Joint research project

Hermatypic corals as natural archives of climate changes in the Mexican Caribbean.

Project leaders
Paolo Montagna, Joan Albert Sánchez Cabeza
MESSICO - CONACYT - Consejo Nacional de Ciencia y Tecnologia
CNR-CONACYT 2017-2018
Earth system science and environmental technologies
Thematic area
Earth system science and environmental technologies
Status of the project

Research proposal

In this project we propose to examine critical aspects of the Caribbean climate change through a multi-disciplinary research effort. Specifically the project aims at reconstructing changes in seawater temperature, pH and levels of inorganic contaminants for the last 100-150 years using the geochemical signals encoded in the aragonite skeleton of corals from the Mexican Caribbean. We intend to reconstruct the pre-industrial (natural) climate variability of the region in order to better understand the anthropogenically-driven climate change and quantify the recent modifications induced by the CO2 released by human activities.

The rapid increase of anthropogenic CO2 has two direct consequences for the global oceans: 1) sea surface temperatures (SSTs) have risen over most parts of the planet at an average of ~ 0.11 °C per decade since 1971 (Cubasch et al., 2013) and 2) pH has decreased globally by ~ 0.1 units (from ~ 8.2 to ~ 8.1) between pre-industrial time and the 1990s due to the CO2 absorption by the oceans (Kleypas and Yates, 2009), a phenomenon known as "ocean acidification" (OA) (Caldeira and Wickett, 2003).

However, warming and OA are not homogeneous in time and space and the rates differ according to the location (Falvey and Garreaud, 2009). For example, SSTs of the Caribbean Sea and the southern Gulf of Mexico have increased significantly over the past 30 years at a rate of ~ 0.27 °C per decade (Chollett et al., 2012; Lluch-Cota et al., 2013), with the largest changes occurring over the past 15 years (Glenn et al., 2015). This temperature increase can have strong impacts on the physiology of marine organisms and, more generally, on marine ecosystem processes and services (Hoegh-Guldberg and Bruno, 2010). Moreover, warmer oceans can drive more intense tropical cyclones (Wu et al., 2010) and other changes to the hydrological cycle, with severe consequences to the society, especially for climate-sensitive regions such as the Caribbean.

The Caribbean region is also experiencing a large increase in OA compared to other world areas, as revealed by a recent model simulation using a state-of-the-art coupled carbon cycle-climate model (Friedrich et al., 2012). Similarly, to ocean warming, OA has been documented to compromise the physiology of marine organisms, mainly affecting calcifying marine species (Kroeker et al., 2013) and their ability to build their carbonate protection. Furthermore, OA can act synergistically with ocean warming and other local-scale disturbance to increase the vulnerability of the marine biota (Anthony et al., 2011).

Most of the recent warming and pH drop have been attributed to the emissions of anthropogenic CO2 (IPCC, 2013), however a full understanding of human-induced modifications requires critical information on the natural variability of the climate system on timescales longer than is possible using direct observations (e.g. satellites, shipboard sensors, floating buoys). In fact, available instrumental records are insufficient to assess decadal to centennial changes in temperature and pH, especially where variations are small and the only way to extend the observational period further back in time (i.e. pre-industrial) is by using proxy reconstructions.

The skeleton of long-lived hermatypic corals has enormous potential to provide continuous, multi-century long records of SST, pH, salinity and human-induced pollution. Therefore, if properly corrected from biologically-mediated vital effects (e.g. Montagna et al., 2014; Trotter et al., 2011), the coral geochemical tracers provide a valid means to extend environmental records well beyond that of the instrumental period.

The proposed project intends to investigate the geochemical signals of long-lived coral specimens from the Caribbean Sea (along the Mexican coast) to reconstruct acidification rates, temperature changes and records of contaminants for the past 100-150 years. In particular, cores of the species Orbicella faveolata will be collected off the coast of Puerto Morelos, Mahahual and Banco Chinchorro and analysed for trace elements and boron isotopes at annual resolution. In parallel, temperature and the inorganic carbon cycle (including pH) will be monitored in one station near Puerto Morelos during the duration of the project in order to provide real data to compare and calibrate the coral record.

This study will enable to obtain, for the first time, multi-decadal records of key environmental parameters improving current understanding of the natural climate variability of the Caribbean region, thereby helping to more accurately interpret the observational record and predict future climate change. In particular, it will provide a rare opportunity to put recent anthropogenically-driven trends in seawater warming and decreasing pH into the context of the natural variability in the Caribbean Sea.

It is anticipated that results of this project will be of interest to a wide range of scientific fields including paleoclimatology, paleoceanography, geochemistry, physical and chemical oceanography and climate modelling. Results of the project will be disseminated through national and international conferences, public talks and peer-reviewed scientific journals and conspicuous energies will be invested in educational activities (e.g. a PhD student from Mexico will be involved in the project and climate and coral-related small workshops will be organized in Italy and Mexico for students and young researchers).

The proposed project is highly multi-disciplinary and will gather biologists, bio-sedimentologists, petrographers, geochemists and paleoceanographers, thus covering a wide range of expertise to reach its scientific goals. Overall, this project will significantly expand and cement links between laboratories in Italy and Mexico and will provide an opportunity to establish an international team working on the Mexican Caribbean corals for paleoclimate reconstructions.

Research goals

The main goal of the proposed research is to generate annually-resolved proxy-based records of past changes in the hydrography of the Caribbean region, with a specific focus on the Mexican Caribbean.

In particular, we identify the following specific objectives:

1) Evaluate the rate of calcification of the coral O. faveolata, a common species occurring in the Caribbean region, and constraint its age through sclerochronology and U/Th dating.

2) Investigate the geochemical composition of its carbonate skeleton to identify species-specific physiological effects that can potentially complicate paleoceanographic reconstructions. "vital effects" will be corrected for using appropriate calibration equations (see Montagna et al., 2014).

3) Determine the long-term trends in SST, pH and metal concentration in the Mexican Caribbean using a unique combination of geochemical proxies (Sr/Ca, Li/Mg, B isotopes and trace elements) applied to precisely dated coral cores.

4) Compare the reconstructed proxies with instrumental records of temperature, the inorganic carbon cycle (including pH) and other ancillary magnitudes in one monitoring station.

5) Evaluate the dominant patterns and climate mechanisms producing the reconstructed multi-decadal variability in the Caribbean region (e.g. correlation between SST and Atlantic Multidecadal Oscillation).

6) Educate students in climate science and proxy reconstructions, and disseminate results to the scientific community and broader public.

Last update: 27/11/2021