Fjord Environments Research Articles

Impacts of glacial discharge on the primary production in a Greenlandic fjord

Subglacial discharge from marine-terminating glaciers in Greenland injects large volumes of freshwater and suspended sediment into adjacent fjord environments. Although the discharge itself is nutrient poor, the formation of meltwater plumes can enhance marine biological production by stimulating upwelling of nutrient-rich fjord water. Despite the importance of meltwater discharge to marine ecosystems, little is known of the quantitative impact of discharge processes on phytoplankton growth, including the effects of local plumes, fjord-wide stirring and mixing, and suspended sediments on net primary production (NPP). Here, we report simulations of Bowdoin Fjord in northwestern Greenland using coupled non-hydrostatic ocean circulation and lower-trophic level ecosystem models, developed using field data. Our findings demonstrate that subglacial discharge plays a crucial role in NPP by stirring and mixing the entire fjord water system, which has a greater effect on NPP than local plume upwelling. Sensitivity tests suggest a 20% increase in NPP under conditions of enhanced discharge anticipated in the future. However, if glacier discharge and retreat exceed critical levels, NPP is predicted to decline by 88% relative to present values. This pattern reflects the negative impact of increased sediment flux on photosynthesis and weakened fjord stirring and mixing resulting from shallower outlet depths.

Rock avalanches in northeastern Baffin Island, Canada: understanding low occurrence amid high hazard potential

Rock avalanches in fjord environments can cause direct catastrophic damage and trigger secondary submarine landslides and tsunamis. These are well-documented in Greenland, Norway, and Alaska but have gone largely unreported in the extensive fjord terrain of the eastern Canadian Arctic. We provide the first inventory of rock avalanche deposits in northeastern Baffin Island—a region characterized by moderate to high seismic hazard, steep and high-walled fjords and glacial valleys, active deglaciation, and observed climate warming. Over a broad study area of ~60,000 km2, one sixth of the terrain had sufficient slope height and gradient to potentially generate rock avalanches. Within that hazard zone, we identified eight rock avalanche deposits at six locations. Only three rock avalanche deposits at two locations are dated, using aerial imagery (1958-present), to the last century while five deposits at four locations are inferred as syn- to post-glacial, likely occurring shortly after local debuttressing. These total numbers fall well below documented inventories from Greenland, Norway, and Alaska. We hypothesize that (1) continuous permafrost persists throughout this region and continues to act as a stabilizing factor and (2) rock mass quality is high in areas of most extreme relief contrast within the study region relative to analogous high-latitude fjord systems such as those in southwestern Greenland. We suggest that Baffin Island is currently in a period of quasi-stability that follows the intense instability during initial deglaciation, yet precedes the higher anticipated slope instability that may occur during permafrost degradation.

Sedimentary ancient DNA and HBI biomarkers as sea‐ice indicators: A complementary approach in Antarctic fjord environments

AbstractReliable high‐resolution, pre‐observational‐period sea‐ice datasets are rare but critical for contextualizing recent sea‐ice declines and future scenarios. We combine sedimentary ancient DNA of the sea‐ice dinoflagellate Polarella glacialis (Pgla‐sedaDNA) with selected highly branched isoprenoid (HBI) biomarkers alongside other indicators to reconstruct sub‐decadal sea‐ice changes in a marine archive from the Antarctic Peninsula that extends to ~ 1900 CE. Pre‐1940 CE, the continuously present sea‐ice biomarker IPSO25 yet absent Pgla‐sedaDNA, along with low open‐water biomarkers and total organic carbon (TOC), imply more prominent seasonal sea ice and lower productivity under cooler climate. Post‐1940 CE, rising Pgla‐sedaDNA and open‐water HBIs under climate warming reflect young ice with a retreating sea‐ice edge. Over the last two decades, lower Pgla‐sedaDNA, higher open‐water HBIs and TOC infer known warming, sea‐ice reduction, and increased productivity. Our multiproxy‐based palaeo‐histories agree well with observational data, highlighting the potential of this combination of proxies for nuanced and long‐term sea‐ice reconstructions.

