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Physical Processes Leading to Export of Fixed Carbon Out of the Surface Ocean


Erickson, Zachary K. (2019) Physical Processes Leading to Export of Fixed Carbon Out of the Surface Ocean. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/XDX7-8J36.


The ocean sequesters carbon on long time scales by depositing it deep in the ocean, where it is no longer in contact with the atmosphere. This sequestration is also termed "carbon export", and is accomplished via a vertical flux of carbon into the interior of the ocean. Marine photosynthesis by phytoplankton, which consume carbon dioxide dissolved in the surface ocean and are transported to depth to be eventually remineralized or form sediments at the ocean surface, is a key component of this flux (the biological pump). This mechanism is primarily thought to occur via sinking of particulates. However, research over the past few decades has highlighted the role of instabilities at the "submesoscale", or 0.1--20 km, to induce large, O(100 m day-1) vertical velocities in the ocean. These vertical velocities can potentially subduct carbon from the surface ocean into the interior, where it would contribute to export. Observations of the ocean are, however, rarely made at scales which would detect these submesoscale instabilities. In this thesis, I use in situ observations from autonomous underwater vehicles, Seagliders, which make measurements in the upper 1000 m of the water column at horizontal scales of 1-3 km, to understand when and where submesoscale instabilities are present, and the extent to which they act to transport biologically fixed carbon out of the surface ocean. Three different types of instabilities are active in the surface mixed layer: baroclinic, gravitational, and symmetric. Each of these has potential to subduct material below the mixed layer; however, these instabilities are generally strongest during the winter, when biological production is at its minimum. An interesting exception is in southern Drake Passage, where interactions between the intense frontal system and the continental shelf result in subduction of water masses off the continental shelf during summer, when phytoplankton are photosynthesizing. In general, however, carbon export via submesoscale instabilities is expected to be largest during spring, when phytoplankton become more productive but conditions can still be ripe for submesoscale subduction. Scaling up these observations to the global ocean system is difficult because in situ observations at submesoscales are sparse. This thesis explores the ability of surface flux measurements, from reanalysis products and remote sensing measurements, to accurately depict carbon export via subduction processes by modeling the water profile in a one-dimensional model following Lagrangian floats in the ocean. This approach holds promise to advance the ultimate goal of determining the global effect of submesoscale-driven carbon export.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:oceanography ; carbon cycle
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Environmental Science and Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Thompson, Andrew F.
Thesis Committee:
  • Adkins, Jess F. (chair)
  • Frankenberg, Christian
  • Gierach, Michelle Marie
  • Thompson, Andrew F.
Defense Date:29 May 2019
Funding AgencyGrant Number
David and Lucille Packard FoundationUNSPECIFIED
National Science FoundationOPP-1246460
Jet Propulsion Laboratory President's and Director's Research and Development FundUNSPECIFIED
Record Number:CaltechTHESIS:06092019-160257514
Persistent URL:
Related URLs:
URLURL TypeDescription for ch. 3 2016GL070565DOIAdapted for ch. 4
Erickson, Zachary K.0000-0002-9936-9881
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11729
Deposited By: Zachary Erickson
Deposited On:11 Jun 2019 19:07
Last Modified:28 Oct 2019 17:25

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