�������� ����� ��

Redox-dependent changes in manganese speciation in Baltic Sea sedimentsfrom the Holocene Thermal Maximum: an EXAFS, XANES and LA-ICP-MSstudy

Conny Lenz, Thilo Behrends, Tom Jilbert, Miguel Silveira, Caroline P.Slomp

PII: S0009-2541(14)00045-XDOI: doi: 10.1016/j.chemgeo.2014.01.013Reference: CHEMGE 17132

To appear in: Chemical Geology

Received date: 29 July 2013Revised date: 17 January 2014Accepted date: 20 January 2014

Please cite this article as: Lenz, Conny, Behrends, Thilo, Jilbert, Tom, Silveira, Miguel,Slomp, Caroline P., Redox-dependent changes in manganese speciation in Baltic Seasediments from the Holocene Thermal Maximum: an EXAFS, XANES and LA-ICP-MSstudy, Chemical Geology (2014), doi: 10.1016/j.chemgeo.2014.01.013

This is a PDF file of an unedited manuscript that has been accepted for publication.As a service to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting, typesetting, and review of the resulting proofbefore it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers thatapply to the journal pertain.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

1

Redox-dependent changes in manganese speciation in Baltic Sea

sediments from the Holocene Thermal Maximum: an EXAFS, XANES

and LA-ICP-MS study

Conny Lenz1,2,*, Thilo Behrends2, Tom Jilbert2, Miguel Silveira3 and Caroline P. Slomp2

1Department of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden

2Department of Earth Sciences, Faculty of Geosciences, Utrecht University, P.O. Box 80.021, 3508 TA Utrecht, The Netherlands

3Katholieke Universiteit Leuven, DUBBLE beamline, ESRF, 38043 Grenoble, France

*Corresponding author

Tel.nr.: 0046 46 2227881 (C. Lenz)

e-mail addresses:

Conny.Lenz@geol.lu.se (C. Lenz)

T.Behrends@uu.nl (T. Behrends)

T.S.Jilbert@uu.nl (T. Jilbert)

Silveira.Miguel@gmail.com (M. Silveira)

C.P.Slomp@uu.nl (C.P. Slomp)

Keywords: manganese speciation, EXAFS spectrometry, sediment, anoxic basin, Baltic

Sea

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

2

Abstract

Manganese (Mn) enrichments in sediments of the deep basins of the Baltic Sea are

believed to consist of Ca-Mn-carbonates that form from Mn-oxides following periodic

inflows of oxygen-rich North Sea waters. However, a range of Mn-bearing mineral phases,

that besides Mn-carbonates (e.g. Ca-rhodochrosite), can include Mn-sulfides are known to

be present in marine sediments, with formation mechanisms that are sensitive to redox

conditions. In this study, we use high resolution synchrotron EXAFS and XANES

combined with LA-ICP-MS and micro-XRF, to investigate the nature of the Mn

enrichments in sediments from the Holocene Thermal Maximum (approx. 8000-4000 cal.

yrs BP) at a site in the northern Gotland Basin. Analyses were performed on epoxy-

embedded sediment sequences. We specifically address the role of changes in redox

conditions in bottom waters, as inferred from sediment molybdenum (Mo) contents, for

Mn sequestration. We find that an up-core increase in Mo, indicating a transition into more

anoxic and sulfidic (euxinic) bottom water conditions, is accompanied by a decline in total

sediment Mn contents. While Mn-carbonates dominate the Mn mineral fraction in the low-

Mo interval, in the more sulfidic, high Mo interval, Mn is associated with framboidal

pyrite. Mn/Fe ratios in the sulfidic interval vary between the investigated sequences but

reach values of up to 7.7 mol percent. This exceeds ratios previously reported for

sedimentary pyrite and EXAFS spectra indicate that sulfide bound Mn is predominately

tetrahedrally coordination when Mn/Fe ratios are high. This suggests that Mn is

incorporated in other Fe-S phases such as mackinawite besides pyrite. There is also

evidence for the presence of a low concentration of Mn associated with detrital

aluminosilicates throughout the investigated intervals. Our results suggest that increased

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

3

bottom water euxinia inhibited the formation of Mn-carbonate at this site during the

Holocene Thermal Maximum, possibly due to a more rapid reduction of Mn-oxides in

more sulfidic bottom waters.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

4

1. Introduction

Manganese (Mn) enrichments in sediments overlain by anoxic bottom waters are common

in many modern and ancient coastal marine basins (Calvert and Pedersen, 1993; Huckriede

and Meischner, 1996; Pedersen and Price, 1982; Russell and Morford, 2001). Typically,

these enrichments consist of authigenic Mn-carbonate phases often associated with

considerable amounts of calcium (Ca), e.g. Ca-rhodochrosite and kutnahorite (Middelburg

et al., 1987; Suess, 1979). The formation of these Mn-carbonates is thought to be related to

short oxygenation events of otherwise anoxic and Mn(II)-rich bottom waters. While Mn-

oxides are initially formed directly following such an oxygenation event, the re-

establishment of anoxia leads to their redissolution. The resulting high dissolved Mn

concentrations in high alkalinity pore waters are particularly conducive for Mn-carbonate

formation. Commonly, Mn-carbonate enrichments are taken as a good proxy for periods of

oxygenation in otherwise anoxic basins (e.g. Calvert and Pedersen, 1996; Huckriede and

Meischner, 1996). However, there are indications that formation of Mn-sulfides in the

sediment is also possible provided that Fe availability is low (Böttcher and Huckriede,

1997; Lepland and Stevens, 1998).

The Baltic Sea is one of the world´s largest present-day anoxic basins. Following its

transition from a freshwater lake to a brackish coastal system approx. 8500 cal. yr BP ago,

it has known two previous periods of extensive hypoxia. These are the Medieval Warm

Period (2000-800 cal. yr BP) and the Holocene Thermal Maximum (8000-4000 cal. yr BP)

(Zillén et al., 2008). The onset of the latter period is characterized by the intrusion of saline

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

5

waters into the previous fresh water lake resulting in major changes in biogeochemical

cycles and redox conditions. Large amounts of Mn previously bound in Mn oxides in

surface sediments (similar to the Gulf of Bothnia today (Glasby et al., 1997; Slomp et al.,

2013)) were released and Mn(II) likely became enriched in the bottom water (Sohlenius et

al., 2001).

