scholarly journals Mid/Late Devonian-Carboniferous collapse basins on the Finnmark Platform and in the southwesternmost Nordkapp basin, SW Barents Sea

2017 ◽  
Author(s):  
Jean-Baptiste Koehl ◽  
Steffen G. Bergh ◽  
Tormod Henningsen ◽  
Jan-Inge Faleide
Keyword(s):  
Shear Zone ◽  
Fault Zone ◽  
Large Scale ◽  
Barents Sea ◽  
Normal Fault ◽  
Early Carboniferous ◽  
Normal Displacement ◽  
Late Devonian ◽  
The North ◽  
Caledonian Orogeny

Abstract. The SW Barents Sea margin experienced a pulse of extensional deformation in the Middle-Late Devonian through the Carboniferous, after the Caledonian Orogeny terminated. These events marked the initial stages of formation of major offshore basins such as the Hammerfest and Nordkapp basins. We mapped and analyzed three major fault complexes, i) the Måsøy Fault Complex, ii) the Rolvsøya fault, iii) the Troms-Finnmark Fault Complex. We discuss the formation of the Måsøy Fault Complex as a possible extensional splay of an overall NE-SW trending, NW-dipping, basement-seated Caledonian shear zone, the Sørøya-Ingøya shear zone, which was partly inverted during the collapse of the Caledonides and accommodated top-to-the-NW normal displacement in Mid/Late Devonian-Carboniferous times. The Troms-Finnmark Fault Complex displays a zigzag-shaped pattern of NNE-SSW and ENE-WSW trending extensional faults before it terminates to the north as a WNW-ESE trending, NE-dipping normal fault that separates the southwesternmost Nordkapp basin in the northeast from the Finnmark Platform west and the Gjesvær Low in the southwest. The WNW-ESE trending, margin-oblique segment of the Troms-Finnmark Fault Complex is considered to represent the offshore prolongation of a major Neoproterozoic fault complex, the Trollfjord-Komagelv Fault Zone, which is made of WNW-ESE trending, subvertical faults that crop out on the island of Magerøya in NW Finnmark. Our results suggest that the Trollfjord-Komagelv Fault Zone dies out to the northwest before reaching the Finnmark Platform west. We propose an alternative model for the origin of the WNW-ESE trending fault segment of the Troms-Finnmark Fault Complex as a possible hard-linked, accommodation cross-fault that developed along the Sørøy-Ingøya shear zone. This brittle fault decoupled the Finnmark Platform west from the southwesternmost Nordkapp basin and merged with the Måsøy Fault Complex in Carboniferous times. Seismic data over the Gjesvær Low and southwesternmost Nordkapp basin show that the low-gravity anomaly observed in these areas may result from the presence of Mid/Late Devonian sedimentary units resembling Middle Devonian, spoon-shaped, late/post-orogenic collapse basins in western and mid Norway. We propose a model for the formation of the southwesternmost Nordkapp basin and its counterpart Devonian basin in the Gjesvær Low by exhumation of narrow, ENE-WSW to NE-SW trending basement ridges along a bowed portion of the Sørøya-Ingøya shear zone in the Mid/Late Devonian-early Carboniferous. Exhumation may have involved part of a large-scale metamorphic core complex that potentially included the Lofoten Ridge, the West Troms Basement Complex and the Norsel High. Finally, we argue that the Sørøya-Ingøya shear zone truncated and decapitated the Trollfjord-Komagelv Fault Zone during the Caledonian Orogeny and that the western continuation of the Trollfjord-Komagelv Fault Zone was mostly eroded and potentially partly preserved in basement highs in the SW Barents Sea.

scholarly journals Middle to Late Devonian–Carboniferous collapse basins on the Finnmark Platform and in the southwesternmost Nordkapp basin, SW Barents Sea

