Globorotalia Truncatulinoides Research Articles

Integrated stratigraphy for the Late Quaternary in the eastern Tyrrhenian Sea

A high-resolution integrated stratigraphy is presented for the Late Quaternary in the southern-eastern Tyrrhenian Sea. It is based on calcareous plankton taxa (planktonic foraminifera and nannoplankton) distribution, δ18OGlobigerinoidesruber record, tephrostratigraphy and radiometric dating methods (210Pb and 137Cs, AMS 14C) for a composite sediment core (from the top to the bottom, C90-1m, C90 and C836) from the continental shelf of the Salerno Gulf. High sedimentation rates from ca 1 cm/100 y for the early Holocene, to 3.45 cm/100 y for the middle Holocene to 8.78 cm/100 y from late Holocene and to 20 cm/100 y for the last 600 AD, make this area an ideal marine archive of secular paleoclimate changes. Quantitative distributional trend in planktonic foraminifera identify seven known (1F–7F) eco-biozones, and several auxiliary bioevents of high potential for Mediterranean biostratigraphic correlation. Recognised were: the acme distribution of Neogloboquadrina pachyderma r.c. between 10.800 ± 0.400 ka BP and 5.500 ± 0.347 ka BP, a strong increase in abundance of Globorotalia truncatulinoides r.c. and l.c. at 5.500 ± 0.347 ka BP and at 4.571 ± 0.96 ka BP, respectively, an acme interval of Globigerinoides quadrilobatus (between 3.702 ± 0.048 ka BP and 2.70 ± 0.048 ka BP) and the acme/paracme intervals of T. quinqueloba (acme between 3.350 ± 0.054 ka BP and 1.492 ± 0.016 ka BP; paracme between 1.492 ± 0.016 ka BP and 0.657 ± 0.025 ka BP; acme beginning 0.657 ± 0.025 ka BP).These results, integrated with trends of selected calcareous nannofossil species (Florisphaera profunda, Brarudosphaera bigelowii, Gephyrocapsa oceanica and Emiliania huxleyi) and δ18OG.ruber signature, are consistent with the most important pre-Holocene and early Holocene paleoclimatic and paleoceanographic phases i.e., the Bölling–Allerod, the Younger Dryas and the time interval of Sapropel S1 deposition in the eastern Mediterranean Sea. These features revealed the high potential of this shallow water environment for high-resolution stratigraphy and correlation for the western Mediterranean.In addition, the chemical characterization of seven tephra layers supplied further data about the age and the dispersal area of some well-known Campi Flegrei explosive events, inferring the possible occurrence of explosive activity at Vesuvius around the middle of the 6th century, and contributing to refine the tephrostratigraphic framework for the last 15 ka in the south-eastern Tyrrhenian Sea.

Bythocythere solisdeus n. sp. and Cytheropteron eleonorae n. sp. (Crustacea, Ostracoda) from the Early Pleistocene Bathyal Sediments of Cape Milazzo (NE, Sicily)

Two new fossil species of Ostracoda belonging to the genus Bythocythere Sars, 1866, Bythocythere solisdeus n. sp. and to the genus Cytheropteron Sars, 1866, Cytheropteron eleonorae n. sp. are described. The specimens come from the upper silty sand layers of the Globorotalia truncatulinoides excelsa Zone (“Sicilian” stage), cropping out in “Cala S. Antonino” along the western side of the Cape Milazzo Peninsula (NE Sicily). Both species belong to a typical Bathyal ostracod association characterized by very low temperatures.

