People at Fort Hoofddijk

Suzhen Liu
Visiting Researcher
Dr. S. Liu
Paleomagnetic Laboratory
Fort Hoofddijk
Nederlandse organisatie voor Wetenschappelijk Onderzoek
Department of Earth Sciences
Utrecht University 
Budapestlaan 17, 3584 CD Utrecht 
The Netherlands 



Research of Suzhen Liu

Biomagnetic response and high-resolution environmental records of Holocene deposits in East Asia
Biomagnetic response to the Holocene Warm Period in semi-arid East Asia
Hyperthermal events in geological times, such as the Palaeocene-Eocene Thermal Maximum, are believed to have profoundy changed global and regional hydrological cycles, and thus significantly reshaped sedimentary and biological processes in both marine and terrestrial environments. The Holocene Warm Period (HWP) provides valuable insights into the climate system and biotic responses to environmental variability during geological thermal events and thus serves as an excellent analogue for future global climate changes.  

The magnetic concentration (represented by ARM in a) and grain size (represented by the ratio in b) have nice correlations with TOC and TIC, used as indicator of nutrition supply into Dali Lake. Therefore, it is inferred that high magnetofossil abundance during the Holocene Warm Period (HWP)  is fostered by better nutrient availability, which can further be linked to warm and wet conditions in the lake region. Our magnetic record documents clearly the beginning of the HWP at ~9.8 ka and a sudden termination of the HWP at ~5.9 ka. A two-stepped increase at ~7.7 ka coincides with inferred water source change: from snow/ice melt to monsoonal precipitation.
Magnetofossils are geologically preserved magnetic minerals produced intra-cellularly by magnetotactic bacteria and have been proposed as  distinctive  environmental indicators. Particularly, links between magnetofossils and geological thermal events have been reported in both marine and haemipelagic sediments.

One theme of Suzhen's PhD thesis is the identification and environmental interpretation of magnetofossils in Dali Lake (inner Mongolia, China) sediments during the HWP. The main conclusions were:
  1. The warm and wet HWP conditions were highly favourable for magnetofossil proliferation in the semi-arid Asian interior.
  2. The increase and termination of biomagnetic signal at ~9.8 ka and ~5.9 ka coincided respectively with the beginning and end of the HWP, and are respectively linked to increased nutrient supply due to postglacial warming and poor nutrition due to drying at ~6 ka in the Asian interior. The two-stage transition at ~7.7 ka correlates well with inferred change of source water into the lake from ice/snow melt to monsoonal precipitation (therefore, ameliorating climate conditions in the East Asian Monsoon area).
  3. Our biomagnetic record correlates well with changes in summer insolation at high northern latitudes, which reflects the response of biotic systems in semi-arid lakes to insolation-driven climate changes through magnetic mineral production and deposition. This record may also represents a good example of magnetofossil abundance during geological thermal periods.

Orientaton of Precambrian extrusive rocks in North China Craton
High-resolution environmental magnetic record of the last deglaciation: contrasting magnetic sources during warm and cold periods

Preservation and alternation of magnetic minerals in lake sediments provide implication of the redox conditions and hydrology during lake development history.

Detailed analysis of magnetic concentration, mineralogy, grain size and domain state can thus assistant in identification of magnetic mineral sources and perhaps lake deposition process.
For instance, allochthonous magnetic minerals in lake sediments may origin from bedrock and soil in the catchment, eolian dust, vocanic ash, while authigenic contribution includes magnetosome (geologically magnetofossils) produced intracellularly by magnetotactic bacteria and iron sulphide as byproduct of iron-reducing bacteria. Moreover, post-depositional alternation such as dissolution, oxidation and dilution can bring ambiguities in environmental interpretation of the magnetic signals.

Field work in Linxia

Another topic of Suzhen’s PhD research is detailed evalution of magnetic sources in Dali Lake since the last deglaciation. Techniques involved are systematic rock magnetic analysis, TEM and SEM observation and XRD. The aim is to constrain the source of magnetic signal during different stage, and to explore the implication of lake depositon process and regional surface and climate changes during this period. 

Autumn view of the Dali Lake catchment area

publications Publications of Suzhen Liu

  • Liu, S., Deng, Chenglong, Xiao, Jule, Li, Jinhua, Paterson, Greig, Chang, Liao, Yi, Liang, Qin, Huafeng, Pan, Yongxin & Zhu, Rixiang (2016). High-resolution enviromagnetic records of the last deglaciation from Dali Lake, Inner Mongolia. Palaeogeography, Palaeoclimatology, Palaeoecology, 454, (pp. 1-11). 
  • Li, S., Deng, Chenglong, Dong, Wei, Sun, Lu, Liu, S., Qin, Huafeng, Yin, Jiyun, Ji, Xueping & Zhu, Rixiang (2015). Magnetostratigraphy of the Xiaolongtan Formation bearing Lufengpithecus keiyuanensis in Yunnan, southwestern China - Constraint on the initiation time of the southern segment of the Xianshuihe–Xiaojiang fault. Tectonophysics, 655, (pp. 213-226).
  • Liu, S., Deng, Chenglong, Xiao, Jule, Li, Jinhua, Paterson, Greig, Chang, Liao, Yi, Liang, Qin, Huafeng, Pan, Yongxin & Zhu, Rixiang (2015). Insolation driven biomagnetic response to Holocene Warm Period in semi-arid East Asia. Scientific Reports, 5 (8001).