Climate-Forced Variability of Ocean Hypoxia Deutsch, Curtis; Brix, Holger; Ito, Taka ...
Science (American Association for the Advancement of Science),
07/2011, Letnik:
333, Številka:
6040
Journal Article
Recenzirano
Oxygen (O 2 ) is a critical constraint on marine ecosystems. As oceanic O 2 falls to hypoxic concentrations, habitability for aerobic organisms decreases rapidly. We show that the spatial extent of ...hypoxia is highly sensitive to small changes in the ocean's O 2 content, with maximum responses at suboxic concentrations where anaerobic metabolisms predominate. In model-based reconstructions of historical oxygen changes, the world's largest suboxic zone, in the Pacific Ocean, varies in size by a factor of 2. This is attributable to climate-driven changes in the depth of the tropical and subtropical thermocline that have multiplicative effects on respiration rates in low-O 2 water. The same mechanism yields even larger fluctuations in the rate of nitrogen removal by denitrification, creating a link between decadal climate oscillations and the nutrient limitation of marine photosynthesis.
In the California Current, subduction by mesoscale eddies removes nutrients from the coastal surface layer, counteracting upwelling and quenching productivity. Submesoscale eddies are also ubiquitous ...in the California Current, but their biogeochemical role has not been quantified yet in the region. Here, we present results from a physical‐biogeochemical model of the California Current run at a resolution of 1 km, sufficient to represent submesoscale dynamics. By comparing it with a coarser simulation run at 4 km resolution, we demonstrate the importance of submesoscale currents for the seasonal cycles of nutrients and organic matter and highlight the existence of different regimes along a cross‐shore gradient. In the productive coastal region, submesoscale currents intensify quenching and reduce productivity, further counteracting wind‐driven upwelling. In the offshore oligotrophic region, submesoscale currents enhance the upward transport of nutrients, fueling a dramatic increase in new production. These effects are modulated by seasonality, strengthening near the coast during upwelling and offshore in wintertime. The intensification of the transport by submesoscale eddies drives an adjustment of the planktonic ecosystem, with a reduction of plankton biomass, productivity, and size near the coast and an increase offshore. In contrast, organic matter export by sinking particles and subduction of detritus and living cells are enhanced nearly everywhere. Similar processes are likely important in other regions characterized by seasonal upwelling, for example, other eastern boundary upwelling systems.
Key Points
In the California Current, submesoscale currents intensify nutrient subduction near the coast and nutrient delivery to the surface offshore
Submesoscale currents drive a reduction in productivity, new production, and phytoplankton size near the coast and an increase offshore
Seasonality modulates the biogeochemical effects of submesoscale, with stronger effects inshore during upwelling and offshore in wintertime
A key control on the magnitude of coastal eutrophication is the degree to which currents quickly transport nitrogen derived from human sources away from the coast to the open ocean before ...eutrophication develops. In the Southern California Bight (SCB), an upwelling-dominated eastern boundary current ecosystem, anthropogenic nitrogen inputs increase algal productivity and cause subsurface acidification and oxygen (O
) loss along the coast. However, the extent of anthropogenic influence on eutrophication beyond the coastal band, and the physical transport mechanisms and biogeochemical processes responsible for these effects are still poorly understood. Here, we use a submesoscale-resolving numerical model to document the detailed biogeochemical mass balance of nitrogen, carbon and oxygen, their physical transport, and effects on offshore habitats. Despite management of terrestrial nutrients that has occurred in the region over the last 20 years, coastal eutrophication continues to persist. The input of anthropogenic nutrients promote an increase in productivity, remineralization and respiration offshore, with recurrent O
loss and pH decline in a region located 30-90 km from the mainland. During 2013 to 2017, the spatially averaged 5-year loss rate across the Bight was 1.3 mmol m
O
, with some locations losing on average up to 14.2 mmol m
O
. The magnitude of loss is greater than model uncertainty assessed from data-model comparisons and from quantification of intrinsic variability. This phenomenon persists for 4 to 6 months of the year over an area of 278,40 km
(
30% of SCB area). These recurrent features of acidification and oxygen loss are associated with cross-shore transport of nutrients by eddies and plankton biomass and their accumulation and retention within persistent eddies offshore within the SCB.
