65
The discussion of today’s climate and its past and potential future changes is often framed in the context of the ocean’s thermohaline circulation. Widespread consequences are ascribed to its shutdown and acceleration—a deus ex machina for climate change. But what is meant by this term? In interdisc...
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Text |
| Language: | English |
| Subjects: | |
| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.390.1308 http://ocean.mit.edu/~cwunsch/papersonline/thermohaline.pdf |
| Summary: | The discussion of today’s climate and its past and potential future changes is often framed in the context of the ocean’s thermohaline circulation. Widespread consequences are ascribed to its shutdown and acceleration—a deus ex machina for climate change. But what is meant by this term? In interdisciplinary fields such as climate change, terminological clarity is of the essence; otherwise, what everyone thinks they understand may in fact be a muddle of mutual misunderstanding. Only if one can define the circulation, can its controlling factors be sensibly discussed. A reading of the literature on climate and the ocean suggests at least seven different, and inconsistent, definitions of the term “thermohaline circulation”: 1) the circulation of mass, heat, and salt; 2) the abyssal circulation; 3) the meridional overturning circulation of mass; 4) the global conveyor, that is, the diffusely defined gross property movements in the ocean that together carry heat and moisture from low to high latitudes; 5) the circulation driven by surface buoyancy forcing; 6) the circulation driven by density and/or pressure differences in the deep ocean; and 7) the net export, by the North Atlantic, of a chemical substance such as the element protactinium. These different usages present important conceptual issues. For example, the deep ocean is in a near-equilibrium state, and it is not possible, without an intricate calculation, to determine if the density/ pressure differences drive the flow field, or the reverse. Some authors claim to be able to separate the fraction of the flow derived from density field gradients from that caused by the wind field (definition 6). But the density gradients are set up primarily by the wind. For present purposes, I define the ocean circulation as that of its mass. The fluxes of |
|---|