Mercury anomalies across the Palaeocene-Eocene Thermal Maximum

Abstract

Abstract. Large-scale magmatic events like the emplacement of the North Atlantic Igneous Province (NAIP) are often coincident with periods of extreme climate change such as the Palaeocene–Eocene Thermal Maximum (PETM). One proxy for volcanism in the geological record that is receiving increased attention is the use of mercury (Hg) anomalies. Volcanic eruptions are among the dominant natural sources of Hg to the environment; thus, elevated Hg/TOC values in the sedimentary rock record may reflect an increase in volcanic activity at the time of deposition. Here we focus on five continental shelf sections located around the NAIP in the Paleogene. We measured Hg, total organic carbon (TOC) concentrations, and δ13C values to assess how Hg deposition fluctuated across the carbon isotope excursion (CIE). We find a huge variation in Hg anomalies between sites. The Grane field in the North Sea, the most proximal locality to the NAIP analyzed, shows Hg concentrations up to 90,100 ppb (Hg/TOC = 95,700 ppb/wt%) in the early Eocene. Significant Hg/TOC anomalies are also present in Danish (up to 324 ppb/wt%) and Svalbard (up to 257 ppb/wt%) sections prior to the onset of the PETM and during the recovery period, while the Svalbard section also shows a continuous Hg/TOC anomaly during the body of the CIE. The combination with other tracers of volcanism, tephra layers and unradiogenic Os isotopes, at these localities suggests that the Hg/TOC anomalies reflect pulses of magmatic activity. In contrast, we do not observe clear Hg anomalies on the New Jersey shelf (Bass River) or the Arctic Ocean (Lomonosov Ridge). This large spatial variance could be due to more regional Hg deposition. One possibility is that phreatomagmatic eruptions and hydrothermal vent complexes formed during the emplacement of sills led to submarine Hg release, which is observed to result in limited distribution in the modern. The Hg/TOC anomalies in strata deposited prior to the CIE may suggest that magmatism linked to the emplacement of the NAIP contributed to the initiation of the PETM. However, evidence for considerable volcanism in the form of numerous tephra layers and Hg/TOC anomalies post-PETM indicates a complicated relationship between LIP volcanism and climate. Factors such as climate system feedbacks, changes to the NAIP emplacement style, and/or varying magma production rates may be key to both the onset and cessation of hyperthermal conditions during the PETM.

Assessing the Contributions of Comet Impact and Volcanism Toward the Climate Perturbations of the Paleocene‐Eocene Thermal Maximum

“…Two further Hg excursions to 30 and 20 ppb are also present above the P‐E boundary at Blake Nose. TOC contents from the Blake Nose samples are generally too low (<0.2 wt%) to yield reliable Hg/TOC ratios [see Jones et al, ]. An elevation in Hg at the base of and within the main body of the PETM CIE is broadly consistent with previous investigations, although individual sedimentary records appear to show different patterns of these enrichments (Jones et al, ; Keller et al, ).…”

“…TOC contents from the Blake Nose samples are generally too low (<0.2 wt%) to yield reliable Hg/TOC ratios [see Jones et al, ]. An elevation in Hg at the base of and within the main body of the PETM CIE is broadly consistent with previous investigations, although individual sedimentary records appear to show different patterns of these enrichments (Jones et al, ; Keller et al, ). Recent studies indicated that Hg enrichments could also be associated with increased sulfur/pyrite contents in highly reducing conditions (Shen et al, ).…”

“…As such and given the sporadic nature of the Hg peaks at Blake Nose, it cannot be unambiguously stated that the Hg trends reported here reflect increased volcanism during the PETM. However, a trend of Hg enrichments in PETM strata has also been reported from several other locations and largely been interpreted as resulting from processes relating to volcanic/intrusive activity of the NAIP (Jones et al, ; Keller et al, ). Thus, while a sedimentological control on the Hg trends from Millville and Blake Nose cannot not be excluded, a NAIP‐related volcanic/thermogenic source for these Hg enrichments would be consistent with the interpretations of previous PETM Hg studies.…”

“…All the Os i excursions have been linked with volcanism related to the NAIP, with the larger unradiogenic Os‐isotope shift at Svalbard being attributed to the proximity of that section to the NAIP (Figure ; Dickson et al, ; Wieczorek et al, ). However, although the Os i shift recorded at Svalbard correlates with an Hg and Hg/TOC enrichment, elevated Hg (Hg/TOC) values in that section are also observed below and continue considerably above that level, whereas Os i returns to preshift values abruptly (Jones et al, ). Similarly, the Os i unradiogenic shift of the Millville core is limited to the P‐E boundary, whereas elevated Hg (Hg/TOC) values continue above the base of the PETM.…”

“…Thus, while a sedimentological control on the Hg trends from Millville and Blake Nose cannot not be excluded, a NAIP‐related volcanic/thermogenic source for these Hg enrichments would be consistent with the interpretations of previous PETM Hg studies. The difference in exact patterns of Hg enrichment in global PETM strata (Jones et al, ), as well as other events (Percival et al, ), has been attributed to one/both of local sedimentological processes specific to each paleoenvironmental setting or the distance of an archive from the proposed source (Jones et al, ; Percival et al, ). To date, there are no constraints on the potential delivery of Hg to the Earth's surface by an extraterrestrial impact body.…”