Riverine Fe input is the primary Fe source for the ocean.
This study is focused on the distribution of Fe along the Lena River
freshwater plume in the Laptev Sea using samples from a 600 km long transect
in front of the Lena River mouth. Separation of the particulate
(>0.22µm), colloidal (0.22 µm–1 kDa), and truly
dissolved (<1 kDa) fractions of Fe was carried out. The total Fe
concentrations ranged from 0.2 to 57 µM with Fe dominantly as
particulate Fe. The loss of >99 % of particulate Fe and about
90 % of the colloidal Fe was observed across the shelf, while the truly
dissolved phase was almost constant across the Laptev Sea. Thus, the truly
dissolved Fe could be an important source of bioavailable Fe for plankton in
the central Arctic Ocean, together with the colloidal Fe. Fe-isotope
analysis showed that the particulate phase and the sediment below the Lena
River freshwater plume had negative δ56Fe values (relative to
IRMM-14). The colloidal Fe phase showed negative δ56Fe values
close to the river mouth (about -0.20 ‰) and positive
δ56Fe values in the outermost stations (about
+0.10 ‰).
We suggest that the shelf zone acts as a sink for Fe particles and colloids
with negative δ56Fe values, representing chemically reactive
ferrihydrites. The positive δ56Fe values of the colloidal
phase within the outer Lena River freshwater plume might represent Fe
oxyhydroxides, which remain in the water column, and will be the predominant
δ56Fe composition in the Arctic Ocean.
Introduction
The cycling of Fe is a key component for understanding water quality and
biogeochemical processes. Iron is the fourth most abundant element in the
continental crust (Wedepohl, 1995). The concentration in seawater is low
compared to riverine input (Martin and Gordon, 1991). The riverine input of
Fe is one of the most important contributions to the oceanic Fe budget, as
well as aeolian dust, recycled sediment, subglacial and iceberg meltwater,
and hydrothermal fluxes (Raiswell and Canfield, 2012). Estimations of
filterable Fe (<0.45µm) fluxes to the global ocean reveal
that about 140 of a maximum of 4800 Gg yr-1 is delivered by rivers (de
Baar and de Jong, 2001; Tagliabue et al., 2010). Particulate Fe supplied by
rivers to the oceans is 3 orders of magnitude higher than filterable Fe
(Martin and Meybeck, 1979). Iron behaves non-conservatively during the
mixing of freshwater and seawater and is removed to sediments (Boyle et al.,
1977; Eckert and Sholkovitz, 1976; Gustafsson et al., 2000; Sholkovitz,
1978, 1976), since Fe-rich particles and colloids flocculate and settle in
this mixing zone (Sholkovitz, 1978).
It has been recognized that dissolved Fe is related to dissolved organic
carbon (DOC) in freshwater (Perdue et al., 1976) and so, to investigate the
pathways for organic carbon (OC) in the Arctic, knowledge about Fe cycling
and the coupling between the boreal–Arctic watershed and the Arctic basin is
crucial. Iron and OC in water samples can be separated using a variety of
filtration techniques. These include both membrane filtration (0.22 to
0.7 µm) and ultrafiltration (1, 10, or 30 kDa) and size fractions
are thus often operationally defined as particulate matter (larger than
0.22 or 0.7 µm), colloidal (smaller than particles but do
not pass an ultrafilter), and truly dissolved phases (passing through an
ultrafilter). Due to the technical complexity with ultrafiltration,
including the extensive filtration time, there are few ultrafiltration Fe
data available (Guo and Santschi, 1996; Ingri et al., 2000; Pokrovsky et al.,
2012). Truly dissolved Fe data are scarce and deliver insights into this
part of the Fe pool.
Previous studies showed that there is a relationship between Fe and OC in
the dissolved fraction and found two main forms of Fe compounds: Fe–OC and
Fe oxyhydroxides (Escoube et al., 2015; Hirst et al., 2017b; Ilina et al.,
2013; Ingri et al., 2006, 2000; Kritzberg et al., 2014; Pokrovsky et al.,
2010, 2006; Pokrovsky and Schott, 2002; Raiswell and Canfield, 2012; Stolpe
et al., 2013). It has also been shown that humic substances (HSs) are
associated with newly formed Fe oxyhydroxides in freshwater (Pédrot et
al., 2011; Tipping, 1981). The behaviour of these Fe and OC particles and
colloids during estuarine mixing depend on their chemical reactivity, which
is defined by their size and speciation (Poulton and Raiswell, 2005;
Tagliabue et al., 2017). Hirst et al. (2017b) found that about 70 % of the
total suspended Fe in the Lena River is in the form of reactive
ferrihydrite. These ferrihydrites are independent particles within a network
of amorphous particulate OC (POC) and are attached to the surfaces of
primary organic matter and clay particles (Hirst et al., 2017b).
Carbon–iron cycling is complex, and stable Fe-isotope data show that the
isotopic compositions might be used to investigate chemical pathways for Fe
and Fe bound to OC during weathering and estuarine mixing in the
boreal–Arctic region (Dos Santos Pinheiro et al., 2014; Escoube et al.,
2015, 2009; Ilina et al., 2013; Ingri et al., 2006; Mulholland et al., 2015;
Poitrasson, 2006; Poitrasson et al., 2014). The 56Fe/54Fe and
57Fe/54Fe ratios are defined relative to the international
reference material IRMM-14 and are expressed as deviations from the standard
in parts per thousand, or δ notation (in per mille
‰), as
δ56Fe=56Fe/54Fesample56Fe/54FeIRMM-14-1×103δ57Fe=57Fe/54Fesample57Fe/54FeIRMM-14-1×103.
Using this definition, the continental crust has a δ56Fe value
of 0.07±0.02 ‰ (Poitrasson, 2006). In low-temperature
environments the δ56Fe can vary by about 5 ‰ (Anbar,
2004; Beard et al., 2003; Fantle and DePaolo, 2004; Rouxel et al., 2005). The
variations in δ56Fe can be used to trace different Fe phases
in rivers (Dos Santos Pinheiro et al., 2014; Ilina et al., 2013; Ingri et
al., 2006; Poitrasson et al., 2014) and to map the origin of Fe (Conway and
John, 2014). Isotope fractionation processes result in a δ56Fe value that can be higher or lower compared to the continental crust.
The Fe-isotopic composition is impacted by redox reactions (Wiederhold et
al., 2006), complexation with organic ligands, and inorganic speciation of
Fe, as well as the immobilization of Fe by precipitation and adsorption
(Beard et al., 2003, 1999; Beard and Johnson, 2004; Brantley et al., 2001;
Bullen et al., 2001; Icopini et al., 2004; Poitrasson and Freydier, 2005;
Skulan et al., 2002; Welch et al., 2003). These processes can yield either
negative or positive δ56Fe values, depending on the initial
Fe-isotopic composition and the fractionation factor. Recent studies showed
that sub-Arctic and temperate rivers, with high Fe and OC concentrations,
have low δ56Fe values in the particulate phase, while the
dissolved phase has high δ56Fe (Escoube et al., 2015, 2009;
Ilina et al., 2013; Ingri et al., 2006; Rouxel et al., 2008; Severmann et
al., 2006). Also, high δ56Fe values have been reported in the
low molecular weight (LMW) fraction (<10 kDa), while colloids and
particles showed high δ56Fe values (Ilina et al., 2013).
Furthermore, seasonal variations in the Fe-isotopic composition and Fe
speciation have been reported (Allard et al., 2004; Escoube et al., 2015;
Ingri et al., 2006).
This study presents Fe concentrations and Fe-isotope compositions in the
particulate and colloidal phase along the Lena River freshwater plume in the
Laptev Sea, as well as Fe concentrations in the truly dissolved phase. The
Lena River–Laptev Sea transect is stratified, with a freshwater layer that
is on top of more saline, dense, deep waters and plays an important role in
the transport of Fe and the distribution of Fe isotopes in the Arctic Ocean.
The main objectives were to study the distribution of Fe in the Lena
River–Laptev Sea transect and the variations in the partitioning of Fe
between the different size fractions, as well as to identify the impact of
processes such as mixing, transformation, and removal by settling on the
export of Fe to the deeper ocean. Furthermore, Fe-isotope analysis of the
colloidal and particulate fraction should help us to gain a better
understanding of the composition of Fe particles and colloids transported out
in the Arctic Ocean.
Sampling site and analytical methodsStudy area
The Lena River is 4387 km long and has the eighth largest discharge in
the world. It is the second largest river draining into the Arctic Ocean
and flows into the Laptev Sea (Fig. 1). The Lena watershed covers an area of
2.46×106 km2 (Rachold et al., 1996) and is bound by the
Verkhoyansk Mountain Ridge in the northeast and the central Siberian uplands
in the west. Larch forests cover 72 % of the watershed area and shrublands
about 12 % (Wagner, 1997; Walter and Breckle, 2002). Permafrost underlies
78 %–93 % of the watershed (Zhang et al., 1999) and extends to depths of up
to 1500 m (Anisimov and Reneva, 2009). The annual discharge to the Arctic
Ocean is 581 km3 (Yang et al., 2002). During the spring flood, from late May to
June, 31 %–45 % of the annual run-off occurs (Amon et al., 2012). The Lena
River delivers 5.6–5.8 Tg of DOC into the Arctic Ocean annually (Holmes et
al., 2012; Raymond et al., 2007), along with about 0.4 Tg of particulate OC
(Semiletov et al., 2011). More than 50 % of the total OC (TOC) is
delivered during a 2-month period in summer, with 6.6 Tg yr-1 in
June (Le Fouest et al., 2013) and 3.5 Tg yr-1 in July (Kutscher et
al., 2017). The run-off from the Lena River accounts for more of 70 % of
the overall river inflow to the Laptev Sea (Antonov, 1967). The freshwater
plume in the Laptev Sea is a mixing zone of about 600 km length and 50 km
width (Fig. 2). A low-salinity freshwater plume overlies denser highly saline
Arctic seawater (Alling et al., 2010). The Lena River plume can be divided
into an inner and an outer plume based on a sharp increase in salinity, with
salinities up to 5 in the inner plume and up to 15 in the outer plume
(Alling et al., 2010). Both parts of the plume are separated by a strong
halocline at about 10 m depth from the underlying dense Arctic seawater
that has salinities up to 35 (Alling et al., 2010; Chester, 2003; Martin et
al., 1993).
