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Climate-driven shifts in lake connectivity and carbon accumulation in the upper Rio Negro Basin evidenced by a multi-proxy record over the past 7000 years
Journal article   Open access   Peer reviewed

Climate-driven shifts in lake connectivity and carbon accumulation in the upper Rio Negro Basin evidenced by a multi-proxy record over the past 7000 years

Juliano F. Soares, Luciane S. Moreira, Naziano Filizola, Christian J. Sanders, Patricia Moreira-Turcq, Bruno Turcq, Nicolás M. Stríkis, Leonardo Amora-Nogueira, Keila Aniceto, Letícia E. Clemente, …
Quaternary science reviews, Vol.392, pp.1-18
15/11/2026
DOI: https://doi.org/10.1016/j.quascirev.2026.110291
Appears in  Recent Faculty of Science and Engineering Publications
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Abstract

Amazon floodplain Carbon dynamics Climate change Hydrological variability Paleoclimate reconstruction
Geochemical studies from blackwater floodplains of the upper Rio Negro remain underrepresented in Holocene hydroclimate syntheses. The sedimentary processes and carbon accumulation in these ecosystems remain a gap in the understanding of these processes in the face of the climate change context. We present here a ∼7000-year, high-resolution multiproxy record from Lake Indio from the upper Rio Negro floodplain, northwestern Amazonia, based on a Bayesian 210Pb and 14C age–depth model. Organic (TOC, TN, C/N, δ13C) and inorganic proxies (XRF elements, Fe/Mn, Al/Si, Si/Ti) resolve threshold shifts between two end-member hydrosedimentary states: (i) organic-rich R-layers, characterized by high TOC, elevated Fe/Mn, and fine grain textures, mark lake isolation, low water level, weak hydrodynamics, and bottom-water anoxia; and (ii) organic-poor P-layers, with Si and Ti peaks, mineral dilution of OM, and coarser grain size, record energetic reconnection to the main channel and clastic incursions. Against a generally drier Middle Holocene (8200–4200 cal yr BP) background, Lake Indio records punctuated high-magnitude floods with a distinctive allochthonous fingerprint characterized by δ13C enrichment toward ∼–22‰ and Ca–Na peaks. These extreme flood events could have caused episodic white-water inputs and interbasin connectivity between the Rio Solimões and Rio Negro Basins through the Japurá-Uneiuxi hydrological corridor during the Middle Holocene, consistent with the distinct geochemical signature. The Late Holocene (4200 cal yr BP – present) features a condensed organic-rich unit (R1, ∼4500–1600 cal yr BP) with reduced sedimentation, and a trend of increasing grain size, indicating the gradual return of wetter conditions. After ∼1600 cal yr BP, the water level rises, and the system resumes a seasonal connect–disconnect rhythm. The increase in sedimentation and carbon accumulation in the last century likely points to the current intensification of extreme events. Collectively, the SASM/ITCZ/ENSO interconnection forcing contributes to local deposition and carbon burial over the Negro floodplain areas. These findings provide rare blackwater evidence for extreme-flood interbasin leakage and suggest that extreme drought and flood events were frequent during the previously considered dry Middle Holocene. •Multi-proxy data clarify 7,000 years of hydrological change in the western Amazon.•Mid-Holocene hydroclimate in the Amazon Basin was highly dynamic, with extreme floods and droughts.•Alternating organic-poor (P-layers) and organic-rich (R-layers) reflect shifts between hydrological connectivity and lake isolation.•Evidence shows episodic interconnection between Rio Solimões and Rio Negro basins.•White-water incursions reached the world’s largest blackwater system during extreme floods.

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