Publication Date:
2020-03-29
Description:
Most palaeo-deep-water reconstructions are based on geochemical information stored in the calcareous shells of
Cibicidoides species but hardly anything is known about their life cycle, population dynamics or ecology. The
number of specimens of a single Cibicidoides species can locally be very limited and species may be lacking
completely during certain intervals in the geological past. As a consequence, geochemical analyses are often
carried out on lumped Cibicidoides spp. assuming that they share the same epizoic to epifaunal habitat and
precipitated their shell in comparable offsets to surrounding bottom water mass properties. However, there is a
growing body of evidence that particularly Cibicidoides pachyderma and its morphotypes C. mundulus and C.
kullenbergi, may not be reliable bottom water recorders.
We have recently developed aquaria that allowed, for the first time, observations of Cibicidoides pachyderma
var. C. mundulus under in situ pressure and temperature. Experiments were carried out with and without artificial
sediments to simulate soft sediments and rocks, respectively. Seawater was set to pH 8 and pH 7.4 to simulate
more or less particulate carbon export or more or less ventilation of bottom water. Our experiments demonstrate
that C. mundulus may opt for an epifaunal or an infaunal habitat depending on elapsed time following physical
disturbance, pH, current activity, the availability of sediments and growth. The specimen's initial response
following transfer from atmospheric pressure into the high-pressure aquaria was to immerse into the sediment or
to cover more or less parts of the test with aggregated sediments or algae. However, within 24 h a strong
rheotaxis became apparent and most specimens moved to sites of increased current activity under normal pH
conditions (pH 8). Only few specimens remained in algae cysts or in the sediment in the pH-8 experiment. On the
contrary, all specimens under pH 7.4 agglutinated a firm sediment cyst around their test and remained infaunal
throughout the experimental period of three months.
Independent of pH, growth was only observed in specimens that lived within an agglutinated cyst or infaunal.
A solid thick cyst covered the specimens of the pH 7.4 experiment throughout the experiment and possibly
restricted water exchange between the in-cyst water and the surrounding artificial bottom water mass. We
suggest that a more fragile and possibly more porous sedimentary envelope may, at least temporally, have
covered the infaunal specimens under pH 8 but no evidence for this was found upon termination of the experiment.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
peerRev
Format:
application/pdf