Richard Hodgkins

Glacier hydrology in Svalbard, Norwegian high arctic

Abstract Progress in glacier hydrology has focused on temperate glaciers, although partly or wholly non-temperate glaciers are found in many parts of the world, and significant areas of former ice sheets were probably non-temperate. It has usually been assumed that drainage from non-temperate glaciers consists of relatively dilute and invariable supraglacial runoff. In this paper, the hydrology of glaciers in the High-Arctic archipelago of Svalbard is examined. Variations in the thermal regimes of glaciers, and their implications for drainage, are first addressed. Results from Svalbard concerning meltwater discharge and storage, and solute and suspended-sediment dynamics are then reviewed. In general, meltwater penetration of non-temperate ice is limited, and drainage from non-temperate glaciers in Svalbard has many of the characteristics of sub-aerial drainage. However, it would be erroneous to view this drainage simply as dilute supraglacial runoff, as significant material transport occurs in suspension and solution. Furthermore, twentieth-century climate change has probably led to changes in the thermal regimes of some Svalbard glaciers, such that relict drainage structures are sometimes observed, while meltwater yields are augmented by runoff which can be attributed to the loss of mass from glaciers. At large spatial scales, turbid plumes observed at the marine margins of polythermal ice caps indicate that meltwater can be routed subglacially through non-temperate ice.

The sizes, frequencies, and freeboards of East Greenland icebergs observed using ship radar and sextant

The Scoresby Sund fjord system, East Greenland, contains the most productive fast-flowing outlet glaciers draining east from the Greenland Ice Sheet, calving 18 km3 a−1 of icebergs. The sizes, frequencies, and freeboards of 1900 icebergs were measured from F.S. Polarstern, using ship X-band radar and sextant. Radar beam spreading exaggerates iceberg width by 60 m per nautical mile of range beyond the first mile. Data sets on iceberg size (e.g., that collated for Antarctic icebergs) collected using ship radars which do not take this effect into account will overestimate iceberg dimensions significantly. The location and concentration of icebergs within the fjord complex can be explained by (1) the locations of the principal source glaciers and (2) fjord topography and bathymetry. Iceberg concentration (maximum 0.6 icebergs km−2) declines with distance from the major iceberg sources. We found that 69% of icebergs within the fjord system are 1 km in length. The largest is 2.7 km long. Icebergs become spread more evenly over the range of size classes in the outer fjord and shelf. Modal iceberg keel depth, calculated from freeboard measurements, is 4–500 m in the inner fjords, shifting to lower values in the outer fjords, reflecting shallower bathymetry. Radar measurements of iceberg width cannot be used to infer keel depths accurately, because width and keel depth are only weakly correlated. Comparison between freeboards and keel depths for icebergs from East Greenland and the Barents Sea indicates that the iceberg source (i.e., floating or grounded) exerts a fundamental control on iceberg dimensions. The drift pattern of icebergs is from the head to the mouth of the fjord system, although fjord bifurcations, bathymetry, and currents provide additional complications. The trends in observed iceberg size and frequency, and in inferred keel depth, in the Scoresby Sund region are likely to be applicable to other fjords and shelves around Greenland.

High-Latitude Dust Over the North Atlantic: Inputs from Icelandic Proglacial Dust Storms

Cold Dust Atmospheric dust affects air quality, air and ocean chemistry, ocean biology, and climate, so understanding its origins is important to many fields. Hot, dry, desert regions at low latitudes are well-understood sources, but the role of higher-latitude regions in dust production has not been considered. Prospero et al. (p. 1078) present a 6-year record of measurements made on an island south of Iceland, which revealed frequent episodes of dust-production associated with glacial outwash plains and outburst floods. Much of this dust is transported southward and deposited in the North Atlantic, making it a potentially important supply of iron to drive ocean production in that region. Cold—higher-latitude regions—not just low-latitude arid regions, can be substantial sources of dust. Mineral aerosols play an important role in the atmosphere-ocean climate system. Research has focused almost exclusively on sources in low-latitude arid regions, but here we show that there are substantial sources in cold, higher latitudes. A 6-year record of measurements made on Heimaey, an island south of Iceland, reveals frequent dust events with concentrations exceeding 20 micrograms per cubic meter. Much of this potentially iron-rich dust is transported southward and deposited in the North Atlantic. Emissions are highest in spring and spatially and temporally associated with active glacial outwash plains; large dust events appear to be associated with glacial outburst floods. In response to global warming, ice retreat on Iceland and in other glacierized areas is likely to increase dust emissions from these regions.