Sampling stations in the Arctic Ocean. Black dots mark the
stations on the detailed East Siberian Arctic Shelf map. Along the Lena
River–Laptev Sea transect, membrane filtration and/or ultrafiltration was
carried out. The sampling stations of this study follow the Lena River
freshwater plume. The green numbers display δ56Fe values measured
in the uppermost sediment.
Sampling and processing
The samples were collected in August 2008 during the International Siberian
Shelf Study (ISSS-08) from the RV Yacob Smirnitskyi. The ISSS-08 was part of
the International Polar Year (IPY) and the Arctic GEOTRACES programmes. The
sampling transect is 600 km long, stretching from off the Lena River mouth
across the Laptev Sea, and samples from ten stations were collected after
the GEOTRACES protocol (Figs. 1 and 2 and Table 1), (Cutter et al., 2010).
Additionally, surface sediment (upper 2 cm) samples were taken from the
Kara, Laptev, and East Siberian seas (Fig. 1). Samples from this region
collected during this cruise have also been studied for DOC (Alling et al.,
2010; Bröder et al., 2016; Karlsson et al., 2016; Salvadó et al.,
2017), dissolved inorganic carbon (Alling et al., 2012), POC (Karlsson et
al., 2016; Sánchez-García et al., 2011), nutrients and alkalinity
(Anderson et al., 2009; Pipko et al., 2017), and stable O isotopes
(Rosén et al., 2015).
The salinity gradient along the Lena River–Laptev Sea transect.
Salinity is based on the Practical Salinity Scale PSS-78. The freshwater
builds an almost 10 m thick surface layer in the Laptev Sea, and the plume
itself extends over an area of about 50×600 km. The plume is divided
into an inner and outer plume between stations YS-8 and YS-11 by a sharp
increase in salinity.
Sampling stations in the Laptev Sea of the ISSS-08 research cruise.
Temperature, salinity, pH, and oxygen data for the Lena River freshwater
plume are obtained from water at a depth of 4 m, whereas the data for the
shelf sediment sample locations are obtained from the overlying bottom
waters. The measurements were done with a CTD Seabird 19+. Salinity is
based on the Practical Salinity Scale PSS-78.
a Station was also sampled for surface sediment.
b Salinity, pH, and oxygen saturation for shelf sediment samples
are measured in bottom water. c Measured with a Hydrosonde M5.
All water samples besides YS-14 were collected between 2.5 and 5.0 m depth
using a peristaltic pump and acid-cleaned, silicon tubing. The tubing was
attached to a flagpole, which was mounted to the bow of the ship. To avoid
contamination from the ship, the flagpole was extended about 10 m in front
of the ship. The samples were pumped into a 25 L container, which was rinsed
with Milli-Q water between each station. Station YS-14 was sampled at 4.0 m
depth using a 60 L Go-Flo® water sampler.
All equipment in contact with the samples were cleaned with 5 %
HNO3, rinsed with Milli-Q water, and dried in a HEPA-filtered
clean-air hood. Membrane filtration was carried out within 12 h of sampling.
All water samples were stored in acid-cleaned polyethylene (PE) bottles and
acidified with ultrapure HNO3 to a pH < 2, and all nitrocellulose
filters (0.22 µm, Millipore®)
were stored at -18∘C until further analysis (Ödman et al.,
1999). Samples for POC were filtered with 0.7 µm GF/F glass-fibre filters
(Whatman®). The filters were pre-combusted
for 4 h at 450 ∘C to limit the C blank.
Sediment samples were taken with a GEMAX gravity corer and a Van Veen grab
sampler as described earlier (Vonk et al., 2012).
During cross-flow ultrafiltration the sample water (<0.22µm)
flows across a membrane surface at a constant pressure. This process prevents
clogging, while particles
smaller than the membrane cut-off can pass, larger suspended particles remain
circulating in the sample water. The sample water progressively decreases in
volume as the permeate crosses the filter, and the larger colloids and
particles remain in the retentate, which is therefore progressively concentrated. The cross-flow ratio
(CFR =QR/QP, where QR and
QP are the flow rates of the retentate and permeate,
respectively) (Forsberg et al., 2006; Ingri et al., 2000; Larsson et al.,
2002) was kept between 60 and 100 to achieve an overall concentration factor
larger than 10: (VP+VR)/VR, where
VP and VR are the final volumes of the permeate and
retentate, respectively. For the concentration factors and cross-flow ratios;
see Table 2. In this study, the water used for ultrafiltration was
pre-filtered through a membrane (<0.22µm) prior to introduction
into the MilliPore® Prep/Scale
ultrafiltration system, which had a cut-off of 1 kDa. Thus, the permeate is
<1 kDa, while the retentate includes colloids between <0.22µm and 1 kDa.
Iron concentrations and isotopic compositions were measured at ALS
Scandinavia AB. All sample manipulations were performed in a clean laboratory
(class 10 000) by personnel wearing clean-room gear and following all
general precautions to reduce contamination (Rodushkin et al., 2010).
High-purity Suprapure® acids were used
throughout sample treatment and analysis. Organic carbon analyses were
carried out at Stockholm University (for analytical details; see Alling et
al., 2010; Sánchez-García et al., 2011).
For element analysis, the water samples (colloidal: 1 kDa to
0.22 µm; truly dissolved: <1 kDa) were diluted (2–200 fold)
with 10 % HNO3. The degree of dilution was dependent on the
salinity of the sample. At least two dilutions of each sample were carried
out: one high dilution for determination of major elements and one low
dilution for minor and trace elements. For Fe analysis, the samples were
diluted by a factor of 50. In order to analyse the particles on the filters,
the filters were treated with a 1000:1 mixture of HNO3:HF
overnight, followed by closed-vessel microwave-assisted digestion. Prior to
analysis, the digests were further diluted in 10 % HNO3.
Multi-elemental analysis of the water and filter samples was performed on an
inductively coupled plasma sector field mass spectrometer (ICP-SFMS, ELEMENT2
Thermo Scientific) at ALS Scandinavia AB. The measurement procedure combines
internal standardization and external calibration. For internal
standardization, indium was added to all the solutions (Rodushkin et al.,
2005; Rodushkin and Ruth, 1997). The analytical procedure was validated with
different reference materials (SLRS-4 river water CRM for trace metals,
SLEW-2 estuarine water CRM for trace metals, and NASS-4 open ocean water – all
supplied from National Research Council, Ottawa, Canada) (Rodushkin et al.,
2005, 2016).
The blanks of digested filters (0.22 µm) for Fe were
2.79 µg L-1, which is about
0.25 % of the average Fe concentration in the samples for the Lena River
sampling transect. Replicated measurements of sample concentrations showed a
precision of ±3 % (n=4). The limit of detection for Fe in seawater
(salinity 35) is 250 ppt, the salinity levels in the analysed samples were much
lower, which decreases the limit of detection. Fe concentrations for the
particulate, colloidal, and truly dissolved phases are reported in Table 3.
Aluminum and titanium concentrations can be found in the Supplement.
For the Fe-isotope ratio measurements, water samples (colloidal: 1 kDa to
0.22 µm) and digested filters were evaporated to dryness, and the
residue was redissolved in 1 mL 9 M HCl. Iron was separated from the
matrix elements by using an AG-MP-1M ion-exchange resin (Ingri et al., 2006;
Rodushkin and Ruth, 1997). After the sample was loaded, the matrix was washed
with 9.6 M HCl, and Cu was eluted with 8 mL 5 M HCl. Afterwards, Fe was
eluted with 6 mL 2 M HCl and can be used for further steps (Rodushkin et
al., 2016). After evaporating to dryness, 50 µL of concentrated
HNO3 was pipetted directly to the residue, followed by the addition
of 5 mL of Milli-Q water. Samples with high Fe content were diluted with
0.2 M HNO3 to a concentration of 2 mg L-1 in the
measurement solutions. Low Fe concentration water samples were further
diluted to 40–50 µg L-1 and measured using high-efficiency
desolvation nebulizer (Aridus) in a separate analytical sequence. Iron was
separated from the matrix by ion exchange, with a recovery rate above
95 %. The Fe-isotope compositions in separated fractions from filters and
water samples were measured using a multicollector inductively coupled
plasma mass spectrometer (MC-ICP-MS, NEPTUNE
PLUS®, Thermo Scientific) equipped with
micro-concentric nebulizer and tandem cyclonic Scott double-pass spray
chamber. Instrumental mass biases were corrected by sample-standard
bracketing using IRMM-14 CRM, while an internal standard (Ni) was added to
all samples and used to correct for instrumental drift. Each sample was
measured twice with the sample-standard bracketing method. Detailed
information on the correction procedures can be found in Baxter et
al. (2006). During the Fe-isotope analysis, δ56Fe and
δ57Fe were measured. In the three-isotope plot of
δ56Fe and δ57Fe, all samples are plotted on a single
mass fractionation line (Fig. S1 in the Supplement). We only discuss the δ56Fe
in this study, although all Fe-isotope data are reported in Table 4, including
2σ (n=4).