Seasonal and interannual changes of planktic foraminiferal fluxes in the Gulf of Lions (NW Mediterranean) and their implications for paleoceanographic studies: Two 12-year sediment trap records

In order to investigate the seasonal and interannual variability of planktic foraminiferal fluxes in the NW Mediterranean, 266 samples from two 12-year-long sediment traps were analyzed. Two mooring lines were deployed at the east (Station Planier) and the west (Station Lacaze Duthiers) of the Gulf of Lions. The moorings were deployed at a water depth of around 1000m and were equipped with sediment traps at 500m above bottom (mab). In addition, an array of 13 core-tops recovered from different key areas of the Gulf of Lions is described. At Lacaze Duthiers, average foraminiferal fluxes were about double (411.8shellsm−2d−1) those found at the Planier sampling site (225.4shellsm−2d−1), probably due to the fertilizing effect of the Rhone river plume and the general oceanographic circulation. The annual total foraminiferal fluxes exhibited a unimodal trend, with maxima recorded during the winter–spring transition, i.e. the spring bloom, and minima during summer. Therefore, planktic foraminifers found in the sedimentary record in the Gulf of Lions may reflect the flux during the winter–spring period, rather than throughout the annual cycle. A total of eleven planktic foraminiferal species were identified in the sediment trap and core-top samples but only four species were dominant in the assemblages: Globigerina bulloides Neogloboquadrina pachyderma (dex.), Globorotalia inflata and Globorotalia truncatulinoides. The foraminiferal assemblages in the Gulf of Lions reflected the relatively cold conditions of the Northern Basin. No clear relationship between the NAO (North Atlantic Oscillation) and planktic foraminiferal fluxes was found in the sediment trap records. The low planktic foraminiferal fluxes recorded during the spring of 1998 were probably related to the anomalous environmental conditions triggered by the 1997–98 El Niño event. Furthermore, sediment trap samples were compared with surficial sediments recovered from different environmental and sedimentary settings of the Gulf of Lions and the application of these results in paleoceanographic reconstructions is discussed.

Upper quaternary biostratigraphy and formation environments of the southwestern Atlantic Core ACB-17-1447 inferred from micropaleontological data

The foraminiferal (planktonic and benthic) and nannofosssil assemblages have been analyzed in the sediments of Core ACB-17-1447 taken from the South America continental slope north of the Rio Grande Rise piedmont during Cruise 17 of the R/V Akademik Sergey Vavilov. The core section is largely composed of carbonate and marly hemipelagic mud. The Quaternary age of the host sediments is evident from the occurrence of the planktonic foraminiferal index species Globorotalia truncatulinoides. Based on the nannofossil assemblages, the core sediments are attributed to the upper Pleistocene-Holocene. They contain abundant reworked Pliocene, Miocene, and Paleogene taxa transported from the slopes of the underwater Rio Grande Rise. The paleotemperature analysis of the planktonic foraminifers provided data for constructing the temperature curve that demonstrates two warm peaks. During the first warm period (Interval of 7–9 cm), the surface water temperature was as high as 26°C (Holocene optimum), which exceeds by 3–4°C its presentday values and implies the more intense warm Brazil Current. The earlier warm peak with temperatures up to 24°C recorded in the upper Pleistocene sediments (Interval of 69–71 cm) most likely reflects the 3rd oxygenisotope stage (MIS 3), which corresponds to the interstadial phase of the last glaciation (30–40 ka ago). Based on the abundances, taxonomic diversity, and proportions of the characteristic species of benthic foraminifers, the Core ASV-17-1447 section is divided into six intervals correlated with the marine isotopic stages defined by both the planktonic foraminifers and climatic changes evident from the variations in the bottom water circulation along the southwestern slope of the Brazilian Basin during the Late Quaternary.

Sensitivity of south‐east Atlantic planktonic foraminifera to mid‐Pleistocene climate change

Abstract: The last one million years are important in terms of climate development during the so‐called Mid‐Pleistocene Transition when amplification of the glacial–interglacial cycles occurred. This study describes abundance changes in fossil planktonic foraminifera in sediments from Core T89‐40, retrieved from the Walvis Ridge in the south‐east Atlantic, across this time period. Cycles between upwelling and subtropical planktonic foraminiferal assemblages are shown to mirror changes between glacial and interglacial periods, respectively. During interglacial marine isotopic stages (MIS) 9, 11 and 31, however, anomalously high abundances of the polar left‐coiled Neogloboquadrina pachyderma occur, presumably linked to unusual seasonal upwelling waters. The planktonic foraminiferal abundance record shows 41‐ky cyclic variations in the regional oceanography linked to cycles in insolation influenced by changes in the Earth’s axial tilt (obliquity). These orbitally induced oscillations in oceanographic change occurred throughout the entire record. The most conspicuous feature of the planktonic foraminiferal record is the near absence of left‐coiled Globorotalia truncatulinoides between 960 and 610 ka (MIS 26‐15). The abrupt disappearance of this species is synchronous with the onset of the Mid‐Pleistocene Transition in MIS 26.

