Showing papers on "Foraminifera published in 2010"

Carbon isotope ratio of Cenozoic CO2: A comparative evaluation of available geochemical proxies

Abstract: [1] The carbon isotope ratio (δ13C) of plant material is commonly used to reconstruct the relative distribution of C3 and C4 plants in ancient ecosystems. However, such estimates depend on the δ13C of atmospheric CO2 (δ13CCO2) at the time, which likely varied throughout Earth history. For this study, we use benthic and planktonic δ13C and δ18O records to reconstruct a long-term record of Cenozoic δ13CCO2. Confidence intervals for δ13CCO2 values are assigned after careful consideration of equilibrium and non-equilibrium isotope effects and processes, as well as resolution of the data. We find that benthic foraminifera better constrain δ13CCO2 compared to planktonic foraminiferal records, which are influenced by photosymbiotes, depth of production, seasonal variability, and preservation. Furthermore, sensitivity analyses designed to quantify the effects of temperature uncertainty and diagenesis on benthic foraminifera δ13C and δ18O values indicate that these factors act to offset one another. Our reconstruction suggests that Cenozoic δ13CCO2 averaged −6.1 ± 0.6‰ (1σ), while only 11.2 million of the last 65.5 million years correspond to the pre-Industrial value of −6.5‰ (with 90% confidence). Here δ13CCO2 also displays significant variations throughout the record, at times departing from the pre-Industrial value by more than 2‰. Thus, the observed variability in δ13CCO2 should be considered in isotopic reconstructions of ancient terrestrial-plant ecosystems, especially during the Late and Middle Miocene, times of presumed C4 grassland expansion.

A Monograph of the Foraminifera of the North Pacific Ocean ...

Abstract: THIS is the first instalment of a work on the fora-miniferal fauna of the North Pacific. It embodies the results of Brady, in the Challenger report, in so far as concerns this area, and of Goes, Flint, Rhumbler, Bagg, and others, and presents the outcome of the author's own investigations. These are based on the examination of material dredged by the United States s.s. Albatross, Nero, and Alert, parts of which have been already used in the reports of Goës, Flint, and Bagg.A Monograph of the Foraminifera of the North Pacific Ocean.Part i., Astrorhizidæ and Lituolidseæ. By J. A. Cushman. Pp. xiv + 134. United States National Museum Bulletin 71. (Washington: Government Printing Office, 1910.)

Traditional and emerging geochemical proxies in foraminifera

Abstract: Geochemical analyses of the carbonate tests calcified by foraminifera have provided much of the foundation for reconstructions of past ocean and climate conditions, and for chemostratigraphy. In particular, reconstructions of climate history (including temperature, salinity, and ice volume), ocean paleocirculation patterns, the carbon cycle, paleoproductivity, marine carbonate chemistry, and chemostratigraphy have relied on measurements of isotopic and trace element composition of foraminiferal calcium carbonate, and variations in these geochemical records through time and space. Substantial work has been done on details of traditional proxies (e.g., d 18 O, d 13 C) and on emerging proxies (e.g., d 11 B, eNd) in recent years; hence, a new overview of these proxies provides a timely reference and educational tool. We review the geochemical proxies that utilize foraminiferal carbonate tests, including potential uses of the proxies for reconstructions through time: d 18 O, d 13 C, trace elements (Mg, Cd, Ba, Zn, B, U), 87 Sr/ 86 Sr, d 26 Mg, d 11 B, and eNd. Both planktic and benthic foraminifera are included; planktic foraminifera provide information on the upper few hundred meters of the surface ocean, whereas benthic foraminifera provide information on conditions at the seafloor and in shallow porewaters, from shallow seas to deep ocean basins.

Modern seawater acidification: the response of foraminifera to high-CO2 conditions in the Mediterranean Sea

Abstract: The seas around the island of Ischia (Italy) have a lowered pH as a result of volcanic gas vents that emit carbon dioxide from the sea floor at ambient seawater temperatures. These areas of acidified seawater provide natural laboratories in which to study the long-term biological response to rising CO 2 levels. Benthic foraminifera (single-celled protists) are particularly interesting as they have short life histories, are environmentally sensitive and have an excellent fossil record. Here, we examine changes in foraminiferal assemblages along pH gradients at CO 2 vents on the coast of Ischia and show that the foraminiferal distribution, diversity and nature of the fauna change markedly in the living assemblages as pH decreases.