Solid Earth ◽  
2018 ◽  
Vol 9 (2) ◽  
pp. 341-372 ◽  
Author(s):  
Jean-Baptiste P. Koehl ◽  
Steffen G. Bergh ◽  
Tormod Henningsen ◽  
Jan Inge Faleide
Keyword(s):  
Shear Zone ◽  
Fault Zone ◽  
Large Scale ◽  
Barents Sea ◽  
Normal Fault ◽  
Early Carboniferous ◽  
Normal Displacement ◽  
Late Devonian ◽  
The North ◽  
Caledonian Orogeny

Abstract. The SW Barents Sea margin experienced a pulse of extensional deformation in the Middle–Late Devonian through the Carboniferous, after the Caledonian Orogeny terminated. These events marked the initial stages of formation of major offshore basins such as the Hammerfest and Nordkapp basins. We mapped and analyzed three major fault complexes, (i) the Måsøy Fault Complex, (ii) the Rolvsøya fault, and (iii) the Troms–Finnmark Fault Complex. We discuss the formation of the Måsøy Fault Complex as a possible extensional splay of an overall NE–SW-trending, NW-dipping, basement-seated Caledonian shear zone, the Sørøya–Ingøya shear zone, which was partly inverted during the collapse of the Caledonides and accommodated top–NW normal displacement in Middle to Late Devonian–Carboniferous times. The Troms–Finnmark Fault Complex displays a zigzag-shaped pattern of NNE–SSW- and ENE–WSW-trending extensional faults before it terminates to the north as a WNW–ESE-trending, NE-dipping normal fault that separates the southwesternmost Nordkapp basin in the northeast from the western Finnmark Platform and the Gjesvær Low in the southwest. The WNW–ESE-trending, margin-oblique segment of the Troms–Finnmark Fault Complex is considered to represent the offshore prolongation of a major Neoproterozoic fault complex, the Trollfjorden–Komagelva Fault Zone, which is made of WNW–ESE-trending, subvertical faults that crop out on the island of Magerøya in NW Finnmark. Our results suggest that the Trollfjorden–Komagelva Fault Zone dies out to the northwest before reaching the western Finnmark Platform. We propose an alternative model for the origin of the WNW–ESE-trending segment of the Troms–Finnmark Fault Complex as a possible hard-linked, accommodation cross fault that developed along the Sørøy–Ingøya shear zone. This brittle fault decoupled the western Finnmark Platform from the southwesternmost Nordkapp basin and merged with the Måsøy Fault Complex in Carboniferous times. Seismic data over the Gjesvær Low and southwesternmost Nordkapp basin show that the low-gravity anomaly observed in these areas may result from the presence of Middle to Upper Devonian sedimentary units resembling those in Middle Devonian, spoon-shaped, late- to post-orogenic collapse basins in western and mid-Norway. We propose a model for the formation of the southwesternmost Nordkapp basin and its counterpart Devonian basin in the Gjesvær Low by exhumation of narrow, ENE–WSW- to NE–SW-trending basement ridges along a bowed portion of the Sørøya-Ingøya shear zone in the Middle to Late Devonian–early Carboniferous. Exhumation may have involved part of a large-scale metamorphic core complex that potentially included the Lofoten Ridge, the West Troms Basement Complex and the Norsel High. Finally, we argue that the Sørøya–Ingøya shear zone truncated and decapitated the Trollfjorden–Komagelva Fault Zone during the Caledonian Orogeny and that the western continuation of the Trollfjorden–Komagelva Fault Zone was mostly eroded and potentially partly preserved in basement highs in the SW Barents Sea.

Kinematic data on major Variscan strike-slip faults and shear zones in the Polish Sudetes, northeast Bohemian Massif

1997 ◽  
Vol 134 (5) ◽  
pp. 727-739 ◽  
Author(s):  
P. ALEKSANDROWSKI ◽  
R. KRYZA ◽  
S. MAZUR ◽  
J. ŻABA
Keyword(s):  
Shear Zone ◽  
Fault Zone ◽  
Bohemian Massif ◽  
Early Carboniferous ◽  
Shear Zones ◽  
Strike Slip ◽  
Late Carboniferous ◽  
Late Devonian ◽  
The West ◽  
West Sudetes

