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

An annually laminated succession in Crawford Lake, Ontario, Canada is proposed as the Global boundary Stratotype Section and Point (GSSP) for the Anthropocene as a series/epoch with a base dated at 1950 CE. Varve couplets of organic matter capped by calcite precipitated each summer in alkaline surface waters reflect environmental change at global to local scales. Spheroidal carbonaceous particles and nitrogen isotopes record an increase in fossil fuel combustion in the early 1950s, coinciding with fallout from nuclear and thermonuclear testing—239+240Pu and 14C:12C, the latter more than compensating for the effects of old carbon in this dolomitic basin. Rapid industrial expansion in the North American Great Lakes region led to enhanced leaching of terrigenous elements by acid precipitation during the Great Acceleration, and calcite precipitation was reduced, producing thin calcite laminae around the GSSP that is marked by a sharp decline in elm pollen (Dutch Elm disease). The lack of bioturbation in well-oxygenated bottom waters, supported by the absence of fossil pigments from obligately anaerobic purple sulfur bacteria, is attributed to elevated salinities and high alkalinity below the chemocline. This aerobic depositional environment, unusual in a meromictic lake, inhibits the mobilization of 239Pu, the proposed primary stratigraphic guide for the Anthropocene

Sediment accumulation rates in subarctic lakes: Insights into age-depth modeling from 22 dated lake records from the Northwest Territories, Canada

Age-depth modeling using Bayesian statistics requires well-informed prior information about the behavior of sediment accumulation. Here we present average sediment accumulation rates (represented as deposition times, DT, in yr/cm) for lakes in an Arctic setting, and we examine the variability across space (intra- and inter-lake) and time (late Holocene). The dataset includes over 100 radiocarbon dates, primarily on bulk sediment, from 22 sediment cores obtained from 18 lakes spanning the boreal to tundra ecotone gradients in subarctic Canada. There are four to twenty-five radiocarbon dates per core, depending on the length and character of the sediment records. Deposition times were calculated at 100-year intervals from age-depth models constructed using the 'classical' age-depth modeling software Clam. Lakes in boreal settings have the most rapid accumulation (mean DT 20±10 yr/cm), whereas lakes in tundra settings accumulate at moderate (mean DT 70±10 yr/cm) to very slow rates, (>100yr/cm). Many of the age-depth models demonstrate fluctuations in accumulation that coincide with lake evolution and post-glacial climate change. Ten of our sediment cores yielded sediments as old as c. 9000cal BP (BP=years before AD 1950). From between c. 9000cal BP and c. 6000cal BP, sediment accumulation was relatively rapid (DT of 20-60yr/cm). Accumulation slowed between c. 5500 and c. 4000cal BP as vegetation expanded northward in response to warming. A short period of rapid accumulation occurred near 1200cal BP at three lakes. Our research will help inform priors in Bayesian age modeling

Wavelet results for total solar irradiance (TSI), three key diatom species and the coarse silt fraction of the Danny’s Lake sediment core.

<p>High values (red color) are assigned to areas where the indicated periodicity is persistent. Low values (blue color) indicate lack of periodicities at the given wavelength and time period, and faded region is outside of the cone of influence. The black line surrounding the high values (red color) indicates 95% significance against red noise background.</p

Spectral results for total solar irradiance (TSI), three key diatom species and the coarse silt fraction in the Danny’s Lake sediment core.

<p>Red and green lines indicate confidence intervals. Spectral peaks are noted.</p

Diatom species shown in the stratigraphic diagram of the Danny’s Lake sediment core.

<p>Taxonomy was updated to reflect present-day naming conventions [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0199872#pone.0199872.ref036" target="_blank">36</a>].</p

Water property data measured at Danny’s Lake, Northwest Territories, in winter 2010 and summer 2011.

<p>A Kemmerer water sampler was used to collect lake-bottom water. Measurements were taken using a hand-held YSI multiprobe.</p

Diatom data from the Danny’s Lake sediment core, along with results of stratigraphically constrained cluster analysis (CONISS).

<p>Only diatom taxa that reached >2% relative abundance in at least one sample were plotted.</p

Sedimentological and ecological parameters for the Danny’s Lake sediment core.

<p>Sedimentological and ecological parameters for the Danny’s Lake sediment core.</p

Bayesian age-depth model for Danny’s Lake constructed using Bayesian software Bacon [32, 33].

<p>The main plot shows the age distributions of calibrated ¹⁴C dates and the grey-scale age-depth model indicates precisely dated sections of the chronology in darker grey, while lighter grey areas indicate less precise sections. The upper panel shows the stability of the Markov Chain Monte Carlo runs (1200 iterations); the prior (thick line) and posterior (thin line) distribution for the accumulation rate (yr/cm), and; the prior (thick line) and posterior (thin line) for the dependence of accumulation rate between sections.</p