Results
The average pH for the water samples was 7.6±0.1 (1 SD) and the oxygen
saturation was 99.4±2.1 % (Table 1), (Andersson and Jutterstrøm,
2008). Within the Lena River freshwater plume the pH ranged from 7.5 to 7.9.
The methodology for pH and oxygen measurements is described in the Supplement
(after Dudarev, 2008).
Organic carbon distributions in the Lena River plume
The DOC concentrations show a small variation between 320 and
442 µM in the surface waters of the inner and outer plume (Table 1;
Fig. 3). The average DOC concentration of 410 µM in the surface
water of the Lena River freshwater plume has been reported by Alling et
al. (2010) and is similar to previous studies (Cauwet and Sidorov, 1996:
300–600 µM). It has been shown that DOC is behaving conservatively
during mixing between Lena River water and Arctic Ocean water along the
sampling profile (Alling et al., 2010; Opsahl et al., 1999; Pugach et al.,
2018). The POC concentrations decrease from high values (89 µM)
close to the coast to low values (8 µM) in the outer plume
(Fig. 3). In the inner plume (YS-14 to YS-10) the POC concentrations are
high, between 89 and 36 µM, whereas in the outer plume the POC
concentrations were almost constant, with an average value of about 12 µM.
The overall average POC concentration of about 28 µM has
been reported earlier by Sánchez-García et al. (2011).
Dissolved (<0.70µm) and particulate (>0.70µm) organic carbon concentrations along the Lena River–Laptev
Sea transect. Close to the Lena River mouth, POC constitutes about 18 % of
the TOC input, while at the outermost station it is only 2 % of the TOC.
Iron concentrations in the Lena River freshwater plume
Three size fractions were analysed for Fe: particulate Fe (PFe; >0.22µm), colloidal Fe (CFe; 1 kDa–0.22 µm), and truly
dissolved Fe (DFe; <1 kDa). The total Fe (TFe) concentration was
calculated as the sum of PFe, CFe, and DFe (Table 3).
Iron concentrations of the different fractions for the Lena River
freshwater plume.
Total Fe is calculated as a sum of particulate, colloidal, and truly dissolved Fe.
The PFe concentration decreased from 56 to 0.1 µM along the Lena
River freshwater plume (Fig. 4). Between the inner and the outer plumes (i.e.
between YS-11 and YS-8), the PFe concentration dropped to 0.9 µM, with a
loss of >99 % of PFe. The loss of Fe was estimated as a fraction of the
maximum Fe concentration of each size fraction (details can be found in the
Supplement). The CFe concentration decreased from 0.6 to 0.1 µM
along the freshwater plume, a loss of about 90 % CFe (Fig. 4). The
concentration of DFe was low, at around 8 nM, and relatively constant along
the plume (Fig. 4). In total, a loss of >99 % TFe was observed between
the first station (YS-14) and the last station (YS-128).
Total, colloidal, and truly dissolved Fe concentrations along the
Lena River freshwater plume. Concentrations of PFe and CFe decreased along
the salinity gradient, while the concentrations of DFe are almost constant.
Note the logarithmic scale and the sharp decrease in PFe between the inner
and the outer plume. The reference for the Lena River is an average of all
analysed samples (PFe n=3; CFe and DFe n=5) by Hirst et
al. (2017b).
We observed non-conservative behaviour of PFe during mixing between Lena
River water and Arctic Ocean water, while CFe showed generally conservative
behaviour, with an almost linear correlation with salinity (Fig. 5). The PFe
concentrations below 1 µM also showed an almost linear correlation
at salinities above 5 in the outer plume. In the inner plume, at salinities
below 5, the PFe showed non-conservative behaviour.
The colloidal and particulate Fe concentrations plotted vs.
salinity. Salinity is based on the Practical Salinity Scale PSS-78. Note the
y-axis break due to the high range of PFe in the inner plume. The linear
correlation between PFe and salinity is based on the data points below
1 µM PFe. In the low-salinity environment, the PFe is much higher
compared to the CFe, whereas at salinities above 5 the differences are
smaller.
Iron isotopes in the Lena River freshwater plume
The Fe-isotope compositions in the particulate and the colloidal phases, as
well as in the surface sediments, are reported in Fig. 6. The δ56Fe values in the particulates varied between -0.05±0.11 ‰ (YS-14) in the inner plume and -0.41±0.12 ‰
(YS-4) in the outer plume (Fig. 6), with the δ56Fe values in
the outer plume all lower compared to the inner plume. The CFe show negative
δ56Fe values (average -0.20±0.06 ‰) in the
inner plume and positive δ56Fe values (average 0.11±0.08 ‰) in the outer plume. The surface sediments from the Laptev
Sea had negative δ56Fe values (-0.23±0.08 ‰
and -0.25±0.12 ‰). Surface sediments obtained from 10 samples
in other parts of the East Siberian Arctic Shelf (ESAS) showed only small
variations (Figs. 1 and 6; Tables 4 and S2 in the Supplement).
Iron-isotope values along the Lena River freshwater plume and the
uppermost sediment of the East Siberian Arctic Shelf (ESAS). The error bars
represent ±2σ. In some cases the symbol is larger than the
error. The δ56Fe values of PFe are negative at all stations:
values close to zero are closer to the coast and more negative ones are towards the open
sea. The δ56Fe values of the CFe are negative in the inner
plume and positive in the outer plume. The δ56Fe of the
sediment samples were around -0.2 ‰, displaying the
overall composition of the entire ESAS area.
Fe-isotope data for the particulate and the colloidal phase as
well as Fe-isotope data for the surface sediments.
In the Laptev Sea, close to the river mouth, about 18 % of the total OC was
present as POC and this was apparently rapidly lost during mixing (Fig. 3).
In the outer plume only about 2 % of the total OC was present as POC. It
has been suggested that POC in the Lena River freshwater plume is transported
in different forms, including large particles, which can sink, and almost
neutrally buoyant flocculates of humic substances (Gustafsson and Gschwend,
1997; Gustafsson et al., 2000; Sánchez-García et al., 2011). The
POC, which is associated with larger particles (>0.7µm), will
settle close to land, whereas the humic substance flocculates will travel
further out (Vonk et al., 2010).
Iron behaviour in the Lena River freshwater plume
The PFe concentrations found in the Laptev Sea close to the shore are higher
than the average PFe concentration in the Lena River but similar to the
highest PFe river values up to 32 µM (Hirst et al., 2017b). The CFe
and DFe in the Lena River (Hirst et al., 2017b) showed higher average
concentrations (CFe: 1.5 µM; DFe: 54 nM) than concentrations found
in the Lena River–Laptev Sea transect. Most likely some of the CFe and DFe
from the Lena River already flocculated at salinities below 1, where the
first sample of our sampling profile was taken (YS-14). Within the Arctic
Ocean, dissolved Fe (CFe + DFe) concentrations vary between 0.2 and
63 nM and the concentrations depend on distance to the shore and depths of
sampling, with generally higher values in surface waters as well as close to
the bottom sediment, which might be related to resuspension, sinking of
brine, or resuspension from the sedimentary Fe (Klunder et al., 2012;
Thuróczy et al., 2011). The CFe concentrations are higher close to the
coast and decrease in the outer plume to values that are similar to CFe
concentrations reported from further out in the Arctic Ocean (e.g.
Thuróczy et al., 2011). Estuarine processes, including flocculation and
sedimentation (e.g. Boyle et al., 1977; Sholkovitz, 1978), are the primary
causes for the sharp decrease in particulate and dissolved Fe concentrations
along the transect from the river towards the open Arctic Ocean. Within the
estuaries, the destabilization of the Fe-rich colloids and particles by
seawater cations causes flocculation along the salinity gradient (Escoube et
al., 2009; Gerringa et al., 2007; Mosley et al., 2003) and successively
sedimentation of the newly built flocculates (Daneshvar, 2015). The
distribution of Fe between the different phases shows that PFe is the
dominant Fe phase in the inner plume system (with a PFe/CFe ratio of
about 90). However, most of the PFe is lost in the inner plume close to the
shore and the ratio PFe/CFe decreases towards a ratio of about 1 in
the outer plume.
We observed non-conservative mixing of PFe at salinities lower than 5 and
conservative mixing at salinities higher than 5 (Fig. 5). Recent studies
showed that the majority of PFe (70±15 %) coming from the Lena River
is in the form of chemically reactive ferrihydrite (Hirst et al., 2017b).
Organic C hinders the coagulation of the particles during riverine transport,
but in the estuarine mixing zone the negatively charged iron-bearing
particles will react with seawater cations and form larger aggregates (Boyle
et al., 1977). The larger aggregates sink more readily to the sediments in
the Lena River–Laptev Sea transect and can thus explain the observed
non-conservative behaviour (Martin et al., 1993). This process is a common
feature for Fe that is observed in other estuaries and is responsible for at
least 80 % loss of “dissolved” riverine Fe (Boyle et al., 1977;
Figuères et al., 1978; Guieu et al., 1996; Windom et al., 1971). The
large amount of PFe (99 %) lost in the inner Lena River freshwater plume
is likely due to removal of chemically reactive ferrihydrite, which is the
main form of PFe in the Lena River. Furthermore, it has been shown that about
20 % of OC in the Eurasian Arctic Shelf is bound to reactive Fe phases
(Salvadó et al., 2015). It has also been shown that part of the
ferrihydrite might be transported via surface attachment to POC in a network
of organic fibrils (Hirst et al., 2017b). The attachment of POC to the
ferrihydrite possibly reduces the density of Fe oxyhydroxides (Passow, 2004),
allowing both POC and PFe to be transported into the Arctic Ocean, where they
are present at about 2 % of their initial concentration in rivers.