Post-glaciation depositional changes in Wijdefjorden, northern Svalbard, using grain-size end-member modelling

Grain-size end-member (EM) modelling is a robust statistical approach for identifying and quantifying dominant grain-size distributions. This approach provides a novel perspective for understanding the impact of interactions between depositional processes in complex sedimentary environments. This study examines grain-size distributions of six glacimarine sediment cores collected along an NS transect from the continental shelf to the Wijdefjorden system in northern Svalbard. In addition, we integrate grain-size EMs with lithologic and acoustic facies, allowing us to identify three distinct groups of EMs (EM1–3), each closely associated with specific depositional processes: turbid meltwater discharge (EM1), sediment winnowing by bottom currents (EM2), and the deposition of ice-rafted debris in glacimarine conditions and subglacial till (EM3). An analysis of the three EM groups reveals that the glacial retreat during the last deglaciation and the Atlantic Water inflow significantly impacted depositional changes within the Wijdefjorden system. In contrast, a decrease in the Atlantic Water inflow during the late Holocene corresponds to glacial re-advance, resulting in shifts in the depositional environment. This study demonstrates the utility of EM modelling in deciphering complex grain-size distributions and reconstructing different climate-driven depositional processes in glacimarine sediments in Svalbard fjords. This integrated approach enhances our understanding of the intricate interplay among climate change, glacier dynamics, and oceanic forcing in polar fjord environments.

Cold-water coral energy reserves and calcification in contrasting fjord environments

The relationship between energy reserves of cold-water corals (CWCs) and their physiological performance remains largely unknown. In addition, it is poorly understood how the energy allocation to different metabolic processes might change with projected decreasing food supply to the deep sea in the future. This study explores the temporal and spatial variations of total energy reserves (proteins, carbohydrates and lipids) of the CWC Desmophyllum dianthus and their correlation with its calcification rate. We took advantage of distinct horizontal and vertical physico-chemical gradients in Comau Fjord (Chile) and examined the changes in energy reserves over one year in an in situ reciprocal transplantation experiment (20 m vs. 300 m and fjord head vs. mouth). Total energy reserves correlated positively with calcification rates. The fast-growing deep corals had higher and less variable energy reserves, while the slower-growing shallow corals showed pronounced seasonal changes in energy reserves. Novel deep corals (transplanted from shallow) were able to quickly increase both their calcification rates and energy reserves to similar levels as native deep corals. Our study shows the importance of energy reserves in sustaining CWC growth in spite of aragonite undersaturated conditions (deep corals) in the present, and potentially also future ocean.

Silicon Isotopes Highlight the Role of Glaciated Fjords in Modifying Coastal Waters

AbstractGlaciers and ice sheets are experiencing rapid warming under current climatic change and there is increasing evidence that glacial meltwaters provide key dissolved and dissolvable amorphous nutrients to downstream ecosystems. However, large debate exists around the fate of these nutrients within complex and heterogenous fjord environments, where biogeochemical cycling is still often poorly understood. We combine silicon (Si) concentration data with isotopic compositions to better understand silicon cycling and export in two contrasting fjordic environments in south‐west Greenland. We show that both fjords have isotopically light dissolved silicon (DSi) within surface waters, despite an apparently rapid biological drawdown of DSi with increasing salinity. We hypothesize that such observations cannot be explained by simple water mass mixing processes, and postulate that an isotopically light source of Si, most likely glacially derived amorphous silica (ASi), is responsible for further modifying these coastal waters within the fjords and beyond. Fjord to coastal exchange is likely a relatively slow process (several months), and thus is less impacted by short‐term (<seasonal) changes of glacial meltwater input into the fjord, which has implications when considering the role of glacial meltwaters on nutrient export beyond the shelf break. We highlight the need for isotopic studies combined with dissolved and particulate nutrient concentration analysis to provide a more detailed analysis into the biogeochemical cycles within these highly dynamic fjord environments.

