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Lette r Geochemical Perspectives Letters
© 2015 Europea n Association of Geo chemistry
Geochem. Pe rsp. Let
. (2015) 1, 94-10 4 | doi: 10.7185/geochemle t.1510
Geochem. Pe rsp. Let
. (2015) 1, 94-10 4 | doi: 10.7185/geochemle t.1510
94 95
The effect of warming climate
on nutrient and solute export
from the Greenland Ice Sheet
J.R. Hawkings1*, J.L. Wadham1, M. Tranter1,
E. Lawson1,2, A. Sole3, T. Cowton3,4, A.J. Tedstone4,
I. Bartholomew4, P. Nienow4, D. Chandler1, J. Telling1
Abstract doi: 10.7185/geochemlet.1510
Glacial meltwater runoff is likely an important sou rce of li miti ng nutrients for dow nstream
primary producers. This has par ticular signi ficance for regions surrounding the Greenland
Ice Sheet, which discharges >40 0 km3 of meltwater a nnually. The Arctic is warming rapidly
but the impact of higher discharge on nutrient expor t is un known. We present four years of
hydrolog ical and geochemical d ata from a large Greenla nd Ice Sheet catchment that includes
the two highest melt years on record (2010, 2012). Measu rements reveal significant variat ion
in dissolved solute (major ion) and estimated diss olved macronutrient (nitrog en, phosphorus
and sil ica) fluxes, with increases in higher melt years. Labile par ticulate macronutrients
dominate nutrient export, accounting for ~50 % of nitrogen and >80 % of both phosphorus
and sil ica. The response of ice sheet nut rient export to enhanced melting is larg ely controlled
by particle bound nutrients, the f uture supply of wh ich is uncerta in. We propose that the
Greenl and Ice Sheet provide s an underappreci ated and annually dy namic source of nutrients
for the pola r oceans, with changes in melt water discharge li kely to impact mar ine primary
productivit y in future decades.
Receive d 10 March 2015 | Accepted 19 June 2015 | Pu blished 23 June 2015
Introduction
Recent estimates predict global mean surface warming of up to 4.8 °C above
the 1986-2005 mean by 2100, with the polar regions subject to more extreme
increases (Collins et al., 2013). Already, the Greenland Ice Sheet has experienced
1. Bris tol Glaciology C entre, School of Ge ographical S ciences, Unive rsity of Bri stol, University Road , Bristol,
BS8 1SS, UK
* Corresponding author (email: jon.hawk ings@bristol.ac.uk)
2. School of Geog raphy, Universit y of Nott ingham, Uni versit y Park, Notti ngha m, NG7 2RD, U K
3. Department of Geog raphy, The Un iversity of Shef field, Western Ba nk, Shef field, S10 2T N, UK
4. School of Geos cience, Un iversity of Ed inbu rgh, Drum mond Street, Edi nburgh, EH8 9X P, UK
increased surface temperatures, with the five highest melt seasons on record
occurring since 2000 (Tedesco et al., 2013). In 2012, surface melting was the most
widespread in over 100 years (Tedesco et al., 2013). By 2100, the annual freshwater
flux from the Greenland Ice Sheet could exceed 1000 km3 a-1, making it one of
the world’s largest sources of freshwater (Fettweis et al., 2013).
Currently, we lack information about the impact of meltwater on down-
stream biogeochemical cycles, even though the coastal waters surrounding the ice
sheet harbour highly productive ecosystems, that are strong CO2 sinks (Rysgaard
et al., 2012). Recent work has highlighted the importance of glacier meltwater,
including deliver y of essential nutrients to the polar oceans (Bhatia et al., 2013;
Wadha m et al., 2013; Hawkings et al., 2014; Lawson et al., 2014). However, whether
glacier melting provides an important negative climate feedback through its effect
on marine primary production and CO2 drawdown remains unknown.
Future changes to Greenland Ice Sheet hydrology will probably impact
the export of solute and reactive sediments to the polar oceans. Much of the
meltwater drains from the surface to the ice sheet bed, chemically weathering
the subglacial sediments (Bartholomew et al., 2011). Supraglacial lake drainage
events are particularly important because they rapidly channel large quantities of
meltwater to the ice sheet bed, flushing out stored, solute-rich, subglacial waters
(Bartholomew et al., 2011; Hawkings et al., 2014). Supraglacial lake formation
and the migration of drainage systems inland in a warming climate (Leeson
et al., 2015) could expose new subglacial areas to meltwater flushing, potentially
enhancing solute evacuation. Glaciers are effective at fracturing and grinding
bedrock (Cowton et al., 2012), producing turbid meltwaters with abundant, very
fine suspended particles, i.e. >1 g L-1 (Cowton et al., 2012). Suspended material
has recently been identified as a potential source of labile nutrients to near coastal
regions (Hodson et al., 2004; Bhatia et al., 2013; Hawkings et al., 2014; Wehrmann
et al., 2014) but data are sparse.
In this study, we present a full suite of geochemical and hydrological data
from Leverett Glacier, a large (~600 km2), land terminating, outlet glacier of the
Greenland Ice Sheet (details in Supplementary Information). The data cover
four years (2009-2012) where melting intensity varied (Fig. 1), including the two
highest melt seasons on record. This is the most comprehensive dataset yet on
major ion and nutrient concentrations from a glacial system.
Results and Discussion
Hydrological data (discharge, electrical conductivity and suspended material
concentration) were collected for all four years (2009-2012) at a stable bedrock
section ~2.2 km downstream of the glacier mouth. Major ion data are available
for 2009, 2010 and 2012 and we used them to interpolate concentrations for
2011. Nutrient flux for 2009, 2010 and 2011 was estimated from 2012 data using
a correlation with electrical conductivity. Further details are provided below and
in Supplementary Information.
Geochemical Perspectives Letters Letter Letter Geochemical Perspectives Letters
Geochem. Pe rsp. Let
. (2015) 1, 94-10 4 | doi: 10.7185/geochemle t.1510
Geochem. Pe rsp. Let
. (2015) 1, 94-10 4 | doi: 10.7185/geochemle t.1510
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Figure 1 Field site and basic hydrological data. (a) Leverett Glacier with the snowline transect
used to determine the point where snow covers the ice surface, derive d from MODIS imag-
ery. Dashed lines represent elevatio n contour s. The catchment area was determined from a
surface digitial elevation model (Palmer et al., 2011). (b) Leverett Glacier meltwater discharge
(Table 1) versus modelle d Greenland Ice Sheet runof f (Tedesco et al., 2013). (c) Leverett Glacier
snowline; o pen circles represent observe d position; connec ting lines are linear estimates of
retreat , interpolated between the measurements. Estimated catchment ex tent is represented
by the dot ted line at ~ 80 km.
