Fjord Research Articles

Glaciers melt noisily into the sea

A joint field and lab study has identified the principal source of noise in glacial fjords.

Modeling the impact of glacial runoff on fjord circulation and submarine melt rate using a new subgrid‐scale parameterization for glacial plumes

AbstractThe injection at depth of ice sheet runoff into fjords may be an important control on the frontal melt rate of tidewater glaciers. Here we develop a new parameterization for ice marginal plumes within the Massachusetts Institute of Technology General Circulation Model (MITgcm), allowing three‐dimensional simulation of large (500 km2) glacial fjords on annual (or longer) time scales. We find that for an idealized fjord (without shelf‐driven circulation), subglacial runoff produces a thin, strong, and warm down‐fjord current in the upper part of the water column, balanced by a thick and slow up‐fjord current at greater depth. Although submarine melt rates increase with runoff due to higher melt rates where the plume is in contact with the ice front, we find that annual submarine melt rate across the ice front is relatively insensitive to variability in annual runoff. Better knowledge of the spatial distribution of runoff, controls on melt rate in those areas not directly in contact with plumes, and feedback mechanisms linking submarine melting and iceberg calving are necessary to more fully understand the sensitivity of glacier mass balance to runoff‐driven fjord circulation.

Estimating Abundance from Counts in Large Data Sets of Irregularly Spaced Plots using Spatial Basis Functions

Monitoring plant and animal populations is an important goal for both academic research and management of natural resources. Successful management of populations often depends on obtaining estimates of their mean or total over a region. The basic problem considered in this paper is the estimation of a total from a sample of plots containing count data, but the plot placements are spatially irregular and non-randomized. Our application had counts from thousands of irregularly spaced aerial photo images. We used change-of-support methods to model counts in images as a realization of an inhomogeneous Poisson process that used spatial basis functions to model the spatial intensity surface. The method was very fast and took only a few seconds for thousands of images. The fitted intensity surface was integrated to provide an estimate from all unsampled areas, which is added to the observed counts. The proposed method also provides a finite area correction factor to variance estimation. The intensity surface from an inhomogeneous Poisson process tends to be too smooth for locally clustered points, typical of animal distributions, so we introduce several new overdispersion estimators due to poor performance of the classic one. We used simulated data to examine estimation bias and to investigate several variance estimators with overdispersion. A real example is given of harbor seal counts from aerial surveys in an Alaskan glacial fjord.

Small-scale spatial variation of soft-bottom polychaete biomass in an Antarctic glacial fjord (Ezcurra Inlet, South Shetlands): comparison of sites at different levels of disturbance

There is still only a small number of studies dedicated to Southern Ocean benthic biomass, especially on species level. Here, we analyze polychaete biomass in two areas of the Antarctic fjord Ezcurra Inlet characterized by different levels of disturbance associated with activity of glaciers. Material was collected in March 2007 in the 90–130 m depth range. Twenty van Veen grab (0.1 m2) samples were collected in the inner area of the fjord and 20 in the fjord mouth. Cluster analysis clearly separated those two parts of the fjord. Mean total biomass was significantly higher in the outer region (14.4 ± 5.5 g/0.1 m2) compared with the inner part (3.6 ± 0.8 g/0.1 m2). The highest biomass in the outer, not disturbed area was noted for Amphitrite kerguelensis, Aphelochaeta/Chaetozone, Scalibregma inflatum, Euchone pallida and Maldane sarsi antarctica, while in the inner region, only Aphelochaeta/Chaetozone had high biomass values. Average individual biomass and biomass of majority of polychaete functional groups was also higher in the outer area. Comparison of species composition and abundance with data collected 30 years ago in the studied area revealed also important differences in community structure.

Quantifying flow regimes in a Greenland glacial fjord using iceberg drifters

AbstractLarge, deep‐keeled icebergs are ubiquitous in Greenland's outlet glacial fjords. Here we use the movement of these icebergs to quantify flow variability in Sermilik Fjord, southeast Greenland, from the ice mélange through the fjord to the shelf. In the ice mélange, a proglacial mixture of sea ice and icebergs, we find that icebergs consistently track the glacier speed, with slightly faster speeds near terminus and episodic increases due to calving events. In the fjord, icebergs accurately capture synoptic circulation driven by both along‐fjord and along‐shelf winds. Recirculation and in‐/out‐fjord variations occur throughout the fjord more frequently than previously reported, suggesting that across‐fjord velocity gradients cannot be ignored. Once on the shelf, icebergs move southeastward in the East Greenland Coastal Current, providing wintertime observations of this freshwater pathway.

