Mercury anomalies across the Palaeocene-Eocene Thermal Maximum

Large-scale magmatic events like the emplacement of the North Atlantic Igneous Province (NAIP) are often 15 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 δC 20 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 25 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 30 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 Clim. Past Discuss., https://doi.org/10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c © Author(s) 2018. CC BY 4.0 License.

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.

Introduction
The Palaeocene-Eocene Thermal Maximum (PETM; 55.8 Ma) was a rapid and prolonged global warming event . It is marked by a sharp negative carbon isotope excursion (CIE) of 3-5 ‰ (McInerney and Wing, 2011), caused by 5 the voluminous release of 13 C-depleted carbon to the ocean-atmosphere system (Dickens et al., 1995;Zachos et al., 2008).
This carbon cycle perturbation and associated global warming (4-5 ºC; Dunkley- Jones et al., 2013;Frieling et al., 2017) instigated changes to both the marine and terrestrial realms (Dickson et al., 2012;Gingerich, 2006;Jaramillo et al., 2010;Zachos et al., 2005). The PETM CIE represents the highest magnitude example of several such excursions from Paleocene and Eocene strata, but is also distinct from the all other Cenozoic hyperthermal events in terms of its long duration (Stap et al., 10 2009;Zeebe et al., 2009). Furthermore, the other Paleogene hyperthermals events are generally considered to be astronomically paced (Cramer et al., 2003;Lourens et al., 2005;Westerhold et al., 2009), while such a relation for the PETM is still debated.
Numerous carbon sources have been suggested, either in concert or individually, to explain the onset and duration of the extreme greenhouse conditions. These include the release of marine gas hydrates (Dickens et al., 1995;Zeebe, 2013), permafrost thawing (DeConto et al., 2012), a bolide impact (Kent et al., 2003;Schaller et al., 2016), and direct and thermogenic 20 degassing associated with large scale magmatism in the North Atlantic Igneous Province (NAIP) (Eldholm and Thomas, 1993;Gutjahr et al., 2017;Storey et al., 2007a;Svensen et al., 2004). It is challenging to directly link these 13 C depleted sources to the PETM in the stratigraphic record. The observed global warming in sedimentary records requires the release of at least 10,000 Gt of C in most state-of-the-art climate models (Frieling et al., 2017), which is greater than any of the estimated fluxes from the above hypothesized sources can solely account for (Aarnes et al., 2015;DeConto et al., 2012;Gu et al., 2011;Gutjahr 25 et al., 2017;Zeebe et al., 2009). Furthermore, several studies have indicated that initial warming leads the CIE by several thousand years, suggesting that a positive feedback triggered the release of a 13 C-depleted source (Dickens, 2011;Frieling et al., 2018;Kender et al., 2012;Sluijs et al., 2007b). This early warming is not associated with a negative shift in δ 13 C values, which indicates that there was either an astronomical configuration favorable to induce (high-latitude) warming (DeConto et al., 2012;Lunt et al., 2011), or that the initial warming was driven by the release of a less 13 C-depleted source compared to 30 emissions during the main PETM CIE. Clim. Past Discuss., https://doi.org/10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c Author(s) 2018. CC BY 4.0 License.
The observation that global warming appears to begin before the onset of the CIE suggests that the emplacement of the NAIP is a mechanism worthy of particular attention. Large igneous provinces (LIPs) such as the NAIP are characterized by the voluminous and rapid emplacement of magma into the shallow crust and at the surface (Burgess and Bowring, 2015;Ernst, 2014). There is a strong positive correlation between the emplacement of LIPs and both rapid climate change events and mass extinctions in Earth history (Courtillot and Renne, 2003;Wignall, 2001), suggesting a possible causal connection. The NAIP 5 is one of the larger known LIPs (Ernst, 2014) and occurred in two main pulses (Wilkinson et al., 2016). The second and more voluminous pulse began at ~56 Ma, emplacing an estimated 5-10  10 6 km 3 of magma and lava within a few million years (Figure 1;Saunders, 2015;White et al., 1987) and is closely associated with the opening of the Northeast Atlantic (Saunders et al., 2007;Storey et al., 2007b;White and McKenzie, 1995). Substantiating a causal relationship between the NAIP and the PETM is complicated by several factors, including limited geochronological data. While extinction and climate records may 10 be readily apparent in sedimentary sections worldwide, it is uncommon to find measureable LIP products such as tephra layers in these sections due to transport limitations, and post-depositional factors such as reworking and weathering (Jones, 2015).
This limits their use as potential marker horizons. Therefore, a well-tested and uniquely volcanic tracer in sedimentary rocks would be a powerful proxy for understanding the relationship between large-scale volcanism and rapid climate change events.

Mercury as a proxy for NAIP activity 15
Mercury (Hg) anomalies in sedimentary records have been proposed as an indicator for periods of major volcanic activity (Sanei et al., 2012). There is a strong positive correlation between Hg and total organic carbon (TOC) in modern sediments (Gehrke et al., 2009;Outridge et al., 2007;Ruiz and Tomiyasu, 2015;Sanei et al., 2014). Normalizing Hg to Hg/TOC helps to correct for variations in sedimentation rate, as TOC is generally the primary phase to complex Hg (Sanei et al., 2012). Therefore, sharp increases in Hg/TOC ratios preserved in the sedimentary record are interpreted as a proxy for enhanced 20 volcanic activity. Such anomalies have been reported as a tracer for volcanism for several major environmental perturbations and/or mass extinctions in the geological record (Font et al., 2016;Grasby et al., 2013;Keller et al., 2018;Percival et al., 2015;2017;Sanei et al., 2012;Sial et al., 2013;Thibodeau et al., 2016). Therefore, this method is an important proxy to assess the relative importance of volcanism as a causal mechanism for the PETM, given the wealth of literature on the PETM and the availability of numerous sedimentary sections worldwide. A recent pioneer study using the Paleocene-Eocene Global 25 Boundary Stratotype Section and Point (GSSP) in Dababiya, Egypt, showed a strong Hg/TOC anomaly within the PETM CIE (Keller et al., 2018).
There are two principal mechanisms for the emplacement of the NAIP to affect the Hg cycle ( Figure 2): 1) Effusive and explosive volcanism, and 2) explosive hydrothermal vent complexes releasing gases generated by contact metamorphism of 30 organic-rich sediments. Clim. Past Discuss., https://doi.org/10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c Author(s) 2018. CC BY 4.0 License.

