Decadal changes in Southern Ocean ventilation inferred from deconvolutions of repeat hydrographies

Abstract

AbstractChanges in Southern Ocean ventilation imprint on dissolved gases, nutrients, radiocarbon, temperature, and salinity. We deconvolve tracer measurements for the distribution, , of times and locations of last ventilation using a maximum‐entropy approach. Decadal changes of are quantified by deconvolving hydrographies measured during the early 1990s and again some 15 years later. Our analysis reveals coherent changes across the five meridional sections analyzed: The fraction of water younger than 30 years decreased by ∼20% per decade south of 40°S in circumpolar deep water (CDW) and increased by ∼10% per decade north of ∼40°S in subantarctic mode water (SAMW). Ventilation locations shifted, with more water south of 40°S being ventilated north of the subantarctic front. These ventilation changes impacted CFC uptake, with concentrations south of 40°S less than (and north of 40°S higher than) expected for steady flow. The inferred changes imply increased SAMW formation and CDW upwelling consistent with strengthened westerly winds.