Sea level changes on the northern northwest Pacific and Atlantic coast
Date
2021
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Global sea level rise (SLR) provides an important indicator of the state of the climate warming. However, what really matters for planning and adaptation to the SLR are those occurring over the regional scales. Reliable predictions of future regional SLR rate are of vital importance for low-lying areas that subject to flooding and erosion on the coast (Kopp et al., 2014; Jackson and Jevejeva, 2016). The rate of regional sea level change can differ significantly from that of the global mean sea level. On top of that, fluctuations of sea level at varying time scales complicate the detection of sea level trends and its acceleration from observations, and sea level variability will continue to be the dominant source of the uncertainty in sea level trends for the coming decades (Palmer et al., 2018). As such, a better understanding of the processes driving interannual to multidecadal sea level variability is warranted to improve the historical estimates and future projections. Under a warming climate, sea level trends along the China and the U.S. northeast coasts are particularly interested, because they are densely populated, and the sea level has been rising much faster than other coastal regions around the globe. ☐ To achieve the above research goal, I conduct the research from three perspectives: the second chapter focuses on the historical trend of sea level and future projection along the coasts of China Seas. I use tide-gauge data and satellite measurements to examine past mean relative sea level trends and then combine climate model output and satellite observations to provide MRSL projections in the 21st century. The results show that the MRSL trend based on tide-gauge data along China Seas shows substantial regional variations, from 1 to 5 mm/yr. The vertical land motion (VLM) based on altimetry and tide-gauge (ATG) data indicates large land subsidence at some tide-gauge locations, consistent with the Global Positioning Systems (GPS)-based VLM but different significantly from small uplift estimated by a Glacial Isostatic Adjustment (GIA) model, which suggests other important factors causing the VLM instead of the GIA process. When GPS- or ATG- based VLM estimates are used, the projected MRSL rise between 1986–2005 and 2081–2100 at tide-gauge sites varies from 60 to 130 cm under the Representative Concentration Pathway 8.5 (RCP8.5) scenario of the Intergovernmental Panel on Climate Change (IPCC). My projections are significantly larger than those of IPCC and other literature because of accounting for the land subsidence derived from observations. Steric and dynamic ocean effects and land-ice melt effects are comparable (about 30 cm each) and do not vary much over the tide-gauge locations. The VLM effect varies from −10 to 60 cm. The projections between 1986–2005 and 2081–2100 under RCP4.5 show a similar spatial distribution to that under RCP8.5, with a smaller amount of rise by 18 cm on average for this region. ☐ The third chapter investigates the interannual sea level variability along the northern northwest Atlantic coast. To be specific, I distinguish the relative contribution from ocean processes mostly concerned in previous research to interannual sea level variability observed in tide-gauge record between the Mid-Atlantic Bight and Nova Scotia coast. The results indicate not only spatial correlation of the sea level variations but also similarity and difference in their contributing factors between sea level variability along Nova Scotia coast and Mid-Atlantic Bight. The interannual sea level variations along the Nova Scotia coast and the Mid‐Atlantic Bight are mainly (41% and 52%) from the steric effect associated with the temperature and salinity changes, and to a less extent (33% and 31%) from the inverse barometric effect. However, the coastal sea level anomalies (SLAs) are significantly correlated with the Gulf Stream strength along the Mid‐Atlantic Bight only, with correlation coefficient of 0.64, while the correlation with alongshore winds is significant along the Nova Scotia coast only. ☐ The fourth chapter examines the decadal and multi-decadal sea level variability in tide-gauge record along Mid-Atlantic Bight. The study emphasizes on the roles played by the variations in local meteorological conditions in decadal sea level variability and the reversal of multi-decadal trend. The North Atlantic Oscillation (NAO) explains 85% and 71% of interannual and decadal sea level variance on the coast and contributes 41% of the trend difference between 1960-1989 and 1990-2017. The further evaluation of individual process indicate that the steric signals propagated via coastally trapped waves explains 30% of the decadal sea level variance. The barotropic response to alongshore wind and the inverse barometer (IB) effect explains 27% and 13% of the decadal sea level variance, respectively. The declined trend in eddy kinetic energy on the boundary of subpolar gyre, as well as the decreased trend in the maximum of barotropic stream function in subpolar gyre region since 1990, proves the weakening of subpolar gyre. Moreover, the weakening of subpolar gyre is highly anti-correlated with the sea level changes on the Mid-Atlantic Bight coast. ☐ Key words: sea level rise; vertical land motion; decadal and multi-decadal variability; atmospheric forcing; oceanic adjustment.
Description
Keywords
Atmospheric forcing, Decadal and multi-decadal variability, Oceanic adjustment, Sea level rise, Vertical land motion