Modification of North Atlantic Deep Water by Pacific/Upper Circumpolar
Deep Water in the Argentine Basin
Abstract
Much of the salty, high oxygen North Atlantic Deep Water (NADW) leaving
the Atlantic flows through the Argentine Basin, where it is diluted by
fresher, low oxygen Circumpolar Deep Water (CDW). This mixing of deep
water masses is often overlooked in the zonally-averaged description of
the overturning circulation. Here, we show that most of the mixing
occurs along the western boundary: (i) extreme, isolated
oxygen/temperature anomalies recorded by three autonomous biogeochemical
floats suggest that subsurface eddies can inject relatively unmodified
CDW far into the northwestern Argentine Basin, and (ii) moderate,
numerous temperature/salinity anomalies indicate a mixing zone from Rio
Grande Rise to the Malvinas Current. This western eddy pathway shortcuts
the gyre-scale cyclonic route for CDW inferred from previous studies.
Significantly, CDW dilution of NADW affects the properties of deep
waters that upwell in the Southern Ocean, and hence the connection
between Northern and Southern Hemisphere polar climates.