NASA Interdisciplinary Science project: Physical and biological processes maintaining a unique floating ecosystem of the North Pacific garbage patch

Nikolai Maximenko (IPRC/SOEST, University of Hawaii, United States)

CoAuthors

Luca Centurioni (Scripps Institution of Oceanography, University of California San Diego, United States); Andrey Shcherbina (Applied Physics Laboratory, University of Washington, United States); Gregory Ruiz (Smithsonian Environmental Research Center, United States); Linsey Haram (Smithsonian Environmental Research Center, United States); Mary Crowley (Ocean Voyages Institute, United States); Jan Hafner (IPRC/SOEST, University of Hawaii, United States); Cathryn C Murray (Fisheries and Oceans, Canada); James Carlton (Williams College, United States); Cynthia Wright (Fisheries and Oceans, Canada); Verena Hormann (Scripps Institution of Oceanography, University of California San Diego, United States)

Event: 2020 Ocean Surface Topography Science Team Meeting (virtual)

Session: Salient results from the 2017-2020 OSTST PIs

Presentation type: Type Forum

This project is co-sponsored by NASA Physical Oceanography, Biodiversity, and Ecological Forecasting as a part of the “Life in Moving Ocean” initiative.

Anthropogenic marine debris is increasingly present in all parts of the World Ocean and poses threats to maritime safety and health of the ecosystem. Carried by currents, waves, and wind, many types of floating debris aggregate in the subtropical oceans, in areas called "garbage patches” where debris can be trapped for many years.

Reports of marine debris, generated in 2011 by the tsunami in East Japan, documented large numbers of items with identifiable origin arriving on North American and Hawaiian shores. When the tsunami debris came ashore, many items were still fouled with the biota characteristic of coastal Japan, as hundreds of coastal species were able to survive the trans-Pacific journey, including some known invasive species.

As a fraction of the tsunami debris was expected to end up in the “North Pacific Garbage Patch”, questions arose on (i) how the ocean-atmosphere dynamics sort different types of floating objects and how they are carried and kept in the patch; and (ii) how long coastal species can survive in the nutrient-poor pelagic ocean and if marine debris helps coastal species to establish and reproduce in the garbage patch.

These questions were addressed in our “FloatEco” (Floating Ecosystem) project by (i) designing and deploying drifting buoys having different geometry and different exposure to the wind; (ii) using a mixed-layer float (“EcoFloat”) to study effects of vertical excursions of weakly buoyant objects on horizontal transport by vertically sheared currents; (iii) analyzing trajectories of satellite trackers attached to large debris items; (iv) designing settlement panels for the open ocean and deploying them on drifters and marine debris; and (v) collection of biological samples from and visual/photo/video reports of macro debris.

The large datasets collected during multiple expeditions in 2018-2020 are under thorough analyses. Preliminary results support the following conclusions:

1. The central part of the garbage patch is highly turbulent. While surface currents averaged over multi-year periods demonstrate robust convergence toward the patch, instantaneous currents are dominated by eddies and winter winds are governed by passing storms. Additionally, the center of the patch significantly shifts between different years and its shape changes facilitating episodic escapes from the patch toward North America, Hawaii or the western Pacific. These stochastic processes reduce the sensitivity of residence time to debris parameters and explain the complex composition of debris items reported from the garbage patch.

2. Close-range interactions between debris items are much more frequent than was expected in the conceptual framework of multi-scale ocean currents. Such interactions are not only due to the observed ubiquity of convergent submesoscale eddies and small-scale features (or slicks) but also to the relative movement induced by different responses of various objects to the same ocean-wind conditions. Such frequent interactions may effectively enhance exchanges between biological communities colonizing individual debris items and increase their resilience to challenging environmental conditions.

3. Large numbers of coastal species have been identified in biological samples. Reproductive condition and size distribution of many individuals demonstrate that these species have established and are reproducing in the garbage patch.

The extensive field studies in the FloatEco project were possible thanks to collaborations with numerous organizations, volunteers, and citizen scientists. Feedback from these partners, combined with the results of the data analyses, helped to validate and improve numerical models of marine debris transport for future applications.
 
Nikolai Maximenko
IPRC/SOEST, University of Hawaii
United States
maximenk@hawaii.edu