Showing papers on "Foraminifera published in 1998"

Larger Foraminiferal Biostratigraphy of the Tethyan Paleocene and Eocene

Abstract: Abundance, diversity, and high evolutionary rates make larger foraminifera useful biostratigraphic tools for datation of sediments deposited in shallow marine platforms. Twenty shallow benthic zones (SBZ) are defined in the time span ranging from the base of Paleocene up to the Eocene-Oligocene boundary. A SBZ zone is characterized upon the stratigraphic distribution of several taxa, belonging mainly to alveolinids, nummulitids and orthophragminids. The correlation of shallow benthic zones with the Paleocene-Eocene Time Scale by Berggren et al. [1995] is proposed on the basis of magnetostratigraphic data from the Pyrenean Basin and by biostratigraphic correlation with the biozonations of calcareous nannoplankton and planktonic foraminifera in the eastern and central part of Tethys.

Magnitudes of sea-level lowstands of the past 500,000 years

Abstract: Existing techniques for estimating natural fluctuations of sea level and global ice-volume from the recent geological past exploit fossil coral-reef terraces or oxygen-isotope records from benthic foraminifera. Fossil reefs reveal the magnitude of sea-level peaks (highstands) of the past million years, but fail to produce significant values for minima (lowstands) before the Last Glacial Maximum (LGM) about 20,000 years ago, a time at which sea level was about 120 m lower than it is today1,2,3,4. The isotope method provides a continuous sea-level record for the past 140,000 years (ref. 5) (calibrated with fossil-reef data6), but the realistic uncertainty in the sea-level estimates is around ±20 m. Here we present improved lowstand estimates—extending the record back to 500,000 years before present—using an independent method based on combining evidence of extreme high-salinity conditions in the glacial Red Sea with a simple hydraulic control model of water flow through the Strait of Bab-el-Mandab, which links the Red Sea to the open ocean. We find that the world can glaciate more intensely than during the LGM by up to an additional 20-m lowering of global sea-level. Such a 20-m difference is equivalent to a change in global ice-volume of the order of today's Greenland and West Antarctic ice-sheets.

Glacial‐age hydrography of the far northwest Pacific Ocean

Abstract: Stable isotope data on benthic foraminifera from more than 30 cores on the northern Emperor Seamounts and in the Okhotsk Sea are synthesized in paleohydrographic profiles spanning the depth range 1000–4000 m. Holocene (core-top) benthic foraminiferal δ18O and δ13C data are calibrated to modern hydrographic properties through measurements of δ13C of ΣCO2 and δ18O of seawater. Cibicidoides stable isotope ratios are close to the δ13C and equilibrium δ18O of seawater, whereas Uvigerina δ18O and δ13C are variably offset from Cibicidoides. Glacial maximum δ13C of Cibicidoides displays a different vertical profile than that of the Holocene. When results are adjusted by +0.32‰ to account for the secular change in δ13C during the last glacial maximum, the data coincide with the modern seawater and foraminiferal curves deeper than ∼2 km. However, at shallower depths δ13C gradually increases by as much as 1‰ above the modern value. Furthermore, above 2 km the benthic δ18O decreases by ∼0.5‰. These results are consistent with a benthic front at ∼2 km in the North Pacific [see Herguera et al., 1992], but they differ from interpretations based on trace metal data which indicate a source of nutrient-depleted deep water during glaciation. The isotopic data suggest that during glaciation there was a better ventilated watermass at intermediate depths in the far northwestern Pacific, it was relatively fresher than deep waters there, and deep waters were as nutrient-rich as today.

