A user's guide to NORVECOM V2.0. the norwegian ecological model system

A coupled 3 dimensional Physical-Chemical-Biological model system, NORWECOM, has been developed through cooperation between several Norwegian institutions. The physical module is based on the Princeton Ocean Model already well documented in several reports. This guide is an attempt to give an introduction to the Chemical-Biological module, and will hopefully help new users to understand the flow between and processes inside the various subroutines. The guide will concentrate on how the chemical-biological dynamics is formulated in the module. Why these formulations is preferred to others, is not a part of such a guide

A user's guide to NORVECOM V2.0. the norwegian ecological model system

A coupled 3 dimensional Physical-Chemical-Biological model system, NORWECOM, has been developed through cooperation between several Norwegian institutions. The physical module is based on the Princeton Ocean Model already well documented in several reports. This guide is an attempt to give an introduction to the Chemical-Biological module, and will hopefully help new users to understand the flow between and processes inside the various subroutines. The guide will concentrate on how the chemical-biological dynamics is formulated in the module. Why these formulations is preferred to others, is not a part of such a guide

Recent warming and freshening of the Norwegian Sea observed by Argo data

Climate variability in the Norwegian Sea, comprising the Norwegian and Lofoten Basins, was investigated based upon monthly estimates of ocean heat and freshwater contents using data from Argo floats during 2002–18. Both local air–sea exchange and advective processes were examined and quantified for monthly to interannual time scales. In the recent years, 2011–18, the Norwegian Sea experienced a decoupling of the temperature and salinity, with a simultaneous warming and freshening trend. This was mainly explained by two different processes; reduced ocean heat loss to the atmosphere and advection of fresher Atlantic water into the Norwegian Sea. The local air–sea heat fluxes are important in modifying the ocean heat content, although this relationship varied with time scale and basins. On time scales exceeding 4 months in the Lofoten Basin and 6 months in the Norwegian Basin, the air–sea heat flux explained half or even more of the local ocean heat content change. There were both a short-term and long-term response of the wind forcing on the ocean heat content. The monthly to seasonal response of increased southerly wind cooled and freshened the Norwegian Basin, due to eastward surface Ekman transport, and increased the influence of Arctic Water. However, after about a 1-yr delay the ocean warmed and became saltier due to an increased advection of Atlantic Water into the region. Increased westerly winds decreased the ocean heat content in both cases due to increased transport of Arctic Water into the Norwegian Sea.publishedVersio

Environmental status of the Skagerak and North Sea 2000

An environmental status for year 2000 of the North Sea and Skagerrak has been done based on outputs from a biophysicaf model (NORWECOM). The model results suggests that in year 2000 the mean annua1 primary production in the North Sea was the highest in the period 1985-2000, and that the net inflow through the English Channel, due to an extreme strong influx in the fourth quarter, was the highest on an annua1 basis in the period 1955-2000. Also the oxygen levels and sedimentation rates in the North Sea and Skagerrak have been examined, and a eutrophication assessment conclude that, except for the winter values of nitrate, eutrophication is not a big problem in most of the Skagerrak and Kattegat area. Key words : Skagerrak, North Sea, environmental status NORSK SAMMENDRAG: En koblet fysisk, kjemisk og biologisk havmodell (NORWECOM) er brukt for å simulere år 2000 i Nordsjøen og Skagerrak. Resultatene fra denne modelkjøringen er så brukt for å lage en miljøstatus for dette året. I statusen presenteres blant annet verdier for primærproduksjon, oxygen-nivå, sedimenteringsrate og vanntransport inn til Nordsjøen. Til slutt blir det gitt en vurdering av eutrofieringsgraden i Skage- rak og Kattegat basert på referanseverdier foreslått av svenske miljøstyresmakter

Eutrophication Scenaria from Reduced Nutrient Loads to the North Sea

The environmental effects of river nutrient loads to the North Sea have been investigated using a numerical biophysical model, NORWECOM, to perform different reduction scenarios. The simulations demonstrate that the river nutrients have a significant contribution on the annual primary production, both in the southern North Sea, in Skagerrak and along the Norwegian west coast. A 50% reduction in the loads of N and P reduces the primary production with 10-30% in the southern North Sea, and 5-10% in Skagerrak and along the Norwegian west coast. Scandinavian rivers only contribute to the 1-2% level in these reductions, thus continental rivers has the major effect on the environment in all downstream areas. However, it should be noted that this reduction, even in the southern North Sea, is less than the natural variability of the production of phytoplankton. A reduction only in the P values, shows that the production regime in the southern North Sea is phosphorous limited, while nitrogen is the limiting nutrient in the northern North Sea. Focusing on the N/P ratio as a possible proxy for eutrophication, a reduction in the N and P loads reduces this ratio by a similar factor, while a reduction in the P loads only, increases it. Based on this it is proposed to use the N/P ratio for eutrophication assessment

Temporal and spatial hydrographic variability in the Skagerrak

This report addresses the tempora1 and spatial variability in the hydrography of the Skagerrak by means of statistical investigations including frequency analyses and spatial correlations. The analysis is based on the fixed hydrographic section across the Skagerrak between Torungen (Arendal), Norway and Hirtshals, Denmark, close to a full year of temporally highly resolved hydrographic measurements by moored automatic current meters, placed off the coast from Torungen, and modelled output from the coupled physical-chemical-biological model system NORWECOM. NORSK SAMMENDRAG: Rapporten omhandler variabilitet i hydrografien i Skagerrak. Ved hjelp av statistiske metoder analyseres variasjonsmønstre i rom og tid. Metodene brukt omfatter frekvensanalyse og romlig korrelasjonsanalyse. Analysen tar utgangspunkt i det faste hydrografiske snittet som går på tvers av Skagerrak fra Torungen (Arendal) til Hirtshals, nær et år med tidsmessig godt oppløste strømmålinger fra en fast montert automatisk strømmåler plassert utenfor Torungen og modellresultater fra den fysisk-kjemisk-biologiske modellen NORWECOM

