Combining sedimentological, trace metal (Mn, Mo) and molecular evidence for reconstructing past water-column redox conditions: The example of meromictic Lake Cadagno (Swiss Alps)

被引：61

作者：

Wirth, Stefanie B. ^{[1
]}

Gilli, Adrian ^{[1
]}

Niemann, Helge ^{[2
]}

Dahl, Tais W. ^{[3
,4
]}

Ravasi, Damiana ^{[5
]}

Sax, Nadja ^{[2
]}

Hamann, Yvonne ^{[1
]}

Peduzzi, Raffaele ^{[5
]}

Peduzzi, Sandro ^{[5
,6
]}

Tonolla, Mauro ^{[5
,6
,7
]}

Lehmann, Moritz F. ^{[2
]}

Anselmetti, Flavio S. ^{[8
]}

机构：

[1] ETH, Inst Geol, CH-8092 Zurich, Switzerland

[2] Univ Basel, Dept Environm Sci, Basel, Switzerland

[3] Univ Southern Denmark, Inst Biol, Odense, Denmark

[4] Univ Southern Denmark, NordCEE, Odense, Denmark

[5] Alpine Biol Ctr Fdn, Piora, Switzerland

[6] Inst Microbiol, Bellinzona, Switzerland

[7] Univ Geneva, Dept Bot & Plant Biol, Microbiol Unit, Geneva, Switzerland

[8] Eawag, Swiss Fed Inst Aquat Sci & Technol, Dubendorf, Switzerland

来源：

GEOCHIMICA ET COSMOCHIMICA ACTA | 2013年 / 120卷

基金：

瑞士国家科学基金会; 新加坡国家研究基金会;

关键词：

PURPLE SULFUR BACTERIA; MOLYBDENUM ISOTOPE FRACTIONATION; ORGANIC-MATTER; BIOMARKER EVIDENCE; MODERN BLACK; M A.S.L; SEDIMENTS; MANGANESE; GREEN; OCEAN;

D O I：

10.1016/j.gca.2013.06.017

中图分类号：

P3 [地球物理学]; P59 [地球化学];

学科分类号：

0708 ; 070902 ;

摘要：

Here, we present sedimentological, trace metal, and molecular evidence for tracking bottom water redox-state conditions during the past 12,500 years in nowadays sulfidic and meromictic Lake Cadagno (Switzerland). A 10.5 m long sediment core from the lake covering the Holocene period was investigated for concentration variations of the trace metals Mn and Mo (XRF core scanning and ICP-MS measurements), and for the presence of anoxygenic phototrophic sulfur bacteria (carotenoid pigment analysis and 16S rDNA real time PCR). Our trace metal analysis documents an oxic-intermediate-sulfidic redox-transition period beginning shortly after the lake formation similar to 12.5 kyr ago. The oxic period is characterized by low sedimentary Mn and Mo concentrations, as well as by the absence of any remnants of anoxygenic phototrophic sulfur bacteria. Enhanced accumulation/preservation of Mn (up to 5.6 wt%) in the sediments indicates an intermediate, Mn-enriched oxygenation state with fluctuating redox conditions during a similar to 2300-year long transition interval between similar to 12.1 and 9.8 kyr BP. We propose that the high Mn concentrations are the result of enhanced Mn2+ leaching from the sediments during reducing conditions and subsequent rapid precipitation of Mn-(oxyhydr) oxide minerals during episodic and short-term water-column mixing events mainly due to flood-induced underflows. At 9800 +/- 130 cal yr BP, a rapid transition to fully sulfidic conditions is indicated by the marked enrichment of Mo in the sediments (up to 490 ppm), accompanied by an abrupt drop in Mn concentrations and the increase of molecular biomarkers that indicate the presence of anoxygenic photosynthetic bacteria in the water column. Persistently high Mo concentrations >80 ppm provide evidence that sulfidic conditions prevailed thereafter until modern times, without any lasting hypolimnetic ventilation and reoxygenation. Hence, Lake Cadagno with its persistently stable chemocline offers a framework to study in great temporal detail over similar to 12 kyr the development of phototrophic sulfur bacteria communities and redox processes in a sulfidic environment, possibly depicting analogous conditions in an ancient ocean. Our study underscores the value of combining sedimentological, geochemical, and microbiological approaches to characterize paleo-environmental and -redox conditions in lacustrine and marine settings. (C) 2013 Elsevier Ltd. All rights reserved.

引用

页码：220 / 238

页数：19