Marine aquaculture presents an opportunity for increasing seafood production in the face of growing demand for marine protein and limited scope for expanding wild fishery harvests. However, the global capacity for increased aquaculture production from the ocean and the relative productivity potential across countries are unknown. Here, we map the biological production potential for marine aquaculture across the globe using an innovative approach that draws from physiology, allometry and growth theory. Even after applying substantial constraints based on existing ocean uses and limitations, we find vast areas in nearly every coastal country that are suitable for aquaculture. The development potential far exceeds the space required to meet foreseeable seafood demand; indeed, the current total landings of all wild-capture fisheries could be produced using less than 0.015% of the global ocean area. This analysis demonstrates that suitable space is unlikely to limit marine aquaculture development and highlights the role that other factors, such as economics and governance, play in shaping growth trajectories. We suggest that the vast amount of space suitable for marine aquaculture presents an opportunity for countries to develop aquaculture in a way that aligns with their economic, environmental and social objectives.

We have rederived the periodic variations of the earth's rotation due to the tidal deformation of the earth by the sun and moon and included all terms with amplitudes ≥0.002 milliseconds (1 mm). This series applies to the mantle (plus crust) and oceans, which rotate together for characteristic tidal periods. The parameter which scales the rotational series is k/C, where k is that fraction of the Love number which causes the tidal variation in the moment of inertia of the coupled mantle and oceans while C is the dimensionless polar moment of inertia of the coupled units. If the whole earth (minus oceans) were coupled rotationally, then k = 0.30 and C = 0.33. Ocean tides increase k by 0.04. Decoupling of the fluid core from the mantle decreases k by 0.06 while C = Cmantle = 0.29, since neither pressure, viscous, nor hydromagnetic coupling locks the fluid to the mantle for periods less than 5 to 25 years. From the analysis of lunar laser ranging data we find that k/C at monthly and fortnightly frequencies equals 0.99 ±0.15 and 0.99 ± 0.20 as compared with a theoretical value of 0.94 ± 0.04. In addition, we have estimated theoretically the effects of ocean tides on earth rotation, nutation and polar motion using models based on the Laplace tidal equations.

Abstract. Over 20 global ocean tide models have been developed since 1994, primarily as a consequence of analysis of the precise altimetric measurements from TOPEX/POSEIDON and as a result of parallel developments in numerical tidal modeling and data assimilation. This paper provides an accuracy assessment of 10 such tide models and discusses their benefits in many fields including geodesy, oceanography, and geophysics. A variety of tests indicate that all these tide models agree within 2-3 cm in the deep ocean, and they represent a significant improvement over the classical Schwiderski 1980 model by approximately 5 cm rms. As a result, two tide models were selected for the reprocessing of TOPEX/POSEIDON Geophysical Data Records in late 1995. Current ocean tide models allow an improved observation of deep ocean surface dynamic topography using satellite altimetry. Other significant contributions include theft applications in an improved orbit computation for TOPEX/POSEIDON and other geodetic satellites, to yield accurate predictions of Earth rotation excitations and improved estimates of ocean loading corrections for geodetic observatories, and to allow better separation of astronomical tides from phenomena with meteorological and geophysical origins. The largest differences between these tide models occur in shallow waters, indicating that the current models are still problematic in these areas. Future improvement of global tide models is anticipated with additional high-quality altimeter data and with advances in numerical techniques to assimilate data into high-resolution hydrodynamic models.

The choice of an orbit for satellite altimetric studies of the ocean's circulation and tides requires an understanding of the orbital characteristics that influence the accuracy of the satellite's measurements of sea level and the temporal and spatial distribution of the measurements. Three orbital parameters determine the temporal and spatial sampling characteristics of the satellite: the orbital altitude, the inclination of the orbit, and the repetition period. The eccentricity of the chosen orbit should be less than 0.001 to minimize altimeter errors caused by uncertainty in determining the time of each altimeter measurement and to maintain the rate of height variation over the oceans within the limits of the altimeter tracker. The choice of the satellite's orbital altitude is constrained by the influences of atmospheric drag and errors in models of the gravity field, which decrease with height, and the required complexity of the altimeter (e.g., the power and/or antenna size required) and the effect on satellite systems of radiation from Earth's radiation belts, which increase with height. The choice of inclination is constrained by a desire to measure sea level over all the ocean, by the requirement that the acute angle between intersections of the subsatellite track be as large as possible, and by the time phasing of the repeat of the satellite's ground track as a function of inclination, which determines the aliased frequencies of the measurements of the oceanic tides. The choice of repetition period is constrained by tradeoffs between temporal and spatial coverage and by the aliasing of tidal constituents. Combining the above constraints leads to a set of orbits in a narrow range of altitude and inclination, called here the "Topex/Poseidon window." This window extends from 1100 to 1500 km altitude and 62 ø to 66 ø inclination for a 10-day repeat period and consists of three subwindows following lines of equal orbit plane precession. There are four choices of orbits within these subwindows that overtly the planned calibration sites at Bermuda and Dakar. These are at 64. 80 ø and 1335 km, 62.01 ø and 1252 km, 65.84 ø and 1255 km, and 62.69 ø and 1173 km. These choices have a minimum separation between the aliased frequencies of the eight largest diurnal and semidiurnal tides of one cycle per 4.71 years, one cycle per 4.86 years, one cycle per 4.87 years, and one cycle per 4.27 years, respectively. Thus there will be less than one cycle separation over the nominal (3 years) mission.Of these four choices, the first at 64.8 ø and 1335 km is preferable, because it is less sensitive to error in estimating the upcoming solar cycle (which will be a maximum during the mission), and because it is more nearly centered in terms of inclination than the other choices. For other calibration sites, other choices would have to be made. Additional work, beyond the scope of this paper, will also be necessary to determine if the Topex/Poseidon mission requires a frozen orbit (i.e., an orbit for which there are no long-term va...