Recent studies have revealed that areas of rich biodiversity in the deep sea are also likely to be microplastic hotspots. With microplastics permeating the global seafloor, the processes controlling their dispersal and concentration remain largely undeciphered. This article explores the spatial distribution of these microplastics, their settling positions, and their impact on the unique ecosystems of the deep sea.
Just as our planetary surface hosts biodiversity hotspots like rainforests and alpine tundras, so too does the underwater world. Marine landforms such as coral reefs and sea mounts foster rich diversity beneath the waves. Unfortunately, these same areas appear to be facing an influx of microplastic pollution.
Understanding Microplastics
Microplastics, pieces of plastic smaller than five millimeters, come in different forms. Microbeads used in cosmetics and personal care products, industrial scrubbers for aggressive cleaning, microfibers from textiles, and virgin resin pellets from plastic manufacturing—all constitute this category.
While some arise from specific uses, most microplastics originate from larger plastic pieces, which break down due to sun exposure or physical wear. These tiny particles harm aquatic life, blocking digestive tracts, altering feeding behavior, and stunting growth and reproductive abilities in marine animals.
The Deep Sea Environment
The deep sea layer, situated below the thermocline and above the seabed, extends beyond 1000 fathoms (approximately 1.8 kilometers). A thermocline is a layer within large bodies of water where temperature changes more dramatically than in surrounding layers. The deep sea is relatively calm compared to the mixed upper layer above the thermocline.
Key Findings: Role of Thermohaline Circulations
Researchers have found that thermohaline circulations, ocean currents driven by water temperature and salinity differences, can control microplastic distribution. These currents create accumulation hotspots.
Surface currents, driven by winds, constitute about 10% of all ocean water and account for the upper 400 meters. However, deep ocean currents, accounting for the remaining 90%, are driven by the thermohaline process.
In polar regions, sea ice formation leaves behind dense, salty seawater, which sinks and pulls in replacement surface water—initiating deep-ocean currents that drive the global conveyor belt.
Impact on Deep-sea Benthos
Thermohaline currents supply oxygen and nutrients to deep-sea benthos, organisms living near or on the seabed. Consequently, these areas rich in deep-sea biodiversity are also likely to become microplastic hotspots, further threatening these critical ecosystems.
Recommended Actions
Addressing this issue requires prioritizing the reduction of single-use plastic sources, such as multi-layer packaging, bread bags, food wrap, and protective packaging.
Policymakers should consider economic incentives like tax rebates, research and development funds, and public-private partnerships to encourage recycling efforts and utilization of waste as a resource. In addition, promoting the use of biodegradable or even edible plastics, made from materials like sugarcane residue (bagasse), corn starch, and grain flour, offers another promising approach to combating this pressing environmental challenge.