We investigate the mechanisms controlling the evolution of Southern Ocean carbon storage under a future climate warming scenario. A subset of Coupled Model Intercomparison Project Phase 5 models ...predicts that the inventory of biologically sequestered carbon south of 40°S increases about 18–34 Pg C by 2100 relative to the preindustrial condition. Sensitivity experiments with an ocean circulation and biogeochemistry model illustrates the impacts of the wind and buoyancy forcings under a warming climate. Intensified and poleward shifted westerly wind strengthens the upper overturning circulation, not only leading to an increased uptake of anthropogenic CO2 but also releasing biologically regenerated carbon to the atmosphere. Freshening of Antarctic Surface Water causes a slowdown of the lower overturning circulation, leading to an increased Southern Ocean biological carbon storage. The rectified effect of these processes operating together is the sustained growth of the carbon storage in the Southern Ocean, even under the warming climate with a weaker global ocean carbon uptake.
Key Points
Warming climate slightly increases the carbon inventory of the Southern Ocean
Regenerated carbon is increased in the deep water
The intensified wind increases anthropogenic carbon uptake
The coastal upwelling region of the California Current System (CalCS) is a well‐known site of high productivity and lateral export of nutrients and organic matter, yet neither the magnitude nor the ...governing processes of this offshore transport are well quantified. Here we address this gap using a high‐resolution (5 km) coupled physical‐biogeochemical numerical simulation (ROMS). The results reveal (i) that the offshore transport is a very substantial component of any material budget in this region, (ii) that it reaches more than 800 km into the offshore domain, and (iii) that this transport is largely controlled by mesoscale processes, involving filaments and westward propagating eddies. The process starts in the nearshore areas, where nutrient and organic matter‐rich upwelled waters pushed offshore by Ekman transport are subducted at the sharp lateral density gradients of upwelling fronts and filaments located at ∼25–100 km from the coast. The filaments are very effective in transporting the subducted material further offshore until they form eddies at their tips at about 100–200 km from the shore. The cyclonic eddies tend to trap the cold, nutrient, and organic matter‐rich waters of the filaments, whereas the anticyclones formed nearby encapsulate the low nutrient and low organic matter waters around the filament. After their detachment, both types of eddies propagate further in offshore direction, with a speed similar to that of the first baroclinic mode Rossby waves, providing the key mechanism for long‐range transport of nitrate and organic matter from the coast deep into the offshore environment.
Key Points:
Mesoscale eddies play dominant roles in offshore transport of organic carbon
Nitrate upwelled is largely subducted at upwelling front before consumed
Dominant roles of eddies and filaments are confirmed by many different methods
We study the dynamics of the planktonic ecosystem in the coastal upwelling zone within the California Current System using a three-dimensional (3-D), eddy-resolving circulation model coupled to an ...ecosystem/biogeochemistry model. The physical model is based on the Regional Oceanic Modeling System (ROMS), configured at a resolution of 15
km for a domain covering the entire US West Coast, with an embedded child grid covering the central California upwelling region at a resolution of 5
km. The model is forced with monthly mean boundary conditions at the open lateral boundaries as well as at the surface. The ecological/biogeochemical model is nitrogen based, includes single classes for phytoplankton and zooplankton, and considers two detrital pools with different sinking speeds. The model also explicitly simulates a variable chlorophyll-to-carbon ratio. Comparisons of model results with either remote sensing observations (AVHRR, SeaWiFS) or in-situ measurements from the CalCOFI program indicate that our model is capable of replicating many of the large-scale, time-averaged features of the coastal upwelling system. An exception is the underestimation of the chlorophyll levels in the northern part of the domain, perhaps because of the lack of short-term variations in the atmospheric forcing. Another shortcoming is that the modeled thermocline is too diffuse, and that the upward slope of the isolines toward the coast is too small. Detailed time-series comparisons with observations from Monterey Bay reveal similar agreements and discrepancies. We attribute the good agreement between the modeled and observed ecological properties in large part to the accuracy of the physical fields. In turn, many of the discrepancies can be traced back to our use of monthly mean forcing. Analysis of the ecosystem structure and dynamics reveal that the magnitude and pattern of phytoplankton biomass in the nearshore region are determined largely by the balance of growth and zooplankton grazing, while in the offshore region, growth is balanced by mortality. The latter appears to be inconsistent with in situ observations and is a result of our consideration of only one zooplankton size class (mesozooplankton), neglecting the importance of microzooplankton grazing in the offshore region. A comparison of the allocation of nitrogen into the different pools of the ecosystem in the 3-D results with those obtained from a box model configuration of the same ecosystem model reveals that only a few components of the ecosystem reach a local steady-state, i.e. where biological sources and sinks balance each other. The balances for the majority of the components are achieved by local biological source and sink terms balancing the net physical divergence, confirming the importance of the 3-D nature of circulation and mixing in a coastal upwelling system.