Diversity of complex polysaccharide degrading bacteria from the sediments of interlinked high Arctic fjords, Svalbard

Polysaccharides comprise a major component of marine organic matter and are mostly produced by phytoplankton through primary production. The present study reports the polysaccharide degrading ability of cold-adapted heterotrophs from interlinked high Arctic fjords in the Svalbard archipelago. One hundred and ninety-five polysaccharide degrading bacteria isolated from inner and outer fjord sediments, 148 bacterial isolates showed complex polysaccharide degrading enzyme activity. Pectinase was the most predominant polysaccharide-degrading enzyme, followed by agarase, alginate lyase, chitinase, and laminarinase. Xylanase and carboxy methyl cellulase were showed in a relatively lesser activity. Heterotrophic bacterial isolates from the inner and outer shelf regions showed variation in their complex polysaccharide utilization ability. In Kongsfjorden, pectinase producing bacteria were more prevalent in the outer fjord, while chitinase producing bacteria dominated the inner fjord. In Krossfjorden, chitinase producing bacteria were frequently encountered in the outer fjord, whereas pectinase, laminarinase, and alginate lyase producing bacteria dominated the inner fjord. The results of the study indicated that a significant difference in polysaccharide-degrading bacterial phylotypes between the inner and outer fjords (p<0.05). Major polysaccharide-degrading bacteria belonged to phylum Proteobacteria, followed by Firmicutes, Actinobacteria, and Bacteroidetes. The dominant polysaccharide-degrading genera are Marinobacter, Bacillus, Salinibacterium, Alcaligenes, and Planococcus. The findings reveal the availability of a wide range of polysaccharide substrates in fjord sediments and the significant functional role of the heterotrophic bacterial community in the remineralization process of fjord environments.

Glacier decay boosts the formation of new Arctic coastal environments—Perspectives from Svalbard

AbstractThe consequences of accelerating climatic warming on Arctic landscape evolution are far‐reaching. In Svalbard, glaciers are rapidly retreating after the Little Ice Age, which leads to exposing new coastal landscapes from marine‐terminating glaciers. Precise quantification of these changes was limited until the complete dataset of Svalbard glacier outlines from 1930's was made available. Here, we analyse the new Svalbard glacier change inventory data and demonstrate that glacier retreat led to a major shift from marine‐terminating towards land‐based glaciers in the last century. This retreat also led to the formation of 922.9 km of new coastline since 1930's creating pristine landscapes governed by paraglacial processes and sediment‐rich nearshore fjord environments. Recent palaeogeographical reconstructions suggest that such a mode of coastal evolution was dominant over the extended periods of the Holocene. Transitions from marine‐terminating to land‐based glaciers have significant implications for fjord circulation, biological production, the state of marine ecosystems, biogeochemical cycles between land and seas and the CO2 budget in coastal waters.

Seasonal mesozooplankton patterns and timing of life history events in high-arctic fjord environments

Seasonal patterns in mesozooplankton composition, vertical distribution, and timing of reproduction are challenging to study in the open sea due to ocean currents and mix of populations of different origins. Sill fjords, on the other hand, with restricted water exchange, are ideal locations for studying taxa- and community-specific adaptations to the prevailing environment. Here, we present re-occurring patterns in the mesozooplankton community structure in Billefjorden, Svalbard, a high Arctic sill fjord with extensive seasonal ice cover, based on monthly sampling from 2011 to 2013. The zooplankton community composition confirmed the Arctic character of this fjord. Predominantly herbivorous taxa, such as Calanus glacialis and Pseudocalanus spp., showed strong seasonal variation in abundance and depth distribution, with population minima in spring being compensated by a rapid population recovery during summer. Omnivorous taxa, such as Microcalanus spp. and copepods of the family Aetideidae, largely remained at depth throughout the year and had an extended or year-round reproductive period. Deep-dwelling omnivorous/carnivorous species peaked in abundance in winter–spring when herbivorous populations were severely depleted. Taxa with seasonally limited occurrences, i.e., meroplankton, peaked in spring and summer at the surface, but were largely absent for the rest of the year. The different life histories, with contrasting feeding modes, depth preferences, and timing of reproduction lead to reduced interspecies competition and allow for a rather high and stable abundance of mesozooplankton year-round despite the short primary production window at high latitudes.