The still highly disputable terrane boundaries in the Sudetic segment of the Variscan belt mostly seem to follow major strike-slip faults and shear zones. Their kinematics, expected to place important constraints on the regional structural models, is discussed in some detail. The most conspicuous is the WNW–ESE Intra-Sudetic Fault Zone, separating several different structural units of the West Sudetes. It showed ductile dextral activity and, probably, displacement magnitude of the order of tens to hundreds kilometres, during late Devonian(?) to early Carboniferous times. In the late Carboniferous (to early Permian?), the sense of motion on the Intra-Sudetic Fault was reversed in a semi-brittle to brittle regime, with the left-lateral offset on the fault amounting to single kilometres. The north–south trending Niemcza and north-east–southwest Skrzynka shear zones are left-lateral, ductile features in the eastern part of the West Sudetes. Similarly oriented (northeast–southwest to NNE–SSW) regional size shear zones of as yet undetermined kinematics were discovered in boreholes under Cenozoic cover in the eastern part of the Sudetic foreland (the Niedźwiedź and Nysa-Brzeg shear zones). One of these is expected to represent the northern continuation of the major Stare Mesto Shear Zone in the Czech Republic, separating the geologically different units of the West and East Sudetes. The Rudawy Janowickie Metamorphic Unit, assumed in some reconstructions to comprise a mostly strike-slip terrane boundary, is characterized by ductile fabric developed in a thrusting regime, modified by a superimposed normal-slip extensional deformation. Thrusting-related deformational fabric was locally reoriented prior to the extensional event and shows present-day strike-slip kinematics in one of the sub-units. The Sudetic Boundary Fault, although prominent in the recent structure and topography of the region, was not active as a Variscan strike-slip fault zone. The reported data emphasize the importance of syn-orogenic strike-slip tectonics in the Sudetes. The recognized shear sense is compatible with a strike-slip model of the northeast margin of the Bohemian Massif, in which the Kaczawa and Góry Sowie Units underwent late Devonian–early Carboniferous southeastward long-distance displacement along the Intra-Sudetic Fault Zone from their hypothetical original position within the Northern Phyllite Zone and the Mid-German Crystalline High of the German Variscides, respectively, and were juxtaposed with units of different provenance southwest of the fault. The Intra-Sudetic Fault Zone, together with the Elbe Fault Zone further south, were subsequently cut in the east and their eastern segments were displaced and removed by the younger, early to late Carboniferous, NNE–SSW trending, transpressional Moldanubian–Stare Mesto Shear Zone.

Palynology and deposition in the Wandel Sea Basin, eastern North Greenland

2000 ◽  
pp. 1-6 ◽  
Author(s):  
Lars Stemmerik
Keyword(s):  
Fault Zone ◽  
Barents Sea ◽  
Sedimentary Basins ◽  
Early Carboniferous ◽  
Upper Jurassic ◽  
Upper Permian ◽  
North East ◽  
The North ◽  
Orogenic Belts ◽  
North Greenland

