Showing papers by "Todd Sowers published in 2009"

Comparison of the microbial diversity at different depths of the GISP2 Greenland ice core in relationship to deposition climates

Abstract: This study presents comparative geochemical, microbiological and molecular analyses of Greenland GISP2 ice core samples representing different depths, ages, deposition climates, in situ temperatures, and gas and ionic compositions. Our goal was to determine whether specific organisms, preserved at different depths, correlate with past climate characteristics recorded chronologically in ice layers. Three clear ice samples were selected from 2495, 2545 and 2578 m to represent distinct climatic periods with milder (-45 degrees C), colder (-51 degrees C) and warmer (-39 degrees C) deposition temperatures, and two Marine Isotope Stages, MIS3 (2495 m) and MIS4 (2545 and 2578 m). Results showed higher microbial abundance in ice deposited during colder climates with higher in situ ion content. The constructed universal SSU rRNA gene clone libraries were dominated by Gram-positive sequences (55-65%), and had fewer Proteobacteria (6-9%) and Archaea (1%). The 2495 m library differed from the other two by being dominated by Actinobacteria (55%) rather than Firmicutes. Fungi were more prevalent in the colder climate (40%). For comparison, a library was constructed from an older silty ice sample (3044 m) possibly originating from underlying permafrost with different in situ characteristics (high temperature, high methane and higher cell numbers). It showed significantly different diversity not found in the clear ice libraries. The bacterial and fungal isolates from the clear ice samples were related to organisms originating from Asian deserts, marine aerosols and volcanic dust, suggesting these environments as sources of deposited microorganisms. The observed differences in microbial diversity patterns, especially with the 2495 m library, support the idea that local climate conditions and global atmospheric circulations at different time periods have influenced the origin and composition of the microbial populations preserved at different depths of Greenland ice. Further investigations may lead to the development of microbial 'markers' for identifying specific deposition climates.

Carbon and hydrogen isotopic composition of methane over the last 1000 years

Abstract: the common era (CE)) The d 13 Co f CH4 data corroborate the record from Law Dome, Antarctica, with high fidelity The new d Do f CH4 data set covaries with the d 13 Co f CH4 record Both d 13 Co f CH4 and d Do f CH4 were relatively stable and close to the present-day values from � 1000 to � 1500 CE Both isotopic ratios decreased to minima around 1700 CE, remained low until the late 18th century, and then rose exponentially to present-day values Our new d Do f CH4 data provide an additional independent constraint for evaluating possible CH4 source histories We searched a broad range of source scenarios using a simple box model to identify histories consistent with the constraints of the CH4 concentration and isotope data from 990–1730 CE Results typically show a decrease over time in the biomass-burning source (found in 85% of acceptable scenarios) and an increase in the agricultural source (found in 77% of acceptable scenarios), indicating preindustrial human influence on atmospheric methane as proposed in previous studies