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Eurofleets-2 Cruise Summary Report Bottom Currents in a Stagnat Environment (BURSTER project)
Abstract and Figures
Eurofleets 2- BURSTER cruise was conducted onboard the German icebreaker RV Polarstern (Expedition PS99-1a) during June 13–23, 2016 (Bremerhaven-Longyearbyen) having the principal objective of investigating the hydrographic and bio-geochemical conditions of the Kveithola glacial trough (south of Svalbard), and to uncover the possible existence of gas seepage activity in the area. Although the BURSTER research was intended as a preparatory study for the writing of a major research project, the amount of planned activities onboard was really ambitious.
Thanks to a tireless, enthusiastic group formed by 13 students out of 23 scientists, a Teacher at Sea (GIFT, EU programme), and a technician from a small-medium enterprise operating with a transportable electron microscope (Nanovision Srl,), 89 multi-cores (22.50 m of sediments and 830 sub-samples), 265 water samples, 28 CTD casts along 7 transects and 2.57 km of benthic camera survey (OFOS), were collected during only 48 hours. In addition, according to the project work program, 24 hours were dedicated to the maintenance/recovery of two moorings that were deployed west of Svalbard during the Eurofleets 2- PREPARED project (RV G.O. Sars, June 2014). BURSTER group was actively supported by 4 scientists of the Italian PNRA project DEFROST, 4 AWI scientists of expedition PS99-1 and the Chief scientist, T. Soltwedel.
The cruise successfully recovered evidences of chemosynthetic activity in the Kveithola Trough with the presence of benthic fauna and large tabular and/or irregular-shaped rocks that share the same characteristics of methanogenic environments observed in gas seepage areas. The promising preliminary results obtained from this initial survey of the area will represent the base for the writing of a major project for a detailed investigation of the microbial, biologic and oceanographic system of the Kveithola Trough.
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... These deposits are covered by several drift units (the "Kveithola Drift"), that are also associated to a field of pockmarks in the innermost part of the trough (Bjarnadóttir et al., 2013;Lantzsch et al., 2017;Rebesco et al., 2011Rebesco et al., , 2016Rüther et al., 2012). Very recently, geophysical and geochemical data acquired by Lucchi et al. (2016) and Mau et al. (2017) in occasion of two surveys conducted along the northwestern Barents Sea margin indicated the presence of a few single gas flares along the northern edge of the Kveithola trough. Furthermore, Weniger et al. (2019) reported high concentrations of bound gases with thermogenic origin (e.g., CH 4 ranging between 340 and 642 ng g −1 ) in near-surface sediments collected at different sites inside the trough, thus suggesting that mature petroleum systems are likely to be present in the study area. ...
... As often observed in continental shelves and slopes, factors favouring AVS preservation are rapid deposition rates and low oxygen to euxinic conditions in the overlying waters (Rickard and Morse, 2005). The Kveithola trough is today crossed by persistent, high-energy and well oxygenated dense bottom currents, rearranging the sedimentary sequences (like the Kveithola Drift) deposited in the trough during the Holocene (Lantzsch et al., 2017;Lucchi et al., 2016;Rebesco et al., Fig. 4. Depth profiles along sediment core PS99/21-5 of A) total reduced inorganic sulphur content (tRIS, black horizontal axis) and its stable isotope composition (δ 34 S tRIS , red horizontal axis); B) total organic carbon (TOC) content (black horizontal axis) and the pyritic sulphur to total organic carbon ratio (S py /TOC, red horizontal axis); C) As and D) Mo content (black horizontal axis) and the relative enrichment factors (EF X , red horizontal axis). The pink and the green areas on the trace element plots highlight the enrichment factor intervals corresponding to detectable (3 < EF < 10) and moderate to strong (EF > 10) enrichments, respectively. ...
At cold seep environments, the detection of large ³⁴S enrichments within bulk sulphide minerals has been frequently used as a proxy to infer the vertical migrations of the sulphate-methane transition zone (SMTZ). Processes related to the oxidative part of the sulphur cycle can alter the original stable sulphur isotope composition (δ³⁴S) of the solid sulphur phases, in particular at the sediment-water interface. Identification of paleo and present positions of methane fronts in the sedimentary records requires the use of multiple geochemical proxies. Authigenic enrichment of Mo has been demonstrated to represent a valid and durable tracer of the past SMTZ depth fluctuations and of the intensities of the related methane seepages. This study is based on two closely-spaced short cores collected from the Main Drift of the Kveithola trough, a glacially-carved depression located in northwestern Barents Sea. Active fluid seepage has been recently reported in this area and a gas flare was specifically observed in proximity of the sampling sites where the cores object of our study were retrieved. In order to collect evidences of the possible occurrence of anaerobic oxidation of methane (AOM) at the sediment-water interface of the investigated area and infer the entity of the associated methane flux, we combined the analyses of reduced sulphur species δ³⁴S, total organic carbon and redox-sensitive elements. The negative δ³⁴S values within the extracted solid sulphur phases (up to −49.1‰ for pyritic sulphur) show that organoclastic sulphate reduction (OSR) coupled with disproportionation of sulphur intermediates are the only active processes in the near-surface sediments. However, moderate to strong enrichments of Mo detected in the relatively organic carbon poor intervals of both cores and the lack of concurrent enrichments of Co, Cu, Ni, V and Zn, usually associated to OSR-dominated environment, suggested that the sulphidic conditions favouring the Mo enrichments were produced by AOM. Therefore, we infer that high methane flux events characterized the drift area of the Kveithola, occasionally moving upward the SMTZ and thus inducing intense AOM in proximity of the sediment-water interface of this part of the trough. Our results confirmed the validity of sedimentary Mo as an indicator of the occurrence and intensity of past methane seepages.
