Погляд на архіви

The resolution at which foraminiferal stable isotopes are applied in paleo-environmental studies is ever increasing, resulting in continuous sampling of sediment cores. The resolution of such continuously sampled records depends on the rate of sedimentation of foraminiferal shells in its relation to the intensity of bioturbation. Bioturbation essentially mixes sediment layers of different age, altering the primary climate signal, thereby impacting the accuracy of both the timing and magnitude of reconstructed climate changes. A new approach to assess and correct the impact of bioturbation is investigated here, based on the δ18O of individual specimens of planktonic foraminifera Globorotalia inflata from a series of boxcore samples in the Eastern North Atlantic. Average δ18O values decrease southward from 1.62 to 1.07‰ with the exception of site T86-11 (1.35‰). The δ18O distribution of each station can be fitted with a uni- to polymodal distribution. A nonunimodal distribution strongly suggests admixing of bioturbated individuals. Quantification of these distributions allows deconvolving the original and bioturbated signals and subsequently provides a correction for bioturbation. © 2013. American Geophysical Union. All Rights Reserved

Early diagenetic overprint in Caribbean sediment cores and its effect on the geochemical composition of planktonic foraminifera

Early diagenetic features are noticed in the vicinity of carbonate platforms. Planktonic foraminifera of two tropical Atlantic deep-sea sediment cores show the strict relation between micro-scale euhydral crystallites of inorganic precipitates, higher oxygen isotope values and Mg/Ca ratios, and lower Sr/Ca ratios than expected for their pelagic environment in the time interval of ~100 000–550 000 calendar years before present. Laser ablation Mg/Ca (Sr/Ca) of crystallite-bearing foraminiferal chamber walls revealed 4–6 times elevated (2–3 times depleted) ratios, when ablating the diagenetic overgrowth. Crystalline overgrowth in proportion of 10–20% are estimated to cause the observed geochemical alteration. The extent of foraminiferal Mg/Ca alteration, moreover, seems to be controlled by the composition of the bulk sediment, especially the content of high-magnesium calcite. Anomalous ratios of >6 mmol/mol only occur, when high-magnesium calcite has dissolved within the sediment. The older parts (back to ~800 kyrs) of the records are characterized by similar trends of Mg/Ca and Sr/Ca. We discuss possible scenarios to accommodate the obtained geochemical information

Salinity control on Na incorporation into calcite tests of the planktonic foraminifera Trilobatus sacculifer – Evidence from culture experiments and surface sediments

The quantitative reconstruction of past seawater salinity has yet to be achieved and the search for a direct and independent salinity proxy is ongoing. Recent culture and field studies show a significant positive correlation of Na/Ca with salinity in benthic and planktonic foraminiferal calcite. For accurate paleoceanographic reconstructions, consistent and reliable calibrations are necessary, which are still missing. In order to assess the reliability of foraminiferal Na/Ca as a direct proxy for seawater salinity, this study presents electron microprobe Na/Ca data, measured on cultured specimens of Trilobatus sacculifer. The culture experiments were conducted over a wide salinity range of 26 to 45, while temperature was kept constant. To further understand potential controlling factors of Na incorporation, measurements were also performed on foraminifera cultured at various temperatures in the range of 19.5 °C to 29.5 °C under constant salinity conditions. Foraminiferal Na/Ca ratios positively correlate with seawater salinity (Na/Caforam = 0.97 + 0.115 ⋅ Salinity, R = 0.97, p < 0.005). Temperature on the other hand exhibits no statistically significant relationship with Na/Ca ratios indicating salinity to be the dominant factor controlling Na incorporation. The culturing results are corroborated by measurements on T. sacculifer from Caribbean and Gulf of Guinea surface sediments. In conclusion, planktonic foraminiferal Na/Ca can be applied as a reliable proxy for reconstructing sea surface salinities, albeit species-specific calibrations might be necessary

Fe-binding organic ligands in coastal and frontal regions of the western Antarctic Peninsula

