Successional blooms of alkenone‐producing haptophytes in Lake George, North Dakota: Implications for continental paleoclimate reconstructions

Susanna Theroux,Jaime L Toney,Robert Andersen,Linda Amaral‐Zettler,Rick Bohn,Yongsong Huang,Leslie Murphy,Jeffrey Salacup,Paul Nyren

doi:10.1002/lno.11311

Abstract

AbstractAlkenone‐derived paleotemperature reconstruction holds great promise in lake environments. However, the occurrence of multiple species of alkenone‐producing haptophyte algae in a single lake can complicate the translation of alkenone unsaturation to temperature if each species requires an individual temperature calibration. Here, we present the first systematic monitoring of two alkenone‐producing haptophytes throughout the course of a seasonal cycle in Lake George, North Dakota, using a combined approach of DNA sequencing and alkenone lipid characterization. Field sampling revealed a nonoverlapping haptophyte succession, with both an early and late season haptophyte bloom event. Culturing experiments demonstrated that the two haptophyte species responsible for these blooms had statistically similar alkenone‐temperature responses, although the culture‐based calibrations were distinct from the in situ calibration. Bloom timing of each haptophyte species corresponded to surface‐water temperatures that differed by more than 10°C, revealing that changes in bloom intensities for each species will skew the sediment‐inferred temperatures to a different stage of the growth season. These results highlight the importance of accounting for bloom timing when interpreting alkenone‐derived temperatures in sediment cores, especially in lakes that experience large seasonal fluctuations in water column temperature and salinity.

Highlights

APresent address: Southern California Coastal Water Research Project, Costa Mesa, California tri-(C37:3), and tetra-(C37:4) unsaturated alkenones are known to reflect algal growth temperatures and form the basis of the
To gain an improved understanding of the timing and provenance of haptophyte-derived alkenones, our study aims to: (1) determine the timing of blooms for the two different haptophyte species in Lake George over a seasonal cycle, (2) identify co-occurring eukaryote populations to better understand bloom triggers, and (3) compare the temperature sensitivities of the two haptophyte species using in situ water column samples and laboratory cultures
As evidenced by a shift in both alkenone and DNA signatures in the water column, the Lake George seasonal cycle consisted of two subsequent haptophyte blooms by two separate haptophyte species

Summary

Introduction

APresent address: Southern California Coastal Water Research Project, Costa Mesa, California tri-(C37:3), and tetra-(C37:4) unsaturated alkenones are known to reflect algal growth temperatures and form the basis of the. Omits the tetra-unsaturated alkenones and is widely used for interpreting marine paleoclimate records, and the recently defined. (Zheng et al 2016) omits the di-unsaturated alkenones and was developed for use in freshwater and brackish water. Alkenone production is restricted to haptophyte algae in the order Isochrysidales and alkenone-producing species have been categorized into three main groups based on phylogenetic relationships and commonly associated habitats (Theroux et al 2010; Longo et al 2016). Paleoclimate implications of succession (hereafter, Group I) have been found in fresh and oligohaline lakes (Theroux et al 2010; Simon et al 2013; Longo et al 2016), and are believed to only occupy environments with salinities lower than

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