Analyses of total Mn in discrete samples for two sites in the euxinic basins in the Baltic

Sea suggest that more Mn was buried in the sediment during the initial phase of the

Holocene Thermal Maximum than in the later stages (Jilbert and Slomp, 2013). While Mn-

carbonate layers are visible in the sediment as distinct white layers during this initial phase

(Sohlenius et al., 2001), the possible contribution of Mn associated with sulfide phases and

detrital minerals such as clays to total Mn is as yet unclear. To probe the redox state and

binding form of Mn in solids X-ray absorption spectroscopy can be used. X-ray absorption

near edge structure (XANES) can be used to deduce the oxidation state of Mn and to

identify Mn minerals based on the comparison with reference spectra. The redox state of

Mn may be derived from the shape of the X-ray absorption feature before the Mn K-edge

(pre-edge feature)(Chalmin et al., 2009), from the position of the Mn K-edge and the

maximum absorption feature (Bargar et al., 2000; Manceau et al., 2012; Schulze et al.,

1995). The coordination environment of Mn is reflected in the extended X-ray absorption

fine structure (EXAFS). EXAFS spectra have been used to identify Mn phases in soils and

sediments (Friedl et al., 1997; Manceau and Gallup, 2005). Modeling of EXAFS provides

information on the short-range structure of Mn phases (Manceau and Combes, 1988) and

has been applied in the field of Earth Sciences in multiple cases (Bargar et al., 2005;

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

6

Grangeon et al., 2010; Jürgensen et al., 2004; McKeown and Post, 2001; Silvester et al.,

1997; Villalobos et al., 2003; Webb et al., 2005). In heterogeneous samples, the spatial

distribution of Mn species has been determined on a micrometer scale by EXAFS and

XANES analyses by applying an X-ray micro beam (Bargar et al., 2009; Pecher et al.,

2003). The relative concentration of different Mn phases in mixed samples can be obtained

by linear combination fitting of XANES or EXAFS spectra (e.g. Bargar et al., 2000).

In this study, we investigate the distribution and speciation of Mn in sediments deposited

in the northern Gotland Basin during the Holocene Thermal Maximum. Special attention is

given to the identification of different Mn species in the sediment using EXAFS and

XANES. To our knowledge, this is the first time these techniques are used to study the

geochemistry of Mn in marine sediments. Insight in the environmental conditions during

the formation of the various sediment Mn phases is obtained using high resolution laser

ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), micro-XRF

mapping and geochemical analyses of discrete sediment samples. We identified Mn

carbonate as the dominate feature controlling Mn distributions with depth in the sediment.

However, with increasing euxinia, Mn sequestration in the form of carbonate is diminished

and, although less abundant, Mn associated with Fe-sulfide becomes the dominate phase.

Mn associated with aluminosilicates is present as a third Mn-phase at low background

concentrations.

2 Materials and Methods

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

7

2.1 Sediment sampling and analysis

A gravity core was recovered from station LL19 (20.3108E 58.8807N) in the Northern

Gotland Basin in June 2009 with R/V Aranda. Sediment sections were sampled from the

core using 20 cm long aluminum trays and the sediment was embedded in Spurr´s epoxy

resin using the method of (Jilbert et al., 2008), but without desalinisation as described by

(Jilbert and Slomp, 2013). The resulting sediment blocks were cut perpendicular to the

plane of sedimentation and the surface was polished. Two blocks were selected for further

analysis in this study, Block 14 covers 290.87 to 292.36 cm sediment depth and Block 22

reaches from 313.28 to 314.685 cm.

The remaining sediment was sampled at 1 cm resolution in a glovebox under nitrogen,

freeze dried and ground. To determine the total organic carbon (TOC) content, 0.5 g of

each sample was treated with 1 M HCl (one rinse of 12 hours, followed by addition of new

HCl and a second rinse of 4 hours) to remove inorganic carbon. After ovendrying at 60°C

and grinding, TOC was measured with a Fisons NA 1500 NCS analyzer. Precision

(≤0.1‰) and accuracy were established using international (Graphite quartzite standard

NAXOS (GQ)), and in-house standards (Ammonium Sulphate (ASS), Acetanilide, and

Atropine). Another subsample of 0.1 g was used for a total destruction with a mixture of

2.5 ml HF and 2.5 ml HClO4/HNO3 in closed Teflon bombs at 90°C. The acid was

evaporated and the remaining gel was redissolved in 1M HNO3. The resulting solution was

analyzed for manganese (Mn), calcium (Ca), iron (Fe), sulfur (S) and molybdenum (Mo)

using ICP-OES. Relative precision (<5%) and accuracy were established by duplicates and

standards (ISE-921).

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

8

2.2. µXRF and LA-ICP-MS

The resin embedded sediment blocks were mounted in an EDAX Orbis Micro XRF

Analyzer (Rh tube at 30 kV, 500 µA, no filter, 300 ms dwell time). The distribution of Mn,

Fe and S in 1.5 cm x 0.5 cm areas of the blocks was mapped at a resolution of 30µm. The

blocks were subsequently analyzed by laser ablation - inductively coupled plasma - mass

spectrometry (LA-ICP-MS) line scanning. A 193 nm laser beam (Lambda Physik, pulse

repetition 10 Hz, spot diameter 120 µm, energy density 8 Jcm-2) was focused onto the

surface of the sediment block in a sealed ablation chamber on a motorized stage. The stage

was then set in steady motion with a velocity of 0.0275mm/s perpendicular to the plane of

lamination, resulting in an overlapping series of ablation craters. Ablated sample material

was transported by He-Ar carrier gas to a Thermo Element 2 ICP-MS, where aluminum

(27Al), iron (57Fe), manganese (55Mn), sulfur (34S), bromine (81Br) and molybdenum (98Mo)

were measured. LA-ICP-MS data for each element were calibrated by reference to the

sensitivities (counts/ppm) of the glass standard NIST SRM 610 (Jochum et al., 2011) and

corrected for the natural abundances of the analyzed isotopes. All data are reported

normalized to Al to correct for variations in sample yield during laser ablation. For S/Al

data, a further sensitivity factor wapplied which compensates for the contrasting relative

yield of S from NIST SRM 610 with respect to embedded sediments.

