Publication Abstract

Rapid Freshening of the Deep North Atlantic over the past Four Decades

R.R. Dickson, I. Yashayaev, J. Meincke, W.R. Turrell, S.R. Dye and J. Holfort

The overflow and descent of cold dense water from the sills of the Denmark Strait and Faroe-Shetland Channel is the principal means by which the deep ocean is ventilated and so is a key element of the global thermohaline circulation (THC). Most projections of greenhouse gas induced climate change anticipate a weakening of the THC in the North Atlantic in response to increased freshening and warming in the subpolar seas and the supposition is that this climate signal will be transferred to the deep ocean via the two overflows. Nevertheless, these simulations do not yet deal adequately with many of the mechanisms believed to control the THC, and our observations cannot yet detect whether the rate of the ocean’s overturning circulation is changing. Here, complementing recent evidence that overflow transport may be slackening, we show that the entire system of overflow and entrainment that ventilates the deep Atlantic has steadily changed in character over the past four decades, resulting in a sustained freshening of the deep and abyssal waters of the Northern North Atlantic --- the ‘headwaters’ of the global thermohaline circulation.

Reference:

R.R. Dickson*, I. Yashayaev, J. Meincke, W.R. Turrell, S.R. Dye* and J. Holfort  (2002) Rapid Freshening of the Deep North Atlantic over the past Four Decades. Nature, 416(6883): 832-837