Structuring of zooplankton and fish larvae assemblages in a freshwater-influenced Greenlandic fjord: influence from hydrography and prey availability

RASMUS SWALETHORP1*, EVANDRO MALANSKI1, METTE DALGAARD AGERSTED1, TORKEL GISSEL NIELSEN1,2 AND PETER MUNK1 1 NATIONAL INSTITUTE OF AQUATIC RESOURCES (DTU AQUA), SECTION FOR OCEANOGRAPHY AND CLIMATE, TECHNICAL UNIVERSITY OF DENMARK, KAVALERGARDEN 6, CHARLOTTENLUND DK-2920, DENMARK AND GREENLAND CLIMATE RESEARCH CENTRE, GREENLAND INSTITUTE OF NATURAL RESOURCES, KIVIOQ 2, PO BOX 570, NUUK 3900, GREENLAND

Directionality of the ambient noise field in an Arctic, glacial bay.

The directionality of ambient noise in an Arctic tidewater glacier bay was measured using two horizontally spaced, broadband hydrophones. Segments of noise were divided into two frequency bands and analyzed for arrival angle. These data show that different classes of source radiate noise in distinct spectral bands and are spatially diverse. A previously unidentified source, the interaction of surface gravity waves with underside of ice ledges at the periphery of icebergs, is described. The generation of noise by ice-wave interaction suggests that surface waves should be measured if ambient noise is to be used to monitor ice dynamics in glacial fjords.

The Dynamics of Greenland's Glacial Fjords and Their Role in Climate.

Rapid mass loss from the Greenland Ice Sheet has sparked interest in its glacial fjords for two main reasons: Increased submarine melting of glaciers terminating in fjords is a plausible trigger for glacier retreat, and the anomalous freshwater discharged from Greenland is transformed by fjord processes before being released into the large-scale ocean. Knowledge of the fjords' dynamics is thus key to understanding ice sheet variability and its impact on climate. Although Greenland's fjords share some commonalities with other fjords, their deep sills and deeply grounded glaciers, the presence of Atlantic and Polar Waters on the continental shelves outside the fjords' mouths, and the seasonal discharge at depth of large amounts of surface melt make them unique systems that do not fit existing paradigms. Major gaps in understanding include the interaction of the buoyancy-driven circulation (forced by the glacier) and shelf-driven circulation, and the dynamics in the near-ice zone. These must be addressed before appropriate forcing conditions can be supplied to ice sheet and ocean/climate models.

Characteristics and dynamics of two major Greenland glacial fjords

Key Points We describe fjord and shelf circulation patterns in two large glacial fjords Time‐dependent, externally driven intermediary circulation dominates both fjords We charactertize these fjords in estuarine parameter space

Influence of a Glacier Melting Cycle on the Seasonal Hydrographic Conditions and Sediment Flux in a Subantarctic Glacial Fjord

Four hydrographic surveys were carried out in Gallegos Sound (54 ∘ 28 ′58 ″S–69 ∘ 50 ′55 ″ W), a subantarctic glacial fjord. This is the first comprehensive seasonal study for the extreme isolated areas in the Cordillera Darwin Ice Field, Chile. The fjord exhibits a strong seasonal pattern in its oceanographic characteristics. The highest values of total suspended solid concentrations were observed in summer (>15 mg L −1), with the lowest concentrations in winter (<5 mg L −1). Seasonality of the oceanographic characteristics in Gallegos Sound is significantly correlated with the air temperature. In spite of the high pluviosity and maritime climate in this region, the Cordillera Darwin mountain range creates drier conditions that contrast with the climate that influences glacial fjords of Alaska. The relatively high salinity observed in the surface layer during winter confirms that the influence of precipitacion on freshwater and TSS concentration is negligible. As Garibaldi Glacier is the most significant freshwater source in the basin of Gallegos Sound, ice melting represents the main forcing that influences the seasonal characteristics of the surface layer. The mean TSS concentrations observed in Gallegos Sound exhibit a higher range in comparison to other Chilean fjords and are more similar to the concentrations observed in the ice-proximal environment of an Antarctic fjords. In general, TSS concentrations in Gallegos Sound are much lower than those of glacial fjords of the Northern Hemisphere.

