New model for seasonal ikaite precipitation: Evidence from White Sea glendonitesстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 1 июня 2022 г.
Аннотация:The mineral ikaite (CaCO3⋅6H2O) and its pseudomorphs (glendonite) are considered as important paleoclimate
indicators in the geological record. Here we examine the youngest known glendonites, their host concretions, and
bivalve shells fossilized within these host concretions from the White Sea, north-western Russia. We applied
mineralogical, geochemical and isotopic methods to shed new light on the paleogeographic and geochemical
environments during ikaite precipitation and ikaite-calcite transformation. We show that White Sea glendonites
are so far the youngest known glendonites in the world (4.1 ± 0.4 cal thousand years before present). Ikaite
precipitation occurred during the cold winter months, accompanied by the formation of extensive sea ice and
presence of decaying organic matter, which resulted in a small negative Ce anomaly and negative δ13C values.
Increasing temperature led to ikaite dehydration and subsequent cementation with aragonite or amorphous
calcium carbonate, containing elevated concentrations of Ba and Sr. Needle-like cements within glendonites
display small negative Ce anomalies and precipitated from pore waters derived from seawater. The high‑magnesium
calcite forming the host concretion precipitated in the sulfate-reduction zone from pore waters derived
from seawater. The geochemistry of these pore waters was modified by interaction with clastic components of the
host sediments, resulting in δ18O values comparable to those of dissolved inorganic carbon (DIC) and almost flat
Post Archean Australian Shale (PAAS)-normalized rare earth element patterns. Therefore, we show that glendonites
can be used as a proxy for near-freezing bottom water temperatures at least seasonally during the cold
winter months. Changes in the geochemical composition of carbonate phases within the glendonites and host
concretions can be used to determine successive changes in the geochemical environment during their formation.