Manman Xie

Seasonal temperature variability during the past 1600 years recorded in historical documents and varved lake sediment profiles from northeastern China

Seasonal temperature variability over longer timescales could offer new insights into understanding different forcing factors and response processes in the climate system. Here we report an alkenone-based temperature reconstruction for growing season over the past 1600 years from the varved sediment in Lake Sihailongwan, northeastern China. The most notable cold spells occurred during the periods ad 480–860, ad 1260–1300, ad 1510–1570 and ad 1800–1900 with a temperature decrease of about 1°C compared with the 20th century. Based on the historical evidence such as ‘snow or frost in the summertime’ and ‘no ice during the wintertime’, we compile extreme cold summer events and warm winter events over the past 1600 years. The ‘Little Ice Age’ time period experienced more extreme cold summer/warm winter events, while the ‘Medieval Warm Period’ had milder winters. Comparatively, the natural proxy data show a general similar pattern with historical documents at decadal time scales, except for between ad 1620 and 1720. Our results show multidecadal to centennial variations in seasonal temperature, possibly caused by interactions of external natural forcing and atmosphere–ocean circulations.

Alkanes, compound-specific carbon isotope measures and climate variation during the last millennium from varved sediments of Lake Xiaolongwan, northeast China

Annually laminated sediments in Lake Xiaolongwan, northeast China, contain a suite of n-alkanes (C17–C33) with a strong odd over even carbon number predominance. Biomarker n-alkane proxies (average chain length, Paq ratio, grass/tree ratio, carbon preference index and compound-specific δ13C values) were used to reconstruct climate changes that occurred over the last millennium. Compound-specific δ13C values show large differences between the distinctive chain length groups of n-alkanes that originate from algae, aquatic macrophytes and terrestrial plants. Long-chain n-alkanes (C27–C33) are predominantly derived from leaf wax lipids in the forest. Variations in long-chain n-alkane δ13C values may mainly record water-use efficiency, inasmuch as the contribution from C4 plants is negligible in the Lake Xiaolongwan catchment. Short- and middle-chain n-alkanes are mainly from algae and aquatic plants. They are strongly depleted in 13C. This feature may be linked to a methane-derived, negative δ13C pool and lake overturn, which regulates dinoflagellate blooms. Parallel fluctuations are observed in δ13C27–31 values, Paq, and the grass/tree ratio throughout the record. Variations in δ13C27–31 values and Paq are in agreement with historical documents on summer and winter climate conditions. They support earlier suggestions that δ13C values in the long-chain n-alkanes and Paq may be useful indicators of effective precipitation or drought stress in this forested area. The δ13C27–31 index and Paq show distinct decadal variations. Periods with high δ13C27–31 values and a low Paq index correspond with the warm phases of the Pacific Decadal Oscillation (PDO). Values are reversed during PDO cool phases. At the decadal timescale, summer monsoon rainfall in northeast China over the last millennium may have been regulated mainly by the PDO.

Minor element variations during the past 1300 years in the varved sediments of Lake Xiaolongwan, north-eastern China

Synchrotron radiation X-ray fluorescence measurement provides a nondestructive in situ analysis of elements. We present a high-resolution minor element dataset covering the past 1300 years from the varved sediments in Lake Xiaolongwan. The variations of lithogenic elements (Rb, Sr, Ti, Zn, As and Fe) in the lake sediment show distinct decadal to centennial features during the past 1300 years. The Medieval Warm Period has a low value of lithogenic elements. In contrast, the Little Ice Age may be a period with stronger physical weathering and a higher value of lithogenic elements. Principal components analysis of our geochemical dataset suggests a link between high Rb/Sr ratio and Zr abundance in the sediment that could be related with both chemical weathering process and dust input. The variations of biogenic bromine (factor-3) show a pattern similar to the decadal drought index in Korea. Wet conditions favor bromine accumulation in lake sediment because high precipitation may transport more bromine from forest soil and increase plankton production in the lake. Spectral analysis of factor-3 yields notable periodicities of 2.6, 3.5, 53–55, 87–89 and 105–110 years, implying that precipitation variability for the past 1400 years could be associated with El Niño–Southern Oscillation and solar activity.

A Soil Water Extraction Method with Accelerated Solvent Extraction Technique for Stable Isotope Analysis

Abstract Soil water is one of the most important components in hydrological cycle. The stable isotopes (e.g., deuterium, 2 H, oxygen-18, 18 O) in soil water have been increasingly used as natural tracers in the ecological, environmental and hydrological research. In view of different techniques for extracting soil water, there are significant differences in the δD and δ 18 O compositions. This paper presents a method for the accelerated solvent extraction (ASE) of soil water for stable isotope analyses by mass spectrometry. The optimum parameters of extracting soil water were as follows: dichloromethane as the extraction solvent, temperature of 100 °C, pressure of 10.3 MPa, static time of 10 min. The samples were extracted three times, and with cycle values four, four and three, respectively. The extracted water was enriched in deuterium and oxygen-18 by 2.12%–4.58% and −0.17%–0.93%, respectively, compared with the added water. The reproducibility of replicate extractions of soil water was around ±0.89% for δD and ±0.37% for δ 18 O.

Long-chain alkenone-inferred temperatures from the last deglaciation to the early Holocene recorded by annually laminated sediments of the maar lake Sihailongwan, northeastern China:

Abrupt temperature changes during the last deglaciation are well recognized in Greenland ice cores and in deep-sea sediment records. On the continent of monsoonal Asia, however, only a few terrestrial temperature reconstructions extend to the Younger Dryas (YD). This hampers the understanding of how the Asian monsoon system responded to large-scale boundary changes in ice-sheet dynamics and reorganizations of atmospheric–oceanic circulation between the last deglaciation and the Holocene. Here, we report an alkenone-inferred temperature record from varved sediments of the maar lake Sihailongwan, northeastern China. Alkenone provides temperatures that represent the water temperature during the growing season when the lake is ice-free. Annually laminated sediments provide a reliable time control. Reconstructed temperatures reveal a distinctive pattern of variations during the last deglaciation: a temperature increase of 6°C at the onset of the Bølling–Allerød, two cold intervals (during the Older Dryas and the intra-Allerød cold period), a relatively minor temperature decrease of 1–3°C during the YD, and a rapid temperature increase of 4–5°C at the early Holocene. The reconstructed temperature records from Lake Sihailongwan and adjacent regions indicate that summer (or growing season) temperature changes were smaller than is evident in Greenland ice core records that are weighted toward winter.