The Importance of Ex-Situ Storage Conditions on Preserving Biomarker Signal Integrity, a Two-Year Study
Abstract
The veracity of sedimentary biomarkers as proxies in reconstructions of paleoclimates and paleoenvironment requires consideration of potential post-depositional changes in their molecular composition. Foremost in such assessments are those molecular changes that occur after sediment deposition, notably microbial alterations associated with diagenesis and maturation, but before sample collection. However, changes in molecular composition can continue after collection during sample storage (ex-situ), although how the conditions of storage affect the nature and extent of alteration is unclear. This experimental study sought to systematically examine the impact over a two-year period of specific storage conditions - light versusdark, freeze-dried versuswet sediment, room temperature versusrefrigerated, and closed versusopen container - on homogenized samples of recent sediment from the Santa Barbara Basin. Collectively, these experiments provide the opportunity to assess the effects of light, hydration, temperature, and oxygen on biomarker compositions during sample storage. Evaluation focused on key compound classes, specifically alkanes, terpanes, hopanoids, and sterenes, which all displayed some statistically significant changes in composition over the two-year experiments. The effects observed in n-alkane distributions were surprising, as they exhibited both increases and decreases in the concentrations of multiple homologs under all conditions. In addition, changes in their distributions were sufficient to alter the values of several n-alkane ratios: odd/even predominance (OEP), carbon preference index (CPI), average chain length (ACL), and terrigenous vs. aquatic ratio (T/R), which are all commonly utilized in paleo-reconstructions. Overall, a loss of longer chain length n-alkanes occurred when in wet samples stored both at room temperature and refrigeration, and in dry samples stored in open containers. Increases in shorter chain n-alkanes occurred in all conditions except refrigeration. The evidence for significant changes in compound concentrations after two years of sample storage highlights the need for a more comprehension understanding of ex situeffects and assessment of potential impacts on interpretations of biomarker proxies.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP14B..04S
- Keywords:
-
- 0419 Biomineralization;
- BIOGEOSCIENCES;
- 0454 Isotopic composition and chemistry;
- BIOGEOSCIENCES;
- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCES;
- 4994 Instruments and techniques;
- PALEOCEANOGRAPHY