Relationship between isotopic composition (Δ18O and Δ13C) and plaktonic foraminifera test size in core tops from the Brazilian Continental Margin

Stable oxygen (δ18O) and carbon (δ13C) isotopic signature registered in fossil planktonic foraminifera tests are widely used to reconstruct ancient oceanographic conditions. Test size is a major source of stable isotope variability in planktonic foraminifera found in sediment samples and thus can compromise paleoceanographic interpretations. Test size/stable isotope (δ18O and δ13C) relationships were evaluated in two planktonic foraminifer species (Globigerinoides ruber (white) and Globorotalia truncatulinoides (right)) in two core tops from the Brazilian Continental Margin. δ18 Omeasurements were used to predict the depth of calcification of each test size fraction. δ13C offsets for each test size fraction were then estimated. No systematic δ18O changes with size were observed in G. ruber (white) suggesting a similar calcification depth range (c.a. 100 m) during ontogeny. For G. truncatulinoides (right) δ18O values increased with size indicating ontogenetic migration along thermocline waters (250-400 m). δ13C measurements and δ13C offsets increased with size for both species reflecting well known physiological induced ontogenetic-related variability. In G. ruber (white) the largest test size fractions (300µm and >355µm) more closely reflect δ13C DIC indicating they are best suited for paleoceanographic studies.

Globorotalia truncatulinoides (dextral) Mg/Ca as a proxy for Gulf of Mexico winter mixed-layer temperature: Evidence from a sediment trap in the northern Gulf of Mexico

Three years of weekly- to biweekly-resolved sediment-trap data show that almost 90% of the total flux of tests of the planktic foraminifer Globorotalia truncatulinoides to sediments in the northern Gulf of Mexico occurs in January and February. Comparison of δ 18 O from tests of non-encrusted Gl. truncatulinoides in sediment-trap samples with calculated calcification depths indicates that the non-encrusted individuals secrete their test in the winter surface-mixed layer, most likely at the bottom of the surface mixed zone. Mg/Ca-temperature estimates from non-encrusted Gl. truncatulinoides in sediment-trap samples are consistent with observed temperatures at the calcification depths inferred from the δ 18 O data. In contrast, Mg/Ca-temperature estimates from encrusted Gl. truncatulinoides in sediment-trap samples indicate the crust is formed in cooler (deeper) waters. A preliminary study in a core recovered near the sediment-trap site demonstrates that non-encrusted and encrusted forms of Gl. truncatulinoides in sediment samples show a similar offset in Mg/Ca values as observed in sediment-trap samples. A short (~ 100 years) Mg/Ca record from non-encrusted Gl. truncatulinoides indicates a warming trend that coincides with a warming trend in mean-annual sea-surface temperature recorded by Mg/Ca in Globigerinoides ruber (white) from the same core. These findings suggest Mg/Ca from non-encrusted Gl. truncatulinoides has clear potential as a proxy for past winter mixed-layer temperature. ► Sediment-trap data show 90% of Gl. truncatulinoides flux occurs in early to mid-winter. ► Non-encrusted Gl. truncatulinoides calcify within the winter surface-mixed layer. ► Mg/Ca of non-encrusted forms can be used as a proxy for past winter variation. ► A pilot study on a sediment core was conducted to show the potential of this proxy. ► Past winter temperature estimates show a warming trend over a 100 year interval.

