Globorotalia Scitula Research Articles

Distribution of recent planktonic foraminifera in surface sediments of the Basque shelf (S Bay of Biscay): Oceanographic implications

In this work we describe for the first time the distribution of planktonic foraminifera assemblages preserved in recent surface sediments that cover the Basque shelf (southern Bay of Biscay), and their relationship with diverse oceanic currents that affect this area. In the 83 studied samples a total of 18 (morpho)species of planktonic foraminifera have been identified, being the most abundant species: Neogloboquadrina pachyderma dex., Globigerinoides ruber, Globigerina bulloides, Globoconella inflata, Orbulina universa and Turborotalita quinqueloba. These species represent the 92.8% of the total hand-picked specimens. The preferential accumulation of planktonic foraminifera shells in fine sediments deposited in the eastern margin of the Basque shelf, and the random distribution of the dominant species in this area, seem to respond to the general surface current that affect the Basque shelf, which flows eastward during most of the year. Moreover, the input of certain currents and deeper water masses in this area has an important impact on assemblage distribution. Thus, the presence of abundant individuals of Globigerinoides ruber indicates the entrance of the warm and salty Iberian Poleward Current (IPC). Likewise, the dominance of subpolar species Globigerina bulloides, Neogloboquadrina pachyderma dex. and Turborotalita quinqueloba, together with the occurrence, as accessories species, of Neogloboquadrina pachyderma sin., Globorotalia scitula, Globorotalia truncatulinoides and Neogloboquadrina dutertrei, suggest the impact of upwelling processes on the Basque shelf. In conclusion, in this work we have evidenced the useful application of planktonic foraminifera assemblages preserved in surface sediments as indicators of oceanic currents and water masses in shallow continental shelves, such as the Basque shelf.

Distribution of planktonic foraminifera in the subtropical South Atlantic: depth hierarchy of controlling factors

Abstract. Temperature appears to be the best predictor of species composition of planktonic foraminifera communities, making it possible to use their fossil assemblages to reconstruct sea surface temperature (SST) variation in the past. However, the role of other environmental factors potentially modulating the spatial and vertical distribution of planktonic foraminifera species is poorly understood. This is especially relevant for environmental factors affecting the subsurface habitat. If such factors play a role, changes in the abundance of subsurface-dwelling species may not solely reflect SST variation. In order to constrain the effect of subsurface parameters on species composition, we here characterize the vertical distribution of living planktonic foraminifera community across an east–west transect through the subtropical South Atlantic Ocean, where SST variability was small, but the subsurface water mass structure changed dramatically. Four planktonic foraminifera communities could be identified across the top 700 m of the transect. Gyre and Agulhas Leakage surface faunas were predominantly composed of Globigerinoides ruber, Globigerinoides tenellus, Trilobatus sacculifer, Globoturborotalita rubescens, Globigerinella calida, Tenuitella iota, and Globigerinita glutinata, and these only differed in terms of relative abundances (community composition). Upwelling fauna was dominated by Neogloboquadrina pachyderma, Neogloboquadrina incompta, Globorotalia crassaformis, and Globorotalia inflata. Thermocline fauna was dominated by Tenuitella fleisheri, Globorotalia truncatulinoides, and Globorotalia scitula in the west and by G. scitula only in the east. The largest part of the standing stock was consistently found in the surface layer, but SST was not the main predictor of species composition either for the depth-integrated fauna across the stations or at individual depth layers. Instead, we identified a pattern of vertical stacking of different parameters controlling species composition, reflecting different aspects of the pelagic habitat. Whereas productivity appears to dominate in the mixed layer (0–60 m), physical properties (temperature, salinity) become important at intermediate depths and in the subsurface, a complex combination of factors including oxygen concentration is required to explain the assemblage composition. These results indicate that the seemingly straightforward relationship between assemblage composition and SST in sedimentary assemblages reflects vertically and seasonally integrated processes that are only indirectly linked to SST. It also implies that fossil assemblages of planktonic foraminifera should also contain a signature of subsurface processes, which could be used for paleoceanographic reconstructions.

Distribution of Foraminiferal Indicator Groups and the Upper Tortonian–Lower Messinian (Miocene) Stratigraphy in the Gibliscemi Section, Sicily, Italy

Planktonic and benthic foraminiferal assemblages from the upper Tortonian-lower Messinian part of the Gibliscemi section (Sicily, Italy), are described. The major stratigraphic markers recorded in the section are (1) the first occurrence of Globigerinoides extremus marking the lower boundary of the corresponding upper Tortonian zone, (2) first occurrence of Globorotalia miotumida that previously was considered as an index form of the Tortonian–Messinian boundary, and (3) the first regular occurrence of Globorotalia conomiozea recording this boundary. The distribution in the section of keeled Globorotalia and Globorotalia miotumida group is traced. The composition of the Globorotalia scitula group is analyzed and the group is proposed to be identified as one species G. praescitula. It is assumed that the Mediterranean in the Middle and Late Miocene was the site where Globigerinoides ruber survived during its complete disappearance in the Atlantic and Pacific.