Volcanism
Present day volcanism is a well-established flux of Hg to the atmosphere (Pyle and Mather, 2003), and the NAIP was particularly active in the late Paleocene and early Eocene (Larsen et al., 1999;Storey et al., 2007b). In East Greenland, studies using fluid inclusions and amphiboles as geobarometers suggested that the Skaergaard intrusion was buried by a huge outpouring of continental flood basalts (5.3-6.3 ±2.7 km) during the voluminous second phase of NAIP as the magma chamber 5 crystallized (Larsen and Tegner, 2006). High precision U-Pb ages indicate an initial emplacement at ca. 56.02 Ma for the intrusion (Wotzlaw et al., 2012). The predicted timescale of cooling and therefore the emplacement of the overlying enormous volumes of flood basalts, is around 100-300 kyr (Larsen and Tegner, 2006). The U-Pb ages in East Greenland at the onset of widespread flood volcanism predate the onset of the PETM by about 200 kyr . A distinctive tephra layer named the Gronau tuff has been identified in the uppermost part of the East Greenland flood basalts (Heister et al., 2001), 10 which is indistinguishable from tephra layer #-17 from the Fur Formation (Denmark) in both chemistry and age (Storey et al., 2007a). The corrected Ar/Ar radiometric age, using the most recent Fish Canyon Tuff correlation (Kuiper et al., 2008), is calculated to be 55.6 ± 0.1 Ma for tephra layer #-17. This indicates that the voluminous flood basalt volcanism in Greenland was emplaced in a 400 kyr time interval that encompasses the PETM.

15
Any Hg/TOC anomalies resulting from flood basalt province emplacement will be affected by the style and frequency of eruptions ( Figure 2). Pulsed activity with considerable repose periods between eruptions might be expected to result in sharp individual Hg/TOC peaks, while continuous eruptions could result in a sustained Hg/TOC anomaly, depending on data resolution and the sedimentary record in question. The explosiveness of eruptions will also dictate the height to which Hg is emitted in the atmosphere, which can affect the regional to global transport of Hg. There are widespread early Eocene tholeiitic 20 basalt tephras from the NAIP preserved in the Balder Formation in the North Sea (Haaland et al., 2000) and in the upper Fur Formation in Denmark (Bøggild, 1918;Larsen et al., 2003), which are interpreted to be formed by shallow marine, Surtseyantype eruptions (Planke et al., 2000). Phreatomagmatic eruptions may transfer part of the erupted Hg to seawater, resulting in more limited global transport ( Figure 2). The modern residence time of Hg in oceanic waters is decades to centuries (Gill and Fitzgerald, 1988;Gworek et al., 2016), which is shorter than the mixing time of the ocean, so any Hg released to the water is 25 likely to be redeposited in closer proximity to the source compared to atmospheric emissions (Scaife et al., 2017).

Contact Metamorphism
There is mounting evidence that magmatic intrusions during the emplacement of the NAIP led to the release of huge volumes of greenhouse gases ( Figure 2). Thousands of submarine hydrothermal vent complexes have been identified by seismic reflection profiles from the offshore Vøring and Møre basins in the Norwegian Sea (Svensen et al., 2004). Vent structures form 30 at the edges of sill intrusions due to overpressure generated by boiling of pore fluids and/or gas generation during contact metamorphism (Aarnes et al., 2015;Iyer et al., 2017). The resulting explosions are capable of ejecting gases into the Clim. Past Discuss., https://doi.org/10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c Author(s) 2018. CC BY 4.0 License.
atmosphere, even from submarine vents (Svensen et al., 2004). Hydrothermal vent complexes around large sill intrusions have also been observed in the Faroe-Shetland basin (Hansen, 2006) and on the northeast Greenland margin (Reynolds et al., 2017) ( Figure 1). It is therefore likely that these features were widespread along the proto-northeast Atlantic margins. Around 95% of the hydrothermal vent complexes in the Vøring and Møre basins terminate at the horizon between Paleocene and Eocene strata, with the remainder terminating within the Paleocene sequence (Planke et al., 2005;Svensen et al., 2004). One zircon 5 U-Pb age from a sill in the Vøring margin was dated to 55.6 Ma (Svensen et al., 2010) and it was recently shown that the only drilled hydrothermal vent complex dates to within the body of the CIE (Frieling et al., 2016). It therefore appears likely that there was considerable emplacement of sills with associated hydrothermal venting of gases along the margins of the NAIP coincident with the PETM, although the activity in these widespread vent systems likely encompasses a more prolonged interval of time (Kjoberg et al., 2017;Svensen et al., 2004). 10 Sill intrusions are likely to be a source of Hg to the environment, both from magmatic degassing and the volatilization of organic material during contact metamorphism of intruded sedimentary rocks. The resulting Hg/TOC signal in the sedimentary record will be dependent on the timescales of thermogenic gas generation and eruption, which for individual sills is predicted to be in the order of 100's to 10,000's years (Heimdal et al., 2018;Stordal et al., 2017). Vent structure appear to have been 15 conduits of multiple gas ejections during their lifetime (Svensen et al., 2003), so gas release is likely to occur in pulsed fashion that would be closely temporally spaced. This would manifest as a larger initial Hg/TOC anomaly following a sill intrusion, followed by continuously elevated Hg/TOC values. As with the phreatomagmatic eruptions, the resulting Hg anomalies would likely be only regional in extent if a substantial part of the Hg was transferred to the water (Figure 2).

20
Here we explore the occurrence of Hg/TOC anomalies in PETM sediments from several shallow marine sections with varying proximity the NAIP. To elucidate the timing and potential causality, we compare our data to the CIE and warming and discuss the relevance in a carbon cycle and climate framework.

Materials and Methods
Five sites were investigated in this study ( Figure 1). Four of these are drill cores through the PETM interval from the North 25 Sea, Svalbard, New Jersey (USA), and the Arctic Ocean, and one is a field outcrop in Denmark. The localities were selected as they are continental shelf successions with little disruption to the stratigraphy, and the organic matter is well preserved with abundant biomarkers and fragile microfossils Schoon et al., 2015;Sluijs et al., 2007a), which minimizes the effects of syn-and post-depositional process on Hg/TOC signals. The sampling of each site is described in turn: Clim. Past Discuss., https://doi.org /10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c Author(s) 2018. CC BY 4.0 License.