The new foraminiferal genus <i>Ammogloborotaloides</i> n. gen. and subfamily Ammogloborotaloidinae n. subfam. from the Neogene of Venezuela: an example of isomorphism between agglutinated and planktonic Foraminifera

Abstract. We report the occurrence of two new species of the new agglutinated foraminiferal genus Ammogloborotaloides in the Miocene of western Venezuela. These two taxa have been assigned informal names and have been known to the petroleum industry in Venezuela for many years, but have never been described. A. truncatulinoidiformis n. sp. is the type species and the second species, A. sp. 16, is left in open nomenclature. The two species of Ammogloborotaloides are strongly isomorphic with the planktonic foraminiferal species Globorotalia truncatulinoides and Globorotalia crassaformis, and illustrate the possible evolutionary connections between agglutinated benthics and the planktonic foraminifera.

Middle Pleistocene sea surface temperature in the Brazil-Malvinas Confluence Zone: Paleoceanographic implications based on planktonic foraminifera

We reconstructed Middle Pleistocene surface hydrography in the western South Atlantic based on planktonic foraminiferal assemblages, modern analog technique and Globorotalia truncatulinoides isotopic ratios of core SP1251 (38o29.7´S / 53o40.7´W / 3400 m water depth). Biostratigraphic analysis suggests that sediments were deposited between 0.3 and 0.12 Ma and therefore correlate to Marine Isotopic Stage 6 or 8. Faunal assemblage-based winter and summer SST estimates suggest that the western South Atlantic at 38oS was 4-6oC colder than at present, within the expected range for a glacial interval. High relative abundances of subantarctic species, particularly the dominance of Neogloboquadrina pachyderma (left), support lower than present SSTs throughout the recorded period. The oxygen isotopic composition of G. truncatulinoides suggests a northward shift of the Brazil-Malvinas Confluence Zone and of the associated mid-latitude frontal system during this Middle Pleistocene cold period, and a stronger than present influence of superficial subantarctic waters and lowering in SSTs at our core site during the recorded Middle Pleistocene glacial.

Progress toward a multi-basin calibration for quantifying deep sea calcite preservation in the tropical/subtropical world ocean

The development of a quantitative and multi-basin deep sea calcite preservation proxy is important for a better understanding of the marine carbonate system, both in modern sediments and in down core work. We present CaCO 3 preservation data from 89 core top samples in tropical and subtropical areas of the Pacific, Atlantic and Indian Oceans. We observe that the Globorotalia menardii Fragmentation Index (MFI) has potential to trace deep sea CaCO 3 dissolution quantitatively across the tropical/subtropical world ocean. This is evident in the robust relationship between MFI and bottom water calcite under-saturation in six depth transects with markedly different bottom water CO 3 2− saturation states. We also found a strong relationship between MFI and modeled estimates of percent CaCO 3 dissolved at our core top locations. Corroboration for MFI's dissolution trend in the subtropics comes from the concurrent drop in size-normalized shell weight of Globorotalia truncatulinoides specimens with increasing CO 3 2− under-saturation, and the dissolution driven drop in Mg/Ca measurements from tests of three foraminifer species: G. truncatulinoides, Globigerina conglobatus and Globorotalia hirsuta. MFI's core top calibration is further corroborated by the fragmentation trend of foraminifers that prefer higher latitudes like Globigerina bulloides, G. truncatulinoides and Neogloboquadrina pachyderma. Our observations suggest that MFI is coming closer to meeting the criteria for an ideal calcite dissolution proxy with world-wide applicability.

Coiling dimorphism within a genetic type of the planktonic foraminifer Globorotalia truncatulinoides

Abstract The coiling direction—sinistral (left-coiled) or dextral (right-coiled)—of planktonic foraminiferal shells is a classical proxy used to assess past environmental changes and to understand their evolutionary patterns. Globorotalia truncatulinoides is composed of five different genetic types (I to V), each with a specific biogeographic distribution. So far, type II is the only type within which both coiling types have been frequently found. Here we examine the coiling direction as a dimorphic variation in a single genetic type, and show that the two forms with different coiling directions differ in ecology. The studied 140 left- and 137 right-coiled specimens from eight depth layers at four stations in the Sargasso Sea all belonged to Type II, based on the phylogenetic analyses of the ITS (internal transcribed spacer) region of ribosomal DNA. The distributions of left- and right-coiled Type II (Type II-L and II-R) differed strongly: Type II-L dominated between 400 and 200 m depth in the central water mass, whereas Type II-R was common in the top 200 m of the subtropical gyre. The left- and right-coiled forms are thus associated with different water masses. However, the vertical distribution along a temperature gradient indicates that their coiling direction is not determined by temperature, and might have some genetic basis. Our molecular phylogenetic analyses showed that the two forms probably share the same gene pool through their dispersals between different water masses. Moreover, the lineage of G. truncatulinoides is young (

