Showing papers on "Foraminifera published in 2001"

Role of Panama uplift on oceanic freshwater balance

Abstract: Comparison between planktic foraminiferal oxygen isotope records from the Caribbean Sea (Ocean Drilling Program [ODP] Site 999) and the equatorial east Pacific (ODP Site 851) suggests an increase in Caribbean surface-water salinity between 4.7 and 4.2 Ma. The modern Atlantic-Pacific salinity contrast of about 1‰ became fully established at 4.2 Ma as reflected by a 0.5‰ planktic foraminifera 18O enrichment in the Caribbean Sea. This is interpreted as the result of restricted surface-water exchange between the tropical Atlantic and Pacific in response to the shoaling of the Central American seaway. As a consequence, the Atlantic and Pacific surface-ocean circulation regime changed, as did the freshwater balance between the major ocean basins. Simultaneous shifts in benthic carbon isotope records in the Caribbean Sea suggest an intensification in North Atlantic thermohaline circulation. These results indicate that the Panamanian isthmus formation caused several new ocean-atmosphere feedback mechanisms that have affected climate since the early Pliocene.

Foraminifera, testate amoebae and diatoms as sea-level indicators in UK saltmarshes: a quantitative multiproxy approach

Abstract: The vertical distribution of foraminifera, testate amoebae and diatoms was investigated in saltmarshes in the Taf estuary (south Wales), the Erme estuary (south Devon) and the Brancaster marshes (north Norfolk), to assess the use of multiproxy indicators in sea-level reconstructions. A total of 116 samples were subjected to regression analyses, using the program calibrate, with duration of tidal flooding as the dependent variable. We found that the relationship between flooding duration and taxa was strongest for diatoms and testate amoebae and weakest for foraminifera. The vertical range of testate amoebae in saltmarshes is small. Their lower tolerance limit in present-day saltmarshes occurs where tides cover the marsh less than a combined total of 7 days (1.9%) in a year. However, they are important sea-level indicators because information for sea-level reconstruction is best derived from sediments that originate in the highest part of the intertidal zone. Diatoms span the entire sampled range in intertidal and supratidal areas, whereas the upper limit of foraminifera is found very close to the highest astronomical tide level. Local training sets provide reconstructions with higher accuracy and precision than combined training sets, but their use is limited if they do not represent adequate modern analogues for fossil assemblages. Although analyses are time consuming, a regional training set of all three groups of micro-organisms yields highly accurate (r2 = 0.80) and precise (low value of root mean square error) predictions of tidal level. This approach therefore could improve the accuracy and precision of Holocene sea-level reconstructions. Copyright © 2001 John Wiley & Sons, Ltd.

The northern North Atlantic : a changing environment

Abstract: The Environment of the Northern North-Atlantic Ocean: Modem Depositional Processes and their Historical Documentation.- An Overview of Sea-Ice Conditions in the Greenland Sea and the Relationship of Oceanic Sedimentation to the Ice Regime.- Constraints on Carbon Drawdown and Export in the Greenland Sea.- Particle Flux Variability in the Polar and Atlantic Biogeochemical Provinces of the Nordic Seas.- Biogenic Particle Sources and Vertical Flux Patterns in the Seasonally Ice-Covered Greenland Sea.- Distribution, Export and Alteration of Fossilizable Plankton in the Nordic Seas.- Distribution of Calcareous, Siliceous and Organic-Walled Planktic Microfossils in Surface Sediments of the Nordic Seas and their Relation to Surface-Water Masses.- Particle Transport, Distribution Patterns of Sedimentological Properties and Biological Communities.- Modem Ocean Current-Controlled Sediment Transport in the Greenland-Iceland-Norwegian (GIN) Seas.- Records and Processes of Near-Bottom Sediment Transport along the Norwegian-Greenland Sea Margins during Holocene and Late Weichselian (Termination I) Times.- Patterns and Determinants of the Distribution and Structure of Benthic Faunal Assemblages in the Northern North Atlantic.- Exchange Processes across the Sediment Water Interface.- Bentho-Pelagic Coupling and Carbon Dynamics in the Northern North Atlantic.- Fluxes of Organic Carbon and Biogenic Silica Reaching the Seafloor: A Comparison of High Northern and Southern Latitudes of the Atlantic Ocean.- Concentration and Microbial Decomposition of Organic Material in Sediments of the Norwegian-Greenland Sea.- Changes in the Hydrate Stability Zone on the Norwegian Margin and their Consequence for Methane and Carbon Releases Into the Oceanosphere.- Climate Change and Paleoceanography.- The Potential of Synoptic Plankton Analyses for Paleoclimatic Investigations: Five Plankton Groups from the Holocene Nordic Seas.- Paleoceanographic Proxies in the Northern North Atlantic.- Examination of the Use of Biomarker Proxies for the Reconstruction of Paleoceanographic Conditions in the Northern North Atlantic.- Fundamental Modes and Abrupt Changes in North Atlantic Circulation and Climate over the last 60 ky-Concepts, Reconstruction and Numerical Modeling.- Planktic and Benthic Foraminifera as Indicators of Past Ocean Changes in Surface and Deep Waters of the Nordic Seas.- Dansgaard-Oeschger Oscillations: A Hydrodynamic Theory.- Circulation of the Glacial Atlantic: A Synthesis of Global and Regional Modeling.- Present and Past Oceanographic Controls of Sediment Formation in the North Atlantic-Arctic Gateway (A Critical Appraisal of SFB 313 Scientific Results).