2.3 Synchrotron EXAFS and XANES

X-ray absorption and fluorescence was measured at the DUBBLE beamline at the ESRF

(BM26A). The layout of the beamline and the X-ray optics are described by (Borsboom et

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

9

al., 1998) and (Nikitenko et al., 2008). Vertical X-ray fluorescence profiles and XAS

spectra were collected with a focused beam to a spot of about 30 µm diameter by using

polycapillary optics or with a vertically focused beam to an horizontal line of 6.0 x 0.4

mm. Due to the lower photon flux upon using polycapillary optics, EXAFS spectra were

only collected with a vertically focused beam. X-ray absorption was measured in

fluorescence mode using a 9-element Ge-detector. For recording the vertical element

profiles, a Vortex silicon drift detector was applied. XAS spectra were processed using the

Athena software 0.8.61 (Ravel and Newville, 2005) and Artemis 0.8.14 was used to fit the

EXAFS spectra. Details about the EXAFS fitting are given in the supplementary content.

Principal component analysis (PCA) and iterative target transformation factor (ITFA)

analysis on all normalized XANES spectra were performed with the ITFA software

(Rossberg et al., 2003). For the statistical analysis, the energy range 6530-6620 eV was

used. The ITFA analysis requires that the relative concentration of each component is

constrained in at least one sample. For this, the spectra having the highest loading of the

respective component were assumed to contain only this component.

3 Results

3.1. Sediment geochemistry

The interval of laminated sediments corresponding to the Holocene Thermal Maximum

(HTM) in the Baltic Sea (Zillén et al., 2008) is identified in the LL19 core as a series of

Corg enrichments between 265 cm and 345 cm depth (Fig. 1). S and Mo contents show

similar profiles to that of Corg, implying low-oxygen conditions at times of high Corg burial

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

10

(Sohlenius et al., 2001). Sequences of high Mn enrichments are found in the lower part of

this interval (Mn >1%, 315 to 345 cm), whereas the upper part has lower Mn contents (Mn

<1%, 265 to 315 cm) (Fig. 1). Many of the individual Mn peaks correspond to peaks in Ca,

suggesting the presence of Ca-rhodochrosite in these layers.

The two sections from the HTM interval selected for high resolution analyses have

contrasting characteristics with respect to both Mn contents and redox conditions. One

section represents a marked transition from high to low Mn contents associated with an

increase in organic C, S and Mo (Block 22; Fig. 1). The second section was retrieved from

the upper part of the profile in a zone without pronounced Mn enrichments, but with high

organic C, S and Mo contents (Block 14; see Fig. 1). Micro-XRF maps of these two

sections further illustrate their contrasting composition (Fig. 2). Block 22 is characterized

by massive Mn-rich layers in the lower part, and Mn, S and Fe laminations in the upper

part. Block 14 has homogeneous Mn-poor sediments in the lower part, and Mn, S and Fe

laminations in the upper part.

High resolution LA-ICP-MS profiling of Block 14 shows generally low Mn concentrations

(Fig. 3). However, enrichments of Mn in this interval correlate with Fe, S and Mo (Fig. 3).

These enrichments follow the visible laminations in the sediments, with interchanging

black and grey layers. A similar pattern of Mn, Fe, S and Mo-rich laminations can also be

recognized in the upper laminated part of Block 22 (Fig. 3). Although Mn and Fe are

correlated in the laminated parts of both blocks, the Mn/Fe ratio is higher in the upper part

of Block 22 than in Block 14 (7.7 versus 3.4 mol %, respectively; Fig. S1 in

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

11

supplementary content). In contrast, the lower part of Block 22 is characterized by

exceptionally high Mn concentrations, which are not related to Fe, S and Mo. These

pronounced enrichments of Mn were visually recognizable as white layers, indicating the

presence of rhodochrosite.

3.2 Manganese speciation (synchrotron XAS)

Principal component analysis indicates that three XANES spectra are sufficient to

reproduce the main features of all collected sample spectra (Fig. 4). Using ITFA analysis,

three end-member spectra were extracted. One of the spectra (component 1) was identical

to the spectrum of the rhodochrosite reference (Fig. 4). The two other end-member spectra

(component 2 and component 3) did not show close similarity with any of the measured

references. The relative contribution of the three components to the individual spectra can

be used to infer the relative concentration of the respective Mn species.

Component 1 was the dominant Mn species in the lower part of Block 22 (Fig. 3). Elevated

Mn concentrations coincided with high concentrations of component 1, in accordance with

the expectation that the white layers with high Mn concentrations contain rhodochrosite. In

the laminated parts of Block 22 and in the whole of Block 14, rhodochrosite (component 1)

was almost absent, while components 2 and 3 became the abundant species (Fig. 3).

Since the spatial resolution achievable with the regular beam was insufficient to investigate

the very high resolution details of vertical profiles of the three components, focused beam

profiles were collected from Block 22 for this purpose (Fig. 5). One profile was collected

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

12

from the Mn-poor upper part of the block (Fig. 5a), and two profiles were collected from

the Mn-rich lower part (Fig. 5b, c). The relative importance of the three components varies

with depth in each focused-beam profile. In the laminated sediments of the upper part of

the block, component 1 (rhodochrosite) is absent and component 2 and 3 alternate as

dominant species (Fig. 5a). In the lower part of the block, rhodochrosite is the dominant

component in the layers with highest Mn concentrations (Fig. 5b,c). These rhodochrosite

layers appear to be preceded by intervals of high relative abundance of component 2.

Intervals with high relative concentrations of component 3 are present in the lower part of

the block (Fig. 5b, c) but are not observed directly adjacent to rhodochrosite layers.

Changes in the relative concentration of individual components do not necessarily coincide

with changes in their absolute concentration. For example, while the relative importance of

component 2 varies considerably, the absolute concentration remains almost constant

(Figs. 3, 5). This suggests that component 2 represents detrital Mn deposited at a constant

rate irrespective of the environmental regime. In contrast, component 3 exhibits high

relative concentrations when its absolute concentration is high in the laminated sequences

(Figs. 3, 5). This implies that the absolute concentration of component 3 follows the total

Mn concentration in the laminated intervals, which, in turn, is correlated to Fe, S and Mo.