Grane Field, North Sea
The Grane field is situated in the Southern Viking Graben in the Norwegian North Sea (Figure 1). Four wells were drilled by Norsk Hydro Produksjon AS (now Equinor ASA) from 1993 to 1995, which have been the focus of previous investigations (Haaland et al., 2000;Mangerud et al., 1999). Two distinct phases of volcanism are recorded by tuffaceous intervals, phase one in the Våle and Lista Formations (mid Paleocene), and phase two in the Sele and Balder Formations of the late Paleocene 5 and early Eocene (Haaland et al., 2000). The Balder Formation is main tuffaceous interval with over 160 discreet ash layers (Haaland et al., 2000). 2°29'07''E)

Central Basin, Svalbard
The Paleogene Central Basin in Svalbard was drilled by Store Norske Spitsbergen Kulkompani (SNSK) at Urdkollen (core BH09/2005; 77°54'09"N, 16°12'59"E; Figure 1). This core has been the focus of numerous previous investigations (Charles 15 et al., 2011;Cui et al., 2011;Dypvik et al., 2011;Nagy et al., 2013;Riber, 2009;Wieczorek et al., 2013), allowing direct comparisons with published datasets. The Central Basin began to form as a rapidly subsiding foreland basin in the mid Paleocene (Jones et al., 2017). By the late Paleocene and early Eocene, the sedimentary environment was consistently marine deposition with varying degrees of terrigenous input. The shale-dominated Frysjaodden Formation begins ~20 m below the onset of the PETM and continues up to 340 m above the CIE (Figure 4). The rapid deposition rate of 21. 5-27.4 cm/kyr 20 during the PETM , combined with little change in lithology across the interval and relatively high and consistent TOC concentrations, makes this expanded section ideal for studying Hg anomalies across the PETM. A total of 127 samples were collected for this study and from previous research (Riber, 2009), covering an interval from 554 to 470 m.b.s.

Fur Island, Denmark
The island of Fur, located within Limfjorden in northern Denmark (Figure 1), features outcrops dominated by the early Eocene 25 Stolleklint Clay and the overlying clay-rich to clay-poor diatomite of the Fur Formation ( Figures 5-6;Heilmann-Clausen et al., 1985;Pedersen et al., 2004;Pedersen and Surlyk, 1983). The ~60 m thick Fur Formation contains over 170 distinct tephra horizons that are interpreted to be derived from explosive NAIP volcanism (Larsen et al., 2003). Tephra layers are also present in the Stolleklint Clay but are less numerous. The ashes are separated into a negative and positive series (Bøggild, 1918), with the boundary between the Stolleklint Clay and the Fur Formation placed at the prominent thick silicic ash layer #-33 30 (Heilmann-Clausen et al., 1985). The Paleocene-Eocene boundary is at the base of the Stolleklint Clay, which overlies the Holmehus Formation and/or the Østerrende Clay (Heilmann-Clausen, 1995;. The base of the Stolleklint Clay is rarely exposed at the surface on Fur Island, except at the type locality of Stolleklint Beach after the occasional extreme storm clears the beach sand (56°50'29"N, 8°59'33"E). One such brief exposure in 2005 has been the focus of several investigations (Heilmann-Clausen et al., 2014;Schoon et al., 2013;.

5
Here we use outcrops at Stolleklint beach and a road-cut into a quarry to the southwest (56°49'51"N, 8°58'45"E) to sample the body and recovery of the PETM, using the tephra layers #-35, #-34, and #-33 as marker horizons to calibrate between sections. In order to evaluate the lower part of the Stolleklint Clay and underlying Holmehus-Østerrende Clay, we excavated a 43 m long and 0.5 m deep trench in the beach. We used numerous dip and strike measurements and trigonometry to obtain a calculated local true thickness for the Stolleklint Clay of 24.4 m (maximum error ±2 m, see Supplementary data for details), 10 from basal contact with the Holmehus-Østerrende Clays to the base of tephra #-33. This estimated thickness of the Stolleklint Clay is at the upper end of previous estimates (Schoon et al., 2013;. Sub-beach samples were collected every 0.01 m across the boundary between the Holmehus-Østerrende Clay and the Stolleklint Clay, then every 0.5 m along the beach. This equates to a sampling interval of 0.2-0.3 m once converted through the trigonometry estimates. Additional samples were collected along the Stolleklint cliff face. The quarry road-cut section was sampled every 0.1 m across a ~7m section below and 15 above tephra layer #-33. Three tephra layers are present at the base of the Stolleklint Clay, with the second layer coinciding with the onset of the CIE (Heilmann-Clausen et al., 2014; Figure 6). These layers are given the names 'SK1', 'SK2' and 'SK3' as they do not correspond to any of the numbered ash series described by Bøggild (1918). Based on textural similarities and known distributions of NAIP 20 tephras (Haaland et al., 2000;Westerhold et al., 2009), it is highly likely these ash layers originated from the NAIP. No other tephra layers have been identified in the underlying Paleocene strata (Holmehus Formation and Østerrende Clay) in this or any other locality in Denmark (Heilmann-Clausen et al., 2014).

Bass River, New Jersey
A core was collected from the ODP 174AX "Bass River" Leg in New Jersey (39°36'42"N, 74°26'12"W; Figure 1) that includes the Paleocene-Eocene boundary (Cramer et al., 1999). The site was located close to the edge of the American continental shelf in the late Paleocene (Miller et al., 2004). The sediments are characterized by glauconite-rich silts and sands that fine into clayrich sediments just below and across the PETM CIE (John et al., 2008). A sandstone unit is found at the top of the CIE, with 5 an unconformity separating it from continued claystone above (Figure 8). This site has been the focus of numerous investigations (Babila et al., 2016;John et al., 2008;Moore and Kurtz, 2008;O'Dea et al., 2014;Sluijs et al., 2007b;Stassen et al., 2012), and represents the most distal locality to the volcanic activity of the NAIP studied here. Samples were collected at 6-50 cm intervals over a 25 m section, with the lowest resolution in sediments recording the onset and recovery of the PETM due to severe core depletion of those strata. 10

