Abyssal teleconnections: Interactive dynamics of the deep ocean circulation
Abstract A teleconnective linkage between two abyssal water masses consists of one or more zones of interaction, arranged sequentially in space and time. The properties, spatial extent, and advective nature of one of these water masses are directly influenced by the presence of the other via the zones of interaction. The sequence of components in the linkage may in some instances be configured linearly and respond in an irreversible fashion. In other instances the linkage is not unidirectional, but may include one or more feedback “loops” representing the dependence of each water mass upon the properties and extent of the other. Three types of water mass interaction are represented in the modern oceans; these are designated as: (1) re-inforcing, (2) lateral blocking/re-direction, and (3) wedging. The criteria for discriminating between these types are geometrical, yet the physical processes and rates of interaction may be distinguishable between, and perhaps characteristics of, these different configurations. Regions of water mass interaction are marked by sharp gradients of water column properties, each of which is spatially restricted to a narrow interval of the overall mixing zone. Sediment characteristics exhibit a similar pattern: There is a broad transition zone within which each geological gradient is restricted to a relatively narrow interval. One must distinguish between sediment indicators which reflect water properties and those which reflect water column advection, and avoid inferring one type of waters characteristic from geological indices which are inappropriate for identifying such characteristics. It is not possible to specify a priori all of the components of a teleconnection linkage. We can identify critical zones of interaction, and search for evidence of “threshold events” which contributed to the initiation or the breaking of a particular linkage. In order to establish the spatial and temporal sequence of components in a complex linkage, we must identify the frequency response and phase response spectra in high-resolution time series of appropriate paleocenographic indices at key locations.