From Holocene stability to industrial acceleration: shifting patterns of carbon accumulation in North American boreal and temperate lakes

Abstract Lakes play a crucial role in the continental carbon cycle by burying large amounts of terrestrial organic matter (OM) in their sediments. Recent increases in carbon accumulation rates (CAR) have been linked to anthropogenic climate and land-use changes. However, the extent to which modern CAR exceeds naturally varying Holocene trends remains unclear because of a lack of datasets combining long-term and recent CAR records with consistent sediment properties across broad spatial scales. Here, we quantify temporal change in CAR from the pre-modern Holocene (11 000 BCE-1850 CE) to the industrial era (post-1850) across boreal and temperate lakes using a novel bulk density (%OM) model. Our model improves predictive accuracy ( R 2 = 0.96) compared to previous approaches and captures variability across a wide range of OM, ranging from 1.1% to 94%. CAR values and variance were lower across cores pre-1850 (14.8 ± 9.3 g C m −22 yr −21 ), whereas post-1850 values were on average 34.6 ± 23.4 g C m −22 yr −21 . Moreover, CAR variation from date to date within cores remained low and stable pre-1850 and tended to deviate positively from zero post-1850 (∼12% ± 18% above baseline), denoting CAR acceleration. However, nearly one-third of post-1850 layers decreased, highlighting enhanced variability in recent observations. The strongest increases occurred in northern, low-elevation lakes with low pre-1850 CAR. Overall, our results suggest that post-industrial human activities have pushed lake carbon burial beyond Holocene baselines, increasing accumulation rates and variability both within and across sediment cores. This shows that anthropogenic influence has reshaped carbon storage in inland waters, with implications for predicting future carbon dynamics.