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Stemmerik, L. (2000). Palynology and deposition in the Wandel Sea Basin, eastern North Greenland. Geology of Greenland Survey Bulletin, 187, 1-6. https://doi.org/10.34194/ggub.v187.5191 _______________ This collection of papers adds to the understanding of the stratigraphic, depositional and structural history of the Wandel Sea Basin in eastern North Greenland (Fig. 1). Most importantly, the ages of the initial (Carboniferous) and final (Palaeogene) depositional events are now much better constrained than previously, allowing correlation with the successions in East Greenland, Svalbard and the Barents Sea. The Wandel Sea Basin was an area of accumulation through the Early Carboniferous to the Palaeogene period, located at the margins of the stable Greenland craton where the Caledonian and Ellesmerian orogenic belts intersect (Fig. 1). Two main epochs of basin evolution have been recognised during previous studies of the basin fill: a Late Palaeozoic – Early Triassic epoch characterised by a fairly simple system of grabens and half-grabens, and a Mesozoic epoch dominated by strike-slip movements (Håkansson & Stemmerik 1989). The Mesozoic epoch only influenced that part of the basin north of the Trolle Land fault zone and its eastward extension (Fig. 1). Thus the northern and southern parts of the basin have very different structural and depositional histories, and accordingly different thermal histories and hydrocarbon potential as exemplified by the tectono-stratigraphic study of northern Amdrup Land by Stemmerik et al. (2000, this volume). This study shows that the Sommerterrasserne fault is the south-eastern extension of the Trolle Land fault zone, dividing Amdrup Land into two areas with different stratigraphic and structural histories. Sediments of the Upper Permian Midnatfjeld Formation are restricted to north-east of the Sommerterrasserne fault where they are conformably overlain by Upper Jurassic sediments. In this area the Carboniferous – Upper Jurassic succession is folded in broad domal folds with NE–SW-oriented axes, whereas the Upper Palaeozoic sediments are gently dipping south-west of the fault. Folding most likely took place during the latest Cretaceous correlating with compressional events that also affected the sedimentary basins at Kilen and Prinsesse Ingeborg Halvø further to the north in the Trolle Land fault zone.

scholarly journals Morphotectonic Analysis along the Northern Margin of Samos Island, Related to the Seismic Activity of October 2020, Aegean Sea, Greece

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 102
Author(s):  
Paraskevi Nomikou ◽  
Dimitris Evangelidis ◽  
Dimitrios Papanikolaou ◽  
Danai Lampridou ◽  
Dimitris Litsas ◽  
...  
Keyword(s):  
Fault Zone ◽  
Seismic Activity ◽  
Volcanic Rocks ◽  
Active Tectonics ◽  
Normal Fault ◽  
Aegean Sea ◽  
Northern Margin ◽  
The North ◽  
Eastern Aegean ◽  
Half Graben

On 30 October 2020, a strong earthquake of magnitude 7.0 occurred north of Samos Island at the Eastern Aegean Sea, whose earthquake mechanism corresponds to an E-W normal fault dipping to the north. During the aftershock period in December 2020, a hydrographic survey off the northern coastal margin of Samos Island was conducted onboard R/V NAFTILOS. The result was a detailed bathymetric map with 15 m grid interval and 50 m isobaths and a morphological slope map. The morphotectonic analysis showed the E-W fault zone running along the coastal zone with 30–50° of slope, forming a half-graben structure. Numerous landslides and canyons trending N-S, transversal to the main direction of the Samos coastline, are observed between 600 and 100 m water depth. The ENE-WSW oriented western Samos coastline forms the SE margin of the neighboring deeper Ikaria Basin. A hummocky relief was detected at the eastern margin of Samos Basin probably representing volcanic rocks. The active tectonics characterized by N-S extension is very different from the Neogene tectonics of Samos Island characterized by NE-SW compression. The mainshock and most of the aftershocks of the October 2020 seismic activity occur on the prolongation of the north dipping E-W fault zone at about 12 km depth.

scholarly journals Μorphometric Analysis for the Assessment of Relative Tectonic Activity in Evia Island, Greece

Geosciences ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 264
Author(s):  
Kanella Valkanou ◽  
Efthimios Karymbalis ◽  
Dimitris Papanastassiou ◽  
Mauro Soldati ◽  
Christos Chalkias ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Fault Zone ◽  
Normal Fault ◽  
Morphometric Parameters ◽  
Tectonic Activity ◽  
Asymmetry Factor ◽  
Drainage Basins ◽  
Fault Systems ◽  
The North ◽  
Integrated Index

