Variability of the Indo-Pacific Ocean exchanges

The ECCO–GODAE global estimate of the ocean circulation 1992–2007 is analyzed in the region of the Indonesian Throughflow (ITF), including the Southern Ocean flow south of Australia. General characteristics are an intense month-to-month noise, only weak trends, and an important annual cycle (which is not the focus of attention). Apart from the details of the unresolved flows within the various passages, and right on the equator, the region and its large-scale climate effects appears to be accurately diagnosed by large-scale geostrophic balance, so that the ITF can be calculated either from the upstream or the downstream balanced flow (but no simple reference level can be defined). The INSTANT program occurs during a more or less typical three-year period. Indications of response to the large 1997–1998 El Niño are weak.National Oceanographic Partnership Program (U.S.)United States. National Aeronautics and Space AdministrationUnited States. National Oceanic and Atmospheric AdministrationGeophysical Fluid Dynamics Laboratory (U.S.)National Center for Atmospheric Research (U.S.)National Science Foundation (U.S.

Speculations on a schematic theory of the Younger Dryas

The possible implications of a change in deep ocean mixing generated by the abrupt coverage of continental shelves during deglaciation is explored schematically. A simple Cartesian continental shelf/deep ocean tidal model is used to mimic the behavior of tidal dissipation at a variety of frequencies relative to a basin-near-resonance. The actual estimated sea level curve is then used to calculate a representative deep water tidal dissipation through time, which is then translated by means of a one-dimensional loop flow to explore the implications of a change in deep ocean mixing. It is possible to pick parameters for the loop model, which is analogous to the Stommel two-state box model, such that interesting transitions occur when diffusion alone is changed, including oscillatory responses. To the extent that the box model is believed to mimic the ocean circulation, it can produce shifts analogous to the re-glaciation and subsequent de-glaciation characterizing the Younger Dryas interval. That changing topography and winds would likely also have a profound influence on mixing by mesoscale disturbances is noted but not pursued

Properties for inverse analysis of sound propagation in simple oceanic waveguides

For a source and receiver on the axis of a deep sound channel we solve the two point boundary value problem for the arriving sound pulse using the classical ray theory approximation. The procedure is a generalization of that of Munk (1974) and we emphasize the determination of parameter changes in the sound channel by inverse techniques. The \u27canonical\u27 profile of Munk is shown to give an arrival structure qualitatively different from an observed profile...

The decadal mean ocean circulation and Sverdrup balance

Elementary Sverdrup balance is tested in the context of the time-average of a 16-year duration time-varying ocean circulation estimate employing the great majority of global-scale data available between 1992 and 2007. The time-average circulation exhibits all of the conventional major features as depicted both through its absolute surface topography and vertically integrated transport stream function. Important small-scale features of the time average only become apparent, however, in the time-average vertical velocity, whether near the surface or in the abyss. In testing Sverdrup balance, the requirement is made that there should be a mid-water column depth where the magnitude of the vertical velocity is less than 10[superscript -8]m/s (about 0.3 m/year displacement). The requirement is not met in the Southern Ocean or high northern latitudes. Over much of the subtropical and lower latitude ocean, Sverdrup balance appears to provide a quantitatively useful estimate of the meridional transport (about 40% of the oceanic area). Application to computing the zonal component, by integration from the eastern boundary is, however, precluded in many places by failure of the local balances close to the coasts. Failure of Sverdrup balance at high northern latitudes is consistent with the expected much longer time to achieve dynamic equilibrium there, and the action of other forces, and has important consequences for ongoing ocean monitoring efforts.United States. National Aeronautics and Space Administration (Contract NNX09AI87G)United States. National Aeronautics and Space Administration (Contract NNX08AV89G

The distribution of eddy kinetic and potential energies in the global ocean

Understanding of the major sources, sinks, and reservoirs of energy in the ocean is briefly updated in a diagram. The nature of the dominant kinetic energy reservoir, that of the balanced variablity, is then found to be indistinguishable in the observations from a sum of barotropic and first baroclinic ordinary quasi-geostrophic modes. Little supporting evidence is available to partition the spectra among forced motions and turbulent cascades, along with significant energy more consistent with weakly non-linear wave dynamics. Linear-response wind-forced motions appear to dominate the high frequency (but subinertial) mooring frequency spectra. Turbulent cascades appear to fill the high wavenumber spectra in altimetric data and numerical simulations. Progress on these issues is hindered by the difficulty in connecting the comparatively easily available frequency spectra with the variety of theoretically predicted wavenumber spectra.National Oceanographic Partnership Program (U.S.)United States. National Aeronautics and Space AdministrationNational Science Foundation (U.S.) (Award OCE-0849233