Trophic structure of benthic communities in a Chilean fjord (45°S) influenced by salmon aquaculture: Insights from stable isotopic signatures

Benthic marine food webs, which recycle organic matter and sustain unique biodiversity, are an important component of estuarine Patagonian fjords; however, these may be heavily influenced by salmon farming activities. Under the above conditions, this study collected several food sources (sediment organic matter, suspended particulate organic matter, macroalgae) and 26 benthic invertebrate species, and analyzed them using a Bayesian mixing model. Briefly, carbon and nitrogen stable isotopes analyses revealed that the highly variable isotopic niche widths respond to food supplies from marine and terrestrial organic matter. In addition, particulate and dissolved waste from salmon farming activities were found to modify isotopic composition ratios in many suspension feeders. Particularly, our results indicate high δ15N values in the sponge Cliona chilensis and the encrusting coral Incrustatus comauensis, which appear to be potential ecological indicators for evaluating stoichiometry imbalances and trace organic pollution sources in fjord environments.

Slope stability hazard in a fjord environment: Douglas Channel, Canada

Abstract Douglas Channel is a 140 km-long fjord system on Canada's west coast where steep topography, high annual precipitation and glacially over-deepened bathymetry have resulted in widespread slope failures. A 5 year project involving numerous marine expeditions to the remote area produced a comprehensive assessment of the magnitude and frequency of slope failures in the region. A classification scheme is presented based on morphology and failure mechanism: (1) debris flows are the most common in all parts of the fjord – they are often small with a subaerial component where fjord wall slope is very high or tend to exceed volumes of 10 6 m 3 where fjord wall slope is lower, allowing for accumulation of marine sediments; (2) large failures of oversteepened glacial sediments occurring at transgressive moraines and glaciomarine plateaus following deglaciation – the largest is at Squally Channel with an estimated volume of 10 9 m 3 ; (3) fjord wall failures that involve bedrock slump or rock avalanche; (4) translation of marine sediments; (5) composite/other slides; and (6) two scallop-shaped sackungen, or deep-seated gravitational slope deformations of granodiorite with volumes exceeding 60 × 10 6 m 3 . The postglacial marine sedimentary record shows evidence of large-scale slope failures of all styles that were especially active following deglaciation. The Holocene marks a transition to a lower frequency and change to primarily debris flows and smaller rock slides. Slope failures that may be capable of generating tsunamis and may be damaging to coastal infrastructure have occurred in all parts of Douglas Channel through much of the Holocene. Here we present a morphological analysis with volume estimates and age control using multibeam bathymetry, high-resolution sub-bottom data and sediment cores. The study details an extensive analysis of slope failures in a fjord network that can be extended to other fjord environments.

Responses of the kelp Saccharina latissima (Phaeophyceae) to the warming Arctic: from physiology to transcriptomics.

The Arctic region is currently facing substantial environmental changes due to global warming. Melting glaciers cause reduced salinity environments in coastal Arctic habitats, which may be stressful for kelp beds. To investigate the responses of the kelp Saccharina latissima to the warming Arctic, we studied the transcriptomic changes of S. latissima from Kongsfjorden (Svalbard, Norway) over a 24-hour exposure to two salinities (Absolute Salinity [SA ] 20 and 30) after a 7-day pre-acclimation at three temperatures (0, 8 and 15°C). In addition, corresponding physiological data were assessed during an 11-days salinity/temperature experiment. Growth and maximal quantum yield for photosystem II fluorescence were positively affected by increased temperature during acclimation, whereas hyposalinity caused negative effects at the last day of treatment. In contrast, hyposalinity induced marked changes on the transcriptomic level. Compared to the control (8°C-SA 30), the 8°C-SA 20 exhibited the highest number of differentially expressed genes (DEGs), followed by the 0°C-SA 20. Comparisons indicate that S. latissima tends to convert its energy from primary metabolism (e.g. photosynthesis) to antioxidant activity under hyposaline stress. The increase in physiological performance at 15°C shows that S. latissima in the Arctic region can adjust and might even benefit from increased temperatures. However, in Arctic fjord environments its performance might become impaired by decreased salinity as a result of ice melting.

