Climate-Associated Changes in Mercury Sources in the Arctic Fjord Sediments

Abstract

Despite the large climatic fluctuations in the Arctic over the Holocene, the dominant mercury (Hg) sources and the potential changes in Hg sources associated with the climate remain unclear. Here, we use Hg isotopes to reconstruct changes in Hg sources and processes in two Svalbard fjord sediment cores spanning the Holocene. The Hg isotope ratios of the fjord sediment cores are similar to bedrock and Hg bound to terrestrial total organic carbon (TOC) but different from other sediment cores influenced by atmospheric Hg drawdowns via the sinking of marine particulate organic matter. The absence of significant Hg and TOC relationships indicates that bedrock erosion caused by glacier dynamics is the major Hg source to the fjord sediment rather than those bound to marine and terrestrial TOC. Measurable shifts in Hg sources are observed at regional cooling (4.3 ka) and during the Medieval Warm Period in the late Holocene. The negative shift in δ202Hg (by −0.5‰) at 4.3 ka from baseline (∼10 ka) is consistent with the rapid increase in glacier-mediated physical and chemical erosions of bedrock. The significant positive shifts in δ202Hg (by 0.5‰) in the late Holocene are explained by enhanced input of atmospheric Hg and its drawdown via the sinking of marine particulate organic matter and some anthropogenic influence, which suppressed the positive Δ199Hg and Δ200Hg shifts. This study suggests that Hg isotope ratios measured in sedimentary archives can be used to decipher climate and other local to global changes modifying Hg sources in the Arctic.

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

“…The typical internal precisions of Hg isotope ratios (e.g., 202 Hg/ 198 Hg) were ≤ 0.04‰ (1SE) for individual analysis. The means and uncertainties of Hg isotope ratios of NIST SRM-8610, TORT-3, DORM-4, MESS-4, NIST SRM-2702, and NIST SRM-1944 were listed in Table S3, which were consistent with the previously reported values [15][16][17][18][19] .…”

“…The Hg isotope ratios of the secondary standard NIST SRM-8610 and procedural CRMs analyzed during different analytic sessions agreed with those reported in previous studies (Table S3). ,− The typical 2σ analytic uncertainties of samples were estimated as larger 2SD uncertainties of Hg isotope ratios between NIST SRM-8610 and procedural CRMs (DORM-4 and TORT-3 for biota; MESS-4, NIST SRM-2702, and NIST SRM-1944 for sulfides). The 2SE uncertainties of Hg isotope ratios in samples with replicate analyses were applied as analytic uncertainties only when they were larger than the typical 2σ analytic uncertainties …”