Hence, component 3 likely reflects Mn species deposited in environments characterized by

oxygen depletion. As mentioned previously, component 1 (identified as rhodochrosite) is

the dominate species in the white layers and therefore, the total concentration of

component 1 follows the total Mn concentrations in these layers.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

13

Analyses of EXAFS spectra indicate that component 2 and 3 represent Mn coordinated

with O and S, respectively. EXAFS spectra collected from spots with high relative

abundance of component 2 or 3 could be reproduced using a model with O and S in the

first coordination shell (Fig. 6) but only when including both elements. In this model,

component 2 reflects Mn octahedrally bound to O, and component 3 Mn associated with S.

Values of the optimized fitting parameters are listed in table 1 and details of the fitting

procedure are described in the supplementary content.

4 Discussion

4.1 Identification of Mn species by XANES/EXAFS

Our XANES results indicate that component 1 is rhodochrosite. EXAFS spectra collected

on spots with high concentrations of component 1 also show great similarity with those of

rhodochrosite (data not shown). Rhodochrosite has been found in a range of marine

sedimentary environments (Calvert and Pedersen, 1993) and is commonly observed in

sediments of various deep basins of the Baltic Sea, such as the Gotland Deep and Landsort

Deep (Huckriede and Meischner, 1996; Jakobsen and Postma, 1989; Lepland and Stevens,

1998; Sternbeck and Sohlenius, 1997). In all cases, rhodochrosite precipitation requires a

high Mn(II) concentration and high alkalinity, allowing supersaturation. In the Baltic Sea,

these conditions are commonly achieved following massive Mn-oxide deposition during

inflows of oxic, saline water into the deep basins (Huckriede and Meischner, 1996;

Neumann et al., 1997; Sohlenius et al., 1996; Sternbeck and Sohlenius, 1997).

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

14

Component 2 most likely reflects a detrital aluminosilicate Mn pool. This is motivated by

the constant concentrations of component 2 in the high resolution profiles (Figs. 3, 5). The

XANES spectrum of component 2 extracted by ITFA analysis (Fig. 6) has two pronounced

maxima (state energies) and has similarities with spectra of synthetic richterite with an

average Mn valence state of 2.5 (richterite #1 (Chalmin et al., 2009)). The XANES

spectrum of component 2 is similar to Mn XANES spectra collected from estuarine

sediments which have been attributed to Mn in detrital phyllosilicates and oxide minerals

(Carroll et al., 2002). It is possible that the extracted spectrum does not originate from one

mineral phase but is a combination of two or more spectra from Mn-containing minerals,

which are deposited contemporaneously and in a constant ratio throughout the investigated

sequences. Fitting of the EXAFS spectra points towards an octahedral coordination of Mn

with O in component 2. A contribution of Mn-oxides to the extracted spectrum of

component 2 is very unlikely due to the differences in the shape of the pre-edge, main edge

position, and the shape of the XANES spectrum (Fig. 4). Comparison of the pre-edge of

component 2 with reference spectra indicates that component 2 contains predominantly

Mn(II). Quantitative analyses of the pre-edge to infer precisely the Mn(II) to Mn(III) ratio

as described by (Chalmin et al., 2009) could not be performed as the quality of the spectra

around the pre-edge was insufficient for quantitative deconvolution. In conclusion,

concentration profiles in combination with the interpretation of XANES and EXAFS

spectra indicate that component 2 represents the Mn aluminosilicate fraction.

Mn in component 3 is associated with sulfides and this Mn pool accounts for Mn burial

under euxinic conditions. Analysis of EXAFS spectra indicates that Mn is coordinated with

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

15

S in component 3. Authigenic formation of Mn-sulfide under euxinic condition has been

reported for the Baltic Sea (Baron and Debyser, 1957; Böttcher and Huckriede, 1997;

Lepland and Stevens, 1998; Suess, 1979). The extracted XANES spectrum of component

3, however, cannot be matched with spectra of pure Mn-sulfides. Instead, the strong

correlation with Fe and S (Fig. 3) suggests that component 3 represents Mn co-precipitated

with Fe-sulfides. The dominant Fe-sulfide phase in the laminated part of the blocks seems

to be framboidal pyrite. Scanning electron micrographs show layers enriched with electron

dense spherical aggregates with diameters between 1-5 µm (Fig. S2 and S3 in

supplementary content). These aggregates consist of smaller particles, which is typical for

the morphology of framboidal pyrite (Wilkin and Barnes, 1997). This interpretation is

supported by energy dispersive X-ray (EDX) spectroscopy, demonstrating that the

spherical particles consist predominately of Fe and S (Fig. S4). Enrichments of Mn in the

laminated part of the block concur with these particles suggesting that the sulfide bound

Mn is associated with the framboidal pyrite aggregates (Fig. S3).

Although the sulfide coordinated Mn seems to co-occur with framboidal pyrite, not all of

the Mn might isomorphically substitute Fe in the pyrite structure. Isomorphic replacement

of Fe by Mn has been described for sedimentary pyrite but reported Mn to Fe ratios are

lower than the Mn to Fe ratio in the laminated part of Block 22. Shikazono et al. (1994)

compiled reported Mn/Fe ratios in pyrite which are typically below 2 Mol % with one

exception of high ratios between 2-8 Mol % measured in one core by Huerta-Diaz and

Morse (1992). Jacobs et al. (1985) determined Mn/ Fe ratios roughly between 2.5 and 3 %

in framboidal pyrite from a permanent anoxic basin in Norway. These values are

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

16

comparable to the Mn/Fe ratios in Block 14 (Fig. S1 supplementary material) while those

in Block 22 around 7.7 Mol % exceed all reported values considerably. This suggests that

part of the Mn does not replace structural Fe in pyrite (Fleischer, 1955).

Fitting of EXAFS spectra support the suggestion that part of the sulfide bound Mn is not

incorporated into the pyrite structure. Optimized Mn-S distances of around 2.3 Å, obtained

from EXAFS fitting, are close to the Fe-S distance of mackinawite (2.26 Å) but longer

than that of pyrite (2.2 Å). At one spot where the contribution of component 3 to the

EXAFS spectrum is relatively high (LL19 22 313.3704 cm), the optimized degeneracy of

the Mn-S path proposes that Mn is tetrahedrally coordinated with S (Tab. 1). A larger

coordination number is obtained when fitting the spectrum with low content of component

3 (LL19 14 290.964 cm, Tab. 1) but due to the low concentration of component 3 at this

spot, the value for the coordination number is only weakly constrained. Hence, component

3 might comprise sulfidic Mn in different phases and coordination environments. In pyrite,

Mn is octahedrally coordinated with S while in mackinawite Fe is tetrahedrally

coordinated. Consequently, when Mn/Fe ratios are high, substitution of Fe by Mn in

mackinawite seems to be more prevalent than in pyrite when comparing these two

authigenic Fe-S minerals. When Mn/Fe ratios are high in sedimentary pore waters,

precipitating mackinawite can contain a few mole percent MnS (Arakaki and Morse,

1993). However, further research is required to unequivocally identify the Mn bearing

phase in these sediments.

