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Anomalous DOC Signatures Reveal Iron Control on Export Dynamics in the Pacific Southern OceanHere we shed light on two mechanisms that stimulate deep particle export via upper-ocean iron fertilization in the Southern Ocean: deep frontal mixing and melting of sea ice. We present data collected a decade apart in the Pacific sector of the Southern Ocean when, serendipitously, seasonal Antarctic ice melt was anomalously low (2008) and anomalously high (2017). In 2008, the low ice melt year, we concluded that vertical mixing of iron into the euphotic zone via deep-mixing fronts was the primary stimulant of export that reached depths of ~1500 meters. This process was evidenced by localized enhancements of dissolved organic carbon (DOC) concentrations up to 4 μmol C kg-1 beneath seven branches of fronts embedded within the Antarctic Circumpolar Current (ACC). We used these enhanced DOC concentrations in the bathypelagic as primary indications of the depths and locations of recent export, as it is a logical residue of such. In 2017, the year in which sea ice melt was anomalously high, we concluded that the main driver of a widespread export event to the seafloor was the lateral influx of iron within the melt. Indications of this event included substantial enhancements of DOC concentrations (2 - 31 6 μmol C kg-1), elevated beam attenuation, and enhanced surface iron concentrations associated with a layer of low salinity water at a nearby station. Further, significant deficits of upper ocean silicic acid during the 2017 occupation indicated that deep export was likely stimulated by an iron-fueled diatom bloom. This analysis highlights the impact of iron supplied from frontal vertical mixing and sea ice melt on export and ultimately for long-term carbon sequestration in the Southern Ocean, as well as the utility of deep DOC enrichments as signatures of particle export. Understanding the impact that ice melt events have on carbon export is crucial given that anomalous events are occurring more often as our climate changes.
Document ID
20230001312
Acquisition Source
Goddard Space Flight Center
Document Type
Accepted Manuscript (Version with final changes)
Authors
Chelsea N. Lopez
(Science Systems and Applications, Inc)
Dennis A. Hansell
(University of Miami Coral Gables, Florida, United States)
Date Acquired
January 26, 2023
Publication Date
February 20, 2023
Publication Information
Publication: Frontiers in Marine Science
Publisher: Frontiers Media
Volume: 10
e-ISSN: 2296-7745
Subject Category
Oceanography
Funding Number(s)
CONTRACT_GRANT: 80GSFC20C0044
CONTRACT_GRANT: OCE 2023500
CONTRACT_GRANT: 80NSSC18K0437
Distribution Limits
Public
Copyright
Portions of document may include copyright protected material.
Technical Review
External Peer Committee
Keywords
Dissolved Organic Carbon
Particle Export
Iron Limitation
Southern Ocean
Antarctic Circumpolar Current
Sea Ice Melt
Pacific Southern Ocean
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