Hydrology
The 2010 and 2012 ablation seasons produced the largest volumes of meltwater
on record (Tedesco et al., 2013). This is reflected in Leverett Glacier discharge
(Fig. S-1), which was proportional to annual ice sheet runoff (R2 = 0.97; Fig. 1b).
The snowline also reached maximum elevation in 2012, 14 km further inland than
in 2010 and 2011 (Table 1; Fig. 1c). 2009 and 2011 can be considered “average”
melt years, with discharge proportional to the mean meltwater flux over the
past decade. 2010 and 2012, with significantly above average discharge, were
“extreme” melt years. This characterisation provides a benchmark for evaluating
future trends because the frequency of extreme seasons is likely to increase
(Fett weis et al., 2013).
Table 1 Flux and hydrological data.
Units Ye ar
2009 2010 2011 2012
Greenland Ice Sheet runoff * km3348 559 466 665
Leverett Glacier discharge km30.94 1.79 1.10 2.03
Snowline above catchment est. days 45 100 73 85
Snowline retreat from margin km 125 135 135 149
Solute Flux eq 3.0 × 1085.6 × 1083.2 × 1085.6 × 108
Sediment Flux t 3.7× 1062.6 × 1063.0 × 1062.2 × 106
Dissolved inorganic nitrogen t 25 46 26 48
Dissolved silica t 130 230 120 230
Dissolved inorganic phosphorus t 6.2 12 6.7 12
Dissolved inorganic nitrogen t 22 41 25 47
Dissolved silica t 110 220 130 240
Dissolved inorganic phosphorus t 7.8 15 8.9 16
Exchangeable NH4** t 19-58 13-41 15-47 11-35
Amorphous silica** t 18,000-
44,000
12,000-
31,000
14,000-
36,000
11,000-
26,000
NaOH extractable phosphorus** t 20-130 14-92 16-110 12-78
All estimates are shown to Decimal Day 230/231, i.e. 17 Aug ust.
Esti mates are reported with 2 significant digits.
eq = molar equiva lent
t = tons of dry element
Snowline: the boundar y where snow covers the u nderlying ice. Down glacier from this point is exposed ice, where
the snow cover has melted.
* Greenla nd Ice Sheet r unoff estimates from Tedesco et al. (2013).
** Sediment fluxes given as ra nge based on minimum and max imum extractable nut rient concentrations.
† Fluxes estimated with electr ical conductivity.
‡ Fluxes estimated using d ischarge weighted mean.
Solute flux
We estimated total solute export for all years from the electrical conductivity (EC)
of the meltwater (Fig. S-3). The major ion (Ca2+, Mg2+, K+, Na+, Cl-, SO42-, HCO3-)
concentrations are a linear function of conductivity with R2 = 0.87 (2009), 0.77
(2010) and 0.98 (2012) (Figs. S-3 and S-4). We have a full hydrological dataset
(discharge, EC and suspended material) from 2011 but major ion data are missing
so using the concentration-conductivity correlation for data from 2009, 2010 and
2012 (n = 368; R2 = 0.89), we estimated 2011 solute concentrations (Fig. S-3).
Solute flux was estimated by cumulatively summing the total solute concentration
Geochemical Perspectives Letters Letter Letter Geochemical Perspectives Letters
Geochem. Pe rsp. Let
. (2015) 1, 94-10 4 | doi: 10.7185/geochemle t.1510
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. (2015) 1, 94-10 4 | doi: 10.7185/geochemle t.1510
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at each conductivity measurement time step (Fig. 2). We differentiated supragla-
cial solute from the total solute flux to assess the importance of subglacial sources
(Fig. 2a). The estimates suggest that flushing of stored subglacial waters and rapid
weathering of subglacial sediments by dilute supraglacial meltwater account for
>95 % of the solute export from the catchment.
Figure 2 Cumulative solute and sediment flux. (a) S olid lines s how solute flux (Ca2+, Mg2+, K+,
Na+, Cl-, SO42-, HCO3-); dashed lin es represent th e estima ted portion originating fr om supraglacial
meltwater (right axis). (b) Cumulative particle borne flux. (c) Cumulative meltwater discharge.
Day 230 (dashed line) was the limit of the datase t interpretation. Values at the dashed line
corresp ond to data presented in Table 1 and Figure 1b.
A key discovery is that solute flux during the two extreme melt years was
~90 % higher than for the average years, indicating that solute export scales
with discharge. Thus, it is likely that increased melting will increase solute fluxes
from the Greenland Ice Sheet. Most of the solute is delivered during peak melt
periods during the ablation season (Fig. S-5). Solute pulses are also released
during supraglacial lake drainage events (Fig. S-5; Bartholomew et al., 2011).
Enhanced solute discharge during extreme years likely results from i) drainage
of concentrated subglacial waters stored in poorly connected regions, e.g., deeper
into the ice sheet, ii) higher flushing rates and iii) rapid weathering of reactive
subglacial sediments by large volumes of supraglacial meltwater. We next ascer-
tain if nutrient fluxes follow the same trend.
Dissolved nutrient fluxes
Nutrient fluxes for all years were estimated from the 2012 dataset, the only
complete macronutrient record available. For the most common, namely NH4+,
NO3-, Si and PO43-, we also estimated annual flux by correlation with conduc-
tivity, as for major ion concentrations. This is justified by the good correlation
of conductivity with nutrient concentrations (Fig. S-6). If the function holds for
2012, we assume it also holds for the other years. Si and P are released during
rock weathering and dissolved inorganic nitrogen is also enhanced by subglacial
biogeochemical processes, such as microbially mediated nitrification (NO3-) and
mineralisation of organic matter (NH4-; Wynn et al., 2007). For example, mean
nitrogen concentrations attributable to subglacial processes (~1 μM) are similar
to supraglacial processes (~1.3 μM). Nitrogen correlates linearly with conductivity
(R2 = 0.74; Fig. S-6). To account for the seasonal evolution in meltwater composi-
tion, we used two regressions (Fig. S-6) for dissolved silica (R2 = 0.72 for early
season and R2 = 0.34 for bulk season runoff), and phosphate (R2 = 0.61 and 0.59,
respectively). We propose that these differences arise from the change in source
of the subglacial water as the melt season progresses, i.e. close to ice margins early
in the season to more isolated inland subglacial waters as the season progresses.
The source influences the subglacial flowpath length, hence water residence times
and pH/redox conditions.
Higher dissolved nutrient flux correlates with higher discharge years. Inor-
ganic nitrogen (86 % ± 9.8 %), dissolved silica (85 % ± 0.1 %) and phosphate (86 %
± 11.9 %) are higher in extreme melt years than for average years. This is signifi-
cant and demonstrates the potential for nutrient release by a warming climate.
