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SUMMARY:EESS talk on "Chromium cycling in euxinic basins: Implications for
  the δ53Cr paleoredox proxy from a modern system (Lake Cadagno\, TI)"
DTSTART:20220405T121500
DTEND:20220405T131500
DTSTAMP:20260921T115831Z
UID:af22fae8d836d7e93331846e8b9761d964f66e98825ff0354acc2f59
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr David Janssen\, Group Leader Tenure Track\, Department Surf
 ace Waters Research & Management\, EAWAG\nAbstract:\nDissolved chromium co
 ncentrations ([Cr]) and stable isotope distributions (δ53Cr) are sensitiv
 e to redox cycling due to variable solubilities of the oxidized and reduce
 d forms of Cr (Cr(VI) and Cr(III)\, respectively)\, and the large isotope 
 fractionations associated with redox interconversions. This redox control 
 of both [Cr] and δ53Cr has driven significant interest in Cr records as a
  potential paleoredox proxy. In addition\, due to the toxicity of Cr(VI)\,
  this redox control on Cr mobility has informed strategies for Cr remediat
 ion efforts. Interpretations of Cr proxy data in the sediment record and s
 trategies for Cr remediation rely on the general geochemical assumption th
 at reducing conditions should result in enhanced reduction and removal iso
 topically light Cr into sediments\, affecting the dissolved Cr pool accord
 ingly. However\, few data from natural modern systems with anoxia are avai
 lable for a direct assessment of this framework. With this motivation\, I 
 present water column and near-surface sediment δ53Cr and [Cr] in the mero
 mictic Lake Cadagno (Ticino\, Switzerland)\, which has been used as a mode
 rn analog for low-sulfate\, euxinic oceanic conditions throughout Earth’
 s history. In Lake Cadagno\, the euxinic monimolimnion is enriched in [Cr]
  relative to overlying oxic waters\, in contrast to expectations from Cr(V
 I) and Cr(III) solubility. This general trend of [Cr]euxinic > [Cr]oxic is
  supported by the limited data available from other anoxic systems (e.g. o
 ceanic inlets and mediterranean seas). While dissolved δ53Cr in euxinic w
 ater column samples is isotopically light relative to overlying oxic water
 s\, deep waters are isotopically heavy relative to sediments. Furthermore\
 , sediment δ53Cr is indistinguishable from average upper continental crus
 t δ53Cr\, and therefore do not record isotope fractionation due to intens
 e redox cycling. These data have important implications for [Cr] and δ53C
 r paleoproxy applications – namely that Cr may not be efficiently seques
 tered into sediments in euxinic systems\, and that reconstructions of wate
 r column δ53Cr from euxinic sediments may require additional corrections\
 , which are unconstrained at present. In addition\, the accumulation and m
 obility of Cr(III) in reducing systems has implications for contaminant re
 mediation efforts\, indicating that efficient Cr reduction alone may be in
 sufficient for Cr sequestration.\n\nShort biography:\nDr. David Janssen fi
 rst began researching aqueous geochemistry during his BSc in Chemistry at 
 Humboldt State University (Ca\, USA)\, where he studied contaminant metals
  in a constructed wetlands treatment system. He conducted his PhD at the U
 niversity of Victoria in BC\, Canada with Dr. Jay Cullen\, focusing on the
  distributions of Zn and Cd in the subarctic northeast Pacific Ocean. Afte
 r briefly working for Fisheries & Oceans Canada on long-term environmental
  monitoring projects\, David began a postdoc at the University of Bern in 
 fall 2017\, working with Dr. Samuel Jaccard\, investigating Cr cycling in 
 the ocean and the potential paleoproxy applications of Cr stable isotopes.
  In October 2021 David started as a tenure track group leader in aqueous g
 eochemistry\, where his research group focuses on the distributions\, tran
 sport and availability of toxin and micronutrient metals\, and the emergin
 g potential of metal stable isotopes as paleoproxies.
LOCATION:GC B1 10 https://plan.epfl.ch/?room==GC%20B1%2010 https://epfl.zo
 om.us/j/66723503475
STATUS:CONFIRMED
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