Concentrations of PFe at salinities >5 and CFe along the whole salinity
gradient show a linear correlation with salinity, suggesting that these
particles and colloids are less affected by changes in ionic strength and
therefore might be mainly in the form of Fe oxyhydroxides. Gregor et
al. (1997) showed that the optimal range for cationic flocculation is a pH
between 6 and 7. At a higher pH, more cations are needed for achieve the same
efficiency of flocculation. Anyhow, Asmala et al. (2014) showed that the pH
range is important at salinities below 1–2, but at higher salinities the pH
is negligible. Furthermore, they showed that it is likely that high Fe
concentrations are a more significant factor and will yield to the same
flocculation rates. The DFe (<1 kDa) concentrations along the freshwater
plume are almost constant around 8 nM (except station YS-14, 1 nM). The
average DFe concentration in the Lena River is about 54 nM (Hirst et al.,
2017b). These data suggest a loss of DFe at low salinities (<1.3) before
the concentration stabilize around 8 nM in the Lena River freshwater plume.
These observations are in accordance with previous studies in the Laptev Sea,
where dissolved Fe concentrations of 3 to 10 nM in the upper 20 m have been
reported (Klunder et al., 2012). It has also been reported that about
74 % to 83 % of the dissolved Fe is present in the truly dissolved
phase in the Arctic Ocean (Thuróczy et al., 2011). Slagter et al. (2017)
report dissolved Fe concentration of 2.6 nM in the Transpolar Drift, which
is transporting surface water from Siberian great rivers, e.g. Lena River,
across the Arctic Ocean into the Atlantic. Available evidence indicates that
the Ob River similarly contributes Fe into the open Arctic Ocean. Along the
Ob River, the DFe shows relatively constant DFe concentrations of 36 to
44 nM in the 10 kDa fraction (Dai and Martin, 1995), which are somewhat
higher than reported here for the Lena, possibly due to a larger
ultrafiltration cut-off size. The overall trend of this and earlier studies
suggests a loss of DFe from the Lena River to the Lena River freshwater plume
and almost constant concentrations along the freshwater plume. The
conservative behaviour of DFe concentrations along a salinity gradient has
been examined in estuarine mixing experiments, and it has been shown that
freshwater Fe oxyhydroxide colloids aggregate into much larger particles in
contact with seawater, whereas the truly dissolved phase was virtually
unaffected (Gustafsson et al., 2000; Stolpe and Hassellöv, 2007). The
observation that the truly dissolved phase is less affected by the increase
in salinity suggests that this phase can be transported through estuaries and
further out into the open ocean (Laglera and Van Den Berg, 2009).
River water is the most important source of Fe for the central Arctic Ocean
(Klunder et al., 2012) and estuarine processes significantly modify the
amount and distribution of Fe between different fractions and therefore also
the bioavailability of the river-derived Fe. Slomp et al. (2013) showed that
Fe concentrations are likely to affect the sedimentation of organic matter
and P in sediments of lakes and coastal seas. Therefore, the loss of Fe–OC
aggregates close to the shoreline might also cause a great loss of
phosphorous and thus contribute to the suggested “rusty carbon sink”
(Lalonde et al., 2012; Salvadó et al., 2015).
Iron isotopes in the Lena River freshwater plume
The measured δ56Fe compositions in the Lena River plume are
broadly similar to those reported in previous studies in other
Arctic/sub-Arctic regions (e.g. Escoube et al., 2009; Staubwasser et al.,
2013). In these areas, within the fully oxidized water column, the PFe phase
shows negative δ56Fe values, while the dissolved phase
generally shows values enriched in Fe(III) compared to the PFe phase (Escoube
et al., 2015, 2009; Ingri et al., 2006; Staubwasser et al., 2013; Zhang et
al., 2015). It has been shown that the Fe-isotope composition is affected by
seasonal variations in water flow paths to the river (Hirst et al., 2017a).
Ingri et al. (2018) showed that the Fe-isotope composition is an indicator of
different Fe aggregates and changing primary Fe sources throughout the
season. Along the freshwater plume the CFe phase has two different Fe-isotope
compositions, positive and negative δ56Fe values. Therefore it
might also represent water masses from different seasons. This would suggest
that the water masses in the inner plume represent spring flood discharge,
whereas the water masses in the outer plume represent summer flow discharge.
In contrast, Alling et al. (2010), claim that the age of the entire
freshwater plume is approximately 2 months. All measured DOC samples
(400–420 µM) from their study plot on a mixing line of Lena River
water measured in August and Arctic deepwater. If the water represented
spring flood discharge, which has much higher DOC concentrations
(1170 µM), their samples would be plotted on a different mixing
line (Alling et al., 2010).
Sundman et al. (2014) measured the speciation of Fe in stream water samples
with X-ray absorption spectroscopy and found iron-organic complexes with
mixed speciation states of Fe as Fe(II, III)–OC and Fe(III)oxyhydroxides
associated with OC. The variations in the distributions of Fe between the
different species in the iron-organic complexes are controlled by pH and OC
concentrations (Neubauer et al., 2013; Sundman et al., 2013). The Fe
speciation of these complexes regulate the Fe-isotopic composition. When
Fe(II) is oxidized to Fe(III), the heavy 56Fe is enriched in the
Fe(III) phase, whereas Fe(II) becomes depleted in the 56Fe isotope
(Bullen et al., 2001; Homoky et al., 2012; Rouxel et al., 2008; Severmann et
al., 2006; Welch et al., 2003; Wu et al., 2011). Laboratory experiments
showed the existence of oxidative precipitation of Fe(II) to Fe(III) (e.g.
Welch et al., 2003), which can occur in natural streams. Bullen et al. (2001)
measured an overall fractionation factor of about 0.9 in natural streams.
Hence, Fe(III)oxyhydroxides should show a enrichment of 56Fe in
oxidized river water, while Fe(II, III)–OC complexes should show a depletion
of 56Fe. The differences in the Fe-isotope composition in the PFe
and CFe fraction clearly indicate different sources for the two phases, as
flocculation of CFe into PFe would result in PFe with the same isotopic
composition (e.g. Escoube et al., 2009). The existence of two different Fe
colloid pools, composed of organic-rich and Fe-rich particles, was shown by
Pokrovsky and Schott (2002) in small boreal rivers. Fe-isotope data from this
study show the existence of two colloidal Fe phases with different
δ56Fe within the Lena River–Laptev Sea transect. The Fe-isotope values of CFe and PFe along the plume and the composition of the
surface sediment suggest that the chemically reactive ferrihydrite represent
colloids and particles, with a negative δ56Fe value,
sedimenting close to the shoreline. The Fe oxyhydroxides that remain in the
water column could then be responsible for the positive δ56Fe
values in the colloidal phase in the outer plume. Therefore, in this case the
Lena River is an important source of positive δ56Fe values to
the Arctic Ocean, along with small OC-rich Arctic and sub-Arctic rivers (Ilina
et al., 2013; Pokrovsky et al., 2014).
The surface sediments in the shelf areas along the Laptev Sea have
δ56Fe values of -0.2 ‰ (Fig. 6). This value
results from the removal of particulate and colloidal Fe(II,
III)oxyhydroxides from the water column and burial in the sediment. As seen
in earlier studies, flocculation during estuarine mixing did not fractionate
the Fe-isotopic composition of the colloids and particles (Bergquist and
Boyle, 2006; Escoube et al., 2009; Fantle and DePaolo, 2004; Poitrasson et
al., 2014). Other processes, such as resuspension of sediment and non-reductive
dissolution of sediment to the seawater (Radic et al., 2011), would lead to a
much more negative (-3.3 ‰ to -1.7 ‰) Fe-isotope
composition of the sediment (Homoky et al., 2009; Severmann et al., 2006,
2010). Therefore, the δ56Fe of the uppermost sediment
reflecting the δ56Fe of the sedimenting colloids and particles
from the water column seems reasonable.
Conclusions
Close to the coast and within the inner part of the river plume, the
concentration of PFe dominates the total Fe budgets. In the outer part of the
plume, the PFe and CFe concentrations are almost equal, as more than 99 %
of the total Fe is lost. The loss of PFe, most likely in the form of
chemically reactive ferrihydrite, results from increasing ionic strength due
to increasing salinities, which promote flocculation. The coagulation and
removal appear at the beginning of the mixing zone at low salinities (0–5).
Colloidal Fe concentrations are almost constant along the inner plume and
decrease along the outer plume due to conservative mixing. The truly
dissolved Fe shows little variation along the Lena River freshwater plume.
Therefore, the river-derived truly dissolved fraction could be an important
source of bioavailable Fe, along with colloidal Fe, which may affect the
primary production in the central Arctic Ocean.
The Fe-isotope compositions in the Lena River freshwater plume provide clear
indications of which forms of Fe reach the deep ocean basin. There are
significant differences between the particulate and colloidal phases. The
negative δ56Fe values, found in the colloidal and particulate
phases, are lost during estuarine mixing and buried in the sediment. These
negative δ56Fe values seem to represent chemically reactive
ferrihydrite. Within the colloidal phase, we measured positive δ56Fe values further out in the plume, which likely represent
Fe oxyhydroxides, which remain
buoyant in the water column, transported along the Lena River freshwater
plume into the Arctic Ocean.
Data availability
Data used to generate all figures are available in the
paper as tables and in the Supplement. Salinity data used to generate Fig. 2 can be found
in the Bolin Centre Database at https://bolin.su.se (last access:
22 March 2019).
The supplement related to this article is available online at: https://doi.org/10.5194/bg-16-1305-2019-supplement.
Author contributions
JG, FN, PSA, DP, ÖG, and IS carried out the field and lab
work. EE and IR performed the stable isotope analysis. SC analysed the data,
prepared the figures, and wrote the manuscript under the supervision of JI and with
contributions from JG, FN, PSA, EE, OS, DP, ÖG, IS, and
BÖ.
