Ice Meltwater Research Articles

River runoff, sea ice meltwater, and Pacific water distribution and mean residence times in the Arctic Ocean

Hydrographic and tracer data collected during ARK IV/3 (FS Polarstern in 1987), ARCTIC91 (IB Oden), and AOS94 (CCGS Louis S. St‐Laurent) expeditions reveal the evolution of the near‐surface waters in the Arctic Ocean during the late 1980s and early 1990s. Salinity, nutrients, dissolved oxygen, and δ18O data are used to quantify the components of Arctic freshwater: river runoff, sea ice meltwater, and Pacific water. The calculated river runoff fractions suggest that in 1994 a large portion of water from the Pechora, Ob, Yenisey, Kotuy, and Lena Rivers did not flow off the shelf closest to their river deltas, but remained on the shelf and traveled via cyclonic circulation into the Laptev and East Siberian Seas. River runoff flowed off the shelf at the Lomonosov Ridge and most left the shelf at the Mendeleyev Ridge. ARCTIC91 and AOS94 Pacific water fraction estimates of Upper Halocline Water, the traditionally defined core of the Pacific water mass, document a decrease in extent compared to historical data. The front between Atlantic water and Pacific water shifted from the Lomonosov Ridge location in 1991 to the Mendeleyev Ridge in 1994. The relative age structure of the upper waters is described by using the 3H‐3He age. The mean 3H‐3He age measured in the halocline within the salinity surface of 33.1±0.3 is 4.3±1.7 years and that for the 34.2±0.2 salinity surface is 9.6±4.6 years. Lateral variations in the relative age structure within the halocline and Atlantic water support the well‐known cyclonic boundary current circulation.

<sup>210</sup>Pb, <sup>137</sup>Cs Dating of Lake Sediments from Ardley Island (Maritime Antarctic)and Their Environmental Implications

The activity of 210 Pb and 137 Cs of lake sediments, namely Y2 and G, respectively from Ardley Island, Antarctica have been measured. According to the profiles of 210 Pb and 137 Cs activity, we used CRS model to date the G lake, which spans about 134±43 years. Base on the dating, we estimate the velocity of deposition. The increased sedimentation rates and the inventories of 210 Pb and 137 Cs as well as their flux being higher than the atmospheric deposition could be reasonably attributed to the supply of a great amount of ice melt water.

The oxygen isotope composition of water masses in the northern North Atlantic

The ratio of oxygen-18 to oxygen-16 (expressed as per mille deviations from Vienna Standard Mean Ocean Water, δ 18O) is reported for seawater samples collected from seven full-depth CTD casts in the northern North Atlantic between 20° and 41°W, 52° and 60°N. Water masses in the study region are distinguished by their δ 18O composition, as are the processes involved in their formation. The isotopically heaviest surface waters occur in the eastern region where values of δ 18O and salinity ( S) lie on an evaporation–precipitation line with slope of 0.6 in δ 18O– S space. Surface isotopic values become progressively lighter to the west of the region due to the addition of 18O-depleted precipitation. This appears to be mainly the meteoric water outflow from the Arctic rather than local precipitation. Surface samples near the southwest of the survey area (close to the Charlie Gibbs Fracture Zone) show a deviation in δ 18O–S space from the precipitation mixing line due to the influence of sea ice meltwater. We speculate that this is the effect of the sea ice meltwater efflux from the Labrador Sea. Subpolar Mode Water (SPMW) is modified en route to the Labrador Sea where it forms Labrador Sea Water (LSW). LSW lies to the right (saline) side of the precipitation mixing line, indicating that there is a positive net sea ice formation from its source waters. We estimate that a sea ice deficit of ≈250 km 3 is incorporated annually into LSW. This ice forms further north from the Labrador Sea, but its effect is transferred to the Labrador Sea via, e.g. the East Greenland Current. East Greenland Current waters are relatively fresh due to dilution with a large amount of meteoric water, but also contain waters that have had a significant amount of sea ice formed from them. The Northeast Atlantic Deep Water (NEADW, δ 18O=0.22‰) and Northwest Atlantic Bottom Waters (NWABW, δ 18O=0.13‰) are isotopically distinct reflecting different formation and mixing processes. NEADW lies on the North Atlantic precipitation mixing line in δ 18O–salinity space, whereas NWABW lies between NEADW and LSW on δ 18O–salinity plots. The offset of NWABW relative to the North Atlantic precipitation mixing line is partially due to entrainment of LSW by the Denmark Strait overflow water during its overflow of the Denmark Strait sill. In the eastern basin, lower deep water (LDW, modified Antarctic bottom water) is identified as far north as 55°N. This LDW has δ 18O of 0.13‰, making it quite distinct from NEADW. It is also warmer than NWABW, despite having a similar isotopic composition to this latter water mass.

