Links between the Seychelles-Chagos thermocline ridge and large scale climate modes and primary productivity; and the annual cycle of chlorophyll-a

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dc.contributor.advisorReason, Chrisen_ZA
dc.contributor.advisorHermes, Juliet Cen_ZA
dc.contributor.authorDilmahamod, Ahmad Fehmien_ZA
dc.date.accessioned2014-11-05T03:58:13Z
dc.date.available2014-11-05T03:58:13Z
dc.date.issued2014en_ZA
dc.descriptionIncludes bibliographical references.en_ZA
dc.description.abstractThe Seychelles-Chagos Thermocline Ridge (SCTR) is a region of upwelling present at 55°E- 90°E and 5°S-12°S in the southwest tropical Indian Ocean. It is a region of strong ocean-atmosphere interactions due to the high variability of the thermocline depth caused by the local Ekman pumping. Sea-viewing Wide Field-of-view Sensor (SeaWiFS) has shown high variability of surface chlorophyll-a (SChl-a) in the SCTR region. The Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) have also driven significant interannual variation of the depth of 20°C isotherm (D20) and SChl-a in the southern tropical Indian Ocean. A 50-years hindcast (RUN58-07) from a coupled bio-physical model was used to study the SChl-a concentration on an annual time scale and the interannual variability of D20 and SChla in the SCTR in response to IOD and ENSO events. Initial analysis revealed a high overestimation of SChl-a in the 50-year run. Therefore, a 44-years hindcast (RUN58-01) of the same coupled model was taken into consideration. Comparisons with observations show that the RUN58-07 reproduces the D20 and SSH better than the RUN58-01 but the RUN58-01 shows better agreement with SeaWiFS. Results reveal that the SCTR exhibits an annual cycle of SChl-a concentration, with a peak in austral winter (June-August) due to the strong southeasterlies, increasing wind stirring and induced upwelling. Vertical sections of the SCTR also indicate that an increase in surface concentration in austral winter is compensated by a decrease in subsurface phytoplankton blooms. Composite figures show that IOD events exhibit a greater influence on the subsurface and surface variability in the SCTR region. The IOD deepens and shoals the D20 in the SCTR and eastern Indian Ocean respectively whereas ENSO displays a weaker and less-extensive influence on the D20. The spatial distribution of SChl-a in the Indian Ocean is completely disrupted by IOD during which the SCTR becomes oligotrophic whereas the eastern Indian Ocean becomes highly productive. ENSO, however, does not display any significant biogeochemical signature in the SCTR. This study should improve our understanding of the interannual variability of the thermocline depth and chlorophyll-a in the SCTR region; and for the optimization of the management of fishery resources and marine ecosystems.en_ZA
dc.identifier.apacitationDilmahamod, A. F. (2014). <i>Links between the Seychelles-Chagos thermocline ridge and large scale climate modes and primary productivity; and the annual cycle of chlorophyll-a</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Oceanography. Retrieved from http://hdl.handle.net/11427/9212en_ZA
dc.identifier.chicagocitationDilmahamod, Ahmad Fehmi. <i>"Links between the Seychelles-Chagos thermocline ridge and large scale climate modes and primary productivity; and the annual cycle of chlorophyll-a."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Oceanography, 2014. http://hdl.handle.net/11427/9212en_ZA
dc.identifier.citationDilmahamod, A. 2014. Links between the Seychelles-Chagos thermocline ridge and large scale climate modes and primary productivity; and the annual cycle of chlorophyll-a. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Dilmahamod, Ahmad Fehmi AB - The Seychelles-Chagos Thermocline Ridge (SCTR) is a region of upwelling present at 55°E- 90°E and 5°S-12°S in the southwest tropical Indian Ocean. It is a region of strong ocean-atmosphere interactions due to the high variability of the thermocline depth caused by the local Ekman pumping. Sea-viewing Wide Field-of-view Sensor (SeaWiFS) has shown high variability of surface chlorophyll-a (SChl-a) in the SCTR region. The Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) have also driven significant interannual variation of the depth of 20°C isotherm (D20) and SChl-a in the southern tropical Indian Ocean. A 50-years hindcast (RUN58-07) from a coupled bio-physical model was used to study the SChl-a concentration on an annual time scale and the interannual variability of D20 and SChla in the SCTR in response to IOD and ENSO events. Initial analysis revealed a high overestimation of SChl-a in the 50-year run. Therefore, a 44-years hindcast (RUN58-01) of the same coupled model was taken into consideration. Comparisons with observations show that the RUN58-07 reproduces the D20 and SSH better than the RUN58-01 but the RUN58-01 shows better agreement with SeaWiFS. Results reveal that the SCTR exhibits an annual cycle of SChl-a concentration, with a peak in austral winter (June-August) due to the strong southeasterlies, increasing wind stirring and induced upwelling. Vertical sections of the SCTR also indicate that an increase in surface concentration in austral winter is compensated by a decrease in subsurface phytoplankton blooms. Composite figures show that IOD events exhibit a greater influence on the subsurface and surface variability in the SCTR region. The IOD deepens and shoals the D20 in the SCTR and eastern Indian Ocean respectively whereas ENSO displays a weaker and less-extensive influence on the D20. The spatial distribution of SChl-a in the Indian Ocean is completely disrupted by IOD during which the SCTR becomes oligotrophic whereas the eastern Indian Ocean becomes highly productive. ENSO, however, does not display any significant biogeochemical signature in the SCTR. This study should improve our understanding of the interannual variability of the thermocline depth and chlorophyll-a in the SCTR region; and for the optimization of the management of fishery resources and marine ecosystems. DA - 2014 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2014 T1 - Links between the Seychelles-Chagos thermocline ridge and large scale climate modes and primary productivity; and the annual cycle of chlorophyll-a TI - Links between the Seychelles-Chagos thermocline ridge and large scale climate modes and primary productivity; and the annual cycle of chlorophyll-a UR - http://hdl.handle.net/11427/9212 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/9212
dc.identifier.vancouvercitationDilmahamod AF. Links between the Seychelles-Chagos thermocline ridge and large scale climate modes and primary productivity; and the annual cycle of chlorophyll-a. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Oceanography, 2014 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/9212en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Oceanographyen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherOcean and Climate Dynamicsen_ZA
dc.titleLinks between the Seychelles-Chagos thermocline ridge and large scale climate modes and primary productivity; and the annual cycle of chlorophyll-aen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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