{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/274006"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/274006","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"Investigating the circulation of Southern Ocean deep water masses over the last 1.5 million years by geochemical fingerprinting of marine sediments","abstract":"The Southern Ocean (SO) is a critical component in the global ocean conveyor. As the only conduit linking the Atlantic, Indian and Pacific Oceans, as well as an important region of upwelling and water mass formation, it is thought to have played a key role in modulating Earth’s past climate. Changes in the circulation of SO deep and bottom waters over the last 1.5 million years are investigated using stable carbon isotope $δ^{13}C$ measurements made on the tests of the benthic foraminfer Cibicidoides ($δ^{13}C_{b}$), and the rare earth element concentrations and Neodymium isotope ($ɛ_{Nd}$) values of marine sediments and their authigenic ferromanganese coatings. Being a proxy for past seawater nutrient contents, $δ^{13}C_{b}$ provides important insights into both past ocean circulation and the potential storage of remineralised organic carbon within the deep ocean, while simultaneously providing information on the past ventilation state of the deep ocean interior. As seawater $ɛ_{Nd}$ remains unaffected by biological fractionation or air-sea exchange processes, reconstructions of past deep and bottom water $ɛ_{Nd}$ provides a tool with which to study past changes in the circulation and mixing of these water masses. A suite of previously published late Holocene (0-6 ka) and Last Glacial Maximum (LGM; 18-24 ka) $δ^{13}C_{b}$ data are used alongside newly acquired $δ^{13}C_{b}$ data from the Amundsen Sea in the eastern Pacific sector of the SO to investigate past changes in the pattern of circum-Antarctic seawater carbon isotope composition. The $δ^{13}C$ signature of deep and bottom waters was much more heterogenous during the LGM than the late Holocene, with negative $δ^{13}C$ excursions occurring within the Atlantic and Indian sectors of the SO below c. 2-3 km water depth. Some of this negative $δ^{13}C$ signal was advected through the SO to the Pacific sector, but this appears to have been restricted by bathymetric barriers within the SO. New $δ^{13}C_{b}$ data spanning the last 800 ka from the Amundsen Sea are presented and suggest differing modes of bottom water formation in the Atlantic vs Pacific sectors of the SO during glacial periods of the last 800 ka. An authigenic $ɛ_{Nd}$ record measured on sediments from a core located in the deep Indian Ocean is used to investigate the palaeocirculation history of modified Circumpolar Deep Water (mCDW) within the Indian Ocean during the last 1.5 million years. Shifts towards more radiogenic $ɛ_{Nd}$ values during glacial periods are interpreted as reflecting a decreased entrainment of deep waters sourced in the North Atlantic (Northern Component Water, NCW) within CDW, which led to a reduced advection of an unradiogenic $ɛ_{Nd}$ NCW signal to the core site. $ɛ_{Nd}$ and REE measurements made on sediments from two cores located on the Pacific-Antarctic Ridge in the western Pacific sector of the SO (to the north of the Ross Sea Embayment) are used to reconstruct the bottom water palaeocirculation in this region across the last 540 ka. The proportion and $ɛ_{Nd}$ signature of Ross Sea Bottom Water (RSBW) bathing these core sites has fluctuated throughout the last 540 ka. These fluctuations suggest the rate and location of bottom water formation within the Ross Sea, and the supply of terrigenous material with radiogenic $ɛ_{Nd}$ values with which to isotopically `labelled' RSBW, may have changed in the past.","abstract_html":"The Southern Ocean (SO) is a critical component in the global ocean conveyor. As the only conduit linking the Atlantic, Indian and Pacific Oceans, as well as an important region of upwelling and water mass formation, it is thought to have played a key role in modulating Earth’s past climate. Changes in the circulation of SO deep and bottom waters over the last 1.5 million years are investigated using stable carbon isotope <span class=\"etd-inline-math\">δ<sup>13</sup>C</span> measurements made on the tests of the benthic foraminfer Cibicidoides (<span class=\"etd-inline-math\">δ<sup>13</sup>C<sub>b</sub></span>), and the rare earth element concentrations and Neodymium isotope (<span class=\"etd-inline-math\">ɛ<sub>Nd</sub></span>) values of marine