Hydrological Response of a Patchy High Arctic Wetland

High Arctic patchy wetlands are ecological oases in a polar desert environment and are vulnerable to climatic warming. At present, understanding of their responses to external factors (climate and terrain) is limited. This study examines a wetland located in a topographic depression maintained by seasonal snowmelt, ground ice melt and lateral inflows. The wetland is located on Cornwallis Island, Nunavut, Canada. Hydrological, climatological and soil observations were made over several summers with different weather conditions. The summers of 1996 and 1997 were cool and wet but the summer of 1998 was warm and dry. The melt in 1996 was rapid due to rain on snow events and only lasted six days. Deeper snow in 1997 prolonged the melt season to 18 days. A shallow snow-cover in 1998 and early melt depleted the snow by early June. Surface, groundwater and storage fluctuations in the wetland were dictated by snowmelt, rainfall, evaporation loss from the wetland and lateral inputs which in turn were controlled by the melting of the late-lying snow storage in the catchment. Soil factors influence the spatial variations in ground thaw which affects the surface and subsurface flow. Streamflow response of the wetland reflects a nival regime and augmentation of streamflow thoughout the summer season in all three years is supported by multiple water sources: ground ice melt and suprapermafrost water from a large late-lying snowpack. Overall, this study suggests that the survival of some patchy wetlands depends on their interaction with the surrounding basin, with a dependency probably being more important during warm and dry seasons.

Detection and Characterization of Ancient Fungi Entrapped in Glacial Ice

Glacial ice is a unique matrix that is ca- pable of protecting microorganisms for long-term preservation. The organisms entrapped in glacial ice can provide information on evolutionary processes and ancient biodiversity. The major objective of this study was to detect and characterize ancient fungi in glacial ice and determine their viability. We devel- oped a protocol using rigorous decontamination pro- cedures, conventional cultural methods, and molec- ular techniques (polymerase chain reaction amplifi- cation of fungal ribosomal DNA internal transcribed spacers, followed by sequence analyses) to examine the ancient fungi entrapped in glacial ice. Fifteen gla- cial ice subcores, ranging in age from several hun- dred to 140 000 yr, from two locations in Greenland were used in this study. One hundred ninety fungal isolates were obtained using conventional cultural methods. In this paper we report the morphological and molecular characteristics of eight isolates, includ- ing two Penicillium spp., three Cladosporium spp., one Ulocladium sp., one basidiomycete (Pleurotus sp.), and one unknown ascomycete. In addition, ten fun- gal sequences were amplified and sequenced directly from ice meltwater. One of them was identified as a basidiomycete. The other nine were classified as as- comycetes, of which three sequences had very low similarities with contemporary sequences in Gen- Bank. The results from this study may facilitate the future use of ancient fungi in studies of fungal ecol- ogy, distribution, epidemiology, phylogeny, and evo- lution.