Morphological deformities of benthic foraminiferal tests in response to pollution by heavy metals; implications for pollution monitoring

Abstract: Live foraminiferal assemblages were studied along the Mediterranean coast of northern Israel. Two hundred seventeen benthic foraminiferal species were identified, 30% of which (65 species from 20 calcareous families and one agglutinated family) exhibited 11 distinct types of morphological deformities of their tests. These include: wrong coiling, aberrant chamber shape and size, poor development of the last whorl, twisted chamber arrangement, additional chambers, protuberances, multiple apertures, irregular keel, twinning, lateral asymmetry, and lack of sculpture. Morphological deformities are independent of latitude, taxonomic position, mode of life and feeding strategy of foraminifera. In small numbers (up to 1% of total live population) they can occur within the range of natural variability of a given species in given environmental conditions. However, several species display an increase in the proportion of deformed foraminifera in live assemblages that can be caused by low salinity (e,g,, for Adelosina cliarensis) or by an increase in concentrations of heavy metals within the sediment. For example, an increase in deformed Amphistegina lobifera indicates an increase in Cd, Cibicides advenum - Cr, Pseudotriloculina subgranulata - Ti concentrations in sediments. The highest concentrations of Cd are attributed to coarse carbonate substrates adjacent to hard grounds, while Cr and Ti have a strong affinity to muddy-clay substrates enriched with organic matter. Test deformities of benthic foraminifera appear to be sensitive in situ monitors of marine pollution by heavy metals. However, the biochemical and crystallographic mechanisms controlling the development of test deformities remain to be studied by culture experiments under controlled conditions.

Live benthic foraminiferal faunas off Cape Blanc, NW-Africa: Community structure and microhabitats

Abstract: Live (Rose-Bengal stained) benthic foraminifera were studied along a transect across the main area of organic matter deposition in the Cape Blanc upwelling region. The faunal analyses suggest that at the shallowest station (1200 m) the benthic ecosystem is permanently influenced by the upwelling, whereas at the deepest stations (3010 and 2530 m depth) the ocean bottom is subject to significant organic influxes only in summer. The vertical zonation of foraminiferal species in the sediment shows a close correspondence with the depth distribution of oxic respiration, nitrate and sulphate reduction. It is suggested that this linkage is caused by the presence of various stocks of anaerobic and sulphate- and nitrate-reducing bacteria. Deep infaunal foraminiferal species are thought to feed selectively, either on the bacterial stocks or on nutritious particles produced by bacterial degradation of more refractory organic matter. As such, foramininiferal microhabitats are only indirectly controlled by pore water oxygen concentrations.

Bathymetric distribution and microhabitat partitioning of live (Rose Bengal stained) benthic Foraminifera along a shelf to bathyal transect in the southern Adriatic Sea

Abstract: Rose Bengal stained foraminifera from box cores, collected in the southern Adriatic Sea along a transect ranging from 146 to 1,200 m water depth, have been studied. Total numbers of supposedly deposit-feeding foraminifera decrease in a fairly regular manner with increasing water depth and distance from land, probably as a consequence of a decreasing flux of organic matter. Suspension-feeding astrorhizid taxa have an irregular distribution, apparently not related to water depth. Highest numbers of stained foraminifera are invariably found at the sediment surface, whereas numbers decrease exponentially deeper in the sediment. Although most species have maximum densities near the sediment surface, a few of the rarer species are concentrated at deeper levels in the sediment. The vertical distribution patterns of a number of common species are variable with depth along the transect, apparently determined by several different environmental parameters.

Living (Rose Bengal stained) benthic foraminifera from the Pakistan continental margin (northern Arabian Sea)