The aim of this study is to evaluate the relative tectonic activity in the north part of the Evia Island, located in Central Greece, and to investigate the contribution of neotectonic processes in the development of the fluvial landscape. Five morphometric parameters, including Drainage Basin Slope (Sb), Hypsometric Integral (Hi), Asymmetry Factor (Af), Relief Ratio (Rh), and Melton’s Ruggedness Number (M), were estimated for a total of 189 drainage basins. The catchments were classified into two groups, according to the estimated values of each morphometric parameter, and maps showing their spatial distribution were produced. The combination of the calculated morphometric parameters led to a new single integrated Index of relative tectonic activity (named Irta). Following this indexing, the basins were characterized as of low, moderate, or high relative tectonic activity. The quantitative analysis showed that the development of the present drainage systems and the geometry of the basins of the study area have been influenced by the tectonic uplift caused by the activity of two NW-SE trending offshore active normal fault systems: the north Gulf of Evia fault zone (Kandili-Telethrion) and the Aegean Sea fault zone (Dirfis), respectively. The spatial distribution of the values of the new integrated index Irta showed significant differences among the drainage basins that reflect differences in relative tectonic activity related to their location with regard to the normal fault systems of the study area.

scholarly journals Influence of Atlantic inflow on the freshwater content in the upper layer of the Arctic basin

2019 ◽  
Vol 65 (4) ◽  
pp. 363-388
Author(s):  
G. V. Alekseev ◽  
A. V. Pnyushkov ◽  
A. V. Smirnov ◽  
A. E. Vyazilova ◽  
N. I. Glok
Keyword(s):  
Fresh Water ◽  
Large Scale ◽  
Barents Sea ◽  
Lower Boundary ◽  
Arctic Basin ◽  
Water Layer ◽  
Atlantic Water ◽  
Water Masses ◽  
The Arctic ◽  
The North

Inter-decadal changes in the water layer of Atlantic origin and freshwater content (FWC) in the upper 100 m layer were traced jointly to assess the influence of inflows from the Atlantic on FWC changes based on oceanographic observations in the Arctic Basin for the 1960s – 2010s. For this assessment, we used oceanographic data collected at the Arctic and Antarctic Research Institute (AARI) and the International Arctic Research Center (IARC). The AARI data for the decades of 1960s – 1990s were obtained mainly at the North Pole drifting ice camps, in high-latitude aerial surveys in the 1970s, as well as in ship-based expeditions in the 1990s. The IARC database contains oceanographic measurements acquired using modern CTD (Conductivity – Temperature – Depth) systems starting from the 2000s. For the reconstruction of decadal fields of the depths of the upper and lower 0 °С isotherms and FWC in the 0–100 m layer in the periods with a relatively small number of observations (1970s – 1990s), we used a climatic regression method based on the conservativeness of the large-scale structure of water masses in the Arctic Basin. Decadal fields with higher data coverage were built using the DIVAnd algorithm. Both methods showed almost identical results when compared.  The results demonstrated that the upper boundary of the Atlantic water (AW) layer, identified with the depth of zero isotherm, raised everywhere by several tens of meters in 1990s – 2010s, when compared to its position before the start of warming in the 1970s. The lower boundary of the AW layer, also determined by the depth of zero isotherm, became deeper. Such displacements of the layer boundaries indicate an increase in the volume of water in the Arctic Basin coming not only through the Fram Strait, but also through the Barents Sea. As a result, the balance of water masses was disturbed and its restoration had to occur due to the reduction of the volume of the upper most dynamic freshened layer. Accordingly, the content of fresh water in this layer should decrease. Our results confirmed that FWC in the 0–100 m layer has decreased to 2 m in the Eurasian part of the Arctic Basin to the west of 180° E in the 1990s. In contrast, the FWC to the east of 180° E and closer to the shores of Alaska and the Canadian archipelago has increased. These opposite tendencies have been intensified in the 2000s and the 2010s. A spatial correlation between distributions of the FWC and the positions of the upper AW boundary over different decades confirms a close relationship between both distributions. The influence of fresh water inflow is manifested as an increase in water storage in the Canadian Basin and the Beaufort Gyre in the 1990s – 2010s. The response of water temperature changes from the tropical Atlantic to the Arctic Basin was traced, suggesting not only the influence of SST at low latitudes on changes in FWC, but indicating the distant tropical impact on Arctic processes. 