Natural and human effects on harbor seal abundance and spatial distribution in an Alaskan glacial fjord

AbstractTidewater glacial fjords support the largest populations of harbor seals (Phoca vitulina richardii) in Alaska and are a prime destination for tour ships. Chronic disturbance from ships, however subtle, could impact long‐term population stability. We examined variation in abundance and distribution of harbor seals on floating ice in Disenchantment Bay, Alaska, a tour ship destination for over a century with near daily visitation by ships in the spring/summer over the last decade. Counts of seals by aerial transect showed a sharp decline in May, prior to pupping and the first ships arriving; counts rebounded by the end of June remaining high until August. Seal distribution and abundance peaked in 5–7 tenths ice cover; total area of ice cover showed no effect. Despite regular flushing of seals by ships, we found no broad‐scale patterns in seal abundance and distribution that could be explained by ship presence. We cannot rule out mechanisms of long‐term disturbance, difficult to detect and that might explain notable differences with other, similar sites. Population declines at disturbed glacial sites and the still rising popularity of vessel‐based tourism indicate a need for individual‐based studies on how seals respond to the dynamics of glacial ice environments and human‐caused stresses.

Structure of bryozoan communities in an Antarctic glacial fjord (Admiralty Bay, South Shetlands)

The study was supported by a grant of Polish Ministry of Science and Higher Education No. 51/N-IPY/2007/0 as well as Census of Antarctic Marine Life Project. Krzysztof Pabis was also partially supported by University of Lodz internal funds. This research was also supported by the Polish Geological Institute-National Research Institute during the realization of the project numbered 40.2900.0903.18.0 titled “Bryozoan assemblage of Admiralty Bay—richness, diversity and abundance.” Urszula Hara is deeply grateful to Leszek Giro (Micro-area Analyses Laboratory at the Polish Geological Institute-National Research Institute, Warsaw), for providing SEM assistance during the project. We also want to thank two anonymous reviewers for their suggestions that helped us improve this article. Thanks are also due to Magdalena Blazewicz-Paszkowycz for language correction and polishing the final version of the manuscript.

Estimates of iceberg submarine melting from high-resolution digital elevation models: application to Sermilik Fjord, East Greenland

AbstractObserved increases in iceberg discharge from Greenland’s marine-terminating glaciers over the past two decades have altered the freshwater flux from glacial fjords into surrounding ocean basins. Although variations in freshwater flux due to ice-sheet discharge change have been investigated on a broad scale, the distribution of the freshwater flux due to melting of calved glacier ice (i.e. icebergs) has not been examined. Logistical challenges to collecting in situ data in glacial fjords have so far prevented a detailed examination of freshwater fluxes arising from melting beneath the waterline (i.e. submarine melting). Here we demonstrate that submarine melting of icebergs can be quantified using repeat digital elevation models derived from very high-resolution stereo satellite images. Analysis of volume changes for icebergs in Sermilik Fjord, East Greenland, yield area-averaged submarine melt rates of ~0.39 m d–1. These rates are in relatively good agreement with simulated winter melt rates along the submerged portion of the Helheim Glacier terminus, providing independent validation of the applied technique. Further, the volume flux of fresh water from iceberg melting scales with surface and submerged iceberg areas, which suggests that iceberg meltwater may be an important freshwater component in fjords with high iceberg concentrations and/or expansive ice melange.

A 100-year long record of alkenone-derived SST changes by Southeast Greenland

Sediment core ER07 from Sermilik Fjord by Helheim Glacier in Southeast Greenland was analyzed for alkenones to document sea surface temperature (SST) changes over the past 100 years. The alkenone SST values, ranging from 8 to 12°C, contrasts with colder values (0–4°C) obtained from recent hydrographic surveys inside the fjord. We suggest that advection of allochtonous alkenones produced in the warm Irminger Current waters circulating on the shelf likely accounts for this difference. The temperature range of the alkenone-derived record is similar to in situ observations of 8–11°C on the shelf just outside Sermilik Fjord, and its variability over the past 100 years resembles the constructed variability over the shelf using remote instrumental data. This suggests that oceanographic changes on the adjacent shelf are linked to regional changes of the Irminger Current and the East Greenland Current. The subsurface water heat content has previously been suggested as an important control on Greenland outlet glacier stability and underlined by an episode of warm subsurface waters ~1940 concurrent with markedly increased calving and retreat of Helheim Glacier. Our results therefore suggest that alkenone-derived SST time series from high-sedimentation rate glacial fjords may provide a new approach for reconstruction of past changes of shelf water properties and variability around Greenland.

