Suspended sediment fluxes in a high-Arctic glacierised catchment: implications for fluvial sediment storage Richard Hodgkins a, * , Richard Cooper b,1 , Jemma Wadham c,2 , Martyn Tranter c,2 a Department of Geography, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK b The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, Scotland, UK c Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, UK Abstract Suspended sediment fluxes from the 68 km 2 Finsterwalderbreen catchment in Svalbard were monitored intensively during the 1999 and 2000 melt seasons, at proximal and distal ends of a 4.2 km 2 proglacial area, which has been deglacierised during the twentieth century. Measured distal sediment fluxes correspond to total catchment denudation rates of 2700 F 710 t km 2 year 1 (1999) and 1800 F 350 t km 2 year 1 (2000). Hourly net sediment flux time series (distal flux minus proximal flux, isolating change within the proglacial area itself) reveal that the proglacial area serves as both a source and a sink of sediment during different periods of the melt season, and that the majority of sediment evacuation from the area occurs during discrete episodes of enhanced meltwater discharge. The mean net flux from the proglacial area itself was 690 F 230 t km 2 year 1 (1999) and + 3800 F 1700 t km 2 year 1 (2000). Therefore, in 1999 there was a net increase in sediment storage in the proglacial area (aggradation), and in 2000 there was a net decrease (denudation). The pattern of sediment storage change appears to be driven by the runoff regime, with net storage occurring during a year of relatively episodic sediment transport in which relative supply exhaustion occurs, and net release in a year of more sustained sediment transport when relative supply exhaustion is absent. Many more years’ monitoring would be required for any trend to emerge from the large interannual variability in sediment yield. D 2003 Elsevier B.V. All rights reserved. Keywords: Glacial erosion; Denudation; Suspended sediment; Sediment budget; Sediment yield; Svalbard; Arctic 1. Sediment yields and storage in glacierised catchments Sediment storage may be the single most important aspect of fluvial sediment systems for determining response to environmental change (Phillips, 1991). Suspended sediment yields in particular are viewed as a sensitive parameter of environmental change (Walling, 1995), since suspended sediment is broadly supply-controlled, while bed load is broadly hydrauli- cally controlled; therefore, it is expected that suspended sediment fluxes are more responsive than bed load fluxes to climate-driven environmental change, other factors being equal. The identification of spatial and temporal patterns of sediment storage is therefore an important task for understanding the interaction of 0037-0738/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0037-0738(03)00218-5 * Corresponding author. Tel.: +44-1784-443570. E-mail addresses: [email protected] (R. Hodgkins), [email protected] (R. Cooper), [email protected](J. Wadham), [email protected] (M. Tranter). 1 Tel.: +44-1224-498200. 2 Tel.: +44-117-928-8307. www.elsevier.com/locate/sedgeo Sedimentary Geology 162 (2003) 105 – 117
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Sedimentary Geology 162 (2003) 105–117
Suspended sediment fluxes in a high-Arctic glacierised catchment:
implications for fluvial sediment storage
Richard Hodgkinsa,*, Richard Cooperb,1, Jemma Wadhamc,2, Martyn Tranterc,2
aDepartment of Geography, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UKbThe Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, Scotland, UK
cBristol Glaciology Centre, School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, UK
Abstract
Suspended sediment fluxes from the 68 km2 Finsterwalderbreen catchment in Svalbard were monitored intensively during
the 1999 and 2000 melt seasons, at proximal and distal ends of a 4.2 km2 proglacial area, which has been deglacierised during
the twentieth century. Measured distal sediment fluxes correspond to total catchment denudation rates of 2700F 710 t km� 2
year� 1 (1999) and 1800F 350 t km� 2 year� 1 (2000). Hourly net sediment flux time series (distal flux minus proximal flux,
isolating change within the proglacial area itself) reveal that the proglacial area serves as both a source and a sink of sediment
during different periods of the melt season, and that the majority of sediment evacuation from the area occurs during discrete
episodes of enhanced meltwater discharge. The mean net flux from the proglacial area itself was � 690F 230 t km� 2 year� 1
(1999) and + 3800F 1700 t km� 2 year� 1 (2000). Therefore, in 1999 there was a net increase in sediment storage in the
proglacial area (aggradation), and in 2000 there was a net decrease (denudation). The pattern of sediment storage change
appears to be driven by the runoff regime, with net storage occurring during a year of relatively episodic sediment transport in
which relative supply exhaustion occurs, and net release in a year of more sustained sediment transport when relative supply
exhaustion is absent. Many more years’ monitoring would be required for any trend to emerge from the large interannual
Suspended sediment yields in particular are viewed
as a sensitive parameter of environmental change
(Walling, 1995), since suspended sediment is broadly
supply-controlled, while bed load is broadly hydrauli-
cally controlled; therefore, it is expected that suspended
sediment fluxes are more responsive than bed load
fluxes to climate-driven environmental change, other
factors being equal. The identification of spatial and
temporal patterns of sediment storage is therefore an
important task for understanding the interaction of
R. Hodgkins et al. / Sedimentary Geology 162 (2003) 105–117106
climate, glacier variations and landscape change. For
example, while sediment yield typically declines with
increasing catchment area, Church and Slaymaker
(1989) found that British Columbian catchments
exhibited a pattern of increasing specific sediment yield
at all spatial scales up to 3� 104 km2, resulting from the
contemporary erosion of Quaternary sediments; stor-
age of sediment during glacial periods in effect con-
founded the ‘normal’ pattern, with larger catchments
taking longer to evacuate this stored, Quaternary sed-
iment. The cycle of sediment production and storage
during episodes of glacial advance, and subsequent
sediment evacuation to ‘background’, nonglacial levels
during episodes of glacial retreat, has been termed the
paraglacial cycle (Church and Ryder, 1972).