Planktic foraminiferal production stimulated by chlorophyll redistribution and entrainment of nutrients

Abstract: During September and October 1996 planktic foraminifers and pteropods were sampled from the upper 2500 m of the water column in the BIOTRANS area (47°N, 20°W), eastern North Atlantic, as part of the JGOFS program. Hydrography, chlorophyll fluorescence, and nutrient content were recorded at high spatial and temporal resolution providing detailed information about the transition time between summer and fall. At the beginning of the cruise a shallow pycnocline was present and oligotrophic conditions prevailed. Over the course of the cruise, the mixed layer depth increased and surface water temperature decreased by 1.5°C. Both chlorophyll-a dispersed in the upper 50 m by vertical mixing and chlorophyll-a concentrations at the sea surface increased. The nitracline shoaled and nutrient enriched waters were entrained into the mixed layer. Planktic foraminifers and pteropods closely reflected the changes in the hydrography by increased growth rates and changes in species composition. Three main groups of planktic foraminiferal species were recognized: (1) a temperate and low-productivity group dominated by Neogloboquadrina incompta characterized the shallow mixed layer depths. (2) A temperate and high-productivity group dominated by Globigerina bulloides characterized the period with wind-induced dispersal of chlorophyll-a and entrainment of nutrient-enriched waters. (3) A warm water group containing Globigerinoides sacculifer, Orbulina universa, Globigerinoides ruber (white), and Globigerinella siphonifera was most common during the first days of sampling. Synchronous with the hydrographic change from summer to fall, planktic foraminiferal and pteropod growth was stimulated by redistribution of chlorophyll-a and entrainment of nutrient-enriched waters into the mixed layer. In addition, the seasonal change in the eastern North Atlantic resulted in a transition of the epipelagic faunal composition and an increased calcareous particle flux, which could be used to trace seasonality in fossil assemblages and allow for better paleoceanographic interpretation of the boreal Atlantic.

A review of eocene nummulite accumulations: structure, formation and reservoir potential

Abstract: Eocene nummulite accumulations, also referred to as nummulite "banks", form important hydrocarbon reservoirs in Tunisia and Libya and may constitute exploration targets in other parts of North Africa, the Mediterranean and the Middle East. Porosities commonly average 10-20% and permeabilities 10-50md. Foraminifera of the genus Nummulites may comprise up to 98% of the bioclasts in these carbonate reservoirs, although only one or two species may be present. The absence of associated fauna is generally taken to indicate an oligotrophic depositional environment.

Millennial‐scale depositional cycles related to British Ice Sheet variability and North Atlantic paleocirculation since 45 kyr B.P., Barra Fan, U.K. margin

Abstract: Lithology, lithic petrology, planktonic foraminiferal abundances, and clastic grain sizes have been determined in a 30 m-long core recovered from the Barra Fan off northwest Scotland. The record extends back to around 45 kyr B.P., with sedimentation rates ranging between 50 and 200 cm/kyr. The abundance of ice-rafted debris indicates 16 glacimarine events, including temporal equivalents to Heinrich events 1–4. Enhanced concentrations of basaltic material derived from the British Tertiary Province suggest that the glacimarine sediments record variations in a glacial source on the Hebrides shelf margin. Glacimarine zones are separated by silty intervals with high planktonic foraminifera concentrations that reflect an interstadial circulation regime in the Rockall Trough. The results suggest that the last British Ice Sheet fluctuated with a periodicity of 2000–3000 years, in common with the Dansgaard-Oeschger climate cycle.