Sample Analyses
Mercury analysis was conducted using the Lumex RA-915 Portable Mercury Analyzer with a PYRO-915 pyrolyzer (Bin et al., 2001) at the University of Oxford. Analytical procedures followed in-house protocols , where 40-60 mg of powdered sample was weighed before being transferred to the pyrolyzer and heated to 700 °C. Sample peaks in the spectrometer were calibrated using the NIMT/UOE/FM/001 peat standard with a known Hg concentration of 169 ±7 ppb, with 15 repeat calibrations every ten samples to account for any drift in the instrument. Each sample was run in duplicate to further reduce the analytical error to around ±5 %.
Carbon isotope and total organic carbon (TOC) values used published data, where available John et al., 2008;Sluijs et al., 2006). Additional TOC analyses were conducted for Svalbard and Fur samples on the Rock Eval 6 ( Espitalié 20 et al., 1977) at the University of Oxford. New carbon isotope analyses were conducted for Fur and Grane samples. Samples were weighed into tin capsules, then the δ 13 C value of each sample was determined in triplicate using a Delta V Advantage Isotope Ratio Mass Spectrometer (Thermo Fisher, Bremen, Germany) configured to a Thermo Finnigan 1112 Series Flash Elemental Analyzer at the University of Louisiana at Lafayette. All data are reported in standard δ-notation (in units of permil, ‰) and normalized to the Vienna Pee Dee Belemnite (VPDB) scale using three internal lab reference materials (JRICE: δ 13 C 25 = -27.44‰; JHIST: δ 13 C = -8.15‰; and JGLY: δ 13 C = -43.51‰). A quality assurance sample (JGLUC) was analyzed as an unknown. Across all analyses, the JGLUC quality assurance sample averaged δ 13 C = -10.64 ± 0.13 (n = 10), which is in agreement with the calibrated value of -10.52‰. For the sediment samples, the median standard deviation of the replicate capsules was 0.10‰. Combustion also resulted in a quantification of percent carbon (%C) in each sample.

Results
The full results are shown in Figures 3-8 for individual localities, and the raw data can be found in the Supplementary data.
Data for the Dababiya Quarry GSSP locality (Keller et al., 2018) is also shown in Figure 9.

Grane Field, North Sea
The extent of the carbon isotope excursion (CIE) is difficult to determine in the Grane core ( Figure 3). The body phase is 5 apparently represented by only one data point (-30.6 ‰ at 1651.05 m.b.s.; Figure 3), which is directly followed by a return to values around -27 ‰, albeit more negative than pre-PETM conditions (-25 ‰). The shape and duration of the CIE in the Grane core is markedly different from other Sele Formation localities in the North Sea (Kemp et al., 2016;Kender et al., 2012), where δ 13 C values remain close to -30 ‰ even after the recovery of the CIE. Therefore, while the onset of the PETM CIE is apparent, it is difficult to unambiguously identify the body and recovery phases of the CIE in the stratigraphy.

Central Basin, Svalbard
The CIE of the core 09/2005 is unusual for a PETM section in that there is a prolonged (6.2 m thick) onset and a gradual recovery from negative δ 13 C values ( Figure 4) , rather than a continuous negative δ 13 C excursion that clearly defines the body of the CIE in other records. Consequently, it is difficult to precisely define where the CIE body ends and recovery begins. Two thin tephra layers of unknown provenance are found at 517 and 511 m.b.s. within this interval. There

Fur Island, Denmark
The results of the samples collected from the Stolleklint beach and road-cut localities are shown in Figures 5 and 6. The stratigraphic logs are calibrated so that the top of the tephra layer #-33 is zero. The onset of the CIE at Fur spans only 0.15 m 5 ( Figure 6), whereas the body and recovery of the CIE ( Figure 5) span around 24.3 and 5 m, respectively. Coupled with a marked change from the heavily bioturbated, glauconite rich Østerrende/Holmehus Clay to the laminated Stolleklint Clay at the onset of the CIE (Figure 6), this suggests a significantly higher accumulation rate during and after the CIE than before. The δ 13 C curve observed during the body phase (-24.3 to 0 m) in the Stolleklint section is consistently stable at around -31‰ ( Figure 5). The beginning of the recovery phase coincides with tephra layer #-33, one of the largest silicic layers within the 10 whole sequence (Larsen et al., 2003), and is also marked by Hg/TOC anomalies ( Figure 5). Sporadic tephras are observed into the Fur Formation, with the main phase of 140 ash layers (from #+1) beginning 27 m above tephra #-33 (Bøggild, 1918).
There are clear Hg/TOC anomalies that coincide with both the onset of the PETM and at the transition from the body to the recovery of the CIE. The measured Hg/TOC ratios and δ 13 C values in the underlying Østerrende/Holmehus Clay are stable up 15 until -24.64 m depth, where the first Hg/TOC anomaly occurs 0.07 m below the base of tephra layer 'SK1' (Figure 6). Hg/TOC ratios continue to fluctuate before and after the deposition of the two thick tephra layers 'SK1' and 'SK2' at the onset of the CIE. The overlying strata record extremely stable Hg/TOC ratios through the majority of the Stolleklint Clay, despite noticeable fluctuations in Hg and TOC concentrations ( Figure 5). These stable Hg/TOC values correlate with an absence of visible tephra layers at this locality, and while the absence of tephra layers does not exclude volcanic activity at the time, it is 20 noteworthy given the abundance of tephra layers above and below this interval at the onset and recovery of the CIE.
Fluctuations away from this stable baseline only begin to occur above -5.6 m depth, just prior to the reemergence of preserved tephra layers in the form of ash #-39 from the numbered ash series (Bøggild, 1918).

Lomonosov Ridge, Arctic Ocean
The results from core 302-4A are shown in Figure 7. The discontinuous core recovery complicates the interpretation of 25 Hg/TOC values, particularly as the onset of the CIE is missing and parts of the recovery period are absent due to insufficient remnant sample material. However, the shape of the preserved CIE, with a stable body followed by a recovery period , is consistent with continental shelf PETM sites. There is substantially less variation in Hg/TOC ratios through this core compared to the sites in Svalbard and Denmark, although this may result from insufficient data during key intervals.
There are two anomalously high Hg/TOC values, one below the onset of the CIE and the other at the beginning of the recovery 30 phase (Figure 7). Based on the data available, there do not appear to be significant Hg/TOC anomalies across the PETM.

