Alberto in 2013

Alberto Malinverno
Lamont Research Professor
Lamont-Doherty Earth Observatory
of Columbia University
P.O. Box 1000
61 Route 9W
Palisades, NY 10964-1000 USA
Tel.: +1-845-365-8577
Fax: +1-845-365-8156
alberto@ldeo.columbia.edu

Microbial methanogenesis, gas hydrates, and carbon cycling at continental margins

The sediments of the world continental margins contain vast amounts of gas hydrate, a solid ice-like compound of water and methane. These deposits accumulate where methane is abundant, pressure is high, and temperature is low. Gas hydrates can dissociate when temperatures rise, and thus are a metastable reservoir in the global carbon cycle, sited between the ocean-atmosphere reservoir and the long-term carbon storage in sedimentary rocks. I have worked on quantifying the gas hydrate content of sediment by combining downhole logs and pore water chemistry, modeling how methane generated in fine-grained muds can migrate to form gas hydrate in coarse-grained layers, and understanding the relationship between the near-seafloor sulfate-methane transition and deeper methane generation. Methane in marine gas hydrates is predominantly microbial, as shown by the lack of higher hydrocarbons and by the stable carbon isotope content. While the origin of methane is clear, the overall process of microbial methanogenesis in marine sediments is still poorly understood and is the focus of my present work.

Geophysical inverse problems and applications to the geological time scale

The goal of geophysical inversion is to infer properties of an Earth model from a finite, noisy data set. These inverse problems have non-unique solutions, in that there is a range of possible Earth models that fit the data (e.g., result in a similar data misfit). My research has concentrated on quantifying this non-uniqueness, which can be viewed as an inherent uncertainty in the inverse problem solution. Bayesian inversion methods are a powerful way to quantify this uncertainty. I have worked on Monte Carlo parsimonious inversion methods, where the complexity of the Earth model is determined by the available data, and on assigning uncertainties to parameters that are not part of the Earth model but affect the solution and may be poorly known a priori (e.g., the amplitude of the data noise). Most recently, I applied these inverse techniques to time scale construction by determining an astrochronology age model based on a high-resolution downhole resistivity log and obtaining a geomagnetic polarity time scale for the M-sequence magnetic anomaly lineations (120- 160 Ma) that simultaneously minimizes the global variability of spreading rates, agrees with radiometric dates, and fits polarity chron durations estimated by astrochronology.

Neogene tectonic evolution of the Mediterranean

The Mediterranean region a prime example of a continent-to-continent collision that does not result in a simple, narrow suture. Instead, the broad plate boundary contains orogenic belts that accommodate considerable shortening and basins that form by extension in internal, back-arc regions. In the Tyrrhenian sea, the ~400 km of E-W extension necessary to explain the crustal thinning in the basin is about the same as the maximum amount of contemporaneous shortening in the Southern Apennines. The tectonics of the Tyrrhenian-Apennine region seem hard to explain from plate motions: during the opening of the Tyrrhenian basin, Africa and Europe converged only by ~70 km in a roughly N-S direction. The solution of this puzzle is that the old Eastern Mediterranean lithosphere sank into the surrounding mantle during subduction, causing an eastward retreat of the subduction hinge and consequent extension in the overriding plate. At the same time, the Apenninic belt developed as an accretionary wedge. This explanation for the formation of the Tyrrhenian-Apennine system has been widely accepted and used in many later studies.