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.

Calibrating Mg/Ca ratios of multiple planktonic foraminiferal species with δ18O-calcification temperatures: Paleothermometry for the upper water column

In order to consistently approximate the thermal vertical structure of past upper water columns, Mg/Ca ratios of eight planktonic foraminiferal species with different preferential calcification depths selected from 76 tropical Atlantic and Caribbean sediment-surface samples were calibrated with δ 18O-derived calcification temperatures with an overall range of ≈ 8–28 °C. Extending the broad number of species-specific calibrations, which agree well especially with our shallow-dweller calibrations, this study presents new bulk calcite Mg/Ca vs. calcification temperature relationships for shallow-dwelling Globigerinoides ruber pink, thermocline-dwelling Globorotalia menardii, and deep-dwelling Globorotalia truncatulinoides dextral and Globorotalia crassaformis not separately calibrated before. The species-specific temperature sensitivities are relatively similar (≈ 7–11% increase in Mg/Ca per 1 °C), yet y-axis intercepts vary from 0.23–0.65 for the shallow and thermocline dwellers to 0.83–1.32 for the deep dwellers. Based on these differences, we established a ‘warm water’ calibration for temperatures > 19 °C (Mg/Ca = 0.29·exp(0.101·T); r = 0.90; shallow and thermocline dwellers) and a ‘cold water’ calibration for temperatures < 15 °C (Mg/Ca = 0.84·exp(0.083·T); r = 0.85; deep dwellers). These calibrations are offset by ≈ 8 °C. This may be significant for paleotemperature reconstructions, which are afflicted with the problem that similar Mg/Ca offsets are probably characteristic of extinct species used to calculate past temperatures.

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.

Mg/Ca and Sr/Ca ratios in planktonic foraminifera: Proxies for upper water column temperature reconstruction

Reliable temperature estimates from both surface and subsurface ocean waters are needed to reconstruct past upper water column temperature gradients and past oceanic heat content. This work examines the relationships between trace element ratios in fossil shells and seawater temperature for surface‐dwelling foraminifera species, Globigerinoides ruber (white) and Globigerina bulloides, and deep‐dwelling species, Globorotalia inflata, Globorotalia truncatulinoides (dextral and sinistral) and Pulleniatina obliquiloculata. Mg/Ca and Sr/Ca ratios in shells picked in 29 modern core tops from the North Atlantic Ocean are calibrated using calculated isotopic temperatures. Mg/Ca ratios on G. ruber and G. bulloides agree with published data and relationships. For deep‐dwelling species, Mg/Ca calibration follows the equation Mg/Ca = 0.78 (±0.04) × exp (0.051 (±0.003) × T) with a significant correlation coefficient of R2 = 0.74. Moreover, there is no significant difference between the different deep‐dwellers analyzed. For the Sr/Ca ratio, the surface dwellers and P. obliquiloculata do not record any temperature dependence. For the Globorotalia species, the thermo dependence of Sr/Ca ratio can be described by a single linear relationship: Sr/Ca = (0.0182 (±0.001) × T) + 1.097 (±0.018), R2 = 0.85. Temperature estimates with a 1 sigma error of ±2.0°C and ±1.3°C can be derived from the Mg/Ca and Sr/Ca ratios, respectively, as long as the Sr geochemistry in the ocean has been constant through time.