Bass River, New Jersey
The results from the Bass River core are shown in Figure 8. This locality has low TOC concentrations (0.06-0.64 wt%) throughout the studied section, which leads to larger uncertainties in the Hg/TOC ratios. Nearly half of the samples have TOC concentrations <0.2 wt%, the threshold recommended by Grasby et al. (2016) for reporting Hg/TOC anomalies. These samples are omitted from the Hg/TOC graph in Figure 8. The variations in Hg/TOC values are considerably smaller than observed at 5 the other sites, but due to the low TOC concentrations in the section this may not be reliable. Despite these limitations, the largest apparent Hg/TOC anomalies occur several meters below and above the CIE, although the unconformity at 347.05 m.b.s. means it is unclear how much later the clay succession was deposited after the PETM.

Discussion
The five sites investigated in this study display a wide variety of Hg/TOC ratios during the late Paleocene and early Eocene. The results from the study of the GSSP locality in Dababiya (Egypt) by Keller et al. (2018) are summarized in Figure 9. The results from the GSSP locality are hampered by several factors, including δ 13 Ccarb and δ 13 Corg showing different shapes of the 20 CIE (Khozyem et al., 2015), which makes it difficult to define various stages of the PETM. Moreover, the section is complicated by the limited number of biomarkers and organic microfossils (Speijer and Wagner, 2002) and the effects of in situ carbonate dissolution and weathering. This locality also suffers from the same problem as Bass River in that TOC concentrations are generally very low, with much of the Paleocene samples falling below the recommended threshold for reporting Hg/TOC values (Grasby et al., 2016). However, the section differs markedly from Bass River in that there are two 25 distinct peaks in Hg concentrations occurring within the CIE (Figure 9). The first peak of 288 ppb occurs in a section that is heavily affected by carbonate dissolution, and is not matched by a concomitant increase in TOC values. The Hg/TOC anomalies appear extreme (up to 1090 ppb/wt%), although this value will have a considerable error due to the very low TOC concentrations. The second Hg peak occurs during a brief interval less affected by acidification, and once normalized to TOC there is no Hg/TOC anomaly (Figure 9). There are a number of potential issues with the studied sections that need to be considered before any interpretation of Hg/TOC anomalies can be made.

Site-specific uncertainties
The extreme Hg concentrations measured throughout the Grane core indicate that something exceptional has occurred at this locality that may have overprinted the primary signal (Figure 3). An important consideration for North Sea localities is the 5 post-depositional effects of oil and gas seepage as the Balder Formation is a known cap rock. Therefore, it is possible that the section has been affected by hydrocarbon migration. However, measurements of the oil sands at 1766.6 and 1783.7 m.b.s. had Hg concentrations of 1135 and 3295 ppb, respectively. Whilst Hg-rich, these values fall well short of the measured Hg concentrations before (36,750 ppb) and after (90,100 ppb) the PETM CIE ( Figure 3). In the absence of a known process that would decouple Hg and C during hydrocarbon migration, we therefore interpret the most likely source of these extreme Hg 10 concentrations as a proximal Hg source that was very localized in depositional extent. The most likely scenario for such a process is the dominant release of Hg to seawater, either through hydrothermal vent complexes and/or Surtseyan-type volcanic eruptions ( Figure 2). The significant Hg/TOC anomalies throughout this section indicate that if the cause is syn-depositional, then significant Hg source(s) were active before, during, and after the PETM.

15
The Lomonosov section (Figure 7) is complicated by poor core recovery during the CIE onset and the unavailability of samples during the CIE recovery. Unfortunately, these missing intervals coincide with the largest Hg/TOC anomalies observed in Svalbard, Fur, and Dababiya. Therefore, the results from the Lomonosov core unlikely paint a fully representative picture. The Bass River and Dababiya localities (Figures 8-9) are affected by low TOC concentrations, which could cause large changes in Hg/TOC ratios that result from TOC variations within measurement uncertainties, hindering interpretation of any peaks 20 (Grasby et al., 2016). As such, it is possible that small to medium Hg/TOC anomalies are lost to the background noise of the Bass River locality, and the uncertainty of the magnitude of the Hg/TOC anomaly at Dababiya is very high. It is conceivable, but unlikely, that the Hg/TOC anomaly at Dababiya could purely be a product of diagenetic and weathering processes, given the amount of dissolution and acidification observed at this site (Figure 9; Keller et al., 2018;Khozyem et al., 2015). However, the effects of such processes on Hg/TOC ratios are poorly understood. 25

Alternative Hg sources
While volcanism is an established source of Hg to the environment, there are a number of other processes that could possibly lead to the rapid release of Hg, including those that have been suggested as possible causes for the PETM. The presence of impact ejecta at the start of the CIE has been used to suggest that a meteorite impact may have triggered the global warming 30 (Schaller et al., 2016). Little is known about how a meteorite may affect the Hg cycle, but presumably the location of impact is key to any disturbance, as the affected sediments can have large variations in organic matter and therefore Hg concentrations. Mercury concentrations in meteorites are believed to be low, based on studies of the Cretaceous-Paleogene boundary (Sial et al., 2013). Any possible Hg anomaly from volatilized impacted rocks would be manifest as a sharp, individual Hg/TOC peak in the rock record. There are several Hg/TOC peaks close to the onset of the PETM at several sites, but none that appear to correlate exactly at the CIE onset where the glass spherules have been observed (Schaller et al., 2016). Given that these records have numerous distinct Hg/TOC peaks, and that chemical and isotopic records lack an extraterrestrial signal during this time 5 (Schmitz et al., 2004), a meteorite impact can be discounted as a possible cause for the observed Hg/TOC anomalies.
Potential terrestrial Hg sources include permafrost thawing (DeConto et al., 2012;Schuster et al., 2018) or wild fires producing widespread fly-ash (Sanei et al., 2012). However, the late Paleocene was abnormally warm, with both poles ice-free and temperatures much higher than present day at high latitudes (Bijl et al., 2009;Sluijs et al., 2006) due to the persistent polar 10 amplification in these warm climates (Frieling et al., 2017), casting doubt as to whether significant permafrost reserves existed at this time. Wild fires can also be discounted as a cause of Hg/TOC anomalies, as increases in Hg loading from fly ash events appear to correlate with increased TOC deposition (Sanei et al., 2012). Moreover, organic matter during the CIE in Svalbard ( Figure 4) is dominated by amorphous material and marine dinocysts , negating a fly-ash source of the Hg/TOC anomalies. At present, there is no available data on marine methane hydrates and their potential role (if any) as a 15 source of Hg to the environment.

