Mercury Isotopes in Deep-Sea Epibenthic Biota Suggest Limited Hg Transfer from Photosynthetic to Chemosynthetic Food Webs

Jingjing Yuan (1) , Yi Liu (1) , Shun Chen (2) , Xiaotong Peng (2) , Yu-Feng Li (3) , Songjing Li (1) , Rui Zhang (4, 1) , Wang Zheng (5, 1) , Jiubin Chen (1) , Ruoyu Sun (1) , Lars-Eric Heimbürger-Boavida (6)

1 Institute of Surface-Earth System Science of Tianjin University
2 IDSSE - Institute of Deep-Sea Science and Engineering [Chinese Academy of Sciences] [Sanya]
3 IHEP - Institute of High Energy Physics [Beijing]
4 NUS - National University of Singapore
5 YSPH - Yale School of Public Health
6 MIO - Institut méditerranéen d'océanologie

Deep oceans receive mercury (Hg) from upper oceans, sediment diagenesis, and submarine volcanism; meanwhile, sinking particles shuttle Hg to marine sediments. Recent studies showed that Hg in the trench fauna mostly originated from monomethylmercury (MMHg) of the upper marine photosynthetic food webs. Yet, Hg sources in the deep-sea chemosynthetic food webs are still uncertain. Here, we report Hg concentrations and stable isotopic compositions of indigenous biota living at hydrothermal fields of the Indian Ocean Ridge and a cold seep of the South China Sea along with hydrothermal sulfide deposits. We find that Hg is highly enriched in hydrothermal sulfides, which correlated with varying Hg concentrations in inhabited biota. Both the hydrothermal and cold seep biota have small fractions (<10%) of Hg as MMHg and slightly positive Δ 199 Hg values. These Δ 199 Hg values are slightly higher than those in near-field sulfides but are 1 order of magnitude lower than the trench counterparts. We suggest that deep-sea chemosynthetic food webs mainly assimilate Hg from ambient seawater/sediments and hydrothermal fluids formed by percolated seawater through magmatic/mantle rocks. The MMHg transfer from photosynthetic to chemosynthetic food webs is likely limited. The contrasting Hg sources between chemosynthetic and trench food webs highlight Hg isotopes as promising tools to trace the deep-sea Hg biogeochemical cycle.

Mots clés: marine mercury cycling; oceans; hydrothermal fluids; cold seeps; biota; mercury isotopes

Domaines: Océanographie; Géochimie

Jingjing Yuan, Yi Liu, Shun Chen, Xiaotong Peng, Yu-Feng Li, et al.. Mercury Isotopes in Deep-Sea Epibenthic Biota Suggest Limited Hg Transfer from Photosynthetic to Chemosynthetic Food Webs. Environmental Science and Technology, inPress, ⟨10.1021/acs.est.3c01276⟩. ⟨hal-04068003⟩