4.2 Temporal variability in the deposition of manganese species

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

17

In the lower part of the HTM interval at LL19, Mn concentrations are relatively high,

while Corg, S and Mo concentrations are relatively low (Fig. 1). In the upper part of the

HTM interval, the opposite is true; namely, Corg, S and Mo concentrations are relatively

high, while Mn concentrations fall to very low values. The profile of total Mn is primarily

determined by the distribution of rhodochrosite.

Rhodochrosite deposition in the Baltic Sea occurs following inflow events in the deep

anoxic basins (Burke and Kemp, 2002; Huckriede and Meischner, 1996; Neumann et al.,

1997; Scholz et al., 2013; Sohlenius et al., 1996; Sternbeck and Sohlenius, 1997). Our data

clearly indicate that during the most severe reducing conditions in the upper part of the

HTM interval, rhodochrosite precipitation at site LL19 was negligible. There are several

possible explanations for this observation.

Firstly, a reduced frequency of inflow events could explain the lack of rhodochrosite. The

frequency of inflow events at LL19 may well have varied during the HTM due to isostatic

changes in the depth of the Danish Straits (Gustafsson and Westman, 2002) and associated

changes in the paleo-depth of the Northern Gotland basin. However, we do not expect that

the inflow frequency was greatly reduced, as reduced inflows would be expected to

decrease the stratification of the water column (Conley et al., 2002; Fonselius, 1981) and

hence improve ventilation, whereas our proxies suggest highly reducing conditions (Fig.

1).

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

18

Second, the lower rhodochrosite content of the upper HTM interval could be related to a

declining availability of Mn in the water column relative to the lower HTM interval. The

availability of Mn for rhodochrosite precipitation in Baltic Sea sediments is expected to

have been at a maximum immediately following the Ancylus-Littorina transition. At the

time, large areas of the seafloor that were likely rich in Mn oxides were covered by low

oxygen waters resulting in large-scale release of Mn(II) and widespread precipitation of

rhodochrosite (Sohlenius et al., 2001). Hence, during the lower HTM interval, inflow

events caused relatively intense accumulations of rhodochrosite, burying a large amount of

Mn into the sediments, potentially lowering the supply of Mn for further precipitation

during the upper HTM. However, this would require very efficient removal of Mn from the

water column and there is no evidence that Mn-carbonate formation has such strong impact

on water column chemistry. In the present day Baltic Sea, for example, Mn-carbonate

precipitation has not led to major changes in Mn(II) in the water column on the time scale

of decades (e.g. Pohl and Hennings, 2005).

A third possible explanation for low rhodochrosite contents in the upper HTM interval is

that inflow events continued to precipitate Mn oxides, but that these were either

redissolved before conversion to rhodochrosite, or resuspended after conversion by

turbulent near-bottom processes, and thus dissolved (e.g. Heiser et al., 2001). The more

reducing conditions may have increased the rate of reduction of Mn oxides by hydrogen

sulfide, in the upper sediments at the onset of a stagnation period. By this mechanism, Mn

oxides deposited during inflows may have been efficiently removed and subsequently

released as Mn(II) before substantial conversion to rhodochrosite could occur.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

19

5 Conclusions

In this study, the speciation of Mn in Baltic Sea sediments from the Holocene Thermal

Maximum (HTM) is investigated. Three major groups of Mn phases are identified. The

most abundant Mn species is Mn-carbonate. Its occurrence is restricted to the lower part of

the studied sequence, where Mn contents are highest and where low organic C, S and Mo

contents indicate relatively oxic conditions. These Mn-carbonates are present as distinct

white layers and are formed following inflow events of oxygenated North Sea water as

described by Huckriede and Meischner (1996). Further up core our results show laminated

sediments with high contents of Corg, S and Mo indicating more reducing conditions. In

this environment the major Mn species, although less abundant than the Mn-carbonate at

greater depth, is Mn bound in Fe-sulfides. Electron microscopy indicates that this Mn is

enriched in aggregates of framboidal pyrite. The tetrahedral coordination given by the

EXAFS spectra of the Mn Fe-sulfide species, however, suggests that in addition to pyrite

other Fe-S minerals such as mackinawite might host Mn. The third Mn-species consists of

Mn-alumino-silicate and is present at a constant background concentration. We have

reviewed the various possible explanations for the lack of Mn-carbonate formation with

increasingly reducing conditions during the HTM and conclude that increased rates of Mn

oxide reduction linked to the more sulfidic bottom water conditions are likely responsible.

Acknowledgements

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

20

We thank the staff of the Dubble beamline for their support and Prof. Dr. Laszlo Vince

from the University Gent, Belgium, for providing us the polycapillary optics. The

performance of the experiment at the ESRF was financially supported by The Netherlands

Organization for Scientific Research, NWO (experiment 26-01-909). Additional funding

was provided by Utrecht University (via UU short stay fellowship 2011), the EU-BONUS

project HYPER, NWO (Vidi), and the European Research Council under the European

Community’s Seventh Framework Programme for ERC Starting Grant #278364. Dr.

Oliver Plümper performed the electron microscopy analyses and we are grateful for his

support. We thank the captain and crew of RV Aranda and all participants of the cruise to

the Baltic Sea in 2009 for their assistance with the field work.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

21

References

Arakaki, T. and Morse, J.W., 1993. Coprecipitation and adsorption of Mn(II) with mackinawite

(FeS) under conditions similar to those found in anoxic sediments. Geochimica et Cosmochimica Acta, 57(1): 9-14.

Bargar, J.R. et al., 2009. Structural characterization of terrestrial microbial Mn oxides from Pinal Creek, AZ. Geochimica et Cosmochimica Acta, 73(4): 889-910.

