From akreiser@GEOGRAPHY.UCL.AC.UKWed Aug 14 12:06:05 1996 Date: Fri, 31 May 1996 12:05:03 +0100 From: Annette Kreiser To: Multiple recipients of list PALEOLIM Subject: Freeze-dried sediment Our lab. will soon have the use of a freeze-drier. Can anyone give me any information on the advantages (or otherwise) of freeze-drying lake sediment compared with conventional drying at 25-30 degrees C? The sediment will subsequently be needed for diatom, carbonaceous particle and possibly pollen analysis. The questions that immediately come to mind are: 1) Does freeze-drying minimise the breakage of diatom frustules in dried sediment and, if so, is the preservation as good as in wet sediment? 2) What are the effects on pollen? 3) Should freeze-dried samples always be stored in rigid containers to avoid crushing? (At the moment our dried samples are stored in 'Whirlpak' bags packed quite tightly into drawers.) Any other points, comments or implications for other types of analysis gratefully received. Annette Kreiser Environmental Change Research Centre UCL From haskell@MAROON.TC.UMN.EDUWed Aug 14 12:06:18 1996 Date: Fri, 31 May 1996 09:45:20 -0500 From: Brian Haskell To: Multiple recipients of list PALEOLIM Subject: Re: Freeze-dried sediment On Fri, 31 May 1996, Annette Kreiser wrote: > Our lab. will soon have the use of a freeze-drier. Can anyone give me any > information on the advantages (or otherwise) of freeze-drying lake sediment > compared with conventional drying at 25-30 degrees C? I am more familiar with people doing oven-drying at 100'C than a hot summer day temperature. The big advantage of freeze drying is that your sediment does not turn into a brick but will usually end up with the individual particles remaining separate. You may find it a lot easier to get clean microfossils from clay rich sediments if the sediments have been freeze-dried. Oven drying (at higher temperatures) is also reputed to drive off more water - water that might be bound to clays or some hydrated materials as opposed to pore water. I suspect that in most cases the difference is very small but I'd be interested if anybody can point to a reference. > 1) Does freeze-drying minimise the breakage of diatom frustules in dried > sediment and, if so, is the preservation as good as in wet sediment? I don't have any direct experience with this but I don't think freeze-drying the sediment would damage diatoms unless the actually freezing of a really wet sediment somehow caused damage. > 2) What are the effects on pollen? > > 3) Should freeze-dried samples always be stored in rigid containers to avoid > crushing? (At the moment our dried samples are stored in 'Whirlpak' bags > packed quite tightly into drawers.) As for long-term storage, use whatever method works for you. I have dried sediment in whirl-pak bags, but unless you take care to bend open the mouth of the container and also to minimize contact between the bag and the sediment you may find that it takes much longer to dry the sediments. It also helps to cover each container (but not seal!) since fine sediment tends to fly about in the chamber. I usually take small pieces of laboratory tissue and stretch this across the top of each vial, using a rubber band to hold it in place. > Any other points, comments or implications for other types of analysis > gratefully received. When freezing your sediment in vials, try to avoid trapping air pockets since these may force your sediment plug completely out of the vial when you apply a vacuum. If I see these in my sediments I use a spatula or something to make an escape hole for the air. If your sediments tend to do this you can also put them in a much larger container. -- _/ _/_/_/ _/_/ Brian J. Haskell Telephone: _/ _/ _/ _/ _/ Limnological Research Center (612) 624-7005 _/ _/_/_/ _/ University of Minnesota _/ _/ _/ _/ _/ 310 Pillsbury Drive. S.E. Fax: _/_/_/ _/ _/ _/_/ Minneapolis, MN 55455-0219 (612) 625-3819 From bdbeierl@acs.ucalgary.caWed Aug 14 12:07:09 1996 Date: Fri, 31 May 1996 10:03:04 -0500 From: bdbeierl To: Multiple recipients of list PALEOLIM Subject: Freeze drying... With regard to the question of freeze drying lake sediments, I have noticed several differences between oven drying and freeze drying. I have been freeze-drying sediments for stable isotope analysis, in an effort to minimize fractionation caused by heating. 1. As someone else mentioned, if there are air pockets in the seds, placing them under vacuum can cause the samples to jump out of whatever you have them in. I presume this could also apply to any sort of macrofossil with a sealed airspace. I don't know if pollen or diatoms fit this category. 2. I have noticed that in a few cases, the sediments have come out sticky. I think this is some sort of organic resin. It gives the sediment the consistency of those little squishy foam earplugs and it can be hard to work with. 3. The freeze dryer I have been using does not actually freeze the sediments, it just places them under vacuum so things will evaporate more quickly. The 'moistened' air is drawn through a chamber at something like -60 C to freeze out the water, but the seds themselves should not be subject to frost-jacking type damage. Brandon Beierle Dept. of Geography, The University of Calgary, Calgary, Alberta, Canada T2N 1N4 bdbeierl@acs.ucalgary.ca