Abstract: The Arabian Sea is characterized by one of the world’s most pronounced oxygen minimum zones (OMZ) (<0.1 O2 ml/l), which impinges on the seafloor at 200–1000 m depths. The OMZ in the Arabian Sea results from extremely high surface water productivity and moderate thermocline ventilation. Nine box cores were taken on two parallel down-slope transects covering depths from 500 to 2000 m. From these nine box cores living (Rose Bengal stained) benthic foraminifera were studied in detail. Within the upper part of the OMZ, Bolivina dilatata and Bulimina exilis are the most abundant species. In the lower part of the OMZ, Uvigerina peregrina and B. exilis are the most abundant. Just below the OMZ, at a water depth of about 1250 m, the assemblage is typically dominated by Rotaliatinopsis semiinvoluta and U. peregrina; in still deeper waters (1500–2000 m) Bulimina aculeata and Epistominella exigua are the most prominent species. Transect II was sampled three weeks after transect I; on the average, standing stocks were four times higher in transect II. However, down-slope species distributions are similar in the two transects, both in the 63 μm and the 150 μm size fractions. Also vertical (in-sediment) distributions are remarkably similar. This indicates that standing stock differences between the two transects can be ascribed either to the effect of patchiness or, more likely, to the nature and the amount of organic flux. We found unambiguous evidence that in and below the OMZ many benthic foraminifera persist in suboxic to anoxic microhabitats. This regards surface as well as subsurface habitats. Evidently, oxygen is not a limiting factor for a considerable number of species. The obvious relationship between species distribution and the OMZ might then be explained in terms of preferences for amount or type of organic flux. An alternative explanation involves favourable effects resulting from the absence of larger predators. The various models pertaining to the limiting balance between organic flux and oxygen are discussed.

Low-latitude sea-surface temperatures for the mid-Cretaceous and the evolution of planktic foraminifera

Abstract: Isotopic data from exceptionally well preserved foraminifera show that the subtropical North Atlantic had sea surface temperatures (SSTs) between 30 and 31 °C during the late Albian and early Cenomanian. These temperatures were warmer than average modern temperatures in the tropical western Atlantic and support previous inferences based on diagenetically suspect material of Albian tropical SSTs of ∼30 °C. This finding is consistent with basic theories of oceanic thermal response in the tropics to the high atmospheric carbon dioxide levels during the middle-Cretaceous greenhouse. However, our data do not support the concept of a super-Tethyan region of hypersaline waters in the western North Atlantic during late Albian and early Cenomanian time, because seawater salinities substantially higher than modern ones would require significantly higher SSTs than those reported here. Isotopic analysis of mid-Cretaceous planktic foraminifera shows that Planomalina , Ticinella , and Biticinella grew in surface waters and provide isotopic proxies for SST, whereas deeper growing species include Hedbergella , Rotalipora , and Praeglobotruncana . None of these taxa display isotopic indications of photosymbiosis, suggesting that this ecology did not evolve in planktic foraminifera before the Late Cretaceous. Contrary to previous hypotheses, none of these species increased their depth habitat during their life cycles, unlike many extant planktic foraminifera. The rotaliporids may have been preferentially susceptible to extinction during oceanic anoxic events because they lived within or below the thermocline for most of their life cycles.

Modern Benthic Foraminifera off Novaya Zemlya Tidewater Glaciers, Russian Arctic

Abstract: Living and dead foraminifera have been investigated along three transects away from tidewater glaciers of northern Novaya Zemlya. There are three glacier-proximal dominant foraminiferal taxa: Allog...

Reconstructing Past Ocean pH-Depth Profiles

Abstract: Measurement of boron isotope compositions in species of planktonic foraminifera that calcified their tests at different depths in the water column are used to reconstruct the pH profile of the upper water column of the tropical ocean Results for five time windows from the middle Miocene to the late Pleistocene indicate pH-depth profiles similar to that of the modern ocean in this area, which suggests that this method may greatly aid in our understanding of the global carbon cycle

Mass extinction in planktic Foraminifera at the Cretaceous/Tertiary boundary in subtropical and temperate latitudes

