ALBERT

Description: The Miocene epoch (23.03–5.33 Ma) was a time interval of global warmth, relative to today. Continental configurations and mountain topography transitioned toward modern conditions, and many flora and fauna evolved into the same taxa that exist today. Miocene climate was dynamic: long periods of early and late glaciation bracketed a ∼2 Myr greenhouse interval—the Miocene Climatic Optimum (MCO). Floras, faunas, ice sheets, precipitation, pCO2, and ocean and atmospheric circulation mostly (but not ubiquitously) covaried with these large changes in climate. With higher temperatures and moderately higher pCO2 (∼400–600 ppm), the MCO has been suggested as a particularly appropriate analog for future climate scenarios, and for assessing the predictive accuracy of numerical climate models—the same models that are used to simulate future climate. Yet, Miocene conditions have proved difficult to reconcile with models. This implies either missing positive feedbacks in the models, a lack of knowledge of past climate forcings, or the need for re-interpretation of proxies, which might mitigate the model-data discrepancy. Our understanding of Miocene climatic, biogeochemical, and oceanic changes on broad spatial and temporal scales is still developing. New records documenting the physical, chemical, and biotic aspects of the Earth system are emerging, and together provide a more comprehensive understanding of this important time interval. Here, we review the state-of-the-art in Miocene climate, ocean circulation, biogeochemical cycling, ice sheet dynamics, and biotic adaptation research as inferred through proxy observations and modeling studies.

Description: The Isle of Arran lies off the Ayrshire coast in the Firth of Clyde, SW Scotland. James Hutton visited Arran in August 1787 with his companion, John Clerk, and together they made the first geological investigation of the island. Hutton returned to Edinburgh satisfied that he had at last found the critical field evidence he had been searching for in support of his Theory of the Earth'. In June 1797, ten years after Hutton's first survey of Arran, Robert Jameson arrived on the island to investigate its geology and mineralogy. Jameson was still only 22 but had already become one of Hutton's most ardent critics. The previous year he had read two papers to the Royal Medical Society of Edinburgh refuting critical elements of Hutton's Theory'. Based at Kilmichael, near Brodick, on the east coast, Jameson spent most of June, July and August systematically exploring Arran entirely on foot. On returning to Edinburgh, he combined a narrative of his observations on Arran with an earlier trip to his parents' native Shetland Islands, in what became the earliest published account of the geology of Arran; An Outline of the Mineralogy of the Shetland Islands, and of the Island of Arran (1798). Jameson returned to Arran for a second, shorter visit in August 1799 and subsequently published a second book, The Mineralogy of the Scottish Isles ... (1800), which presented a revised and updated geological description of Arran. Jameson's handwritten journals for both his 1797 and 1799 tours of Arran survive. In this paper we draw on these first-hand accounts of Jameson's field observations and discuss them alongside his two subsequent books describing Arran's geology. The journals clearly show that Jameson was an acute observer in the field and consistently made his interpretations in accordance with Wernerian principles. Although he had read the published Volumes I and II of Hutton's Theory', it appears that he had not seen the unpublished Volume III manuscript prior to either tour. Nevertheless, Jameson's exploration of the island closely follows that of Hutton's and they visited many of the same field localities. Here, we use Jameson's Arran journals to retrace his field investigations and discuss them in the light of Hutton's previous work on the island and in relation to Jameson's own Wernerian views. The difference of approach and interpretation between the two in the field on Arran mirrors the wider conflict between Plutonists and Neptunists at this time.

Description: The first stop on Charles Darwin's famous voyage around the world in HMS Beagle was at Porto Praya (Praia), the principal town on the island of St Jago (Sao Tiago) in the Cape Verde archipelago. From 16 January to 8 February 1832, Darwin enjoyed his first substantive opportunity to study the natural history of an exotic place. Darwin himself regarded this occasion as a significant turning point in his life because, according to his autobiography, it was here that he decided to research and publish a book on the geology of the places visited on the voyage. He also recalled that it was here, the very first port call, that convinced him of the wonderful superiority' of Charles Lyell's uniformitarian geology over the doctrine of successive cataclysms that he had been taught in England. Later commentators have generally accepted this account, which is significant for understanding the intellectual background to the Origin of Species, at face value. In this paper we reconstruct some of Darwin's observations at St Jago based on his contemporaneous notes and diary, and in the light of our own visit made in January 2002. We find little evidence to substantiate the claim that he interpreted the geology in Lyellian terms at the time. Instead, he formulated a theory involving a great cataclysm to explain the dramatic scenery in the island's interior. He speculated that a torrent of water had carved the main valleys of the island, leaving deposits of diluvium in their beds. It is indisputable that Darwin came to embrace gradualist thinking enthusiastically during the voyage. Some of his observations made on St Jago, especially relating to uplift of the coast, were instrumental in this change of view, but the conversion was gradual, not sudden. His later published works make no mention of his original catastrophist interpretations.

