Diatom preservation: experiments and observations on dissolution and breakage in modern and fossil material

Abstract

Selected aspects of diatom preservation in both laboratory and field environments are examined with a view to improving techniques and to help understand why only some lake sediments have good diatom preservation .Laboratory measurements of biogenic silica following diatom dissolution by alkali digestion are questioned because results are shown to be dependant on initial sample size . Diatom breakage experiments identified drying carbonate rich sediment as a major cause of fragmentation of the large robust diatom Campylodiscus clypeus Ehrenb . Diatom dissolution experiments in carbonate media indicated that carbonate rich lakes should preserve diatoms better in order of the particular alkali metal type (Ca> Mg> Na) . A preliminary assessment of the role of depth in diatom preservation is made for Lake Baikal where partly dissolved Cyclotella are more common in deep water surface sediments . The effect of time on diatom dissolution is examined in a saline lake sediment core and by comparing dissolution rates of recent and geologically old diatom samples in the laboratory . A simple link between diatom dissolution and sample age was not established . Factors thought to be important in controlling diatom preservation in lake sediments are discussed .

Sedimentary DNA versus morphology in the analysis of diatom-environment relationships

“…Reasons for qualitative and quantitative differences between the two approaches fall into two main areas: (1) the fossil recording processes (taphonomy) (Flower 1993) of DNA and diatom valves, and (2) differences in the diversity retrieved from the record. With respect to taphonomy, differences originate mainly from the number of available units of analysis in a single diatom (i.e.…”

Physical and chemical predictors of diatom dissolution in freshwater and saline lake sediments in North America and West Greenland

“…Amount of variance captured by axes 1 and 2 is shown. energy environments (e.g., nearshore shallows and wavemixed zones within lakes ;Round 1964;Flower and Nicholson 1987) may play an important role in promoting dissolution through initial breakage of valves, implying a role for water depth, wind speed, and fetch on dissolution. In this study, poor preservation in some relatively low-alkalinity and low-salinity shallow lakes (,3 m deep; e.g., Long, Madison, and Twin within the NGP and SS47 in West Greenland), may be due in part to turbulent mixing of the uppermost sediments.…”

“…Physical characteristics of lakes may also be important, especially where long-term stratification develops (meromixis; Merilä inen 1971). Water depth may play a role where surface sediments are subject to physical resuspension from wind (Flower and Nicholson 1987), and dissolution of finer taxa can occur during sedimentation over deeper water columns (Haberyan 1990;Ryves et al 2003). Water-body permanence has been shown to be important among saline lakes in Spain (Reed 1998) and experimentally (Flower 1993).…”

“…Water depth may play a role where surface sediments are subject to physical resuspension from wind (Flower and Nicholson 1987), and dissolution of finer taxa can occur during sedimentation over deeper water columns (Haberyan 1990;Ryves et al 2003). Water-body permanence has been shown to be important among saline lakes in Spain (Reed 1998) and experimentally (Flower 1993). The organic content of sediments has been invoked to explain good preservation in tropical, alkaline lakes (Hecky and Kilham 1973).…”

Vegetation changes in the Neotropical Gran Sabana (Venezuela) around the Younger Dryas chron

“…Valve concentrations per unit weight of wet sediment were estimated using plastic microspheres (Battarbee and Kneen, 1982). At least 300 valves were counted whenever possible (Flower, 1993;Battarbee et al, 2001;Abrantes et al, 2005). In poorer quality samples, counting was stopped after counting around 1000 microspheres and the results were expressed as traces.…”