Einar Svendsen

Modelling the primary production in the North Sea using a coupled three-dimensional physical-chemical-biological ocean model

A coupled three-dimensional physical-chemical-biological model system has been implemented, and applied to study mass and volume transports and primary production throughout the North Sea. The model was run twice for the year 1985 with specified (for the North Sea Task Force) time series of riverine and atmospheric inputs of nutrients, and also with these nutrient inputs reduced by 40 and 50%, respectively. In particular, the evolution of the chemical and biological variables in the two situations was studied. The model output agreed quite well with the general quantitative and qualitative knowledge of the total yearly production. The intercomparison with some salinity profiles also indicated that the model handles the large-scale circulation and vertical mixing fairly well. Estimates for the transport of excess nutrients to Skagerrak and Kattegat in the highly pulsating Jutland coastal current are given. The estimates demonstrate the need for such models for calculating transport of matter from one area to another. Significant reductions in both primary production and transport of matter were seen from comparisons between the two runs.

Ecological modelling in coastal waters: Towards predictive physical-chemical-biological simulation models

Abstract A simple, but general, simulation model is specified according to the state-of-the-art within phytoplankton modelling: Process representations are based upon prevailing theoretical and empirical representations given in the literature, and a set of earlier published values of model coefficients that have demonstrated good fit to reliable observations was selected. The emerging phytoplankton model was then validated against data obtained from enclosure experiments with light-, N-, P- and Si-limitations. We applied no tuning of the coefficients as the purpose of this test was to estimate the predictive power of the proposed model. The general standard deviations between model predictions and observations were on the range 0.04–0.36 and 0.13–0.42 for the nutrient and phytoplankton state variables respectively. Not surprisingly, these values are higher than those obtained in tuned simulations. Nevertheless, several characteristics, such as the balance between diatoms and flagellates, were predicted b...

Model simulation of the Skagerrak circulation and hydrography during Skagex

Abstract A 3-dimensional barotropic/baroclinic numerical circulation/transport model system is set up and run for an extended North Sea area in the period October 1989 to August 1990. The model system consists of a “large scale” model with a 20 × 20 km2 horizontal resolution, coupled to a finer scale (4 × 4 Km2 similar model set up for the Skagerrak/Kattegat area. The performance of this model system is evaluated against the Skagex-90 data set containing several drifting buoy tracks, transport estimates from moored current meters, ship-mounted ADCP current velocities, and 10 synoptic hydrographical field data over most of the area obtained every third day in May/June 1990. The Skagex data set also contains chemical (nutrients) and biological (chlorophyll concentration, primary production etc.) data which later will be used for evaluation of this physical model system coupled to a primary production model. The model system is forced with realistic wind and atmospheric pressure fields. Although some of the outputs (after more than half a year prognostic running) still are questionable, the results so far are very promising both with respect to the simulated vertical and horizontal structure and magnitude of the circulation and the salinity distribution.

Quantifying volume transports during SKAGEX with the Norwegian Ecological Model system

Abstract A coupled 3-dimensional physical, chemical and biological model system, NORWECOM (the NORWegian ECOlogical Model system), is validated and used to identify and quantify the short-term variability of the different water masses being transported into and out of Skagerrak. The model system is a nesting between a coarse grid model set up for an extended North Sea, and a fine grid defined in the Skagerrak/Kattegat area. Originating from the extensive SKAGEX (SKAGerrak EXperiment) database, several interesting events have been identified and become the focus of the modeling. Through interactive use of the SKAGEX data set and NORWECOM, it is possible to gain a new insight into a very complex hydrodynamic system, an insight that is hard to achieve based on measurements only.

A possible separation between a northern and a southern stock of the northeast Atlantic blue whiting

Abstract Blue whiting ( Micromesistius poutassou ) in the northeast Atlantic system, probably consists of several stocks. For assessment purposes two main components, one spawning along the slope north of and one along the slope south of the Porcupine Bank, have been assumed. The Porcupine Bank area has been considered a transition zone. We address the question of the existence of a separation line between the southern and the northern stock. Our hypothesis is that this can be explained from the drift patterns of the larvae in such a way that the northern stock larvae tend to drift northwards, and the southern ones southwards. To check this, a Lagrangian transport model has been used in connection with a hydrodynamic circulation model. The circulation model has been run with realistic forcing for 20 separate years (1976–1995). For each year particles assumed to simulate blue whiting larvae have been transported from the spawning grounds using the transport model. Based on the modelled drift a separation line north of Porcupine Bank has been found. The line shows a large interannual variability indicating a mix between the two stocks.