Seal Occurrence and Habitat Use during Summer in Petermann Fjord, Northwestern Greenland

Ice-associated seals are considered especially susceptible and are potentially the first to modify distribution and habitat use in response to physical changes associated with the changing climate. Petermann Glacier, part of a unique ice-tongue fjord environment in a rarely studied region of northwestern Greenland, lost substantial sections of its ice tongue during major 2010 and 2012 calving events. As a result, changes in seal habitat may have occurred. Seal occurrence and distribution data were collected in Petermann Fjord and adjacent Nares Strait region over 27 days (2 to 28 August) during the multidisciplinary scientific Petermann 2015 Expedition on the icebreaker Oden. During 239.4 hours of dedicated observation effort, a total of 312 individuals were recorded, representing four species: bearded seal (Erignathus barbatus), hooded seal (Crystophora cristata), harp seal (Pagophilus groenlandicus), and ringed seal (Pusa hispida). Ringed seals were recorded significantly more than the other species (χ2 = 347.4, df = 3, p &lt; 0.001, n = 307). We found significant differences between species in haul-out (resting on ice) behavior (χ2 = 133.1, df = 3, p &lt; 0.001, n = 307). Bearded seals were more frequently hauled out (73.1% n = 49), whereas ringed seals were almost exclusively in water (93.9%, n = 200). Differences in average depth and ice coverage where species occurred were also significant: harp seals and bearded seals were found in deeper water and areas of greater ice coverage (harp seals: 663 ± 366 m and 65 ± 14% ice cover; bearded seals: 598 ± 259 m and 50 ± 21% ice cover), while hooded seals and ringed seals were found in shallower water with lower ice coverage (hooded seals: 490 ± 163 m and 38 ± 19% ice cover; ringed seals: 496 ± 235 m, and 21 ± 20% ice cover). Our study provides an initial look at how High Arctic seals use the rapidly changing Petermann Fjord and how physical variables influence their distribution in one of the few remaining ice-tongue fjord environments.

Seasonal succession, distribution, and diversity of planktonic protists in relation to hydrography of the Godthåbsfjord system (SW Greenland)

High-latitude fjord environments are undergoing dynamic seasonal changes, affecting spatio-temporal patterns in planktonic abundances. To investigate how physical gradients impact sub-Arctic planktonic protists (> 20 μm), a seasonal transect study was performed in 2013 during three periods of planktonic succession: spring, summer, and autumn. The samples were collected from the glacier-fjord-ocean transect in SW Greenland using two complementary sampling methods, i.e. net hauls (20-μm net) and Niskin bottles. The key drivers of the distribution of planktonic groups and dominant taxa were hydrographic properties (defined as ‘time’, salinity, and temperature) reflecting the area’s seasonally changing circulation system. Cold and relatively saline waters in spring favoured the single haptophyte species Phaeocystis cf. pouchetii, while in summer, fresher waters influenced by glacial discharge favoured diatoms, followed by dinoflagellates and predatory ciliates in autumn. Our findings reveal a monodominant structure among the planktonic protists observed in each key sub-region and in each season. (1) Gedaniella boltonii (spring) was associated with inner fjord upwelling, (2) Chaetoceros sp. (summer) and Chaetoceros cf. socialis (autumn) were linked to ‘glacial meltwater’ circulation in the main fjord, and (3) Thalassiosira poroseriata (summer) and Skeletonema sp. (autumn) characterized warm and relatively saline offshore waters influenced by the West Greenland Current. The observed spatio-temporal patterns were linked to changes in hydrographic regimes driven by the interplay between the melting of the Greenland Ice Sheet and inflows of offshore, Atlantic-sourced waters.

Exploring the Diversity and Antimicrobial Potential of Marine Actinobacteria from the Comau Fjord in Northern Patagonia, Chile.