Detection and characterization of ancient fungi entrapped in glacial ice

Glacial ice is a unique matrix that is capable of protecting microorganisms for long-term preservation. The organisms entrapped in glacial ice can provide information on evolutionary processes and ancient biodiversity. The major objective of this study was to detect and characterize ancient fungi in glacial ice and determine their viability. We developed a protocol using rigorous decontamination procedures, conventional cultural methods, and molecular techniques (polymerase chain reaction amplification of fungal ribosomal DNA internal transcribed spacers, followed by sequence analyses) to examine the ancient fungi entrapped in glacial ice. Fifteen glacial ice subcores, ranging in age from several hundred to 140 000 yr, from two locations in Greenland were used in this study. One hundred ninety fungal isolates were obtained using conventional cultural methods. In this paper we report the morphological and molecular characteristics of eight isolates, including two Penicillium spp., three Cladosporium spp., one Ulocladium sp., one basidiomycete (Pleurotus sp.), and one unknown ascomycete. In addition, ten fungal sequences were amplified and sequenced directly from ice meltwater. One of them was identified as a basidiomycete. The other nine were classified as ascomycetes, of which three sequences had very low similarities with contemporary sequences in Gen-Bank. The results from this study may facilitate the future use of ancient fungi in studies of fungal ecology, distribution, epidemiology, phylogeny, and evolution.

The Summer Hydrography and Surface Circulation of the East Siberian Shelf Sea*

During the ice-free summer season in 1995 the authors deployed and subsequently tracked 39 surface drifters to test the hypothesis that the discharge from the Kolyma River forces a buoyancy-driven coastal current from the East Siberian Sea toward Bering Strait. The observed mean flow is statistically significant at the 95% level of confidence, but its direction contradicts their initial hypothesis. Instead of a coastally trapped eastward flow, the authors find a laterally sheared westward flow with maximum velocities offshore that correlate only weakly with the local winds. At a daily, wind-dominated timescale the drifter data reveal spatially coherent flows of up to 0.5 m s21. The Lagrangian autocorrelation scale is about 3 days and the Lagrangian eddy length scale reaches 40 km. This spatial scale exceeds the nearshore internal deformation radius by a factor of 3; however, it more closely corresponds to the internal deformation radius associated with the offshore ice edge. Bulk estimates of the horizontal mixing coefficient resemble typical values of isotropic open ocean dispersion at midlatitudes. Hydrographic observations and oxygen isotope ratios of seawater indicate a low proportion of riverine freshwater relative to sea ice melt in most areas of the East Siberian Sea except close to the Kolyma Delta. The observations require a reevaluation of the conceptual view of the summer surface circulation of the East Siberian Sea. Eastward buoyancy-driven coastal currents do not always form on this shelf despite large river discharge. Instead, ice melt waters of a retreating ice edge act as a line source of buoyancy that in 1995 forced a westward surface flow in the East Siberian Sea.

Isotopic composition of ice cores and meltwater from upper fremont glacier and galena creek rock glacier, wyoming

