Antarctic ice sheet and oceanographic response to eccentricity forcing during the early Miocene

Stable isotope records of benthic foraminifera from ODP Site 1264 in the southeastern Atlantic Ocean are presented which resolve the latest Oligocene to early Miocene (~24–19 Ma) climate changes at high temporal resolution (<3 kyr). Using an inverse modelling technique, we decomposed the oxygen isotope record into temperature and ice volume and found that the Antarctic ice sheet expanded episodically during the declining phase of the long-term (~400 kyr) eccentricity cycle and subsequent low short-term (~100 kyr) eccentricity cycle. The largest glaciations are separated by multiple long-term eccentricity cycles, indicating the involvement of a non-linear response mechanism. Our modelling results suggest that during the largest (Mi-1) event, Antarctic ice sheet volume expanded up to its present-day configuration. In addition, we found that distinct ~100 kyr variability occurs during the termination phases of the major Antarctic glaciations, suggesting that climate and ice-sheet response was more susceptible to short-term eccentricity forcing at these times. During two of these termination-phases, ?18O bottom water gradients in the Atlantic ceased to exist, indicating a direct link between global climate, enhanced ice-sheet instability and major oceanographic reorganisations

The adequacy, use and compliance with internal auditing standards – South African perceptions in comparison with other specific regions

This article focusses on determining the adequacy of the International Standards for the Professional Practice of Internal Auditing (Standards) for use in South Africa, as well as examining how local entities comply with the Standards as compared to those in other specific regions, from both emerging economies and developed economies. Data used in this article’s analysis, interpretation, and comparisons comes from the USA-based Institute of Internal Auditors Research Foundation’s Common Body of Knowledge questionnaire respondents database. Findings indicated that the Standards provide adequate guidance to internal auditors, with South African respondents providing the highest rating. South African respondents also indicated that their organisations have the highest rate of compliance with the Standards, compared to those of other specific regions. Reasons for and theories explaining the non-compliance with the Standards are discussed. The findings of the study can be valuable to internal auditors in other emerging economies (as they shed light on possible reasons for non-compliance with the Standards), as well as for internal audit researchers as a basis for further research.http://www.saiga.co.za/publications-sajaar.htmam201

Astronomical forcing of mediterranean climate during the last 5.3 million years

The prime target of this investigation was to provide a better understanding of the processes underlying the onset of major south- and northern hemisphere glaciations around 2.8 Ma BP. Two issues had to be considered before we started our investigation. Firstly, are there sufficiently long and uninterrupted (marine) sequences available and, secondly, what climatic proxies are suitable for paleoclimatic reconstructions

Klimaatextremen

Ons menselijk besef van klimaatextremen beperkt zich in grote mate tot kortstondige periode van excessieve weersomstandigheden. Door de wereldwijde opwarming van de aarde is er een toenemende ongerustheid dat deze extremen vaker zullen voorkomen. Maar hoe verontrustend is die opwarming van de aarde nu eigenlijk? Of is er toch een nieuwe ijstijd in het vooruitzicht? In zijn oratie ‘Klimaatextremen’ plaatst Lucas Lourens de huidige opwarming van de aarde in een geologisch perspectief, waarbij wordt ingegaan op extreme broeikasperioden, die de aarde 56-50 miljoen jaar geleden teisterden en de invloed van astronomische cycli op het klimaat. Het vakgebied paleoklimatologie bestudeert klimaatveranderingen die in het verleden hebben plaatsgevonden op basis van reconstructies en modelstudies. Voor de reconstructies worden verschillende indicatoren gebruikt, zoals de stabiele isotopensamenstelling van foraminiferen. Dit zijn eencellige micro-organismen, die een kalkschaaltje maken dat in grote aantallen als gefossiliseerd materiaal in diepzee sedimenten wordt aangetroffen. Mede door de ontwikkeling van hoge resolutie astronomische dateringtechnieken worden er steeds nauwkeuriger klimaatreconstructies gemaakt, die kunnen worden gebruikt om de uitkomsten van lange tijdexperimenten met geavanceerde klimaatmodellen te toetsen. Door de vraag naar steeds betrouwbaardere modellen om toekomstscenario’s beter te kunnen voorspellen zal dit multidisciplinaire vakgebied zich blijven ontwikkelen

Revised tuning of Ocean Drilling Program Site 964 and KC01B (Mediterranean) and implications for the delta 0-18, tephra, calcareous nannofossil, and geomagnetic reversal chronologies of the past 1.1 Myr

