of Globigerinita glutinata and Candeina nitida shells (clade 3 planktonic species). The latter are significantly less twinned and have a different shell calcite microstructure.We demonstrate that the calcite of all rotaliid species is twinned, however, to different degrees. We discuss for the species of the three planktonic clades characteristics of the twinned calcite and of other systematic misorientations. We address the strong functionalization of foraminiferal calcite and indicate how the twinning affects biocalcite material properties.     

ULTRASTRUCTURE OF A NEW INTRACELLULAR SYMBIOTIC ALGA FOUND WITHIN PLANKTONIC FORAMINIFERA1

A small intracellular eukaryotic algal symbiont, 1.5–3.5 μm in diameter, occurs abundantly and persistently in nine planktonic Foraminifera host species. This alga is different from the dinoflagellate, from 8–12 μm in diameter, known to occur in the four spinose species Orbulina universa, Globigerinoides sacculifer, G. ruber, and G. conglobatus. Transmission and epifluorescent microscopy were used to confirm the presence cophyta. The evidence supporting this classification includes the presence of a chloroplastic endoplasmic reticulum surrounding the plastids and tubular cristae, as opposed to flattened cristae, in the mitochondria. Three classes of algae may be represented including the Chrysophyceae, Bacillariophyceae, and Prymnesiophyceae. Ultrastructural analysis indicated that the alga in the spinose Globigerinella aequilateralis resembles a prymnesiophyte because the chloroplasts lack a girdle lamella. The algae in the non-spinose species and the short-spined Globigerina cristata resemble endocytic chrysophytes or diatoms because of the presence of a girdle lamella. Ultrastructural characteristics of the chrysophycophycean alga present in planktonic Foraminifera are discussed and compared to those of non-dinoflagellate symbiotic algae associated with other invertebrate hosts.     

Distribution and ecology of planktonic foraminifera from the seas around the Indonesian Archipelago

Planktonic foraminiferal assemblages in 50 core-top samples from the western and southern areas of the Indonesian Archipelago and 29 core tops retrieved northwest of Australia were grouped using cluster analysis. These assemblages make it possible to sub-divide the studied area in five provinces: 1/ the Banda/Java region (I); 2/ the Timor region (II); 3/ the Java upwelling region (III); 4/ the Indian monsoon Sumatra region (IV), and 5/ the NW Australia margin region (V). The foraminiferal assemblage groups reflect differences in sea-surface temperature, salinity, thermocline depth, and nutrient supply between these five provinces. These differences are related to surface circulation patterns. The carbonate dissolution is rather intense compared to that in other areas of the eastern Indian Ocean. Within the studied area, the strongest dissolution occurs in samples from the Java upwelling region, with the lysocline level rising above ∼2800 m. The increase in abundance of Globigerina bulloides at 10–8 ka BP in core SHI-9034 (the Java upwelling region) corresponds to the decrease in core SHI-9006 (the Banda/Java region) which indicates an intensification of upwelling in relation to a strengthened southeastern monsoon over the studied area.     

Fertility tracers and monsoon forcing at an equatorial site of the Somali Basin (Northwest Indian Ocean)

Temporal changes in biological and isotopic tracers have successfully been used to monitor monsoon variability in the Arabian Sea. Convincing evidence that fertility indicators, such as the relative abundance of the planktic foraminifer Globigerina bulloides, and SiO₂ and Ba fluxes, can monitor monsoon changes, has also been published. Time series of the ¹³C content of the thermocline foraminifer Neogloboquadrina dutertrei, and of an Upwelling Radiolarian Index (URI), have been used to reconstruct upwelling changes in the Somali Basin at 5 °N for the last 160 kyr. In order to establish a reference site for comparison with other upwelling and/or fertility records from the same area, a time series of 8 climatic and fertility proxies (¹³C content of N. dutertrei and Globorotalia menardii, percentages of G. bulloides and of a thermocline foraminiferal group, minimal δ¹⁸ values of Globigerinoides sacculifer, N. dutertrei and G. menardii) are investigated in the spectral domain for the last 360 kyr, at a site located at the equator and outside the Somali upwelling centers (Core MD 85668).Chronostratigraphies for these records are developed by correlation of oxygen isotope record of G. sacculifer to the Martinson standard stacked benthic oxygen isotope record. The temporal resolution of the data, is between 2 and 5 kyr.Cross spectral comparisons with ETP (Eccentricity + Tilt + Precession-composite signal) were used to estimate coherences in conjunction with phase relationships and to quantify relationships between fertility and climatic indicators. The timing of fertility indicator cycles at the equator shows little (obliquity band) or no (other orbital bands) coincidence with monsoon proxies of the Arabian Sea. At the equator, fertility responses are dissociated, and present important leads or lags with ETP signal at the three orbital bands (with the exception of the thermocline foraminifera, in phase with maximum eccentricity). Due to significant leads with ETP in the timing of ¹³C minima and URI cycles, no relationships with the Northern Hemisphere radiation can be deduced. At the obliquity and precessional frequency bands, thermocline foraminifera cycles display significant lag with ETP and ice volume minima, which suggests that radiation is not the sole forcing mechanism. Global climatic and ice volume changes may be an important forcing mechanism for these fertility proxies. The G. bulloides record is more complicated with cycles in phase with Arabian Sea monsoon proxies at the obliquity band, and ¹⁸O minima at the precession frequency.It appears that, at the equator, the southwest monsoon winds are not the main force driving radiolarian and foraminiferal productivity.     

Pulleniatina Minimum Events in the Andaman Sea (NE Indian Ocean): Implications for winter monsoon and thermocline changes

The late Quaternary record of Pulleniatina obliquiloculata was investigated from two well dated sediment cores from the Andaman Sea (NE Indian Ocean) to examine its paleoceanographic significance and the presence of the Pulleniatina Minimum Events (PME) in the western North Pacific. As in the Pacific, our study shows that PMEs exist in the Indian Ocean albeit with a lower intensity. The Holocene PME occurs between 4.5 and 3.0 cal ka BP with a considerable reduction in P. obliquiloculata abundance, and which matches well with the Pacific records influenced by the Kuroshio Current. Additionally, two significant minimum events of P. obliquiloculata are also seen during the Younger Dryas (YD) and late Last Glacial Maximum (LGM, 20–18 cal ka BP). Overall, the PMEs of the Andaman Sea are not current driven events like in the western Pacific margin either by the weakening of the Kuroshio Current or reduced winter SSTs. The PMEs of the Andaman Sea are characterised by lower abundances of thermocline species indicating the increased depth of the thermocline (DOT) and reduced winter SSTs mainly during the minimum events of the YD and late LGM. The high SSTs during the Holocene PME make this event a mystery. However, the presence of PMEs in the Andaman Sea suggests that these events are not confined to areas influenced by the Kuroshio Current but may be responding to a broad scale oceanographic–climatic process or mechanism which needs to be explored with a detailed study.