Abstract: The high resolution sampling across the Cretaceous/Tertiary (K/T) boundary of the most expanded and continuous sections located in Spain and Tunisia allows us to test and elucidate the extinction model of Cretaceous planktic foraminifera in subtropical and temperate latitudes. The planktic foraminiferal extinction occurred over a short period, with 5% of the species disappearing in the late Maastrichtian, 70% of the species became extinct at the K/T boundary and about 25% of the species are ranging into the early Danian. The species that became extinct at the K/T boundary were large, complex tropical and subtropical forms that dwelled in deep and intermediate water depths. Their disappearance constitutes the largest and most sudden extinction event in the history of planktic foraminifera. Nevertheless, the small cosmopolitan surface dwellers with simple morphologies appear to have survived and the last of them gradually disappeared in the early Danian. The planktic foraminiferal extinction model can be interpreted as a catastrophic mass extinction that was centred at the K/T boundary, and was superimposed on a less evident and controversial gradual mass extinction which apparently began in the late Maastrichtian and continued into the early Danian. The catastrophic pattern of extinction of 70% of the species at the K/T boundary is very compatible with the effect of a large asteroid impact.

Deep-sea benthic foraminiferal species diversity in the NE Atlantic and NW Arabian sea: a synthesis

Abstract: We present a synthesis of species diversity data (Fishers’ alpha index, Shannon–Wiener (log 2 ), ES (100), Rank 1 Dominance) for “live” (stained) foraminifera from five bathyal (1340 m depth) and abyssal (4450–4950 m depth) sites in the NE Atlantic and a 3400 m-deep site in the Arabian Sea. Three Atlantic sites (Porcupine Seabight, BIOTRANS, Porcupine Abyssal Plain) are subject to seasonal phytodetritus inputs that support low diversity populations (8–17 species). In other respects the foraminifera are highly diverse. The meiofaunal fractions (>45 or >63 μm; including fragmented and phytodetritus species) of abyssal Atlantic samples yielded >110 and >170 species in the 0–1 cm and 0–10 cm layers, respectively; the Arabian Sea sample (0–1 cm layer only) yielded 232 species. In both cases, values for diversity measures were very high. Diversity was rather lower in bathyal Porcupine Seabight samples (0–1 cm layer), which yielded 500 μm; Porcupine and Madeira Abyssal Plains) was also speciose (113–133 species), but diversity measures were lower and dominance higher than for the meiofauna. All assemblages contained numerous undescribed species, many belonging to poorly known monothalamous, soft-bodied taxa. Sample diversity was influenced by several factors. Combining phytodetrital and sediment populations reduced diversity and increased dominance slightly; the inclusion of deeper sediment layers and finer sieve fractions had the opposite effect. The inclusion of fragments had more impact on macrofaunal than on meiofaunal diversity, although in both cases the effect was inconsistent (either positive or negative). Porcupine and Madeira Abyssal Plain multicore samples (>63 μm fraction) contained substantially more foraminiferal species than nematode species; the numbers of foraminiferal species in boxcore samples (>500 μm fraction) were comparable to, or greater than, literature values for macrofaunal taxa such as polychaetes and isopods. Few of the more abundant species at our Atlantic abyssal plain and Arabian Sea sites are endemic. This is consistent with literature evidence that many common deep-sea foraminiferal species are cosmopolitan and implies that global foraminiferal diversity may be more modest than the high sample diversity might suggest. Calcareous foraminifera, which are well-known taxonomically and have a good fossil record, may provide a model for diversity patterns among the deep-sea benthic biota in general.

The impact of seasonality on the benthos as reflected in the assemblages of deep-sea foraminifera