Depth habitats and seasonal distributions of recent planktic foraminifers in the Canary Islands region (29°N) based on oxygen isotopes

Seasonal depth stratified plankton tows, sediment traps and core tops taken from the same stations along a transect at 29°N off NW Africa are used to describe the seasonal succession, the depth habitats and the oxygen isotope ratios (δ 18O shell) of five planktic foraminiferal species. Both the δ 18O shell and shell concentration profiles show variations in seasonal depth habitats of individual species. None of the species maintain a specific habitat depth exclusively within the surface mixed layer (SML), within the thermocline, or beneath the thermocline. Globigerinoides ruber (white) and (pink) occur with moderate abundance throughout the year along the transect, with highest abundances in the winter and summer/fall season, respectively. The average δ 18O shell of G. ruber (w) from surface sediments is similar to the δ 18O shell values measured from the sediment-trap samples during winter. However, the δ 18O shell of G. ruber (w) underestimates sea surface temperature (SST) by 2 °C in winter and by 4 °C during summer/fall indicating an extension of the calcification/depth habitat into colder thermocline waters. Globigerinoides ruber (p) continues to calcify below the SML as well, particularly in summer/fall when the chlorophyll maximum is found within the thermocline. Its vertical distribution results in δ 18O shell values that underestimate SST by 2 °C. Shell fluxes of Globigerina bulloides are highest in summer/fall, where it lives and calcifies in association with the deep chlorophyll maximum found within the thermocline. Pulleniatina obliquiloculata and Globorotalia truncatulinoides, dwelling and calcifying a part of their lives in the winter SML, record winter thermocline (∼180 m) and deep surface water (∼350 m) temperatures, respectively. Our observations define the seasonal and vertical distribution of multiple species of foraminifera and the acquisition of their δ 18O shell.

Cd/Ca ratios of in situ collected planktonic foraminiferal tests

The Cd/Ca ratios of planktonic foraminiferal tests have been used to reconstruct surface water nutrient utilization and paleoproductivity. The reliability of this proxy has hitherto not been comprehensively studied, however. To fill this gap, we present novel Cd/Ca data for in situ sampled and sedimentary planktonic foraminifers of the species Globigerinoides ruber, G. sacculifer, Globigerina bulloides, Orbulina universa, and Globorotalia truncatulinoides from the Arabian Sea and the North Atlantic. The Cd/Ca ratios obtained for G. ruber sampled from the live habitat generally display a correlation with seawater phosphate content, but no such trend is observed for G. sacculifer. This distinct behavior may reflect different ecological niches or species‐specific incorporation of Cd into the calcite shells of the organisms. The Cd/Ca ratios of G. ruber, G. sacculifer, and G. bulloides from surface sediments are consistently higher than those obtained for live collected specimens of the same species. Postdepositional alteration of the tests is unlikely to be responsible for these systematic differences. Rather, they appear to reflect a combination of factors, including the formation of calcite crusts with high Cd contents, the different timescales that are represented by in situ and sedimentary foraminiferal tests, and the dominance of tests from periods of high productivity in sediments. Our results also reveal higher Cd/Ca ratios for live G. ruber than for settling tests of the same species. This suggests that planktonic foraminiferal shells are partially dissolved while they individually settle through the water column. Sedimentary tests, however, will be less affected by dissolution processes because these shells are primarily deposited in mass sinking events, which feature much higher settling velocities than those experienced by single settling shells.

Paleoceanographic conditions in the western Caribbean Sea for the last 560 kyr as inferred from planktonic foraminifera

