In situ LA-ICPMS U Pb dating and geochemical characterization of fault-zone calcite in the central Tarim Basin, northwest China: Implications for fluid circulation and fault reactivation

Bivalve shells are extensively used as bioarchives for paleoclimate and paleoenvironmental reconstructions. Proxy calibrations in recent shells are the basis for sclerochronology and the applications of geochemistry data to fossils. Shell geochemical information, however, could be altered with the disappearance of intercrystalline organic matrix components, including those linked to shell growth increments, during early diagenesis. Thus, an evaluation of the chemistry of such organics is needed for the correct use of sclerochronological records in fossil shells. Here, we use atom probe tomography (APT) for in situ geochemical characterization of the insoluble organic matrix in shell growth increments in the Antarctic scallop, Adamussium colbecki. We confirm the presence of carboxylated S-rich proteoglycans, possibly involved in calcite nucleation and growth in these scallops, with significant concentrations of magnesium and calcium. Diagenetic modification of these organic components could impact proxy data based on Mg/Ca ratios, but more importantly the use of the δ15N proxy, since most of the shell nitrogen is likely bound to the amide groups of proteins. Overall, our findings reinforce the idea that shell organics need to be accounted for in the understanding of geochemical proxies.

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In-situ measurement of atmospheric CO<sub>2</sub> at the four WMO/GAW stations in China

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-27287-2013 ◽

2013 ◽

Vol 13 (10) ◽

pp. 27287-27326 ◽

Cited By ~ 3

Author(s):

S. X Fang ◽

L. X. Zhou ◽

P. P. Tans ◽

P. Ciais ◽

M. Steinbacher ◽

...

Keyword(s):

Atmospheric Carbon Dioxide ◽

Northwest China ◽

North East ◽

Production Area ◽

Wind Regimes ◽

Carbon Dioxide Co2 ◽

The City ◽

Observation Period

Abstract. Atmospheric carbon dioxide (CO2) mole fractions were continuously measured from January 2009 to December 2011 at 4 atmospheric observatories in China ((Lin'an, LAN), (Longfengshan, LFS), (Shangdianzi, SDZ), and (Waliguan, WLG)) using Cavity Ring Down Spectroscopy instruments. All sites are regional (LAN, LFS, SDZ) or global (WLG) measurement stations of the World Meteorological Organization/Global Atmosphere Watch program (WMO/GAW). LAN is located near the megacity of Shanghai, in China's most economically developed region. LFS is in a forest and rice production area, close to the city of Harbin in the northern east of China. SDZ is located 150 km north east of Beijing. WLG, hosting the longest record of measured CO2 mole fractions in China, is a high altitude site in northwest China recording background CO2 values. The CO2 growth rates are 2.2 ± 0.2 ppm yr−1 for LAN, 2.3 ± 0.2 ppm yr−1 for LFS, 2.0 ± 0.2 ppm yr−1 for SDZ, and 1.2 ± 0.1 ppm yr−1 (1σ) for WLG, during the period of 2009 to 2011. The growth rate at WLG may be underestimated due to the data gaps during the observation period. The highest annual mean CO2 mole fraction of 404.1 ± 4.1 ppm was observed at LAN in 2011. A comprehensive analysis of CO2 variations, their diurnal and seasonal cycles as well as the analysis of the influence of different wind regimes on the CO2 mole fractions allows a thorough characterization of the sampling sites and of the key processes driving the CO2 mole fractions. These data form a basis to improve our understanding of atmospheric CO2 variations in China and the underlying fluxes, using atmospheric inversion models.

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