Abstract: A surface sediment study of benthic foraminiferal assemblages in the eastern Pacific (Loubere, 1994) yielded a regression equation for estimating surface ocean productivity from assemblage composition with an r2=0.98. This equation was tested with samples from locations outside the calibration data set area and yielded estimates with an error of about 11% of the estimate. The estimation equation has an r2=0.86 for the non-calibration data set samples. This equation was then applied to surface sediment samples from the Indian Ocean, which represent benthic conditions identical to those of the Pacific calibration data set, except that surface ocean productivity in the Indian Ocean is highly seasonal. There is relatively little seasonal variation in productivity over the areas sampled for the Pacific calibration data. Although it is difficult to quantify average annual surface ocean productivity in the Indian Ocean, it appears that the benthic foraminiferal transfer function yields estimates of only qualitative value. At highest productivities it is likely that the equation underestimates productivity. Using Discriminant Function Analysis to compare sample groups from the Pacific and Indian Oceans representing identical environmental conditions, except for seasonality, shows that the Indian Ocean samples are increasingly anomalous, or “no-analog”, from the Pacific Ocean perspective as productivity increases. At higher productivities, Indian Ocean samples are deficient in Uvigerina species, Chilostomella sp., Pullenia sp. and E. tumidulus while having an excess of E. exigua, C. hooperi, Gyroidina grp. species, B. mexicana and Nonion species, from the Pacific viewpoint. The differences in benthic foraminiferal assemblages between the two oceans can be ascribed to changes in benthic community structure that occur as organic carbon flux to the seabed becomes increasingly episodic or seasonal. Overall, Indian Ocean foraminiferal assemblages follow compositional trends similar to those seen in the Pacific Ocean as surface productivity changes. Hence, a Pacific based benthic foraminiferal transfer function can still reasonably estimate productivity gradients from Indian Ocean assemblages. However, there are 4 sufficient assemblage differences between the two oceans to make seasonality a variable that should be incorporated in a calibration data set, and to make estimation of paleo-seasonality a possibility.

Life History and Stable Isotope Geochemistry of Planktonic Foraminifera

Abstract: Application of planktonic foraminifera to micropaleontological, paleoceanographic and paleoclimatic research has enjoyed more than 150 years of activity. During the first century, foraminifera were used primarily for biostratigraphic analysis. Although fossil shells were recognized from beach sands and deep sea sediments as early as 1826 (d'Orbigny, 1826; Parker and Jones, 1865), it wasn't until Owen (1867) and the scientific results of the Challenger expedition (Brady, 1884) that the planktonic life habitat of these marine protozoans was clearly established. By the early 20th century, researchers were studying the biology of planktonic foraminifera at the cellular level (Rhumbler, 1901; Le Calvez, 1936), and linking their distributional patterns to regions of the ocean surface (Lohmann, 1920; Schott, 1935).

Decline of the Maastrichtian pelagic ecosystem based on planktic foraminifera assemblage change: Implication for the terminal Cretaceous faunal crisis

Abstract: An outer shelf–upper slope tropical Tethyan pelagic environment existed over southern Israel during Maastrichtian time. Planktic foraminifera in the >63 and >149 µm size fractions from four sections in this area were studied quantitatively for a high-resolution ecostratigraphic analysis of the pre–Cretaceous-Tertiary (K-T) paleoenvironment. During the Maastrichtian, 41% of the planktic foraminifera species became extinct, mostly keeled Globotruncanidae , which also became quantitatively reduced near the end of the Maastrichtian from as much as 35% to only 5% of the planktic foraminifera population. Evolutionary replacement of extinct species by new forms nearly ceased in that interval. Two major opportunistic blooms of Guembelitria took place, associated with reduced abundances of keeled forms and the dominant species Heterohelix globulosa . The first bloom occurred within the upper Gansserina gansseri to lower Abathomphalus mayaroensis Zones and the second within the Plummerita hantkeninoides Zone. The extinctions, concomitant changes in faunal dominance, and opportunist blooms indicate that the pelagic ecosystem in the Negev area experienced multiple stresses during the Maastrichtian. The planktic foraminiferal assemblages were taxonomically impoverished and in decline prior to the K-T boundary crisis.