Meltwater runoff from glaciers can result from various sources, including recent precipitation and melted glacial ice. Determining the origin of the meltwater from glaciers through isotopic analysis can provide information about such things as the character and distribution of ablation on glaciers.A 9.4 m ice core and meltwater were collected in 1995 and 1996 at the glacigenic Galena Creek rock glacier in Wyoming's Absaroka Mountains. Measurements of chlorine‐36 (36Cl), tritium (3H), sulphur‐35 (35S), and delta oxygen‐18 (δ18O) were compared to similar measurements from an ice core taken from the Upper Fremont Glacier in the Wind River Range of Wyoming collected in 1991–95. Meltwater samples from three sites on the rock glacier yielded 36Cl concentrations that ranged from 2.1±1.0×106 to 5.8±0.3×106 atoms/l. The ice‐core 36Cl concentrations from Galena Creek ranged from 3.4±0.3×105 to 1.0±0.1×106 atoms/l. Analysis of an ice core from the Upper Fremont Glacier yielded 36Cl concentrations of 1.2±0.2×106 and 5.2±0.2×106 atoms/l for pre‐1940 ice and between 2 ×106 and 3×106 atoms/l for post‐1980 ice. Purdue's PRIME Lab analyzed the ice from the Upper Fremont Glacier. The highest concentration of 36Cl in the ice was 77±2×106 atoms/l and was deposited during the peak of atmospheric nuclear weapons testing in the late 1950s. This is an order of magnitude greater than the largest measured concentration from both the Upper Fremont Glacier ice core that was not affected by weapons testing fallout and the ice core collected from the Galena Creek rock glacier.Tritium concentrations from the rock glacier ranged from 9.2±0.6 to 13.2±0.8 tritium units (TU) in the meltwater to −1.3±1.3 TU in the ice core. Concentrations of 3H in the Upper Fremont Glacier ice core ranged from 0 TU in the ice older than 50 years to 6–12 TU in the ice deposited in the last 10 years. The maximum 3H concentration in ice from the Upper Fremont Glacier deposited in the early 1960s during peak weapons testing fallout for this isotope was 360 TU.One meltwater sample from the rock glacier was analyzed for 35S with a measured concentration of 5.4±1.0 millibecquerel per liter (mBeq/l). Modern precipitation in the Rocky Mountains contains 35S from 10 to 40 mBeq/L. The δ18O results in meltwater from the Galena Creek rock glacier (−17.40±0.1 to −17.98±0.1 per mil) are similar to results for modern precipitation in the Rocky Mountains. Comparison of these isotopic concentrations from the two glaciers suggest that the meltwater at the Galena Creek site is composed mostly of melted snow and rain that percolates through the rock debris that covers the glacier. Additionally, this water from the rock debris is much younger (less than two years) than the reported age of about 2000 years for the subsurface ice at the mid‐glacier coring site. Thus the meltwater from the Galena Creek rock glacier is composed primarily of melted surface snow and rain water rather than melted glacier ice, supporting previous estimates of slow ablation rates beneath the surface debris of the rock glacier.

The modelling of sea ice melt-water ponds for the High Arctic using an Airborne line scan camera, and applied to the Satellite Special Sensor Microwave/Imager (SSM/I)

Melt-water ponds on sea ice in the Northeast Water Polynya (77-82 N, 1-18 W) were mapped using a line scan camera (LSC) mounted on a helicopter. Passive microwave satellite data from the Special Sensor Microwave/ Imager (SSM/I) were employed to analyse the temporal trend of radiances of shorefast ice for 1993 and sea ice during sixteen flights of the LSC (June-July). A simple, linear algorithm tailored to accommodate the summer ice regime, was developed. The LSC measurements of ice (50.9 12.5%), water and melt-water pond fractions compared very well with the SSM/I derived mean ice concentrations (50.9 12.8%). The comparison resulted in a correlation coefficient of 0.953. Combining the LSC melt-water pond fraction data with other data available from the literature provided the basis to construct a second degree polynomial function of a melt-water empirical model to correct the under estimation of SSM/I derived sea ice concentration due to the effect of melt-water ponds.

Oxygen isotope studies from Iceland to an East Greenland Fjord: behaviour of glacial meltwater plume