Competing interests
The authors declare that they have no conflict of
interest.
Acknowledgements
The ISSS-08 programme was supported by the Knut and Alice Wallenberg
Foundation, the Far Eastern Branch of the Russian Academy of Sciences, the
Swedish Research Council (621-2004-4039 and 211-621-2007), the U.S. National
Oceanic and Atmospheric Administration, the Russian Foundation for Basic
Research, the Swedish Polar Research Secretariat, and the Stockholm
University Bert Bolin Centre for Climate Research. Örjan Gustafsson also
acknowledge a Distinguished Professor Grant from the Swedish Research Council
(VR contract no. 2017-05687), an advanced grant from the European Research
Council (ERC-AdG CC-TOP project #695331). Igor Semiletov acknowledges the
Russian Government (14.Z50.31.0012) and the Russian Scientific Foundation
(15-17-20032). The ISSS-08 programme is part of the IPY (International Polar
Year) and the GEOTRACES programme.
Review statement
This paper was edited by Aninda Mazumdar and reviewed by two
anonymous referees.
ReferencesAllard, T., Menguy, N., Salomon, J., Calligaro, T., Weber, T., Calas, G., and
Benedetti, M. F.: Revealing forms of iron in river-borne material from major
tropical rivers of the Amazon Basin (Brazil), Geochim. Cosmochim. Ac., 68,
3079–3094, 10.1016/J.GCA.2004.01.014, 2004.Alling, V., Sanchez-Garcia, L., Porcelli, D., Pugach, S., Vonk, J. E., Van
Dongen, B., Mörth, C. M., Anderson, L. G., Sokolov, A., Andersson, P.,
Humborg, C., Semiletov, I., and Gustafsson, Ö.: Nonconservative behavior
of dissolved organic carbon across the Laptev and East Siberian seas, Global
Biogeochem. Cy., 24, 1–15, 10.1029/2010GB003834, 2010.Alling, V., Porcelli, D., Mörth, C. M., Anderson, L. G., Sanchez-Garcia,
L., Gustafsson, Ö., Andersson, P. S., and Humborg, C.: Degradation of
terrestrial organic carbon, primary production and out-gassing of CO2
in the Laptev and East Siberian Seas as inferred from δ13C
values of DIC, Geochim. Cosmochim. Ac., 95, 143–159,
10.1016/j.gca.2012.07.028, 2012.Amon, R. M. W., Rinehart, A. J., Duan, S., Louchouarn, P., Prokushkin, A.,
Guggenberger, G., Bauch, D., Stedmon, C., Raymond, P. A., Holmes, R. M.,
McClelland, J. W., Peterson, B. J., Walker, S. A., and Zhulidov, A. V.:
Dissolved organic matter sources in large Arctic rivers, Geochim. Cosmochim.
Ac., 94, 217–237, 10.1016/j.gca.2012.07.015, 2012.Anbar, A. D.: Iron stable isotopes: Beyond biosignatures, Earth Planet. Sc.
Lett., 217, 223–236, 10.1016/S0012-821X(03)00572-7, 2004.Andersson, L. and Jutterstrøm, S.: Seawater carbonate chemistry and
nutrients measured on water bottle samples during the International Siberian
Shelf Study 2008 (ISSS-08) in the Laptev, East Siberian and Chukchi Seas,
Department of Chemistry, University of Gothenburg, PANGAEA,
10.1594/PANGAEA.715045, 2008.Anderson, L. G., Jutterstrøm, S., Hjalmarsson, S., Wåhlström, I.,
and Semiletov, I. P.: Out-gassing of CO2 from Siberian Shelf seas
by terrestrial organic matter decomposition, Geophys. Res. Lett., 36, L20601,
10.1029/2009GL040046, 2009.Anisimov, O. and Reneva, S.: Permafrost and Changing Climate: The Russian
Perspective, AMBIO, 35, 169–175,
10.1579/0044-7447(2006)35[169:PACCTR]2.0.CO;2, 2006.
Antonov, V. S.: The Mouth Area of the Lena, in: The Hydrographic Review,
Gidrometeoizdat, Leningrad, 1967.Asmala, E., Bowers, D., Autio, R., Kaartokallio, H., and Thomas, D. N.:
Qualitative changes of riverine dissolved organic matter at low salinities
due to flocculation, J. Geophy. Res.-Biogeo., 119, 1919–1933,
10.1002/2014JG002722, 2014.Baxter, D. C., Rodushkin, I., Engström, E., and Malinovsky, D.: Revised
exponential model for mass bias correction using an internal standard for
isotope abundance ratio measurements by multi-collector inductively coupled
plasma mass spectrometry, J. Anal. Atom. Spectrom., 21, 427–430,
10.1039/b517457k, 2006.Beard, B. L. and Johnson, C. M.: Ancient Earth and Other Planetary Bodies,
Rev. Mineral., 55, 319–357, 10.2138/gsrmg.55.1.319, 2004.Beard, B. L., Johnson, C. M., Cox, L., Sun, H., Nealson, K. H., and Aguilar,
C.: Iron isotope biosignatures, Science, 285, 1889–1891,
10.1126/science.285.5435.1889, 1999.Beard, B. L., Johnson, C. M., Von Damm, K. L., and Poulson, R. L.: Iron
isotope constraints on Fe cycling and mass balance in oxygenated Earth
oceans, Geology, 31, 629–632,
10.1130/0091-7613(2003)031<0629:IICOFC>2.0.CO;2, 2003.Bergquist, B. A. and Boyle, E. A.: Iron isotopes in the Amazon River system:
Weathering and transport signatures, Earth Planet. Sc. Lett., 248, 39–53,
10.1016/j.epsl.2006.05.004, 2006.Boyle, E. A., Edmond, J. M., and Sholkovitz, E. R.: The mechanism of iron
removal in estuaries, Geochim. Cosmochim. Ac., 41, 1313–1324,
10.1016/0016-7037(77)90075-8, 1977.Brantley, S. L., Liermann, L., and Bullen, T. D.: Fractionation of Fe
isotopes by soil microbes and organic acids, Geology, 29, 535–538,
10.1130/0091-7613(2001)029<0535:FOFIBS>2.0.CO;2, 2001.Bröder, L., Tesi, T., Salvadó, J. A., Semiletov, I. P., Dudarev, O.
V., and Gustafsson, Ö.: Fate of terrigenous organic matter across the
Laptev Sea from the mouth of the Lena River to the deep sea of the Arctic
interior, Biogeosciences, 13, 5003–5019,
10.5194/bg-13-5003-2016, 2016.Bullen, T. D., White, A. F., Childs, C. W., Vivit, D. V., and Schultz, M. S.:
Demonstration of a significant iron isotope fractionation in nature, Geology,
29, 699–702, 10.1130/0091-7613(2001)029<0699:DOSAII>2.0.CO;2, 2001.Cauwet, G. and Sidorov, I.: The biogeochemistry of Lena River: organic carbon
and nutrients distribution, Mar. Chem., 53, 211–227,
10.1016/0304-4203(95)00090-9, 1996.
Chester, R.: Marine geochemistry, 2nd Edn., Blackwell Pub, Malden, 2003.Conway, T. M. and John, S. G.: Quantification of dissolved iron sources to
the North Atlantic Ocean, Nature, 511, 212–215, 10.1038/nature13482,
2014.Cutter, G., Andersson, P., Codispoti, L., Croot, P., Francois, R., Lohan, M.,
van der Loeff, M. R.: Sampling and sample handling protocol for GEOTRACES
cruises, Version 1.0, available at:
http://www.geotraces.org/science/intercalibration/222-sampling-and-sample-handling-protocols-for-geotraces-cruises
(last access: 22 March 2019), 2010.Dai, M.-H. and Martin, J.-M.: First data on trace metal level and behaviour
in two major Arctic river-estuarine systems (Ob and Yenisey) and in the
adjacent Kara Sea, Russia, Earth Planet. Sc. Lett., 131, 127–141,
10.1016/0012-821X(95)00021-4, 1995.Daneshvar, E.: Dissolved Iron Behavior in the Ravenglass Estuary Waters, An
Implication on the Early Diagenesis, Universal Journal of Geoscience, 3,
1–12, 10.13189/ujg.2015.030101, 2015.
de Baar, H. J. W. and de Jong, J. T. M.: Distributions, sources and sinks of
iron in seawater, in: Biogeochemistry of Iron in Seawater, edited by: Turner,
D. R. and Hunter, K. A., Wiley, New York, 123–253, 2001.Dos Santos Pinheiro, G. M., Poitrasson, F., Sondag, F., Cochonneau, G., and
Vieira, L. C.: Contrasting iron isotopic compositions in river suspended
particulate matter: The Negro and the Amazon annual river cycles, Earth
Planet. Sc. Lett., 394, 168–178, 10.1016/j.epsl.2014.03.006, 2014.
Dudarev, O.: Cruise report International Siberian Shelf Study 2008 (ISSS-08),
Swedish Knut and Alice Wallenberg Foundation, the Far-Eastern Branch of the
Russian Academy of Sciences, the Swedish Research Councli, the Russian
Foundation for Basic Research, NoAA, and the Swedish Polar Research
Secretariat, Bremerhaven, PANGAEA Documentation, Hdl:10013/epic32714, 2008.