Coral provides way to age deep water

Abstract: We propose a new method for computing the ratio of the isotopes carbon-14 to carbon-12 in deep water from the past, and for testing the results derived from the normal method of age difference between benthic and planktic foraminifera in deep-sea sediments1

Impact of climatic changes on the benthic foraminiferal fauna in the Ionian Sea during the last 330,0000 years

Abstract: To reconstruct paleoceanographic changes in the eastern Mediterranean during the last 330,000 years, we studied benthic foraminifera in a piston core from the Ionian Sea. The fauna exhibits large fluctuations in foraminiferal number, diversity, and species composition. Interglacials are characterized by low foraminiferal number and diversity indicating oligotrophic conditions. Directly below or above interglacial sapropels, increased numbers of low-oxygen-tolerant species indicate a strong reduction of deep water circulation. Glacials are characterized by increased foraminiferal number and diversity and faunas that are dominated by shallow infaunal species indicating mesotrophic conditions. Around glacial sapropel S6 very high foraminiferal numbers and the dominance of shallow and deep infaunal species suggest enhanced organic matter fluxes. These faunal results provide information about changes in the African and North Atlantic climate systems (monsoon and westerlies) controlling the humidity and wind stress in the Mediterranean region.

Tolerance of benthic foraminifera (Protista: Sarcodina) to hydrogen sulphide

Abstract: Benthic foraminifera are dominant members of tb meiofauna, commonly occurring below the anoxic-oxic interface in marine sediments. The absence of oxygen in marine coastal sediments is often correlated with the formation of hydrogen sulphide. In this study the tolerance of benthic foraminifera (from the northwestern Adriatic Sea) to hydrogen sulphide was examined experimentally. Although the foraminiferal assemblage exhibited a high tolerance to short-term exposure (21 d), prolonged exposure to sulphidic conditions (66 d with a final concentration of 12 mu M dissolved hydrogen sulphide) resulted in a significant reduction of total foraminiferal densities with time. Reproduction was evident under oxic conditions but none of the genera proliferated under sulphidic conditions. This implies that tolerance of sulphidic conditions was restricted to survival and that sulphide may be a prominent distributional factor for benthic foraminifera. [KEYWORDS: hydrogen sulphide; meiofauna; foraminifera; laboratory experiments Macoma-balthica bivalvia; northern adriatic sea; pore-water oxygen; differential response; thiobiotic meiofauna; subsurface activity; continental-margin; body-size; sulfide; microhabitats]

Coralline algal facies and their palaeoenvironments in the Late Eocene of Northern Italy (Calcare di Nago, Trento)

Abstract: The Calcare di Nago is a carbonate unit of Middle-Late Eocene (Bartonian and Priabonian) age which is well exposed at the north-eastern end of Lake Garda, on the western margin of the Lessini Shelf (Southern Alps). This unit is highly fossiliferous as far as the coralline red algae and large foraminifera are concerned. Corals, bryozoans, echinoderms, and molluscs are also present. The present study deals with the relationships among the coralline taxa, the coralline growth-forms, and their facies development in the Priabonian part of the type section of the Calcare di Nago. The taxonomic investigation led to the identification of 15 coralline red algal species belonging to 7 non-geniculate and 2 geniculate genera. One species of Peyssonneliacean (red alga) and one of Halimedacean (green alga) were also recognized. The quantitative and qualitative analyses based on coralline red algae and large foraminifera enabled five facies to be distinguished: Algal crust-branch rudstone, Algal/Discocyclina packstone, Coralalgal boundstone, Rhodolith mound wacke/packstone, and Rhodolith pavement. According to the coralline assemblages, coralline growth-forms, and large foraminiferal associations, the five facies reflect solid and soft substrate types. Some of these facies are dominated byin situ rhodoliths, others by reworked algal debris. In the architecture of an interpreted prograding carbonate ramp, shallow water facies are dominated by members of the subfamily Mastophoroideae, while deeper water facies are dominated by those of the subfamily Melobesioideae and family Sporolithaceae. There is a significant increase both in size and in constructional voids of the rhodoliths with depth. A concomitant decrease in algal species diversity with depth has been also recognized. LargeDiscocyclina assemblages are localized across the inner and mid ramp boundary.Pellatispira andBiplanispira are present only in the uppermost mid-ramp.Nummulites, Assilina, andSpiroclypeus are dominant together with small orthophragminids both in the mid- and uppermost outer ramp facies.