Diversity and Bioprospective Potential (Cold-Active Enzymes) of Cultivable Marine Bacteria from the Subarctic Glacial Fjord, Kongsfjorden

The diversity and abundance of culturable bacteria in Kongsfjorden water (15 stations) and sediments (12 stations) were studied. Viable numbers ranged between 105–106 CFU l−1 in water and 102–104 CFU g−1 in the sediments. A total of 291 and 43 bacterial isolates were retrieved from the water (KJF) and sediments (FS), respectively. Based on 16S rRNA gene sequence similarities, the KJF and FS isolates were grouped into 49 and 23 phylotypes, respectively. The KJF and FS phylotypes represented three phyla namely, Actinobacteria, Bacteroidetes, and Proteobacteria. At the genus level, Flavobacterium and Shewanella and at the species level, Pseudoaltermonas arctica and Colwellia psychrerythraea were dominant in the water and sediments, respectively. Most phylotypes were psychrotolerant with upper growth temperature limit of 25–37 °C and tolerated 0.3–2.5 M NaCl and pH values of 5.0–11.0. Majority of the phylotypes produced one or more of the extracellular hydrolytic enzymes amylase, lipase, caseinase, urease, gelatinase, and DNase at 4 and 18 °C, while none were chitinolytic. Few of the FS phylotypes exhibited extracellular activity only at 4 or 18 °C. Nine FS and 21 KJF isolates were pigmented. The predominant cellular fatty acids were unsaturated, branched, and modified fatty acids, which are unique to cold-adapted bacteria.

Distribution patterns of polychaete fauna in an Arctic fjord (Hornsund, Spitsbergen)

Polychaetes are one of the most important groups of benthic organisms in marine ecosystems. They dominate on the Arctic shelf and play an important role in ecosystem functioning. This study focuses on the polychaete biodiversity and their distribution patterns in Hornsund, an open glacial fjord, in western Spitsbergen and provides important baseline data for future studies of temporal fluctuations in benthic fauna. The main aim of this study was to assess how the polychaete abundance, biomass, diversity, community structure, and function vary along the Hornsund fjord’s axis, in relation to the environmental factors. Eighty-eight polychaete taxa were identified; an average density was 457 ind. m−2 ± 237.5 SD. Three assemblages were distinguished (INNER, MIDDLE, and OUTER) along the fjord axis, reflecting the intensity of glacial disturbance. A clear division between the highly disturbed inner part of the fjord (Brepollen) and the less impacted middle and outer parts was observed. Continuous gradients in abundance, biomass, and diversity were found with all those values diminishing toward the inner region of the fjord. The polychaete assemblages' indices were significantly correlated with bottom temperature, sediment characteristics (grain size), and distance to the glacier (longitude). No significant correlations were found with depth or total organic carbon content. Carnivore and motile surface deposit feeding polychaete species dominated in the areas close to the glaciers, while the OUTER community was dominated by carnivores and surface sessile and discretely motile species, and had more complex trophic structure, with multiple species representing different functional groups including carnivores, sessile, discretely motile, and motile surface deposit feeders and motile burrowers.

Do foraminifera mirror diversity and distribution patterns of macrobenthic fauna in an Arctic glacial fjord?