Mass balance change as a control on the frequency and occurrence of glacier surges in Svalbard, Norwegian High Arctic

The end of the Little Ice Age (LIA) in Svalbard (76–81°N), a climate-sensitive region at the northern extreme of strong poleward heat transfer, was marked by an abrupt increase in mean annual air temperature of up to 5°C around 1920. Glacier mass balance has been consistently negative since this time, and large cumulative net losses of mass have occurred at most glaciers. Energy-balance modelling confirms the sensitivity of Svalbard glaciers to climate change, predicting a negative shift in net mass balance of up to 0.8 m a−1 (water equivalent) per degree temperature rise. This climate-related shift in glacier mass balance has reduced the intensity of glacier surge activity in Svalbard. One glacier, known to have surged since the end of the LIA, has since failed to accumulate the mass required to re-initiate the surge cycle, and is also now cold at its base and incapable of rapid flow by basal sliding. Three overviews of the total number of actively-surging glaciers in Svalbard between 1936–90 show a decrease from 18 to 5. This is significant compared with the expected numbers of surges based on LIA conditions. Post-LIA climate change in Svalbard has therefore affected not only glacier extent, but also ice dynamics. This is trend will probably continue given CO2-induced climate-warming.

Groundwater hydrochemistry in the active layer of the proglacial zone, Finsterwalderbreen, Svalbard

Abstract Glacial bulk meltwaters and active-layer groundwaters were sampled from the proglacial zone of Finsterwalderbreen during a single melt season in 1999, in order to determine the geochemical processes that maintain high chemical weathering rates in the proglacial zone of this glacier. Results demonstrate that the principle means of solute acquisition is the weathering of highly reactive moraine and fluvial active-layer sediments by supra-permafrost groundwaters. Active-layer groundwater derives from the thaw of the proglacial snowpack, buried ice and glacial bulk meltwaters. Groundwater evolves by sulphide oxidation and carbonate dissolution. Evaporation- and freeze-concentration of groundwater in summer and winter, respectively produce Mg–Ca-sulphate salts on the proglacial surface. Re-dissolution of these salts in early summer produces groundwaters that are supersaturated with respect to calcite.There is a pronounced spatial pattern to the geochemical evolution of groundwater. Close to the main proglacial channel, active layer sediments are flushed diurnally by bulk meltwaters. Here, Mg–Ca-sulphate deposits become exhausted in the early season and geochemical evolution proceeds by a combination of sulphide oxidation and carbonate dissolution. At greater distances from the channel, the dissolution of Mg–Ca-sulphate salts is a major influence and dilution by the bulk meltwaters is relatively minor. The influence of sulphate salt dissolution decreases during the sampling season, as these salts are exhausted and waters become increasingly routed by subsurface flowpaths.

Controls on suspended-sediment transfer at a high-arctic glacier, determined from statistical modelling

Simple linear regression models have been widely employed in the analysis of suspended-sediment concentration (SSC) time series from glacierized catchments, although they have many limitations. This paper builds regression models which address these shortcomings and permit inferences concerning the controls on suspended-sediment transfer from a glacier at 78°N in the Svalvard archipelago. A bivariate regression model, deterministically predicting SSC from discharge alone, explained less than 15 per cent of the variance in SSC. A multivariate model, incorporating additional potentially explanatory variables, offered little improvement. Diurnal hysteresis in the data gives rise to quasi-autocorrelation in the residual series from regression models. This was effectively removed by incorporating dummy diurnal variables into the multivariate model. The presence of a first-order autoregressive, stochastic process gives rise to true autocorrelation in the residual series from regression models. This was accommodated by incorporating an ARIMA (1,0,0) term into a multivariate autoregression model. The model-building process yielded a systematic progression in the explanation of variance in SSC, stripping away pattern in the autocorrelation function of the residual series; mean model error was reduced from 54 per cent to 6 per cent. The dependence of SSC on the magnitude of discharge is weak and highly variable, whereas the dependence of current SSC on recent values of SSC, revealed through the stochastic term, is an order of magnitude greater and relatively constant during the melt season. The dominant control on SSC throughout the melt season is therefore short-term sediment availability. The simple and largely unchanging stochastic process generally responsible for generating the observed SSC series implies a simple and unchanging glacier drainage system. Copyright