New insights in late Miocene lower Chelif basin biostratigraphy based on planktonic foraminifera (Algeria)

Quantitative and qualitative analyses based on planktonic foraminifera of two sections (Oued Derdoussa and Djebel Meni) from lower Chelif basin (northern Algeria) enable us to identify for the first time a sequence of bioevents calibrated with the geomagnetic polarity time scale. The identified bioevents of late Miocene formations are useful for a high-resolution correlation in the whole western Mediterranean at local and regional scales. In particular, this work reveals that the sequence covers an interval of time that extends from the upper Tortonian up to the pre-evaporite Messinian period. Indeed, the base of the succession starts with a change in the coiling direction (from dextral to sinistral) of Neogloboquadrina acostaensis as the first bioevent. This later corresponds to the bioevent (1–8) assigned to the Tortonian sediments. This period is marked by the presence of Globorotalia menardii in sinistral coiled form that was substituted gradually with dextral coiled. The Tortonian/Messinian (T/M) boundary coincides to some extent with a sharp replacement of G. menardii group (I and II) with the first common occurrence (FCO) of Globorotalia miotumida plexus few meters below the development of the Tripoli diatomite formation (bioevent 9). This later is dominated mainly by highly convex species (G. miotumida plexus) marked by the presence of Globorotalia mediterranea in contrast with the marly formation at the base of the section. In this part, the recorded bioevents (10 to 17) are assigned to the Messinian sediments. Thus, the Tripoli formation shows the influx of Globorotalia nicolae and a small incursion of the dextrally coiled of Globorotalia scitula at the top of Oued Derdoussa section as a local bioevent that may be related to the local palaeoenvironment. We notice the absence of the change in the coiling from sinistral to dextral of N. acostaensis during the upper Messinian, this may be due to the coincidence of this bioevent with the barren levels.

Factors controlling the depth habitat of planktonic foraminifera in the subtropical eastern North Atlantic

Abstract. Planktonic foraminifera preserved in marine sediments archive the physical and chemical conditions under which they built their shells. To interpret the paleoceanographic information contained in fossil foraminifera, the recorded proxy signals have to be attributed to the habitat and life cycle characteristics of individual species. Much of our knowledge on habitat depth is based on indirect methods, which reconstruct the depth at which the largest portion of the shell has been calcified. However, habitat depth can be best studied by direct observations in stratified plankton nets. Here we present a synthesis of living planktonic foraminifera abundance data in vertically resolved plankton net hauls taken in the eastern North Atlantic during 12 oceanographic campaigns between 1995 and 2012. Live (cytoplasm-bearing) specimens were counted for each depth interval and the vertical habitat at each station was expressed as average living depth (ALD). This allows us to differentiate species showing an ALD consistently in the upper 100 m (e.g., Globigerinoides ruber white and pink), indicating a shallow habitat; species occurring from the surface to the subsurface (e.g., Globigerina bulloides, Globorotalia inflata, Globorotalia truncatulinoides); and species inhabiting the subsurface (e.g., Globorotalia scitula and Globorotalia hirsuta). For 17 species with variable ALD, we assessed whether their depth habitat at a given station could be predicted by mixed layer (ML) depth, temperature in the ML and chlorophyll a concentration in the ML. The influence of seasonal and lunar cycle on the depth habitat was also tested using periodic regression. In 11 out of the 17 tested species, ALD variation appears to have a predictable component. All of the tested parameters were significant in at least one case, with both seasonal and lunar cyclicity as well as the environmental parameters explaining up to > 50 % of the variance. Thus, G. truncatulinoides, G. hirsuta and G. scitula appear to descend in the water column towards the summer, whereas populations of Trilobatus sacculifer appear to descend in the water column towards the new moon. In all other species, properties of the mixed layer explained more of the observed variance than the periodic models. Chlorophyll a concentration seems least important for ALD, whilst shoaling of the habitat with deepening of the ML is observed most frequently. We observe both shoaling and deepening of species habitat with increasing temperature. Further, we observe that temperature and seawater density at the depth of the ALD were not equally variable among the studied species, and their variability showed no consistent relationship with depth habitat. According to our results, depth habitat of individual species changes in response to different environmental and ontogenetic factors and consequently planktonic foraminifera exhibit not only species-specific mean habitat depths but also species-specific changes in habitat depth.