Bioprospecting natural products in marine bacteria from fjord environments are attractive due to their unique geographical features. Although, Actinobacteria are well known for producing a myriad of bioactive compounds, investigations regarding fjord-derived marine Actinobacteria are scarce. In this study, the diversity and biotechnological potential of Actinobacteria isolated from marine sediments within the Comau fjord, in Northern Chilean Patagonia, were assessed by culture-based approaches. The 16S rRNA gene sequences revealed that members phylogenetically related to the Micrococcaceae, Dermabacteraceae, Brevibacteriaceae, Corynebacteriaceae, Microbacteriaceae, Dietziaceae, Nocardiaceae, and Streptomycetaceae families were present at the Comau fjord. A high diversity of cultivable Actinobacteria (10 genera) was retrieved by using only five different isolation media. Four isolates belonging to Arthrobacter, Brevibacterium, Corynebacterium and Kocuria genera showed 16S rRNA gene identity <98.7% suggesting that they are novel species. Physiological features such as salt tolerance, artificial sea water requirement, growth temperature, pigmentation and antimicrobial activity were evaluated. Arthrobacter, Brachybacterium, Curtobacterium, Rhodococcus, and Streptomyces isolates showed strong inhibition against both Gram-negative Pseudomonas aeruginosa, Escherichia coli and Salmonella enterica and Gram-positive Staphylococcus aureus, Listeria monocytogenes. Antimicrobial activities in Brachybacterium, Curtobacterium, and Rhodococcus have been scarcely reported, suggesting that non-mycelial strains are a suitable source of bioactive compounds. In addition, all strains bear at least one of the biosynthetic genes coding for NRPS (91%), PKS I (18%), and PKS II (73%). Our results indicate that the Comau fjord is a promising source of novel Actinobacteria with biotechnological potential for producing biologically active compounds.

Relatively high antibiotic resistance among heterotrophic bacteria from arctic fjord sediments than water – Evidence towards better selection pressure in the fjord sediments

The objective of this study was to determine the prevalence of antibiotic resistance among aerobic heterotrophic bacteria and coliform bacteria from water and sediment of Kongsfjord. The study was based on the assumption that arctic fjord environments are relatively pristine and offer very little selection pressure for drug resistant mutants. In order to test the hypothesis, 200 isolates belonging to aerobic heterotrophic bacteria and 114 isolates belonging to coliforms were tested against 15 antibiotics belonging to 5 different classes such as beta lactams, aminoglycosides, quinolones, sulpha drugs and tetracyclines. Resistance to beta lactam and extended spectrum beta lactam (ESBL) antibiotics was considerably high and they found to vary significantly (p < 0.05) between heterotrophic and coliform bacteria. Though the coliforms showed significantly high level of antibiotic resistance against ESBL's extent and diversity of antibiotic resistance (as revealed by multiple antibiotic resistance index and resistance patterns), was high in the aerobic heterotrophic bacteria. Most striking observation was that isolates from fjord sediments (both heterotrophic bacteria and coliforms) in general showed relatively high prevalence of antibiotic resistance against most of the antibiotics tested, indicating to better selection pressure for drug resistance mutants in the fjord sediments.

First assessment of flux rates of jellyfish carcasses (jelly-falls) to the benthos reveals the importance of gelatinous material for biological C-cycling in jellyfish-dominated ecosystems

There is accumulating evidence that jellyfish contribute significantly to biological carbon cycling and that their carcasses can have controversial effects on seafloor ecosystems. Moreover, changes in the thermal properties of the ocean, ocean chemistry and direct anthropogenic effects can seriously modify jellyfish populations in surface waters and potentially alter the importance of jellyfish in the biological pump relative to other forms of detritus. However, no studies have ever quantified the flux rate of jellyfish carcasses (jelly-falls) to the seafloor, or quantified how jelly-fall C and N fluxes compare to phytodetrital fluxes. In this study, we documented the seafloor abundance of jelly-falls over a 1-year period in the jellyfish-dominated Lurefjord, western Norway. A total of 9 jelly-falls were documented from 768 seafloor images over the course of the study, equivalent to 0-13.4 mg C m-2 and 0-2.1 mg N m-2 of jellyfish material being deposited in the deep fjord basin. Assuming that jellyfish removal rates and phytodetrital flux rates from nearby fjord environments are similar to Lurefjorden, we estimate that the jellyfish C and N fluxes to the seafloor were 0-72.8 mg C m-2 d-1 and 0-11.2 mg N m-2 d-1 at the time of sampling. In addition, we estimate that the maximum jellyfish carcass flux rates were equivalent to 96 and 160% of the phytodetrital C and N flux that would arrive at the seafloor where the jelly-falls were recorded. These results imply that jelly-falls most likely contribute significantly to detrital C and N fluxes in at least one jellyfish-dominated environment, despite often being recorded in low abundances. If more fjord environments become jellyfish hotspots as a result of water column darkening, the contribution of jellyfish C and N in the biological pump will potentially increase, necessitating the conceptual inclusion of a jelly-pump in future fjord biogeochemical cycling studies.