A different approach for estimating nutrient flux is to combine discharge
weighted mean concentrations and total discharge flux (Hawkings et al., 2014).
Estimates from this method and the EC-based method are similar (Table 1). The
weighted mean dissolved nitrogen and silica fluxes were marginally lower (~7 %
and ~5 %) and phosphate flux was higher (~23 %), probably because of late melt
season influence, when phosphate concentrations were high and where the bulk
of the discharge occurred.
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Geochem. Pe rsp. Let
. (2015) 1, 94-10 4 | doi: 10.7185/geochemle t.1510
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. (2015) 1, 94-10 4 | doi: 10.7185/geochemle t.1510
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An important assumption is that the correlation of nutrient concentra-
tion with conductivity is consistent over the years. We have a limited dataset
for NO3- and Si from 2009. Results are sparse so estimates are crude but they
serve as a benchmark for comparison. Flux derived from 2009 data for NO3-N is
12 tons, compared with 15 tons estimated using 2012 data. Flux for dissolved Si is
180 tons, compared with 130 tons estimated using 2012 measurements (Table 1).
Both are well within an order of magnitude, which offers confidence that our
estimates from 2012 data are reasonable.
Nutrient flux on particles
Glaciers effectively fracture and grind bedrock into high surface area, highly
reactive, clay and silt sized particles, some of which are transported in runoff
as suspended material (Gurnell and Clark, 1987; Brown et al., 1996). By using
data derived from the labile nutrients in the 2012 suspended material (n > 25),
we estimated the range of nutrient concentrations associated with the particu-
late fraction (Table 1; Fig. 3). We assumed that the 2009-2011 mean extractable
nutrient concentrations lie within the 2012 minimum and maximum concentra-
tions, which is reasonable because the runoff comes from the same catchment
and the mineral composition is relatively constant (Hawkings et al., 2014).
Figure 3 Estimated nutrient flux. Minimum (lef t column), mean (middle) and maximum
(right) possible values give an impression of the range for phosphate, silicate and nitrogen
compoun ds. Dis solved flux was determined u sing the electrical condu ctivity correlation.
Particulate bound nutrients account for a large portion of the estimated
nutrient flux (Table 1; Fig. 3), which is significant in all years. The particulate
transported f raction correlates with the nutrient source (lithogenic or atmospheric)
and the tendency for the ion to complex. Nutrients derived directly from rocks
associate more with solids, i.e. for Si, >99 % and for P, ~80 % of the total flux.
Nitrogen, which has a supraglacial component, is transported less on solids, i.e.
<50 %. Our results are consistent with the low solubility of Si and the high affinity
for P absorption onto solids, such as iron (oxyhyd)roxides. Ammonium is only
weakly absorbed and nitrate remains preferentially in solution. This suggests that
annual nitrogen flux is more sensitive to changes in ice sheet water discharge
than particle flux.
We have demonstrated that, as in riverine systems (Mayer et al., 1998;
Ruttenberg, 2014), a high fraction of ice sheet nutrient export is associated with
suspended material. This is consistent with prev ious research from Arctic glaciers
(Hodson et al., 2004) and supports recent assertions that the impact of terrige-
neous material on the oceans is underestimated in global element cycling (Jeandel
and Oelkers, 2015). Our results underline the need for more information about
ice sheet sediment flux dynamics. As in previous studies, we observed highly
variable annual sediment fluxes, which do not correlate well with discharge on
a catchment basis (Fig. 2; Gurnell and Clark, 1987). Sediment flux might be less
influenced by total meltwater discharge and more sensitive to meltwater access
to fresh, subglacial sediment sources (Cowton et al., 2012). However, evidence
from past deglaciation events indicates that climate warming increases sedi-
ment export (Jeandel and Oelkers, 2015) and analysis of sediment plumes from
meltwater rivers demonstrates a higher sediment flux in recent years (Hudson
et al., 2014).
The extent of biological consumption of the nutrients bound to particles
before deposition and subsequent burial is unknown. Particulates from melt-
water are extremely fine, e.g., >95 % of particles can be <32 μm in size (Brown
et al., 1996), so surface area is high and nutrient transport in the buoyant, fresh
water plumes in near coastal regions is likely to be significant. Evidence from
recent polar studies shows that particle borne nutrients are carried far offshore
(Schroth et al., 2014; Wehrmann et al., 2014) and nutrients deposited with glacial
sediments in fjords can be resuspended in the water column (Wehrmann et al.,
2014). However, the scarcity of data means that the contribution of particle bound
nutrients on oceanic productivity near Greenland remains uncertain.
Terrestrial and marine studies have shown that large fractions (75-95 %)
of amorphous Si can be dissolved and recycled (Treguer et al., 1995; Gibson et al.,
2000). Amorphous Si is an order of magnitude more soluble in saline solutions
than in fresh water (Icenhower and Dove, 2000; Loucaides et al., 2008) and recy-
cling is favoured in estuaries (Loucaides et al., 2008). NaOH extractable phosphate
is commonly termed “algae available” (DePinto et al., 1981) and its bioavail-
ability has previously been demonstrated (Bostrom et al., 1988). High salinity in
ocean and fjord waters also favours P and NH4 desorption (Garner et al., 1991;
Hodson et al., 2004; Zhang and Huang, 2011), enhancing their bioavailability.
Thus, annual sediment flux is an important factor in downstream productivity.
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Conclusions
Changes in the hydrological output from the Greenland Ice Sheet in a warming
climate could have significant effect on solute and nutrient delivery to near
coastal regions. Our data, from Leverett Glacier, a large representative ice sheet
catchment, indicate that bulk solute and dissolved nutrient fluxes will increase
as “extreme” melt year frequency increases. A significant fraction of nutrients,
especially silica and phosphorous, will be transported by suspended particles.
The extent of their influence depends on desorption before burial, bioavailability
and change in the ice sheet particulate flux, which are currently uncertain. Our
study demonstrates that retreating snowline and higher meltwater input into less
efficiently drained subglacial regions are likely to increase the dissolved macronu-
trient flux. Particle bound nutrients have been largely overlooked but contribute
significant mass to nutrient cycling. Increased warming, thus increased meltwater
runoff, will likely impact regional nutrient availability, and thus, the carbon cycle.
Acknowledgements
This research was part of the UK Natural Environment Research Council Project,
DELVE (NERC grant NE/I008845/1) and the associated PhD studentship to JH.
EL, AT, TC and IB were funded by NERC studentships and a MOSS scholarship.
