CICTERRA   20351
CENTRO DE INVESTIGACIONES EN CIENCIAS DE LA TIERRA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Tracking recurring drought/wet intervals and human impact over subtropical South America since the end of the Little Ice Age using Hg content in sediments
Autor/es:
D. ARIZTEGUI; S. GUEDRON; L. COIANIZ; E. PIOVANO
Lugar:
Foz de Iguazú
Reunión:
Congreso; AGU-The meeting of the Americas; 2010
Institución organizadora:
AGU
Resumen:
ABSTRACT BODY: Recent investigations have shown that variations of Hg content in lacustrine sediments
can reflect natural- and anthropogenically-induced changes in the lake catchment. Various natural
processes, including volcanic eruptions, atmospheric escapes from the ocean and rock weathering can
release Hg into water bodies, soils and the atmosphere. More recently, Hg atmospheric emissions have
substantially increased as a result of industrialization and ore mining (i.e., gold and silver). Additional
sources such as forest burning remains important anthropogenic causes for atmospheric Hg emissions. Due
to its long residence time in the atmosphere (i.e., at least one year), atmospheric Hg deposition can be
recorded worldwide even in remote areas. Once deposited, Hg is incorporated into the biosphere (trapped
into organic matter) and, thus, measurable Hg content in lake sediments can also be attributed to
vegetation, forest fires and soils erosion.
Laguna Mar Chiquita, a saline terminal lake located in the central north Pampean plains of Argentina,
contains a sedimentary record of lake level fluctuations. These historically documented and instrumentally
recorded shifts have been induced by substantial changes in rainfall affecting the watershed of this
subtropical region during the last two centuries. Lake level changes have resulted in large variations in both
surface and volume of the basin. The latter has dramatically affected mineral precipitation, sediment
distribution, and primary productivity as well as associated biological processes. These most recent lake level variations are also shown by substantial changes in the Hg content of the bulk sediment in concert
with changes in the nature and type of the sedimentary organic matter. Laguna Mar Chiquita sediments
show a clear increase in Hg content that correlates well with increasing percentages of organic matter
coinciding with lake level highstands. Conversely, they both display an antiphase behavior with carbonate
content highlighting the affinity of Hg with the sulfur associated with the sedimentary organic fraction. The
Laguna Mar Chiquita excellent chronological model allows us identifying human-induced changes such as
World War II and enhanced industrial activity during the second half of the 20th century. These
anthropogenic changes, however, do not mask the natural trend resulting from changes in the E/P ratio.
Ongoing analyses will apply this combined biogeochemical approach to older sediments aiming to
reconstruct - and eventually disentangle - the history of natural and anthropogenically-induced
environmental changes throughout the Holocene.