Effectiveness of benthic foraminiferal and coral assemblages as water quality indicators on inshore reefs of the Great Barrier Reef, Australia

Abstract: Although the debate about coral reef decline focuses on global disturbances (e.g., increasing temperatures and acidification), local stressors (nutrient runoff and overfishing) continue to affect reef health and resilience. The effectiveness of foraminiferal and hard-coral assemblages as indicators of changes in water quality was assessed on 27 inshore reefs along the Great Barrier Reef. Environmental variables (i.e., several water quality and sediment parameters) and the composition of both benthic foraminiferal and hard-coral assemblages differed significantly between four regions (Whitsunday, Burdekin, Fitzroy, and the Wet Tropics). Grain size and organic carbon and nitrogen content of sediments, and a composite water column parameter (based on turbidity and concentrations of particulate matter) explained a significant amount of variation in the data (tested by redundancy analyses) in both assemblages. Heterotrophic species of foraminifera were dominant in sediments with high organic content and in localities with low light availability, whereas symbiont-bearing mixotrophic species were dominant elsewhere. A similar suite of parameters explained 89% of the variation in the FORAM index (a Caribbean coral reef health indicator) and 61% in foraminiferal species richness. Coral richness was not related to environmental setting. Coral assemblages varied in response to environmental variables, but were strongly shaped by acute disturbances (e.g., cyclones, Acanthaster planci outbreaks, and bleaching), thus different coral assemblages may be found at sites with the same environmental conditions. Disturbances also affect foraminiferal assemblages, but they appeared to recover more rapidly than corals. Foraminiferal assemblages are effective bioindicators of turbidity/light regimes and organic enrichment of sediments on coral reefs.

Cenomanian-Turonian transition in a shallow water sequence of the Sinai, Egypt

Abstract: Environmental and depositional changes across the Late Cenomanian oceanic anoxic event (OAE2) in the Sinai, Egypt, are examined based on biostratigraphy, mineralogy, δ13C values and phosphorus analyses. Comparison with the Pueblo, Colorado, stratotype section reveals the Whadi El Ghaib section as stratigraphically complete across the late Cenomanian–early Turonian. Foraminifera are dominated by high-stress planktic and benthic assemblages characterized by low diversity, low-oxygen and low-salinity tolerant species, which mark shallow-water oceanic dysoxic conditions during OAE2. Oyster biostromes suggest deposition occurred in less than 50 m depths in low-oxygen, brackish, and nutrient-rich waters. Their demise prior to the peak δ13C excursion is likely due to a rising sea-level. Characteristic OAE2 anoxic conditions reached this coastal region only at the end of the δ13C plateau in deeper waters near the end of the Cenomanian. Increased phosphorus accumulations before and after the δ13C excursion suggest higher oxic conditions and increased detrital input. Bulk-rock and clay mineralogy indicate humid climate conditions, increased continental runoff and a rising sea up to the first δ13C peak. Above this interval, a dryer and seasonally well-contrasted climate with intermittently dry conditions prevailed. These results reveal the globally synchronous δ13C shift, but delayed effects of OAE2 dependent on water depth.

Carbon-isotope stratigraphy, biostratigraphy and organic matter distribution in the Aptian - Lower Albian successions of southwest Iran (Dariyan and Kazhdumi formations)

Abstract: The lateral transition from carbonate platforms to intra-shelf basin in Aptian – Early Albian times is documented along a regional transect in the excellent exposures of the Zagros Mountains. An integrated dataset, including carbonate carbon-isotope curves, and ammonite and planktonic foraminifera biostratigraphy constrains the regional correlations, and forms the basis for an age revision of the Kazhdumi and Dariyan formations. Of particular importance in this study is the Kuh-e-Bangestan section, wherein a continuous succession of Aptian – Albian intra-shelf basinal deposits was used to erect a detailed ammonite and planktonic foraminifera biostratigraphic zonation scheme, in combination with a carbon-isotope curve and organic-matter measurements. Key observations are: (1) the oldest Kazhdumi intra-shelf deposits are of Early Aptian age (D. deshayesi Zone), indicating a timeequivalent initiation of the Kazhdumi and neighbouring intra-shelf Bab Basin. (2) The presence of well-developed organic matter-rich sediments in the N. nolani and H. jacobi zones is interpreted as equivalent to part of the OAE1b set. (3) The presence of an exceptionally well-developed Upper Aptian – Lower Albian succession (80 m thick) shows a clear positive carbon-isotope excursion and a faunal crisis, with the turn-over of the planktonic foraminifera assemblage (only small and low diversity Globigerinelloides and Hedbergellids) and the total absence of ammonites. A composite carbon-isotope curve is proposed based on sections measured in both the platform and basin settings. This curve deserves attention because it has an expanded Upper Aptian - Lower Albian section, which is well dated (ammonites, planktonic foraminifera and orbitolinids).