We examine the living and dead benthic foraminiferal assemblages from the topmost 10 cm (using 150 μm sieve fraction) of three sedimentological short records collected in the Kveithola Trough (northwest Barents Sea). Our aim is to reconstruct the environmental variations of the last decades, connected to the interaction among the North Atlantic and the Arctic water masses. Our samples are collected at water depths between 150 and 380 m during the Eurofleets2-BURSTER oceanographic cruise, on board of the R/V Polarstern (June 2016).
In the Cell Tracker Green (CTG) labelled living foraminiferal fauna, the main species are Pullenia bulloides, Globobulimina auriculata, and Nonionellina labradorica, while in the dead assemblages the main species are Cassidulina neoteretis, Cibicidoides lobatulus, and Cassidulina reniforme (outer, inner, and shelf stations, respectively). The dead foraminiferal assemblages show no significant traceable environmental changes in the Kveithola Trough area occurred during the last ca. 100 years. Conversely, the living foraminiferal fauna shows that this area is subject to variations related to circulation changes and organic matter burial in sediments, to which the biota adapts quickly. Moreover, the species that are only observed in the dead foraminiferal assemblages and not in the living CTG-labelled foraminiferal assemblages (e.g. C. reniforme) are typical of colder water and highlight the ongoing warming of the Arctic area. We find that the preservation of foraminiferal tests may bias the paleontological results. The agglutinated tests are often disintegrated, and the delicate calcareous ones are broken. The environmental conditions (style of sedimentation, bottom currents, interaction with other communities) can weaken the foraminiferal tests and make them prone to breakage or dissolution.
The Mar Piccolo of Taranto, classified as a 'Site of National Interest' (SIN), is a semi-enclosed basin divided into two inlets with lagoon features and sea influences, seriously affected by anthropic activities. In the framework of the RITMARE project, a study has been carried out to evaluate the functionality of this ecosystem. As part of this work, measurements of the water abiotic parameters were performed in order to assess the physical-chemical features of this area after the activation, in the last decade, of treatment plants for various urban and industrial dumping. Seawater intrusions and continental inputs, as well as several submarine freshwater springs, clearly affect physical-chemical characteristics of the water column in the two inlets. This finding suggests that small-scale patterns in water circulation have the potential to influence the chemical properties of the seawater. The comparison with a 20-year dataset reveals a drastic decrease in nutrient concentrations after the year 2000, validating the functionality of the treatment plants. The reduction of nutrient inputs into the basin (up to -90 % in the first inlet characterized by lower hydraulic residence time) has changed the biogeochemical characteristics of the Mar Piccolo from being relatively eutrophic to moderately oligotrophic.
The Eurofleets-2 PREPARED cruise was conducted during June 5–15, 2014 on board the Norwegian R/V G.O. Sars to investigate the present and past oceanographic flow regime and patterns around two contourite drifts located in the eastern side of the Fram Strait (south-western margin of Spitsbergen). To achieve the main objective of the project, we plan to use a full range of time scaled measurements, from instantaneous (CTD) and seasonal (moorings) oceanographic measurements, to the recent (Box corer) and geologic (Calypso core) past record.
Good weather and calm sea conditions allowed to fulfil the cruise program and to obtain a high-quality and valuable dataset including: about 2780 km of underway measurements (hull-mounted ADCP and thermosalinograph); 60 CTD sites along 5 main transects; 22 sites for water sampling at different depths for biogeochemical characterization of water masses; 13 meso-zooplankton samplings carried out by vertical hauls (WP2 net) and 20 by horizontal hauls (Manta net) for the study of the present biological productivity of the area; about 120 km of site survey including high-resolution multibeam map and sub-bottom profiles for the identification of current-related structures; 5 Box cores; and 2 Calypso piston cores 19.67 and 17.37 m long with an excellent sediment recovery up to 92%. In addition, 3 moorings were deployed for seasonal measurements of water currents direction and velocity, water mass temperature and salinity and to determine the annual amount of local sediment input.
