The Tides They Are a‐Changin': A comprehensive review of past and future non‐astronomical changes in tides, their driving mechanisms and future implications

Ivan D. Haigh, Mark D. Pickering, J.A. Mattias Green, Brian K. Arbic, Arne Arns, Sönke Dangendorf, David Hill, Kevin Horsburgh, Tom Howard, Déborah Idier, David A. Jay, Leon Jänicke (+6 others)
<span title="2019-12-13">2019</span> <i title="American Geophysical Union (AGU)"> <a target="_blank" rel="noopener" href="" style="color: black;">Reviews of Geophysics</a> </i> &nbsp;
Scientists and engineers have observed for some time that tidal amplitudes at many locations are shifting considerably due to nonastronomical factors. Here we review comprehensively these important changes in tidal properties, many of which remain poorly understood. Over long geological time scales, tectonic processes drive variations in basin size, depth, and shape and hence the resonant properties of ocean basins. On shorter geological time scales, changes in oceanic tidal properties are
more &raquo; ... ated by variations in water depth. A growing number of studies have identified widespread, sometimes regionally coherent, positive, and negative trends in tidal constituents and levels during the 19th, 20th, and early 21st centuries. Determining the causes is challenging because a tide measured at a coastal gauge integrates the effects of local, regional, and oceanic changes. Here, we highlight six main factors that can cause changes in measured tidal statistics on local scales and a further eight possible regional/global driving mechanisms. Since only a few studies have combined observations and models, or modeled at a temporal/spatial resolution capable of resolving both ultralocal and large-scale global changes, the individual contributions from local and regional mechanisms remain uncertain. Nonetheless, modeling studies project that sea level rise and climate change will continue to alter tides over the next several centuries, with regionally coherent modes of change caused by alterations to coastal morphology and ice sheet extent. Hence, a better understanding of the causes and consequences of tidal variations is needed to help assess the implications for coastal defense, risk assessment, and ecological change. Plain Language Summary Tides are one of the most persistent and dominant forces that shape our planet. The regular and predictable daily, fortnightly, monthly, annual, interannual, and longer-term changes in tides, driven by astronomical forces, are well understood. However, scientists and engineers have observed for some time that tides at many locations are shifting considerably due to nonastronomical factors. Here, we carry out a review of these important changes in tides, many of which remain poorly understood. We highlight that over long geological time scales, changes in tides are driven by tectonic processes, which alter the size, depth, and shape of the ocean. Over shorter geological time scales, changes in tides are mainly driven by changes in water depth. In recent decades, a growing number of studies have identified widespread, and sometimes regionally coherent, changes in tides during the last 150 years. However, determining exactly what has caused these more recent changes in tides has proven difficult. We discuss the local and regional/global mechanisms that might be responsible for the observed changes.
<span class="external-identifiers"> <a target="_blank" rel="external noopener noreferrer" href="">doi:10.1029/2018rg000636</a> <a target="_blank" rel="external noopener" href="">fatcat:lpvzn3ep6jctrmfzrn2z4av3am</a> </span>
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