Changes in southern ocean ventilation inferred from repeat hydrographies: a maximum entropy approach
This thesis investigates the ventilation of the Southern Ocean in terms of its state in the early 1990s, its decadal changes from the 1990s to the early 2000s, and the implications of these changes for anthropogenic carbon (CANT) storage. A maximum entropy (ME) approach is used to deconvolve tracer...
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UNSW Sydney
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Online Access: | https://dx.doi.org/10.26190/unsworks/2802 http://hdl.handle.net/1959.4/54814 |
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ftdatacite:10.26190/unsworks/2802 2023-05-15T13:49:35+02:00 Changes in southern ocean ventilation inferred from repeat hydrographies: a maximum entropy approach Ting, Yu-Heng 2015 https://dx.doi.org/10.26190/unsworks/2802 http://hdl.handle.net/1959.4/54814 unknown UNSW Sydney https://creativecommons.org/licenses/by-nc-nd/3.0/au/ cc by-nc-nd 3.0 CC-BY-NC-ND Decadal change Southern Ocean Ventilation Maximum entropy Tracers Dissertation thesis master thesis Thesis 2015 ftdatacite https://doi.org/10.26190/unsworks/2802 2022-04-01T18:46:08Z This thesis investigates the ventilation of the Southern Ocean in terms of its state in the early 1990s, its decadal changes from the 1990s to the early 2000s, and the implications of these changes for anthropogenic carbon (CANT) storage. A maximum entropy (ME) approach is used to deconvolve tracer measurements to estimate the boundary propagator, which is the joint distribution of the locations and times since last ventilation. We use Southern Ocean data from five meridional repeat hydrography sections (P16, P18, A16, I8S/I9N and S3) of the World Ocean Circulation Experiment and the Climate Variability and Predictability project for CFC-11, CFC-12 temperature, salinity, oxygen, and phosphate, as well as data from the Global Ocean Data Analysis Project (GLODAP) for radiocarbon, combined with surface histories derived from atmospheric CFC-11 and CFC-12 measurements and the World Ocean Atlas and GLODAP databases. We quantify Southern Ocean ventilation in terms of the water-mass fraction older than 30 years, the fractions of water last ventilated in specific regions that tile the global ocean surface, the global and regional mean transit times, and the width-to-mean ratio of the global transit-time distribution (TTD). By independently deconvolving the original and repeat hydrographies for the boundary propagator, we find that Circumpolar Deep Water (CDW) has become older with a narrower TTD and an increased fraction last ventilated in the North Atlantic. Subantarctic Mode Water (SAMW) has become younger with a broader TTD and an increased fraction last ventilated in the Southern Ocean. Antarctic Bottom Water (AABW) has become younger. The inferred decadal changes in ventilation are consistent with increased upwelling of CDW and enhanced SAMW formation driven by strengthened mid-latitude westerly winds. The inferred boundary propagators are used to propagate CANT into the ocean interior assuming constant disequilibrium. We estimate that the section-averaged water-column CANT storage per unit area has increased by 0.56+/-0.02 mol/m2/yr in the 60S-20S latitude strip along the sections. The changes in CANT storage due to changes in ventilation correspond to a pronounced increase of CANT in SAMW. There are no significant changes in CANT for CDW due to changes in ventilation. The net effect of the changes in ventilation contributes 0.08+/-0.02 mol/m2/yr to the CANT storage in the Southern Ocean. Master Thesis Antarc* Antarctic North Atlantic Southern Ocean DataCite Metadata Store (German National Library of Science and Technology) Antarctic Southern Ocean |
institution |
Open Polar |
collection |
DataCite Metadata Store (German National Library of Science and Technology) |
op_collection_id |
ftdatacite |
language |
unknown |
topic |
Decadal change Southern Ocean Ventilation Maximum entropy Tracers |
spellingShingle |