Eckert, J. M. and Sholkovitz, E. R.: The flocculation of iron, aluminum and
humates from river water by electrolytes, Geochim. Cosmochim. Ac., 40,
847–848, 1976.Escoube, R., Rouxel, O. J., Sholkovitz, E., and Donard, O. F. X.: Iron
isotope systematics in estuaries: The case of North River, Massachusetts
(USA), Geochim. Cosmochim. Ac., 73, 4045–4059,
10.1016/j.gca.2009.04.026, 2009.Escoube, R., Rouxel, O. J., Pokrovsky, O. S., Schroth, A., Max Holmes, R.,
and Donard, O. F. X.: Iron isotope systematics in Arctic rivers, CR Geosci.,
347, 377–385, 10.1016/j.crte.2015.04.005, 2015.Fantle, M. S. and DePaolo, D. J.: Iron isotopic fractionation during
continental weathering, Earth Planet. Sc. Lett., 228, 547–562,
10.1016/j.epsl.2004.10.013, 2004.
Figuères, G., Martin, J. M., and Meybeck, M.: Iron behaviour in the Zaire
Estuary, Neth. J. Sea Res., 12, 329–337, 1978.Forsberg, J., Dahlqvist, R., Gelting-Nyström, J., and Ingri, J.: Trace
metal speciation in brackish water using diffusive gradients in thin films
and ultrafiltration: comparison of techniques, Environ. Sci. Technol., 40,
3901–3905, 10.1021/es0600781, 2006.Gerringa, L. J. A., Rijkenberg, M. J. A., and Wolterbeek, H. Th., Verburg, T.
G., Boye, M., and de Abar, H. J. W.: Kinetic study reveals weak Fe-binding
ligand, which affects the solubility of Fe in the Scheldt estuary, Mar.
Chem., 103, 30–45, 10.1016/j.marchem.2006.06.002, 2007.
Gregor, J. E., Nokes, C. J., and Fenton, E.: Optimising natural organic
matter removal from low turbidity waters by controlled pH adjustment of
aluminium coagulation, Water Res., 31, 2949–2958, 1997.Guieu, C., Huang, W. W., Martin, J. M., and Yong, Y. Y.: Outflow of trace
metals into the Laptev Sea by the Lena River, Mar. Chem., 53, 255–267,
10.1016/0304-4203(95)00093-3, 1996.Guo, L. and Santschi, P.: A critical evaluation of cross-flow ultrafiltration
technique for sampling colloidal organic carbon in seawater, Mar. Chem., 55,
113–127, 10.1016/S0304-4203(96)00051-5, 1996.Gustafsson, C. and Gschwend, P. M.: Aquatic colloids: Concepts, definitions,
and current challenges, Limnol. Oceanogr., 42, 519–528,
10.4319/lo.1997.42.3.0519, 1997.Gustafsson, Ö., Widerlund, A., Andersson, P. S., Ingri, J., Roos, P., and
Ledin, A.: Colloid dynamics and transport of major elements through a boreal
river – Brackish bay mixing zone, Mar. Chem., 71, 1–21,
10.1016/S0304-4203(00)00035-9, 2000.Hirst, C., Andersson, P., Mörth, M., Kutscher, L., Murphy, M., Schmitt,
M., Petrov, R., Maximov, T., and Porcelli, D.: Seasonal Variations in the
Sources and Formation of Fe-Bearing Particles in the Lena River Basin;
Evidence from Iron Isotopes, Goldschmidt Abstracts, 1643, available at:
https://goldschmidtabstracts.info/abstracts/abstractView?id=2017004101
(last access: 22 March 2019), 2017a.Hirst, C., Andersson, P. S., Shaw, S., Burke, I. T., Kutscher, L., Murphy, M.
J., Maximov, T., Pokrovsky, O. S., Mörth, C. M., and Porcelli, D.:
Characterisation of Fe-bearing particles and colloids in the Lena River
basin, NE Russia, Geochim. Cosmochim. Ac., 213, 553–573,
10.1016/j.gca.2017.07.012, 2017b.Holmes, R. M., McClelland, J. W., Peterson, B. J., Tank, S. E., Bulygina, E.,
Eglinton, T. I., Gordeev, V. V., Gurtovaya, T. Y., Raymond, P. A., Repeta, D.
J., Staples, R., Striegl, R. G., Zhulidov, A. V., and Zimov, S. A.: Seasonal
and Annual Fluxes of Nutrients and Organic Matter from Large Rivers to the
Arctic Ocean and Surrounding Seas, Estuar. Coast., 35, 369–382,
10.1007/s12237-011-9386-6, 2012.Homoky, W. B., Severmann, S., Mills, R. A., Statham, P. J., and Fones, G. R.:
Proe-fluid Fe isotopes reflect the extent of benthic Fe redoc recycling:
Evidence from continental shelf and deep-sea sediments, Geology, 37,
751–754, 10.1130/G25731A.1, 2009.Homoky, W. B., Severmann, S., McManus, J., Berelson, W. M., Riedel, T. E.,
Statham, P. J., and Mills, R. A.: Dissolved oxygen and suspended particles
regulate the benthic flux of iron from continental margins, Mar. Chem.,
134–135, 59–70, 10.1016/j.marchem.2012.03.003, 2012.Icopini, G. A., Anbar, A. D., Ruebush, S. S., Tien, M., and Brantley, S. L.:
Iron isotope fractionation during microbial reduction of iron: The importance
of adsorption, Geology, 32, 205–208, 10.1130/G20184.1, 2004.Ilina, S. M., Poitrasson, F., Lapitskiy, S. A., and Alekhin, Y. V.: Extreme
iron isotope fractionation between different size colloids of boreal
organic-rich waters, Geochim. Cosmochim. Ac., 101, 96–111,
10.1016/j.gca.2012.10.023, 2013.Ingri, J., Widerlund, A., Land, M., Gustafsson, Ö., Andersson, P., and
Öhlander, B.: Temporal variations in the fractionation of the rare earth
elements in a Boreal river; the role of colloidal particles, Chem. Geol.,
166, 23–45, 10.1016/S0009-2541(99)00178-3, 2000.Ingri, J., Malinovsky, D., Rodushkin, I., Baxter, D. C., Widerlund, A.,
Andersson, P., Gustafsson, Ö., Forsling, W., and Öhlander, B.: Iron
isotope fractionation in river colloidal matter, Earth Planet. Sc. Lett.,
245, 792–798, 10.1016/j.epsl.2006.03.031, 2006.Ingri, J., Conrad, S., Lidman, F., Nordblad, F., Engström, E., Rodushkin,
I., and Porcelli, D.: Iron isotope pathways in the boreal landscape: Role of
the riparian zone, Geochim. Cosmochim. Ac., 239, 49–60,
10.1016/j.gca.2018.07.030, 2018.Karlsson, E., Gelting, J., Tesi, T., van Dongen, B., Andersson, A.,
Semiletov, I., Charkin, A., Dudarev, O., and Gustafsson, Ö.: Different
sources and degradation state of dissolved, particulate, and sedimentary
organic matter along the Eurasian Arctic coastal margin, Global Biogeochem.
Cy., 30, 898–919, 10.1002/2015GB005307, 2016.Klunder, M. B., Bauch, D., Laan, P., De Baar, H. J. W., Van Heuven, S., and
Ober, S.: Dissolved iron in the Arctic shelf seas and surface waters of the
central Arctic Ocean: Impact of Arctic river water and ice-melt, J. Geophys.
Res.-Oceans, 117, 1–18, 10.1029/2011JC007133, 2012.Kritzberg, E. S., Villanueva, A. B., Jung, M., and Reader, H. E.: Importance
of boreal rivers in providing iron to marine waters, PLoS One, 9, e107500,
10.1371/journal.pone.0107500, 2014.Kutscher, L., Mörth, C. M., Porcelli, D., Hirst, C., Maximov, T. C.,
Petrov, R. E., and Andersson, P. S.: Spatial variation in concentration and
sources of organic carbon in the Lena River, Siberia, J. Geophys.
Res.-Biogeo., 122, 1999–2016, 10.1002/2017JG003858, 2017.Laglera, L. M. and Van Den Berg, C. M. G.: Evidence for geochemical control
of iron by humic substances in seawater, Limnol. Oceanogr., 54, 610–619,
10.4319/lo.2009.54.2.0610, 2009.Lalonde, K., Mucci, A., Ouellet, A., and Gélinas, Y.: Preservation of
organic matter in sediments promoted by iron, Nature, 483, 198–200,
10.1038/nature10855, 2012.Larsson, J., Ingri, J., and Gustafsson, Ö.: Evaluation and optimization
of two complementary cross-flow ultrafiltration systems toward isolation of
coastal surface water colloids, Environ. Sci. Technol., 36, 2236–2241,
10.1021/ES010325V, 2002.Le Fouest, V., Babin, M., and Tremblay, J.-É.: The fate of riverine
nutrients on Arctic shelves, Biogeosciences, 10, 3661–3677,
10.5194/bg-10-3661-2013, 2013.Martin, J. H., Gordon, R. M., and Fitzwater, E. S.: Iron Limitation?, Limnol.
Oceanogr., 36, 1793–1802, 10.4319/lo.1991.36.8.1793, 1991.
Martin, J. M. and Meybeck, M.: Elemental mass-balance or material carried by
major world rivers, Mar. Chem., 7, 173–206, 1979.Martin, J. M., Guan, D. M., Elbazpoulichet, F., Thomas, A. J., and Gordeev,
V. V.: Preliminary Assessment of the Distributions of Some Trace-Elements
(as, Cd, Cu, Fe, Ni, Pb and Zn) in a Pristine Aquatic Environment – the Lena
River Estuary (Russia), Mar. Chem., 43, 185–199,
10.1016/0304-4203(93)90224-C, 1993.Mosley, L. M., Hunter, K. A., and Ducker, W. A.: Forces between colloid
particles in natural waters, Environ. Sci. Technol., 37, 3303–3308,
10.1021/es026216d, 2003.Mulholland, D. S., Poitrasson, F., Boaventura, G. R., Allard, T., Vieira, L.
