Simulated upwellings is the mechanical transport of deeper, cooler, and often nutrient-rich waters to the euphotic zone, aiming to alleviate thermal stress and provide essential nutrients and clean water to marine organisms. 

See our draft paper on the incredible results that are possible with cooling less than 1ºC for less than 2 days. 

Thermal Regulation

Elevated sea temperatures disrupt the symbiotic relationship between corals and their photosynthetic endosymbionts, leading to bleaching. Natural upwelling zones, characterized by the ascent of cooler subsurface waters, often exhibit reduced bleaching incidence. For instance, regions with consistent upwelling have been observed to serve as thermal refugia, mitigating the impacts of heat stress on coral communities (Zhu et al., 2022). Simulated upwellings can replicate this cooling effect. Sawall et al. (2020) demonstrated that discrete pulses of cooler deep water, simulating upwellings, decelerated coral bleaching during thermal stress events, suggesting that this approach can effectively reduce heat-induced coral bleaching.

Nutritional Enhancement

Coral reefs typically thrive in oligotrophic conditions, relying on efficient nutrient cycling. Natural upwelling introduces nutrients such as nitrate and phosphate into surface waters, enhancing primary productivity. Johnson et al. (2020) reported that upwelling regions exhibited increased biomass of primary producers, including corals and algae, due to elevated nutrient availability. 

Disease Mitigation

Coral health is compromised by diseases, often exacerbated by thermal stress and poor water quality. Natural upwelling can dilute pathogen concentrations and enhance water quality, thereby reducing disease prevalence. By introducing cooler, cleaner waters, upwellings have the potential to lower pathogen loads and improve coral health. However, empirical studies directly linking upwellings to disease mitigation in corals are limited, necessitating further research. 

Pollution Reduction

Coastal pollution, including agricultural runoff and sewage discharge, contributes to nutrient loading and deteriorates water quality, adversely affecting coral reefs. Natural upwelling can ameliorate these effects by diluting pollutants and enhancing water exchange. Similarly, simulated upwellings could facilitate the dispersion of pollutants, thereby improving water quality and alleviating stress on coral ecosystems. 

Insights from Natural Upwelling Systems

Studies of natural upwelling systems provide valuable insights into the potential outcomes of simulated upwellings. For example, upwelling regions often support high coral cover and diversity due to favorable thermal and nutrient conditions. However, the effects of upwelling are context-dependent, with some areas experiencing increased bioerosion and algal dominance (Reymond et al., 2018). These findings underscore the importance of site-specific considerations when implementing simulated upwellings to ensure that the benefits outweigh potential drawbacks.

Ecosystem Dynamics 

The introduction of upwellings can have cascading effects on reef ecosystems. Enhanced primary productivity may support higher trophic levels, potentially increasing fish biomass and biodiversity. However, shifts in community composition could occur if certain species disproportionately benefit from altered conditions, particularly algae. There does seem to be a differential response for reefs that are under the influence of upwellings between those that also receive land-based sources of nutrients from runoff, and oceanic sources of nutrients from currents, internal waves, and upwellings. 

Strategy

Implementing simulated upwellings presents technical and ecological challenges, including the design of efficient upwelling systems, energy requirements, and potential impacts on local hydrodynamics and ecology. It is imperative to conduct pilot studies and environmental impact assessments to evaluate the feasibility and ecological ramifications before large-scale deployment. While some mechanisms are understood from the analogue of natural upwellings and a small number of lab studies, simulated upwellings require controlled field trials in reefs with different types of ecology before they can be safely implemented. Many reefs will not be suitable for simulated upwellings, either due to unfavorable bathymetry or ecological traits that render them more vulnerable to additional nutrient loads. However, it is likely the most powerful tool for mitigating bleaching in otherwise robust reefs. 

Stay tuned for a comprehensive white paper on the mechanisms of action, risks, current state of understanding, and recent engineering developments on this promising approach. 

References

• Zhu, W., et al. (2022). The impact of coastal upwelling on coral reef ecosystems under anthropogenic influence: Coral reef community and its response to environmental factors. Frontiers in Marine Science, 9, 888888. https://doi.org/10.3389/fmars.2022.888888

• Sawall, Y., et al. (2020). Discrete pulses of cooler deep water can decelerate coral bleaching during thermal stress: Implications for artificial upwelling during heat stress events. Frontiers in Marine Science, 7, 720. https://doi.org/10.3389/fmars.2020.00720

• Johnson, M. D., et al. (2020). Ecophysiology of coral reef primary producers across an upwelling gradient in the tropical central Pacific. PLOS ONE, 15(2), e0228448. https://doi.org/10.1371/journal.pone.0228448