Calcification response of planktic foraminifera to environmental change in the western Mediterranean Sea during the industrial era

Abstract

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.

Planktic foraminifera assemblage composition and flux dynamics inferred from an annual sediment trap record in the Central Mediterranean Sea

“…Firstly, the Mediterranean Sea is supersaturated with respect to calcite (Álvarez et al, 2014;Millero et al, 1979) and the depth of the studied material is substantially shallower than the calcite saturation horizon (Álvarez et al, 2014). Secondly, recent work suggests that calcite experiences little to negligible changes in the water column and burial in recent sediments (Béjard et al, 2023;Pallacks et al, 2023). All this evidence suggests that dissolution played a negligible role in the preservation of planktonic foraminifera preserved in the sediment record in the study region.…”

“…Data availability. All data used in this study are presented in the Supplement and are available online at doi: 10.17632/tp4v6hm7dc.1 (Béjard et al, 2023). Supplement.…”

“…Previous work suggests that global communities of planktic foraminifera have already been affected by environmental change since the onset of industrialization (Jonkers et al, 2019). Moreover, recent work has shown that the calcification of several planktic foraminifera species has decreased during the industrial era in the northwestern Mediterranean (Béjard et al, 2023). Therefore, here we aim to assess if modern planktonic foraminifera communities dwelling in the Sicily Strait differ from their pre-industrial counterparts.…”

“…As marine calcifying organisms, they are considered particularly vulnerable to the ongoing ocean warming and acidification (Bijma et al, 2002;Fox et al, 2020). Shell calcification of several foraminifera species has been showed to decrease in response to ocean acidification, and therefore, changes in the weight of their shells are considered an indicator of the ocean acidification impact on different timescales (Béjard et al, 2023;de Moel et al, 2009;Fox et al, 2020;Kroeker et al, 2013;Moy et al, 2009;Pallacks et al, 2023). In contrast, ocean warming has been proposed to produce an opposite effect on foraminifera calcification, as some studies have documented that an increase in water temperature results in larger shells and enhanced growth rates (Lombard et al, 2011(Lombard et al, , 2009Schmidt et al, 2006).…”

Reduction in size of the calcifying phytoplankton Calcidiscus leptoporus to environmental changes between the Holocene and modern Subantarctic Southern Ocean

“…Comparison of materials collected from sediment traps (representative of the industrial era) and seafloor sediments (representative of pre-industrial times) have been used to evaluate the response of key calcifying microplankton to recent environmental change (e.g. Jonkers et al, 2019;Bejard et al, 2023). Moy et al (2009) demonstrated that modern populations of the planktonic foraminifera Globigerina bulloides are about 30-35% lighter than those from the pre-industrial era in the SAZ and attributed this change to a physiological response of G. bulloides to ongoing human-induced ocean acidification.…”