A new study about ocean circulation in the Pacific Ocean region concludes that currents in the Pacific and Indian oceans may be altered by climate change.

New research shows that ozone depletion and greater levels of atmospheric CO₂ has caused changes in wind patterns, intensifying high-latitude westward winds and weakening mid-latitude trade winds. Changes in wind patterns and currents may have contributed to more severe monsoons and droughts in Southeast Asia, particularly in Indonesia.

Climate change has caused ocean temperatures along the path of subtropical western boundary currents to increase two to three times greater than the global average, contributing to shifts in wind and currents in the region.

Janet Sprintall, a physical oceanographer at Scripps Institution of Oceanography, UC San Diego, and her co-authors compiled and analyzed existing data on the structure and variability of the Pacific western boundary currents (WBCs) in Southeast Asia to understand how climate change could potentially alter these currents and to see how the different flows are interconnected.

The study, “Pacific Western Boundary Currents and their Roles in Climate” appeared in the June 18 issue of Nature. Sprintall was part of a team led by Dunxin Hu of the Institute of Oceanology at the Chinese Academy of Sciences.

The research area has a unique convergence of the Mindanao Current directly north of the equator and the New Guinea Coastal Undercurrent directly south of the equator.  These two currents are part of the Pacific Western Boundary Current system, and are the main source of heat and moisture to Southeast Asia.  These currents move water from the Pacific Ocean, through a series of straits around the Indonesian islands, to the Indian Ocean.

This Pacific Western Boundary Current system is characterized by two equator-ward currents that move water through subtropical-to-tropical pathways. The movement and timing of these currents are important to the climate of the region, as the area can experience extreme monsoons or droughts during an El Niño or El Niña.

Sprintall’s previous research on Indonesian Throughflow, a series of straits that pass through Indonesian islands only focused on the currents during El Niño and La Niña conditions.  The Indonesian Throughflow connects the Pacific Ocean to the Indian Ocean in the equatorial region.

“This is the first study that looks at the physical structure and dynamics of these currents in the Pacific Ocean with such a broad scope. It also considers the impact of Pacific western boundary currents on the Indonesian Throughflow, especially as it relates to climate change,” said Sprintall.

The data show that there is a strong correlation between the variability of the Pacific western boundary currents and climate change.  Seawater near the equator has been getting warmer and more acidic, as a result of more CO₂ in the atmosphere. Changes in wind strengths coincide with increased global temperatures and has decreased the amount of water that has flowed from the Pacific Ocean to the Indonesian Seas.  Over time, this will lead to less fresh water and cooler temperatures in the Indonesian straits.

Sprintall hopes to examine the effects of water buoyancy and sea surface height on the Indonesian Throughflow in future studies in this region.

The study was funded by grants from NOAA, the National Science Foundation of China, the National Basic Research Program of China, and the Australian Climate Change Science Program.

Co-authors of this study include researchers from the Chinese Academy of Sciences, Qingdao, China; Physical Oceanography Laboratory, Ocean University of China, Qingdao, China; CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia; Australian Research Council (ARC) Centre of Excellence for Climate System Science, The University of South Wales, Sydney, Australia; Institut de Recherche por le Development (IRD), Toulouse, France; University of Hawaii at Manoa, Honolulu, Hawaii; Earth Institute at Columbia University; Palisades, New York; University of Hawaii, Honolulu, Hawaii; Japan Agency for Earth Science and Technology (JAMSTEC), Yokohama, Kanagawa, Japan; NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington. (Scripps Oceanography)