Bargar, J.R. et al., 2005. Biotic and abiotic products of Mn(II) oxidation by spores of the marine

Bacillus sp. strain SG-1. The American mineralogist, 90(1): 143-154. Bargar, J.R., Tebo, B.M. and Villinski, J.E., 2000. In situ characterization of Mn(II) oxidation by

spores of the marine Bacillus sp. strain SG-1. Geochimica et Cosmochimica Acta, 64(16): 2775-2778.

Baron, G. and Debyser, J., 1957. Sur la presence dans les vases organiques de la mer Baltique du

sulfure manganeux b hexagonal. CR Acad. Sci. Paris, 245: 1148-1150. Borsboom, M. et al., 1998. The Dutch-Belgian beamline at the ESRF. Journal of Synchrotron

Radiation, 5(3): 518-520. Böttcher, M.E. and Huckriede, H., 1997. First occurrence and stable isotope composition of

authigenic γ-MnS in the central Gotland Deep (Baltic Sea). Marine Geology, 137(3): 201-

205. Burke, I.T. and Kemp, A.E., 2002. Microfabric analysis of Mn-carbonate laminae deposition and

Mn-sulfide formation in the Gotland Deep, Baltic Sea. Geochimica et Cosmochimica Acta, 66(9): 1589-1600.

Calvert, S. and Pedersen, T., 1993. Geochemistry of recent oxic and anoxic marine sediments:

Implications for the geological record. Marine Geology, 113(1): 67-88. Calvert, S. and Pedersen, T., 1996. Sedimentary geochemistry of manganese; implications for the

environment of formation of manganiferous black shales. Economic Geology, 91(1): 36-47.

Carroll, S., O'Day, P.A., Esser, B. and Randall, S., 2002. Speciation and fate of trace metals in

estuarine sediments under reduced and oxidized conditions, Seaplane Lagoon, Alameda Naval Air Station(USA). Geochemical Transactions, 3(10): 81.

Chalmin, E., Farges, F. and Brown Jr, G., 2009. A pre-edge analysis of Mn K-edge XANES spectra to help determine the speciation of manganese in minerals and glasses. Contributions to

Mineralogy and Petrology, 157(1): 111-126.

Conley, D.J., Humborg, C., Rahm, L., Savchuk, O.P. and Wulff, F., 2002. Hypoxia in the Baltic Sea and Basin-Scale Changes in Phosphorus Biogeochemistry. Environmental science &

technology, 36(24): 5315-5320. Fleischer, M., 1955. Minor elements in some sulfide minerals. Econ. Geol, 50(970): 1024.

Fonselius, S., 1981. Oxygen and hydrogen sulphide conditions in the Baltic Sea. Marine Pollution Bulletin, 12(6): 187-194.

Friedl, G., Wehrli, B. and Manceau, A., 1997. Solid phases in the cycling of manganese in

eutrophic lakes: New insights from EXAFS spectroscopy. Geochimica et Cosmochimica Acta, 61(2): 275-290.

Glasby, G. et al., 1997. Environments of formation of ferromanganese concretions in the Baltic Sea: a critical review. Manganese mineralization: Geochemistry and mineralogy of

terrestrial and marine deposits(119): 213-237.

Grangeon, S., Lanson, B., Miyata, N., Tani, Y. and Manceau, A., 2010. Structure of nanocrystalline phyllomanganates produced by freshwater fungi. The American mineralogist, 95(11-12):

1608-1616. Gustafsson, B.G. and Westman, P., 2002. On the causes for salinity variations in the Baltic Sea

during the last 8500 years. Paleoceanography, 17(3).

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

22

Heiser, U., Neumann, T., Scholten, J. and Stüben, D., 2001. Recycling of manganese from anoxic sediments in stagnant basins by seawater inflow: A study of surface sediments from the

Gotland Basin, Baltic Sea. Marine Geology, 177(1): 151-166. Huckriede, H. and Meischner, D., 1996. Origin and environment of manganese-rich sediments

within black-shale basins. Geochimica et Cosmochimica Acta, 60(8): 1399-1413. Huerta-Diaz, M.A. and Morse, J.W., 1992. Pyritization of trace metals in anoxic marine sediments.

Geochimica et Cosmochimica Acta, 56(7): 2681-2702.

Jacobs, L., Emerson, S. and Skei, J., 1985. Partitioning and transport of metals across the O2H2S interface in a permanently anoxic basin: Framvaren Fjord, Norway. Geochimica et

Cosmochimica Acta, 49(6): 1433-1444. Jakobsen, R. and Postma, D., 1989. Formation and solid solution behavior of Ca-rhodochrosites in

marine muds of the Baltic deeps. Geochimica et Cosmochimica Acta, 53(10): 2639-2648.

Jilbert, T., de Lange, G. and Reichart, G.-J., 2008. Fluid displacive resin embedding of laminated sediments: preserving trace metals for high-resolution paleoclimate investigations.

Limnology and Oceanography-Methods, 6: 16-22.

Jilbert, T. and Slomp, C.P., 2013. Iron and manganese shuttles control the formation of authigenic

phosphorus minerals in the euxinic basins of the Baltic Sea. Geochimica et Cosmochimica Acta, 107: 155-169.

Jochum, K.P. et al., 2011. Determination of reference values for NIST SRM 610–617 glasses

following ISO guidelines. Geostandards and Geoanalytical Research, 35(4): 397-429.

Jürgensen, A. et al., 2004. The structure of the manganese oxide on the sheath of the bacterium

Leptothrix discophora: An XAFS study. The American mineralogist, 89(7): 1110-1118. Lepland, A. and Stevens, R.L., 1998. Manganese authigenesis in the Landsort Deep, Baltic Sea.

Marine Geology, 151(1): 1-25.

Manceau, A. and Combes, J.M., 1988. Structure of Mn and Fe oxides and oxyhydroxides: A

topological approach by EXAFS. Physics and Chemistry of Minerals, 15(3): 283-295.

Manceau, A. and Gallup, D.L., 2005. Nanometer-sized, divalent-Mn, hydrous silicate domains in geothermal brine precipitates. The American mineralogist, 90(2-3): 371-381.

Manceau, A., Marcus, M.A. and Grangeon, S., 2012. Determination of Mn valence states in mixed-

valent manganates by XANES spectroscopy. The American mineralogist, 97(5-6): 816-

827.