PN was supported by the Carnegie Trust for The University of Scotland and The
University of Edinburgh Development Trust. Additional support was provided by
the Leverhulme Trust, in a research fellowship to JLW. We thank all of those who
assisted with fieldwork at Leverett Glacier and the technical staff in LOWTEX
labs, School of Geographical Sciences, University of Bristol. We are grateful to
our anonymous reviewers for constructive comments on the manuscript.
Editor: Susan S.L. Stipp
Additional Information
Supplementary Information accompanies this letter at www.geochemicalper-
spectivesletters.org/article1510
Reprints and permission information is available online at http://www.
geochemicalperspectivesletters.org/copyright-and-permissions
Cite this letter as: Hawkings, J.R., Wadham, J.L., Tranter, M., Lawson, E., Sole,
A., Cowton, T., Tedstone, A.J., Bartholomew, I., Nienow, P., Chandler, D., Telling,
J. (2015) The effect of warming climate on nutrient and solute export from the
Greenland Ice Sheet. Geoche m. Persp. Let. 1, 94-104.
Author Contributions
All authors contributed. JLW and MT conceived the project. JRH, EL, AS, TC, IB,
AT, PN, DC and JLW collected field data. JRH, JRH, EL and JT undertook the lab
analysis. JRH, JLW and MT wrote the paper.
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The effect of warming climate
on nutrient and solute export
from the Greenland Ice Sheet
J.R. Hawkings1*, J.L. Wadham1, M. Tranter1,
E. Lawson1,2, A. Sole3, T. Cowton3,4, A.J. Tedstone4,
I. Bartholomew4, P. Nienow4, D. Chandler1, J. Telling1
Supplementary Information
The Supplementary Information includes:
Study Site and Methods
Figures S-1 to S-6
Supplementar y Information References
Study Site and Methods
Study area
Research was conducted at Leverett Glacier (LG; Fig. 1a; 67.06 °N, 50.17 °W), a
large, land terminating glacier on the southwestern margin of the Greenland Ice
Sheet (GrIS). The catchment extends >80 km into the ice sheet and is estimated
to cover an area of >600 km2 (Palmer et al., 2011; Cowton et al., 2012). Leverett
overlies bedrock of Archean gneiss and granite, common to much of Greenland
(Henriksen et al., 2009). Catchment hydrolog y is typical of large Greenland outlet
glaciers and is described elsewhere (Chandler et al., 2013). A catchment hydrolog-
ical record was maintained during the 2009-2012 summer ablation seasons, with
monitoring of discharge, electrical conductivity (EC) and turbidity (suspended
material), recorded at 5-10 minute intervals (Fig. S-1).
1. Bris tol Glaciology C entre, School of Ge ographical S ciences, Unive rsity of Bri stol, University Road , Bristol,
BS8 1SS, UK
* Corresponding author (email: jon.hawk ings@br istol.ac.uk)
2. School of Geog raphy, Universit y of Nott ingham, Uni versit y Park , Notti ngha m, NG7 2RD, UK
3. Depart ment of Geog raphy, The Un iversity of Shef field, Western Ba nk, Sheffield, S10 2T N, UK
4. School of Geoscience, Un ivers ity of Ed inbu rgh, D rum mond Street, Edi nburgh, EH8 9X P, UK
© 2015 Europea n Association of Geo chemistry
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Figure S -1 Leveret t Glacier discharge hydrographs and electrical conductivity. Shaded areas in
the discharge plot s show when discharge excee ded 200 m3 sec-1. The dashe d line represents
the cut of f date use d for flux estimates.
Water sample collection and filtration
Bulk meltwater samples for geochemical analysis were collected at least once
a day (2009, 2010, 2012), from a sampling site located ~1 km (2012) or ~2 km
(2009, 2010) downstream from the Leverett Glacier terminus, throughout the
main melt period (May-August). Our confidence that these waters represent the
bulk discharge is based on the drainage of Leverett from a single portal. The
composition of point samples taken there were within the uncertainty of those
taken further downstream.
Grab samples were immediately passed through 47 mm 0.45 μm cellulose
nitrate filters (W hatman®), mounted on a PES filtration stack (NalgeneTM), that
had been rinsed 3 times with the sample. The filtrate was immediately frozen
in clean HDPE 30 mL NalgeneTM bottles that had been rinsed 3 times with
the filtered sample. Major ion analysis (Ca2+, Mg2+, K+, Na+, Cl-, SO42-, HCO3-)
and NO3- was completed within three months of collection. We used a Thermo
ScientificTM DionexTM DX-500 (2009, 2010) or a Thermo ScientificTM DionexTM
capillary ICS-5000 (2012), fitted with simultaneous anion and cation columns.
Measurement accuracy was ~ ±4 % and precision was ~ ±7 % for the DX-500, and
~ ±3 % and ~ ±3 % for the ICS-5000. Dissolved macronutrients were measured
from the 2012 samples using a LaChat QuickChem® 8500 flow injection analyser
system using low level detection methods (Si, PO4-) or by manual colormetric
techniques (NH4+), as described by Le and Boyd (2012). All samples were field
blank corrected where the blank concentrations were above the detection limit
of the instrument. In total, 408 samples were analysed for major ions and 75
samples, for nutrient concentrations. In 2012, snow and supraglacial meltwaters
draining into a moulin ~30 km from the catchment margin were sampled for
geochemical analysis (n = 32), using the same methods as the bulk geochemical
samples. Snow samples were placed in new Whirl-Pak® bags (Nasco) and left
in a water bath to melt. Samples were filtered, as above, as soon as melting was
complete.
Sediment nutrient extrac tions
Particulate bound nutrient samples were taken during the 2012 melt season
(n = 25 for P and Si, n = 39 for N). Briefly, a meltwater sample of 300-400 mL
was filtered through a 0.45 μm cellulose nitrate filter (PSi and PP; Whatman®)
or a 0.7 μm glass microfibre filter. Suspended particulate material was retained
for the commonly used labile nutrient extractions, “algae available” P (Hodson
et al., 2004), exchangeable NH4 (PN; Maynard et al., 2007), and amorphous
Si (PSi; DeMaster, 1981). Particulate material was removed carefully by gentle
scraping from the filter, and weighed. Mean extractable concentrations were
combined with the total sediment flux from Leverett Glacier, to determine the
labile particulate nutrient flux.
