Ecology: Coral crisis captured
The Great Barrier Reef is the world's largest reef system, but is being increasingly affected by climate change. Terry Hughes and colleagues examine changes in the geographic footprint of mass bleaching events on the Great Barrier Reef over the last two decades, using aerial and underwater survey data combined with satellite-derived measurements of sea surface temperature. They show that the cumulative footprint of multiple bleaching events has expanded to encompass virtually all of the Great Barrier Reef, reducing the number and size of potential refuges. The 2016 bleaching event proved the most severe, affecting 91% of individual reefs. The authors call for immediate global action to reduce the magnitude of climate warming in order to secure a future for coral reefs.
Nesteretal A, A Novel Class of Cage-Like Polyketide from Marine-Derived Actinomycete Nesterenkonia halobia.
An intriguing cage-like polyhemiketal, nesteretal A (1), was isolated from the coral-derived actinomycete Nesterenkonia halobia. Its structure was established by extensive spectroscopic and computational methods. Nesteretal A is a highly oxygenated compound featuring an unprecedented 5/5/5/5 tetracyclic scaffold. A possible biosynthetic pathway of 1 from naturally occurring diacetyl was proposed. Compound 1 showed a weak retinoid X receptor-α (RXRα) transcriptional activation effect.
The role of early lithification in development of chalky porosity in calcitic micrites: Upper Cretaceous chalks, Egypt
Abstract Petrological and geochemical examination of Upper Cretaceous chalks from the Abu Roash area and Bahariya Oasis (Egypt) provide insights into factors which control porosity development in fine-grained calcitic carbonates. Petrological studies indicate that primary skeletal fabrics of coccoliths and foraminifera in micrites of Abu Roash are well preserved. In contrast, primary skeletal fabrics of the Bahariya Oasis chalks are pervasively altered. Geochemical analysis of these chalks reveals a striking contrast in composition. The high porosity chalks at Bahariya Oasis have depleted isotopic values ( δ 13 C = −5.0‰, δ 18 O = −8.9‰ PDB ) and low concentrations of trace elements (Sr and Na). In contrast, the low porosity chalks at Abu Roash are less depleted in terms of their isotopic values ( δ 13 C = 1.0‰, δ 18 O = −4.0‰ ) and possess elevated concentrations of Sr, Na, Fe and Zn. Importantly, fracture and collapse veins, present only at Abu Roash, are filled with calcite whose δ18O value is coincident with that of altered micrites at Bahariya Oasis. The lithic fragments cemented by this calcite, however, retain compositions identical to other lithified limestones at Abu Roash. Differences in fabric and chemistry of the pelagic marine micrites observed between Abu Roash and Bahariya Oasis reflect the degree of early lithification and compaction prior to exposure and meteoric diagenetic alteration associated with regional Late Cretaceous/pre-Eocene subaerial unconformity.