Bidecadal Thermal Changes in the Abyssal Ocean

A dynamically consistent state estimate is used for the period 1992–2011 to describe the changes in oceanic temperatures and heat content, with an emphasis on determining the noise background in the abyssal (below 2000 m) depths. Interpretation requires close attention to the long memory of the deep ocean, implying that meteorological forcing of decades to thousands of years ago should still be producing trendlike changes in abyssal heat content. Much of the deep-ocean volume remained unobserved. At the present time, warming is seen in the deep western Atlantic and Southern Oceans, roughly consistent with those regions of the ocean expected to display the earliest responses to surface disturbances. Parts of the deeper ocean, below 3600 m, show cooling. Most of the variation in the abyssal Pacific Ocean is comparatively featureless, consistent with the slow, diffusive approach to a steady state expected there. In the global average, changes in heat content below 2000 m are roughly 10% of those inferred for the upper ocean over the 20-yr period. A useful global observing strategy for detecting future change has to be designed to account for the different time and spatial scales manifested in the observed changes. If the precision estimates of heat content change are independent of systematic errors, determining oceanic heat uptake values equivalent to 0.1 W m−2 is possibly attainable over future bidecadal periods.Earth and Planetary Science

An adjoint sensitivity study of chlorofluorocarbons in the North Atlantic

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C01007, doi:10.1029/2003JC002014.Adjoint sensitivities of CFC-11 concentrations and CFC-11/CFC-12 ratio ages in a North Atlantic general circulation model are analyzed. These sensitivities are compared with those of spiciness, T − (β/α) S, where α, β are the thermal and haline expansion coefficients, respectively. High-sensitivity fields are candidates for providing the most powerful constraints in the corresponding inverse problems. In the dual (adjoint) solutions all three variables exhibit the major ventilation pathways and define the associated timescales in the model. Overall, however, spiciness shows the highest sensitivity to the flow field. In the North Atlantic Deep Water, sensitivities of CFC properties and spiciness to the isopycnal mixing and thickness diffusion are of the same order of magnitude. In the lower subtropical thermocline, sensitivities of CFC properties to the isopycnal mixing and thickness diffusion are higher. The utility of this sensitivity is undermined by the need to reconstruct their boundary conditions. Given the influence of T, S measurements on the density field, they produce the most powerful constraints on the model on the large scale. It still remains possible, however, that transient tracers can provide a larger relative information content concerning the mixing process between the near-surface boundary layer and the thermocline but dependent upon the ability to reconstruct accurate initial and boundary conditions.This work was supported by NSF Award OCE-9730071, OCE-9617570, NASA Award NAG5-7857 and NAG5- 11933

On combining satellite altimetry with hydrographic data

It is shown, by random construction of many sea surfaces, each consistent with geostrophy and mass conservation in the underlying ocean, that absolute sea surface topography relative to a geopotential surface can be estimated to 10 cm accuracy from appropriate in situ measurements of density...

Simultaneous pressure, velocity and temperature measurements in the Florida Straits

We present a descriptive picture of the variability in the Florida Current as measured by a large number of current meters, temperature sensors, and bottom mounted pressure sensors in the period March-August, 1974. Because of the very high velocities, only measurements made in the near-bottom region were possible. The tidal regime is found to be somewhat more complex than postulated from earlier measurements...

Oceanic tracer and proxy time scales revisited

Quantifying time-responses of the ocean to tracer input is important to the interpretation of paleodata from sediment cores – because surface-injected tracers do not instantaneously spread throughout the ocean. To obtain insights into the time response, a computationally efficient statetransition matrix method is demonstrated and used to compute successive states of passive tracer concentrations in the global ocean. Times to equilibrium exceed a thousand years for regions of the global ocean outside of the injection and convective areas and concentration gradients give time-lags from hundreds to thousands of years between the Atlantic and Pacific abyss, depending on the injection region and the nature of the boundary conditions employed. Equilibrium times can be much longer than radiocarbon ages – both because the latter are strongly biased towards the youngest fraction of fluid captured in a sample, and because they represent distinct physical properties. Use of different boundary conditions – concentration, or flux – produces varying response times, with the latter depending directly upon pulse duration. With pulses, the sometimes very different transient approach to equilibrium in various parts of the ocean generates event identification problems.National Science Foundation (U.S.) (Grant OCE-0824783)United States. National Aeronautics and Space Administration (Award NNX08AF09G