Monterey Bay cold-seep biota: Assemblages, abundance, and ultrastructure of living foraminifera

Abstract: Although there is a growing body of evidence indicating benthic foraminifera inhabit hydrocarbon and cold seep environments, biochemical and ultrastructural data on seep foraminiferal communities are not available. Therefore, sediments collected from cold seeps in Monterey Bay, CA (900–1000 m), were examined for the presence of live benthic foraminifera. Results from three independent methods (ATP assay, ultrastructural analysis, rose Bengal staining) indicate that certain species inhabit the Clam Flat and Clam Field seeps. Abundances in our seep samples were lower than in comparable non-seep sites, although not atypical for these bathyal depths. Of 38 species represented at these two seep sites by cytoplasm-containing specimens, only Spiroplectammina biformis was restricted to the seep environment. However, because S . biformis is also known from non-seep sites in other areas, it should not be considered as endemic to seeps. Ultrastructural studies show abundant peroxisomes in seep specimens, which may allow inhabitation of such environments. One specimen of Uvigerina peregrina had prokaryotes nestled in test pores, suggesting that bacteria may play a role in the survival of foraminifera in this seep environment.

Glacial-to-Holocene redistribution of carbonate ion in the deep sea.

Abstract: We have reconstructed the glacial-age distribution of carbonate ion concentration in the deep waters of the equatorial ocean on the basis of differences in weight between glacial and Holocene foraminifera shells picked from a series of cores spanning a range of water depth on the western Atlantic's Ceara Rise and the western Pacific's Ontong Java Plateau. The results suggest that unlike today's ocean, sizable vertical gradients in the carbonate ion concentration existed in the glacial-age deep ocean. In the equatorial Pacific, the concentration increased with depth, and in the Atlantic, it decreased with depth. In addition, the contrast between the carbonate ion concentration in deep waters produced in the northern Atlantic and deep water in the Pacific appears to have been larger than in today's ocean.

Temporal variability in vertical distributions of live (stained) intertidal foraminifera, southern england

Abstract: The temporal variability (over 27 months) in abundance, depth of life in the sediment, and species diversity of hard-shelled, live (stained) foraminifera in an intertidal area has been determined. Throughout the investigation period, the same three species (Haynesina germanica, Ammonia beccarii (tepida), Elphidium excavatum) were dominant at the two investigated stations, the maximum abundance of all species (dominant and subsidiary) was in the surface 0.25 cm, and there was a general lack of seasonal change in the vertical distribution of the foraminifera. Seasonality does not seem to be a controlling factor for the vertical distribution of individuals in this area and none of the foraminifera showed high subsurface abundances. Because of the difference in depth position of the redox boundary within the sediment (often 1 cm) and the maximum abundance of individuals (surface 0.25 cm) the former cannot be the main factor limiting their vertical distribution of abundance. The generally high dominance of individuals in the surface few millimeters is probably related to the presence there of microalgal food and limited burrowing activity of the sparse macrofauna. Subsidiary species colonized the area ephemerally, thus the number of species recorded varied from one season to another. The minimum and maximum number of species found at any single sampling event were 5 and 22, whereas the cumulative number of stained species found throughout the investigation period was 35 (plus at least three soft-shelled forms). Species diversity is one of the principal univariate methods used to assess both natural variability and possible human impacts. The large natural seasonal variability demonstrated here suggests that caution should be taken in assessing the significance of diversity changes when based on occasional sampling only.

Response of deep-sea benthic foraminifera from the mediterranean sea to simulated phytoplankton pulses under laboratory conditions

Abstract: Food and oxygen concentrations have been identified as environmental constraints influencing the vertical distribution of benthic foraminifera. Field studies, however, have been largely inconclusive as to which degree each factor regulates the observed distribution pattern. For this reason, different experiments were performed to investigate the response of deep-sea benthic foraminifera to simulated phytodetritus pulses under laboratory conditions, where oxygen concentrations can be influenced separately. In the laboratory, deep-sea foraminifera developed a normal vertical distribution pattern, and the habitats of single species reflected the results obtained from field investigations. Therefore, conclusions from the data produced in the laboratory can be transferred to nature. A mainly epifaunal life style was shown for Adercotryma glomerata and Spiroplectinella earlandi, but also indicated for Uvigerina peregrina. Hippocrepina sp. was spread over the entire sediment column with a shallow infaunal maximum. Epistominella pusilla, Seabrookia earlandi and Alveolophragmium wiesneri showed an epifaunal to shallow infaunal distribution. Ceratobulimina arctica, Trochammina inflata and Melonis barleeanum preferred an infaunal habitat. No suspension feeders were observed in the experiments. The addition of algae as food material resulted in elevated population densities. Under the influence of high oxygen contents with no or only short-term fluctuations, no migration to the upper layers was recorded after the addition of food. However, more specimens were found in deeper layers, because more organic material was transported downward into the sediment after the food pulse. The experimental laboratory results support the theoretical scenarios outlined in the TROX-model.