Paleoredox changes across the Paleocene-Eocene thermal maximum, Walvis Ridge (ODP Sites 1262, 1263, and 1266): Evidence from Mn and U enrichment factors

Abstract: An understanding of sediment redox conditions across the Paleocene?Eocene thermal maximum (PETM) (?55 Ma) is essential for evaluating changes in processes that control deep?sea oxygenation, as well as identifying the mechanisms responsible for driving the benthic foraminifera extinction. Sites cored on the flanks of Walvis Ridge (Ocean Drilling Program Leg 208, Sites 1262, 1266, and 1263) allow us to examine changes in bottom and pore water redox conditions across a ?2 km depth transect of deep?sea sediments of PETM age recovered from the South Atlantic. Here we present measurements of the concentrations of redox?sensitive trace metals manganese (Mn) and uranium (U) in bulk sediment as proxies for redox chemistry at the sediment?water interface and below. All three Walvis Ridge sites exhibit bulk Mn enrichment factors (EF) ranging between 4 and 12 prior to the warming, values at crustal averages (Mn EF = 1) during the warming interval, and a return to pre?event values during the recovery period. U enrichment factors across the PETM remains at crustal averages (U EF = 1) at Site 1262 (deep) and Site 1266 (intermediate depth). U enrichment factors at Site 1263 (shallow) peaked at 5 immediately prior to the PETM and dropped to values near crustal averages during and after the event. All sites were lower in dissolved oxygen content during the PETM. Before and after the PETM, the deep and intermediate sites were oxygenated, while the shallow site was suboxic. Our geochemical results indicate that oxygen concentrations did indeed drop during the PETM but not sufficiently to cause massive extinction of benthic foraminifera.

A synthesis of marine sediment core δ 13 C data over the last 150 000 years

Abstract: . The isotopic composition of carbon, δ13C, in seawater is used in reconstructions of ocean circulation, marine productivity, air-sea gas exchange, and biosphere carbon storage. Here, a synthesis of δ13C measurements taken from foraminifera in marine sediment cores over the last 150 000 years is presented. The dataset comprises previously published and unpublished data from benthic and planktonic records throughout the global ocean. Data are placed on a common δ18O age scale suitable for examining orbital timescale variability but not millennial events, which are removed by a 10 ka filter. Error estimates account for the resolution and scatter of the original data, and uncertainty in the relationship between δ13C of calcite and of dissolved inorganic carbon (DIC) in seawater. This will assist comparison with δ13C of DIC output from models, which can be further improved using model outputs such as temperature, DIC concentration, and alkalinity to improve estimates of fractionation during calcite formation. High global deep ocean δ13C, indicating isotopically heavy carbon, is obtained during Marine Isotope Stages (MIS) 1, 3, 5a, c and e, and low δ13C during MIS 2, 4 and 6, which are temperature minima, with larger amplitude variability in the Atlantic Ocean than the Pacific Ocean. This is likely to result from changes in biosphere carbon storage, modulated by changes in ocean circulation, productivity, and air-sea gas exchange. The North Atlantic vertical δ13C gradient is greater during temperature minima than temperature maxima, attributed to changes in the spatial extent of Atlantic source waters. There are insufficient data from shallower than 2500 m to obtain a coherent pattern in other ocean basins. The data synthesis indicates that basin-scale δ13C during the last interglacial (MIS 5e) is not clearly distinguishable from the Holocene (MIS 1) or from MIS 5a and 5c, despite significant differences in ice volume and atmospheric CO2 concentration during these intervals. Similarly, MIS 6 is only distinguishable from MIS 2 or 4 due to globally lower δ13C values both in benthic and planktonic data. This result is obtained despite individual records showing differences between these intervals, indicating that care must be used in interpreting large scale signals from a small number of records.