sediments and their authigenic ferromanganese coatings. Being a proxy for past seawater nutrient contents, <span class=\"etd-inline-math\">δ<sup>13</sup>C<sub>b</sub></span> provides important insights into both past ocean circulation and the potential storage of remineralised organic carbon within the deep ocean, while simultaneously providing information on the past ventilation state of the deep ocean interior. As seawater <span class=\"etd-inline-math\">ɛ<sub>Nd</sub></span> remains unaffected by biological fractionation or air-sea exchange processes, reconstructions of past deep and bottom water <span class=\"etd-inline-math\">ɛ<sub>Nd</sub></span> provides a tool with which to study past changes in the circulation and mixing of these water masses. A suite of previously published late Holocene (0-6 ka) and Last Glacial Maximum (LGM; 18-24 ka) <span class=\"etd-inline-math\">δ<sup>13</sup>C<sub>b</sub></span> data are used alongside newly acquired <span class=\"etd-inline-math\">δ<sup>13</sup>C<sub>b</sub></span> data from the Amundsen Sea in the eastern Pacific sector of the SO to investigate past changes in the pattern of circum-Antarctic seawater carbon isotope composition. The <span class=\"etd-inline-math\">δ<sup>13</sup>C</span> signature of deep and bottom waters was much more heterogenous during the LGM than the late Holocene, with negative <span class=\"etd-inline-math\">δ<sup>13</sup>C</span> excursions occurring within the Atlantic and Indian sectors of the SO below c. 2-3 km water depth. Some of this negative <span class=\"etd-inline-math\">δ<sup>13</sup>C</span> signal was advected through the SO to the Pacific sector, but this appears to have been restricted by bathymetric barriers within the SO. New <span class=\"etd-inline-math\">δ<sup>13</sup>C<sub>b</sub></span> data spanning the last 800 ka from the Amundsen Sea are presented and suggest differing modes of bottom water formation in the Atlantic vs Pacific sectors of the SO during glacial periods of the last 800 ka. An authigenic <span class=\"etd-inline-math\">ɛ<sub>Nd</sub></span> record measured on sediments from a core located in the deep Indian Ocean is used to investigate the palaeocirculation history of modified Circumpolar Deep Water (mCDW) within the Indian Ocean during the last 1.5 million years. Shifts towards more radiogenic <span class=\"etd-inline-math\">ɛ<sub>Nd</sub></span> values during glacial periods are interpreted as reflecting a decreased entrainment of deep waters sourced in the North Atlantic (Northern Component Water, NCW) within CDW, which led to a reduced advection of an unradiogenic <span class=\"etd-inline-math\">ɛ<sub>Nd</sub></span> NCW signal to the core site. <span class=\"etd-inline-math\">ɛ<sub>Nd</sub></span> and REE measurements made on sediments from two cores located on the Pacific-Antarctic Ridge in the western Pacific sector of the SO (to the north of the Ross Sea Embayment) are used to reconstruct the bottom water palaeocirculation in this region across the last 540 ka. The proportion and <span class=\"etd-inline-math\">ɛ<sub>Nd</sub></span> signature of Ross Sea Bottom Water (RSBW) bathing these core sites has fluctuated throughout the last 540 ka. These fluctuations suggest the rate and location of bottom water formation within the Ross Sea, and the supply of terrigenous material with radiogenic <span class=\"etd-inline-math\">ɛ<sub>Nd</sub></span> values with which to isotopically `labelled&#x27; RSBW, may have changed in the past.","abstract_has_math":true,"creators":["Williams, Thomas"],"institution":"University of Cambridge","degree_name":"Doctor of Philosophy (PhD)","degree_level":"Doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Piotrowski, Alexander"],"committee_chairs":[],"committee_members":[],"year":2018,"date_issued":"2018-04-28","date_published":"2018-04-28","updated_at":"2026-07-22T22:24:31Z","subjects":["palaeoclimate","palaeoceanography","Southern Ocean","geochemistry"],"languages":["en"],"rights":[],"rights_urls":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/3e59cc4b-3ca9-47a3-ad71-dd4640c2c1c9/download","https://www.rioxx.net/licenses/all-rights-reserved/"],"identifier_entries":[]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.21086","outbound_label":"DOI","outbound_source":"dc:identifier.doi"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Piotrowski, Alexander"]},{"key":"dc:creator","label":"Author","values":["Williams, Thomas"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2018-04-28"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cambridge"]},{"key":"dc:relation.isreferencedby.uri","label":"Dc