Investigating the Coastal Sea Level Variability in the Northwest Atlantic

Abstract

The Northwest Atlantic, a region spanning the Eastern seaboard of North America, is one of the global sea level rise (SLR) acceleration hotspots and experiences strong sea level variability (SLV). The SLV can accelerate or mask the low-frequency SLR signals and contribute to the sea level extremes.
Nevertheless, the contributions of SLV drivers are still disputed. Only recently the advances in coastal altimetry have enabled reliable observations within several kilometres from the coast, which hindered the research before. To help address these research gaps, this thesis uses in-situ data, high-resolution reanalysis, and Sentinel-3A synthetic aperture radar altimeter (S3A-SRAL) to investigate the SLV, with a focus on the shorter (sub-interannual) timescales and validate the use of S3A-SRAL for SLV detection.
The first results chapter evaluates the altimeter corrections with S3A-SRAL in the Northwest Atlantic coastal zone. The results show that the default corrections mostly provide equally good or better noise reduction than the alternative corrections. However, the S3A-SRAL is still affected by an increased variance in the first 6 km from the coast, where error budget is likely dominated by the geophysical correction uncertainty.
The second results chapter uses several S3A-SRAL retrackers to validate the altimeter data with in-situ measurements and evaluates the S3A-SRAL’s ability to detect regional variability in the coastal zone of the Northwest Atlantic. The results show that coastal retrackers improve data availability while the data consistency with tide gauges (TGs) is better for the SAMOSA retrackers. In addition, the results demonstrate mostly barotropic variability on the shelf and identify the reduction in length scales (from 150–230 km to 50–80 km) where the shelf is narrow.
The third results chapter uses high-resolution reanalysis, TGs, and S3A-SRAL to investigate the sources of sea level variability over the Northwest Atlantic shelves. The results show the importance of the seasonal wind-driven mass redistribution between the coast and the shelf edge (up to 70% of explained variance) and the role of the Labrador Sea in seasonal circulation.
The results have contributed to the understanding of the Northwest Atlantic shelves’ SLV sources and validated S3A-SRAL for SLV applications in the region.

Date of Award	10 Dec 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	Samantha Royston (Supervisor) & Jonathan L Bamber (Supervisor)