Benthic foraminifera and pore-water oxygen profiles: a re-assessment of species boundary conditions at the western iberian margin

Abstract: The depth distribution of living (Rose Bengal-stained) benthic foraminifera in near-surface sediments was analyzed along 4 short cores from the western Iberian Margin and Gulf of Cadiz at water depths from 800 to 1920 m. Pore-water oxygen, Chloroplastic Pigment Equivalent (CPE), and total organic carbon (C org ) concentrations were measured in the same or adjacent cores. These values were used to constrain the limiting oxygen and nutrient levels that defined the ranges in sediment depth and abundance maxima of foraminiferal species. The population density showed a good correlation with pore-water oxygenation indicating that oxygen is a limiting factor for endobenthic foraminiferal assemblages at mid-depths between 800 and 1200 m. At the deep-water site, however, the fauna appeared nutrient limited. More than half of the benthic species occupied extended sediment depth habitats and a wide range of oxygen levels among the sites studied. Thirty-nine of 103 species occurred in two or more cores and showed distinct abundance maxima, 36 in the uppermost 2.0 cm where the CPE concentrations were high. Living foraminifers were not found at depths where the CPE-values were lower than 0.1 μg/g. This level indicates trophic conditions critical for the survival of endobenthic species. The frequency distribution of the lower oxygen range limits of all species showed maxima at the high oxic/low oxic (3 ml/l), low oxic/suboxic (1.5 ml/l), and suboxic/dysoxic (0.3 ml/l) boundaries and thus depicted the ecological significance of these previously recognized ecolimits. Only 30 % of the species display consistent patterns in relation to pore water oxygen. Dysoxic indicators were Globobulimina affinis, Chilostomella ovoidea and Bathysiphon capillare. Many species previously designated as suboxic indicators were ubiquitous or preferred microhabitats at oxic levels. Boundary conditions for the dysoxic indicator G. affinis were pelagic flux rates higher than 3.5 g C m −2 yr −1 , a habitat depth below the homogeneously bioturbated layer in areas outside of high productivity zones, and CPE concentrations of 0.1 to 1.0, preferentially 0.7 to 0.8 μg/g. The distribution pattern suggested that G. affinis thrives mainly on dysoxic bacteria and actively seeks this nutrient resource.

Living (stained) benthic foraminiferal response to primary production and hydrography in the deepest part of the gullmar fjord, swedish west coast, with comparisons to höglund’s 1927 material

Abstract: Living (stained) benthic foraminifera were studied in the deepest part (116 m) of the classical marine study area, the Gullmar Fjord on the Swedish west coast. This is a silled fjord with a strongly stratified water column where stagnant conditions temporarily develop in the deeper parts. The aim of this study is to determine how the living foraminiferal assemblage develops with seasonal variations in bottom water hydrography and primary production in the surface water. From August 1993 to December 1994, monthly hydrographic and oxygen measurements were made. Parallel undisturbed sediment cores were taken using a Multiple-corer. Foraminifera from the >63 μm fraction were stained with Rose Bengal to separate living from dead specimens. Monthly values of the surface water chlorophyll a content were also available and give a measure of the primary production. During spring 1994 the dominant foraminiferal species, Stainforthia fusiformis, multiplied its population size by seven times during one month as a consequence of food input from the spring phytoplankton bloom. The abundance of this species correlates positively with the surface water chlorophyll a content. Populations of several other species also increased during the spring of 1994. A deep-water inflow in February 1994 may have triggered reproduction of several foraminiferal species, recognized as a temporary population decline. We also compared our results with Hoglund’s (1947) foraminiferal study, performed in the same area in the summer of 1927. We found that a major alteration trending towards a more opportunistic low oxygen tolerant fauna has occurred since then.

Benthic foraminifera at the Cretaceous-Tertiary boundary around the Gulf of Mexico

