Why are parts of the Pacific bluer and greener? The latest research says it may be caused by the increased concentration of microplastics

China News Service, Beijing, November 8 (Reporter Sun Zifa) A newly published environmental research paper in the professional academic journal "Communications-Earth and Environment" owned by Springer Nature stated that researchers analyzed satellite monitoring data and found that between 2002 and 2022, the color of parts of the Pacific Ocean in the Pacific Garbage Patch seems to have changed, with some areas becoming significantly bluer and greener. The reason may be due to the increased concentration of microplastics in seawater.

Map of color changes in the Pacific Garbage Patch calculated from three evaluated satellite data sets (image from the paper). Photo courtesy Springer Nature

According to the paper, marine pollution caused by microplastic particles less than 300 microns in diameter is difficult to directly measure because existing methods are labor-intensive and cannot be applied on a large scale. However, laboratory experiments have shown that microplastics of this size have specific optical properties that may allow their concentration in seawater to be measured remotely. The Pacific Garbage Patch is a good place to test this approach because in situ measurements in 2016 showed that levels of larger microplastic particles in near-surface waters in the area may exceed 17 milligrams per cubic meter.

In this study, Shea Cheatham, the first author and corresponding author of the paper and the University of Bergen in Norway, collaborated with colleagues to analyze three satellite ocean water color data sets of the Northeast Pacific between 2002 and 2022. They found that the waters inside and around the Pacific Garbage Patch significantly brightened in the blue and green light bands, which may cause the seawater in this area to look more cyan (a mixture of blue and green) compared with the surrounding ocean. They then built models to study how microplastic concentrations affect ocean lightening across the entire visible spectrum, and whether these changes might be caused by common natural factors that cause ocean color changes.

The author of the paper found that even a very low concentration of microplastics will increase the brightness of the entire visible spectrum, with the cyan band having the largest increase. In simulations that included microplastics, cyan brightening occurred more than four times as often (13%) as in simulations that included only natural factors (3%). They also found that satellite sensors could detect this cyan brightening when microplastic concentrations reached about 5 milligrams per cubic meter of seawater.

The findings suggest that greener waters may mean rising concentrations of microplastics. However, the authors caution that there are differences in the color change estimates shown by different satellite data sets, and that natural environmental factors in other sea areas may be different. They say follow-up research will need to conduct direct measurements of microplastic concentrations and properties near the Pacific Garbage Patch to confirm this study's findings and improve future monitoring efforts. (over)