Coral reefs are one of the most diverse ecos♥α♣ystems in the world, and thousands♣§ of species depend on fragile reefs for their su♣ ↔rvival. How do scientists learn climate f™≥π↔rom these beautiful and impσ'≈ortant underwater ecosystem↔¶s? Many coral reefs haveα∑ existed for millions of year₹™ δs, but they are extremely sensitive to changes i¶λ∑÷n climate change. Corals are €Ω& affected by ocean warming (some®®₽∏times whitening when temperatures rise or fall)β₹, pollution and runoff, and changes &δ♠₩in seawater pH, which tend to reduce ocean acid¥α♠εification as more carbon dioxide enters the o'↑ ←cean.
As corals grow, they form skeletons by prod¶✘σσucing calcium carbonate from seaw¥πater. The density of these>∑ £ calcium carbonate skeletons changes with c≥★λ₽hanges in water temperature, light $→and nutrient conditi<εons, making coral skeletons th& at form in summer at different densit↑®♠®ies than those that form in winter. These season∑∞≠♣al density changes create tree-like ringsαβ. Scientists can study these growth rings and 'γother characteristics to determΩ∏ine climatic conditions du •∑×ring the coral growing season. These growth zonφ♥×γes also allow scientists to pinpoint co₽♣"φral samples to year and season.
To gather data and information about ✘δ≤coral growth zones, scientist☆ β÷s bring their submersiblesλ≤γ and dive in the reef. Once i∞♦©∑n place, they use a hollow, diamond-encrusted dri ♥ ll to collect small samples of coral€↔≥ without harming the animals. $ Sometimes the bandinΩ↔≤αg patterns in these samplesδ♥♣ are apparent only by vi® sual inspection, but scientists usu✔£&ally use x-ray imaging software t€↕o see the patterns. The scienti₹λ↕sts then label the differ± ♥ent layers by year and season, and extra∏Ωct samples from the layers for precise che∞<mical analysis.
For example, analyzing the©¶↕ composition of trapped oxygen a✔$→÷toms is used to estimate seasonal t§¶Ω←emperature and rainfa Ω↕✔ll and build a record of how≤₩→ it changes over time. Times of en♦$→♠vironmental stress, including disease outbreaks o→♦r bleaching - can also be identified withi₽®↑≈n the strips when coral ±α✘animals expel the symbiotic algae that inhabit ÷σ them and give them their color. These mark󀕙ers help scientists identify exσβtreme climatic conditions that are£ detrimental to coral re♥'>efs.
By using corals to determi ε↔ne the past climate of tr↕γ←₽opical oceans, scientists can also ₽ $predict future trends in the climaσ→te system
Information about tropic★<al ocean corals can be very useful in examining ∞$☆the El Ni?o Southern Oscillation←ε¶. El Ni?o, produced by the Pacifi↔♦c Ocean, greatly affects we≤ ♠ather from Asia and Australia to North an&φ©↕d South America. By samplin←g corals in the Pacific Oceanα ↓§, scientists can identify El Ni?&®✘↑o over the past few h±→σ₹undred years and use this information to improve©←' predictions about future αevents and changes in this¶♦ natural climate pat✘®tern.