Real-Time Ichthyoplankton Drift in Northeast Arctic Cod and Norwegian Spring-Spawning Herring

Background Individual-based biophysical larval models, initialized and parameterized by observations, enable numerical investigations of various factors regulating survival of young fish until they recruit into the adult population. Exponentially decreasing numbers in Northeast Arctic cod and Norwegian Spring Spawning herring early changes emphasizes the importance of early life history, when ichthyoplankton exhibit pelagic free drift. However, while most studies are concerned with past recruitment variability it is also important to establish real-time predictions of ichthyoplankton distributions due to the increasing human activity in fish habitats and the need for distribution predictions that could potentially improve field coverage of ichthyoplankton. Methodology/Principal Findings A system has been developed for operational simulation of ichthyoplankton distributions. We have coupled a two-day ocean forecasts from the Norwegian Meteorological Institute with an individual-based ichthyoplankton model for Northeast Arctic cod and Norwegian Spring Spawning herring producing daily updated maps of ichthyoplankton distributions. Recent years observed spawning distribution and intensity have been used as input to the model system. The system has been running in an operational mode since 2008. Surveys are expensive and distributions of early stages are therefore only covered once or twice a year. Comparison between model and observations are therefore limited in time. However, the observed and simulated distributions of juvenile fish tend to agree well during early fall. Area-overlap between modeled and observed juveniles September 1st range from 61 to 73%, and 61 to 71% when weighted by concentrations. Conclusions/Significance The model system may be used to evaluate the design of ongoing surveys, to quantify the overlap with harmful substances in the ocean after accidental spills, as well as management planning of particular risky operations at sea. The modeled distributions are already utilized during research surveys to estimate coverage success of sampled biota and immediately after spills from ships at sea.

Natural fertilisation of the marine environment — modelling of the Glomma flood 1995

Abstract The flood in the Norwegian river Glomma in May-June 1995 was among the largest ones during this century. Besides being devastating for man and buildings, it implied an extra supply of nutrients to the Skagerrak. This paper will focus on the possible effects this natural fertilisation could have had on the primary production in the receiving water. The NORWegian ECOlogical Model system (NORWECOM) has been used to quantifY this effect. The model has been run three times with different runoff scenarios to isolate the effects of the flood. To investigate the dispersion and dilution of the water from Glomma, this water has been labelled in the model. The model results have also been compared with a set of field data obtained during the period. During the flood the model gives a significant change in primary production over large areas of the Skagerrak, and all extra nutrients added from the flooded rivers were consumed by the algae. However, the flood seems to have only a small impact on the annual pr...

Quantification of Transports to Skagerrak

A coupled 3-dimensional physical, chemical and biological model system, NOR-WECOM (the NORWegian ECOlogical Model system), is used to identify and quantify the variability of the different water masses being transported in and out of Skagerrak. The model system consist of a fine grid for the Skagerrak/Kattegat area, embedded in a coarse grid for an extended North Sea.

Modeling emergent life histories of copepods

The distribution and population dynamics of zooplankton are affected by the interplay between currents, behaviour and selective growth, mortality and reproduction. Here, we present an individual based model for a copepod where life-history and behavioural traits are adapted using a genetic algorithm approach. The objectives were to investigate the importance of spatial and inter-annual variability in biophysical forcing and different predator densities on the adaptation of emergent life history traits in a copepod. The results show that in simulations with adaptation, the populations remained viable (positive population growth) within the study area over 100-year simulation whereas without adaptation populations were unviable. In one dimensional simulations with fixed spatial position there were small differences between replicate simulations. Inter-annual variability in forcing resulted in increased difference in fitness between years. Simulations with spatial-, but without inter-annual variability in forcing produced large differences in the geographic distribution, fitness and life history strategies between replicate simulations. In simulations with both spatial and inter-annual variability the replicates had rather small variability in traits. Increased predator density lead to increased day depth and avoidance of the lit upper waters. The model can be used for a range of different applications such as studying individual and population responses to environmental changes including climate change as well as to yield robust behavioral strategies for use in fully coupled end to end ecosystem models.