Organic ligands are a key factor determining the availability of dissolved iron (DFe) in the high-nutrient low-chlorophyll (HNLC) areas of the Southern Ocean. In this study, organic speciation of Fe is investigated along a natural gradient of the western Antarctic Peninsula, from an ice-covered shelf to the open ocean. An electrochemical approach, competitive ligand exchange – adsorptive cathodic stripping voltammetry (CLE-AdCSV), was applied. Our results indicated that organic ligands in the surface water on the shelf are associated with ice-algal exudates, possibly combined with melting of sea ice. Organic ligands in the deeper shelf water are supplied via the resuspension of slope or shelf sediments. Further offshore, organic ligands are most likely related to the development of phytoplankton blooms in open ocean waters. On the shelf, total ligand concentrations ([Lt]) were between 1.2 and 6.4 nM eq. Fe. The organic ligands offshore ranged between 1.0 and 3.0 nM eq. Fe. The southern boundary of the Antarctic Circumpolar Current (SB ACC) separated the organic ligands on the shelf from bloom-associated ligands offshore. Overall, organic ligand concentrations always exceeded DFe concentrations (excess ligand concentration, [L′] = 0.8–5.0 nM eq. Fe). The [L′] made up to 80 % of [Lt], suggesting that any additional Fe input can be stabilized in the dissolved form via organic complexation. The denser modified Circumpolar Deep Water (mCDW) on the shelf showed the highest complexation capacity of Fe (αFe'L; the product of [L′] and conditional binding strength of ligands, KFe'Lcond). Since Fe is also supplied by shelf sediments and glacial discharge, the high complexation capacity over the shelf can keep Fe dissolved and available for local primary productivity later in the season upon sea-ice melting.</p

Impact of salinity on element incorporation in two benthic foraminiferal species with contrasting magnesium contents

Accurate reconstructions of seawater salinity could provide valuable constraints for studying past ocean circulation, the hydrological cycle and sea level change. Controlled growth experiments and field studies have shown the potential of foraminiferal Na ∕ Ca as a direct salinity proxy. Incorporation of minor and trace elements in foraminiferal shell carbonate varies, however, greatly between species and hence extrapolating calibrations to other species needs validation by additional (culturing) studies. Salinity is also known to impact other foraminiferal carbonate-based proxies, such as Mg ∕ Ca for temperature and Sr ∕ Ca for sea water carbonate chemistry. Better constraints on the role of salinity on these proxies will therefore improve their reliability. Using a controlled growth experiment spanning a salinity range of 20 units and analysis of element composition on single chambers using laser ablation-Q-ICP-MS, we show here that Na ∕ Ca correlates positively with salinity in two benthic foraminiferal species (<i>Ammonia tepida</i> and <i>Amphistegina lessonii</i>). The Na ∕ Ca values differ between the two species, with an approximately 2-fold higher Na ∕ Ca in <i>A. lessonii</i> than in <i>A. tepida</i>, coinciding with an offset in their Mg content ( ∼  35 mmol molM<super>−2</super> versus  ∼  2.5 mmol mol−<super>1</super> for <i>A. lessonii</i> and <i>A. tepida</i>, respectively). Despite the offset in average Na ∕ Ca values, the slopes of the Na ∕ Ca–salinity regressions are similar between these two species (0.077 versus 0.064 mmol mol<super>−1</super> change per salinity unit). In addition, Mg ∕ Ca and Sr ∕ Ca are positively correlated with salinity in cultured <i>A. tepida</i> but show no correlation with salinity for <i>A. lessonii</i>. Electron microprobe mapping of incorporated Na and Mg of the cultured specimens shows that within chamber walls of <i>A. lessonii</i>, Na ∕ Ca and Mg ∕ Ca occur in elevated bands in close proximity to the primary organic lining. Between species, Mg banding is relatively similar, even though Mg content is 10 times lower and that variation within the chamber wall is much less pronounced in <i>A. tepida</i>. In addition, Na banding is much less prominent in this species than it is in <i>A. lessonii</i>. Inter-species differences in element banding reported here are hypothesized to be caused by differences in biomineralization controls responsible for element uptake

Planktonic foraminiferal spine versus shell carbonate Na incorporation in relation to salinity

Sea surface salinity is one of the most important parameters to reconstruct in paleoclimatology, reflecting amongst other things the hydrological cycle, paleodensity, ice volume, and regional and global circulation of water masses. Recent culture studies and a Red Sea field study revealed a significant positive relation between salinity and Na incorporation within benthic and planktonic foraminiferal shells. However, these studies reported varying partitioning of Na between and within the same species. The latter could be associated with ontogenetic variations, most likely spine loss. Varying Na concentrations were observed in different parts of foraminiferal shells, with spines and regions close to the primary organic sheet being especially enriched in Na. In this study, we unravel the Na composition of different components of the planktonic foraminiferal shell wall using electron probe micro-analysis (EPMA) and solution ICP-MS. A model is presented to interpret EPMA data for spines and spine bases to quantitatively assess differences in composition and contribution to whole-shell Na∕Ca signals. The same model can also be applied to other spatial inhomogeneities observed in foraminiferal shell chemistry, like elemental (e.g., Mg, Na, S) banding and/or hotspots. The relative contribution of shell carbonate, organic linings, spines and spine bases to whole-shell Na chemistry is considered quantitatively. This study shows that whereas the high Na areas may be susceptible to taphonomic alterations, the Na chemistry of the shell itself seems relatively robust. Comparing both shell and spine Na∕Ca values with salinity shows that shell chemistry records salinity, albeit with a very modest slope.</p

