The diffusive ocean conveyor

Mark Holzer,François W. Primeau

doi:10.1029/2006gl026232

Mark Holzer, François W. Primeau

Open Access

https://doi.org/10.1029/2006gl026232

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Abstract

We use a novel path‐density transport diagnostic to trace out the deep branch of the ocean conveyor in a global circulation model. Our results suggest that the majority of the world's deep water is not transported back to the surface along the current systems of the standard great ocean conveyor (GOC). Standard GOC routes are evident only for waters with interior residence times, τ, less than about a thousand years, accounting for less than a quarter of the ventilation‐to‐re‐exposure flux. Waters with longer τ are spread across the deep oceans by the “diffusive conveyor” and, by τ ∼ 3000 years, organized into a characteristic deep‐North‐Pacific pattern that is dominated by eddy diffusion. The observed depletion of oxygen and 14C in the deep N Pacific is consistent with a diffusive conveyor and should not be interpreted as evidence of an advective terminus of the GOC deep branch.

Highlights

[2] Broecker’s great ocean conveyor (GOC) [Broecker, 1991] has become a paradigm for oceanic interbasin transport that is often used to interpret the global patterns of long-lived tracers
We find that only the fast paths, accounting for less than half the flux of water connecting the N Atlantic (NA) formation region to the Tropical Eastern Pacific (TEP) surface, follow routes expected from the traditional GOC picture
[7] For the general case where eddy motion imparts a random diffusive component to the particle motion, and different parts of the conveyor run at different speeds, one can characterize the conveyor by the local volume fraction h(r, t) dt of fluid elements that will eventually make it to B after a transit time, and residence time on the HOLZER AND PRIMEAU: DIFFUSIVE OCEAN CONVEYOR

Summary

The diffusive ocean conveyor

Received 7 March 2006; revised 6 June 2006; accepted 9 June 2006; published 29 July 2006. Our results suggest that the majority of the world’s deep water is not transported back to the surface along the current systems of the standard great ocean conveyor (GOC). Standard GOC routes are evident only for waters with interior residence times, t, less than about a thousand years, accounting for less than a quarter of the ventilation-to-re-exposure flux. Waters with longer t are spread across the deep oceans by the ‘‘diffusive conveyor’’ and, by t $ 3000 years, organized into a characteristic deep-North-Pacific pattern that is dominated by eddy diffusion. The observed depletion of oxygen and 14C in the deep N Pacific is consistent with a diffusive conveyor and should not be interpreted as evidence of an advective terminus of the GOC deep branch.

Introduction

Results

Conclusions