Paleoenvironments in the Fram Strait during Marine Isotope Stages 2–6 based on planktonic paleobiological and stable-isotope proxies and ice-rafted debris

Two sediment cores from the Knipovich Ridge in the Fram Strait have been studied to examine paleoceanographic and climatic changes in the Polar North Atlantic during the late Middle and Late Pleistocene. As inferred from the data on foraminifers, nannofossils, diatoms, IRD, oxygen isotope values, and AMS 14C ages, the recovered deposits span the interval of MIS 2–6. Several beds marked by a high productivity of microplankton and often by a great IRD content are recorded in MIS 2, MIS 5a, 5c, 5e, and MIS 6 suggesting a repeated occurrence of seasonally ice-free waters and strong meridional circulation in the eastern Fram Strait. The planktonic foraminifers Globigerinoides ruber, Globorotalia scitula, G. crassaformis, and pink-colored Globigerina rubescens, exotic for this latitude, were identified in three points of the section. A hiatus in one of the cores studied was revealed from comparison of IRD variations and the occurrence of Pullenia bulloides.

Reconciling single-chamber Mg / Ca with whole-shell δ<sup>18</sup>O in surface to deep-dwelling planktonic foraminifera from the Mozambique Channel

Abstract. Most planktonic foraminifera migrate vertically through the water column during life, meeting a range of depth-related conditions as they grow and calcify. For reconstructing past ocean conditions from geochemical signals recorded in their shells, it is therefore necessary to know vertical habitat preferences. Species with a shallow habitat and limited vertical migration will reflect conditions of the surface mixed layer and short-term and mesoscale (i.e. seasonal) perturbations therein. Species spanning a wider range of depth habitats, however, will contain a more heterogeneous, intra-specimen variability (e.g. Mg / Ca and δ18O), which is less for species calcifying below the thermocline. Obtained single-chamber Mg / Ca ratios are combined with single-specimen δ18O and δ13C of the surface-water inhabitant Globigerinoides ruber, the thermocline-dwelling Neogloboquadrina dutertrei and Pulleniatina obliquiloculata, and the deep dweller Globorotalia scitula from the Mozambique Channel. Species-specific Mg / Ca, δ13C and δ18O data combined with a depth-resolved mass balance model confirm distinctive migration and calcification patterns for each species as a function of hydrography. Whereas single-specimen δ18O rarely reflects changes in depth habitat related to hydrography (e.g. temperature), measured Mg / Ca of the last chambers can only be explained by active migration in response to changes in temperature stratification. Foraminiferal geochemistry and modelled depth habitats shows that the single-chamber Mg / Ca and single shell δ18O are in agreement with each other and in line with the changes in hydrography induced by eddies.

Global analysis of seasonality in the shell flux of extant planktonic Foraminifera

Abstract. Shell fluxes of planktonic Foraminifera species vary intra-annually in a pattern that appears to follow the seasonal cycle. However, the variation in the timing and prominence of seasonal flux maxima in space and among species remains poorly constrained. Thus, although changing seasonality may result in a flux-weighted temperature offset of more than 5° C within a species, this effect is often ignored in the interpretation of Foraminifera-based paleoceanographic records. To address this issue we present an analysis of the intra-annual pattern of shell flux variability in 37 globally distributed time series. The existence of a seasonal component in flux variability was objectively characterised using periodic regression. This analysis yielded estimates of the number, timing and prominence of seasonal flux maxima. Over 80% of the flux series across all species showed a statistically significant periodic component, indicating that a considerable part of the intra-annual flux variability is predictable. Temperature appears to be a powerful predictor of flux seasonality, but its effect differs among species. Three different modes of seasonality are distinguishable. Tropical and subtropical species (Globigerinoides ruber (white and pink varieties), Neogloboquadrina dutertrei, Globigerinoides sacculifer, Orbulina universa, Globigerinella siphonifera, Pulleniatina obliquiloculata, Globorotalia menardii, Globoturborotalita rubescens, Globoturborotalita tenella and Globigerinoides conglobatus) appear to have a less predictable flux pattern, with random peak timing in warm waters. In colder waters, seasonality is more prevalent: peak fluxes occur shortly after summer temperature maxima and peak prominence increases. This tendency is stronger in species with a narrower temperature range, implying that warm-adapted species find it increasingly difficult to reproduce outside their optimum temperature range and that, with decreasing mean temperature, their flux is progressively more focussed in the warm season. The second group includes the temperate to cold-water species Globigerina bulloides, Globigerinita glutinata, Turborotalita quinqueloba, Neogloboquadrina incompta, Neogloboquadrina pachyderma, Globorotalia scitula, Globigerinella calida, Globigerina falconensis, Globorotalia theyeri and Globigerinita uvula. These species show a highly predictable seasonal pattern, with one to two peaks a year, which occur earlier in warmer waters. Peak prominence in this group is independent of temperature. The earlier-when-warmer pattern in this group is related to the timing of productivity maxima. Finally, the deep-dwelling Globorotalia truncatulinoides and Globorotalia inflata show a regular and pronounced peak in winter and spring. The remarkably low flux outside the main pulse may indicate a long reproductive cycle of these species. Overall, our analysis indicates that the seasonality of planktonic Foraminifera shell flux is predictable and reveals the existence of distinct modes of phenology among species. We evaluate the effect of changing seasonality on paleoceanographic reconstructions and find that, irrespective of the seasonality mode, the actual magnitude of environmental change will be underestimated. The observed constraints on flux seasonality can serve as the basis for predictive modelling of flux pattern. As long as the diversity of species seasonality is accounted for in such models, the results can be used to improve reconstructions of the magnitude of environmental change in paleoceanographic records.