Denudation estimates based on sediment yields are
only strictly valid if change in storage is negligible: it is
important to distinguish how much of the sediment
transport is derived directly from contemporary ero-
sion, and how much is reworked (Harbor and Warbur-
ton, 1993). Storage effects are particularly relevant to
the study of sediment transfer in glacierised catch-
ments, where sediment transport is often in large,
discontinuous events, and there are significant varia-
tions in sediment supply on diurnal and seasonal time
scales (e.g. Bogen, 1980; Fenn, 1989; Gurnell et al.,
1994; Hodgkins, 1996). Furthermore, the majority of
glaciers globally have probably been in retreat for
several decades or more, meaning that there may be
no meaningful equilibrium between contemporary gla-
cial and hydrological configurations and sediment
production, storage and availability for transport in
any given catchment. Warburton (1999) considers that
it is proglacial river systems, i.e. rivers immediately
downstream of glaciers that are influenced by fluxes of
glacial meltwater and sediment, which provide the key
link between glacial processes and the wider environ-
ment. For example, Maizels (1979) found that 16% of
fluvial sediment from Glacier des Bossons, France was
redeposited in the proglacial valley sandur; conversely,
Warburton (1990) found that 23% of the sediment yield
of Bas Glacier d’Arolla, Switzerland was eroded from a
similar location. However,Warburton (1999) notes that
few such studies are available from high-Arctic loca-
tions, by comparison with alpine locations. Hodson et
al. (1998) believed that the proglacial sandur at Austre
Brøggerbreen in Svalbard functioned as both a net
source and sink of suspended sediment during the melt
season, although they were unable precisely to quantify
these results. The lack of high-Arctic data is under-
standable, given the significant logistical constraints of
working in high latitudes, but remains a significant gap
in our understanding of fluvial sediment delivery in
glacierised catchments.
2. Aims of this study
Given the issues raised above, the aims of this study
are to determine, from hydrological monitoring, de-
tailed suspended sediment fluxes for a high-Arctic
glacierised catchment, in order to (1) partition denuda-
tion rates between the proglacial area, the glacierised
part of the catchment and the entire catchment; (2)
determine the suspended sediment budget of the pro-
glacial area, specifically to identify whether it consti-
tutes a net source or sink of sediment. Suspended
sediment is the focus of this study because its supply-
driven nature should reflect catchment-scale environ-
mental variations rather than reach-scale, hydraulic
controls; an example of environmental variations may
be storage changes within the proglacial area. Fluvial
sediment budget data of any kind are particularly sparse
in high-Arctic environments, where there are typically
complex histories of environmental change, reflected
in glacier variations, hydrological fluctuations and
sediment supply and storage changes.
3. Location of this study
Finsterwalderbreen is a 44 km2 polythermal glacier
occupying a 68 km2 catchment on the southern shore
of van Keulenfjorden at 77jN in the Norwegian high-
Arctic archipelago of Svalbard (Spitsbergen), with an
altitude range of ca. 50–1000 m a.s.l. (Fig. 1; Hagen
et al., 1993). Hodson and Ferguson (1999) indicate
that 96% of the glacier base along the centreline is
temperate, and Wadham et al. (2001b) show that a
significant subglacial drainage system is present. The
most recent maximum advance of the glacier followed
a surge between 1898 and 1910 (Liestøl, 1969), since
when there has been steady retreat of up to about 2
km, which has exposed a proglacial area of 4.2 km2
behind a 70 m-high terminal moraine complex. The
lithology of the catchment includes Precambrian car-
Fig. 1. (Clockwise from top left) Location of Finsterwalderbreen within the Svalbard archipelago (inset). Topographic map of the glacier terminus
and proglacial area, elevations in m a.s.l. 1995 aerial photograph of the glacier terminus and proglacial area (subset of aerial photograph S95 1113nNorwegian Polar Institute): stream monitoring locations are indicated (see text for further explanation; note that many of the stream courses
apparent on the map and photograph, e.g. X, are not currently active, and that all of the runoff from the catchment is channelled through the outlet).
Upstream views of the outlet stream on 24 June (discharge ca. 5m3 s� 1) and 21 July (discharge ca. 25m3 s� 1) 1999; the lighter colour of the stream
on 21 July is a result of the angle of the sun, rather than lower turbidity. High-elevation view of the Finsterwalderbreen proglacial area looking
northeast, showing stream monitoring locations (although the east stream location is to the right of the image).
R. Hodgkins et al. / Sedimentary Geology 162 (2003) 105–117 107
bonates, phyllite and quartzite, Permian sandstones,
dolomites and limestones, and Triassic to Cretaceous
siltstones, sandstones and shales (Dallmann et al.,
1990). The proglacial area, however, is covered with
recent, unconsolidated till and fluvial deposits. The
central part of the proglacial area consists of a
R. Hodgkins et al. / Sedimentary Geology 162 (2003) 105–117108