Proxies for atmospheric circulation over the Amazon basin from the
aerosol composition in a Nevado Illimani firn core, Bolivia
Abstract
Current changes in tropical South America due to atmospheric warming,
deforestation, and glacier retreat impact moisture and water exchange
between the Amazon basin and the Andes. Thus, a deeper understanding of
past atmospheric variability is crucial for developing strategies for
climate and environmental change scenarios in this region. Within this
context, we investigated an 18-year firn core drilled at the Illimani to
interpret its aerosol composition (trace elements and major ions) in
relation to seasonal processes, particularly atmospheric circulation
over the Amazon basin. The resulting 21st-century record showed reduced
Cr contamination over the Altiplano in comparison to the late 20th
century, which was probably related to reduced emissions from mining
activities. Sulfur records suggest the influence of volcanic eruptions
in 2006 (Rabaul) and 2014 (Nyamuragira-Nyiragongo). Overall, the aerosol
composition was mainly modulated by precipitation variability over the
Altiplano at both annual and seasonal timescales. However, Mn was
enriched due to strengthened low-level jets in the Amazon basin during
the dry season, especially in 2015. This was corroborated by the
reanalysis data. Furthermore, Mn, Co, and Fe showed an unprecedented
peak in the record during the wet season of 2014, which was consistent
with the arrival of a dust plume from Africa over Amazonia. Therefore,
the Mn enrichment record can be used as a new proxy for obtaining
information about the South American Low-Level Jet, and, when considered
together with more elements, might also indicate snow layers that were
possibly loaded with aerosols from Africa.