A detailed study of the oxygen isotope composition (δ18O) was carried out along a transect between Iceland and East Greenland, which includes the West Iceland Shelf, Denmark Strait, the Kangerdlugssuaq Trough on the East Greenland Shelf and the Kangerdlugssuaq Fjord. Vertical profiles of the oxygen isotope composition in a fjord with tidewater glaciers were studied for the first time. In this study, three distinct water masses are identified from oxygen isotope measurements: (1) North Atlantic Water of δ18O ≈ 0%. occupies the Icelandic Shelf, Denmark Strait subsurface, and deep waters of the Kangerdlugssuaq Trough and Fjord; (2) the East Greenland Current of δ18O ≈ −2%. occupies surface water at the western Denmark Strait and the Kangerdlugssuaq Trough; (3) glacial meltwater (δ18O ranges from −30 to −20%. in source) flows at the surface of the Kangerdlugssuaq Fjord. Surface δ18O data distinctively identify the East Greenland Front between North Atlantic Water and the East Greenland Current in Denmark Strait. Vertical profiles of δ18O show the steady increase from surface to deep water at the stations west of the front with well mixed water at stations east of the front. We did not find any subsurface glacial meltwater intrusion in Kangerdlugssuaq fjord, unlike the reported ‘cold tongue’ in Antarctic fjords. Instead Arctic Intermediate Water (winter cooled North Atlantic Water) penetrates to the head of the fjord and fills the bottom part of the fjord. A linear relationship between salinity and δ18O shows that there was no significant contribution from the sea ice meltwater in this study site. The dominant source of freshwater in the Kangerdlugssuaq Fjord is glacial meltwater. A simple model using δ18O was developed to illustrate glacial meltwater dynamics in the fjord, and to estimate the length of the glacial meltwater plume. Model results agree well with the data within the fjord and near the fjord mouth and a plume length is estimated to be 250 km from the glacial face. However, a diversion of the model from the data is observed at about 70 km away from the mouth of the fjord because of the influence by the East Greenland Current and the Coriolis effect.

Polycyclic aromatic hydrocarbons (PAHs) in Antarctic Martian meteorites, carbonaceous chondrites, and polar ice

Recent analyses of the carbonate globules present in the Martian meteorite ALH84001 have detected polycyclic aromatic hydrocarbons (PAHs) at the ppm level (McKay et al., 1996). The distribution of PAHs observed in ALH84001 was interpreted as being inconsistent with a terrestrial origin and were claimed to be indigenous to the meteorite, perhaps derived from an ancient martian biota. We have examined PAHs in the Antarctic shergottite EETA79001, which is also considered to be from Mars, as well as several Antarctic carbonaceous chondrites. We have found that many of the same PAHs detected in the ALH84001 carbonate globules are present in Antarctic carbonaceous chondrites and in both the matrix and carbonate (druse) component of EETA79001. We also investigated PAHs in polar ice and found that carbonate is an effective scavenger of PAHs in ice meltwater. Moreover, the distribution of PAHs in the carbonate extract of Antarctic Allan Hills ice is remarkably similar to that found in both EETA79001 and ALH84001. The reported presence of L-amino acids of apparent terrestrial origin in the EETA79001 druse material (McDonald and Bada, 1995) suggests that this meteorite is contaminated with terrestrial organics probably derived from Antarctic ice meltwater that had percolated through the meteorite. Our data suggests that the PAHs observed in both ALH84001 and EETA79001 are derived from either the exogenous delivery of organics to Mars or extraterrestrial and terrestrial PAHs present in the ice meltwater or, more likely, from a mixture of these sources. It would appear that PAHs are not useful biomarkers in the search for extinct or extant life on Mars.

Sea ice and oxygen isotopes in Foxe Basin, Hudson Bay, and Hudson Strait, Canada

The summer distribution of sea ice meltwater and river runoff and the surface circulation in Foxe Basin, Hudson Bay, and Hudson Strait have been studied by oxygen isotope techniques. On the basis of oxygen isotope and salinity relationships, the reduction of surface salinity in summer in Foxe Basin is predominantly due to sea ice meltwater. River runoff and sea ice meltwater contribute equally to the summer surface layer in northern Hudson Bay. The isotopic data clearly show the flow of Foxe Basin water through Roes Welcome Sound into northwestern Hudson Bay, but no evidence for this outflow is found in the passages connecting Hudson Bay and Hudson Strait. Oxygen isotopes indicate that recent river runoff is concentrated in a narrow band along the south side of Hudson Strait. The wide variety of relationships between oxygen isotope ratios and salinity is explained by the known ice dynamics and the seasonal variability predicted from ice melting and freezing models.