“Algae available” phosphorus ex traction
Owing to its importance as an essential nutrient, phosphorus extraction tech-
niques are well documented in the literature (Dorich et al., 1980; DePinto et al.,
1981; Sharpley et al., 1991; Ekholm and Krogerus, 2003; Hodson et al., 2004). Here
we used a common extraction method that aims to determine the amount that is
bioavailable (Bostrom et al., 1988; Hodson et al., 2004). We adapted the standard
method to allow for analysis of very small quantities of sediment, i.e. “micro-
extraction”. Briefly, 1.5 mL of 0.1 M NaOH solution was added to ~50 mg of sedi-
ment, that was accurately measured to ±0.001 g using a high precision/accuracy
balance. We used 2 mL microcentrifuge tubes, which allow similar sediment to
extractant ratios to those used by others (Hodson et al., 2004). Microcentrifuge
tubes were capped and placed on a reciprocating (rotary) shaker at 200 rpm for
16 hours. Tubes were then centrifuged at 2600 rpm for 10 minutes, the superna-
tant was transferred to new 2 mL tubes using a 1 mL plastic syringe (PP/PE) and
filtered through a sy ringe filter (Whatman® Puradisc PP).
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Exchangeable ammonium extraction
We adopted the method described by Maynard et al. (2007) and applied elsewhere
(Telling et al., 2011, 2012, 2014). 10 mL of 2.0 M KCl solution was added to 0.7 μm
filters (GF/F Whatman®) in a 15 mL plastic centrifuge tube. Tubes were capped
and placed on a reciprocating (rotary) shaker (160 rpm) for 30 minutes. Solu-
tions were then decanted into fresh plastic tubes, centrifuged, filtered through
a 0.45 μm syringe filter (Whatman® Puradisc PP) and frozen at -20 °C until
analysis. All sediment from filters was retained, rinsed with Milli-Q deionised
water (18.2 MΩ cm-1 Millipore) to remove extract solution and dried in an oven
overnight at ~50 °C to provide dry sediment weights. These were cross checked
against weights expected from hydrological suspended sediment records, i.e.
300 mL of water was filtered so an expected weight could be generated from
the recorded meltwater suspended material. Nine blanks were treated in the
same manner as the samples, using the same types of filter, to test for filter
contamination.
Amorphous silica ex traction
This is the first study to present data on extraction of amorphous silica in glacial
sediments. Here we use a method commonly employed in marine and riverine
systems that was developed by DeMaster (1981) and validated for terrestrial soils
and sediments (Sauer et al., 2006). The technique uses 0.1 M Na2CO3, a weak base,
which maximises dissolution of amorphous Si, with minimal impact on crystal-
line material. About 30 mg of sediment was accurately weighed into a 60 mL
HDPE bottle (Nalgene®) and 50 mL of 0.1 M Na2CO3 solution was added. Bottles
were placed in a hot water bath (85 °C) and 1 mL aliquots were removed after 1,
2, 3 and 5 hours. Aliquots were refrigerated in 2 mL microcentrifuge tubes at 4 °C
until analysis, less than 24 hours later. Just prior to analysis, 0.5 mL of sample was
neutralised with 4.5 mL 0.021 M HCl in plastic centrifuge tubes. Three blanks
were processed alongside the samples to check for method contamination. A mor-
phous silica was determined by using the intercept of the regression line drawn
through Si concentrations obtained from the time series aliquots; amorphous
silica dissolves within the first hour of the extraction procedure (DeMaster, 1981).
Analysis of extrac t solutions and filtered meltwater
Phosphorus and silica extraction solutions were measured on a LaChat Quick-
Chem® 8500 flow injection analyser system (Method Numbers 31-115-01-1-I for
P and 31-114-27-1D for Si). The coefficient of variation (CoV) for the method was
±0.5 % for silica (based on seven replicate standards) and ±3.2 % for dissolved
orthophosphate (five replicate standards). Limits of detection were 0.3 μM (8.4 μg
Si L-1) and 0.01 μM (0.3 μg P L-1). Ammonium was determined using a Bran and
Luebbe Autoanalyzer 3 (for extractants) or by the manual salicylate method (Le
and Boyd, 2012). The Luebbe Autoanalyzer 3 method had a CoV of ±1.5 % (eight
replicate standards) and a detection limit of 0.5 μM (6.4 μg N L-1). The manual
method had a CoV of ±4.9 % (five replicate standards) and a limit of detection of
0.6 μM (8.4 μg N L-1). All samples were blank corrected where blank concentra-
tions were higher than the detection limits.
Contribution of supraglacial solute to total solute flux
Measured mean major ion concentration in supraglacial melt (snow and ice melt
from 2012, n = 32) was 15 μeq L-1 (±7 μeq L-1). There is no reason to expect there
to be significant annual variation in these concentrations, which are more than an
order of magnitude lower than mean bulk meltwaters (~400 μeq L-1). The mean
supraglacial major ion value of 15 μeq L-1 was multiplied by catchment discharge
at each time step and cumulatively summed (Fig. 2) to derive solute fluxes from
supraglacial sources.
Catchment hydrological monitoring and meltwater/sediment fluxes
Leverett Glacier runoff was hydrologically gauged throughout the 2009-2012
summer melt seasons, from late Apri l or early May at the onset of melting, through
to late August or early September. Briefly, the discharge, electrical conductivity
and turbidity (suspended material concentration) of the meltwater river were
logged every 5 minutes at a stable bedrock section ~2.2 km downstream from
the glacier terminus (Cowton et al., 2012). Discharge was determined using the
method described by Bartholomew et al. (2011). A wired water pressure sensor
monitored stage, which was converted into discharge using a (stage-discharge)
rating curve of Rhodamine W T dye dilution injections. Twenty nine dye dilu-
tions were used in 2009 and 2010, 26 in 2011 and 41 in 2012. Leverett meltwater
and particulate material fluxes were determined by multiplying discharge and
suspended material concentrations at the 5 minute time points by 300 (to derive
values for each second over the 5 minute period between new recordings) and
summed over the entire melt season. For comparison, modelled meltwater runoff
data for the Greenland Ice Sheet were taken from Tedesco et al. (2013).
Snowline determination
Snowline retreat throughout the 2009-2012 melt seasons was monitored using
MODIS (moderate resolution imaging spectroradiometer) on the Terra plat-
form. Surface reflectance band 1-2 images (Product Number MOD09GQ) were
processed using the QGIS analysis package, to determine snowline extent
(Fig. S-2). Maximum snowline position from monitored years is shown in
Figure 1. A minimum of 18 cloud free images were used per year to determine
snowline migration.
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Figure S -2 An example of the MODIS satellite imagery use d to determine snowline exte nt.
