Coupling between offshore and inshore biogeochemical processes on the Bermuda Coral reef

Coral growth and calcium carbonate (CaCO3) formation are the foundation of coral reef ecosystems. Climate change, ocean acidification and coastal development drive changes in environmental conditions and constitute a major threat to net CaCO3 production in the future. Despite intensive research, little is known about the natural calcification variability and its controls. This includes how features such as the North Atlantic Oscillation (NAO) and mesoscale eddies impact this natural variability. Here, we present one of the longest coral reef carbonate chemistry monthly records across the Bermuda carbonate platform throughout a 9 years dataset (2007-2016). Our results provide evidence that reef seawater CO2-carbonate chemistry is strongly influenced by the main biogeochemical processes occurring on the reef: net ecosystem calcification (NEC = calcification – CaCO3 dissolution) and net ecosystem production (NEP = primary production – respiration). Four anomalously high NEC events, occurring during the summer 2010, 2011, 2012 and 2013 were observed throughout the study. Three of those events (2010, 2011 and 2013) were linked to extensive offshore mixing and primary productivity that coincided with a negative winter NAO index. The last event (summer 2012), however, was linked to a positive phase of the NAO, suggesting a different set of drivers compared to the other anomalous events. Regardless, our observations indicate potential strong coupling between reef and offshore physical and biogeochemical processes. Finally, our results revealed that mesoscale eddies passing by the Bermuda coral reef resulted in an anomaly in both reef sea surface height and temperature. However, further analysis is required to conclude about the effect of eddies on the reef seawater biogeochemistry.