The sea surface temperature in the Fijian archipelago, located in the southwestern Pacific, has now reached its highest point in over 600 years. This conclusion is from an international research team’s analysis of a new coral record, which highlights significant warming in the western Pacific Ocean. Notably, 2022 has been marked as the hottest year in this region since 1370. The scientists utilized data from a giant coral colony known as Diploastrea heliopora in Fiji. These long-lived corals keep track of long-term changes in the climate and environment through their chemical makeup, which shapes the reef and the corals themselves over centuries. They serve as crucial records of historical climate variations in tropical areas and often connect to human experiences of past climate changes.
The research team extracted a core measuring over 2 meters from this coral colony, which grows only about 3 to 6 millimeters yearly. They analyzed the chemical structure of the skeleton to determine temperature shifts over 627 years, complemented by 26 years of data from water temperature measurements. The southwestern Pacific plays a key role in climate variability, influencing phenomena like the El Niño-Southern Oscillation—a crucial factor in global climate, impacting both human activities and natural ecosystems worldwide.
Corals — living temperature gauges
The study was led by researchers from the Universidad Nacional Autónoma de México and the University of Leicester in the UK. They have created the most extensive continuous record of Strontium/Calcium ratio in corals for tracking sea surface temperatures, revealing important long-term climate variations in the Pacific. Collaborators from Johannes Gutenberg University Mainz (JGU) aided in developing an annually resolved timeline of the coral record. “We employed the uranium-thorium dating method to ascertain the age of each layer. This allowed us to verify and confirm the counting of individual annual layers, leading to precise dating of the coral,” explained Professor Denis Scholz, head of the Isotope-geochemical Palaeoclimatology/Speleothem Research group at the JGU Institute of Geosciences.
Given their capability to live for centuries or even millennia, corals act as natural temperature sensors, consistently recording the chemical makeup of their surrounding ocean in their skeletons. They change the ratio of Strontium to Calcium in their skeletal makeup, where lower ratios indicate higher temperatures. This research reveals that current sea surface temperatures in the Fijian archipelago are surpassing those of the last 653 years. Continuous warming patterns in the western and central Pacific may pose threats to Pacific Island ecosystems and communities. Furthermore, the research brings to light the relationship between ocean temperature shifts across the tropical and subtropical Pacific over six centuries, showing that the warming trend of the late 20th century has become more synchronized between regions that typically conflict, which is crucial for the shifting rainfall patterns observed in recent centuries. Considering current climate models, scientists anticipate increased drought and heavy rainfall in specific Pacific regions as the 21st century progresses. Without intervention, these changes could have harmful effects on the local populations of vulnerable Pacific islands and their ecosystems.
International collaboration across three continents
This research involved collaborative efforts among the Universidad Nacional Autónoma de México, Universidad Autónoma de Baja California, the University of Leicester, the University of New South Wales, Monash University, Université de Bordeaux, the Helmholtz-Zentrum Hereon, and Johannes Gutenberg University Mainz.
