And Antarctic Bottom Water Research Articles

Equilibrium Response of Ocean Deep-Water Circulation to Variations in Ekman Pumping and Deep-Water Sources

Abstract A multilayer ocean model that is physically simple and computationally efficient is developed for studies of competition and interaction among deep-water sources in determining ocean circulation. The model is essentially geostrophic and hydrostatic in the ocean interior with Rayleigh friction added in boundary-layer and equatorial regions. A stably stratified density structure is specified at static equilibrium, and cross-isopycnal mixing is parameterized as a diffusive flux. The model is forced by latitudinally varying Ekman pumping velocities at the base of the ocean surface Ekman layer and localized deep-water sources. A four-layer version of the model has been run in a rectangular basin with 5000-m depth, extending from 65°S to 65°N latitude and covering 70 degrees of longitude. The four layers mimic the major water masses observed in the Atlantic Ocean: thermocline water, intermediate water, North Atlantic Deep Water (NADW), and Antarctic Bottom Water (AABW). For forcing corresponding to the...

Miocene to Recent bottom water masses of the north-east Atlantic: an analysis of benthic foraminifera

Summary The modern benthic foraminifera of the north-east Atlantic Ocean show a distribution pattern related to bottom water masses. Varimax factor analysis of data from depths > 2000 m gives factors which correlate with North-East Atlantic Deep Water (NEADW), North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW); a fourth factor corresponds with the basal part of the Mediterranean Water. Miocene to Pleistocene benthic foraminiferal assemblages have been compared with the modern assemblages. On the assumption that species have not changed their environmental preferences through time, the fossil assemblages can be used to infer the past existence of water masses similar to those of today. The results presented here show that in the late Miocene, AABW penetrated to the southern flank of Rockall Plateau at the time of build-up of the East Antarctic ice sheet. During the early Pliocene the rate of production of NADW increased, perhaps as a result of a decrease in size of the Antarctic ice sheet, which in turn led to the southward retreat of the limit of penetration of AABW. Throughout much of the Pleistocene, as now, AABW has not penetrated north of the Azores Ridge. NEADW was the most extensive bottom water mass in the late Pliocene and Pleistocene.

Antarctic circulation

The circulation of antarctic waters is responsible for massive interoceanic water exchange and for what may be thought of as the ‘airing out’ of abyssal waters by exposing large quantities of these waters to the antarctic atmosphere. Estimates of zonal and meridional volume transports have been made, in addition to further investigations of water mass distribution and alteration of the circumpolar deep water (CDW) to antarctic intermediate water (AAIW) and antarctic bottom water (AABW).