Direct effect of ice sheets on terrestrial bicarbonate, sulphate and base cation fluxes during the last glacial cycle: minimal impact on atmospheric CO2 concentrations

Chemical erosion in glacial environments is normally a consequence of chemical weathering reactions dominated by sulphide oxidation linked to carbonate dissolution and the carbonation of carbonates and silicates. Solute fluxes from small valley glaciers are usually a linear function of discharge. Representative glacial solute concentrations can be derived from the linear association of solute flux with discharge. These representative glacial concentrations of the major ions are f25% of those in global river water. A 3-D thermomechanically coupled model of the growth and decay of the Northern Hemisphere ice sheets was used to simulate glacial runoff at 100-year time steps during the last glacial cycle (130 ka to the present). The glacially derived fluxes of major cations, anions and Si over the glaciation were estimated from the product of the glacial runoff and the representative glacial concentration. A second estimate was obtained from the product of the glacial runoff and a realistic upper limit for glacial solute concentrations derived from theoretical considerations. The fluxes over the last glacial cycle are usually less than a few percent of current riverine solute fluxes to the oceans. The glacial fluxes were used to provide input to an oceanic carbon cycling model that also calculates changes in atmospheric CO2. The potential change in atmospheric CO2 concentrations over the last glacial cycle that arise from perturbations in glacial solute fluxes are insignificant, being < 1 ppm. D 2002 Elsevier Science B.V. All rights reserved.

Enhancement of glacial solute fluxes in the proglacial zone of a polythermal glacier

Annual proglacial solute fluxes and chemical weathering rates at a polythermal high-Arctic glacier are presented. Bulk meltwater chemistry and discharge were monitored continuously at gauging stations located at the eastern and western margins of the glacier terminus and at the Outlet, 2.5 km downstream where meltwaters discharge into the fjord. Fluxes of non-snowpack HCO 3 - , SO 4 2- , Ca 2+ and Mg 2+ increase by 30-47% between the glacier terminus and the Outlet, indicating that meltwaters are able to access and chemically weather efflorescent sulphates, carbonates and sulphides in the proglacial zone. Smaller increases in the fluxes of non-snowpack-derived Na + , K + and Si indicate that proglacial chemical weathering of silicates is less significant. En3hanced solute fluxes in the proglacial zone are mainly due to the chemical weathering of active-layer sediments. The PCO 2 of active-layer ground-waters is above atmospheric pressure. This implies that solute acquisition in the active layer involves no drawdown of CO 2 . The annual proglacial chemical weathering rate in 1999 is calculated to be 2600 meqΣ + m -2 This exceeds the chemical weathering rate for the glaciated part of the catchment (790 meqΣ + m -2 ) by a factor of 3.3. Hence, the proglacial zone at Finster-walderbreen is identified as an area of high geochemical reactivity and a source of CO 2 .

The hydrochemistry of runoff from a ‘cold-based’ glacier in the High Arctic (Scott Turnerbreen, Svalbard)

This article is Restricted Access. It was published in the journal, Hydrological Processes [© John Wiley & Sons, Ltd.] and is available at: http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=0885-6087

A chronology for the Dome C deep ice‐core site through radio‐echo layer Correlation with the Vostok Ice Core, Antarctica

Ice at the new Dome C drill site is correlated directly with the Vostok ice-core record using internal radio-echo layering in the Antarctic Ice Sheet. Layering observed on 60 MHz radar records at ice depths greater than 1000 m is a result of electro-magnetic wave reflections from acidic ice layers formed, it is assumed, by volcanic eruption-derived aerosols. These acidic layers represent isochronous surfaces within the ice sheet. We are able to trace five prominent layers for over 500 km across the Antarctic Ice Sheet, between Vostok and the new ice-core site at Dome C. This correlates the stratigraphy and depth-age relationship between the two sites. The thickness of ice deposited over the last glacial cycle (120,000 years) at Dome C is 300 m greater than at Vostok and, at comparable depths, the ice at Dome C is between about 10,000 and 25,000 years younger than at Vostok.