Publication Date:
2019-07-17
Description:
The Mg/ Ca ratio of Foraminifera calcium carbonate
tests is used as proxy for seawater temperature
and widely applied to reconstruct global paleo-climatic
changes. However, the mechanisms involved in the carbonate
biomineralization process are poorly understood. The
current paradigm holds that calcium ions for the test are
supplied primarily by endocytosis of seawater. Here, we
combine confocal-laser scanning-microscopy observations
of a membrane-impermeable fluorescent marker in the extant
benthic species Ammonia aomoriensis with dynamic 44Calabeling
and NanoSIMS isotopic imaging of its test. We infer
that Ca for the test in A. aomoriensis is supplied primarily
via trans-membrane transport, but that a small component
of passively transported (e.g., by endocytosis) seawater
to the site of calcification plays a key role in defining the
trace-element composition of the test. Our model accounts
for the full range of Mg/ Ca and Sr / Ca observed for benthic
Foraminifera tests and predicts the effect of changing seawater
Mg/ Ca ratio. This places foram-based paleoclimatology
into a strong conceptual framework.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
isiRev
Format:
application/pdf