Other influences on Hg/TOC values
The source of organic matter may also be an important factor for Hg/TOC values. Terrestrial and marine environments are inherently different in terms of ecosystem dynamics and nutrient cycling, which may affect the degree of Hg enrichment in 20 various organic carbon reservoirs on land and in the oceans. There is compelling evidence that the organic matter sources varied across the PETM for many localities. In Svalbard, palynological evidence indicates that there was a distinct transient shift towards marine-derived organic matter across the PETM . The organic matter before and after the CIE is dominated by terrestrially-derived phytoclasts of cuticle and wood, while the body of the PETM is largely comprised of amorphous organic matter and marine dinocysts . The same trend is observed at the Lomonosov ridge, 25 with abundant terrestrial organic matter observed before and after the CIE Weller and Stein, 2008) and changes to salinity and runoff Sluijs et al., 2008;Waddell and Moore, 2008). Fluctuations in salinity and terrestrial runoff are also observed around the Bass River locality (Gibson et al., 2000;John et al., 2008;Zachos et al., 2006).
It is therefore possible that a shift in the source of organic matter would lead to a change in the Hg/TOC baseline during the PETM, such as that observed in Svalbard (Figure 3). However, a study of shelf sections during the emplacement of the Karoo-30 Ferrar LIP suggest that terrestrial organic matter generally has a higher Hg/TOC ratio than marine organic matter (Percival et al., 2015), implying that given the increased marine contribution to the TOC content, Hg/TOC values should decrease during the PETM, which is the opposite effect to that observed in the Svalbard core. The δ 13 C curve in Svalbard also has multiple transitional values between the onset and peak of the CIE, suggesting multiple admixed sources of organic matter (Harding et Clim. Past Discuss., https://doi.org/10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c Author(s) 2018. CC BY 4.0 License.
al., 2011) that could mute a step change in Hg/TOC ratios. Indeed, the observed sea level rise across the PETM makes an increased marine contribution to TOC a likely factor at many shallow sites (e.g. Sluijs et al. 2008, Sluijs & Dickens 2012. While more work is needed to constrain Hg enrichments in various organic reservoirs (i.e. source specific Hg analyses) the source of organic matter does not appear to be a principal driver of Hg/TOC concentrations in these studied sections. Therefore, if organic matter sourcing influenced Hg/TOC values, it is more likely to have muted Hg/TOC anomalies during the body of 5 the CIE than to have caused them.

NAIP magmatism as the cause of the Hg/TOC anomalies
There are a number of lines of evidence that suggest that the emplacement of the NAIP is the prime candidate for the observed Hg/TOC anomalies. While there is considerable variation between localities, there are three discreet intervals at which Hg/TOC anomalies most regularly occur: 1) just prior to the onset of the PETM, 2) during the recovery phase, and 3) later in the Eocene. 10 These intervals also contain abundant tephra layers in the Grane, Fur, and, to a lesser extent, Svalbard localities (Figures 3-6), indicating that these Hg/TOC anomalies are likely to be volcanic/magmatic in origin. There are also elevated 'baseline' Hg/TOC values observed at Svalbard and Dababiya during the body of the CIE (Figures 4, 9).

Pre-CIE onset 15
The observed Hg/TOC anomalies prior to the onset of the CIE coincide with the first evidence of volcanism preserved after a significant hiatus in both Denmark (Heilmann-Clausen et al., 2014) and the North Sea (Haaland et al., 2000). At Fur, the stratigraphic level featuring the first rise of Hg/TOC also records numerous NAIP tephra beds (Figure 6), while at Grane Hg/TOC anomalies are present in the lowermost sample studied (Figure 3). In Svalbard, the numerous Hg/TOC anomalies from around 5 m below the CIE onset are correlative with a shift to unradiogenic 187 Os/ 188 Os ratios (Wieczorek et al., 2013), 20 which may indicate an enhanced flux of volcanically derived osmium to the ocean. This interval corresponds to around 18-23 kyr using the estimated CIE deposition rate . Such features are also observed from localities in the Arctic and Tethys Oceans prior to the onset of the CIE (Dickson et al., 2015;Schmitz et al., 2004). The temporal correlation of several volcanic proxies prior to the onset of the CIE suggests that the emplacement of the NAIP could be a primary factor driving global warming prior to the PETM (Frieling et al., 2018;Sluijs et al., 2007b) and hence may function as a trigger for the CIE 25 and extreme warming.

CIE body
The Hg/TOC results of the body of the CIE, defined as a period of stable negative δ 13 C values, show significant variations between the studied localities. In Svalbard, the consistently elevated Hg/TOC ratios during the body and into the recovery of 30 the CIE suggest a prolonged source of Hg emissions that enhanced Hg deposition at this locality (Figure 4), possibly supported by the Dababiya section (Figure 9). For Grane, the analyzed core interval is swamped with extremely high Hg concentrations throughout (Figure 3). At Fur, there is no such enrichment in Hg, although this trend may be complicated by the sharp change in lithology across the PETM interval (Figures 5-6). The Lomonosov and Bass River localities also show no evidence of increased Hg/TOC in the CIE body (Figures 7-8). The 187 Os/ 188 Os ratios during the CIE body in Svalbard lack a basaltic signature (Wieczorek et al., 2013), consistent with records from other ocean basins where the 187 Os/ 188 Os record is dominated by continental weathering (Dickson et al., 2015;Ravizza et al., 2001). Other volcanic proxies such as tephra layers are uncommon at the Grane and Fur localities. Therefore, the sustained Hg/TOC increase observed in the Svalbard and Egypt 5 sections appears regional in extent, and there is little other evidence for volcanism at that time.