Abstract: Cretaceous-Tertiary (K-T) boundary sections in northeastern Mexico contain marly formations separated by a controversial clastic unit. Benthic foraminifera in seven sections indicate middle and lower bathyal depths of deposition for the marls, with the exception of the upper bathyal northernmost section. Mixed neritic-bathyal faunas were present in the clastic unit, indicating redeposition in the deep basin by mass-wasting processes resulting from the K-T bolide impact in the Gulf of Mexico. Benthic foraminifera in the Mexican sections, and at other deep-sea locations, were not subject to major extinction at the time of impact, but there were temporary changes in assemblage composition. Benthic faunas indicate welloxygenated bottom waters and mesotrophic conditions during the late Maastrichtian and increased food supply during the latest Maastrichtian. The food supply decreased drastically just after the K-T boundary, possibly because of the collapse of surface productivity. Cretaceous and early Paleogene benthic foraminifera, however, did not exhibit the benthic-pelagic coupling of present-day faunas, as documented by the lack of significant extinction at the K-T collapse of surface productivity. Much of the food supplied to the benthic faunas along this continental margin might have been refractory material transported from land or shallow coastal regions. The decrease in food supply at the K-T boundary might be associated with the processes of mass wasting, which removed surface, food-rich sediment. Benthic faunas show a staggered pattern of faunal recovery in the lowermost Paleogene, consistent with a staged recovery of the vertical organic flux but also with a gradual buildup of organic matter in the sediment.

Upper Cretaceous and lower Paleogene benthic Foraminifera from northeastern Mexico

Abstract: The deep-sea, Upper Cretaceous through Paleocene benthic Foraminifera from the Mendez and Velasco Formation (Tampico Embayment, northeastern Mexico) were first described in classical papers of the 1920s. These faunas were among the first deep-water faunas of this age to be described, and many of the species have been recognized in Deep Sea Drilling Project and Ocean Drilling Program sites worldwide. We present the first taxonomic update of these classic faunas since the 1920s, with special attention to species first described from this area, and species that have been widely used in paleobathymetric reconstructions. Benthic foraminiferal assemblages were analyzed from the Cretaceous Mendez and Paleocene Velasco Formations in seven sections in the northeastern and central-eastern parts of Mexico. The Foraminifera are generally well preserved, although commonly recrystallized and filled with sparry calcite. They indicate paleodepths ranging from upper to middle bathyal for the three northernmost sections, and lower bathyal for the other sections. The clastic unit between the Mendez and Velasco Formations contains a mixture of neritic and bathyal species, and probably originated as a result of mass-wasting associated with the bolide impact on the Yucatan peninsula. From the about 140 benthic foraminiferal taxa identified, we describe 88 species belonging to 41 genera. These correspond to the most representative taxa in northeastern Mexico across the Cretaceous-Paleogene transition, because of their common occurrence, paleobathymetric significance, or first description from this region.

Reef-island accretion and soil development on Makin, Kiribati, central Pacific

Abstract: The late Holocene accretionary history of reef islands on Makin, the northernmost table reef of the Gilbert atoll chain, western Kiribati, has been reconstructed based on conventional radiocarbon dating of coral shingle and bulk sand samples, and AMS radiocarbon dating of individual grains. Makin is geomorphologically and sedimentologically simple, comprising one main island with only a minor residual lagoon, and composed of sand dominated by the reef-flat foraminifera Calcarina spengleri, Amphistegina lobifera and Baculogypsina sphaerulata. Deposition commenced in mid platform around 2500 years ago; in situ fossil coral (Heliopora) dated at 2400±80 years BP indicates that sea level was 0.4–0.5 m above present at that time. Progradation occurred progressively to westward at a relatively constant rate of 200–300 m ka−1. However, progradation was interrupted on the eastern side by lagoon encapsulation around 1400 years ago. The soil and vegetation characteristics are uniform over most of the reef islands as a result of clearance and the planting and maintenance of coconuts, and do not reflect reef-island depositional history. Remnant stands of Pisonia forest, with an associated phosphatic soil, are not related to any particular geomorphological feature, or period of deposition. The reef islands are continuing to accrete as a result of production of foraminifera on the reef flat.

Seasonality of foraminiferal flux in sediment traps at Chatham Rise, SW Pacific: implications for paleotemperature estimates

Abstract: Analysis of sediment traps located either side of the Subtropical Front east of New Zealand reveals a strong association between water masses and foraminiferal assemblages. The composition and timing of foraminiferal productivity is distinct between waters north and south of the front, and these differences are also reflected in the assemblages of nearby core-tops. The sediment trap data indicate highly seasonal flux patterns in this region, so sedimentary records may represent flux during a particular season, rather than throughout the annual cycle. This pronounced seasonality has implications for our estimates of the annual temperature range based on faunal assemblages. This study shows that despite strong flux seasonality the annual sea-surface temperature (SST) range is reliably estimated from the sediment trap foraminiferal assemblages by the modern analog technique. The successful estimation of the annual SST range also indicates that the annual flux obtained from these sediment traps is representative of the longer term flux preserved in surface sediments. Core-top assemblages from this region can therefore be directly related to modern sea-surface conditions, providing an analogue for interpreting past environmental change from fossil assemblages.