GSA Connects 2022 meeting in Denver, Colorado

Paper No. 51-11
Presentation Time: 4:20 PM

CLIMATIC AND ENVIRONMENTAL FACTORS GOVERNING ALKENONE DISTRIBUTIONS AND UNSATURATION INDICES IN LACUSTRINE SEDIMENTS


BRASSELL, Simon, Earth and Atmospheric Sciences, Indiana University, 1001 East 10th Street, Bloomington, IN 47408

Sedimentary alkenones reflect survival of intact biosynthetic products derived from a few haptophyte species defined as three phylotypes, Groups I, II, and III, that are associated with freshwater environments, saline or alkaline settings, and marine systems, respectively [1]. Subclades of Group II haptophytes have also been proposed [2], while both the timing of divergence of phylotypes I, II, and III are poorly defined [1,2,3]. Complexities in the origins of lacustrine alkenones parallel the proliferation of reports affirming their prevalence in diverse lake environments and expanding their geographical range, predominantly in the northern hemisphere [4]. The capability of alkenone unsaturation indices to record lake temperatures has also been proven, albeit typically restricted to localized settings [5]. However, alkenone distributions can also reflect temporal changes in contributions from Group I versus Group II phylotypes associated with fluctuations in salinity [6]. They may also derive from a Group II subclade favored during warmer seasons that doesn’t produce alkatetraenones [7]. Thus, alkenone compositions in lacustrine sediments can record fluctuations in haptophyte populations associated with changes in salinity or alkalinity rather than temperature [8], which may govern stratigraphic variations in unsaturation indices for lakes experiencing climatic shifts from warm/dry to cold/wet conditions [9]. A global compilation of alkenones in lake sediments [4] reveals expansive ranges for unsaturation indices in saline/alkaline systems from arid regions, likely reflecting variations in strains of alkenone-producing haptophytes in response to hydrological changes associated with alternating wetter/drier cycles driven by climate.

[1] Theroux et al. (2010) doi:10.1002/lno.11311; [2] Wang et al. (2021) doi:10.1038/s41467-020-20187-z; [3] Richter et al. (2019) doi:10.1111/gbi.12330; [4] Brassell et al. (2022) doi:10.1016/j.orggeochem.2022.104437; [5] Toney et al. (2010) doi:10.1016/j.gca.2009.11.021; [6] Liu et al. (2008) doi:10.1016/j.gca.2007.11.016; [7] Yao et al. (2022) doi:10.1016/j.gca.2021.11.001; [8] Randlett et al. (2014) doi:10.1002/2016GC006621; [9] He et al. (2021) doi:10.1016/j.apgeochem.2021.105105