ISOTOPIC AND IONIC VARIATIONS IN GLACIER RIVER WATER DURING THREE CONTRASTING ABLATION SEASONS

The significance of the baseflow component of glacier river discharge in summer varies with geographical location, altitude, glacier geometry and glacier size. Baseflow is maintained by meltwater generated above the transient equilibrium line and by water released from temporary storage on, in or beneath the glacier. At the Norwegian glacier Austre Okstindbreen, where precipitation is generally high throughout the year and the summers are cool and wet, observations in three successive, but contrasting, years have shown that Na+ ion concentrations in the glacier river water are influenced strongly by the amount of snowmelt. This itself depends on the preceding winter conditions, which determine the amount of accumulation, and on the current summer's weather. The efficiency of the glacier's drainage systems depends on the general progress of summer ablation. The speed with which the systems develop influences ion provision from subglacial sources. Ca2+ ion concentrations are largely determined by subglacial conditions. Oxygen isotope variations in glacier river water reflect the relative contributions made to total discharge by snow meltwater and other sources; the composition of the snow cover, which is a function of winter temperatures, has a strong influence. Ice meltwater has low isotopic variability, but the isotopic composition of rainfall varies markedly. A simple model of mixing of englacial and subglacial waters, each of a constant composition, cannot be applied to a high-latitude glacier of the size and altitudinal range of Austre Okstindbreen.

Oxygen Isotope and Ionic Concentrations in Glacier River Water: Multi-Year Observations in the Austre Okstindbreen Basin, Norway

Austre Okstindbreen, the largest glacier of the Okstindan area, Norway, covers about 14 km2 within a drainage basin of 22.5 km2. Each year, about one third of the discharge of the glacier river results from snowmelt outside the glacier margins. Snow melting on the glacier contributes about twice as much water to the river as does glacier ice. Early in the melt season, the glacier river is supplied almost entirely by snow meltwater. Na+ ion concentrations in the snow are much higher than those of Ca2+; percolation of meltwater from the surface results in chemical changes. Water entering the body of the glacier from the melting snow cover is relatively depleted of 18O, whilst the residual snow is more enriched. As the ablation season proceeds and the transient equilibrium line rises up-glacier, an increasing amount of ice meltwater is mixed with snow meltwater, diluting the overall concentration of ions in the river. Ice meltwater is 18O-rich, and the δl8O value of glacier river water rises at times of high ice ablation. Water which percolates through the snow cover above the transient equilibrium line during the melt season may maintain river discharge in late summer. Mean concentrations of the principal cations in the river water vary between years; after winters with above-average snow accumulation, Na+ values tend to be high. Ca2+ concentrations are determined largely by subglacial conditions.

Reply: Inferred subglacial meltwater origin of lakes on the southern border of the Canadian Shield

Paleozoic rocks form an escarpment up to 35 m high at the border with the Frontenac Axis of the Canadian Shield in southeastern Ontario. The escarpment, which lies nearly transverse to the flow direction of Pleistocene ice and subglacial meltwater in the region, is cut by a series of deep channels locally incised into the bedrock at the escarpment. A subbottom acoustic survey of two of these channels and mapping of a third, partly flooded channel revealed the shape of the bedrock surface beneath the water and glacial and postglacial sediments of lakes now occupying the channels. Most cross sections show a smooth-walled, dominant depression eroded up to 100 m below the land surface nearby, and flanked by one or more secondary depressions. The pattern changes considerably in detail, making secondary depressions especially difficult to trace along the length of the lake. The pattern is similar to that of subglacial fluvial erosion marks more than three orders of magnitude smaller found in bedrock throughout ...

