Holocene pyrolytic nitrogen compounds by using pyrolysis-GC/MS and its paleoclimatic implication from Jinchuan peatbog, NE China

Abstract

We present a Holocene record of pyrolytic nitrogen (N) composition from the Jinchuan peat bog within the Longgang Volcanic Field (LVF), NE China. Based on pyrolysis gas chromatography and mass spectrometry (Py-GC/MS) analysis, N-compounds including acetamide, NHetero and NAro have been identified and quantified. Aromatic N-compounds (NAro, benzonitrile and benzamide) are mainly derived from phytoplankton and higher plants, and are resistant to microbial degradation. We propose ‘NHetero/NAro’ as a proxy based on microbial degradation, and has lower values between 10 and 5.8 ka BP, and higher values during the late Holocene. We suggest that temperature is main factor for NHetero/NAro, and sedimentary facies changed from floodplain to peat deposition, variation of effective precipitaion and pH value have limited influence on the performance of the proxy in Jinchuan. Low NHetero/NAro levels, combined with high levels of non-protein derived acetamide, indicate warmer conditions, and vice versa. NHetero/NAro is sensitive to temperature change, and follows a similar pattern to those of previous paleo-temperature time series derived from br-GDGT and long chain alkenones in this region. This Spectral analysis of the NHetero/NAro time series reveals significant periodicities of 103–105, 145 and 482–506 years, suggesting strong influences of solar radiation and monsoon intensity on temperature variations in NE China during the Holocene.