Tracers, time scales, and the thermohaline circulation: The lower limb in the North Atlantic Ocean

Abstract

This paper reviews the contributions of transient tracer research to our understanding of the lower limb of the thermohaline circulation in the North Atlantic Ocean. The review is limited geographically to the North Atlantic because of its importance for decadal scale climate variability. The tracers reviewed are the transient tracers of anthropogenic origin that give decadal time scale information, the chlorofluorocarbons (CFCs) and tritium/3He. The emphasis is on work by United States (US) investigators from 1991–94. Also included are some non‐US and earlier contributions as they are linked to the recent work and have not been reviewed in this publication before.

On the world ocean circulation. Volume I, Some global features/North Atlantic circulation

“…The flow of NADW (that is above LNADW, 7. The NADW Meridional Cell and Deep Western Boundary Current above about (J = 2°C) in a DWBC from formation region to low latitudes along the continental slope (Figure 1-93) has been nicely documented by Pickart (1992), Pickart and Hogg (1989), Pickart and Watts (1990); see also , who observed igure 1-92: The path of the DWBC, partly according to Fine (1995), and including my take on recent ideas by McCartney (personal communication, 1996) Atlantic is a topic of considerable interest (Thompson and Schmitz, 1989;Pickart and Smethie, 1993;Pickart, 1994a, b;Spall, 1996a, b). One area of particular emphasis has been with regard to influences on the path of the Gulf Stream, especially separation.…”

“…This is an oversimplifed representation of:: complex of regjon::l processes over the gloh::l oce::n, ::lthongh the foni::-tion process occurs predominantly in the northern North Atlantic. There is a recent review article on NADW (Fine, 1995) (Pickart, 1994a, b;Pickart and Smethie, 1993;Spall, 1996a, b). The flow of NADW (that is above LNADW, 7.…”

Denitrification and N2 fixation in the Pacific Ocean

“…The age of a water mass, defined as the time elapsed since it was at the surface, is estimated by matching CFC-12 concentrations to the atmospheric history of CFC-12 partial pressure (see Fine [1995] for a review). Undersaturation of the water parcel with respect to the atmosphere at the time of water parcel isolation will lead to an overestimate of the age.…”

Chaotic advection, mixing, and property exchange in three-dimensional ocean eddies and gyres

“…I begin with a tracer advection-diffusion equation assuming no sources: 18) where is the tracer concentration, ⃗ is the fluid velocity, and is the diffusivity without stirring.…”

“…This reforming gyre is warmer and fresher than its surroundings, with a clear connection to the Strait of Gibraltar visible when examining a series of subsurface images from this gyre formation (figures [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]…”