Month: April 2013

Deep-sea chemosynthetic communities may be particularly vulnerable to large climatic changes that affect ocean temperatures and circulation patterns. Chemosynthetic animals occupy narrow redox zones, mostly at hydrothermal vents, hydrocarbon seeps, or sites of organic deposition where subsurface fluids laden with reduced gases (e.g., sulfides, methane, hydrogen) meet oxygenated seawater. Dependence on chemolithoautotrophic bacteria as primary producers renders these communities susceptible to climatic changes that alter the breadth of the oxic/anoxic interface. The fossil record reveals major transitions of chemosynthetic faunas during the middle to late Mesozoic, failing to support prior hypotheses that these environments harbor an extraordinary number of ancient relics and living fossils. The molecular phylogenetic analyses summarized herein support Cenozoic (<65 Myr old) radiations for most of the dominant invertebrate taxa now occupying these habitats. Although stem ancestors for many of the mollusks, annelids and crustaceans found at vents and seeps survived the Cretaceous/Tertiary (K/T) extinction event, their contemporary crown taxa radiated mostly after the Paleocene/Eocene thermal maximum (PETM), which led to a widespread anoxic/dysoxic event in the world’s deep-ocean basins. Perhaps these findings provide a window for viewing the future of our oceans on a warming planet.

Polar ice sheets are progressively becoming one of the most critical components of the Earth System. Indeed, in a warming climate, the Antarctic and Greenland ice sheets are contributing larger amounts of fresh water to the oceans, which results in increasing sea level rise. Here, we look at recent developments within the Ice Sheet System Model (ISSM) that have resulted in improved projections of sea level rise. Our focus will be on understanding what uncertainties remain in such projections, and how to improve them using a combination of modeling and observations.

There is moderately strong evidence that the Earth experienced one or more magma ocean episodes during which large-scale magmas were at or close to the surface. Because the rates of heat loss is very high, such episodes could only be powered by impacts and the periods during which magma was exposed were very brief. It has been popular to discuss magma oceans in the Asteroid Belt; in particular, several studies have inferred that the HED (howardite, eucrite, diogenite) meteorites formed in a magma ocean on Vesta. In fact, it appears to be impossible to create true magma oceans in the Asteroid Belt because impact heating liberates less heat and 26Al heats at much too low a rate. What the authors really are discussing is global magmas located beneath an insulating megaregolithic shell. All igneous models of asteroids use 26Al as the heat source even though the 26Al/27Al ratios in the chondrites in our museums are too low to produce appreciable melting. The general justification is that impact heating doesn’t work so it must have been 26Al heating. In effect, 26Al is treated as a free parameter. Until recently this was justified because Hf/W model ages for iron meteorites implied that the irons are older than chondrites. And modelers are now producing large melt fractions in porous asteroids at relatively low impact velocities (~5 km s-1). The most cited paper justifying a magma ocean on the HED parent asteroid is by Greenwood et al. (2005) who showed that most HEDs formed a very tight cluster. The cluster does indeed imply a single, well mixed magma but the data only require a relatively small magma. In fact, the D17O and e54Cr data favor a model in which the HEDs form on the same asteroid as the IIIAB magmatic irons (and thus not on Vesta). Richter and Drake (1997) suggested that a magma ocean was the best way to explain the low alkali contents in eucrites. However, internal heating by 26Al is not expected to result in much volatile loss because there is no carrier phase at volatilization temperatures . Impact heat is probably much more efficient at evaporating alkalis. The isotopic links between the HEDs and IIIAB irons seem stronger than the spectroscopic links between HEDs and the surface of Vesta. These groups probably formed in one or more regional magmas produced by minor impacts on a porous asteroid.

In hopes of seeding ideas for joint UCLA-JPL projects, I will briefly
describe a half-dozen topics showing the capabilities at JPL for
modeling planet-forming environments in protostellar disks. The
common thread is our desire to translate the flood of data from
Spitzer, Herschel, SOFIA, ALMA, JWST and other telescopes into an
understanding of the origins of the observed population of planetary
systems. Specifically I’ll give a taste of our work on (1) young
planets perturbing their surroundings in ways that might soon be
observed, (2) delivering ices to planets massive enough to open a gap
in the circumstellar disk, (3) using molecular line emission to probe
turbulence in the disk atmosphere, (4) infrared variability as a gauge
of the disk magnetic activity, (5) the origins of Jupiter’s moons in a
circumplanetary disk, and/or (6) water abundances near the protosolar
disk’s snow line, in the face of destruction by stellar ultraviolet
photons.