Long-Chain Unsaturated Ketones In Qinghai Lake Sediments

Li Jinggui; Fan Pu; Cui Mingzhong; R.P.Philp; J.Allen

Long-chain methyl and ethyl alkenones (C₃₇-C₄₀) containing 2- 4 double bonds have been detected in sediments from Qinghai lake cores (QE, Q-16A and QG).This is the first report of the long-chain ketones in lake sediments deposited under a variety of salinity conditions (Erhai,fresh water ;Qinghai lake, brackish; Gabal, saline).The C₃₇ unsaturated ketone mixture consisted of the C_{37: 4}, C_{37: 3} and C_{37: 2} isomers; The C₃₈ unSaturated ketone mixture generally comPOsed the C_{38: 4},C_{38: 3} and C_{38: 2}isomers, whereas the C₃₉ unsaturated ketones were dominated in most cases by asingle C_{39: 3} isomer.A small numbe of samples in all the cores also contained low concentrations of the C_{40: 3} isomer.C₃₇ and C₃₉ ketones were recognized as methyl alkenones on the basis of their molecular ions, characteristic fragment ions at M-15, M-18, M-33, M-44 and M-58,and bAse peak at either m/z 43.81 or 95/96.The C₃₈ and C₄₀ isomers were recognized as ethyl alkenones from thediagnostic fragment ions at M-15, M-18, M-29,M-47,M-57 and M-72, and base peak at m/z 57.The C₃₇-C₄₀ alkenones are tentatively suggested to be derived from Chromulina sp in the lake.Differences in the abundance and unsaturated patterns of these alkenones in the sediments probably reflect compositional variations in the original algal input, and also reflect variations in salinity and temperature at time of deposition.With additional study, the alkenones in lacustrine environments may ultimately be useful for paleoclimate studies in manner analogous to that used in marine environmentS after additional calibration is made.

Long-Chain Unsaturated Ketones In Qinghai Lake Sediments

1 Lanzhou Institute of Geology, Academia Sinica, Lanzhou, 730000;

2 School of Geology and Geophysics, University of Oklahoma, Norman,OK, 73019, U.S.A.

Received Date: 1994-04-30

Publish Date: 1995-03-10

Abstract: Long-chain methyl and ethyl alkenones (C₃₇-C₄₀) containing 2- 4 double bonds have been detected in sediments from Qinghai lake cores (QE, Q-16A and QG).This is the first report of the long-chain ketones in lake sediments deposited under a variety of salinity conditions (Erhai,fresh water ;Qinghai lake, brackish; Gabal, saline).The C₃₇ unsaturated ketone mixture consisted of the C_{37: 4}, C_{37: 3} and C_{37: 2} isomers; The C₃₈ unSaturated ketone mixture generally comPOsed the C_{38: 4},C_{38: 3} and C_{38: 2}isomers, whereas the C₃₉ unsaturated ketones were dominated in most cases by asingle C_{39: 3} isomer.A small numbe of samples in all the cores also contained low concentrations of the C_{40: 3} isomer.C₃₇ and C₃₉ ketones were recognized as methyl alkenones on the basis of their molecular ions, characteristic fragment ions at M-15, M-18, M-33, M-44 and M-58,and bAse peak at either m/z 43.81 or 95/96.The C₃₈ and C₄₀ isomers were recognized as ethyl alkenones from thediagnostic fragment ions at M-15, M-18, M-29,M-47,M-57 and M-72, and base peak at m/z 57.The C₃₇-C₄₀ alkenones are tentatively suggested to be derived from Chromulina sp in the lake.Differences in the abundance and unsaturated patterns of these alkenones in the sediments probably reflect compositional variations in the original algal input, and also reflect variations in salinity and temperature at time of deposition.With additional study, the alkenones in lacustrine environments may ultimately be useful for paleoclimate studies in manner analogous to that used in marine environmentS after additional calibration is made.

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Long-Chain Unsaturated Ketones In Qinghai Lake Sediments

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