Preliminary onboard analyses outlined the presence of a cold-oxygenated and low salinity water mass moving in the deep northern part of the Storfjorden Trough under the effect of the Corilis force and tide configuration considerably affecting the velocity and bottom distribution of the cold water mass. The long Calypso cores contain the record of the past 20 ka with an expanded Holocene sequence (over 5 m-thick) that will allow us to obtain very-high resolution palaeoceanographic and palaeoenvironmental reconstructions in the area.
A pockmark field has been encountered in the northwestern Barents Sea, 50 km southeast of Hopen island. High resolution seismic records and side scan sonographs show that the features are small (10-20m diameter), shallow (< 1 m deep) structures that may cover up to 25% of the sea floor in local areas. Pockmark existence seem to be dependent on the presence of soft, Holocene mud. In more firm sea-floor they seem to concentrate in the partly infilled troughs of iceberg plough marks. The pockmark distribution, characteristics of the underlying sedimentary bedrock and thin cover of glacigenic sediments in the area, indicate they are formed by ascending gas from a deeper, probably petrogenic source. It is inferred that pockmarks may be found in larger parts of the Barents Sea.
In the shallow environment, the nutrient and carbon exchanges at the sediment-water interface contribute significantly to determine the trophic status of the whole water column. The intensity of the allochthonous input in a coastal environment subjected to strong anthropogenic pressures determines an increase in the benthic oxygen demand leading to depressed oxygen levels in the bottom waters. Anoxic conditions resulting from organic enrichment can enhance the exchange of nutrients between sediments and the overlying water. In the present study, carbon and nutrient fluxes at the sediment-water interface were measured at two experimental sites, one highly and one moderately contaminated, as reference point. In situ benthic flux measurements of dissolved species (O2, DIC, DOC, N-NO3 (-), N-NO2 (-), N-NH4 (+), P-PO4 (3-), Si-Si(OH)4, H2S) were conducted using benthic chambers. Furthermore, undisturbed sediment cores were collected for analyses of total and organic C, total N, and biopolymeric carbon (carbohydrates, proteins, and lipids) as well as of dissolved species in porewaters and supernatant in order to calculate the diffusive fluxes. The sediments were characterized by suboxic to anoxic conditions with redox values more negative in the highly contaminated site, which was also characterized by higher biopolymeric carbon content (most of all lipids), lower C/N ratios and generally higher diffusive fluxes, which could result in a higher release of contaminants. A great difference was observed between diffusive and in situ benthic fluxes suggesting the enhancing of fluxes by bioturbation and the occurrence of biogeochemically important processes at the sediment-water interface. The multi-contamination of both inorganic and organic pollutants, in the sediments of the Mar Piccolo of Taranto (declared SIN in 1998), potentially transferable to the water column and to the aquatic trophic chain, is of serious concern for its ecological relevance, also considering the widespread fishing and mussel farming activities in the area.
A marine geophysical study reveals a complex deglaciation pattern in the Kveithola trough, W Barents Sea. The data set includes multibeam swath bathymetry and sub‐bottom sediment profiler (chirp) data acquired for the whole extent of a palaeo, marine‐terminating ice stream, along with high‐resolution single‐channel seismic data from chosen profiles. The multibeam data show a geomorphic landform assemblage characteristic of ice streams. The results of a combination of seismic and chirp unit stratigraphy reveal that the seabed geomorphology is governed by a deeper‐lying reflector. The reflector dominates surface expressions of several subglacial and ice‐marginal units, each connected to a separate episode of ice‐margin stillstand/advance. Analysis of the combined data set has resulted in a conceptual model of the ice‐stream retreat. The model depicts complex deglaciation of a small, confined ice‐stream system through episodic retreat. It describes the formation of several generations of grounding‐zone systems, characterized by high meltwater discharges and the deposition of fine‐grained grounding‐line fans. The inferred style of grounding‐zone deposition in Kveithola deviates from that of other accounts, and is suggested to be intermediate in the previously described continuum between morainal banks and grounding‐line wedges. The results of this paper have implications for grounding‐zone theory and should be of interest to modellers of grounding‐line dynamics and ice‐stream retreat.
