MOM (Monitoring - Ongrowing fish farms - Modelling)Turnover og energy and matter by fish - a general model with application to salmon

The fish model described in this paper is quite general and deals simultaneously with all fundamental aspects of fish metabolism and growth. The model conserves energy and matter, resolved in protein, fat, carbohydrates, nitrogen and phosphorus. Here the main application is to derive output from the model of interest for water quality in and around fish farms. Thus, oxygen consumption due to fish respiration and emissions of various biologically active dissolved substances from a fish farm are derived for given fish stock, food composition, feeding rate and temperature. The fluxes of particulate organic matter (uneaten food and faeces) from a farm are also derived. The model can be used for many purposes. It can be used to find food compositions fulfilling different objectives, for instance, minimising the emission of plant nutrients or food costs. It should be possible to adapt the model to other fish species for use in, for instance, models of natural populations of fish interacting with each other

On the seasonal nitrogen dynamics of the Baltic proper biogeochemical reactor

During the last decade it has become increasingly obvious that the turnover of dissolved organic nitrogen DON in marine environments is quite vigorous. This paper quantifies the turnover of DON in the Baltic proper regarded as a biogeochemical reactor. In a nitrogen model for the reactor, dissolved inorganic nitrogen DIN, DON and molecular N, fixed by cyanobacteria, can be used for plant production. The decomposition of particulate organic matter is assumed to produce DON and DIN as end products in the proportions (1- η) to η (0 ≤ η ≤ 1). The model includes two internal sink processes, denitrification and sequestering in the bottom sediments and accounts for external sources and sinks by import and export of DIN and DON. The annual net production in the Baltic proper is about 12.8 106 ton C (50 gC m-2) requiring about 2.3 106 ton N. However only about 1.0 106 ton N are available as DIN and the deficit has to be covered by an uptake of N from DON and/or fixed molecular nitrogen. The results of the model depend on the value of η. With η = 1 the use of DON for primary production is at a minimum (0.19 106 ton N) while there are maxima for nitrogen fixation (1.0 106 ton N) and denitrification (1.5 106 ton N). However, both these values are considered unrealistically large. A more likely value of η is determined from the model in such a way that the annual rate of nitrogen fixation in the Baltic proper is in accordance with a recent estimate from the literature (0.11 106 ton N). This gives η = 0.55 implying that about 0.67 106 ton N is denitrified, and 1.10 106 ton DON is used for net production, and 0.91 106 ton DON is produced by decomposition of particulate organic matter and the turnover time for DON is about 4 years. The finding that there is a vigorous turnover of DON on the reactor level has important consequences. Firstly, earlier estimates of denitrification rates were based on budgets for oxygen and DIN and overlooked the DON decomposition pathway, why denitrification rates are severely overestimated, often by a factor of 2 or greater. Secondly, the extensive use of DON for primary production in the Baltic proper in combination with abundance of DON, challenge the widely accepted opinion that nitrogen is the production-limiting nutrient on the systems (reactor) level in the Baltic proper

A model for the dynamics of nutrients and oxygen in the Baltic proper

A horizontally integrated, time-dependent physical-biogeochemical model of high vertical resolution has been developed for the Baltic Sea proper. A seasonal pycnocline model computes the physical state of the mixed surface layer. Below this is an advective-diffusive model. The vertical advection is caused by a time-dependent, entraining bottom current which transports dense seawater into the system. The vertical distributions of volumes and sediment areas are accounted for by the use of the hypsographic function of the system. The chemical/biological processes controlling the distributions of nitrogen and oxygen are modelled as follows: Primary production is controlled by light, temperature, nutrients and density stratification (critical depth). Nutrient recycling, nitrification and sedimentation are accounted for using simple, rather general process descriptions. Organic matter is broken down both in the water column and at the bottom. Denitrification in the water and sediment is controlled by the concentrations of oxygen, nitrate and organic substrate and by temperature. Sulphate reduction to hydrogen sulphide occurs during anaerobic conditions once nitrate has been depleted. The daily meteorological forcing of the model is synthetic and randomly selected from monthly statistical distributions of observed weather components. The dense water inflow from the sea used in the model is synthetic as well. Loadings of biologically active nitrogen compounds from rivers and atmospheric fall-out, representative of contemporary conditions, are used. We have run the model for a 20 year period. When compared to the field data the computed dynamics of the mixed layer and the patterns of primary production, nutrients and oxygen appear quite realistic. Due to the effect of intermittent convection in early spring nutrients are utilized down to the perennial halocline (at about 65 m depth). The conditions in the deep water, below the perennial halocline, are also well reproduced by the model, possibly except for too high ammonia concentrations during anoxic conditions. Since the dense bottom current usually is interleaved in or just below the perennial halocline the upper deep water is well oxygenated. The renewal of the lower deep water, below about 130 m, is a discontinuous process and this water may be stagnant for several years. During such periods the water becomes anoxic and high concentrations of ammonia and hydrogen sulphide may eventually result. Denitrification at the sediment redoxcline is quantitatively much more important than denitrification in the water column. Primarily since the lower deep water holds only 5% of the total volume, the influence of processes in this water mass upon the total nitrogen budget is found to be negligible