High-resolution color reflectance records of KC01 and KC01B (Calabrian Ridge, Ionian Sea) are presented and compared with a modified spliced high-resolution color reflectance record of Ocean Drilling Program (ODP) Site 964. This comparison revealed that KC01B is characterized by intensive deformation between ∼27 and 28.5 m piston depth and that some sapropels are tectonically reduced in thickness. Moreover, the piston coring has caused considerable stretching in the top of KC01 and KC01B. Using a new splice of ODP Site 964 as guide, previous astronomical tuned timescales of KC01B and ODP Site 964 were evaluated. This evaluation resulted in a new sapropel-based astronomical timescale for the last 1.1 Myr. The new timescale implies a much more uniform change in sedimentation rate for the Ionian Sea cores. Two prominent excursions to lighter values in the δ¹⁸O record of the planktonic foraminiferal species Globigerinoides ruber occur during marine isotopic stages 12 and 16 applying the new timescale. These shifts correspond with maxima in obliquity and are punctuated by minima in the precession cycle. They are absent in global ice volume records and are interpreted as reflecting a (summer) low-salinity surface water lens that floats on top of extremely saline intermediate and deep waters at times of the very low sea levels during these glacial periods. All biostratigraphic and magnetostratigraphic events found in KC01B and ODP Site 964 were re-dated according to the new timescale, and the ages of 33 tephra layers were reviewed. The new ages for the Calabrian Ridge 2 and 3 magnetic events in the Brunhes are concordant with minima in the global Sint800 composite record, derived from worldwide deep-sea records of relative paleointensity and have been attributed to the Big Lost and La Palma excursions, respectively

Obliquity forcing of low-latitude climate

Contains fulltext : 190091.pdf (publisher's version ) (Open Access

Geologically constrained astronomical solutions for the Cenozoic era

Astronomical solutions provide insight into the Solar System's dynamical evolution and are indispensable tools in cyclostratigraphy and astrochronology. Constructing an absolute, fully calibrated astronomical time scale (ATS) has hitherto been hindered beyond ∼50 Ma because orbital calculations disagree before that age due to solar system chaos. We have recently developed a new approach that allows extending the fully calibrated astronomical time scale to ∼58 Ma. Here, we present geologic data and new astronomical solutions, extending our approach across the Paleocene epoch (∼66 to ∼56 Ma). New astronomical solutions were generated using numerical solar system integrations following our earlier work, which now provides geologically constrained astronomical solutions for the Cenozoic era (66-0 Ma). The orbital solutions are available to 300 Ma — we caution, however, that the time interval 300-66 Ma is unconstrained due to dynamical chaos in the solar system. We have tested the sensitivity of our new solutions to various parameters, including numerical stepsize, solar quadrupole moment, number of asteroids included, initial positions, and tidal dissipation. We demonstrate that our new solutions yield improved agreement with the geologic record across the Paleocene epoch, compared to previously available astronomical solutions for that period. Furthermore, we discuss implications of our results for solar system chaos and resonance transitions. We have also obtained K/T boundary (KTB) ages based on our new solutions, which suggest slightly younger KTB ages than those inferred from most recent 40Ar/39Ar radiometric dating

The Messinian on Gavdos (Greece) and the status of currently used ages for the onset of the MSC and gypsum precipitation

The Upper Tortonian and Messinian in the already classic Metochia section on Gavdos Island (Greece) is made up of deep marine, laminated and homogeneous marls with the latter being replaced by evaporitic limestones at the very top of the section. Previous tuning of the section to the La90 time series of northern summer insolation provided ages for sedimentary cycles, polarity reversals, and bioevents. Earlier work on foraminifers and stable isotopes focused on the last 2.45 Myr of the Tortonian and the first 470 kyr of the Messinian. This study extends the stable isotope record and the set of semi-quantitative data on planktonic foraminifers into the youngest 820 kyr of the section which include the precursor and initial stages of the Messinian Salinity Crisis (MSC). New and old foraminiferal oxygen and carbon isotope data have been combined into a ~25 kyr resolution record for the entire pre-evaporitic Messinian and show a major change at 6.74 ± 0.04 Ma which we interpret to reflect an abrupt change in salinity from normal marine to hypersaline and thus marks the prelude to the MSC. Field and thin-section observations on the limestones in the top of the section confirm their evaporitic origin and suggests that salinities has risen to values of >70 psu. We further discuss the biotic response to the two-step salinity increase during the Messinian. Tuning provides an age of 6.00 Ma for the base of the first evaporitic limestone on Gavdos and this age is therefore the age for the onset of the MSC in this part of the Mediterranean. An evaluation of the published ages for the MSC onset in sections Perales (SE Spain), Monticino (N Italy), and Falconara (Sicily) shows that the onset in Falconara, just as on Gavdos, begins at ~6.00 Ma with calcium carbonate precipitation, whereas in Perales and Monticino, onset begins at 5.97 Ma (similar to the currently used age of 5.971 Ma) with gypsum precipitation, i.e. some 30 kyr later than the onset of the MSC on Gavdos and Sicily (Falconara)

Stable isotope stratigraphy of the early Quaternary of borehole Noordwijk, southern North Sea

Between 2.58Ma and 2.4Ma, most of the present onshore sector of the Netherlands was an epicontinental sea. Previous studies suggest the occurrence of multiple cold and warm phases in shallow marine successions of the Maassluis Formation in conjunction with the first prominent Northern Hemisphere ice sheet expansions. Nevertheless, correlation with deep marine isotope stages is tentative and relies on relative dating as absolute dating techniques are difficult to apply. Here, we present for the first time an early Quaternary, high-resolution benthic stable isotope record from the onshore sector of the Netherlands, taken from borehole Noordwijk. We tune our record to MIS 100-94 using the characteristic δ18O signature and complementary biostratigraphic data. This new high resolution isotope chronology is providing important insights on stratigraphy and palaeoenvironmental development of the southern North Sea area during the early Quaternary