Present day sea level: global and regional variations

Abstract : Sea level is an integrated climate parameter that involves interactions of all components of the climate system (oceans, ice sheets, glaciers, atmosphere, and land water reservoirs) on a wide range of spatial and temporal scales. Over the 20th century, tide gauge records indicate a rise in global sea level between 1.6 mm/yr and 1.8 mm/yr. Since 1993, sea level variations have been measured precisely by satellite altimetry. They indicate a faster sea level rise of 3.3 mm/yr over 1993-2015. Owing to their global coverage, they also reveal a strong regional sea level variability that sometimes is several times greater than the global mean sea level rise. Considering the highly negative impact of sea level rise for society, monitoring sea level change and understanding its causes are henceforth high priorities. In this thesis, we first validate the sea level variations measured by the new satellite altimetry mission, SARAL-AltiKa by comparing the measurements with Jason-2 and tide gauge records. We then attempt to close the global mean sea level budget since 2003 and estimate the deep ocean contribution by making use of observational data from satellite altimetry, Argo profiles and GRACE mission. We show that uncertainties due to data processing approaches and systematic errors of different observing systems still prevent us from obtaining accurate results. In the second part of the thesis, by making use of past sea level reconstruction, we study the patterns of the regional sea level variability and estimate climate related (global mean plus regional component) sea level change over 1950-2009 at three vulnerable regions: Indian Ocean, South China and Caribbean Sea. For the sites where vertical crustal motion monitoring is available, we compute the total relative sea level (i.e. total sea level rise plus the local vertical crustal motion) since 1950. On comparing the results from these three regions with already existing results in tropical Pacific, we find that tropical Pacific displays the highest magnitude of sea level variations. In the last part of the thesis, we therefore focus on the tropical Pacific and analyze the respective roles of ocean dynamic processes, internal climate modes and external anthropogenic forcing on tropical Pacific sea level spatial trend patterns since 1993. Building up on the relationship between thermocline and sea level in the tropical region, we show that most of the observed sea level spatial trend pattern in the tropical Pacific can be explained by the wind driven vertical thermocline movement. By performing detection and attribution study on sea level spatial trend patterns in the tropical Pacific and attempting to eliminate signal corresponding to the main internal climate mode, we further show that the remaining residual sea level trend pattern does not correspond to externally forced anthropogenic sea level signal. In addition, we also suggest that satellite altimetry measurement may not still be accurate enough to detect the anthropogenic signal in the 20-year tropical Pacific sea level trends.
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Submitted on : Wednesday, May 18, 2016 - 4:04:15 PM
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Hindumathi K. Palanisamy. Present day sea level: global and regional variations. Oceanography. Universite Toulouse III Paul Sabatier, 2016. English. ⟨tel-01317607⟩

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