Науково-практичний семінар “Архівна україніка: пошук, реєстрація та комплектування архівів”

28 жовтня 2010 р. у Державному комітеті архівів України відбувся науково-практичний семінар “Архівна україніка: пошук, реєстрація та комплектування архівів”, організований Державним комітетом спільно з Центральним державним архівом зарубіжної україніки (ЦДАЗ У) і Українським науково-дослідним інститутом архівної справи та документознавства (УНДІА СД) на виконання Указу Президента України від 13.10.2006 № 875/2006 “Про національну концепцію співпраці із закордонними українцями, державної програми співпраці із закордонним українством та галузевої програми “Зарубіжна україніка”

Southern ocean warming, sea level and hydrological change during the Paleocene-Eocene thermal maximum

A brief (~150 kyr) period of widespread global average surface warming marks the transition between the Paleocene and Eocene epochs, ~56 million years ago. This so-called "Paleocene-Eocene thermal maximum" (PETM) is associated with the massive injection of &lt;sup&gt;13&lt;/sup&gt;C-depleted carbon, reflected in a negative carbon isotope excursion (CIE). Biotic responses include a global abundance peak (acme) of the subtropical dinoflagellate &lt;i&gt;Apectodinium&lt;/i&gt;. Here we identify the PETM in a marine sedimentary sequence deposited on the East Tasman Plateau at Ocean Drilling Program (ODP) Site 1172 and show, based on the organic paleothermometer TEX&lt;sub&gt;86&lt;/sub&gt;, that southwest Pacific sea surface temperatures increased from ~26 °C to ~33°C during the PETM. Such temperatures before, during and after the PETM are &gt;10 °C warmer than predicted by paleoclimate model simulations for this latitude. In part, this discrepancy may be explained by potential seasonal biases in the TEX&lt;sub&gt;86&lt;/sub&gt; proxy in polar oceans. Additionally, the data suggest that not only Arctic, but also Antarctic temperatures may be underestimated in simulations of ancient greenhouse climates by current generation fully coupled climate models. An early influx of abundant &lt;i&gt;Apectodinium&lt;/i&gt; confirms that environmental change preceded the CIE on a global scale. Organic dinoflagellate cyst assemblages suggest a local decrease in the amount of river run off reaching the core site during the PETM, possibly in concert with eustatic rise. Moreover, the assemblages suggest changes in seasonality of the regional hydrological system and storm activity. Finally, significant variation in dinoflagellate cyst assemblages during the PETM indicates that southwest Pacific climates varied significantly over time scales of 10&lt;sup&gt;3&lt;/sup&gt; – 10&lt;sup&gt;4&lt;/sup&gt; years during this event, a finding comparable to similar studies of PETM successions from the New Jersey Shelf

Orbital and physical parameters of eclipsing binaries from the ASAS catalogue -- III. Two new low-mass systems with rapidly evolving spots

We present the results of our spectroscopic and photometric analysis of two newly discovered low-mass detached eclipsing binaries found in the All-Sky Automated Survey (ASAS) catalogue: ASAS J093814-0104.4 and ASAS J212954-5620.1. Using the GIRAFFE instrument on the 1.9-m Radcliffe telescope at SAAO and the UCLES spectrograph on the 3.9-m Anglo-Australian Telescope, we obtained high-resolution spectra of both objects and derived their radial velocities (RVs) at various orbital phases. The RVs of both objects were measured with the TODCOR technique using synthetic template spectra as references. We also obtained V and I band photometry using the 1.0-m Elizabeth telescope at SAAO and the 0.4-m PROMPT instruments located at the CTIO. The orbital and physical parameters of the systems were derived with PHOEBE and JKTEBOP codes. We compared our results with several sets of widely-used isochrones. Our multi-epoch photometric observations demonstrate that both objects show significant out-of-eclipse modulations, which vary in time. We believe that this effect is caused by stellar spots, which evolve on time scales of tens of days. For this reason, we constructed our models on the basis of photometric observations spanning short time scales (less than a month). Our modeling indicates that (1) ASAS-09 is a main sequence active system with nearly-twin components with masses of M1 = 0.771(33) Msun, M2 = 0.768(21) Msun and radii of R1 = 0.772(12) Rsun and R2 = 0.769(13) Rsun. (2) ASAS-21 is a main sequence active binary with component masses of M1 = 0.833(17) Msun, M2 = 0.703(13) Msun and radii of R1 = 0.845(12) Rsun and R2 = 0.718(17) Rsun. Both systems confirm the characteristic of active low-mass stars, for which the observed radii are larger and the temperatures lower than predicted by evolutionary models. Other parameters agree within errors with the models of main sequence stars.Comment: 15 pages, 7 figures, 7 tables, to appear in A&