Eearth 

About: Eearth is an academic journal. The journal publishes majorly in the area(s): Mineral resource classification & Climate change. It has an ISSN identifier of 1943-345X. Over the lifetime, 294 publications have been published receiving 1455 citations.

A normalised seawater strontium isotope curve: possible implications for Neoproterozoic-Cambrian weathering rates and the further oxygenation of the Earth

Abstract: The strontium isotope composition of seawater is strongly influenced on geological time scales by changes in the rates of continental weathering relative to ocean crust alteration. However, the potential of the seawater 87 Sr/ 86 Sr curve to trace globally integrated chemical weathering rates has not been fully realised because ocean 87 Sr/ 86 Sr is also in- fluenced by the isotopic evolution of Sr sources to the ocean. A preliminary attempt is made here to normalise the seawa- ter 87 Sr/ 86 Sr curve to plausible trends in the 87 Sr/ 86 Sr ratios of the three major Sr sources: carbonate dissolution, sili- cate weathering and submarine hydrothermal exchange. The normalised curve highlights the Neoproterozoic-Phanerozoic transition as a period of exceptionally high continental influ- ence, indicating that this interval was characterised by a tran- sient increase in global weathering rates and/or by the weath- ering of unusually radiogenic crustal rocks. Close correlation between the normalised 87 Sr/ 86 Sr curve, a published seawa- ter 34 S curve and atmospheric pCO2 models is used here to argue that elevated chemical weathering rates were a ma- jor contributing factor to the steep rise in seawater 87 Sr/ 86 Sr from 650 Ma to 500 Ma. Elevated weathering rates during the Neoproterozoic-Cambrian interval led to increased nutri- ent availability, organic burial and to the further oxygenation of Earth's surface environment. Use of normalised seawater 87 Sr/ 86 Sr curves will, it is hoped, help to improve future geo- chemical models of Earth System dynamics.

Stimulated infrared emission from rocks: assessing a stress indicator

Abstract: To study the effect of stress-activated positive hole (p-hole) charge carriers on the infrared (IR) emission from rocks, we subjected a portion (10 vol.%) of a large (30◊60◊7.5 cm 3 ) block of anorthosite, a nearly monomin- eralic (Ca-rich feldspar) igneous rock, to uniaxial deviatory stress up to failure. We measured the IR emission from a flat surface 40 cm from the stressed rock volume over the 800-1300 cm 1 (7.7-12.5µm) range. Instantly, upon loading, the emission spectrum and intensity change. At first narrow bands appear at 930 cm 1 (10.75µm), 880 cm 1 (11.36µm), 820 cm 1 (12.4µm) plus additional narrow bands in the 1000-1300 cm 1 (7.7-10.0µm) range. The 10.75-12.4µm bands are thought to arise from vibrationally excited O-O stretching modes, which form when p-hole charge carriers, which spread from the stressed rock volume into the unstressed rock, recombine at the surface. They ra- diatively decay, giving rise to "hot" bands due to transitions between excited states. Before failure the broad emission bands at 1170 cm 1 and 1030 cm 1 (8.7 and 9.7µm) also increase slightly in intensity, suggesting a small increase in temperature due to thermalization of the energy deposited into the surface through p-hole recombination. Stimulated IR emission due to hole-hole recombination and its follow- on effects may help understand the enhanced IR emission seen in night-time satellite images of the land surface before major earthquakes known as "thermal anomalies".

Stable isotope compositions of a late Jurassic ammonite shell: a record of seasonal surface water temperatures in the southern hemisphere?

Abstract: Exceptional preservation of aragonite secreted by ammonites offers an opportunity to determine the sea- sonal temperature variations of Mesozoic surface waters. Ontogenetic profiles of carbon and oxygen isotope com- positions have been obtained from the nacreous layer of a well-preserved Late Jurassic (Oxfordian) ammonite (Perisphinctes) from Madagascar. A similar range of oxygen isotope compositions was also obtained from an associated benthic bivalve (Astarte) which suggests the absence of sam- pling bias. Late Jurassic seasonal variations in the southern hemisphere were close to 2.5 C and relatively weak when compared to the 2.5-6.5 C temperature range prevailing in the present-day Indian Ocean at a paleolatitude of 40±1 S. According to the hypothesis of an ice cap-free Late Jurassic Earth, average sea surface temperatures may have been up to 7 C higher than now.

Decline of coral reefs during late Paleocene to early Eocene global warming

Abstract: Since the 1980s the frequency of warming events has intensified and simultaneously widespread coral bleach- ing, and enhanced coral mortality have been observed. Yet, it remains unpredictable how tropical coral reef communi- ties will react to prolonged adverse conditions. Possibly, coral reef systems are sufficiently robust to withstand con- tinued environmental pressures. But if coral mortality in- creases, what will platform communities of the future look like? The co-evolution of early Paleogene carbonate plat- forms and palaeoclimate may provide insight. Here we doc- ument the impact of early Paleogene global warming on shallow-water carbonate platforms in the Tethys. Between 59 and 55 Ma, three discrete stages in platform development can be identified Tethys-wide: during the first stage carbon- ate platforms mainly consisted of coralgal reefs; during the second - transitional - stage coralgal reefs thrived only at middle latitudes and gave way to larger foraminifera as dom- inant carbonate producer in low latitudes; finally, during the third stage, newly developing larger foraminifera lineages completely took over the role as main carbonate-producing organisms in low to middle latitudes. We postulate that ris- ing temperatures led to a stepwise demise of Paleocene coral reefs, giving way to an unprecedented expansion of larger foraminifera, dominating Tethyan platforms during the early Eocene.