Faunal analyses of planktonic foraminifera and upper-water temperature reconstructions with the modern analog technique are studied and compared to the magnetic susceptibility and gamma ray logs of ODP Core 999A (western Caribbean) for the past 560 kyr in order to explore changes in paleoceanographic conditions in the western Caribbean Sea. Long-term trends in the percentage abundance of planktonic foraminifera in ODP Core 999A suggest two hydrographic scenarios: before and after 480 ka. High percentage abundances of Neogloboquadrina pachyderma and Globorotalia inflata, low abundances of Globorotalia menardii and Globorotalia truncatulinoides, low diversity, and sea-surface temperatures (SST) under 24 °C are typical characteristics occurring from 480 to 560 ka. These characteristics suggest a “shallow” well-oxygenated upper thermocline and the influx of nutrients by either seasonal upwelling plumes and/or eddy-mediated entrainment. The second scenario occurred after 480 ka, and it is characterized by high and fluctuating percentage abundances of Neogloboquadrina dutertrei, G. truncatulinoides, G. menardii, Globigerinita glutinata, Globigerinella siphonifera, and Globigerinoides ruber; a declining trend in diversity; and large SSTs. These characteristics suggest a steady change from conditions characterized by a “shallow” thermocline and chlorophyll maximum to conditions characterized by a “deep” thermocline (mainly during glacial stages) and by more oligotrophic conditions. The influence of the subtropical North Atlantic on the upper thermocline was apparently larger during glacial stages, thus favoring a deepening of the thermocline, an increase in sea-surface salinity, and a dramatic reduction of nutrients in the Guajira upwelling system. During interglacial stages, the influx of nutrients from the Magdalena River is stronger, thus resulting in a deep chlorophyll maximum and a fresher upper ocean. The eddy entrainment of nutrients is the probable mechanism responsible of transport from the Guajira upwelling and Magdalena River plumes into ODP 999A site.

Planktonic foraminifera, calcareous nannoplankton and ascidian variations during the last 25 kyr in the Southwestern Atlantic: A paleoproductivity signature?

Micropaleontological and geochemical analyses from western South Atlantic core SAN-76 (off Southeast Brazil) revealed changes in stable isotope values, and in the assemblages of calcareous nannoplankton and planktonic foraminifera during the past 25 kyr that point to significant paleoceanographic and climatic changes leading to an increase in productivity during the last deglaciation. The enhanced surface productivity was clearly indicated by increased relative abundances of the planktonic foraminifera Globigerina bulloides and Neogloboquadrina dutertrei and the decreased values of δ 13C in planktonic foraminiferal tests. A coeval shoaling of the nutricline and thermocline was indicated by decreased relative abundances of the calcareous nannoplankton Florisphaera profunda and an increased relative abundance of the planktonic foraminifera Globorotalia truncatulinoides (right coiling). We speculate that these changes are related to N-S shifts of the Atlantic Intertropical Convergence Zone (ITCZ). A significant increase in the Cd/Ca ratio and decrease in δ 13C values in the benthic foraminifer Hoeglundina elegans, along with a significant increase in the relative abundance of ascidian spicules during the deglaciation suggest that benthic communities in this area strongly benefited from increased surface water productivity.

Signature of the Brazil-Malvinas Confluence (Argentine Basin) in the isotopic composition of planktonic foraminifera from surface sediments

We explored the potential to use the stable isotopic compositions of planktonic foraminifera as a proxy for the position of the Brazil-Malvinas Confluence (BMC) in the Argentine Basin. For this purpose, we measured the oxygen and carbon isotopic compositions of Globigerinoides ruber (pink and white varieties measured separately), Globigerinoides trilobus, Globigerina bulloides, Globorotalia inflata and Globorotalia truncatulinoides (left- and right-coiling forms measured separately) from a latitudinal transect of 56 surface sediment samples from the continental slope off Brazil, Uruguay and Argentina between 20 and 48°S. Lowest oxygen isotopes values were found in G. ruber (pink), followed by G. ruber (white) and G. trilobus reflecting the highly stratified near surface water conditions north of the BMC. Globigerina bulloides was present mainly south of the BMC and records subsurface conditions supporting earlier plankton tow studies. Globorotalia inflata and G. truncatulinoides (left and right) were both available over the whole transect and calcify in the depth level with the steepest temperature change across the BMC. Accordingly, the δ 18O of these species depict a sharp gradient of 2‰ at the confluence with remarkably stable values north and south of the BMC. Our data show that the oxygen isotopic composition of G. inflata and G. truncatulinoides (left and right) are the most reliable indicators for the present position of the BMC and can therefore be used to define the past migration of the front if appropriate cores are available.