The Settlement of Industrial Disputes in Great Britain

The external phosphorus (P) loading has been halved, but the P content in the water column and the area of anoxic bottoms in Baltic proper has increased during the last 30 years. This can be explained by a temporary internal source of dissolved inorganic phosphorus (DIP) that is turned on when the water above the bottom sediment becomes anoxic. A load-response model, explaining the evolution from 1980 to 2005, suggests that the average specific DIP flux from anoxic bottoms in the Baltic proper is about 2.3 g P m(-2) year(-1). This is commensurable with fluxes estimated in situ from anoxic bottoms in the open Baltic proper and from hydrographic data in the deep part of Bornholm Basin. Oxygenation of anoxic bottoms, natural or manmade, may quickly turn off the internal P source from anoxic bottoms. This new P-paradigm should have far-reaching implications for abatement of eutrophication in the Baltic proper.Funding Agencies|Swedish EPA [NV 08/302 F-255-08]</p

Consequences of artificial deepwater ventilation in the Bornholm Basin for oxygen conditions, cod reproduction and benthic biomass – a model study

We develop and use a circulation model to estimate hydrographical and ecological changes in the isolated basin water of the Bornholm Basin. By pumping well-oxygenated so-called winter water to the greatest depth, where it is forced to mix with the resident water, the rate of deepwater density reduction increases as well as the frequency of intrusions of new oxygen-rich deepwater. We show that pumping 1000 m(3) s(-1) should increase the rates of water exchange and oxygen supply by 2.5 and 3 times, respectively. The CRV cod reproduction volume), the volume of water in the isolated basin meeting the requirements for successful cod reproduction (S > 11, O-2 > 2 mL L-1), should every year be greater than 54 km(3), which is an immense improvement, since it has been much less in certain years. Anoxic bottoms should no longer occur in the basin, and hypoxic events will become rare. This should permit extensive colonization of fauna on the earlier periodically anoxic bottoms. Increased biomass of benthic fauna should also mean increased food supply to economically valuable demersal fish like cod and flatfish. In addition, re-oxygenation of the sediments should lead to increased phosphorus retention by the sediments

Subglacial discharge‐driven renewal of tidewater glacier fjords

The classic model of fjord renewal is complicated by tidewater glacier fjords, where submarine melt and subglacial discharge provide substantial buoyancy forcing at depth. Here we use a suite of idealized, high‐resolution numerical ocean simulations to investigate how fjord circulation driven by subglacial plumes, tides, and wind stress depends on fjord width, grounding line depth, and sill height. We find that the depth of the grounding line compared to the sill is a primary control on plume‐driven renewal of basin waters. In wide fjords the plume exhibits strong lateral recirculation, increasing the dilution and residence time of glacially‐modified waters. Rapid drawdown of basin waters by the subglacial plume in narrow fjords allows for shelf waters to cascade deep into the basin; wide fjords result in a thin, boundary current of shelf waters that flow toward the terminus slightly below sill depth. Wind forcing amplifies the plume‐driven exchange flow; however, wind‐induced vertical mixing is limited to near‐surface waters. Tidal mixing over the sill increases in‐fjord transport of deep shelf waters and erodes basin stratification above the sill depth. These results underscore the first‐order importances of fjord‐glacier geometry in controlling circulation in tidewater glacier fjords and, thus, ocean heat transport to the ice.NNX12AP50G150452