Data are from surface reflec tance bands 1-2 (Pro duct Number MO D09GQ). Levere tt Glacier
moves from east to west. The estimated catchment area is outlined in black (Palmer et al.,
2011) and the snowline transect is displayed by the red d otted line (space between each dot =
5 km). False colour imaging differentiates betwee n snow (dark blue) and ice (light blue). The
margin of the ice sheet is evident at the bord er of the red colouring (black arrow). The blue
dashed line represents the interpreted position of the snowline. The image displayed is from
21 July 2012. Fig. 1a provides more information about the catchme nt.
Figure S -3 Re gression plots for major ions as a func tion of electric al conductivit y. Shaded
blue lines represent the st andard error (σ, also written in the top lef t of plots). The 2011
regression plot ( bottom left), which enco mpasess data from 2009, 2010 and 2012, is magnified
to demonstrate the linear relationship of electrical conductivity with major ions in the dilute
waters.
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Figure S -4 Comparison of regression plots for the major io ns for 2009, 2010 and 2012, whe re
data are available. The differences in th e regres sion equations us ed to determine majo r ion
concentrations are very small.
Figure S -5 Temporal variation in meltwater discharge and e stimated solute flux. Coloured
lines indi cate solute flux calculated by the EC based method (eq min-1), and black lines, melt-
water discharge (m3 min-1 ), during the 2009 -2012 melt seas ons. Shaded areas corres pond to
meltwater pulse events. These are associated with spring eve nts, i.e. the annual opening of
the subglacial drainage system, or rapid drainage of meltwater from supraglacial lake drain-
age event s. These melt water pulses flush concentrated waters from the subglacial drainage
syste m (Bartholomew et al., 2011 and Hawkings et al., 2014).
Figure S -6 Regression plot s for nutrient concentrations as a func tion of electrical condu ctivity.
The regression plots for Si and PO43- represent early (blue) versus later seas on (red) hydro-
logical and asso ciated bio geochemical changes. Early season regre ssions are applie d to time
points b efore Day 153 in 20 09, Day 128 in 2010, Day 160 in 2011 and Day 150 in 2012, which
are before the initial change in drainage hydrology occurred, i.e. the spring event (Figs S -1
and S-5). Shaded areas show a ssociated standard error.
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Reconstructions of sea-surface conditions during the Holocene were achieved using three sediment cores from northeastern Baffin Bay (GeoB19948-3 and GeoB19927-3) and the Labrador Sea (GeoB19905-1) along a north-south transect based on sea-ice IP 25 and open-water phytoplankton biomarkers (brassicasterol, dinosterol and HBI III). In Baffin Bay, sea-surface conditions in the Early Holocene were characterized by extended (early) spring sea ice cover (SIC) prior to 7.6 ka BP. The conditions in the NE Labrador Sea, however, remained predominantly ice-free in spring/autumn due to the enhanced influx of Atlantic Water (West Greenland Current, WGC) from 11.5 until~9.1 ka BP, succeeded by a period of continued (spring-autumn) ice-free conditions between 9.1 and 7.6 ka BP corresponding to the onset of Holocene Thermal Maximum (HTM)-like conditions. A transition towards reoccurring ice-edge and significantly reduced SIC conditions in Baffin Bay is evident in the Middle Holocene (~7.6-3 ka BP) probably caused by the variations in the WGC influence associated with the ice melting and can be characterized as HTM-like conditions. These HTM-like conditions are predominantly recorded in the NE Labrador Sea area shown by (spring-autumn) ice-free conditions from 5.9-3 ka BP. In the Late Holocene (last~3 ka), our combined proxy records from eastern Baffin Bay indicate low in-situ ice algae production; however, enhanced multi-year (drifted) sea ice in this area was possibly attributed to the increased influx of Polar Water mass influx and may correlate with the Neoglacial cooling. The conditions in the NE Labrador Sea during the last 3 ka, however, continued to remain (spring-autumn) ice-free. Our data from the Baffin Bay-Labrador Sea transect suggest a dominant influence of meltwater influx on sea-ice formation throughout the Holocene, in contrast to sea-ice records from the Fram Strait area, which seem to follow predominantly the summer insolation trend.
... Another explanation for the increased accumulation rates of the phytoplankton biomarkers in the Late Holocene (Fig. 8F) might be the increased nutrient supply (e.g. Fe, Si) associated with the enhanced local meltwater discharge (Bhatia et al. 2013;Hawkings et al. 2015;Arrigo et al. 2017;Cape et al. 2019). Based on exploration studies from the nearby Sinarsuk deposit, Secher (1980) and Grammatikopoulos et al. (2002) found a significant amount of magnetite in the host rock, which might be a potential source of high Fe contents recorded in the Late Holocene section of the core GeoB19905-1 (Weiser et al. 2021). ...
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Reconstructions of sea‐surface conditions during the Holocene were achieved using three sediment cores from northeastern Baffin Bay (GeoB19948‐3 and GeoB19927‐3) and the Labrador Sea (GeoB19905‐1) along a north–south transect based on sea‐ice IP25 and open‐water phytoplankton biomarkers (brassicasterol, dinosterol and HBI III). In Baffin Bay, sea‐surface conditions in the Early Holocene were characterized by extended (early) spring sea ice cover (SIC) prior to 7.6 ka BP. The conditions in the NE Labrador Sea, however, remained predominantly ice‐free in spring/autumn due to the enhanced influx of Atlantic Water (West Greenland Current, WGC) from 11.5 until ~9.1 ka BP, succeeded by a period of continued (spring–autumn) ice‐free conditions between 9.1 and 7.6 ka BP corresponding to the onset of Holocene Thermal Maximum (HTM)‐like conditions. A transition towards reoccurring ice‐edge and significantly reduced SIC conditions in Baffin Bay is evident in the Middle Holocene (~7.6–3 ka BP) probably caused by the variations in the WGC influence associated with the ice melting and can be characterized as HTM‐like conditions. These HTM‐like conditions are predominantly recorded in the NE Labrador Sea area shown by (spring–autumn) ice‐free conditions from 5.9–3 ka BP. In the Late Holocene (last ~3 ka), our combined proxy records from eastern Baffin Bay indicate low in‐situ ice algae production; however, enhanced multi‐year (drifted) sea ice in this area was possibly attributed to the increased influx of Polar Water mass influx and may correlate with the Neoglacial cooling. The conditions in the NE Labrador Sea during the last 3 ka, however, continued to remain (spring–autumn) ice‐free. Our data from the Baffin Bay–Labrador Sea transect suggest a dominant influence of meltwater influx on sea‐ice formation throughout the Holocene, in contrast to sea‐ice records from the Fram Strait area, which seem to follow predominantly the summer insolation trend.
... Glacier runoff can have counteracting effects on the productivity of Arctic fjords (e.g., Hopwood et al., 2020). Glacier runoff may be a direct source of nutrients to downstream ecosystems, for example bioavailable iron, nitrogen, phosphate or silicate (Hodson et al., 2005;Bhatia et al., 2013;Hawkings et al., 2015;Fransson et al., 2015;Meire et al., 2016;Dubnick et al., 2017;Milner et al., 2017;Hopwood et al., 2018). However, glacial meltwater is generally characterized by low nutrient concentrations in comparison with the ambient seawater (Halbach et al., 2019;Cantoni et al., 2020;Hopwood et al., 2020). ...