scholarly journals Sevier Fault at Red Canyon

Geosites ◽  
2019 ◽  
Vol 1 ◽  
pp. 1-6
Author(s):  
Robert Biek
Keyword(s):  
Lava Flow ◽  
Fault Zone ◽  
Hanging Wall ◽  
Slip Rate ◽  
Normal Fault ◽  
Coarse Grained ◽  
Seismic Reflection Data ◽  
The North ◽  
Total Displacement ◽  
Reflection Data

The Sevier fault is spectacularly displayed on the north side of Utah Highway 12 at the entrance to Red Canyon, where it offsets a 500,000-year-old basaltic lava flow. The fault is one of several active, major faults that break apart the western margin of the Colorado Plateau in southwestern Utah. The Sevier fault is a “normal” fault, a type of fault that forms during extension of the earth’s crust, where one side of the fault moves down relative to the other side. In this case, the down-dropped side (the hanging wall) is west of the fault; the upthrown side (the footwall) lies to the east. The contrasting colors of rocks across the fault make the fault stand out in vivid detail. Immediately south of Red Canyon, the 5-million-year-old Rock Canyon lava flow, which erupted on the eastern slope of the Markagunt Plateau, flowed eastward and crossed the fault (which at the time juxtaposed non-resistant fan alluvium against coarse-grained volcaniclastic deposits) (Biek and others, 2015). The flow is now offset 775 to 1130 feet (235-345 m) along the main strand of the fault, yielding an anomalously low vertical slip rate of about 0.05 mm/yr (Lund and others, 2008). However, this eastern branch of the Sevier fault accounts for only part of the total displacement on the fault zone. A concealed, down-to-the-west fault is present west of coarse-grained volcaniclastic strata at the base of the Claron cliffs. Seismic reflection data indicate that the total displacement on the fault zone in this area is about 3000 feet (900 m) (Lundin, 1987, 1989; Davis, 1999).

scholarly journals Late Devonian-Early Carboniferous isolated carbonate platforms of the North of the Urals and Pay-Khoy

2021 ◽  
Vol 10 ◽  
pp. 3-15
Author(s):  
D. A. Gruzdev ◽  
Keyword(s):  
Barents Sea ◽  
Early Carboniferous ◽  
Water Type ◽  
Carbonate Platforms ◽  
Polar Urals ◽  
The North ◽  
Three Stages ◽  
Eustatic Fluctuations ◽  
Regional Tectonics ◽  
The Polar Urals

The article considers isolated carbonate platforms known in the Sub-Polar Urals (basin of the Bolshaya Nadota River; boreholes of the Yunyakha and Levaya Grubeyu areas) and the NW Pay-Khoy (basin of the Lymbad’yakha River and coast of the Barents Sea). The three stages of formation of the platforms (Frasnian, Famennian-Tournaisian, and Visean-Serpukhovian) are distinguished, and the sedimentological models of these platforms are developed. Subsidence curves based on the back-striping demonstrate some differences in the evolution of the studied isolated carbonate platforms. Similarities and differences in the history and structure of the platforms are observed. Formation of the intra-shelf depressions (the Kozhim Depression in the Sub-Polar Urals, and the Korotaikha Depression in the Pay-Khoy) in the Frasnian — Early Famennian caused appearance of isolated carbonate platforms. The depressions probably were formed by the regional tectonics. The following development of the carbonate platforms was controlled by eustatic fluctuations. The isolated platforms differ by stratigraphic spans (Late Frasnian — Serpukhovian for the Polar Urals Platform and Famennian-Tournaisian for the Pay-Khoy Platform), relief, facies, and size. The isolated depressions differ in size as well: the Kozhim Depression is larger than the Korotaikha Depression. Additionally, it is supposed that the Polar Urals platform was of warm-water type, but the Pay-Khoy platfrom was of cool-water type.

