title: Two centuries of limited variability in subtropical North Atlantic thermocline ventilation.
abstract: Ventilation and mixing of oceanic gyres is important to ocean-atmosphere heat and gas transfer, and to mid-latitude nutrient supply. The rates of mode water formation are believed to impact climate and carbon exchange between the surface and mid-depth water over decadal periods. Here, a record of (14)C/(12)C (1780-1940), which is a proxy for vertical ocean mixing, from an annually banded coral from Bermuda, shows limited inter-annual variability and a substantial Suess Effect (the decrease in (14)C/(12)C since 1900). The Sargasso Sea mixing rates between the surface and thermocline varied minimally over the past two centuries, despite changes to mean-hemispheric climate, including the Little Ice Age and variability in the North Atlantic Oscillation. This result indicates that regional formation rates of sub-tropical mode water are stable over decades, and that anthropogenic carbon absorbed by the ocean does not return to the surface at a variable rate.
authors.affiliation: Department of Earth Sciences, University of Hong Kong, Pokfulam, Hong Kong, SAR, China. goodkin@hku.hk
authors.forename: Nathalie F
authors.initials: NF
authors.lastname: Goodkin
authors.forename: Ellen R M
authors.initials: ER
authors.lastname: Druffel
authors.forename: Konrad A
authors.initials: KA
authors.lastname: Hughen
authors.forename: Scott C
authors.initials: SC
authors.lastname: Doney