Hydrography of Marian Cove, King George Island, West Antarctica: implications for ice-proximal sedimentation during summer

AbstractDuring the summer, from 1996–2000, vertical profiles of conductivity, temperature and transmissivity were obtained near the tidewater glacier of Marian Cove, King George Island, Antarctic Peninsula. The aims for the study were to determine the short-term variations of water structure due to hydrographic forcings and to understand sedimentation of suspended particulate matter in Antarctic fjord environments. Four distinct water layers were identified in the ice-proximal zone of the cove: i) a surface layer composed of cold and turbid meltwater, ii) a relatively warm Maxwell Bay inflow layer with characteristics of outer fjord water, iii) a turbid/cold mid-depth layer (40–70 m) originating from subglacial discharge, and iv) a deep layer comprised of the remnant winter water. The main factor influencing the characteristics of glacial meltwater layers and driving deposition of suspended particles in the cove is tidal forcing coupled with wind stress. The relatively small amount of meltwater discharge in Marian Cove yields low accumulation rates of non-biogenic sedimentary particles in the cove. The response to north-western and western winds, coupled with flood tide, may promote settling and sedimentation of suspended particles from turbid layers in the ice-proximal zone of the cove.

Benthic ecosystem functioning beneath fish farms in different hydrodynamic environments

To quantify how fish farming modifies short‐term benthic carbon cycling in fjord environments and the role of hydrodynamics in modifying effects on the benthos, we assessed benthic ecosystem structure and respiration and used isotope labeled algae as a tracer to quantify C flow over 48 h through macrofauna and bacteria in sediments collected from beneath fish farm sites in (1) high water‐flow areas, (2) low water‐flow areas, and (3) two appropriate control sites situated downstream from the farms. Bacterial biomass was significantly greater in sediments collected from the fish farm sites relative to the controls. This was also true for sediment oxygen consumption (SOC) rates averaged over each 48 h investigation, which were significantly correlated with total benthic (macrofauna and bacteria) biomass. Short‐term C‐uptake rates by macrofauna were elevated in both fish farm treatments compared with bacterial C uptake and were significantly higher in sediments from the low flow fish farm site relative to both controls. While SOC rates were significantly higher in experiments using sediments from the low flow fish farm site; faunal abundance, biomass uptake, C uptake, bacterial biomass, and metabolism in sediments from both fish farm treatments were not significantly different from one another. Fish farming can dramatically alter benthic ecosystem functioning, and significant effects can occur around fish farms irrespective of the water‐flow regime the farms are moored in.

Caracterización taxonómica y paleoecológica de la ingresión del Holoceno en el Canal Beagle (Tierra del Fuego), en base a las asociaciones de dinoquistes y otros palinomorfos acuáticos

TAXONOMIC AND PALEOECOLOGICAL CHARACTERIZATION OF HOLOCENE INGRESSION IN THE BEAGLE CHANNEL (TIERRA DEL FUEGO), BASED ON DINOCYST ASSEMBLAGES AND OTHER AQUATIC PALYNOMORPHS. On the southern coast of Tierra del Fuego, Argentina, the Holocene marine ingression took place around 8,000 C 14 years BP, and it is represented by several discontinuous marine terraces along the north coast of the Beagle Channel. During the beginning of the marine incursion, the aquatic assemblages developed in Bahia Lapataia and Rio Varela localities, were characterized by a scarce participation of marine components, especially of dinofl agellate cysts. After 6,000 C 14 years BP, in Rio Ovando and Albufera Lanushuaia localities, an increase in the number of aquatic species was observed with a major participation of Peridiniales dinocysts in the associations, suggesting the establishment of marginal marine environments with low to moderate salinities and high nutrient content in the water. The analysis of the dinofl agellate cysts and other aquatic palynomorphs assemblages recorded in the marine sediments from northern coast of the Beagle Channel, indicate that the environmental conditions during the middle-late Holocene correspond to fjord (estuarine) environments close to ice fi elds affected by glacier meltwater discharge with anomalously low salinities. These aquatic assemblages identifi ed have a similar composition to those observed in modern sediments of the Beagle Channel.