Anti-cyclonic eddy imprint on calcite geochemistry of several planktonic foraminiferal species in the Mozambique Channel

Highlights: • We coupled LA-ICP-MS Me/Ca single-chamber composition of four planktonic foraminifera with eddy induced hydrographic changes • The Mg/Ca-based temperature difference between N. dutertrei and G. scitula are likely to be an eddy proxy suitable for down-core application • Near-surface dwelling species inhabit well oxygenated surface waters and show lower test Mn/Ca values, compared to deeper dwelling species • Planktonic foraminifera Mn/Ca test values are in line with water column variability in dissolved Mn concentrations Hydrographic conditions in the Mozambique Channel are dominated by the passing of large anticyclonic eddies, propagating poleward into the upstream Agulhas area. Further south, these eddies have been found to control the shedding of Agulhas rings into the Atlantic ocean, thereby playing a key role in Indo-Atlantic Ocean exchange. The element composition of several planktonic foraminifera species collected from sediment trap samples, was compared to in situ water column data from the Mozambique Channel. Single-chamber trace element composition of these foraminifera reveals a close coupling with hydrographic changes induced by anticyclonic eddies. Obtained Mg/Ca values for the surface dwelling Globigerinoides ruber as well as the thermocline dwelling Neogloboquadrina dutertrei follow temperature changes and reduced temperature stratification during eddy conditions. At greater depth. Globorotalia scitula and Pulleniatina obliquiloculata record stable temperatures and thus respond to hydrographic changes with a deepening in habitat depth. Furthermore, test Mn/Ca values indicate a close relationship between water column oxygenation and Mn incorporation in these planktonic foraminiferal species

Seasonal variations in planktonic foraminiferal flux and oxygen isotopic composition in the western North Pacific: Implications for paleoceanographic reconstruction

The oxygen isotopic composition (δ 18 O) of planktonic foraminiferal shells in seafloor sediment provides information on past surface oceanography. Knowledge of seasonal and depth habitat, as well as the δ 18 O disequilibrium (vital effect), is essential to constrain the interpretation of sedimentary δ 18 O. Here, we present a 1-year time series of planktonic foraminiferal shell fluxes and δ 18 O from a sediment trap moored in the northwestern margin of the North Pacific. The vital effect and calcification depth for four species were estimated by comparing shell δ 18 O and the predicted values of equilibrium calcite calculated from temperature and estimated δ 18 O in seawater. Six major species ( Neogloboquadrina incompta , Neogloboquadrina dutertrei , Neogloboquadrina pachyderma , Globigerina quinqueloba , Globigerina bulloides , and Globorotalia scitula ) constituted 97% of the total foraminiferal flux. Most major species showed large fluxes in June and December, corresponding to periods of the development and disruption of the seasonal thermocline, implying the importance of nutrient injection and/or circulation for foraminiferal fluxes. Additional peaks in N. dutertrei and N. pachyderma were observed in August. The seasonal successions of foraminiferal fluxes corresponded to surface ocean stratification conditions and food availability, which are closely related to circulation of local currents. Vital effect estimations suggest that shells calcified in equilibrium for G. bulloides and N. pachyderma [sinistral (s)] and with a − 0.7‰ offset for N. dutertrei [dextral (d)], a − 1.0‰ offset for N.incompta (d), and a − 0.3‰ offset for N. pachyderma (d). The calculation of flux-weighted δ 18 O values reveals that the sedimentary δ 18 O values of G. bulloides , N. dutertrei (d), and N. incompta (d) reflect surface temperature in winter season, and those of N. pachyderma (s) and N. pachyderma (d) reflect summer and annual mean subsurface temperature, respectively. The shallow calcification depths for the four species suggest that δ 18 O between different species (Δδ 18 O) in the western North Pacific does not work for reconstructing past stratification conditions, unlike in other regions. Rather, the Δδ 18 O between N. pachyderma (s) and G. bulloides , N. dutertrei (d) or N. incompta (d) may be a more suitable proxy for past seasonality. • Seasonal variations in planktonic foraminiferal shell flux and δ 18 O are observed. • Stratification condition plays a major role in shell flux variations. • The δ 18 O vital effects and calcification depths for four species were determined. • Multi-species Δδ 18 O as a proxy of the past seasonality in the western North Pacific.