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... This would lead to higher temperatures in the Arctic Ocean, including Spitsbergen, causing the glaciers to melt earlier in the annual cycle and then freeze, increase precipitation and reduce sea ice cover. In addition, glacial melt drains downstream, leading to changes of biogeochemical and nutrient salt in downstream ecosystems (Bhatia et al. 2013;Hawkings et al. 2015;Hood et al. 2015;Hood Berner 2009;Lawson et al. 2014;Schroth et al. 2014). ...
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Due to the inflow of meltwater from the Midre Lovénbreen glacier upstream of Kongsfjorden, the salinity of Kongsfjorden increases from the estuary to the interior of the fjord. Our goal was to determine which bacterial taxa and metabolism-related gene abundance were affected by changes in salinity, and whether salinity is correlated with genes related to nitrogen and sulfur cycling in fjord ecosystem using metagenomic analysis. Our data indicate that changes in salinity may affect some bacterial taxa, such as the relative abundance of Alphaproteobacteria and Deltaproteobacteria is higher at high salinity sites, while the relative abundance of Gammaproteobacteria and Betaproteobacteria is more dominant at low salinity sites. In addition, the relative abundance of some bacteria at the high and low salinity sites was different at the family level. For example, Rhodobacteraceae, Pseudoalteromonadaceae, Flavobacteriaceae, Vibrionaceae at the high salinity site Colwelliaceae, Chromatiaceae and Alteromonadaceae at the low salinity site are affected by salinity. In terms of functional gene diversity, our study proved that salinity could affect the relative abundance of related genes by affecting the metabolic mechanism of microorganisms. In addition to salinity, functional attributes of microorganisms themselves were also important factors affecting the relative abundance of metabolism-related genes. In addition, salinity has a certain effect on the relative abundance of genes related to nitrogen and sulfur cycling.
... Biogeochemical studies from glacierized watersheds show strong variability in nutrient and solute fluxes on diel to seasonal timescales (Dzikowski & Jobard, 2012;Fairchild et al., 1999;Hawkings et al., 2015;Hindshaw et al., 2011;Hood & Berner, 2009;Koch et al., 2010). Hydrologically, stream discharge timing and magnitude is typically dominated by snow and glacier melt and impacted by the configuration and efficiency of the subglacial drainage network, even with low percent glacier covered area (Fountain & Tangborn, 1985;Jansson et al., 2003). ...
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During past periods of advance, Arctic glaciers and ice sheets overrode soil, sediments, and vegetation and buried significant stores of organic matter (OM); these glaciers are now shrinking rapidly due to climate warming. Little is known about the biogeochemical processing of the OM buried beneath glacier ice which makes the processes associated with deglaciation difficult to predict. Subglacial sediments exposed at receding glacier fronts may represent a legacy of past biogeochemical processes. Here, we analysed sediments from retreating fronts of 19 Arctic glaciers for their mineralogical and elemental composition, contents of major nutrients, OM biomarkers (aliphatic lipids and lignin-derived phenols), 14C age, and microbial community structure. We show the character of the sediments is mostly determined by local glaciation history and bedrock lithology. Most subglacial sediments offer high amounts of readily bioavailable phosphorus (i.e. loose, labile, and Fe/Al P fractions) but lack readily accessible carbon substrates. The subglacial OM originated mainly from overridden terrestrial vascular plants. The results of OM biomarker analysis and 14C dating suggest the OM substrates degrade in the subglacial environment and are reworked by the resident microbial communities. We argue the biogeochemical legacy of the perishing subglacial environments is an important determinant for the early processes of proglacial ecological succession.
Chapter
The geochemistry of glacial outflows is best developed in the case of valley glaciers, where more than four decades of research have provided major insights into solute acquisition and biogeochemical processes. This chapter describes these processes and draws important distinctions between valley glaciers and larger, less understood polar ice sheets. Key reactions that define the composition of glacial outflows are described, giving emphasis to their major ion, nutrient, stable isotope and minor or trace element composition. Qualitative and quantitative attempts to use this information to separate glacial outflow hydrographs into delayed (distributed) and rapid (channelized) flow paths are also described.
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The Greenland and Antarctic Ice Sheets cover ~ 10% of global land surface, but are rarely considered as active components of the global iron cycle. The ocean waters around both ice sheets harbour highly productive coastal ecosystems, many of which are iron limited. Measurements of iron concentrations in subglacial runoff from a large Greenland Ice Sheet catchment reveal the potential for globally significant export of labile iron fractions to the near-coastal euphotic zone. We estimate that the flux of bioavailable iron associated with glacial runoff is 0.40-2.54 Tg per year in Greenland and 0.06-0.17 Tg per year in Antarctica. Iron fluxes are dominated by a highly reactive and potentially bioavailable nanoparticulate suspended sediment fraction, similar to that identified in Antarctic icebergs. Estimates of labile iron fluxes in meltwater are comparable with aeolian dust fluxes to the oceans surrounding Greenland and Antarctica, and are similarly expected to increase in a warming climate with enhanced melting.
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The seasonal melting of ice entombed cryoconite holes on McMurdo Dry Valley glaciers provides oases for life in the harsh environmental conditions of the polar desert where surface air temperatures only occasionally exceed 0°C during the Austral summer. Here we follow temporal changes in cryoconite hole biogeochemistry on Canada Glacier from fully frozen conditions through the initial stages of spring thaw toward fully melted holes. The cryoconite holes had a mean isolation age from the glacial drainage system of 3.4 years, with an increasing mass of aqueous nutrients (dissolved organic carbon, total nitrogen, total phosphorus) with longer isolation age. During the initial melt there was a mean nine times enrichment in dissolved chloride relative to mean concentrations of the initial frozen holes indicative of an ionic pulse, with similar mean nine times enrichments in nitrite, ammonium, and dissolved organic matter. Nitrate was enriched twelve times and dissolved organic nitrogen six times, suggesting net nitrification, while lower enrichments for dissolved organic phosphorus and phosphate were consistent with net microbial phosphorus uptake. Rates of bacterial production were significantly elevated during the ionic pulse, likely due to the increased nutrient availability. There was no concomitant increase in photosynthesis rates, with a net depletion of dissolved inorganic carbon suggesting inorganic carbon limitation. Potential nitrogen fixation was detected in fully melted holes where it could be an important source of nitrogen to support microbial growth, but not during the ionic pulse where nitrogen availability was higher. This study demonstrates that ionic pulses significantly alter the timing and magnitude of microbial activity within entombed cryoconite holes, and adds credence to hypotheses that ionic enrichments during freeze-thaw can elevate rates of microbial growth and activity in other icy habitats, such as ice veins and subglacial regelation zones.