A search for endogenous amino acids in the Martian meteorite EETA79001

The Antarctic shergottite EETA79001 is believed to be an impact-ejected fragment of the planet Mars. Samples of the carbonate (white druse) and the basaltic (lithology A) components from this meteorite have been found to contain amino acids at a level of approximately 1 ppm and 0.4 ppm, respectively. The detected amino acids consist almost exclusively of the L-enantiomers of the amino acids commonly found in proteins, and are thus terrestrial contaminants. There is no indication of the presence of α-aminoisobutyric acid, one of the most abundant amino acids in several carbonaceous chondrites. The relative abundances of amino acids in the druse material resemble those in Antarctic ice, suggesting that the source of the amino acids may be ice meltwater. The level of amino acids in EETA79001 druse is not by itself sufficient to account for the 600–700 ppm of volatile C reported in druse samples and suggested to be from endogenous martian organic material. However, estimates of total terrestrial organic C present in the druse material based on our amino acid analyses and the organic C content of polar ice can account for most of the reported putative organic C in EETA79001 druse.

Were micrometeorites a source of prebiotic molecules on the early Earth?

“Interplanetary Dust Particles” with sizes ≈ 10 μm collected in the stratosphere (IDPs), as well as much larger “giant” micrometeorites retrieved from Antarctic ice melt water (AMMs), are mostly composed of unequilibrated assemblages of minerals, thus being related to primitive unequilibrated meteorites. Two independent evaluations of the mass flux of micrometeorites measuring ≈ 50 μm to ≈ 200 μm, recovered from either the Greenland or the Antarctic ice sheets have been reported (≈ 20,000 tons/a). A comparison with recent evaluation of the flux of meteorites reaching the Earth's surface (up to masses of 10,000 tons), indicates that micrometeorites represent about 99.5% of the extraterrestrial material falling on the Earth's surface each year. As they show carbon concentrations exceeding that of the most C-rich meteorite (Orgueil), they are the major contributors of extraterrestrial C-rich matter accreting to the Earth today. Moreover they are complex microstructured aggregates of grains. They contain not only a variety of C-rich matter, such as a new “dirty” magnetite phase enriched in P, S, and minor elements, but also a diversity of potential catalysts (hydrous silicates, oxides, sulfides and metal grains of Fe/Ni composition, etc.). They could have individually functioned on the early Earth, as “micro-chondritic-reactors” for the processing of prebiotic organic molecules in liquid water. Future progress requires the challenging development of meaningful laboratory simulation experiments, and a better understanding of the partial reprocessing of micrometeorites in the atmosphere.

Nitrogen dynamics in the Bellingshausen Sea during the Austral spring of 1992

A series of 15N experiments were conducted in the early summer of 1992 during the course of cruise 198 of R.R.S. Discovery, with a focus on the seasonal ice zone (SIZ) of the Bellingshausen Sea. Nitrogen (NO3, NH4 and urea) uptake was measured over the nominal euphotic zone, and size fractionation experiments of a similar nature were conducted on surface waters. The most productive zone during this study was not associated with stable ice-melt water but with a west-east oriented, haline dominated density front centred around 67.3°S. The pelagic bloom coincident with the area south of the front had a banded structure with chlorophyll a concentrations up to 5 mg m 3. Integrated N uptake rates within the bloom varied between 56 and 34 mmol N m −2 day −, with a decreasing trend from north to south. A similar trend was evident in the |-ratios, where values decreased from 0.6 to 0.3. From size fractionated experiments in the bloom it was found that 82–87% of the chlorophyll a was in the netplankton fraction, which also accounted for 28 to 95% of the N uptake. The bloom was dominated by Porosira glacialis, Coscinodiscus bouvet, Thalassiosira antarctica and Phaeocystis spp. North of the front, integrated N uptake was 25 mmol N m −2 day − (f-ratio 0.28) and 60 to 69% of the uptake in surface waters was in the netplankton fraction. Waters adjacent to the ice-edge exhibited a lower rate of N uptake than the frontal stations (19 mmol N m −2 day −1) with an f-ratio of 0.1. Specific rates on N uptake indicated strong bloom viability in an Antarctic context but a lack of response of VN0P 3 to [N0 3]. The cross-frontal trends may provide an explanation of bloom development and persistence in the SIZ of the Bellingshausen Sea. Rates of new production in mature waters of the SIZ were comparable to those of previous studies in other regions, but rates measured within the bloom were higher. The rates of new production presented here are the first to have been made in the Bellingshausen Sea and as such can be incorporated in regional and global models relating to the sink of carbon.