Meteorological influence on summertime baroclinic exchange in the Straits of Mackinac

Straits flows can impose a complex hydrodynamic environment with high seasonal variability and significant impacts to nearby water bodies. In the Straits of Mackinac, exchange flow between Lake Michigan and Lake Huron influences water quality and ecological processes, as well as the transport of any contaminants released in or near the straits. Although previous work has shown that a Helmholtz mode is responsible for the barotropic flow oscillations in the straits, baroclinic effects impose opposite surface and subsurface flows during the summer months. In this study, we use observations of currents and water temperatures from instruments deployed in the straits to validate a hydrodynamic model of the combined Lake Michigan‐Huron system and then use the model results to investigate the baroclinic flow and determine the forcing mechanisms that drive exchange flow in the Straits of Mackinac. Analysis shows that although the Helmholtz mode drives a 3 day oscillation throughout the year, thermal stratification in the summer establishes a bidirectional flow that is governed by a shift from regional‐scale to local‐scale meteorological conditions. These results detail the seasonal variability in the straits, including the barotropic and baroclinic contributions to exchange flow and the influence of local atmospheric forcing on transport through the Straits of Mackinac.Key PointsExchange flow in the Straits of Mackinac is governed by a Helmholtz mode and summer baroclinic modeSeasonal variability in flow is driven by thermal stratification and is marked by a shift from regional‐scale to local‐scale meteorologyFlow due to the baroclinic mode is controlled by the local wind forcingPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136720/1/jgrc22183_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136720/2/jgrc22183.pd

The Baltic Sea Tracer Release Experiment. Part I: Mixing rates

In this study, results from the Baltic Sea Tracer Release Experiment (BATRE) are described, in which deep water mixing rates and mixing processes in the central Baltic Sea were investigated. In September 2007, an inert tracer gas (CF3SF5) was injected at approximately 200 m depth in the Gotland Basin, and the subsequent spreading of the tracer was observed during six surveys until February 2009. These data describe the diapycnal and lateral mixing during a stagnation period without any significant deep water renewal due to inflow events. As one of the main results, vertical mixing rates were found to dramatically increase after the tracer had reached the lateral boundaries of the basin, suggesting boundary mixing as the key process for basin-scale vertical mixing. Basin-scale vertical diffusivities were of the order of 10−5 m2 s−1 (about 1 order of magnitude larger than interior diffusivities) with evidence for a seasonal and vertical variability. In contrast to tracer experiments in the open ocean, the basin geometry (hypsography) was found to have a crucial impact on the vertical tracer spreading. The e-folding time scale for deep water renewal due to mixing was slightly less than 2 years, the time scale for the lateral homogenization of the tracer patch was of the order of a few months. Key Points: Mixing rates in the Gotland Basin are dominated by boundary mixing processes; The time scale for Gotland Basin deep water renewal is approximately 2 years; Mixing rates determined from the tracer CF3SF

Influences of precipitation on water mass transformation and deep convection

Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 1684–1700, doi:10.1175/JPO-D-11-0230.1.The influences of precipitation on water mass transformation and the strength of the meridional overturning circulation in marginal seas are studied using theoretical and idealized numerical models. Nondimensional equations are developed for the temperature and salinity anomalies of deep convective water masses, making explicit their dependence on both geometric parameters such as basin area, sill depth, and latitude, as well as on the strength of atmospheric forcing. In addition to the properties of the convective water, the theory also predicts the magnitude of precipitation required to shut down deep convection and switch the circulation into the haline mode. High-resolution numerical model calculations compare well with the theory for the properties of the convective water mass, the strength of the meridional overturning circulation, and also the shutdown of deep convection. However, the numerical model also shows that, for precipitation levels that exceed this critical threshold, the circulation retains downwelling and northward heat transport, even in the absence of deep convection.This study was supported by the National Science Foundation underGrantsOCE-0850416, OCE-0959381, andOCE-0859381.2013-04-0