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The Greenland and Antarctic Ice Sheets cover ~\n10% of global land surface, but are rarely considered as active components of the global iron cycle. The ocean waters around both ice sheets harbour highly productive coastal ecosystems, many of which are iron limited. Measurements of iron concentrations in subglacial runoff from a large Greenland Ice Sheet catchment reveal the potential for globally significant export of labile iron fractions to the near-coastal euphotic zone. We estimate that the flux of bioavailable iron associated with glacial runoff is 0.40-2.54 Tg per year in Greenland and 0.06-0.17 Tg per year in Antarctica. Iron fluxes are dominated by a highly reactive and potentially bioavailable nanoparticulate suspended sediment fraction, similar to that identified in Antarctic icebergs. Estimates of labile iron fluxes in meltwater are comparable with aeolian dust fluxes to the oceans surrounding Greenland and Antarctica, and are similarly expected to increase in a warming climate with enhanced melting.
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A combined analysis of remote sensing observations, regional climate model (RCM) outputs and reanalysis data over the Greenland ice sheet provides evidence that multiple records were set during summer 2012. Melt extent was the largest in the satellite era (extending up to ∼97% of the ice sheet) and melting lasted up to ∼2 months longer than the 1979-2011 mean. Model results indicate that near surface temperature was ∼3 standard deviations (σ) above the 1958-2011 mean, while surface mass balance (SMB) was ∼3σ below the mean and runoff was 3.9σ above the mean over the same period. Albedo, exposure of bare ice and surface mass balance also set new records, as did the total mass balance with summer and annual mass changes of, respectively, -627 Gt and -574 Gt, 2σ below the 2003-2012 mean. We identify persistent anticyclonic conditions over Greenland associated with anomalies in the North Atlantic Oscillation (NAO), changes in surface conditions (e.g., albedo, surface temperature) and preconditioning of surface properties from recent extreme melting as major driving mechanisms for the 2012 records. Less positive if not increasingly negative SMB will likely occur should these characteristics persist.
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To estimate the sea level rise (SLR) originating from changes in surface mass balance (SMB) of the Greenland ice sheet (GrIS), we present 21st century climate projections obtained with the regional climate model MAR (Modèle Atmosphérique Régional), forced by output of three CMIP5 (Coupled Model Intercomparison Project Phase 5) general circulation models (GCMs). Our results indicate that in a warmer climate, mass gain from increased winter snowfall over the GrIS does not compensate mass loss through increased meltwater run-off in summer. Despite the large spread in the projected near-surface warming, all the MAR projections show similar non-linear increase of GrIS surface melt volume because no change is projected in the general atmospheric circulation over Greenland. By coarsely estimating the GrIS SMB changes from GCM output, we show that the uncertainty from the GCM-based forcing represents about half of the projected SMB changes. In 2100, the CMIP5 ensemble mean projects a GrIS SMB decrease equivalent to a mean SLR of &plus;4 ± 2 cm and &plus;9 ± 4 cm for the RCP (Representative Concentration Pathways) 4.5 and RCP 8.5 scenarios respectively. These estimates do not consider the positive melt-elevation feedback, although sensitivity experiments using perturbed ice sheet topographies consistent with the projected SMB changes demonstrate that this is a significant feedback, and highlight the importance of coupling regional climate models to an ice sheet model. Such a coupling will allow the assessment of future response of both surface processes and ice-dynamic changes to rising temperatures, as well as their mutual feedbacks.
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Predictions of the Greenland Ice Sheet's response to climate change are limited in part by uncertainty in the coupling between meltwater lubrication of the ice-sheet bed and ice flow. This uncertainty arises largely from a lack of direct measurements of water flow characteristics at the bed of the ice sheet. Previous work has been restricted to indirect observations based on seasonal and spatial variations in surface ice velocities and on meltwater flux. Here, we employ rhodamine and sulphur hexafluoride tracers, injected into the drainage system over three melt seasons, to observe subglacial drainage properties and evolution beneath the Greenland Ice Sheet, up to 57km from the margin. Tracer results indicate evolution from a slow, inefficient drainage system to a fast, efficient channelized drainage system over the course of the melt season. Further inland, evolution to efficient drainage occurs later and more slowly. An efficient routing of water was established up to 41km or more from the margin, where the ice is approximately 1km thick. Overall, our findings support previous interpretations of drainage system characteristics, thereby validating the use of surface observations as a means of investigating basal processes.
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A study was conducted to compare the precision and accuracy of the phenate method and the salicylate method for determining total ammonia nitrogen concentration in water over a wide range of salinities. The two methods provided results that were highly correlated (P n = 29, r = 0.996; low salinity (≫4 ppt), n = 17, r = 0.994; high salinity (≫24 ppt), n = 11, r = 0.981. Considering all samples the regression equation for the two methods was Y = 0.939X + 0.0038 where X = salicylate method (mg/L) and Y = phenate method (mg/L); the r value was 0.984 (P P P > 0.05). In replicate analyses of the same samples, the salicylate method often gave a higher mean concentration of total ammonia nitrogen than was obtained with the phenate method. Also, precision was usually better for the salicylate method. Accuracy, as determined by spike recovery, was slightly superior for the salicylate method. The findings suggest that the salicylate method is a preferable alternative to the phenate methods for use in freshwater and saline water aquaculture applications.
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The micronutrient iron is thought to limit primary productivity in large regions of the global ocean. Ice sheets and glaciers have been shown to deliver bioavailable iron to the coastal and open ocean in the form of sediment released from the base of icebergs and glacially derived dust. More direct measurements from glacial runoff are limited, but iron concentrations are thought to be in the nanomolar range. Here we present measurements of dissolved and particulate iron concentrations in glacial meltwater from the southwest margin of the Greenland ice sheet. We report micromolar concentrations of dissolved and particulate iron. Particulate iron concentrations were on average an order of magnitude higher than those of dissolved iron, and around 50% of this particulate iron was deemed to be potentially bioavailable, on the basis of experimental leaching. If our observations are scalable to the entire ice sheet, then the annual flux of dissolved and potentially bioavailable particulate iron to the North Atlantic Ocean would be approximately 0.3Tg. This is comparable to dust-derived soluble iron inputs to the North Atlantic. We suggest that glacial runoff serves as a significant source of bioavailable iron to surrounding coastal oceans, which is likely to increase as melting of the Greenland ice sheet escalates under climate warming.