The North Sea — A shelf sea in the Anthropocene

Emeis, Kay–Christian; Beusekom, Justus van; Callies, Ulrich; Ebinghaus, Ralf; Kannen, Andreas; Kraus, Gerd; Kröncke, Ingrid; Lenhart, Hermann; Lorkowski, Ina; Matthias, Volker; Möllmann, Christian; Pätsch, Johannes; Scharfe, Mirco; Thomas, Helmuth; Weisse, Ralf; Zorita, Eduardo

doi:10.1016/j.jmarsys.2014.03.012

Cited by 104 publications

(108 citation statements)

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“…The North Sea is one of the shelf regions regularly experiencing seasonal O 2 deficiency in the bottom water (Diaz and Rosenberg, 2008;Emeis et al, 2015;Rabalais et al, 2010). However, not all areas of the North Sea are similarly affected by low O 2 conditions (e.g., Queste et al, 2013) due to different characteristics with respect to stratification and O 2 consumption.…”

Section: Discussionmentioning

confidence: 99%

“…In contrast, Gröger et al (2013) predicted a North Sea wide reduction in primary production by about 30 % due to reduced winter nutrient import from the Atlantic. As these potential changes in the O 2 conditions will also affect the biocoenosis of the North Sea (Emeis et al, 2015), it is important to foster the analysis of potential impacts of climate change and changes in nutrient loads on the O 2 dynamics.…”

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confidence: 99%

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Looking beyond stratification: a model-based analysis of the biological drivers of oxygen deficiency in the North Sea

et al. 2016

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Abstract. Low oxygen conditions, often referred to as oxygen deficiency, occur regularly in the North Sea, a temperate European shelf sea. Stratification represents a major process regulating the seasonal dynamics of bottom oxygen, yet, lowest oxygen conditions in the North Sea do not occur in the regions of strongest stratification. This suggests that stratification is an important prerequisite for oxygen deficiency, but that the complex interaction between hydrodynamics and the biological processes drives its evolution.In this study we use the ecosystem model HAMSOM-ECOHAM to provide a general characterisation of the different zones of the North Sea with respect to oxygen, and to quantify the impact of the different physical and biological factors driving the oxygen dynamics inside the entire subthermocline volume and directly above the bottom.With respect to oxygen dynamics, the North Sea can be subdivided into three different zones: (1) a highly productive, non-stratified coastal zone, (2) a productive, seasonally stratified zone with a small sub-thermocline volume, and (3) a productive, seasonally stratified zone with a large subthermocline volume. Type 2 reveals the highest susceptibility to oxygen deficiency due to sufficiently long stratification periods ( > 60 days) accompanied by high surface productivity resulting in high biological consumption, and a small subthermocline volume implying both a small initial oxygen inventory and a strong influence of the biological consumption on the oxygen concentration.Year-to-year variations in the oxygen conditions are caused by variations in primary production, while spatial differences can be attributed to differences in stratification and water depth. The large sub-thermocline volume dominates the oxygen dynamics in the northern central and northern North Sea and makes this region insusceptible to oxygen deficiency. In the southern North Sea the strong tidal mixing inhibits the development of seasonal stratification which protects this area from the evolution of low oxygen conditions. In contrast, the southern central North Sea is highly susceptible to low oxygen conditions (type 2).We furthermore show that benthic diagenetic processes represent the main oxygen consumers in the bottom layer, consistently accounting for more than 50 % of the overall consumption. Thus, primary production followed by remineralisation of organic matter under stratified conditions constitutes the main driver for the evolution of oxygen deficiency in the southern central North Sea. By providing these valuable insights, we show that ecosystem models can be a useful tool for the interpretation of observations and the estimation of the impact of anthropogenic drivers on the North Sea oxygen conditions.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Looking beyond stratification: a model-based analysis of the biological drivers of oxygen deficiency in the North Sea

