A huge amount of litter has been reported to be continuously exported into the oceans. What is the fate of the exported litter? A research team from the Biodiversity Research Center and Research Center for Environmental Changes at Academia Sinica and Institute of Fisheries Science at National Taiwan University recently published their findings on global distribution and cleanup opportunities for macro ocean litter and where the potential destination of the litter is through considering both ocean surface currents and winds using big data during 1993-2017. Their findings were based on assessments of changes in the accumulation of offshore- and coastal-source macro ocean litter, respectively, under simulations of four windage scenarios. The study was published on October 6, 2020 in Environmental Research Letters.
Simulated accumulation of macro ocean litter reasonably demonstrated its severe occurrence in all ocean areas of the world as well as considerable variability in accumulation percentage, with hundreds of 1000-fold differences between certain areas. The ocean litter became more concentrated over time, while the litter distributions shifted with increasing windage effect.
New macro ocean litter hotspots: tropics and polar area
The windage was an important factor pushing litter to the shore and landing. Simulated accumulation of offshore-source litter continuously floating offshore based on zero and low windage effects showed a latitudinal peak at 20-30°N and 20-50°S and widespread areas of low accumulated litter concentrations near the equator, whereas offshore-source litter with moderate and high windage effects were predicted to peak at tropics (10°N and 10°S) and polar area (60°S) and greatly concentrated in the Central Pacific Ocean as previously mentioned. The offshore-source litter also showed high landing possibilities at 10°N and additionally at 5°S-15°S no matter what windage effects were. The relatively even distributions of coastal-source litter accumulation along latitudes and longitudes re-emphasized this global environmental threat.
With increasing windage effect, the accumulation patterns gradually shifted its concentrated areas from the subtropics to the tropics and high latitudes in both the Northern and Southern Hemisphere; in particular, the Pacific Ocean contained the most severe accumulation areas with intensively high concentrations relative to other oceans. The Pacific litter accumulation transferred from the eastern Pacific to the western Pacific and increased to the highest cumulative percentage, and the equatorial region of the Pacific Ocean and offshore northeastern Australia were particularly predicted to be heavily covered and impacted by macro ocean litter. Furthermore, more low-density, i.e., high-windage, litter could be delivered towards or stay in the polar regions, such as the Southern Ocean and Arctic Ocean, showing that the Southern Ocean and Arctic Ocean were a source for litter with the zero and low windage effects, whereas they became a sink for the moderate-high windage litter.
Differences were observed in a comparison of the proportions of macro ocean litter accumulation among the seven major subregions of the world’s oceans. More litter in the North Pacific Ocean, the South Pacific Ocean, the North Atlantic Ocean, the South Atlantic Ocean, and the South Indian Ocean left its original oceans and then entered the North Indian Ocean and the Southern Ocean as the windage effect increased, indicating the important role of wind in transporting litter across oceans. Moreover, through the Antarctic circumpolar current in the Southern Ocean, macro ocean litter in the southern parts of the Pacific, Atlantic, and Indian Ocean was relatively likely to be brought to the other oceans, as was litter in the Southern Ocean, further indicating that the Antarctic circumpolar current plays a critical transmission medium in exchanging materials among oceans.
Overlaps of macro ocean litter accumulation and areas with high marine biodiversity and fishing activities
Larger windage had significant consequences for the specific geographic patterns of overlaps of top 25% areas of ocean services, including marine biodiversity, marine primary production and fishery. Specifically, global marine biodiversity priority areas exhibited 2.03% consistently overlapping with macro ocean litter accumulation regardless of the windage. If litter continuously increases, the entire marine ecosystem as well as economic activities would be affected.
Dr. Jeng and his team’s research article entitled “Global distribution and cleanup opportunities for macro ocean litter: a quarter century of accumulation dynamics under windage effects” is available at: https://doi.org/10.1088/1748-9326/abae29