McKeown, D.A. and Post, J.E., 2001. Characterization of manganese oxide mineralogy in rock varnish and dendrites using X-ray absorption spectroscopy. The American mineralogist, 86(5-6): 701-713.

Middelburg, J.J., De Lange, G.J. and van Der Weijden, C.H., 1987. Manganese solubility control in marine pore waters. Geochimica et Cosmochimica Acta, 51(3): 759-763.

Neumann, T., Christiansen, C., Clasen, S., Emeis, K.-C. and Kunzendorf, H., 1997. Geochemical records of salt-water inflows into the deep basins of the Baltic Sea. Continental Shelf Research, 17(1): 95-115.

Nikitenko, S. et al., 2008. Implementation of a combined SAXS/WAXS/QuEXAFS set-up for time-resolved in situ experiments. Journal of Synchrotron Radiation, 15: 632-640.

Pecher, K. et al., 2003. Quantitative charge state analysis of manganese biominerals in aqueous suspension using scanning transmission X-ray microscopy (STXM). Geochimica et

Cosmochimica Acta, 67(6): 1089-1098. Pedersen, T. and Price, N., 1982. The geochemistry of manganese carbonate in Panama Basin

sediments. Geochimica et Cosmochimica Acta, 46(1): 59-68.

Pohl, C. and Hennings, U., 2005. The coupling of long-term trace metal trends to internal trace metal fluxes at the oxic–anoxic interface in the Gotland Basin (57° 19, 20′ N; 20° 03, 00′

E) Baltic Sea. Journal of Marine Systems, 56(1): 207-225. Ravel, B. and Newville, M., 2005. ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray

absorption spectroscopy using IFEFFIT. Journal of Synchrotron Radiation, 12(4): 537-541.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

23

Rossberg, A., Reich, T. and Bernhard, G., 2003. Complexation of uranium (VI) with protocatechuic acid—application of iterative transformation factor analysis to EXAFS

spectroscopy. Analytical and bioanalytical chemistry, 376(5): 631-638. Russell, A.D. and Morford, J.L., 2001. The behavior of redox-sensitive metals across a laminated–

massive–laminated transition in Saanich Inlet, British Columbia. Marine Geology, 174(1–4): 341-354.

Scholz, F., McManus, J. and Sommer, S., 2013. The manganese and iron shuttle in a modern

euxinic basin and implications for molybdenum cycling at euxinic ocean margins. Chemical Geology, 355(0): 56-68.

Schulze, D.G., Sutton, S.R. and Bajt, S., 1995. Determining manganese oxidation state in soils using X-ray absorption near-edge structure (XANES) spectroscopy. Soil Science Society of America journal. Soil Science Society of America, 59(6): 1540-1548.

Shikazono, N., Nakata, M. and Tokuyama, E., 1994. Pyrite with high Mn content from the Nankai Trough formed from subduction-induced cold seepage. Marine Geology, 118(3–4): 303-

313.

Silvester, E., Manceau, M. and Drits, V.A., 1997. Structure of synthetic monoclinic Na-rich

birnessite and hexagonal birnessite: II. Results from chemical studies and EXAFS spectroscopy. The American mineralogist, 82: 962-978.

Slomp, C.P. et al., 2013. Coupled dynamics of iron and phosphorus in sediments of an oligotrophic

coastal basin and the impact of anaerobic oxidation of methane. PLoS One, 8(4): e62386.

Sohlenius, G., Emeis, K.C., Andren, E., Andren, T. and Kohly, A., 2001. Development of anoxia

during the Holocene fresh-brackish water transition in the Baltic Sea. Marine Geology, 177(3-4): 221-242.

Sohlenius, G., Sternbeck, J., Andrén, E. and Westman, P., 1996. Holocene history of the Baltic Sea

as recorded in a sediment core from the Gotland Deep. Marine Geology, 134(3): 183-201.

Sternbeck, J. and Sohlenius, G., 1997. Authigenic sulfide and carbonate mineral formation in

Holocene sediments of the Baltic Sea. Chemical Geology, 135(1-2): 55-73. Suess, E., 1979. Mineral phases formed in anoxic sediments by microbial decomposition of organic

matter. Geochimica et Cosmochimica Acta, 43(3): 339-352.

Villalobos, M., Toner, B., Bargar, J. and Sposito, G., 2003. Characterization of the manganese

oxide produced by pseudomonas putida strain MnB1. Geochimica et Cosmochimica Acta,

67(14): 2649-2662. Webb, S.M., Tebo, B.M. and Bargar, J.R., 2005. Structural characterization of biogenic Mn oxides

produced in seawater by the marine bacillus sp. strain SG-1. The American mineralogist,

90(8-9): 1342-1357. Wedepohl, K., 1971. Environmental influences on the chemical composition of shales and clays.

Physics and Chemistry of the Earth, 8: 305-333. Wilkin, R.T. and Barnes, H.L., 1997. Formation processes of framboidal pyrite. Geochimica et

Cosmochimica Acta, 61(2): 323-339.

Zillén, L., Conley, D.J., Andrén, T., Andrén, E. and Björck, S., 2008. Past occurrences of hypoxia in the Baltic Sea and the role of climate variability, environmental change and human

impact. Earth-Science Reviews, 91(1): 77-92.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

24

Figures

Figure 1 Discrete-sample chemical profiles in a section of the gravity core from site LL19.

The section spans the entire interval of widespread hypoxic conditions in the Baltic Sea

during the Holocene Thermal Maximum (approx. 8000-4000 yr. BP) as indicated by the

grey bar. The position of the two epoxy resin blocks used in the EXAFS, XANES, micro-

XRF and LA-ICP-MS analyses are show by dark grey bars (showing true thickness of

blocks).

Figure 2 Micro XRF maps (1.5 to 0.5 cm) of epoxy embedded sediments showing the

distribution of Mn, Fe and S for Block 14 and Block 22. Greyscale intensity within each

map is internally proportional to XRF counts, but relative scaling has been modified to

highlight features.

Figure 3 Downcore variations in Mn, Fe, S, Mo, and Br (normalized to Al) from LA-ICP-

MS measurements (in %/%)(maximum values indicated at peak cutoff). The dashed line in

the first column displaying the Mn/Al represents the average shale content (Wedepohl,

1971). Columns 6 and 7 show the distribution of the three components identified from the

PCA of the XANES spectra. Column 6 is the relative contribution of a component to total

manganese content and column 7 is the concentration of each component in the sediments,

in arbitrary units. Grey bars indicate laminated sediment. In Block 22, sections for very

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

25

high resolution synchrotron radiation analyzes shown in figure 5 appear as dark grey bars,

which reflect the true thickness of the analyzed sections.

