Showing papers on "World Ocean Atlas published in 2000"

An optimal definition for ocean mixed layer depth

Abstract: A new method is introduced for determining ocean isothermal layer depth (ILD) from temperature profiles and ocean mixed layer depth (MLD) from density profiles that can be applied in all regions of the world's oceans. This method can accommodate not only in situ data but also climatological data sets that typically have much lower vertical resolution. The sensitivity of the ILD and MLD to the temperature difference criteria used in the surface layer depth definition is discussed by using temperature and density data, respectively: (1) from 11 ocean weather stations in the northeast Pacific and (2) from the World Ocean Atlas 1994. Using these two data sets, a detailed statistical error analysis is presented for the ILD and MLD estimation by season. MLD variations with location due to temperature and salinity are properly accounted for in the defining density (Δσt) criterion. Overall, the optimal estimate of turbulent mixing penetration is obtained using a MLD definition of ΔT =0.8°0, although in the northeast Pacific region the optimal MLD criterion is found to vary seasonally. The method is shown to produce layer depths that are accurate to within 20 m or better in 85% or more of the cases. The MLD definition presented in this investigation accurately represents the depth to which turbulent mixing has penetrated and would be a useful aid for validation of one-dimensional bulk mixed layer models and ocean general circulation models with an embedded mixed layer.

A global monthly climatology of phosphate, nitrate, and silicate in the upper ocean: Spring‐summer export production and shallow remineralization

Abstract: We have created monthly climatologies of nutrients in the upper 500 m of the ocean using the 1998 release of the World Ocean Atlas from the Ocean Climate Laboratory at the National Oceanographic Data Center. The data processing is similar to that used by Najjar and Keeling [1997] to create an oxygen climatology. The spatial extrapolation of the nutrients exploits regional relationships between nutrients and temperature in the ocean. The annual mean horizontal and vertical distributions of the nutrients follow the large scale patterns of oceanic circulation as previously reported in the literature. Surface seasonal variations of nutrients are high in the high latitudes and some restricted upwelling areas, whereas in the subtropical oligotrophic gyres nutrients are low all year. Surface seasonal variations are characterized by high values in winter and low values in summer, consistent with the dominance of entrainment during the winter and biological production during the summer. Good agreement is found between the climatologies and the limited reports of seasonal nutrient variations in the literature. Weaker seasonal variations of opposite phasing are found below roughly 100 m and likely reflect the dominance of remineralization during the summer and ventilation during the winter. Spring-summer export production derived from the seasonal nutrient drawdown in the upper 100 m is 4.2±0.6 Tmol P, 59±8 Tmol N, and 70±15 Tmol Si. The N:P drawdown ratio is, within the error, in agreement with the traditional value of 16. Similarly, the Si:N drawdown ratio is in agreement with the value of 1 expected for diatom growth in unstressed conditions. The export of organic carbon estimated from the phosphate drawdown is 5.3±0.8 Gt C. The shallow remineralization inferred from seasonal phosphate variation between 100 and 200 m is 2.6±1.1 Gt C. The carbon and silica fluxes, considering that they are lower bounds on global export production because they do not capture the production signal in advectively dominated systems, are in reasonable agreement with other large scale estimates of organic carbon and silica export. The computed f ratio (using satellite-based estimates of primary production) and the ratio of shallow aphotic zone remineralization to new production tend to increase with increasing latitude, supporting an increase in respiration with temperature, as suggested in recent studies.

Seasonal Variations of Water Masses and Sea Level in the Southwestern Part of the Okhotsk Sea

Abstract: A new grid data set for the southwestern part of the Okhotsk Sea was compiled by using all the available hydrographic data from the Japan Oceanographic Data Center, World Ocean Atlas 1994 and the other additional data sources with the resolution of about 10 km. We examine the seasonal variations of areas and volumes of Soya Warm Current Water (SWCW) and East Sakhalin Current Water (ESCW) and show that the exchanges of these water masses drastically occur in April and November. The peculiar variation of sea level in this region is also related with the water mass exchange. Sea level at the Hokkaido coast of the Okhotsk Sea reaches its minimum in April about two months later than in the case of ordinary mid-latitude ocean, and its maximum in December besides the summer peak. The winter peak of sea level in December is caused by the advent of fresh and cold ESCW which is accumulated at the subsurface layers (20–150 m) through the Ekman convergence by the prevailing northerly wind. Sea level minimum in April is caused by the release of the convergence and the recovery of dense SWCW that is saline and much colder than that in summer.

A Comparison Between the World Ocean Atlas and Hydrobase Climatology

Abstract: The newly developed 1/4 degrees World Ocean Atlas (WOA, Boyer and Levitus, 1998) is compared with the 1 degree WOA (Levitus et al., 1994) over the North Atlantic Ocean.

Predicting acoustic effects of internal waves from the basic climatology of the world ocean

Abstract: Internal waves of a given strength will produce acoustic effects that vary from water mass to water mass. Presented here is a means of predicting the strength of acoustic fluctuations due to internal waves, given the basic climatology, that is, measurements of depth, temperature, and salinity of an oceanic region. An acoustic fluctuation strength parameter F is defined as the ratio of the fractional potential sound-speed change to the fractional potential-density change. Here F is calculated at three depth levels (275, 550, and 850 m), on a one-degree grid of latitude and longitude, using NODC/OCL's World Ocean Atlas 1994. Representative values of F are presented for 15 upper water masses that range from F = 5 in the North Pacific to F = 34 in the North Atlantic, with a typical value for most of the upper waters being F = 15. Results for two depth levels within 12 intermediate water masses range from F = 7 in the North Pacific to F = 62 in the North Atlantic, with a typical value of F = 20, although there is considerable variation. In general, F exhibits higher values in the Atlantic Basin than in the Indian or Pacific, and has a maximum at 550 m. The main use of F will be the prediction of travel-time fluctuations in acoustic propagation experiments, which will be proportional to the value of F, given a universal strength of internal waves.