et al. 2016

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“…Modeling the biogeochemistry of coastal and shelf systems requires the representation of a multitude of interacting processes, not only within the water but also in the adjacent earth system components such as the atmosphere (e.g., nitrogen (N) deposition), land (e.g., riverine inputs), sediment (e.g., diagenetic processes) and biochemical processes in water (see., e.g., Cloern et al, 2014;Emeis et al, 2015). For being able to reproduce the large-scale spatial and temporal distribution of biogeochemical variables in coastal systems, a realistic representation of hydrodynamical processes is often critically important, at least those relevant to the circulation patterns and stratification dynamics: the former is needed to describe the spread of nutrient-rich river plumes and exchange at the open ocean boundaries, and the latter for being able to capture the vertical gradients in the light and…”

Section: Introductionmentioning

confidence: 99%

The acclimative biogeochemical model of the southern North Sea

Kerimoglu¹,

Hofmeister²,

Maerz³

et al. 2017

Biogeosciences

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Abstract. Ecosystem models often rely on heuristic descriptions of autotrophic growth that fail to reproduce various stationary and dynamic states of phytoplankton cellular composition observed in laboratory experiments. Here, we present the integration of an advanced phytoplankton growth model within a coupled three-dimensional physicalbiogeochemical model and the application of the model system to the southern North Sea (SNS) defined on a relatively high resolution ( ∼ 1.5-4.5 km) curvilinear grid. The autotrophic growth model, recently introduced by Wirtz and Kerimoglu (2016), is based on a set of novel concepts for the allocation of internal resources and operation of cellular metabolism. The coupled model system consists of the General Estuarine Transport Model (GETM) as the hydrodynamical driver, a lower-trophic-level model and a simple sediment diagenesis model. We force the model system with realistic atmospheric and riverine fluxes, background turbidity caused by suspended particulate matter (SPM) and open ocean boundary conditions. For a simulation for the period 2000-2010, we show that the model system satisfactorily reproduces the physical and biogeochemical states of the system within the German Bight characterized by steep salinity; nutrient and chlorophyll (Chl) gradients, as inferred from comparisons against observation data from long-term monitoring stations; sparse in situ measurements; continuous transects; and satellites. The model also displays skill in capturing the formation of thin chlorophyll layers at the pycnocline, which is frequently observed within the stratified regions during summer. A sensitivity analysis reveals that the vertical distributions of phytoplankton concentrations estimated by the model can be qualitatively sensitive to the description of the light climate and dependence of sinking rates on the internal nutrient reserves. A non-acclimative (fixed-physiology) version of the model predicted entirely different vertical profiles, suggesting that accounting for physiological flexibility might be relevant for a consistent representation of the vertical distribution of phytoplankton biomass. Our results point to significant variability in the cellular chlorophyll-to-carbon ratio (Chl : C) across seasons and the coastal to offshore transition. Up to 3-fold-higher Chl : C at the coastal areas in comparison to those at the offshore areas contribute to the steepness of the chlorophyll gradient. The model also predicts much higher phytoplankton concentrations at the coastal areas in comparison to its non-acclimative equivalent. Hence, findings of this study provide evidence for the relevance of physiological flexibility, here reflected by spatial and seasonal variations in Chl : C, for a realistic description of biogeochemical fluxes, particularly in the environments displaying strong resource gradients.

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“…PCA of full 3D model output would be computationally much more demanding and also provide higher dimensional output. In their large-scale studies, Emeis et al (2014) and Mathis et al (2015) therefore either integrated or averaged 3D model results in the vertical. Calculating daily PCs of residual currents based on 3D simulations in the German Bight is a challenge for future studies.…”

Section: Discussionmentioning

confidence: 99%

“…Referring to mean summer (June to August) and winter (December to February) conditions, Mathis et al (2015) focussed on inter-annual variations during the years 1961-2000. A PCA of North Sea volume fluxes of 1962-2004 reported by Emeis et al (2014) was based on monthly mean fields. Kauker and von Storch (2000) performed PCA for daily surface velocity stream function data from the winters (December to February) of 1979-1993, referring also to the whole North Sea.…”

Section: Introductionmentioning

confidence: 99%