Diatom ooze—A large marine mercury sink

Abstract

The role of algae for sequestration of atmospheric mercury in the ocean is largely unknown owing to a lack of marine sediment data. We used high-resolution cores from marine Antarctica to estimate Holocene global mercury accumulation in biogenic siliceous sediments (diatom ooze). Diatom ooze exhibits the highest mercury accumulation rates ever reported for the marine environment and provides a large sink of anthropogenic mercury, surpassing existing model estimates by as much as a factor of 7. Anthropogenic pollution of the Southern Ocean began ~150 years ago, and up to 20% of anthropogenic mercury emitted to the atmosphere may have been stored in diatom ooze. These findings reveal the crucial role of diatoms as a fast vector for mercury sequestration and diatom ooze as a large marine mercury sink.

Five hundred years of anthropogenic mercury: spatial and temporal release profiles*

“…The long timescales required for Hg to reach the deep ocean mean that anthropogenic releases lag atmospheric emissions by hundreds of years and are temporally integrated. These results are consistent with a deep marine sediment record from the Southern Ocean [65] and show an approximately two-fold overall enrichment from human activity in deep marine sediment. This contrasts with the assertion of Zaferani et al [65] that globally significant anthropogenic Hg releases were confined to the last 150 years.…”

“…These results are consistent with a deep marine sediment record from the Southern Ocean [65] and show an approximately two-fold overall enrichment from human activity in deep marine sediment. This contrasts with the assertion of Zaferani et al [65] that globally significant anthropogenic Hg releases were confined to the last 150 years. Instead, we conclude that the new emissions inventory produced in this study provides better agreement with historical archive data than earlier inventories and reinforces the significance of the last 500 years of anthropogenic Hg pollution.…”

“…Time-course of burial of Hg in estuarine and marine sediments simulated using a global biogeochemical model [7,8] and the releases of Hg to air, land, and water estimated in this study. Flux enhancement factor is defined as the ratio of the rate of Hg deposition for a given year relative to the rate of deposition at the beginning of the published sediment records (1725 for the estuarine core [54] and prior to human activity for the ocean core [65]). Panel A is based on riverine discharges of Hg to the North Atlantic Ocean and subsequent accumulation in coastal sediment.…”

Biogeochemical processes accounting for the natural mercury variations in the Southern Ocean diatom ooze sediments

“…In contrast to the well studied Hg cycling in terrestrial environments knowledge about the temporal and spatial distribution of Hg in the marine environment is limited to model estimations (Mason and Sheu, 2002;Sunderland and Mason, 2007) and water column measurements (Cossa et al, 2011;Lamborg et al, 2014). A main reason for our limited understanding of the fate of Hg in the oceans is the lack of high resolution marine sedimentary records, especially from the deep ocean (Zaferani et al, 2018).…”

“…One area in particular that highlights this uncertainty is the underestimation of the role of biological productivity in the global Hg cycle. The marine biogeochemical cycle of many elements (Morel and Price, 2003), including Hg (Lamborg et al, 2016;Zaferani et al, 2018), in seawater is controlled directly and indirectly by biological productivity. Regions of high biological productivity play an important role in the downward transport and burial of biologically essential and nonessential elements in the sediments of the deep sea (Schlesinger and Bernhardt, 2013).…”