Abstract: The technology of environmental magnetism has been increasingly widely applied in marine sediment research. Marine sediment contains a lot of water which is a kind of antimagnetic material. However, it’s not clear that loss of water during sample preparation and preservation is influential to its magnetic properties or not. Magnetic parameters were measured before and after drying for hundreds of marine sediment samples collected from the South China Sea. 685 samples were dried at room temperature, and their magnetic parameters κlf, κhf, SIRM, S-300 and κfd were measured every 40 days, totally 5 measurements. The other sixty samples were freeze dried and the same magnetic parameters were measured before and after drying. The results are shown as follows : 1) For samples dried at room temperature, κ decreased for most samples and increased for a few of samples while both S-300 and κfd decreased except the outliers; SIRM decreased at first 40 days and then increased, and it showed an increasing trend on the whole. 2) Magnetic parameters κ, S-300 and κfd showed an increasing trend and SIRM showed a trend of decrease for samples dried under freeze condition. 3) The variation trends of κ, SIRM and S-300 in profiles didn’t change during drying process. However, dehydration played a significant influence on profile variation of κfd. The variations of magnetic parameters may be due to comprehensive factors such as a weak oxidation during drying process, the reducing of “negative contribution” of water caused by water loss, the transition when fine magnetite and maghemite in wet state changed into paramagnetism and incomplete antiferromagnetism. Therefore, the same drying method must be used for the same batch of samples.

Key words: marine sediment, dehydration, magnetic properties, natural drying at room temperature, freeze drying