Showing papers by "Jan Kramers published in 2008"

Hydrogen sulphide release to surface waters at the Precambrian/Cambrian boundary

Abstract: Changes in environmental conditions at the Precambrian–Cambrian transition (around 542 million years ago) have been suggested as a possible explanation for the apparent rapid increase in abundance of multicellular organisms known as the 'Cambrian explosion'. The nature of the environmental changes is still a matter of debate, however. Wille et al. now report molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of about 542 million years. With the help of a box model of the oceanic molybdenum cycle, they find that intense upwelling of hydrogen sulphide-rich deep ocean water best explains the observed early Cambrian molybdenum isotope signal. This suggests that the early Cambrian animal radiation may have been triggered by a major change in ocean circulation, following a long period during which the ocean was stratified, with sulphidic deep water. This paper reports molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of around 542 million years. The findings suggest that the Early Cambrian animal radiation may have been triggered by a major change in ocean circulation, terminating a long period during which the Proterozoic ocean was stratified, with sulphidic deep water. Animal-like multicellular fossils appeared towards the end of the Precambrian, followed by a rapid increase in the abundance and diversity of fossils during the Early Cambrian period, an event also known as the ‘Cambrian explosion’1,2,3. Changes in the environmental conditions at the Precambrian/Cambrian transition (about 542 Myr ago) have been suggested as a possible explanation for this event, but are still a matter of debate1,2,3. Here we report molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of around 542 Myr. We find a transient molybdenum isotope signal immediately after the Precambrian/Cambrian transition. Using a box model of the oceanic molybdenum cycle, we find that intense upwelling of hydrogen sulphide-rich deep ocean water best explains the observed Early Cambrian molybdenum isotope signal. Our findings suggest that the Early Cambrian animal radiation may have been triggered by a major change in ocean circulation, terminating a long period during which the Proterozoic ocean was stratified, with sulphidic deep water.

Evidence for a widespread climatic anomaly at around 9.2 ka before present

Abstract: [1] The 8.2 ka event was triggered by a meltwater pulse (MWP) into the North Atlantic and resultant reduction of the thermohaline circulation (THC). This event was preceded by a series of at least 14 MWPs; their impact on early Holocene climate has remained almost unknown. A set of high-quality paleoclimate records from across the Northern Hemisphere shows evidence for a widespread and significant climatic anomaly at ∼9.2 ka B.P. This event has climatic anomaly patterns very similar to the 8.2 ka B.P. event, cooling occurred at high latitudes and midlatitudes and drying took place in the northern tropics, and is concurrent with an MWP of considerable volume (∼8100 km3). As the 9.2 ka MWP occurs at a time of enhanced baseline freshwater flow into the North Atlantic, this MWP may have been, despite its relatively small volume, sufficient to weaken THC and to induce the observed climate anomaly pattern.

The evolution of matter : from the big bang to the present day earth

Abstract: The Evolution of Matter explains how all matter in the Universe developed following the Big Bang and through subsequent stellar processes It describes the evolution of interstellar matter and its differentiation during the accretion of the planets and the history of the Earth Unlike many books on geochemistry, this volume follows the chemical history of matter from the very beginning to the present, demonstrating connections in space and time It provides also solid links from cosmochemistry to the geochemistry of Earth The book presents comprehensive descriptions of the various isotope systematics and fractionation processes occurring naturally in the Universe, using simple equations and helpful tables of data With a glossary of terms and over 900 references, this volume is a valuable reference for researchers and advanced students studying the chemical evolution of the Earth, the Solar System and the wider Universe