Updating the marine biostratigraphy of the Granada Basin (central Betic Cordillera). Insight for the Late Miocene palaeogeographic evolution of the Atlantic – Mediterranean seaway

The marine stratigraphic record of the Granada Basin (central Betic Cordillera, Spain) is composed of three Late Miocene genetic units deposited in different sea-level contexts (from base to top): Unit I (sea-level rise), Unit II (high sea-level), and Unit III (low sea-level). The latter mainly consists of evaporites precipitated in a shallow-basin setting. Biostratigraphic analyses based on planktonic foraminifera and calcareous nannoplankton indicate four late Tortonian bioevents (PF1-CN1, PF2, PF3, and PF4), which can be correlated with astronomically-dated events in other sections of the Mediterranean. PF1-CN1 (7.89 Ma) is characterized by the influx of the Globorotalia conomiozea group (including typical forms of Globorotalia mediterranea) and by the first common occurrence of Discoaster surculus; PF2 (7.84 Ma) is marked by the first common occurrence of Globorotalia suterae; PF3 (7.69 Ma) is typified by the influx of dextral Neogloboquadrina acostaensis; and PF4 (7.37 Ma) is defined by the influx of the Globorotalia menardii group II (dextral forms). The PF1 event occurred in the upper part of Unit I, whereas PF2 to PF4 events occurred successively within Unit II. The age of Unit III (evaporites) can only be estimated in its lower part based on the presence of dextral Globorotalia scitula, which, together with the absence of the first common occurrence of the G. conomiozea group (7.24 Ma), points to the latest Tortonian. Comparisons with data from the other Betic basins indicate that the evaporitic phase of the Granada Basin (7.37–7.24 Ma) is not synchronous with those from the Lorca Basin (7.80 Ma) and the Fortuna Basin (7.6 Ma). In the Bajo Segura Basin (easternmost Betic Cordillera), no evaporite deposition occurred during the late Tortonian. The evaporitic unit of the Granada Basin (central Betics) records the late Tortonian restriction of the Betic seaway (the marine connection between the Atlantic and Mediterranean). The diachrony in the restriction of the Betic seaway is related to differing tectonic movements in the central and eastern sectors of the Betic Cordillera.

Biostratigraphic and palaeoenvironmental analyses of the Messinian/Zanclean boundary and Zanclean succession in the Moncucco quarry (Piedmont, northwestern Italy)

Abstract Integrated biostratigraphic and palaeoenvironmental analyses of foraminiferal, ostracod and calcareous nannofossil assemblages were carried out on the Messinian/Zanclean succession of the Moncucco quarry (Piedmont, northwestern Italy). The uppermost Messinian deposits may be correlated to the “Lago-Mare” deposits of the Mediterranean area. They yield a brackish ostracod assemblage, which belongs to the Loxocorniculina djafarovi zone of the Messinian post-evaporitic interval, indicating their deposition in oligo-mesohaline shallow waters and the influx of Paratethyan faunas. Only reworked marine microfossils are present. The boundary between the “Lago-Mare” deposits and the overlying Zanclean Argille Azzurre Fm. is marked by an irregular erosional surface, followed by a barren, 10–50 cm thick, black arenitic layer. The Zanclean succession consists of grey to whitish clayey marls (Argille Azzurre Fm.), rich in microfossils, which document the MPl1 (Sphaeroidinellopsis acme) zone up to the MPl4a foraminiferal zone, and the MNN12 to MNN14-15 calcareous nannofossil zones. Micropalaeontological data confirm that the Pliocene flooding event was synchronous at the Mediterranean scale. Some foraminiferal bioevents recognized at the Mediterranean scale and related to precessional cycles are recorded in the studied succession : the Globorotalia scitula common occurrence (CO) (cycle 3), the occurrence of Siphonina reticulata (cycle 6), and the Globorotalia margaritae first common occurrence (FCO) (cycle 10). A short hiatus could be inferred in the lowermost Zanclean sediments for the absence of Triquetrorhabdulus rugosus and of the Reticulofenestra pseudoumbilicus paracme. Hiatuses or reduced sedimentation could also have affected the bottom during the MPl2-MPl3 zones. Foraminiferal and ostracod assemblages document a rather deep basin just from the lower Zanclean, warm surficial waters (common Globigerinoides spp.), rather high seasonal primary productivity (common phytoplankton grazer Neogloboquadrina acostaensis) and mesotrophic bottom (common Eponides pusillus, Hoeglundina elegans, Argilloecia acuminata, Krithe compressa, Paijenborchella iocosa). Bottom depths in the lower Zanclean of northwestern Italy appear to be shallower than depths suggested by coeval southernmost assemblages. A deepening of the basin during the MPl1 and MPl2 zones is suggested by the increasing diversity of microfossils and by the spreading of deep bathyal taxa (Cibicidoides robertsonianus, Paijenborchella malaiensis cymbula). Warm, oligotrophic conditions in the water column become more constant. Palaeoenvironmental conditions change progressively during the upper MPl2, the MPl3 and MPl4a zones. Cold, eutrophic planktonic foraminifers (Globigerina bulloides, N. acostaensis) become dominant, as well as benthic taxa tolerant of low oxygen content and high organic matter (Uvigerina peregrina, Brizalina spp.), suggesting an increase in eutrophic conditions. Deep benthics such as Cibicidoides kullenbergi, C. robertsonianus disappear, and many outer neritic to bathyal taxa decrease in abundance, whereas inner shelf taxa increase, suggesting a shallowing of the basin and episodes of strong winnowing, probably tectonically controlled, in the uppermost Zanclean succession.

