Dynamic sea level changes following changes in the thermohaline circulation

Using the coupled climate model CLIMBER-3a, we investigate changes in sea surface elevation due to a weakening of the thermohaline circulation (THC). In addition to a global sea level rise due to a warming of the deep sea, this leads to a regional dynamic sea level change which follows quasi-instantaneously any change in the ocean circulation. We show that the magnitude of this dynamic effect can locally reach up to ~1m, depending on the initial THC strength. In some regions the rate of change can be up to 20-25 mm/yr. The emerging patterns are discussed with respect to the oceanic circulation changes. Most prominent is a south-north gradient reflecting the changes in geostrophic surface currents. Our results suggest that an analysis of observed sea level change patterns could be useful for monitoring the THC strength.Comment: Climate Dynamics (2004), submitted. See also http://www.pik-potsdam.de/~ander

A decomposition of the Atlantic Meridional Overturning Circulation into physical components using its sensitivity to vertical diffusivity

International audienceThe sensitivity of the Atlantic Ocean meridional overturning circulation to the vertical diffusion coefficient in the global coupled atmosphere–ocean–sea ice model CLIMBER-3 is investigated. An important feature of the three-dimensional ocean model is its low-diffusive tracer advection scheme. The strength Mmax of the Atlantic overturning is decomposed into three components: 1) the flow MS exported southward at 30°S, 2) the large-scale upward flow that balances vertical diffusion in the Atlantic, and 3) a winddependent upwelling flux Wbound along the Atlantic boundaries that is not due to vertical diffusion. The export of water at 30°S varies only weakly with , but is strongly correlated with the strength of the overflow over the Greenland–Scotland ridge. The location of deep convection is found to be mixing dependent such that a shift from the Nordic seas to the Irminger Sea is detected for high values of . The ratio R MS/Mmax gives a measure of the interhemispheric overturning efficiency and is found to decrease linearly with . The diffusion-induced upwelling in the Atlantic is mostly due to the uniform background value of while parameterization of enhanced mixing over rough topography and in stratified areas gives only a weak contribution to the overturning strength. It increases linearly with . This is consistent with the classic 2/3 scaling law only when taking the linear variation of the density difference to into account. The value of Wbound is roughly constant with but depends linearly on the wind stress strength in the North Atlantic. The pycnocline depth is not sensitive to changes in in the model used herein, and the results suggest that it is primarily set by the forcing of the Southern Ocean winds. The scaling of the total overturning strength with depends on the combined sensitivity of each of the terms to . In the range of background diffusivity values in which no switch in deep convection sites is detected, Mmax scales linearly with the vertical diffusivity. It is argued that scalings have, in general, to be interpreted with care because of the generally very small range of but also because of possible shifts in important physical processes such as deep convection location

Changes in Global Ocean Circulation due to Isopycnal Diffusion

We investigate changes in the ocean circulation due to the variation of isopycnal diffusivity (k(iso)) in a global non-eddy-resolving model. Although isopycnal diffusion is thought to have minor effects on interior density gradients, the model circulation shows a surprisingly large sensitivity to the changes: with increasing k(iso), the strength of the Atlantic residual overturning circulation (AMOC) and the Antarctic Circumpolar Current (ACC) transport weaken. At high latitudes, the isopycnal diffusion diffuses temperature and salinity upward and poleward, and at low latitudes downward close to the surface. Increasing isopycnal diffusivity increases the meridional isopycnal fluxes whose meridional gradient is equatorward, hence leading to a negative contribution to the flux divergence in the tracer equations and predominant cooling and freshening equatorward of 40 degrees. The effect on temperature overcompensates the countering effect of salinity diffusion, such that the meridional density differences decrease, along with which ACC and AMOC decrease. We diagnose the adjustment process to the new equilibrium with increased isopycnal diffusion to assess how the other terms in the tracer equations react to the increased k(iso). It reveals that around +/- 40 degrees latitude, the cooling induced by the increased isopycnal flux is only partly compensated by warming by advection, explaining the net cooling. Overall, the results emphasize the importance of isopycnal diffusion on ocean circulation and dynamics, and hence the necessity of its careful representation in models. SIGNIFICANCE STATEMENT: The effect of mixing by mesoscale eddies, represented as diffusion along surfaces of constant density in models, on the ocean circulation is not well understood. Here, we show that an increase in the eddy diffusivity in different setups of a global ocean model leads to a surprisingly large change of the ocean circulation. The strength of the Atlantic overturning circulation and the Antarctic Circumpolar Current decrease. We find that the interior ocean becomes cooler and fresher and that the temperature effect on density dominates over salinity, resulting in a decrease in the density gradients. Our results point out the importance of eddy diffusion on ocean circulation, and hence the necessity of its correct representation in ocean and climate models

A Multiwavenumber Theory for Eddy Diffusivities and Its Application to the Southeast Pacific (DIMES) Region

A multiwavenumber theory is formulated to represent eddy diffusivities. It expands on earlier single-wavenumber theories and includes the wide range of wavenumbers encompassed in eddy motions. In the limiting case in which ocean eddies are only composed of a single wavenumber, the multiwavenumber theory is equivalent to the single-wavenumber theory and both show mixing suppression by the eddy propagation relative to the mean flow. The multiwavenumber theory was tested in a region of the Southern Ocean (70°–45°S, 110°–20°W) that covers the Drake Passage and includes the tracer/float release locations during the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). Cross-stream eddy diffusivities and mixing lengths were estimated in this region from the single-wavenumber theory, from the multiwavenumber theory, and from floats deployed in a global k[subscript 0]° Parallel Ocean Program (POP) simulation. Compared to the single-wavenumber theory, the horizontal structures of cross-stream mixing lengths from the multiwavenumber theory agree better with the simulated float-based estimates at almost all depth levels. The multiwavenumber theory better represents the vertical structure of cross-stream mixing lengths both inside and outside the Antarctica Circumpolar Current (ACC). Both the single-wavenumber and multiwavenumber theories represent the horizontal structures of cross-stream diffusivities, which resemble the eddy kinetic energy patterns

Erratum to: The earth system model of intermediate complexity CLIMBER-3α. Part I: description and performance for present-day conditions

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New facile method to measure cyanide in blood.

Cyanide, a well-known toxic substance that could be used as a weapon of mass destruction, is likely responsible for a substantial percentage of smoke inhalation deaths. The vitamin B(12) precursor cobinamide binds cyanide with high affinity, changing color and, correspondingly, its spectrophotometric spectrum in the ultraviolet/visible light range. Based on these spectral changes, we developed a new facile method to measure cyanide in blood using cobinamide. The limit of detection was 0.25 nmol, while the limit of quantitation was approximately 0.5 nmol. The method was reliable, requires minimal equipment, and correlated well with a previously established method. Moreover, we adapted it for rapid qualitative assessment of cyanide concentration, which could be used in the field to identify cyanide-poisoned subjects for immediate treatment

New facile method to measure cyanide in blood.

Cyanide, a well-known toxic substance that could be used as a weapon of mass destruction, is likely responsible for a substantial percentage of smoke inhalation deaths. The vitamin B(12) precursor cobinamide binds cyanide with high affinity, changing color and, correspondingly, its spectrophotometric spectrum in the ultraviolet/visible light range. Based on these spectral changes, we developed a new facile method to measure cyanide in blood using cobinamide. The limit of detection was 0.25 nmol, while the limit of quantitation was approximately 0.5 nmol. The method was reliable, requires minimal equipment, and correlated well with a previously established method. Moreover, we adapted it for rapid qualitative assessment of cyanide concentration, which could be used in the field to identify cyanide-poisoned subjects for immediate treatment