14,000-year carbon accumulation dynamics in a Siberian lake reveal catchment and lake productivity changes
Résumé
A multi-proxy paleolimnological analysis of a sediment core sequence from Lake Malaya
Chabyda in Central Yakutia (Eastern Siberia, Russia) was conducted to investigate
changes in lake processes, including lake development, sediment and organic carbon
accumulation, and changes in primary productivity, within the context of Late Pleistocene
and Holocene climate change. Age-depth modeling with 14C indicates that the maximum
age of the sediment core is ∼14 cal kBP. Three distinct sedimentary units were identified
within the sediment core. Sedimentological and biogeochemical properties in the deepest
section of the core (663–584 cm; 14.1–12.3 cal kBP) suggests a lake environment mostly
influenced by terrestrial vegetation, where organic carbon accumulation might have been
relatively low (average ∼100 g OC m−2 a−1), although much higher than the global modern
average. The middle section of the core (584–376 cm; 12.3–9.0 cal kBP) is characterized
by higher primary productivity in the lake, much higher sedimentation, and a remarkable
increase in OC delivery (average ∼300 g OC m−2 a−1). Conditions in the upper section of
the core (<376 cm; < 9.0 cal kBP) suggest high primary productivity in the lake and high
OC accumulation rates (average ∼200 g OC m−2 a−1), with stable environmental
conditions. The transition from organic-poor and mostly terrestrial vegetation inputs
(TOC/TNatomic ratios ∼20) to conditions dominated by aquatic primary productivity
(TOC/TNatomic ratios <15) occurs at around 12.3 cal kBP. This resulted in an increase
in the sedimentation rate of OC within the lake, illustrated by higher sedimentation rates
and very high total OC concentrations (>30%) measured in the upper section of the core.
Compact lake morphology and high sedimentation rates likely resulted in this lake acting as
a significant OC sink since the Pleistocene-Holocene transition. Sediment accumulation
rates declined after ∼8 cal k BP, however total OC concentrations were still notably high.
TOC/TNatomic and isotopic data (δ13C) confirm the transition from terrestrial-influenced to
aquatic-dominated conditions during the Early Holocene. Since the mid-Holocene, there
was likely higher photosynthetic uptake of CO2 by algae, as suggested by heavier
(isotopically enriched) δ13C values (>−25‰).
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