Tracing the Century‐Long Evolution of Microplastics Deposition in a Cold Seep

Abstract

Microplastic (MP) pollution is one of the greatest threats to marine ecosystems. Cold seeps are characterized by methane-rich fluid seepage fueling one of the richest ecosystems on the seafloor, and there are approximately more than 900 cold seeps globally. While the long-term evolution of MPs in cold seeps remains unclear. Here, how MPs have been deposited in the Haima cold seep since the invention of plastics is demonstrated. It is found that the burial rates of MPs in the non-seepage areas significantly increased since the massive global use of plastics in the 1930s, nevertheless, the burial rates and abundance of MPs in the methane seepage areas are much lower than the non-seepage area of the cold seep, suggesting the degradation potential of MPs in cold seeps. More MP-degrading microorganism populations and functional genes are discovered in methane seepage areas to support this discovery. It is further investigated that the upwelling fluid seepage facilitated the fragmentation and degradation behaviors of MPs. Risk assessment indicated that long-term transport and transformation of MPs in the deeper sediments can reduce the potential environmental and ecological risks. The findings illuminated the need to determine fundamental strategies for sustainable marine plastic pollution mitigation in the natural deep-sea environments.

Microplastic Contamination of a Benthic Ecosystem in a Hydrothermal Vent

“…The MP contamination results for sediments from the hydrothermal vent, which generates upwelling, are remarkable because the level of MP contamination in the hydrothermal vents is comparable to or lower than those detected in some of the most affected deep-sea locations. The level of MP contamination found was within a comparable range to the Mariana Trench (0.13 MP/g) and deep-sea abyssal plains (0.053 MP/g) at depths exceeding 4900 m. However, the levels did not exceed the contamination levels observed in sediment samples taken from polar regions, such as the Arctic (0.41–63.48 MPs/g) and Antarctic (0–9.52 MPs/g). ,, The MP contamination in our site is lower than in relatively shallower regions, such as the Mediterranean continental slope (3.8 MPs/g) and Tokyo Bay (1.85–5.39 MPs/g), and notably lower than in environments akin to the hydrothermal vent system, such as the cold seeps in the South China Sea (30–90 MPs/g). ,, These differences in MP contamination levels can be attributed to the distance from the inland and the depth. − This remoteness from land suggests that MPs may have been transported over considerable distances via air or seawater currents. MP may also be transported to the seafloor through vertical settling and easily resuspended in benthic environments. ,, The unique formation of the hydrothermal vent system, driven by the release of hot fluids from the mantle, generates an upwelling current that could reduce the shear stress on the surrounding sediment, potentially preventing the deposition of sinking MP. , While research on benthic currents remains limited, these benthic flows could influence the dispersion, sedimentation, and resuspension of MPs .…”

“…MPs have been found in various marine environments, including coastal ecosystems near inland areas, such as estuaries, beaches, tidal flats, coral reefs, sea forests, open sea regions far from land, polar regions, , open seas, deep-sea environments, − cold seeps, , trench areas, and more. No prior research has been conducted in deep-sea hydrothermal vents, which represent one of the most unique and extreme marine environments.…”

Microbial communities and mineral assemblages in sediments from various habitats at the Haima Cold Seep, South China Sea

“…In the in-situ observations, ROV1 had no characteristic species and low-rate methane bubbles, while ROV2 had significant mussels and methane bubbles. Based on the theory of the developmental stages of cold seeps (Feng et al, 2023), Stations ROV1 and ROV2 were in the early and early-mid stages of cold seep development, respectively. ROV5 was in the mid-late stage of nonseepage and was evidenced by live and dead mussels and some exposed hydrates.…”

“…After extraction of pore waters from sediments, the samples were filtered through a 0.22 µm membrane to remove sediment and then were diluted according to the detection limit of the analyzing instrument. The anions (NO 3 and SO 4 2-) were detected using ion chromatography (Thermo Fisher AQ-1200, Waltham, MA, USA) operating at 30°C (Feng et al, 2023). An AS11-HC column was used at a flow rate of 1 mL/min.…”

“…The Haima Seep is a cold seep system recently discovered in the South China Sea (SCS), which is located in the western Qiongdong Southeast Basin. This seep system is active and at the early and middle development stage (Feng et al, 2023). Submersible surveys have revealed that the Haima seep consisted of multiple unique habitats containing faunal communities and carbonate mounds (Xu et al, 2020).…”