Seasonal production patterns of planktonic foraminifera in the NE Atlantic Ocean: Implications for paleotemperature and hydrographic reconstructions

[1] Sediment trap samples from OMEX 2 (49°N, 13°W) provide a continuous record of the seasonal succession of planktonic foraminifera in the midlatitude North Atlantic and reveal a complex relationship between periods of production and specific hydrographic conditions. Neogloboquadrina pachyderma dextral coiling (d.), Globigerina bulloides, and Globorotalia inflata are found in great numbers during both the spring and summer seasons, whereas Globigerina quinqueloba, Globorotalia hirsuta, Globorotalia scitula, and Globigerinita glutinata are associated predominantly with the increase in productivity during the spring bloom. Globigerinella aequilateralis, Orbulina universa, and Globigerinoides sacculifer are restricted to late summer conditions following the establishment of a warm, well-stratified surface ocean. An annually integrated fauna from the sediment trap, comprising ∼13,000 individuals, is used to evaluate the accuracy of five faunal-based statistical methods of paleotemperature estimation. All of the temperature reconstruction techniques produce estimates of ∼16°C and ∼11°C for summer and winter surface temperature, respectively, which are in excellent agreement with regional hydrographic data and suggest that the sediment trap assemblage is well represented in the core top faunas. Analysis of the key species that dominate the OMEX 2 sediment trap fauna, G. bulloides, G. inflata, and N. pachyderma d., based on δ18O derived temperatures from North Atlantic core top samples, suggests that seasonal variations in planktonic foraminiferal production are nonuniform across the midlatitudes and that this is likely to complicate reconstructing past seasonal hydrographic dynamics using these taxa.

Environmental versus biomineralization controls on the intratest variation in the trace element composition of the planktonic foraminifera G. inflata and G. scitula

The intratest variation in the chemical composition of Globorotalia scitula and G. inflata recovered from a sediment trap sample collected at 3000 m in the North Atlantic in early spring has been investigated using laser ablation inductively coupled plasma–mass spectrometry and electron microprobe. Mg/Ca, Li/Ca, B/Ca, Mn/Ca, and Ba/Ca vary by up to a factor of 10 through the test walls. Water column properties, including temperature and salinity, are well documented at the trap site, and the observed variations are too large to be explained by vertical migration of the foraminifera. However, changes in calcite precipitation rate, crystal structure, or the chemical composition of the internal calcification reservoir also cannot, by themselves, fully account for the pattern of intratest variability. Nevertheless, the average Mg/Ca for each chamber generally produces a Mg/Ca temperature that matches that measured in the water column. The exception is small, morphologically distinct G. inflata tests that have anomalously high Mg/Ca.

Calcareous nannofossil and planktonic foraminiferal distributional patterns during deposition of sapropels S6, S5 and S1 in the Libyan Sea (Eastern Mediterranean)

