ALBERT

Description: Subduction zones are often characterized by wedge-shaped sedimentary complexes—called accretionary prisms—that form when sediments are scraped off the subducting plate and added to the overriding plate. Large, landward-dipping thrust faults can cut through such a prism: these faults, known as 'megasplay faults'1, 2, originate near the top of the subducting plate and terminate at the shallow, landward edge of the prism1, 3, 4, 5, 6. Megasplay faults have been the subject of numerous geological and geophysical studies4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, but their initiation and evolution through time remains poorly constrained. Here we combine seismic reflection data from the Nankai accretionary wedge with geological data collected by the Integrated Ocean Drilling Program (IODP) and find that the splay fault cutting this wedge initiated approx1.95 Million years (Myr) ago in the lower part of the prism as an out-of-sequence thrust (OOST). After an initial phase of high activity, the movement along the fault slowed down, but uplift and reactivation of the fault resumed about 1.55 Myr ago. The alternating periods of high and low activity along the splay fault that we document hint at episodic changes in the mechanical stability of accretionary prisms.

Description: As scientists discover more about the genomes of marine microorganisms, new views of their physiology and ecosystem networks are opening up, explain Alexandra Z. Worden and Darcy McRose. "Alien Ocean: Anthropological Voyages in Microbial Seas by Stefan Helmreich University of California Press: 2009. 464 pp."

Description: Our understanding of the composition and activities of microbial communities from diverse habitats on our planet has improved enormously during the past decade, spurred on largely by advances in molecular biology. Much of this research has focused on the bacteria, and to a lesser extent on the archaea and viruses, because of the relative ease with which these assemblages can be analyzed and studied genetically. In contrast, single-celled, eukaryotic microbes (the protists) have received much less attention, to the point where one might question if they have somehow been demoted from the position of environmentally important taxa. In this paper, we draw attention to this situation and explore several possible (some admittedly lighthearted) explanations for why these remarkable and diverse microbes have remained largely overlooked in the present era of the microbe. © 2009 International Society for Microbial Ecology All rights reserved.

Description: Widespread evidence of a +4–6-m sea-level highstand during the last interglacial period (Marine Isotope Stage 5e) has led to warnings that modern ice sheets will deteriorate owing to global warming and initiate a rise of similar magnitude by ad 2100 (ref. 1). The rate of this projected rise is based on ice-sheet melting simulations and downplays discoveries of more rapid ice loss2, 3. Knowing the rate at which sea level reached its highstand during the last interglacial period is fundamental in assessing if such rapid ice-loss processes could lead to future catastrophic sea-level rise. The best direct record of sea level during this highstand comes from well-dated fossil reefs in stable areas4, 5, 6. However, this record lacks both reef-crest development up to the full highstand elevation, as inferred7 from widespread intertidal indicators at +6 m, and a detailed chronology, owing to the difficulty of replicating U-series ages on submillennial timescales8. Here we present a complete reef-crest sequence for the last interglacial highstand and its U-series chronology from the stable northeast Yucatán peninsula, Mexico. We find that reef development during the highstand was punctuated by reef-crest demise at +3 m and back-stepping to +6 m. The abrupt demise of the lower-reef crest, but continuous accretion between the lower-lagoonal unit and the upper-reef crest, allows us to infer that this back-stepping occurred on an ecological timescale and was triggered by a 2–3-m jump in sea level. Using strictly reliable 230Th ages of corals from the upper-reef crest, and improved stratigraphic screening of coral ages from other stable sites, we constrain this jump to have occurred approx121 kyr ago and conclude that it supports an episode of ice-sheet instability during the terminal phase of the last interglacial period.