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The hydrogen isotopic composition of lake water (δ2Hlw) contains hydrologic information and can be used as a recorder of lake water hydrology, including the extent of evaporation of the lake system. Initial studies indicate that the hydrogen isotopes of highly branched isoprenoids (δ2HHBI), synthesized by lake diatoms and preserved in lake sediments are a promising proxy for constraining past δ2Hlw values that are free from terrestrial in- fluences. However, there are many aspects of this proxy, including the seasonality of HBI production, that are unknown and need to be addressed more fully before the proxy can by widely applied. To determine when HBIs are produced throughout the year, and whether there are seasonal biases in δ2Hlw reconstructions, we deployed two sediment traps at Brown’s Lake, in northeastern Ohio. We present HBI concentrations, δ2HHBI values, HBI carbon isotopes and bulk sediment carbon isotopes from sediment traps collected monthly for 26 months to investigate seasonality of HBIs. We observed HBIs in each of the monthly sediment traps throughout the study interval with an increase in HBI concentration during September and October, suggesting that HBIs are made throughout the year with greater production during fall. We calculated the difference between δ2HHBI and δ2Hlw values (ε2HHBI/lw) and observe a range in ε2HHBI/lw values of up to 64‰, which we speculate is related to changes in the diatom communities that synthesize HBIs throughout the year and between different years. Different diatom communities may have different biosynthetic pathways or metabolisms that result in isotope effects. This study is the first that examines the seasonality of HBIs in lake sediments and provides framework for interpreting the seasonality of hydroclimate records generated from δ2HHBI values in temperate eutrophic lakes.
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This content will become publicly available on April 4, 2026
Diatom-derived highly branched isoprenoids are diverse and widespread in lakes
Diatom-derived highly branched isoprenoid lipids (HBIs) are found extensively in marine sediments, but to date are only reported in a few lacustrine sediments. To expand on prior lake studies, we collected lake surface sediment samples, water samples, and filtered photic zone water from 50 lakes from the Great Plains to the northeastern United States. Samples were collected in May and June and a few sites were revisited in September and October. Studied lakes vary in climate, water chemistry (e.g., pH, salinity, alkalinity), size, and trophic states. They also vary in their diatom species compositions with 344 diatom taxa reported. We characterized HBI assemblages in each lake and found 11 different HBI compounds including one C20:0 HBI, five C20:1 HBI isomers, C21:0 HBI, C25:2 HBI, two C25:3 HBIs, and C25:4 HBI. C20:0 HBI was present in all but two lakes and was often the most abundant HBI present. HBIs were also detected in nearly all the water filter samples indicating they are produced in the photic zone. C20:0 HBI was present in all freshwater lakes, but not present or at very low con- centration in the highest salinity lakes, which were dominated by C21:0 HBI and C25 HBIs. Many of the lakes were dominated by diatom genera and species that are not known to be HBI-producing genera, suggesting there are unrecognized HBI-producing diatom taxa. This inventory, illustrating the widespread presence and diversity of HBIs from lakes across large differences in water chemistries and climate, further suggests that HBIs may be useful diatom biomarkers for paleoclimate applications.
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- Award ID(s):
- 2039939
- PAR ID:
- 10648831
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Organic geochemistry
- Volume:
- 205
- ISSN:
- 0146-6380
- Subject(s) / Keyword(s):
- Diatoms Highly branched isoprenoids Biomarkers Lake sediments Lakes Lacustrine sediments
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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