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

Abstract

Alkenone‐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.

Group 2i Isochrysidales produce characteristic alkenones reflecting sea ice distribution

“…Group 2i may produce alkenones within multiyear sea ice, but there is no prior report of alkenones detected from the surface sediments in the central Arctic. Bloom of Group 2i has been observed upon ice-melt in Lake George, USA, followed by a bloom of non-ice lineage Isochrysidales 44 . Group 2i and other Group 2 Isochrysidales are able to form cysts in sediments and potentially re-emerge to surface water during water-overturning under increased insolation 35,36 , which could occur in blooms during ice-melt.…”

Lake Dynamics Modulate the Air Temperature Variability Recorded by Sedimentary Aquatic Biomarkers: A Holocene Case Study From Western Greenland

“…If Lake E and Braya Sø remained dominated by Group I species throughout the Holocene, it is unlikely that Lake Gus would have been more susceptible to a shift to Type II species. There is phylogenetic diversity within Group I (Richter et al., 2019), and even if the $${\mathrm{U}}_{37}^{\mathrm{K}}$$‐temperature sensitivity was the same, differences in bloom timing as have been observed among Group II species could change $${\mathrm{U}}_{37}^{\mathrm{K}}$$‐air temperature sensitivity (Theroux et al., 2020). However, given the lack of genetic evidence that alkenone producing species shifted over the course of the record or that biosynthetic $${\mathrm{U}}_{37}^{\mathrm{K}}$$‐water temperature sensitivity varies among Group I species, this remains a purely speculative explanation for the observed $${\mathrm{U}}_{37}^{\mathrm{K}}$$ variability.…”

“…For example, whether brGDGTs are produced primarily in the lake basin or in soils or where in the water column can vary in response to environmental changes (Tierney & Russell, 2009; van Bree et al., 2020; Weber et al., 2018). Similarly, alkenone‐producing haptophyte species can be sensitive to changes in salinity and lake mixing regime (Longo et al., 2018; Theroux et al., 2020). Even more, non‐stationarities resulting from proxy dynamics can be compounded by changes in the relationships between seasonal air and water temperatures (Cao et al., 2020; Dee et al., 2021), as lacustrine heat budgets are impacted by positive radiative feedbacks analogous to those operating at the Arctic‐wide scale.…”

Biomarker proxies for reconstructing Quaternary climate and environmental change

“…The accuracy and precision of the temperature proxies vary, especially at the upper and lower ends of the calibrations or close to detection limits, and not all proxies are found in all settings. Many of the proxies are calibrated to mean annual surface water temperature (Table 1), but if the producers have preferred seasons or water depths, a seasonal or subsurface temperature signal may be reconstructed (D'Andrea et al, 2005(D'Andrea et al, , 2011Jaeschke et al, 2017;Tierney and Tingley, 2018;Inglis and Tierney, 2020;Theroux et al, 2020;Spencer-Jones et al, 2021). Although marine biomarkers have global calibrations (Table 1), there can also be local controls over the biomarker-temperature relationship in all aquatic settings (e.g.…”

“…With the increasing application of (seda)DNA approaches to identify and understand the biomarker producers (e.g. Wang et al ., 2019b; Theroux et al ., 2020), more nuanced interpretations of past temperature or other environmental changes are also likely to result from reduced uncertainty estimates and through advances in our understanding of signals related to key producers and their potentially varied responses to factors including seasonality and nutrient availability. There is therefore the potential to add to the rich environmental information provided by both biomarkers and other geochemical and palaeoecological proxies, with new assessments of biogeochemical cycling, sea ice evolution and human–environment interactions, as well as new data on how that organic matter has been preserved, recycled and transported through palaeoenvironments.…”