C., Santos, R. V., Mancini, L., and Seyler, P.: Insights into iron sources
and pathways in the Amazon River provided by isotopic and spectroscopic
studies. Geochim. Cosmochim. Ac., 150, 142–159,
10.1016/j.gca.2014.12.004, 2015.Neubauer, E., Köhler, S. J., Von Der Kammer, F., Laudon, H., and Hofmann,
T.: Effect of pH and stream order on iron and arsenic speciation in boreal
catchments, Environ. Sci. Technol., 47, 7120–7128, 10.1021/es401193j,
2013.Ödman, F., Ruth, T., and Pontér, C.: Validation of a field filtration
technique for characterization of suspended particulate matter from
freshwater. Part I. Major elements, Appl. Geochem., 14, 301–317,
10.1016/S0883-2927(98)00050-X, 1999.Opsahl, S., Benner, R., and Amon, R. M. W.: Major flux of terrigenous
dissolved organic matter through the Arctic Ocean, Limnol. Oceanogr., 44,
2017–2023, 10.4319/lo.1999.44.8.2017, 1999.Passow, U.: Switching perspectives: Do mineral fluxes determine particulate
organic carbon fluxes or vice versa?, Geochem. Geophy. Geosy., 5, Q04002,
10.1029/2003GC000670, 2004.Pédrot, M., Le Boudec, A., Davranche, M., Dia, A., and Henin, O.: How
does organic matter constrain the nature, size and availability of Fe
nanoparticles for biological reduction?, J. Colloid Interf. Sci., 359,
75–85, 10.1016/j.jcis.2011.03.067, 2011.Perdue, E. M., Beck, K. C., and Reuter, J. H.: Organic complexes of iron and
aluminium in natural waters, Nature, 260, 418–420, 10.1038/260418a0,
1976.Pipko, I. I., Pugach, S. P., Semiletov, I. P., Anderson, L. G., Shakhova, N.
E., Gustafsson, Ö., Repina, I. A., Spivak, E. A., Charkin, A. N., Salyuk,
A. N., Shcherbakova, K. P., Panova, E. V., and Dudarev, O. V.: The spatial
and interannual dynamics of the surface water carbonate system and air–sea
CO2 fluxes in the outer shelf and slope of the Eurasian Arctic Ocean,
Ocean Sci., 13, 997–1016, 10.5194/os-13-997-2017, 2017.Poitrasson, F.: On the iron isotope homogeneity level of the continental
crust, Chem. Geol., 235, 195–200, 10.1016/j.chemgeo.2006.06.010, 2006.Poitrasson, F. and Freydier, R.: Heavy iron isotope composition of granites
determined by high resolution MC-ICP-MS, Chem. Geol., 222, 132–147,
10.1016/j.chemgeo.2005.07.005, 2005.Poitrasson, F., Cruz Vieira, L., Seyler, P., Márcia dos Santos Pinheiro,
G., Santos Mulholland, D., Bonnet, M. P., Martinez, J. M., Alcantara Lima,
B., Resende Boaventura, G., Chmeleff, J. Ô., Dantas, E. L., Guyot, J. L.,
Mancini, L., Martins Pimentel, M., Ventura Santos, R., Sondag, F., and
Vauchel, P.: Iron isotope composition of the bulk waters and sediments from
the Amazon River Basin, Chem. Geol., 377, 1–11,
10.1016/j.chemgeo.2014.03.019, 2014.Pokrovsky, O. S. and Schott, J.: Iron colloids/organic matter associated
transport of major and trace elements in small boreal rivers and their
estuaries (NW Russia), Chem. Geol., 190, 141–179,
10.1016/S0009-2541(02)00115-8, 2002.Pokrovsky, O. S., Schott, J., and Dupré, B.: Trace element fractionation
and transport in boreal rivers and soil porewaters of permafrost-dominated
basaltic terrain in Central Siberia, Geochim. Cosmochim. Ac., 70, 3239–3260,
10.1016/j.gca.2006.04.008, 2006.Pokrovsky, O. S., Viers, J., Shirokova, L. S., Shevchenko, V. P., Filipov, A.
S., and Dupré, B.: Dissolved, suspended, and colloidal fluxes of organic
carbon, major and trace elements in the Severnaya Dvina River and its
tributary, Chem. Geol., 273, 136–149, 10.1016/j.chemgeo.2010.02.018,
2010.Pokrovsky, O. S., Shirokova, L. S., Zabelina, S. A., Vorobieva, T. Ya.,
Moreva, O. Yu., Klimov, S. I., Chupakov, A. V., Shorina, N. V., Kokryatskaya,
N. M., Audry, S., Viers, J., Zoutien, C., and Freydier, R.: Size
fractionation of trace elements in a seasonally stratified boreal lake:
control of organic matter and iron colloids, Aquat. Geochem., 18, 115–139,
10.1007/s10498-011-9154-z, 2012.Pokrovsky, O. S., Shirokova, L. S., Viers, J., Gordeev, V. V., Shevchenko, V.
P., Chupakov, A. V., Vorobieva, T. Y., Candaudap, F., Causserand, C.,
Lanzanova, A., and Zouiten, C.: Fate of colloids during estuarine mixing in
the Arctic, Ocean Sci., 10, 107–125, 10.5194/os-10-107-2014,
2014.Poulton, S. W. and Raiswell, R.: Chemical and physical characteristics of
iron oxides in riverine and glacial meltwater sediments, Chem. Geol., 218,
203–221, 10.1016/j.chemgeo.2005.01.007, 2005.Pugach, S. P., Pipko, I. I., Shakhova, N. E., Shirshin, E. A., Perminova, I.
V., Gustafsson, Ö., Bondur, V. G., Ruban, A. S., and Semiletov, I. P.:
Dissolved organic matter and its optical characteristics in the Laptev and
East Siberian seas: spatial distribution and interannual variability
(2003–2011), Ocean Sci., 14, 87–103, 10.5194/os-14-87-2018,
2018.Rachold, V., Alabyan, A., Hubberten, H.-W., Korotaev, V. N., and Zaitsev, A.
A.: Sediment transport to the Laptev Sea–hydrology and geochemistry of the
Lena River, Polar Res., 15, 183–196, 10.3402/polar.v15i2.6646, 1996.Radic, A., Laca, F., and Murray, J. W.: Iron isotopes in the seawater of the
equatorial Pacif Ocean: New constraints for the oceanic iron cycle, Earth
Planet. Sc. Lett., 306, 1–10, 10.1016/j.epsl.2011.03.015, 2011.Raiswell, R. and Canfield, D. E.: The Iron Biogeochemical Cycle Past and
Present, Geochem. Perspect, 1, 1–220, 10.7185/geochempersp.1.1, 2012.Raymond, P. A., McClelland, J. W., Holmes, R. M., Zhulidov, A. V., Mull, K.,
Peterson, B. J., Striegl, R. G., Aiken, G. R., and Gurtovaya, T. Y.: Flux and
age of dissolved organic carbon exported to the Arctic Ocean: A carbon
isotopic study of the five largest arctic rivers, Global Biogeochem. Cy., 21,
1–9, 10.1029/2007GB002934, 2007.Rodushkin, I. and Ruth, T.: Determination of Trace Metals in Estuarine and
Sea-water Reference Materials by High Resolution Inductively Coupled Plasma
Mass Spectrometry, J. Anal. Atom. Spectrom., 12, 1181–1185,
10.1039/a702486j, 1997.Rodushkin, I., Nordlund, P., Engström, E., and Baxter, D. C.: Improved
multi-elemental analyses by inductively coupled plasma-sector field mass
spectrometry through methane addition to the plasma, J. Anal. Atom.
Spectrom., 20, 1250–1255, 10.1039/b507886e, 2005.Rodushkin, I., Engström, E., and Baxter, D.: Sources of contamination and
remedial strategies in the multi-elemental trace analysis laboratory, Anal.
Bioanal. Chem., 396, 365–377, 10.1007/s00216-009-3087-z, 2010.Rodushkin, I., Pallavicini, N., Engström, E., Sörlin, D.,
Öhlander, B., Ingri, J., and Baxter, D. C.: Assessment of the natural
variability of B, Cd, Cu, Fe, Pb, Sr, Tl, and Zn concentrations and isotopic
compositions in leaves, needles, and mushrooms using single sample digestion
and two-column matrix separation, J. Anal. Atom. Spectrom., 31, 220–233,
10.1039/C5JA00274E, 2016.Rosén, P.-O., Andersson, P. S., Alling, V., Mörth, C.-M., Björk,
G., Semiletov, I., and Porcelli, D.: Ice export from the Laptev and East
Siberian Sea derived from δ18O values, J. Geophys.
Res.-Oceans, 120, 5997–6007, 10.1002/2015JC010866, 2015.
Rouxel, A., Bekker, K. J., and Edwards, O. J.: Iron isotope constraints on
the Archaen and Paleoproterozoic Ocean redox state, Science, 307, 1088–1091,
2005.Rouxel, O., Sholkovitz, E., Charette, M., and Edwards, K. J.: Iron isotope
fractionation in subterranean estuaries, Geochim. Cosmochim. Ac., 72,
3413–3430, 10.1016/j.gca.2008.05.001, 2008.Salvadó, J. A., Tesi, T., Andersson, A., Ingri, J., Dudarev, O. V.,
Semiletov, I. P., and Gustafsson, Ö.: Organic carbon remobilized from
thawing permafrost is resequestered by reactive iron on the Eurasian Arctic
Shelf, Geophys. Res. Lett., 42, 8122–8130, 10.1002/2015GL066058, 2015.Salvadó, J. A., Bröder, L., Andersson, A., Semiletov, I. P., and
Gustafsson, Ö.: Release of black carbon from thawing permafrost estimated
by sequestration fluxes in the East Siberian Arctic Shelf recipient, Global
Biogeochem. Cy., 31, 1501–1515, 10.1002/2017GB005693, 2017.Sánchez-García, L., Alling, V., Pugach, S., Vonk, J., Van Dongen,
B., Humborg, C., Dudarev, O., Semiletov, I., and Gustafsson, Ö.:
Inventories and behavior of particulate organic carbon in the Laptev and East
Siberian seas, Global Biogeochem. Cy., 25, 1–13, 10.1029/2010GB003862,
2011.Semiletov, I. P., Pipko, I. I., Shakhova, N. E., Dudarev, O. V., Pugach, S.