CIE Recovery
There are numerous Hg/TOC anomalies preserved in the Fur and Svalbard sections close to the recovery of the PETM CIE.
This interval marks the beginning of hundreds of tephra layers deposited in Danish and North Sea sections during the early 10 Eocene (Haaland et al., 2000;Larsen et al., 2003). The basaltic and silicic tephras in Denmark are >1200 km from the nearest known source volcano, indicative of the largest and most violent explosive eruptions known to occur (Mason et al., 2004).
Individual explosive eruptions that deposited each Fur tephra layer are likely to have been 100's to 1000's km 3 in magma volume (Baines et al., 2008;Baines and Sparks, 2005), which is rare (~0.1 to 1 Myr recurrence time) for silicic volcanism and unheard of for basaltic volcanism. These tephras are interpreted to have formed by shallow marine, phreatomagmatic eruptions 15 that postdate both the opening of the northeast Atlantic Ocean (Planke et al., 2000) and the exposed east Greenland flood basalts (Storey et al., 2007b). It is therefore likely that the observed Hg/TOC anomalies in the early Eocene are caused by NAIP volcanism.

NAIP magmatism as a cause for the PETM?
The results presented here show significant Hg anomalies throughout the latest Paleocene and early Eocene, with the largest 20 Hg/TOC anomalies occurring prior to the onset of the CIE and at the start of the recovery phase. The presence of abundant tephra layers at these intervals and the apparent variation in magnitude of Hg/TOC anomalies with proximity to the NAIP suggests that these anomalies are likely to represent volcanic and/or thermogenic eruptions releasing Hg to the environment.
The temporal correlation with the onset of the CIE suggests that the emplacement of the NAIP could be a primary factor in initiating the extreme global warming observed during the PETM. However, the relationship between the NAIP and global 25 climate appears complex, as Hg/TOC anomalies and evidence for volcanism continue into the global cooling of the recovery phase and early Eocene. Moreover, the continuously elevated Hg/TOC concentrations observed during the CIE in Svalbard and Dababiya are less clearly volcanic in origin due to the absence of tephras and unradiogenic Os isotopes. Therefore, if the NAIP is responsible for initiating the PETM, then a combination of climate system feedbacks, varying magma production rates, and/or the changes in the dominant method of magma emplacement are required to reconcile the available data. 30 The dominant emplacement style and magma production rates of the NAIP varied considerably during the Paleogene (Saunders, 2015;Storey et al., 2007b;Wilkinson et al., 2016), and potentially also across the PETM (Storey et al., 2007a). Clim. Past Discuss., https://doi.org/10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c Author(s) 2018. CC BY 4.0 License.
One limitation is that volcanic proxies such as tephra deposition and Os isotopes may not reflect the true extent of magmatic activity, as they are dependent on the degree of explosive volcanism and basalt weathering, respectively. If the eruptions are dominantly effusive, or gas-dominated submarine eruptions from thermogenic sources, then tephra and Os isotope evidence may be more limited. Mercury anomalies may also be regionally limited by seawater interactions in the case of submarine eruptions or hydrothermal venting (Figure 2), which may account for the extreme concentrations measured in the Grane core 5 ( Figure 3). Since volcanic eruptions and thermogenic gas release from contact metamorphism are inherently different processes, it is reasonable to assume that this is also reflected in mechanistic differences in C and Hg release ( Figure 2). Therefore, the magnitude and spatial variations in Hg/TOC anomalies from these two sources may differ considerably, such that Hg/TOC anomalies do not necessarily always equate to the same C input. If the dominant mode of emplacement shifted from volcanism to intrusions during the CIE, a mechanism proposed for other LIPs , this could be 10 consistent with more localized aqueous Hg dispersal and the release of 13 C depleted carbon that could have maintained negative δ 13 C conditions (Frieling et al., 2016).

Conclusions
This study presents Hg/TOC anomalies across the PETM from five continental shelf sections. Extremely high Hg concentrations are present in the Grane core in the North Sea and significant Hg/TOC anomalies are observed in Svalbard, 15 Denmark, and Egypt (Keller et al., 2018). No such clear anomalies are observed in the Lomonosov Ridge or Bass River sections, although these localities are complicated by incomplete core recovery and low TOC concentrations, respectively.
With exception of the Egypt section, the magnitude of Hg/TOC anomalies generally correlates with proximity to the NAIP, and the coincidence of other volcanic proxies indicates that the NAIP is the most likely source of the observed Hg/TOC anomalies. The large variation in magnitudes of Hg/TOC anomalies between localities indicates that Hg deposition was 20 regionally constrained. One possible explanation is that phreatomagmatic eruptions and submarine degassing from hydrothermal vent complexes meant greater transference of Hg to seawater, leading to localized deposition. Different organic matter sourcing may have muted Hg/TOC signals at some of these sites, but this effect is unlikely to cause positive Hg/TOC anomalies during the PETM.

25
There are two distinct disruptions to the Hg cycle, preserved in sections that are proximal to the NAIP. Tephra layers and Hg/TOC anomalies are most prevalent before the onset of the CIE and during the CIE recovery. In addition, the Svalbard section has Hg/TOC ratios that are consistently elevated during the CIE body. The most likely candidates for the observed Hg/TOC anomalies are the emplacement of an extensive flood basalt province along the margins of the nascent Northeast Atlantic Ocean and the thermogenic gas release due to widespread sill intrusions. The anomalous Hg/TOC a few millennia 30 prior to the CIE provides additional support that NAIP magmatism could have triggered a positive carbon cycle feedback, which released 13 C-depleted carbon from a surface reservoir. Evidence for elevated magmatism at the end of the CIE, however, Clim. Past Discuss., https://doi.org/10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c Author(s) 2018. CC BY 4.0 License.
highlights the relationship between postulated volcanic forcing and the climate is complex. Factors such as (sensitivity of) feedbacks in the climate system, a change in the emplacement style of the NAIP, and/or magma production rates may be key to both the onset and cessation of hyperthermal conditions during the PETM.

Supplement link (will be included by Copernicus)
Data Tables and Fur Island sampling description.

Competing interests 10
The authors declare that they have no conflict of interests.

