SEASONALITY OF HYDROGEN ISOTOPES AND CONCENTRATIONS OF HIGHLY BRANCHED ISOPRENOIDS (HBIS) PRODUCED BY LAKE DIATOMS

The hydrogen isotopic composition of lake water (δ²H_lw) contains hydrologic information, and when combined with other proxies that record the δ²H of precipitation, lake water hydrology and extent of evaporation can be determined. Initial studies indicate that highly branched isoprenoids (HBIs), synthesized by lake diatoms and preserved in lake sediments, are a promising proxy for δ²H_lw. However, there are several aspects of this proxy, such as the seasonality of HBI production, that are poorly understood and need to be constrained before reconstructions of δ²H_lw using the δ²H of HBIs (δ²H_HBI) are possible. The season when HBIs are produced may bias δ²H_HBI records depending on the extent that δ²H_lw changes throughout the year due to precipitation δ²H, evaporation, ground water contribution and the amount of precipitation falling into the lake and surrounding catchment. The timing of when HBIs are produced is difficult to determine from sediment archives because HBIs found in lake sediments reflect the time and flux integrated accumulation of HBIs. We deployed two sediment traps at Brown’s Lake, in northeastern Ohio, to determine when HBIs are produced and whether δ²H changes throughout the year. We present HBI concentration and δ²H from the sediment traps collected monthly for the past 12+ months. In addition, we plan to determine the diatom groups that are producing HBIs throughout the year. This record of HBI concentration and δ²H throughout the year will highlight if there should be any seasonal adjustments when interpreting hydroclimate records using HBIs.