P., Charkin, A. N., McRoy, C. P., Kosmach, D., and Gustafsson, Ö.: Carbon
transport by the Lena River from its headwaters to the Arctic Ocean, with
emphasis on fluvial input of terrestrial particulate organic carbon vs.
carbon transport by coastal erosion, Biogeosciences, 8, 2407–2426,
10.5194/bg-8-2407-2011, 2011.Severmann, S., Johnson, C. M., Beard, B. L., and McManus, J.: The effect of
early diagenesis on the Fe isotope compositions of porewaters and authigenic
minerals in continental margin sediments, Geochim. Cosmochim. Ac., 70,
2006–2022, 10.1016/J.GCA.2006.01.007, 2006.Severmann, S., McManus, J., Berelson, W. M., and Hammond, D. E.: The
continental shelf benthic iron flux and its isotope composition, Geochim.
Cosmochim. Ac., 74, 3984–4004, 10.1016/j.gca.2010.04.022, 2010.
Sholkovitz, E. R.: Floculation of dissolved organic and inorganic matter
during the mixing of river water and seawater, Geochim. Cosmochim. Ac., 40,
831–845, 1976.Sholkovitz, E. R.: The flocculation of dissolved Fe, Mn, Al, Cu, Ni, Co and
Cd during estuarine mixing, Earth Planet. Sc. Lett., 41, 77–86,
10.1016/0012-821X(78)90043-2, 1978.Skulan, J. L., Beard, B. L., and Johnson, C. M.: Kinetic and equilibrium Fe
isotope fractionation between aqueous Fe(III) and hematite, Geochim.
Cosmochim. Ac., 66, 2995–3015, 10.1016/S0016-7037(02)00902-X, 2002.Slagter, H. A., Reader, H. E., Rijkenberg, M. J. A., Rutgers van der Loeff,
M., De Baar, H. J. W. W., Gerringa, L. J. A., Salvadó, J. A., Tesi, T.,
Andersson, A., Ingri, J., Dudarev, O. V., Semiletov, I. P., Gustafsson,
Ö., Kutscher, L., Mörth, C. M., Porcelli, D., Hirst, C., Maximov, T.
C., Petrov, R. E., Andersson, P. S., Klunder, M. B., Bauch, D., Laan, P., De
Baar, H. J. W. W., Van Heuven, S., Ober, S., Forsberg, J., Dahlqvist, R.,
Gelting-Nyström, J., Ingri, J., Pokrovsky, O. S., Shirokova, L. S.,
Viers, J., Gordeev, V. V., Shevchenko, V. P., Chupakov, A. V., Vorobieva, T.
Y., Candaudap, F., Causserand, C., Lanzanova, A., and Zouiten, C.: Trace
metal speciation in brackish water using diffusive gradients in thin films
and ultrafiltration: comparison of techniques, J. Geophys. Res.-Biogeo., 40,
8122–8130, 10.1016/j.marchem.2017.10.005, 2017.Slomp, C. P., Mort, H. P., Jilbert, T., Reed, D. C., Gustafsson, B. G., and
Wolthers, M.: Coupled dynamics of iron and phosphorous in sediments of an
oligotrophic coastal basin and the impact of anaerobic oxidation of methane,
PLoS ONE, 8, e62386, 10.1371/journal.pone.0062386, 2013.Staubwasser, M., Schoenberg, R., von Blanckenburg, F., Krüger, S., and
Pohl, C.: Isotope fractionation between dissolved and suspended particulate
Fe in the oxic and anoxic water column of the Baltic Sea, Biogeosciences, 10,
233–245, 10.5194/bg-10-233-2013, 2013.Stolpe, B. and Hassellöv, M.: Changes in size distribution of fresh water
nanoscale colloidal matter and associated elements on mixing with seawater,
Geochim. Cosmochim. Ac., 71, 3292–3301,
10.1016/j.gca.2007.04.025, 2007.Stolpe, B., Guo, L., and Shiller, A. M.: Binding and transport of rare earth
elements by organic and iron-rich nanocolloids in alaskan rivers, as revealed
by field-flow fractionation and ICP-MS, Geochim. Cosmochim. Ac., 106,
446–462, 10.1016/j.gca.2012.12.033, 2013.Sundman, A., Karlsson, T., and Persson, P.: An experimental protocol for
structural characterization of Fe in dilute natural waters, Environ. Sci.
Technol., 47, 8557–8564, 10.1021/es304630a, 2013.Sundman, A., Karlsson, T., Laudon, H., and Persson, P.: XAS study of iron
speciation in soils and waters from a boreal catchment, Chem. Geol., 364,
93–102, 10.1016/j.chemgeo.2013.11.023, 2014.Tagliabue, A., Bopp, L., Dutay, J.-C., Bowie, A. R., Chever, F.,
Jean-Baptiste, P., Bucciarelli, E., Lannuzel, D., Remenyi, T., Sarthou, G.,
Aumont, O., Gehlen, M., and Jeandel, C.: Hydrothermal contribution to the
oceanic dissolved iron inventory, Nat. Geosci., 3, 252–256,
10.1038/ngeo818, 2010.Tagliabue, A., Bowie, A. R., Boyd, P. W., Buck, K. N., Johnson, K. S., and
Saito, M. A.: The integral role of iron in ocean biogeochemistry, Nature,
543, 51–59, 10.1038/nature21058, 2017.Thuróczy, C.-E., Gerringa, L. J. A., Klunder, M., Laan, P., Le Guitton,
M., and de Baar, H. J. W.: Distinct trends in the speciation of iron between
the shallow shelf seas and the deep basins of the Arctic Ocean, J. Geophys.
Res., 116, C10009, 10.1029/2010JC006835, 2011.Tipping, E.: The adsorption of aquatic humic substances by iron oxides.
Geochim. Cosmochim. Ac., 45, 191–199, 10.1016/0016-7037(81)90162-9,
1981.Vonk, J. E., van Dongen, B. E., and Gustafsson, Ö.: Selective
preservation of old organic carbon fluvially released from sub-Arctic soils,
Geophys. Res. Lett., 37, L11605, 10.1029/2010GL042909, 2010.Vonk, J. E., Sánchez-García, L., van Dongen, B. E., Alling, V.,
Kosmach, D., Charkin, A., Semiletov, I. P., Dudarev, O. V., Shakhova, N.,
Roos, P., Eglinton, T. I., Andersson, A., and Gustafsson, Ö.: Activation
of old carbon by erosion of coastal and subsea permafrost in Arctic Siberia,
Nature, 489, 137–140, 10.1038/nature11392, 2012.
Wagner, V.: Analysis of a Russian landscape map and landscape classification
for use in computer-aided forestry research, IIASA Interim Report
IR-97-54.56, International Institute for Applied Systems Analysis, Laxenburg,
1997.
Walter, H. and Breckle, S.-W.: Walter's Vegetation of the earth?: the
ecological systems of the geo-biosphere, Springer-Verlag, Berlin Heidelberg,
2002.Wedepohl, K. H.: INGERSON LECTURE The composition of the continental crust,
Geochim. Cosmochim. Ac., 59, 1217–1232, 10.1016/0016-7037(95)00038-2,
1995.
Welch, S. A., Beard, B. L., Johnson, C. M., and Braterman, P. S.: Kinetic and
equilibrium Fe isotope fractionation between aqueous Fe(II) and Fe(III),
Geochim. Cosmochim. Ac., 67, 4231–4250, 10.1016/S0016-7037(03)00266-7,
2003.Wiederhold, J. G., Kraemer, S. M., Teutsch, N., Borer, P. M., Halliday, A.
N., and Kretzschmar, R.: Iron isotope fractionation during proton-promoted,
ligand-controlled, and reductive dissolution of goethite, Environ. Sci.
Technol., 40, 3787–3793, 10.1021/es052228y, 2006.
Windom, H. L., Beck, K., and Smith, R.: Transport of trace metals to the
Atlantic Ocean by three southeastern rivers, Southeast Geol., 12, 169–181,
1971.Wu, L., Beard, B. L., Roden, E. E., and Johnson, C. M.: Stable Iron Isotope
Fractionation Between Aqueous Fe(II) and Hydrous Ferric Oxide, Environ. Sci.
Technol., 45, 1847–1852, 10.1021/es103171x, 2011.Yang, D., Kane, D. L., Hinzman, L. D., Zhang, X., Zhang, T., and Ye, H.:
Siberian Lena River hydrologic regime and recent change, J. Geophys.
Res.-Atmos., 107, ACL14-1–ACL14-10, 10.1029/2002JD002542, 2002.Zhang, F., Zhu, X., Yan, B., Kendall, B., Peng, X., Li, J., Algeo, T. J., and
Romaniello, S.: Oxygenation of a Cryogenian ocean (Nanhua Basin, South China)
revealed by pyrite Fe isotope compositions, Earth Planet. Sc. Lett., 429,
11–19, 10.1016/J.EPSL.2015.07.021, 2015.Zhang, T., Barry, R. G., Knowles, K., Heginbottom, J. A., and Brown, J.:
Statistics and characteristics of permafrost and ground-ice distribution in
the Northern Hemisphere, Polar Geogr., 23, 132–154,
10.1080/10889379909377670, 1999.