Abstract This paper compares the distribution and diversity patterns of benthic foraminifera (all taxa and only calcareous forms) and macrozoobenthos in an Arctic glacial fjord. The samples were collected at 22 stations located in Hornsund (west Spitsbergen). The activity of tidal glaciers located in the inner basins causes steep environmental gradients of turbidity, organic matter supply, and sediment stability. Clear differences in density, diversity and species composition were documented for both foraminifera and macrofauna between the groups of stations located in three zones along a gradient of increasing tidal glacier impact. The assemblages of both benthic compartments in the glacial bay were dominated by small, opportunistic, infaunal species (i.e., Cassidulina reinforme for foraminifera and cirratulid polychaetes for macrofauna) which occurred throughout the fjord, but showed an increase in density and/or dominance when approaching the glaciers. A parallel decreasing pattern from the central basin to the inner glacial bay was noted with regard to species richness and faunal density of both groups. Macrofaunal evenness decreased close to glaciers, but this was not observed in the foraminiferal assemblages. The distribution patterns of calcareous foraminifera were correlated (p = 0.001) both with those of all foraminifera (agglutinated and calcareous taxa) and with macrofauna, with the Spearman's rank correlation between the respective Bray Curtis similarity matrices ranging from 0.94 to 0.99 (total foraminifera), and from 0.37 to 0.67 (macrofauna), respectively. Species richness, expressed as the number of species per sample, and diversity, expressed by the Shannon–Wienner index, of foraminifera and macrofauna were also significantly correlated (Pearson correlation r = 0.79, r2 = 0.62, p

Standing waves in Norway's fjords caused by earthquakes

Standing waves in Norway's fjords caused by earthquakes

Seasonal variability of submarine melt rate and circulation in an East Greenland fjord

The circulation in a glacial fjord driven by a large tidewater glacier is investigated using a nonhydrostatic ocean general circulation model with a melt rate parameterization at the vertical glacier front. The model configuration and water properties are based on data collected in Sermilik Fjord near Helheim Glacier, a major Greenland outlet glacier. The approximately two‐layer stratification of the fjord's ambient waters causes the meltwater plume at the glacier front to drive a “double cell” circulation with two distinct outflows, one at the free surface and one at the layers' interface. In summer, the discharge of surface runoff at the base of the glacier (subglacial discharge) causes the circulation to be much more vigorous and associated with a larger melt rate than in winter. The simulated “double cell” circulation is consistent, in both seasons, with observations from Sermilik Fjord. Seasonal differences are also present in the vertical structure of the melt rate, which is maximum at the base of the glacier in summer and at the layers' interface in winter. Simulated submarine melt rates are strongly sensitive to the amount of subglacial discharge, to changes in water temperature, and to the height of the layers. They are also consistent with those inferred from simplified one‐dimensional models based on the theory of buoyant plumes. Our results also indicate that to correctly represent the dynamics of the meltwater plume, care must be taken in the choice of viscosity and diffusivity values in the model.

Virus dynamics in a large epishelf lake (Beaver Lake, Antarctica)

Summary Virus concentrations, virus‐to‐bacterium ratios (VBRs) and levels of lysogenic phage were measured throughout the 110‐m water column of epishelf Beaver Lake during the austral summer of 2003/2004. The aim was to determine which factor(s) controlled viral dynamics using detailed concomitant published data on inorganic nutrients, chlorophyll a, dissolved organic carbon (DOC) and bacterial production for Beaver Lake (Freshwater Biology, 51, 2006, 1119). Denaturing Gradient Gel Electrophoresis (DGGE) analysis of the bacterial community was also undertaken to investigate the potential relationship between bacterial community composition and viral dynamics. Virus concentration ranged between 1.43 × 104 and 302.4 × 104 viruses mL−1 and showed a clear increase over the summer, while bacterial concentrations exhibited no seasonal pattern (range: 9.6 × 104 to 44.6 × 104 cells mL−1). Consequently, VBR varied with highest values in January (3.32–7.33). The percentage of lysogenic phage was low, ranging from 0 to 11.69%, suggesting that other life cycles (i.e. lytic or possibly pseudolysogeny) were taking place. Attempts to measure viral production using both the TdR incorporation technique and the dilution technique failed to produce consistent results, in common with other ultra‐oligotrophic Antarctic lakes. There were significant correlations between viral concentration and each of chlorophyll a, DOC, ammonium and nitrate concentrations and bacterial production, but not between bacterial abundance and either soluble reactive phosphorus or temperature. Lack of change in the dominant bacterial community composition over summer suggests that changes in viral concentrations were a function of changes in other biological and physicochemical factors, rather than changes in host/phage infection. The results suggest a significant connection between viruses and bacteria, with the DOC pool acting as a conduit for the movement of carbon between the two components.