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2011 Annual Science Report

Massachusetts Institute of Technology Reporting  |  SEP 2010 – AUG 2011

Neoproterozoic Carbon Cycle

Project Summary

The rock record late Neoproterozoic (540-800 Ma) appears to exhibit strong
perturbations to Earth’s carbon cycle. This project seeks an understanding
of the mechanisms that drive such events and their biogeochemical significance.

4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

The carbon isotopic record suggests that the Neoproterozoic was a time of strong perturbations to Earth’s carbon cycle. One hypothesis suggests that one or more of these perturbations results from the remineralization of a large reservoir of recalcitrant dissolved organic carbon (DOC). To better understand the extent to which this hypothesis can be supported, we are taking two approaches.

The first approach formulates dynamical constraints. We have found that consistency with the carbonate and organic carbon-isotopic record requires that the remineralization event must play out over a period faster than the typical time over which DOC resides in the ocean. If we take this time to be less than 10,000 yr, as commonly assumed for the modern ocean, then this result calls into question recent interpretations of the so-called Shuram excursion that invoke the remineralization of DOC.

Our second approach is to ask if major isotopic events in other periods may be plausibly related to the remineralization of large stores of recalcitrant organic carbon. We focus on the late Permian,
for which a growing body of evidence, much of which is due to work in the Summons group, indicates that the oceans were anoxic prior to the end-Permian extinction. Our recent work suggests in addition that the end-Permian extinction was accompanied by a major perturbation of the carbon cycle that was initially excited about 100 Kyr before the peak extinction activity. Our analysis, based on carbon-isotopic data in widely separated locations, suggests that the changes took the form of a dynamical instability with characteristics similar to a singular blow-up. This dynamical signature is consistent with a transfer of a large reservoir of slow, recalcitrant DOC to a faster, more labile state. In collaboration with the groups of Eric Alm and Roger Summons, we are exploring ways in which this transfer may be related to late-Permian microbial evolution and synchronous environmental changes.

    Dan Rothman
    Project Investigator

    Objective 3.2
    Origins and evolution of functional biomolecules

    Objective 4.2
    Production of complex life.

    Objective 5.1
    Environment-dependent, molecular evolution in microorganisms

    Objective 5.2
    Co-evolution of microbial communities

    Objective 6.1
    Effects of environmental changes on microbial ecosystems