In core ADE3-23 collected in the Libyan Sea, the nannofossil species Coccolithus pelagicus, Coronosphaera spp., Helicosphaera spp., Syracosphaera spp., Calcidiscus spp., small Gephyrocapsa spp., and the planktonic foraminifers Globigerina bulloides, Neogloboquadrina pachyderma, Globorotalia scitula, Turborotalita quinqueloba and Neogloboquadrina dutertrei prevail in sapropel S6 (midpoint at 172 ka b.p.), indicative of cold and highly productive surface conditions. Warm and highly stratified water-column conditions are recorded by the characteristic assemblage of Globigerinoides ruber, Globoturborotalita rubescens, Florisphaera profunda, Rhabdosphaera spp. during the sapropel S5 depositional interval (midpoint at 124 ka b.p.). Compared with S5, Globigerinita glutinata, Globorotalia inflata, Globigerinella siphonifera, Globorotalia truncatulinoides and the calcareous nannofossil Emiliania huxleyi characterise less stratified conditions within sapropel S1 (midpoint at 8.5 ka b.p.). Multivariate statistical analyses of calcareous nannofossil and planktonic foraminifers in core ADE3-23 identify planktonic assemblages which typify sapropels S6, S5 and S1 in the Libyan Sea. A warmer interval is recognised in the middle part of the cold S6, and can be associated with an influx of less saline waters and the occurrence of a faint, temporary deep chlorophyll maximum. Evidence for enhanced surface productivity and breakdown of stratification is observed in the middle–upper part of the warm S5, associated with climatic deterioration. Moreover, an increase in surface productivity in the upper S1 implies weak stratification. Our combined calcareous nannofossil and planktonic foraminiferal data add to the evidence that climate variability was more pronounced than commonly considered to date for all the three studied Eastern Mediterranean sapropel depositional intervals.

Stable isotopes of planktonic foraminifera from tropical Atlantic/Caribbean core-tops: Implications for reconstructing upper ocean stratification

δ 18O values of nine tropical–subtropical planktonic foraminiferal species with different preferential habitat depths collected from 62 core–top samples along an east–west transect across the tropical Atlantic/Caribbean were used to test the applicability of interspecific δ 18O gradients for reconstructions of tropical upper ocean stratification. In general, the δ 18O difference (Δ δ 18O) between intermediate- and shallow-dwelling species decreases, and Δ δ 18O between deep and intermediate dwellers increases with increasing thermocline depth towards the west. The statistical significance of regional differences in Δ δ 18O highlights Δ δ 18O between the intermediate dwellers (in particular Globorotalia scitula and Globorotalia tumida) and the shallow dweller Globigerinoides ruber pink, as well as Δ δ 18O between the deep dwellers Globorotalia crassaformis or Globorotalia truncatulinoides dextral and intermediate dwellers as most sensitive to changes in tropical Atlantic thermocline depth. Based on the observed regional variations in interspecific Δ δ 18O, we propose a multispecies stratification index “STRA trop” = ( δ 18O intermediate − δ 18O shallow) / ( δ 18O deep − δ 18O shallow) for the tropical ocean. Statistically significant differences in STRA trop values between the E-Atlantic and the Caribbean suggest that this index may be a useful tool to monitor variations in tropical upper ocean stratification in the geological record.

Seasonal and interannual variability of the planktic foraminiferal flux in the vicinity of the Azores Current

Planktic foraminiferal (PF) flux and faunal composition from three sediment trap time series of 2002–2004 in the northeastern Atlantic show pronounced year-to-year variations despite similar sea surface temperature (SST). The averaged fauna of the in 2002/2003 is dominated by the species Globigerinita glutinata, whereas in 2003/2004 the averaged fauna is dominated by Globigerinoides ruber. We show that PF species respond primarily to productivity, triggered by the seasonal dynamics of vertical stratification of the upper water column. Multivariate statistical analysis reveals three distinct species groups, linked to bulk particle flux, to chlorophyll concentrations and to summer/fall oligotrophy with high SST and stratification. We speculate that the distinct nutrition strategies of strictly asymbiontic, facultatively symbiontic, and symbiontic species may play a key role in explaining their abundances and temporal succession. Advection of water masses within the Azores Current and species expatriation result in a highly diverse PF assemblage. The Azores Frontal Zone may have influenced the trap site in 2002, indicated by subsurface water cooling, by highest PF flux and high flux of the deep-dwelling species Globorotalia scitula. Similarity analyses with core top samples from the global ocean including 746 sites from the Atlantic suggest that the trap faunas have only poor analogs in the surface sediments. These differences have to be taken into account when estimating past oceanic properties from sediment PF data in the eastern subtropical North Atlantic.

Integrated quantitative biostratigraphy of the latest Tortonian–early Messinian Pissouri section (Cyprus): An evaluation of calcareous plankton bioevents

A quantitative study was performed on planktonic foraminifera and calcareous nannofossils of the astronomically dated Late Miocene Pissouri section (Cyprus). Our results confirm the reliability of well-known planktonic foraminiferal events as Catapsydrax parvulus LO (Last Occurrence), sinistral coiling change of Globorotalia scitula, Globorotalia miotumida group FRO (First Regular Occurrence), Globorotalia nicolae FO (First occurrence) and LO, sinistral coiling change of Neogloboquadrina acostaensis and also of several important calcareous nannofossil events ( Amaurolithus primus FO, Amaurolithus delicatus FO, Reticulofenestra rotaria FO and FCO). Integrated planktonic foraminifera and calcareous nannoplankton data contribute to an enhanced time resolution of the Tortonian - early Messinian interval in the Levantine basin, and contribute to detailed correlations throughout the Eastern Mediterranean. In addition, we compare methodologies commonly used in calcareous plankton biostratigraphy, and shortly outline sources of bias that can influence the results of stratigraphic studies.