Description: The impact of an asteroid at the end of the Cretaceous caused mass extinctions in the oceans. A rapid collapse in surface to deep-ocean carbon isotope gradients suggests that transfer of organic matter to the deep sea via the biological pump was severely perturbed. However, this view has been challenged by the survival of deep-sea benthic organisms dependent on surface-derived food and uncertainties regarding isotopic fractionation in planktic foraminifera used as tracers. Here we present new stable carbon ( 13 C) and oxygen ( 18 O) isotope data measured on carefully selected planktic and benthic foraminifera from an orbitally dated deep-sea sequence in the southeast Atlantic. Our approach uniquely combines 18 O evidence for habitat depth of foraminiferal tracer species with species-specific 13 C eco-adjustments, and compares isotopic patterns with corresponding benthic assemblage data. Our results show that changes in ocean circulation and foraminiferal vital effects contribute to but cannot explain all of the observed collapse in surface to deep-ocean foraminiferal 13 C gradient. We conclude that the biological pump was weakened as a consequence of marine extinctions, but less severely and for a shorter duration (maximum of 1.77 m.y.) than has previously been suggested.

Description: In a study of a sediment core from the US Atlantic Coastal Plain (Ocean Drilling Program Site 174X-Millville), Wright and Schaller (1) claim to have resolved the onset of the Paleocene/Eocene carbon isotope excursion (CIE) across 13 y. Such a rapid change would require an enormous and instantaneous release of...

Description: The Paleocene–Eocene Thermal Maximum (PETM), ca. 56 Ma, was a major global environmental perturbation attributed to a rapid rise in the concentration of greenhouse gases in the atmosphere. Geochemical records of tropical sea-surface temperatures (SSTs) from the PETM are rare and are typically affected by post-depositional diagenesis. To circumvent this issue, we have analyzed oxygen isotope ratios ( 18 O) of single specimens of exceptionally well-preserved planktonic foraminifera from the PETM in Tanzania (~19°S paleolatitude), which yield extremely low 18 O, down to 〈–5. After accounting for changes in seawater chemistry and pH, we estimate from the foraminifer 18 O that tropical SSTs rose by 〉3 °C during the PETM and may have exceeded 40 °C. Calcareous plankton are absent from a large part of the Tanzania PETM record; extreme environmental change may have temporarily caused foraminiferal exclusion.

Description: The impact of an asteroid at the end of the Cretaceous caused mass extinctions in the oceans. A rapid collapse in surface to deep-ocean carbon isotope gradients suggests that transfer of organic matter to the deep sea via the biological pump was severely perturbed. However, this view has been challenged by the survival of deep-sea benthic organisms dependent on surface-derived food and uncertainties regarding isotopic fractionation in planktic foraminifera used as tracers. Here we present new stable carbon ( 13 C) and oxygen ( 18 O) isotope data measured on carefully selected planktic and benthic foraminifera from an orbitally dated deep-sea sequence in the southeast Atlantic. Our approach uniquely combines 18 O evidence for habitat depth of foraminiferal tracer species with species-specific 13 C eco-adjustments, and compares isotopic patterns with corresponding benthic assemblage data. Our results show that changes in ocean circulation and foraminiferal vital effects contribute to but cannot explain all of the observed collapse in surface to deep-ocean foraminiferal 13 C gradient. We conclude that the biological pump was weakened as a consequence of marine extinctions, but less severely and for a shorter duration (maximum of 1.77 m.y.) than has previously been suggested.

Description: Strotz and Allen (1) examined our recently published phylogeny of Cenozoic macroperforate planktonic foraminifera (2) to assess the relative frequency of anagenesis (evolution within a single evolving lineage) and cladogenesis (lineage branching) in the production of new morphospecies. They conclude that anagenesis is much less prevalent than indicated in our...