Oxygen and carbon isotope composition of Quaternary bivalve shells as a water mass indicator: Last interglacial and Holocene, East Greenland

Oxygen and carbon isotope composition of arctic bivalve shells are used in an attempt to reconstruct surface water temperature and salinities in Scoresby Sund, East Greenland. The oxygen isotope compositions of Mya truncata, Hiatella arctica and Tridonta borealis have been compared with present day hydrological parameters. Modern shells yield oxygen isotope values that, on the whole, reproduce the environmental temperature and sea water isotopic composition. Furthermore, it is possible to estimate the living depth of the analysed specimens. Analyses of growth increments from single shells show that there are large variations from year to year in temperature and oxygen isotope composition of the surface waters of Scoresby Sund and that these variations decrease with depth. Analyses of Holocene shells indicate that the Polar Current water, which flows from north to south along the East Greenland coast was also present during the Holocene climatic optimum 8000-7000 yr B.P. Analyses of bivalve shells from the last interglacial show that Scoresby Sund during that time was well circulated and that meltwater from the Greenland ice sheet and sea ice meltwater was important for the temperature, salinity and isotopic composition of the surface waters.

Stable oxygen and carbon isotopes in planktic foraminifers from Arctic Ocean surface sediments: Reflection of the low salinity surface water layer

Planktic foraminifers Neogloboquadrina pachyderma (sin.) from 87 eastern and central Arctic Ocean surface sediment samples were analyzed for stable oxygen and carbon isotope composition. Additional results from 52 stations were taken from the literature. The lateral distribution of δ 18O ( 18 O 16 O ) values in the Arctic Ocean reveals a pattern of roughly parallel, W-E stretching zones in the Eurasian Basin, each ∼0.5‰ wide on the δ 18O scale. The low horizontal and vertical temperature variability in the Arctic halocline waters (0–100 m) suggests only little influence of temperature on the oxygen isotope distribution of N. pachyderma (sin.). The zone of maximum δ 18O values of up to 3.8‰ is situated in the southern Nansen Basin and relates to the tongue of saline (> 33%.) Atlantic waters entering the Arctic Ocean through the Fram Strait. δ 18O values decrease both to the Barents Shelf and to the North Pole, in accordance with the decreasing salinities of the halocline waters. In the Nansen Basin, a strong N-S δ 18O gradient is in contrast with a relatively low salinity change and suggests contributions from different freshwater sources, i.e. salinity reduction from sea ice meltwater in the south and from light isotope waters (meteoric precipitation and river-runoff) in the northern part of the basin. North of the Gakkel Ridge, δ 18O and salinity gradients are in good accordance and suggest less influence of sea ice melting processes. The δ 13C ( 13 C 12 C ) values of N. pachyderma (sin.) from Arctic Ocean surface sediment samples are generally high (0.75–0.95‰). Lower values in the southern Eurasian Basin appear to be related to the intrusion of Atlantic waters. The high δ 13C values are evidence for well ventilated surface waters. Because the perennial Arctic sea ice cover largely prevents atmosphere-ocean gas exchange, ventilation on the seasonally open shelves must be of major importance. Lack of δ 13C gradients along the main routes of the ice drift from the Siberian shelves to the Fram Strait suggests that primary production (i.e. CO 2 consumption) does probably not change the CO 2 budget of the Arctic Ocean significantly.