Sources of mercury in deep-sea sediments of the Mediterranean Sea as revealed by mercury stable isotopes

Ogrinc, Nives; Hintelmann, Holger; Kotnik, Jože; Horvat, Milena; Pirrone, Nicola

doi:10.1038/s41598-019-48061-z

Cited by 39 publications

(13 citation statements)

References 54 publications

(88 reference statements)

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“…If significant fraction of IHg(II) was to be assimilated from the surrounding environments, we would expect a more scattered Hg isotope distribution due to the mixing of IHg(II) and MMHg. We would expect that the trench fauna with high IHg(II)% to have low δ 202 Hg and Δ 199 Hg, because IHg(II) in the oceans has relatively low δ 202 Hg and Δ 199 Hg, as seen from our measured seafloor sediments and previously reported open ocean particles 32 and sediments 46,47 , and coastal seawater 48,49 . (4) Insignificant differences (<0.1‰) in Hg isotope compositions are observed between the whole tissues and the separated tissues (muscle, lipid, and gut contents) of amphipods, although their Hg concentrations and speciation vary significantly (Supplementary Table 2).…”

Section: Discussionsupporting

confidence: 57%

Methylmercury produced in upper oceans accumulates in deep Mariana Trench fauna

et al. 2020

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is a potent toxin that bioaccumulates and magnifies in marine food webs. Recent studies show abundant methylated Hg in deep oceans (>1000 m), yet its origin remains uncertain. Here we measured Hg isotope compositions in fauna and surface sediments from the Mariana Trench. The trench fauna at 7000-11000 m depth all have substantially positive mass-independent fractionation of odd Hg isotopes (odd-MIF), which can be generated only in the photic zone via MMHg photo-degradation. Given the identical odd-MIF in trench fauna and North Pacific upper ocean (<1000 m) biota MMHg, we suggest that the accumulated Hg in trench fauna originates exclusively from MMHg produced in upper oceans, which penetrates to depth by sorption to sinking particles. Our findings reveal little in-situ MMHg production in deep oceans and imply that anthropogenic Hg released at the Earth's surface is much more pervasive across deep oceans than was previously thought.

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Section: Discussionsupporting

confidence: 57%

Methylmercury produced in upper oceans accumulates in deep Mariana Trench fauna

et al. 2020

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“…pHg stable isotopes sampled in 2017 at two stations, Julio and K1, closer to the coast were similar to the open sea station (K2) with no clear trends in water depth or distance from the shore (Figure S3). Marine sediments, analyzed for station Julio only (700m depth, Table S4), had similar  202 Hg = -0.75 ‰  0.12‰, 199 Hg = 0.04 ‰  0.10‰, and  200 Hg = 0.03 ‰  0.06‰ (mean  2, n=4) to mean water Non-peer reviewed EarthArXiv preprint column pHg (K1, K2, Julio), and were similar to sediment samples taken elsewhere in the Mediterranean Sea 35,36 .…”

Section: Phg Isotopessupporting

confidence: 54%

Mercury stable isotope composition of seawater suggests important net gaseous elemental mercury uptake

Jiskra¹,

Heimbürger‐Boavida²,

Desgranges³

et al. 2020

Preprint

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Human exposure to toxic mercury (Hg) is dominated by the consumption of seafood. Earth system models suggest that Hg in marine ecosystems is supplied by Hg(II) deposition, with a 3x smaller contribution from gaseous Hg(0) uptake, and that photochemical reduction of marine Hg(II) drives important Hg(0) evasion to the atmosphere. Observations of marine Hg(II) deposition and gas exchange are sparse however, leaving the suggested importance of air-sea exchange unconstrained. Here we present the first Hg stable isotope measurements of total Hg (tHg) in surface and deep Atlantic and Mediterranean seawater. We use an isotope mass balance to estimate that sea water tHg can be explained by the mixing of 41% atmospheric Hg(II) deposition and 59% Hg(0) uptake. In the particulate Hg (pHg) fraction, which includes phytoplankton at the base of the marine food web, and in a compilation of marine fish Hg isotope data, we estimate similarly important marine Hg(0) uptake fractions of 73% and 49%. We observe no photochemical odd Hg isotope anomalies in tHg, which calls into question the large model Hg(0) evasion flux. Our findings indicate that direct atmospheric Hg(0) uptake is important and has implications for our understanding of atmospheric Hg dispersal and marine ecosystem recovery.

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“…Modern oceanic sedimentary Hg has not been comprehensively constrained, and in many settings is thought to be contaminated by anthropogenic input 22 , 31 – 33 . Recent work has shown the Mediterranean Sea seafloor sediments from ~0.2 to 4 km water depth contain average Hg concentrations of 66 ppb and Hg/TOC values of 133 ppb/wt%, with isotopic modelling suggesting ~75% of the Hg may be from urban or industrial pollution 33 . Perhaps more comparable to the Paleogene North Sea, Baltic Sea sediments show average Hg concentrations of 20–40 ppb, and Hg/TOC of ~15 ppb/wt%, for preindustrial sediments 32 .…”

Section: Resultsmentioning

confidence: 99%

Paleocene/Eocene carbon feedbacks triggered by volcanic activity

et al. 2021

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The Paleocene–Eocene Thermal Maximum (PETM) was a period of geologically-rapid carbon release and global warming ~56 million years ago. Although modelling, outcrop and proxy records suggest volcanic carbon release occurred, it has not yet been possible to identify the PETM trigger, or if multiple reservoirs of carbon were involved. Here we report elevated levels of mercury relative to organic carbon—a proxy for volcanism—directly preceding and within the early PETM from two North Sea sedimentary cores, signifying pulsed volcanism from the North Atlantic Igneous Province likely provided the trigger and subsequently sustained elevated CO2. However, the PETM onset coincides with a mercury low, suggesting at least one other carbon reservoir released significant greenhouse gases in response to initial warming. Our results support the existence of ‘tipping points’ in the Earth system, which can trigger release of additional carbon reservoirs and drive Earth’s climate into a hotter state.

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Sources of mercury in deep-sea sediments of the Mediterranean Sea as revealed by mercury stable isotopes

Cited by 39 publications

References 54 publications

Methylmercury produced in upper oceans accumulates in deep Mariana Trench fauna

Methylmercury produced in upper oceans accumulates in deep Mariana Trench fauna

Mercury stable isotope composition of seawater suggests important net gaseous elemental mercury uptake

Paleocene/Eocene carbon feedbacks triggered by volcanic activity

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