1,721,091 research outputs found
Trace elements in marine biogenic carbonates: analysis and application to past ocean chemistry
No full textTrace elements in marine biogenic carbonates may be used as proxies for past oceanchemistry provided that there is an established relationship between the trace elementproxy and a parameter of interest, this relationship is preserved within biogeniccarbonate, and the trace element can be determined sufficiently accurately. Successfulapplication of any trace element proxy requires both development of the analyticalmethodology to ensure accurate data with the necessary sensitivity, and anunderstanding of the relationship between proxy and seawater chemistry.Herein I develop methods for the determination of Mg/Ca, Sr/Ca and Cd/Ca inplanktonic foraminiferal calcite, using inductively coupled plasma optical emissionspectrophotometry and isotope dilution thermal ionisation mass spectrometry, andpropose a potential reference material for Mg/Ca in foraminiferal calcite. The developedtechniques are applied to an investigation of the Mg/Ca temperature proxy overChatham Rise in the Southwest Pacific Ocean and a calibration study of the partitioncoefficient, DCd, for cadmium incorporation into planktonic foraminifera.Comparisons of planktonic foraminiferal Mg/Ca, shell weight and oxygenisotope records from sites north and south of the Subtropical Front on Chatham Rise,demonstrate the effects of hydrography, foraminiferal habitat and dissolution as controlson Mg/Ca. Determinations of Cd/Ca in seven species of planktonic foraminiferaconfirm that the dominant controls on Cd/Ca are foraminiferal habitat and hydrography,with only a minor influence of post depositional dissolution. The major uncertainty indetermination of DCd from core top samples comes from uncertainty in estimation of thedepth distribution and seasons of calcification of planktonic foraminifera
Southwest Pacific deep-water carbonate chemistry during the Mid-Pleistocene Transition
Full text linkAfter more than 40 years of research, there is still wide disagreement in defining when the Mid-Pleistocene Transition (MPT) occurred, with climate reconstructions ranging from an abrupt versus gradual transition that began as early as 1500 ka and ended as late as 600 ka. Our recent work in the Southwest Pacific (Ocean Drilling Program Site 1123) has provided some evidence for a rapid transition, suggesting that the MPT was initiated by an abrupt increase in global ice volume 900 thousand years ago [1]. This study uses shallow-infaunal benthic foraminifera Uvigerina spp. to disentangle the contributions of deep-water temperature (using Mg/Ca ratios) and ice volume to the oxygen isotopic composition of foraminiferal calcite over the last 1.5 Ma. The resulting sea-level reconstruction across the MPT shows that the critical step in ice-volume variation was associated with the suppression of melting in Marine Isotope Stage (MIS) 23, followed by renewed ice growth in MIS 22 to yield a very large ice sheet with 120 m of sea level lowering.
Here, we built on this work with the aim to investigate further the abrupt event centered on MIS 24 to 22 (the ‘900-ka event’) and try to shed some light on the processes and mechanisms that caused the MPT. Different hypotheses account for the origin of the MPT as a response to long-term ocean cooling, perhaps because of lowering CO2. To better quantify the role of the carbon system during the MPT, we reconstruct past changes in bottom water inorganic carbon chemistry from the trace element (B/Ca) and stable isotopic composition of calcite shells of the infaunal benthic foraminifera Uvigerina spp. from 1100 ka to 350 ka at ODP Site 1123. This site was retrieved from Chatham Rise, east of New Zealand in the Southwest Pacific Ocean (41o47.2’S, 171o 29.9’ W, 3290 m water depth) and lies under the Deep Western Boundary Current (DWBC) that flows into the Pacific Ocean, and is responsible for most of the deep water in that ocean; DWBC strength is directly related to processes occurring around Antarctica. The ratio of boron to calcium (B/Ca) in benthic foraminifer shells has proven to be a reliable indicator of the calcite saturation state of ocean bottom waters. The comparison between benthic foraminifera δ18O and δ13C shows a similar trend at ODP Site 1123, implying a close relationship between these climate and carbon cycle signals, and we use our B/Ca record reconstructed from the same samples to explore the potential processes behind this tight coupling.
These results permit preliminary discussion on the deep-water carbonate saturation state during glacial/interglacial cycles. Deep-water temperatures estimates using Mg/Ca and oxygen isotopic composition of seawater (δ18Osw) are available from Site 1123 for the last 1.5 million years [1] and the phase relationship between the different signals is tentatively assessed for the early/middle Pleistocene, when different patterns of climate variability have been inferred from marine and ice cores records.