Figure 2:
A schematic diagram (not to scale) showing the various emplacement methods of the NAIP and their control on the magnitude and distribution of Hg in the environment. A) Shallow marine eruptions lead to highly explosive Surtseyan-type volcanism, resulting in wide dispersal of tephra and Hg in the high atmosphere. Some Hg may be transferred to seawater. B) Effusive flood basalt volcanism releases Hg to the atmosphere, either the troposphere or stratosphere depending on the explosiveness of the eruption. C) Hydrothermal vent complex 5 explosions from the edges of sill intrusions in organic-rich sedimentary basins. Mercury is likely to be added to the overlying water column, but some Hg may also reach the atmosphere.
Clim. Past Discuss., https://doi.org /10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c Author(s) 2018. CC BY 4.0 License. Figure 3: Mercury (Hg), total organic carbon (TOC), Hg/TOC, and δ 13 CTOC data from sections from core 25/11-17 from the Grane Field in the Norwegian North Sea. Mercury concentrations (ppb) are shown in red, total organic carbon (TOC) concentrations (wt %) in black, Hg/TOC ratios in purple, and δ 13 C values in green. The stratigraphic log is adapted from Haaland et al. (2000). Incomplete core recovery is 5 marked by crossed squares. The grey shaded area shows the approximate onset, body, and recovery phases of the carbon isotope excursion (CIE). Identified tephra layers are shown as dark grey bands across the figure. The red dashed line in the TOC graph denotes the recommended threshold for TOC concentrations to report Hg/TOC values (Grasby et al., 2016). Clim. Past Discuss., https://doi.org/10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c Author(s) 2018. CC BY 4.0 License. Figure 4: Mercury (Hg), TOC, Hg/TOC, δ 13 CTOC, and 187 Os/ 188 Os data from sections from the BH09/2005 core from the Central Basin in Svalbard. The coloring system for Hg, TOC, Hg/TOC and δ 13 CTOC is the same as in Figure 3, while 187Os/188Os values are shown in light blue. The carbon isotope data and stratigraphic log are from Charles et al. (2011), while the Os isotope data is from Wieczorek et al. (2013).

5
The grey shaded area shows the approximate onset, body, and recovery phases of the CIE. Identified tephra layers are shown as dark grey bands across the figure. The first of the two tephra layers has been radioisotopically dated to 55.785 ± 0.086 Ma . The red dashed line in the TOC graph denotes the recommended threshold for TOC concentrations to report Hg/TOC values (Grasby et al., 2016). Clim. Past Discuss., https://doi.org/10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c Author(s) 2018. CC BY 4.0 License. Figure 5: Mercury, TOC, Hg/TOC, and δ 13 CTOC data for the outcrops on Fur Island, Denmark. The coloring system is the same as in Figure  3. The depth estimates are calibrated using the tephra layers #-34 and #-33, with the top of tephra layer #-33 set to zero. See the Supplementary data for full details. Only the body and recovery phases of the CIE are marked due to the condensed nature of the onset phase 5 (see Figure 6 for an expanded section). The stratigraphic log is based on the beach and cliff sections at Stolleklint. Boundaries between local formations are shown on the right (Heilmann-Clausen et al., 1985). Prominent tephra layers from the numbered ash series are marked with their corresponding number (Bøggild, 1918), along with the tephra layers 'SK1' and SK2' at the base of the Stolleklint Clay. The red dashed line in the TOC graph denotes the recommended threshold for TOC concentrations to report Hg/TOC values (Grasby et al., 2016).  Figure 5). The coloring scheme is the same as in Figure 3. The grey shaded area shows the approximate onset and body phases of the CIE. Tephra layers 'SK1', SK2', and 'SK3' are marked at their respective depths, along with a stratigraphic log based on the beach section at Stolleklint. The y-axis scale is the calculated depth below the top of tephra layer #-33 (see supplementary data). The red dashed line in the TOC graph denotes the recommended threshold for TOC concentrations to report Hg/TOC values (Grasby 15 et al., 2016). Samples with TOC values below this threshold were omitted from the Hg/TOC graph. Clim. Past Discuss., https://doi.org/10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c Author(s) 2018. CC BY 4.0 License. Figure 7: Mercury, TOC, Hg/TOC, and δ 13 CTOC data from the 302-4A core collected from the Lomonosov Ridge as part of the IODP Arctic Coring Expedition (ACEX). The coloring scheme is the same as in Figure 3. Incomplete core recovery is marked by crossed squares, with the middle fragment occurring at some unknown interval somewhere between the two sections of complete core recovery. The onset of the CIE is missing. The grey shaded area shows the approximate CIE body and recovery phases. Carbon isotope 5 measurements are from Sluijs et al. (2006). The stratigraphic log is from Backman et al. (2004). The red dashed line in the TOC graph denotes the recommended threshold for TOC concentrations to report Hg/TOC values (Grasby et al., 2016). Clim. Past Discuss., https://doi.org/10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c Author(s) 2018. CC BY 4.0 License. Figure 8: Mercury, TOC, Hg/TOC, and δ 13 Cbulk data from the Ocean Drilling Project (ODP) leg 174 'Bass River' locality (Cramer et al., 1999). The coloring scheme is the same as in Figure 3, with the exception of δ 13 Cbulk, which is shown as white points. The δ 13 C data and stratigraphic log are from John et al. (2008). An unconformity is found at 347.05 m.b.s. in the stratigraphy (Cramer et al., 1999). The grey shaded area shows the approximate onset, body, and recovery phases of the CIE. The red dashed line in the TOC graph denotes the 5 recommended threshold for TOC concentrations to report Hg/TOC values (Grasby et al., 2016). Samples with TOC values below this threshold were omitted from the Hg/TOC graph. Clim. Past Discuss., https://doi.org/10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c Author(s) 2018. CC BY 4.0 License. Figure 9: Mercury, TOC, Hg/TOC, δ 13 CCARB and δ 13 CTOC data from the Dababiya GSSP locality in Egypt (Keller et al., 2018). The coloring scheme is the same as in Figure 3, with the addition of δ 13 CCARB Data shown as white points. The red dashed line in the TOC graph denotes the recommended threshold for TOC concentrations to report Hg/TOC values (Grasby et al., 2016). Samples with TOC values below this threshold were omitted from the Hg/TOC graph. Yellow bands denote sections of stratigraphy heavily affected by dissolution and 5 acidification (Keller et al., 2018). Clim. Past Discuss., https://doi.org/10.5194/cp-2018-121 Manuscript under review for journal Clim. Past Discussion started: 9 October 2018 c Author(s) 2018. CC BY 4.0 License.