Decadal change Southern Ocean Ventilation Maximum entropy Tracers Ting, Yu-Heng Changes in southern ocean ventilation inferred from repeat hydrographies: a maximum entropy approach |
topic_facet |
Decadal change Southern Ocean Ventilation Maximum entropy Tracers |
description |
This thesis investigates the ventilation of the Southern Ocean in terms of its state in the early 1990s, its decadal changes from the 1990s to the early 2000s, and the implications of these changes for anthropogenic carbon (CANT) storage. A maximum entropy (ME) approach is used to deconvolve tracer measurements to estimate the boundary propagator, which is the joint distribution of the locations and times since last ventilation. We use Southern Ocean data from five meridional repeat hydrography sections (P16, P18, A16, I8S/I9N and S3) of the World Ocean Circulation Experiment and the Climate Variability and Predictability project for CFC-11, CFC-12 temperature, salinity, oxygen, and phosphate, as well as data from the Global Ocean Data Analysis Project (GLODAP) for radiocarbon, combined with surface histories derived from atmospheric CFC-11 and CFC-12 measurements and the World Ocean Atlas and GLODAP databases. We quantify Southern Ocean ventilation in terms of the water-mass fraction older than 30 years, the fractions of water last ventilated in specific regions that tile the global ocean surface, the global and regional mean transit times, and the width-to-mean ratio of the global transit-time distribution (TTD). By independently deconvolving the original and repeat hydrographies for the boundary propagator, we find that Circumpolar Deep Water (CDW) has become older with a narrower TTD and an increased fraction last ventilated in the North Atlantic. Subantarctic Mode Water (SAMW) has become younger with a broader TTD and an increased fraction last ventilated in the Southern Ocean. Antarctic Bottom Water (AABW) has become younger. The inferred decadal changes in ventilation are consistent with increased upwelling of CDW and enhanced SAMW formation driven by strengthened mid-latitude westerly winds. The inferred boundary propagators are used to propagate CANT into the ocean interior assuming constant disequilibrium. We estimate that the section-averaged water-column CANT storage per unit area has increased by 0.56+/-0.02 mol/m2/yr in the 60S-20S latitude strip along the sections. The changes in CANT storage due to changes in ventilation correspond to a pronounced increase of CANT in SAMW. There are no significant changes in CANT for CDW due to changes in ventilation. The net effect of the changes in ventilation contributes 0.08+/-0.02 mol/m2/yr to the CANT storage in the Southern Ocean. |
format |
Master Thesis |
author |
Ting, Yu-Heng |
author_facet |
Ting, Yu-Heng |
author_sort |
Ting, Yu-Heng |
title |
Changes in southern ocean ventilation inferred from repeat hydrographies: a maximum entropy approach |
title_short |
Changes in southern ocean ventilation inferred from repeat hydrographies: a maximum entropy approach |
title_full |
Changes in southern ocean ventilation inferred from repeat hydrographies: a maximum entropy approach |
title_fullStr |
Changes in southern ocean ventilation inferred from repeat hydrographies: a maximum entropy approach |
title_full_unstemmed |
Changes in southern ocean ventilation inferred from repeat hydrographies: a maximum entropy approach |
title_sort |
changes in southern ocean ventilation inferred from repeat hydrographies: a maximum entropy approach |
publisher |
UNSW Sydney |
publishDate |
2015 |
url |
https://dx.doi.org/10.26190/unsworks/2802 http://hdl.handle.net/1959.4/54814 |
geographic |
Antarctic Southern Ocean |
geographic_facet |
Antarctic Southern Ocean |
genre |
Antarc* Antarctic North Atlantic Southern Ocean |
genre_facet |
Antarc* Antarctic North Atlantic Southern Ocean |
op_rights |
https://creativecommons.org/licenses/by-nc-nd/3.0/au/ cc by-nc-nd 3.0 |
op_rightsnorm |
CC-BY-NC-ND |
op_doi |
https://doi.org/10.26190/unsworks/2802 |
_version_ |
1766251833668403200 |