This paper is the first of two that present a 16-year hindcast solution from a coupled physical and biogeochemical model of the California Current System (CCS) along the U. S. West Coast and validate ...the physical solution with respect to mean, seasonal, interannual, and subseasonal fields and, to a lesser degree, eddy variability. Its companion paper is Deutsch et al. (2021). The intent is to construct and demonstrate a modeling tool that will be used for mechanistic explanations, attributive causal assessments, and forecasts of future evolution for circulation and biogeochemistry, with particular attention to the increasing oceanic stratification, deoxygenation, and acidification. A well-resolved mesoscale (dx=4 km) simulation of the CCS circulation is made with the Regional Oceanic Modeling System over a hindcast period of 16 years from 1995 to 2010. The oceanic solution is forced by a high-resolution (dx=6 km) regional configuration of the Weather and Research Forecast (WRF) atmospheric model. Both of these high-resolution regional oceanic and atmospheric simulations are forced by lateral open boundary conditions taken from larger-domain, coarser-resolution parent simulations that themselves have boundary conditions from the Mercator and Climate Forecast System reanalyses, respectively. We show good agreement between the simulated atmospheric forcing of the oceanic and satellite measurements for the spatial patterns and temporal variability for the surface fluxes of momentum, heat, and freshwater. The simulated oceanic physical fields are then evaluated with satellite and in situ measurements. The simulation reproduces the main structure of the climatological upwelling front and cross-shore isopycnal slopes, the mean current patterns (including the California Undercurrent), and the seasonal, interannual, and subseasonal variability. It also shows agreement between the mesoscale eddy activity and the windwork energy exchange between the ocean and atmosphere modulated by influences of surface current on surface stress. Finally, the impact of using a high frequency wind forcing is assessed for the importance of synoptic wind variability to realistically represent oceanic mesoscale activity and ageostrophic inertial currents.
We investigate the relationship between annually integrated new and export production for the central Californian marine upwelling system using an eddy‐resolving coupled ...physical‐ecosystem‐biogeochemical model. We find that when averaged over the annual cycle lateral transport leads to a substantial spatial decoupling of export from new production, with a length‐scale of decoupling on the order of 300 km. The decoupling is largely caused by mean horizontal fluxes induced by persistent meso‐ and submesoscale circulation structures and to a lesser degree by the mean lateral offshore transport induced by Ekman transport. This indicates that the concept of numerically equal new and export production has to be used with great care, particularly in dynamic oceanic environments.
This paper examines the verdict in the case of Mrs Sule Eisele Gaffaroglu vR+V Lebensversicherungs AG, Wiesbaden Labour Court. The economic analysis of law focuses on the three main paragraphs of the ...General Equal Treatment Act1 (Allgemeines Gleichbehandlungsgesetz, abbreviated to AGG): §22 – Burden of proof for the plaintiff and reversing the onus of proof to the defendant; §15 Para. 1 – Compensation of material losses; and §15 Para. 2 – Monetary compensation for non-economic loss. The analysis of the verdict concludes that the AGG, in the version currently in force, is not efficient. However, this paper also suggests possible ways of increasing the efficiency of the AGG.
Abstract
Dieser Beitrag untersucht das Urteil in dem Verfahren Frau Sule Eisele-Gaffaroglu gegen die R++V Lebensversicherungs AG, Arbeitsgericht Wiesbaden. Mittelpunkt der rechtsökonomischen Analyse ...bilden die drei für das Arbeitsrecht wesentlichen Paragrafen des Allgemeinen Gleichbehandlungsgesetzes (AGG): § 22 - Beweislast durch den Kläger und die mögliche Beweisverlagerung auf den Beklagten, § 15 Abs. 1 - Ersatz des materiellen Schadens und § 15 AGG Abs. 2 - Ersatz des immateriellen Schadens. Das Ergebnis der Urteilsanalyse ergibt, dass das AGG in der derzeit geltenden Fassung nicht effizient ist. Gleichzeitig zeigt der Beitrag aber auch Möglichkeiten zur Effizienzsteigerung des AGG auf.
Improvement in Efficiency of the General Act on Equal Treatment (AGG) - a Legal and Economic Analysis
This article analyses the verdict reached at the end of the proceedings of Mrs Sule Eisele-Gaffaroglu versus R++V Lebensversicherungs AG, which was heard at the Wiesbaden labour court. The focal points of the analysis, which adopts both legal and economic perspectives, are the three main paragraphs of the General Act on Equal Treatment (Allgemeines Gleichbehandlungsgesetz - abbreviated AGG). These are paragraph 22, which covers the burden of proof for the plaintiff and reverses the onus of proof to the defendant; paragraph 15 (1), which addresses compensation for material damage; and paragraph 15 (2), which details monetary compensation for non-economic loss. The analysis shows that the AGG is, in its current form, not efficient. Building on the analysis and findings, this article provides recommendations for the adequate improvement of the AGG.
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