Planktic Foraminiferal Content in a Mature Agulhas Eddy from the SE Atlantic: Any Influence on Foraminiferal Export Fluxes?

The Agulhas eddies, large-scale rings of warm salty water, occasionallyintrude into the Benguela Current system from the Indian Ocean and progress northwards across the Cape Basin and the Walvis Ridge. This inter-ocean exchange of heat and salt along the Cape of Good Hope is considered to play a crucial role for the global thermohaline circulation. Yet, the modern faunal composition of mature eddies from the northern Cape Basin and Walvis Ridge was uninvestigated in spite of the global importance of the Agulhas inflow, preventing firm micropalaeontological study of the palaeoceanographic variability of the ocean exchange in this area.This paper describes the composition of the modern planktic foraminiferal assemblages collected from a mature Agulhas eddy when it entered into the northern Benguela Current system. The effect of the eddy’s gradual decay on the foraminiferal communities in the upper water column is specifically examined, using plankton tow and CTD-rosette profiles, obtained within and outside the ring. In addition,exported foraminiferal fluxes beneath the eddy were investigated in order to determine their impact on the accumulation assemblages as recorded in sediment traps moored near the sea floor and in the core-top sediment from a box corer.The examined mature eddy “W” was clearly evident on the satellitealtimetry images by its elevated surface. It was distinguished from the surrounding ocean by a slightly higher salinity, deeper surface mixed layer and higher planktic foraminiferal standing stocks. Similarto planktic foraminiferal fauna in freshly formed eddies from the Agulhas retroflection, species such as Globigerinoides trilobus s.l., Globigerinoides ruber, Orbulina universa, Globigerinella siphoni-fera and Globorotalia scitula dominated in the ring “W” assemblages. However, Globorotalia menardii, a species previously believed to be characteristic for the Agulhas leakage into the S. Atlantic, was virtuallyabsent in the eddy “W” fauna. Also Globorotaloides hexagona, a species endemic in Indian Ocean waters, was not found in the water column, in the export flux or underlying sediment. The February to July foraminiferal flux patterns recorded by the sediment traps mirror the February standing stocks from the water column. Here in contrast, the core-top results show dominance of intermediate/cold water speciesthat originate from the seasonal spring bloom. This signal prevailsin sediment to the extent that any potential Agulhas eddy signaturein the sediment was overprinted.

Seasonal succession, vertical distribution, and dissolution of planktonic foraminifera along the Subarctic Front: Implications for paleoceanographic reconstruction in the northwestern Pacific

The regional spatial and depth distribution of planktonic foraminifera were studied through sediment trap observations at two stations, Stations WCT-5 (about 41° N, 150° E) and WCT-6 (about 42° N, 155° E), along the Subarctic Front in the northwestern Pacific Ocean. The sediment traps were moored, at 1000 and 4500 m depths at Station WCT-5, and 1091, 2051 and 4871 m depths at Station WCT-6. The samples were collected from 17 August 1998 to 10 August 1999 at Station WCT-5 and from 15 August 1999 to 6 August 2000 at WCT-6. At Station WCT-5, two distinct annual periods of increased total foraminiferal and species production were evident: the period of highest production was in autumn, with a secondary period in early summer. At Station WCT-6, high total foraminiferal shell fluxes occurred in April–May and September–October. The April–May “spring bloom” of planktonic foraminifera apparently began each year as the sea surface temperature (SST) increased after winter and the decrease of thickness of the mixed water layer during June–July in every year following the cessation of bloom. The most common foraminiferal species in the study region were Globigerina quinqueloba, Neogloboquadrina pachyderma, Neogloboquadrina dutertrei, Neogloboquadrina incompta, Globigerinita glutinata, Globigerina bulloides, Globigerina falconensis, Globorotalia theyeri, Globorotalia scitula, and Globigerinella calida. Foraminiferal fluxes displayed a distinct seasonality at all trap depths at both stations. At Station WCT-5 in 1998–1999, foraminiferal species were scarce in the surface water during spring and summer, and the dominant foraminiferal species were most productive during winter and autumn. At Station WCT-6, the dominant foraminiferal species were most productive during late winter to spring, and all species showed a peak in middle spring (May). A comparison of seasonal patterns of dominant foraminiferal species between the northwestern and northeastern Pacific demonstrated that foraminiferal productivity was a good proxy for sea surface temperature and mixing of water column. Significant dissolution of foraminiferal tests was evident in the deepwater column and was used to estimate the foraminiferal lysocline depth (∼4500 m) in the northeastern Pacific basin.