Figure 4 Spectra of the three components obtained from iterative target transformation

factor analysis in comparison to normalized XANES spectra of different reference

materials.

Figure 5 High resolution LA-ICP-MS data for Mn, Fe, S, Mo and Br (normalized to Al in

%/%) of three selected sections within Block 22 (see Fig. 3). Columns 6 and 7 give the

relative contribution of component 1, 2 and 3 to total Mn, and their concentration in

arbitrary units, respectively. The last column displays the XANES spectra (hollow circles

show the actual spectra and the black line is the reproduction using the three components).

Figure 6 Results from fitting the EXAFS spectra and the contribution of the O and S shells.

Information about the fitting can be found in the supplementary content.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

26

Figure 1

360

320

280

De

pth

be

low

se

dim

en

t su

rfa

ce (

cm)

0 2 4 6 8 10

Corg (%)

0 1 2

Mn (%)

0 0.8 1.6

Ca (%)

0 2 4 6 8

Fe (%)

0 1 2 3 4 5

S (%)

0 200

Mo (ppm)

Block 14

Block 22

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

27

Figure 2

SFeMnMn Fe S

313.6

314

314.4

291.2

291.6

292

De

pth

(c

m)

Block 14 Block 22

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

28

Figure 3

314.4

314

313.6

De

pth

(cm

)

0 0.4 0.8

Mn/Al0 0.8 1.6

Fe/Al0 0.4

S/Al0 0.008

Mo/Al0 0.008

Br/Al0 0.4 0.8

rel. conc.0 0.4 0.8

conc.

[arbit. unit]

Block 22

292

291.6

291.2

De

pth

(cm

)

0 0.05 0.1

Mn/Al0 0.8 1.6

Fe/Al0 0.4

S/Al0 0.008

Mo/Al0 0.008

Br/Al0 0.4 0.8

rel. conc.0 0.16

conc.

[arbit. unit]

comp 1 comp 2 comp 3laminations

Block 14

Fig. 5a

b

c

0.120.016

0.02

3.48 1.09

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

29

Figure 4

6540 6560 6580 6600 6620

energy [eV]

no

rma

lize

d µ

(E)

6530 6540 6550 6560 6570

energy [eV]

de

riva

tive

no

rma

lize

d µ

(E)

component 1

component 2

component 3

rhodochrosite

alabandite

rambergite

Mn phosphate

hausmannite

bixbyite

pyrolusite

birnesite

component 1

component 2

component 3

rhodochrosite

alabandite

rambergite

Mn phosphate

hausmannite

bixbyite

pyrolusite

birnesite

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

30

Figure 5

314.48

314.47

314.46

314.45

314.44

De

pth

(cm

)

0 0.2Mn/Al

0 0.6 1.2Fe/Al

0 0.4S/Al

0 0.004Mo/Al

0 0.004Br/Al

0 0.40.8rel.conc.

0 0.16conc.

[arbit. unit]

6540 6560 6580 6600 6620

energy (eV)

c,

b,

6540 6560 6580 6600 6620

energy (eV)

313.74

313.72

313.70

De

pth

(cm

)

0 0.16Mn/Al

0 0.6 1.2Fe/Al

0 0.4S/Al

0 0.004Mo/Al

0 0.004Br/Al

0 0.40.8rel.conc.

0 0.08conc.

[arbit. unit]

a,

6540 6560 6580 6600 6620

energy (eV)

313.48

313.46

De

pth

(cm

)

0 0.16Mn/Al

0 0.6 1.2Fe/Al

0 0.4S/Al

0 0.004Mo/Al

0 0.004Br/Al

0 0.40.8rel. conc.

0 0.08conc.

[arbit. unit]

comp 3comp 2comp 1

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

31

Figure 6

2 4 6 8 10 12

k[Å-1]

χ(k

)*k

3

0 1 2 3 4 5

R[Å]

Iχ(R

)I [Å

-4]

0 1 2 3 4 5

R[Å]

Re

{χ(R

)} [Å

-4]

313.3704 cmfit

290.964 cmfit

290.964 cmfit

313.3704 cmfit

313.3704 cmfit

290.964 cmfit

O

O

O

O

O

O

S

S

S

S

S

S

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

32

Table 1 Parameters of the Mn-O and Mn-S paths obtained from modeling the EXAFS

spectra. The spot LL19 14 (290.964 cm) contained 19% of component 3 and the spot LL19

22 (313.3704 cm) 56 % of component 3 according to the ITFA analysis. N reflects the

coordination number, Rfit the distance between Mn and the ligand, and σ 2 is the mean-

square displacement of the half-path length. The values in parenthesis indicate the

coordination number with oxygen of component 1 and with sulfur of component 3. Note

that only the uncertainty due to the fitting itself is given in the table. The overall

uncertainty of the coordination number of component 3 also includes the error of

estimating its relative concentration in the sample. Assuming that the error of the ITFA

analysis is about ± 5%, the uncertainty becomes ± 5.2 for the spectrum from block LL19

14 (290.964 cm) and ± 1.2 for block LL19 22 (313.3704 cm). Details about the modeling

of EXAFS spectra can be found in the supplementary content.

Path LL19 14 (290.964 cm) LL19 22 (313.3704 cm) N Rfit[Å] σ2[10-

3Å2] N Rfit[Å] σ2[10-3Å2]

Mn -> O 4.9 (6) 2.18±0.02 3.1±1.4 2.6 (6) 2.12±0.02 3.1±1.4 Mn -> S 1.7

(8.9±2.9) 2.28±0.03 3.1±1.4 2.3 (4.1±0.8) 2.31±0.01 3.1±1.4

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

33

Highlights

Mn contents in the northern Gotland Basin vary during the Holocene Thermal Maximum.

In these sediments, three major Mn species are identified.

Mn-carbonates are most abundant and are restricted to relatively oxic conditions.

Mn is bound in Fe-sulfides when conditions are anoxic and sulfidic.

Mn bound in aluminosilicates is present at a constant but low background content.