Isopycnal

About: Isopycnal is a research topic. Over the lifetime, 1220 publications have been published within this topic receiving 54355 citations.

Isopycnal mixing in ocean circulation models

Abstract: A subgrid-scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non-eddy-resolving ocean circulation models. The mixing is applied in isopycnal coordinates to isopycnal layer thickness, or inverse density gradient, as well as to passive scalars, temperature and salinity. The transformation of these mixing forms to physical coordinates is also presented.

Global patterns of marine nitrogen fixation and denitrification

Abstract: A new quasi-conservative tracer N*, defined as a linear combination of nitrate and phosphate, is proposed to investigate the distribution of nitrogen fixation and denitrification in the world oceans. Spatial patterns of N* are determined in the different ocean basins using data from the Geochemical Ocean Sections Study (GEOSECS) cruises (1972–1978) and from eight additional cruises in the Atlantic Ocean. N* is low ( 2.0 µmol kg−1) indicative of prevailing nitrogen fixation are found in the thermocline of the tropical and subtropical North Atlantic and in the Mediterranean. This suggests that on a global scale these basins are acting as sources of fixed nitrogen, while the Indian Ocean and parts of the Pacific Ocean are acting as sinks. Nitrogen fixation is estimated in the North Atlantic Ocean (10°N–50°N) using the N* distribution along isopycnal surfaces and information about the water age. We calculate a fixation rate of 28 Tg N yr−1 which is about 3 times larger than the most recent global estimate. Our result is in line, however, with some recent suggestions that pelagic nitrogen fixation may be seriously underestimated. The implied flux of 0.072 mol N m−2 yr−1 is sufficient to meet all the nitrogen requirement of the estimated net community production in the mixed layer during summer at the Bermuda Atlantic Time-series Study (BATS) site in the northwestern Sargasso Sea. Extrapolation of our North Atlantic estimate to the global ocean suggests that the present-day budget of nitrogen in the ocean may be in approximate balance.

GFDL’s ESM2 Global Coupled Climate–Carbon Earth System Models. Part I: Physical Formulation and Baseline Simulation Characteristics

Abstract: The authors describe carbon system formulation and simulation characteristics of two new global coupled carbon–climate Earth System Models (ESM), ESM2M and ESM2G. These models demonstrate good climate fidelity as described in part I of this study while incorporating explicit and consistent carbon dynamics. The two models differ almost exclusively in the physical ocean component; ESM2M uses the Modular Ocean Model version 4.1 with vertical pressure layers, whereas ESM2G uses generalized ocean layer dynamics with a bulk mixed layer and interior isopycnal layers. On land, both ESMs include a revised land model to simulate competitive vegetation distributions and functioning, including carbon cycling among vegetation, soil, and atmosphere. In the ocean, both models include new biogeochemical algorithms including phytoplankton functional group dynamics with flexible stoichiometry. Preindustrial simulations are spun up to give stable, realistic carbon cycle means and variability. Significant differences...

Oceanic Isopycnal Mixing by Coordinate Rotation

Abstract: Current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only. In order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces, the isopycnal mixing tensor has been transformed from a diagonal second-rank tensor in the isopycnal coordinate system to a tensor containing off-diagonal elements in the geopotential coordinate system.

Evidence for slow mixing across the pycnocline from an open-ocean tracer-release experiment

Abstract: THE distributions of heat, salt and trace substances in the ocean thermocline depend on mixing along and across surfaces of equal density (isopycnal and diapycnal mixing, respectively). Measurements of the invasion of anthropogenic tracers, such as bomb tritium and 3He (see, for example, refs 1 and 2), have indicated that isopycnal processes dominate diapycnal mixing, and turbulence measurements have suggested that diapycnal mixing is small3,4, but it has not been possible to measure accurately the diapycnal diffusivity. Here we report such a measurement, obtained from the vertical dispersal of a patch of the inert compound SF6 released in the open ocean. The diapycnal diffusivity, averaged over hundreds of kilometres and five months, was 0.11 ± 0.02 cm2 s−1, confirming previous estimates1–4. Such a low diffusivity can support only a rather small diapycnal flux of nitrate into the euphotic zone; it justifies the neglect of diapycnal mixing in dynamic models of the thermocline25–27, and implies that heat, salt and tracers must penetrate the thermocline mostly by transport along, rather than across, density surfaces.