Dynamical controls on the longevity of a non-linear vortex : The case of the Lofoten Basin Eddy

The Lofoten Basin is the largest oceanic reservoir of heat in the Nordic Seas, and the site of important heat fluxes to the atmosphere. An intense permanent anticyclone in the basin impacts the regional hydrography, energetics, and ecosystem. Repeated sampling of this Lofoten Basin Eddy from dedicated cruises, autonomous profiling gliders, and acoustically-tracked subsurface floats enables the documentation of its dynamics and energetics over the course of 15 months. The eddy core, in nearly solid-body rotation, exhibits an unusually low vertical vorticity close to the local inertial frequency and important strain rates at the periphery. Subsurface floats as deep as 800 m are trapped within the core for their entire deployment duration (up to 15 months). The potential vorticity is reduced in the core by two orders of magnitude relative to the surroundings, creating a barrier. In the winter, this barrier weakens and lateral exchanges and heat flux between the eddy and the surroundings increase, apparently the result of dynamical instabilities and a possible eddy merger. Based on a simple energy budget, the dissipation timescale for the eddy energy is three years, during which wintertime convection seasonally modulates potential and kinetic energy.publishedVersio

Atlantic water transformation along its poleward pathway across the Nordic Seas

The warm and salty Atlantic Water is substantially modified along its poleward transit across the Nordic Seas, where it reaches deeper isopycnals. In particular, the Lofoten Basin, exposed to intense air‐sea interactions, plays a crucial role in the transformation of Atlantic Water. Averaged over a seasonal cycle, Atlantic Water releases approximately 80 W/m2 of heat to the atmosphere over a large area, leading to winter mixed layer depths of up to 500 m (locally exceeding 1,000 m in the Lofoten Basin Eddy, a permanent vortex located in the basin center) and substantial water mass transformation. We investigate spiciness injection (temperature and salinity increase) by winter mixing, by performing an isopycnal analysis using a comprehensive observational data set covering the 2000–2017 period. Compared to the Atlantic Water properties at the Svinøy section, representative of the inflowing Atlantic Water, some isopycnals reveal an important warming (up to 1.5°C) and salinification (up to 0.2 g/kg). Key areas for spiciness injection are the western Lofoten Basin and west of Bear Island. The modified spicy Atlantic Waters coincide with low potential vorticity with strongly density‐compensated layers at their base, allowing double‐diffusion processes to occur farther downstream toward the Arctic. Despite its limited spatial extent, the Lofoten Basin Eddy exhibits the greatest spiciness injection, as well as the deepest mixed layer and thickest low potential vorticity layer of the Norwegian Seas. The Atlantic Water spiciness at Svinøy shows a downstream correlation in the Lofoten Basin and farther north toward the Arctic with a lag of 1 to 1.5 years.publishedVersio

Analysis of tidal currents in the North Sea from shipboard acoustic Doppler current profiler data

North Sea tidal currents are determined by applying harmonic analysis to ship-borne acoustic Doppler current profiler data recorded from 1999 to 2016, covering large areas of the northern North Sea. Direct current measurement data sets of this magnitude are rare in the otherwise well investigated North Sea, and thus it is a valuable asset in studying and expanding our understanding of its tidal currents and circulation in general. The harmonic analysis is applied to a least squares fit of the current observations at a set of knot points. Results from the harmonic analysis compare favorably to tidal parameters estimated from observations from moored instruments. The analysis shows that the tides are characterized by strong semi-diurnal component, with amplitudes of the principal Lunar constituent ranging from 1.6 cm/s in the Skagerrak to 67 cm/s in the Fair Isle Channel. Diurnal tides are found to be approximately one fifth the strength of the predominant semi-diurnal constituent. Output from a regional barotropic tide model compares well to tidal current determined from the harmonic analysis of the Acoustic Doppler Current Profiler data.publishedVersio

The mid-depth circulation of the Nordic Seas derived from profiling float observations

Article published in Tellus Series A-Dynamic meterology and oceanography, 62 (4): 516-529 AUG 2010The trajectories of 61 profiling Argo floats deployed at mid-depth in the Nordic Seas—the Greenland, Lofoten and Norwegian Basins and the Iceland Plateau—between 2001 and 2009 are analysed to determine the pattern, strength and variability of the regional circulation. The mid-depth circulation is strongly coupled with the structure of the bottom topography of the four major basins and of the Nordic Seas as a whole. It is cyclonic, both on the large-scale and on the basin scale, with weak flow (<1 cm s−1) in the interior of the basins and somewhat stronger flow (up to 5 cm s−1) at their rims. Only few floats moved from one basin to another, indicating that the internal recirculation within the basins is by far dominating the larger-scale exchanges. The seasonal variability of the mid-depth flow ranges from less than 1 cm s−1 over the Iceland Plateau to more than 4 cm s−1 in the Greenland Basin. These velocities translate into internal gyre transports of up to 15 ± 10 × 106 m3 s−1, several times the overall exchange between the Nordic Seas and the subpolar North Atlantic. The seasonal variability of the Greenland Basin and the Norwegian Basin can be adequately modelled using the barotropic vorticity equation, with the wind and bottom friction as the only forcing mechanisms. For the Lofoten Basin and the Iceland Plateau less than 50% of the variance can be explained by the wind