Late Devonian – Early Carboniferous volcanism in western Cape Breton Island, Nova Scotia

1984 ◽  
Vol 21 (7) ◽  
pp. 762-774 ◽  
Author(s):  
Marie-Claude Blanchard ◽  
Rebecca A. Jamieson ◽  
Elizabeth B. More
Keyword(s):  
Tectonic Setting ◽  
Early Carboniferous ◽  
Alluvial Fan ◽  
Late Devonian ◽  
Fluvial Sediments ◽  
Western Cape ◽  
Cape Breton Island ◽  
The North ◽  
Cape Breton ◽  
Geochemical Studies

The Fisset Brook Formation of western Cape Breton Island and its equivalents at MacMillan Mountain and the north Baddeck River are examples of Late Devonian and Early Carboniferous volcanic sequences associated with the formation of post-Acadian successor basins in the northeastern Appalachians. They consist of bimodal basalt–rhyolite suites interbedded with alluvial fan, lacustrine, and rare fluvial sediments. The earliest volcanic products are rhyolites and somewhat evolved basalts associated with coarse sediments, followed by tholeiitic to transitional basalt flows interlayered with lacustrine-type deposits. Geochemical studies on the Fisset Brook Formation indicate extensive remobilization of alkalies, Ca, Rb, and Sr, making these elements inappropriate for determining tectonic setting or magmatic affinity. Use of less mobile elements (Ti, Nb, Y, and Zr) suggests that the basalts are tholeiitic and that the apparent alkalinity of the type section lavas is a result of alteration. We conclude that volcanism in western Cape Breton Island started at MacMillan Mountain and migrated westwards, probably towards the centre of the deepening Magdalen Basin.

Jellyfish abundance and climatic variation: contrasting responses in oceanographically distinct regions of the North Sea, and possible implications for fisheries

2005 ◽  
Vol 85 (3) ◽  
pp. 435-450 ◽  
Author(s):  
Christopher P. Lynam ◽  
Stephen J. Hay ◽  
Andrew S. Brierley
Keyword(s):  
North Sea ◽  
Large Scale ◽  
Barents Sea ◽  
Species Abundance ◽  
Current Strength ◽  
Aurelia Aurita ◽  
North West ◽  
The North ◽  
The North Sea ◽  
Negative Relationships

Jellyfish medusae prey on zooplankton and may impact fish recruitment both directly (top-down control) and indirectly (through competition). Abundances of Aurelia aurita, Cyanea lamarckii and Cyanea capillata medusae (Scyphozoa) in the North Sea appear to be linked to large-scale inter-annual climatic change, as quantified by the North Atlantic Oscillation Index (NAOI), the Barents Sea-Ice Index (BSII) and changes in the latitude of the Gulf Stream North Wall (GSNW). Hydroclimatic forcing may thus be an important factor influencing the abundance of gelatinous zooplankton and may modulate the scale of any ecosystem impact of jellyfish. The population responses are probably also affected by local variability in the environment manifested in intra-annual changes in temperature, salinity, current strength/direction and prey abundance. Aurelia aurita and C. lamarckii in the north-west and south-east North Sea exhibited contrasting relationships to change in the NAOI and BSII: north of Scotland, where the North Sea borders the Atlantic, positive relationships were evident between the abundance of scyphomedusae (data from 1974 to 1986, except 1975) and the indices; whereas west of northern Denmark, a region much less affected by Atlantic inflow, negative relationships were found (data from 1973 to 1983, except 1974). Weaker negative relationships with the NAOI were also found in an intermediate region, east of Scotland, for the abundance of A. aurita and C. capillata medusae (1971 to 1982). East of Shetland, the abundance of jellyfish was not correlated directly with the NAOI but, in contrast to all other regions, the abundances of A. aurita and C. lamarckii (1971 to 1986, not 1984) were found to correlate negatively with changes in the GSNW, which itself was significantly positively correlated to the NAOI with a two year lag. On this evidence, we suggest that, for jellyfish, there exist three regions of the North Sea with distinct environmental processes governing species abundance: one north of Scotland, another east of Shetland, and a more southerly group (i.e. east of Scotland and west of northern Denmark). Impacts by jellyfish are likely to vary regionally, and ecosystem management may benefit from considering this spatial variability.

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