Relation Isreferencedby URI","values":["https://www.repository.cam.ac.uk/handle/1810/274006"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["palaeoclimate","palaeoceanography","Southern Ocean","geochemistry"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/3e59cc4b-3ca9-47a3-ad71-dd4640c2c1c9/download","https://www.rioxx.net/licenses/all-rights-reserved/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.doi","label":"DOI","values":["10.17863/CAM.21086"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/12155904-aced-474c-b637-94aa55a26eee/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["The Southern Ocean (SO) is a critical component in the global ocean conveyor. As the only conduit linking the Atlantic, Indian and Pacific Oceans, as well as an important region of upwelling and water mass formation, it is thought to have played a key role in modulating Earth’s past climate. Changes in the circulation of SO deep and bottom waters over the last 1.5 million years are investigated using stable carbon isotope $δ^{13}C$ measurements made on the tests of the benthic foraminfer Cibicidoides ($δ^{13}C_{b}$), and the rare earth element concentrations and Neodymium isotope ($ɛ_{Nd}$) values of marine sediments and their authigenic ferromanganese coatings. Being a proxy for past seawater nutrient contents, $δ^{13}C_{b}$ provides important insights into both past ocean circulation and the potential storage of remineralised organic carbon within the deep ocean, while simultaneously providing information on the past ventilation state of the deep ocean interior. As seawater $ɛ_{Nd}$ remains unaffected by biological fractionation or air-sea exchange processes, reconstructions of past deep and bottom water $ɛ_{Nd}$ provides a tool with which to study past changes in the circulation and mixing of these water masses. A suite of previously published late Holocene (0-6 ka) and Last Glacial Maximum (LGM; 18-24 ka) $δ^{13}C_{b}$ data are used alongside newly acquired $δ^{13}C_{b}$ data from the Amundsen Sea in the eastern Pacific sector of the SO to investigate past changes in the pattern of circum-Antarctic seawater carbon isotope composition. The $δ^{13}C$ signature of deep and bottom waters was much more heterogenous during the LGM than the late Holocene, with negative $δ^{13}C$ excursions occurring within the Atlantic and Indian sectors of the SO below c. 2-3 km water depth. Some of this negative $δ^{13}C$ signal was advected through the SO to the Pacific sector, but this appears to have been restricted by bathymetric barriers within the SO. New $δ^{13}C_{b}$ data spanning the last 800 ka from the Amundsen Sea are presented and suggest differing modes of bottom water formation in the Atlantic vs Pacific sectors of the SO during glacial periods of the last 800 ka. An authigenic $ɛ_{Nd}$ record measured on sediments from a core located in the deep Indian Ocean is used to investigate the palaeocirculation history of modified Circumpolar Deep Water (mCDW) within the Indian Ocean during the last 1.5 million years. Shifts towards more radiogenic $ɛ_{Nd}$ values during glacial periods are interpreted as reflecting a decreased entrainment of deep waters sourced in the North Atlantic (Northern Component Water, NCW) within CDW, which led to a reduced advection of an unradiogenic $ɛ_{Nd}$ NCW signal to the core site. $ɛ_{Nd}$ and REE measurements made on sediments from two cores located on the Pacific-Antarctic Ridge in the western Pacific sector of the SO (to the north of the Ross Sea Embayment) are used to reconstruct the bottom water palaeocirculation in this region across the last 540 ka. The proportion and $ɛ_{Nd}$ signature of Ross Sea Bottom Water (RSBW) bathing these core sites has fluctuated throughout the last 540 ka. These fluctuations suggest the rate and location of bottom water formation within the Ross Sea, and the supply of terrigenous material with radiogenic $ɛ_{Nd}$ values with which to isotopically `labelled' RSBW, may have changed in the past."]