Multibeam echosounder surveys conducted on the southern slope of the Norwegian Trench between Norway and Denmark, show that elongate depressions interpreted as current-modified pockmarks are widespread in water depths of 100–500 m, in the Holocene–Recent succession. The long axes of the depressions are oriented at an angle of about 15° downslope, relative to the depth contours. The long axes appear to almost exactly parallel the effective bottom currents in this part of the Skagerrak. The present current directions were probably established about 4000 years ago, following a major shift in the oceanographic circulation pattern. The most characteristic feature of the depressions is their large size, with maximum depths of 45 m, widths of 400 m and lengths of 2 km. Strong bottom currents continuously transport particles thrown into suspension by the seepage process away from the pockmarks and prevent further deposition. Continuous seepage of shallow gas at fixed pockmark sites over long time periods combined with generally high sedimentation rates are thought to be responsible for the exceptional size of many depressions. The shallow gas probably has a mixed biogenic/thermogenic origin; however, the thermogenic component is considered to be most important for the formation of pockmarks. Seepage from permeable layers in the Jurassic–Cretaceous bedrock is evidenced by linear rows of depressions above these horizons, while pockmarks above sub-surface faults indicate gas seeps also from there. In shallow-water areas, the shape and size of pockmarks are locally dependent on their location with respect to giant sand waves, which trend sub-parallel to the depth contours and are interpreted to be of late Weichselian to early Holocene age. In deeper-water areas, the pockmarks have been further modified by gravity slides caused by collapse of steep pockmark walls.
The study of contourite drifts is an increasingly used tool for
understanding the climate history of the oceans. In this paper we
analyse two contourite drifts along the continental margin west of
Spitsbergen, just south of the Fram Strait where significant water mass
exchanges impact the Arctic climate. We detail the internal geometry and
the morphologic characteristics of the two drifts on the base of
multichannel seismic reflection data, sub-bottom profiles and
bathymetry. These mounded features, that we propose to name Isfjorden
and Bellsund drifts, are located on the continental slope between 1200
and 1800 m depth, whereas the upper slope is characterized by reduced-
or non-deposition. The more distinct Isfjorden Drift is about 25 km wide
and 45 km long, and over 200 ms TWT thick. We revise the 13 years-long
time series of velocity, temperature, and salinity obtained from a
mooring array across the Fram Strait. Two distinct current cores are
visible in the long-term average. The shallower current core has an
average northward velocity of about 20 cm/s, while the deeper bottom
current core at about 1450 m depth has an average northward velocity of
about 9 cm/s. We consider Norwegian Sea Deep Water episodically
ventilated by relatively dense and turbid shelf water from the Barents
Sea responsible for the accumulation of the contourites. The onset of
the drift growth west of Spitsbergen is inferred to be about 1.3 Ma and
related to the Early Pleistocene glacial expansion recorded in the area.
The lack of mounded contouritic deposits on the continental slope of the
Storfjorden is related to consecutive erosion by glacigenic debris
flows. The Isfjorden and Bellsund drifts are inferred to contain the
record of the regional palaeoceanography and glacial history and may
constitute an excellent target of future scientific drilling.
Grounding-zone wedges form where halts of decades to centuries during ice-sheet retreat across polar shelves allow sediment buildup at the grounding zone through delivery of deforming basal debris from fastflowing ice streams. Thirty grounding-zone wedges were identified on two-dimensional seismic-reflection profiles across the continental shelves of NE and NW Greenland. Grounding-zone wedges close to the seafloor are probably of late Weichselian age; others are on paleoshelves, buried beneath thick prograding glacial sediments. Several Greenland-shelf grounding-zone wedges occur on topographic highs that provide stabilizing pinning points in relatively shallow water. Grounding-zone wedges are asymmetric in the ice-flow direction with steeper ice-distal sides. Typical grounding-zone wedges are approximately 5-20 km long and 50-100 m thick, with a lateral width of several tens of kilometers. Forty grounding-zone wedges from the Greenland, Norwegian, and Antarctica margins show considerable varia bility about these values. Grounding-zone wedge dimensions are controlled by sediment flux, the duration of halts in ice retreat, subice cavity shape, and ice-stream width. Lowangle ice-shelf cavity roofs immediately beyond the grounding-zone probably restrict vertical accommodation space, preventing formation of high-amplitude ridges. Grounding-zone wedges are mainly transparent or chaotic on seismic profiles, probably resulting from delivery of diamictic debris. Offlapping reflectors represent progradation into an ice-roofed cavity. Reflector truncations of grounding-zone wedge bases indicate erosion during initiation. Channels are present within some grounding-zone wedges; meltwater flow is under high pressure, and V-shaped incisions suggest high-energy flow. Channels are not ubiquitous within Greenland grounding-zone wedges and may represent nonsteady meltwater release, perhaps through lake drainage. Where ice-sheet mass loss is dominated by meltwater runoff, groundingzone wedges probably contain more sorted sediment than those from Greenland. Simple models of grounding-zone wedge architecture are presented. Grounding-zone wedges indicate episodic rather than catastrophic ice-sheet retreat and are a mechanism for ice-shelf stabilization because wedge growth counteracts collapse induced by ice-sheet thinning and sea-level rise.