[1] Elderfield et al. (2012). Evolution of ocean temperature and ice volume through the Mid Pleistocene Climate Transition. Science, vol. 337, 6095, 704-70
Physiological responses of coccolithophores to abrupt exposure of naturally low pH deep seawater
No full textUpwelling is the process by which deep, cold, relatively high-CO2, nutrient-rich seawater rises to the sunlit surface of the ocean. This seasonal process has fueled geoengineering initiatives to fertilize the surface ocean with deep seawater to enhance productivity and thus promote the drawdown of CO2. Coccolithophores, which inhabit many upwelling regions naturally ‘fertilized’ by deep seawater, have been investigated in the laboratory in the context of ocean acidification to determine the extent to which nutrients and CO2 impact their physiology, but few data exist in the field except from mesocosms. Here, we used the Porcupine Abyssal Plain (north Atlantic Ocean) Observatory to retrieve seawater from depths with elevated CO2 and nutrients, mimicking geoengineering approaches. We tested the effects of abrupt natural deep seawater fertilization on the physiology and biogeochemistry of two strains of Emiliania huxleyi of known physiology. None of the strains tested underwent cell divisions when incubated in waters obtained from <1,000 m (pH = 7.99–8.08; CO2 = 373–485 p.p.m; 1.5–12 μM nitrate). However, growth was promoted in both strains when cells were incubated in seawater from ~1,000 m (pH = 7.9; CO2 ~560 p.p.m.; 14–17 μM nitrate) and ~4,800 m (pH = 7.9; CO2 ~600 p.p.m.; 21 μM nitrate). Emiliania huxleyi strain CCMP 88E showed no differences in growth rate or in cellular content or production rates of particulate organic (POC) and inorganic (PIC) carbon and cellular particulate organic nitrogen (PON) between treatments using water from 1,000 m and 4,800 m. However, despite the N:P ratio of seawater being comparable in water from ~1,000 and ~4,800 m, the PON production rates were three times lower in one incubation using water from ~1,000 m compared to values observed in water from ~4,800 m. Thus, the POC:PON ratios were threefold higher in cells that were incubated in ~1,000 m seawater. The heavily calcified strain NZEH exhibited lower growth rates and PIC production rates when incubated in water from ~4,800 m compared to ~1,000 m, while cellular PIC, POC and PON were higher in water from 4,800 m. Calcite Sr/Ca ratios increased with depth despite constant seawater Sr/Ca, indicating that upwelling changes coccolith geochemistry. Our study provides the first experimental and field trial of a geoengineering approach to test how deep seawater impacts coccolithophore physiological and biogeochemical properties. Given that coccolithophore growth was only stimulated using waters obtained from >1,000 m, artificial upwelling using shallower waters may not be a suitable approach for promoting carbon sequestration for some locations and assemblages, and should therefore be investigated on a site-by-site basis
Chemical concentration of major metal and rare reath elements (REE) for manganese deposits in the Bauer Basin (Pacific Ocean)
No full textThe samples were collected from R/V "Yaquina" at 13°40'S, 102°8'W during cruise YALOC-73 of Oregon State University. The Mn nodules were sorted by morphological type before analysis. The Mn nodules and crust were analysed for REE by mixed-solvent ion exchange and mass spectrometric isotope dilution. Isotope analyses were performed on an A.E.I. MS5 mass spectrometer. The determinations of Fe, Mn, Co, Cu, Ni (atomic absorption spectrophotometry) and P (colorimetry) were made on the leachate from 0.1 M HCl
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Benthic and planktic foraminiferal stable isotopes, benthic foraminiferal Mg/Ca data and BWT stack, relative abundance of main benthic foraminiferal species, IRD concentration and magnetic susceptibility of core HH15-1252PC (western Svalbard margin)
No full textPiston core HH15-1252PC was collected in Vestnesa Ridge in the Western Svalbard margin. The core was logged with a GEOTEK Multi Sensor Core Logger and color imaged with a Jai L-107CC 3 CCD RGB line scan camera installed on an Avaatech XRF. One cm thick slices at 1 to 5 cm intervals. Samples were weighed, freeze-dried, and weighed again. They were subsequently wet-sieved over mesh-sizes 63 μm, 100 μm and 500 μm. The residues were dried at 40°C and weighed and weight percent of each grain size was calculated. Oxygen and carbon isotopes were measured on up to 20 pristine benthic (Cassidulina neoteretis and/or Melonis barleeanus; 150 to 250 μm size fraction) and planktic foraminifera (Neogloboquadrina pachyderma 100 to 500 μm size fraction). For trace element analyses, 10 to 30 pristine C. neoteretis (150 to 250 μm size fraction) or M. baleeanus (150 to 350 μm size fraction) were picked, crashed between two glass slides and cleaned following the oxidative-reductive approach (Boyle and Keigwin, 1985/1986; Pena et al., 2005). Mg/Ca ratios were then converted to bottom water temperature using calibrations from Kristjánsdóttir et al. (2007). Up to 300 benthic foraminifera were counted on each sample in the 100 to 1000 μm size fraction and relative abundance of the species was calculated in samples with at least 50 specimens. Ice rafted debris was counted in the 150 to 500 μm and >500 μm size fractions and the concentration was calculated. The grain-size ratio was calculated using the equation from Jessen and Rasmussen (2019).
Option
(Table S1) Foraminiferal trace element ratios from ODP 177-1090D and sediment core TTN057-6-PC4
No full textSediment depth is given in mcd, age is tuned to the LR04 benthic d18O stack
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
