Siliceous algae response to the “Great Acceleration” of the mid-20th century in Crawford Lake (Ontario, Canada): A potential candidate for the Anthropocene GSSP

Abstract

Diatom and chrysophyte assemblages from varved sediments of meromictic Crawford Lake, Ontario record major environmental changes resulting from spatially broadening anthropogenic environmental stressors related to the “Great Acceleration” in the mid-20th century. Biannual assessment of diatom and chrysophyte assemblages over the last ~200 years allowed for rate of change analysis between adjacent samples that increased substantially during the mid-20th century, concurrent with significant generalized additive model trends. Changes in diatom and chrysophyte assemblages were likely driven by multiple anthropogenic stressors including local forestry harvesting, agriculture, and milling activities, acidic deposition from regional industrial processes, and anthropogenic climate warming. Novel siliceous algal assemblages now exist in Crawford Lake, likely related to the complexities of the above mentioned local and regional stressors. The major assemblage changes at the proposed base of the Anthropocene Epoch detected in this study support the laminated sequence from Crawford Lake as a strong potential candidate for the Anthropocene GSSP.

The varved succession of Crawford Lake, Milton, Ontario, Canada as a candidate Global boundary Stratotype Section and Point for the Anthropocene series

“…Constrained cluster analysis of the siliceous microfossil dataset spanning the early 19 th through early 21 st centuries identified a sharp increase in the scaled chrysophyte genus Synura relative to the otherwise dominant genus Mallomonas in the mid-20 th century ( Figure 16 ), with abundant Mallomonas acaroides var. acaroides from ~1950 CE to the top of the core section ( Gushulak et al, 2022 ; Marshall et al, 2023 ). Increases in non-planktonic diatom taxa drive a major change in diatom assemblages at ~1942 and elevated concentrations of Asterionella formosa characterize diatom assemblages since ~1980 CE ( Ekdahl et al, 2004 ; Gushulak et al, 2022 ; Figures 1 and 17 ).…”

“…Climate exerts a strong control on varve thickness (Supplemental Figure S10), so the thickest white lamina was attributed to the warmest, driest year of the “Dust Bowl” interval (1935 CE; see Supplemental Information for additional details about varve chronology and sampling) and all subsequent sampling used this baseline. Samples taken for radiocarbon analysis (Table 2) and siliceous microfossils in June 2019 (Gushulak et al, 2022) followed the chronology of Krueger (2012) that had assigned ages of 1953–1955 CE to three prominent white laminae near the center of a 2 cm-thick dark band in which the proposed base of the Anthropocene lies. Lafond et al (2022) assigned ages of 1956–1958 CE to these laminae by counting laminae above the distinctive 1935 CE varve (Figures 6 and 7 and Supplemental Figure S9).…”

“…Samples aggregating 2-3 varve years between the early 19 th and 20 th centuries from core CRA19-2FT-B1 were processed for siliceous microfossil analysis at Queen's University (Gushulak et al, 2022;Marshall, 2021) following the methodology of Battarbee et al (2001). Diatom valves and chrysophyte scales were identified and enumerated using a Leica DMRB microscope with an oil immersible Fluotar objective using DIC (differential interference contrast) at 1000× magnification; identifications were to the lowest taxonomic resolution possible using numerous guides (see Supplemental Information).…”

Anthropogenic life strategy of plants

“…A very common example of the effect of chemical substances produced by anthropogenic activities is the eutrophication of waters (Brolin and Kander, 2022; Gushulak et al, 2022; Häder et al, 2020; Wang et al, 2021). Due to the increased presence of nitrogen and phosphorus compounds, there are significant changes in the species composition of the aquatic flora (Ayele and Atlabachew, 2021; Kitsiou and Karydis, 2011; Zub et al, 2019).…”

The importance of effective moisture and landscape controls on diatom assemblages and primary production in Roche Lake, British Columbia, Canada over the past ca. 1800 years

“…This is an important finding because it highlights the pathway by which this system is likely to be most affected by future changes in climate. It is also evident that twentieth-century human activity has put Roche Lake into an ecological state that is unprecedented within the context of the past 2000 years, highlighting the additional, unique challenges associated with managing fisheries in the epoch of the Anthropocene (e.g., Gushulak et al, 2021). Indeed, the pathways by which localized human activity has affected Roche Lake differ from those of climate because modern eutrophication of this system was likely caused by a combination of lake damming, shoreline development, and timber harvesting in the watershed (Mushet et al, 2019).…”