Decreased influx of Calanus spp. into the south-western Norwegian Sea since 2003

Kristiansen, Inga; Hátún, Hjálmar; Pétursdóttir, Hildur; Gíslason, Ástþór; Broms, Cecilie; Melle, Webjørn; Jacobsen, Jan Arge; Eliasen, Sólvá Káradóttir; Gaard, Eilif

doi:10.1016/j.dsr.2019.05.008

Cited by 17 publications

(35 citation statements)

References 32 publications

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“…A strong NSG draws large amounts of MEIW and likely also of Arctic intermediate water masses from the Iceland Sea (Figure 6B), and these contain high concentrations of large and lipid-rich zooplankton types (Calanus hyperboreus and large overwintering stages of Calanus finmarchicus) (Kristiansen et al, 2016(Kristiansen et al, , 2019. The marked NSG weakening after 2002 resulted in a wider (northward extended) AW wedge, and a deeper interface at the northern flank of the FC.…”

Section: Ecological Implicationsmentioning

confidence: 99%

“…A standard meridional monitoring section (Section N, Figure 1) cuts across these two deep flow cores (Hansen and Østerhus, 2000). These observations have hitherto primarily been used to estimate transports of the Atlantic inflow, although recent studies have also focused on the influence of the deeper IFSJ (Semper et al, 2020), and the eastward flow of Modified East Icelandic Water (MEIW) (Kristiansen et al, 2016(Kristiansen et al, , 2019. Dynamics of the deep flow core (between the 2000 and 3000 m isobaths), which likely carries the highest transport through Section N, has not been studied previously.…”

Section: Introductionmentioning

confidence: 99%

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The Norwegian Sea Gyre – A Regulator of Iceland-Scotland Ridge Exchanges

2021

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The Norwegian Sea gyre (NSG) is a large body of Arctic intermediate water and deep dense overflow waters, which circulate counterclockwise within the Norwegian Sea. Argo float trajectories presented in this study suggest that the NSG attains its strongest and most focused flow downstream of a confluence of subarctic waters from the Iceland Sea and the Jan Mayen Ridge at steep bathymetry north of the Faroe slope. Based on hydrographic data from a meridional standard section across this flow (1988 to present), the first baroclinic estimate of the NSG circulation strength is provided. We, furthermore, show that the NSG circulation regulates key aspects of both the poleward Atlantic Water (AW) currents and the equatorward near-bottom and mid-depth flows in the Norwegian Sea – the main arteries of the Meridional Overturning Circulation. More specifically, we demonstrate close links between the NSG circulation and (i) the observed Faroe Bank Channel Overflow (FBCO) transport, (ii) variable depth of the main thermocline separating AW from the underlying colder and denser subarctic water masses, and (iii) satellite-derived sea-surface heights (SSHs) in the southern Nordic Seas. In general, a strong NSG and weak FBCO transport are associated with an uplifted thermocline and depressed SSH. Along a narrow band near the Norwegian and Shetland slopes, a strong NSG – oppositely – links to a depressed interface. Daily records of the FBCO transport, and satellite altimetry in a sensitive region north of the Iceland-Faroe Ridge, complement our hydrographic monitoring of the NSG strength. Together these records constitute valuable indicators for aspects of the Norwegian Sea physical oceanography, which likely have an impact on regional climate, ecology and biological productivity.

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Section: Ecological Implicationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Norwegian Sea Gyre – A Regulator of Iceland-Scotland Ridge Exchanges

2021

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“…In addition, the oceanic silicate concentrations may also be an indicator of the oceanic concentration of C. finmarchicus (Hátún et al, 2016(Hátún et al, , 2017a. The zooplankton biomass south of Iceland (Hátún et al, 2016(Hátún et al, , 2017a and in subarctic waters north of the Faroe slope (Kristiansen et al, 2019) has been linked to the gyre index. Hence, the marked peaks in silicate that are also recognized in the 0-group length index may also represent an increased production of off-shelf C. finmarchicus.…”

Section: Bottom-up Processes During Springmentioning

confidence: 99%

Environmentally Driven Ecological Fluctuations on the Faroe Shelf Revealed by Fish Juvenile Surveys

et al. 2019

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Comprehensive late June surveys have for decades been carried out on the Faroe shelf in order to estimate the abundance of juvenile fish-the 0-group. The abundance of cod juveniles has previously been used in recruitment studies, while the ecological implication of the 0-groups has hitherto received less attention. Here we examined the pelagic 0-group stage in four of the main fish species on the Faroe shelf: cod, haddock, Norway pout and sandeel, representing more than 90% of all juvenile fish on the shelf. A positive relationship between length and abundance at the 0-group stage is observed for all juveniles, and the inter-annual variability was highly similar among the four fish species. Based on this knowledge, we produced a new ecological indicator for the central Faroe shelf ecosystem-the 0-group length index. The 0-group length index is characterized by marked peaks

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“…There have been large changes in water transport and circulation patterns in the Northeast-Atlantic since the 1990-ies. The strength of both the subpolar-gyre and the East-Icelandic current was reduced in the early 2000s, and this has reduced the inflow of nutrients and plankton west and north of Ireland and into the Norwegian Sea (Hatun et al 2017, Kristiansen et al 2019. This is not expected to affect post-smolt directly, but its impact on the Norwegian Sea ecosystem can have a negative effect on important prey for post-smolt.…”

Section: Modelmentioning

confidence: 99%

Poor feeding opportunities and reduced condition factor for salmon post-smolts in the Northeast Atlantic Ocean

Utne

Pauli

Haugland

et al. 2021

ICES Journal of Marine Science

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During the last few decades, many wild Atlantic salmon populations have declined dramatically. One possible contributing factor for the decline is reduced prey availability at sea. Here, we examine post-smolt diet and investigate if post-smolts show signs of selective feeding based on 2546 post-smolts sampled from west of Ireland to the northern Norwegian Sea over a 25-year period. We also test for changes over time in stomach fullness, diet, condition factor and body length. There was a clear reduction in condition factor for post-smolts sampled in the Norwegian Sea in the period 2003–2012. The post-smolt stomach fullness was also reduced in the same period. The reduction in condition factor is partly explained by reduced stomach fullness, including a reduction of highly energetic fish larvae and Amphipoda in the diet. Feeding on other prey, such as meso-zooplankton and insects, cannot substitute the high-quality fish larvae and Amphipoda in the post-smolt diet. This is the first study to document how salmon post-smolts feeding in the Norwegian Sea are affected by reduced feeding conditions. Possible causes for the observed changes in post-smolt feeding are ocean warming, decreased primary productivity, and reduced recruitment of important fish larvae.

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Decreased influx of Calanus spp. into the south-western Norwegian Sea since 2003

Cited by 17 publications

References 32 publications

The Norwegian Sea Gyre – A Regulator of Iceland-Scotland Ridge Exchanges

The Norwegian Sea Gyre – A Regulator of Iceland-Scotland Ridge Exchanges

Environmentally Driven Ecological Fluctuations on the Faroe Shelf Revealed by Fish Juvenile Surveys

Poor feeding opportunities and reduced condition factor for salmon post-smolts in the Northeast Atlantic Ocean

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