Calcification response of planktic foraminifera to environmental change in the western Mediterranean Sea during the industrial era
Authors: Béjard Thibauld M. , Rigual-Hernández Andrés S. , Flores José A. , Tarruella Javier P. , Durrieu de Madron Xavier , Cacho Isabel , Haghipour Neghar , Hunter Aidan , Sierro Francisco J. 
Published: April 2023

Abstract. The Mediterranean Sea sustains a rich and fragile ecosystem currently
threatened by multiple anthropogenic impacts that include, among others,
warming, pollution, and changes in seawater carbonate speciation associated
to increasing uptake of atmospheric CO2. This environmental change
represents a major risk for marine calcifiers such as planktonic
foraminifera, key components of pelagic Mediterranean ecosystems and major
exporters of calcium carbonate to the sea floor, thereby playing a major
role in the marine carbon cycle. In this study, we investigate the response
of planktic foraminifera calcification in the northwestern Mediterranean Sea
on different timescales across the industrial era. This study is based on
data from a 12-year-long sediment trap record retrieved in the in the Gulf
of Lions and seabed sediment samples from the Gulf of Lions and the
promontory of Menorca. Three different planktic foraminifera species were
selected based on their different ecology and abundance: Globigerina bulloides, Neogloboquadrina incompta, and
Globorotalia truncatulinoides. A total of 273 samples were weighted in both sediment trap and seabed
samples. The results of our study suggest substantial different seasonal
calcification patterns across species: G. bulloides shows a slight calcification
increase during the high productivity period, while both N. incompta and G. truncatulinoides display a
higher calcification during the low productivity period. The comparison of
these patterns with environmental parameters indicate that controls on
seasonal calcification are species-specific. Interannual analysis suggests
that both G. bulloides and N. incompta did not significantly reduce their calcification between
1994 and 2005, while G. truncatulinoides exhibited a constant and pronounced increase in its
calcification that translated in an increase of 20 % of its shell weight.
The comparison of these patterns with environmental data reveals that
optimum growth conditions affect positively and negatively G. bulloides and
G. truncatulinoides calcification, respectively. Sea surface temperatures (SSTs) have a positive
influence on N. incompta and G. truncatulinoides calcification, while carbonate system parameters appear
to affect positively the calcification of three species in the Gulf of Lions
throughout the 12-year time series. Finally, comparison between sediment trap data and seabed sediments allowed
us to assess the changes of planktic foraminifera calcification during the
late Holocene, including the pre-industrial era. Several lines of evidence
indicate that selective dissolution did not bias the results in any of our
data sets. Our results showed a weight reduction between pre-industrial and
post-industrial Holocene and recent data, with G. truncatulinoides experiencing the largest
weight loss (32 %–40 %) followed by G. bulloides (18 %–24 %) and N. incompta (9 %–18 %). Overall, our
results provide evidence of a decrease in planktic foraminifera
calcification in the western Mediterranean, most likely associated with
ongoing ocean acidification and regional SST trends, a feature consistent
with previous observations in other settings of the world's oceans.