},{"key":"dc:format.checksum.md5","label":"Dc Format Checksum Md5","values":["87eda9de84448d1f82354d60eee3eb5f","05a2ae1a99f0e53795c3c92eb0ec8be6"]},{"key":"dc:title","label":"Title","values":["Investigating the circulation of Southern Ocean deep water masses over the last 1.5 million years by geochemical fingerprinting of marine sediments"]}]}],"canonical_facts":{"dc:contributor.advisor":["Piotrowski, Alexander"],"dc:creator":["Williams, Thomas"],"dc:date.issued":["2018-04-28"],"dc:description.abstract":["The Southern Ocean (SO) is a critical component in the global ocean conveyor. As the only conduit linking the Atlantic, Indian and Pacific Oceans, as well as an important region of upwelling and water mass formation, it is thought to have played a key role in modulating Earth’s past climate. Changes in the circulation of SO deep and bottom waters over the last 1.5 million years are investigated using stable carbon isotope $δ^{13}C$ measurements made on the tests of the benthic foraminfer Cibicidoides ($δ^{13}C_{b}$), and the rare earth element concentrations and Neodymium isotope ($ɛ_{Nd}$) values of marine sediments and their authigenic ferromanganese coatings. Being a proxy for past seawater nutrient contents, $δ^{13}C_{b}$ provides important insights into both past ocean circulation and the potential storage of remineralised organic carbon within the deep ocean, while simultaneously providing information on the past ventilation state of the deep ocean interior. As seawater $ɛ_{Nd}$ remains unaffected by biological fractionation or air-sea exchange processes, reconstructions of past deep and bottom water $ɛ_{Nd}$ provides a tool with which to study past changes in the circulation and mixing of these water masses. A suite of previously published late Holocene (0-6 ka) and Last Glacial Maximum (LGM; 18-24 ka) $δ^{13}C_{b}$ data are used alongside newly acquired $δ^{13}C_{b}$ data from the Amundsen Sea in the eastern Pacific sector of the SO to investigate past changes in the pattern of circum-Antarctic seawater carbon isotope composition. The $δ^{13}C$ signature of deep and bottom waters was much more heterogenous during the LGM than the late Holocene, with negative $δ^{13}C$ excursions occurring within the Atlantic and Indian sectors of the SO below c. 2-3 km water depth. Some of this negative $δ^{13}C$ signal was advected through the SO to the Pacific sector, but this appears to have been restricted by bathymetric barriers within the SO. New $δ^{13}C_{b}$ data spanning the last 800 ka from the Amundsen Sea are presented and suggest differing modes of bottom water formation in the Atlantic vs Pacific sectors of the SO during glacial periods of the last 800 ka. An authigenic $ɛ_{Nd}$ record measured on sediments from a core located in the deep Indian Ocean is used to investigate the palaeocirculation history of modified Circumpolar Deep Water (mCDW) within the Indian Ocean during the last 1.5 million years. Shifts towards more radiogenic $ɛ_{Nd}$ values during glacial periods are interpreted as reflecting a decreased entrainment of deep waters sourced in the North Atlantic (Northern Component Water, NCW) within CDW, which led to a reduced advection of an unradiogenic $ɛ_{Nd}$ NCW signal to the core site. $ɛ_{Nd}$ and REE measurements made on sediments from two cores located on the Pacific-Antarctic Ridge in the western Pacific sector of the SO (to the north of the Ross Sea Embayment) are used to reconstruct the bottom water palaeocirculation in this region across the last 540 ka. The proportion and $ɛ_{Nd}$ signature of Ross Sea Bottom Water (RSBW) bathing these core sites has fluctuated throughout the last 540 ka. These fluctuations suggest the rate and location of bottom water formation within the Ross Sea, and the supply of terrigenous material with radiogenic $ɛ_{Nd}$ values with which to isotopically `labelled' RSBW, may have changed in the past."],"dc:format.checksum.md5":["87eda9de84448d1f82354d60eee3eb5f","05a2ae1a99f0e53795c3c92eb0ec8be6"],"dc:identifier.doi":["10.17863/CAM.21086"],"dc:identifier.uri":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/12155904-aced-474c-b637-94aa55a26eee/download"],"dc:language":["en"],"dc:publisher.institution":["University of Cambridge"],"dc:relation.isreferencedby.uri":["https://www.repository.cam.ac.uk/handle/1810/274006"],"dc:rights":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/3e59cc4b-3ca9-47a3-ad71-dd4640c2c1c9/download","https://www.rioxx.net/licenses/all-rights-reserved/"],"dc:subject":["palaeoclimate","palaeoceanography","Southern Ocean","geochemistry"],"dc:title":["Investigating the circulation of Southern Ocean deep water masses over the last 1.5 million years by geochemical fingerprinting of marine sediments"],"dc:type":["Thesis"],"dc:type.qualificationlevel":["Doctoral"],"dc:type.qualificationname":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-22T22:24:31Z"}