Norwegian Slope Research Articles

Discovery of an unrecognized pathway carrying overflow waters toward the Faroe Bank Channel

The dense overflow waters of the Nordic Seas are an integral link and important diagnostic for the stability of the Atlantic Meridional Overturning Circulation (AMOC). The pathways feeding the overflow remain, however, poorly resolved. Here we use multiple observational platforms and an eddy-resolving ocean model to identify an unrecognized deep flow toward the Faroe Bank Channel. We demonstrate that anticyclonic wind forcing in the Nordic Seas via its regulation of the basin circulation plays a key role in activating an unrecognized overflow path from the Norwegian slope – at which times the overflow is anomalously strong. We further establish that, regardless of upstream pathways, the overflows are mostly carried by a deep jet banked against the eastern slope of the Faroe-Shetland Channel, contrary to previous thinking. This deep flow is thus the primary conduit of overflow water feeding the lower branch of the AMOC via the Faroe Bank Channel.

Monitoring the Norwegian Atlantic slope current using a single moored current meter

Monitoring the Atlantic inflow (AI) of warm and saline water into the Nordic Seas (Norwegian, Greenland and Iceland Seas) is of great importance becauce of its impact on climate and ecology in Northern Europe and Arctic. In this study, an observation system for establishment of simple, robust and cost effective monitoring of the AI is validated in the Svinøy section, cutting through the AI just to the north of the Faroe-Shetland Channel. We concentrate on the eastern branch of the AI, the Norwegian Atlantic Slope Current (NwASC), an about 40 km wide flow along the steep Norwegian slope. The database is an array of 15 current meters on 4 moorings covering the NwASC over a 2-year period 1998–2000. We test the hypothesis that long-term monitoring of the NwASC can be performed by using one single current meter suitable placed in the flow. The volume flux can then be estimated by construction of simple regression models using the single current meter record as the independent variable. For validation of statistical properties as stability, confidence and stationarity, the time series is split into two 1-year segments: a model period and a test period. Gridded correlation fields between currents and volume transport show correlation maxima in the core of the NwASC, ranging from 0.84 on a daily timescale to 0.97 on a monthly timescale. A more comprehensive correlation/coherence analysis for each current meter record against volume transport on 7-day timescales, enable us to choose the optimal current meter for a linear regression model with (correlation, slope) coefficients of (0.87, 0.13) for the model period and (0.80, 0.13) for the test period. The similarity of the statistical properties for the model and test periods substantiates the stationarity, stability and robustness of the model. A linear regression model underestimates large fluxes and is thus extended to a second degree polynomia. This improves the curve fitting for strong currents with a minor increase in overall correlation, but is more sensistive and less stable. Overall, we find a linear regression model to be more robust and applicable for monitoring the NwASC. The applicability of a linear regression model as an estimator for volume flux of the NwASC is demonstrated using a 2-year time series, and validated against calculated transport. The calculated transport agrees with the statistical analysis and reveals a noisy fit on daily timescale, while the curves coincide well on both 7- and 30-day timescales with correlation coefficients of 0.84 and 0.86, respectively. On all timescales, the calculated and model transport give an overall mean flow of 4.4 Sv and show fluctuations on timescales of days to months, with the seasonal cycle being the most prominent.

Benthic foraminiferal distribution and abundance changes in Skagerrak surface sediments: 1937 (Höglund) and 1992/1993 data compared

Both living (stained) and dead (unstained) foraminiferal assemblages from surface sediments (0–2 cm) in the northwestern part of the Skagerrak have been studied in order to (1) define and characterize the distribution of various modern benthic environments and (2) by comparing these findings with surface samples collected 40–60 years ago, to document possible faunal changes that might have occurred. The investigated area is physiographically divided into the Norwegian slope, the Skagerrak Basin, and the Danish slope. The latter is under the influence of the Jutland Current, while the basin and the investigated parts of the Norwegian slope are bathed in Atlantic water. All areas have bottom waters with a high oxygen concentration. Three living (stained) and three dead (unstained) assemblages occupy the three physiographic areas. Only one assemblage (on the Norwegian slope) is common to both the living and dead assemblages but the boundaries between them lie at comparable depths. The higher standing crops are found on the fertile Danish slope while the lower ones are in the deep basin where the diversity is at a maximum. In the dead assemblages, the relative abundance of agglutinated tests increases with depth. Comparison with data collected 40 to 60 years ago shows increases in absolute numbers of tests, especially in the deep basin. There are changes in assemblage compositions in all areas. The dominant species found in 1937 are different from those of 1992/1993. There is a major change in the basin where one agglutinated species has changed its depth distribution downslope and two present day abundant species are new arrivals. These faunal events are probably linked to environmental changes.

Notolepis rissoi(Bonaparte)(Myctophiformes, Paralepididae) postlarvae, adolescents, and adults in north Norwegian slope waters

The first records of postlarvae and adolescents of Notolepis rissoi from Norwegian waters are reviewed together with additional adult specimens. The specimens were collected by pelagic trawl hauls in August 1981 and 1982 from off Lofoten and Vestera,len, northern Norway. It is suggested that the species is more common and abundant in Norwegian slope waters than previously presumed. The records of postlarvae in these northern waters show that they tolerate a temperature 4–5°C lower than previously known. The presence of postlarval and adolescent stages is considered to be due to current drift from spawning areas south of 60° N, and these young stages are predicted to be confined to the epipelagial at higher latitudes. It is suggested that the abundant occurrence of postlarvae off southwestern Ireland and in the Bay of Biscay does not indicate that this is the main spawning area of the species, but a current-dependent postlarval accumulation along the steep continental slope. The main spawning area is predi...

New recodrs of luminous fishes in north Norwegian waters

Abstract The first records of Cyclothone alba, Lampanyctus macdonaldi, and Protomyctophum arcticum from Norwegian waters are reviewed together with some records of the rare Argyropelecus hemigymnus, Argyropelecus olfersi, and Notolepis rissoi. The specimens originate partly from stomach contents of Atlantic salmon, Salmo salar, long-line caught in 1969–72, and partly from pelagic trawl hauls in 1980, off Vesteralen, N. Norway. Environmental conditions of the Norwegian slope mesopelagial are briefly discussed, and it is pointed out that diversity of smaller luminous fishes here may be larger than previously assumed. The presence of ripe Argyropelecus females is suggested to indicate existing spawning populations in these waters.