Document Type

Post-Print

Publication Date

2-2020

Subjects

Oceanography -- Columbia River Estuary (Or. and Wash.) -- Mathematical models, Columbia River Estuary (Or. and Wash.)

Abstract

Few tidal records are available pre-1900 for the Pacific Ocean. We improve data coverage by recovering historical tabulations and digitizing analog tide rolls from Astoria, Oregon for 1853-1876. Nearly 13,500 overlapping images of tides from 1855-1870 were digitized at a 6 minute resolution using a line-finding algorithm. Available hourly and high/low tabulations were also digitized, as were nearby hourly records from 1933-1943. Uncertainty was assessed by evaluating manual staff measurements, historical documents, and leveling surveys. Results suggest that uncertainty in mean sea level varies from ± 0.07m (early 1850s) to ± 0.03m (1867-1876) and is driven primarily by datum and benchmark uncertainty, rather than measurement precision, data reduction procedures, or hydrodynamic changes. We also corrected an up-to 0.05m error in the 1925-1960 tidal datum at Astoria. Harmonic analysis shows that major tidal constituents increased by up to 7% between 1855 and 2018. Mean tidal range increased by 0.1m (5%), with more change occurring in July (0.17m larger than winter (0.07m larger). By contrast, sea level increased most in winter, and least in spring/summer. Tidally-based estimates of river discharge suggest that these observations are caused by a ~50% reduction in peak spring discharge and a 30-60% increase in winter discharge. No evidence of altered upwelling is found. Overall, Astoria relative sea level (RSL) increased by 0.06m ± 0.04m since the 1858-1876 epoch, or, after accounting for vertical land motion, 0.11 ± 0.09m. Consistent with GNSS measurements, RSL has dropped near the estuary mouth since 1905, indicating a strong tectonic influence.

Description

This is the author’s version of a work that was accepted for publication in the Journal of Geophysical Research: Oceans. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication.

The data that supports this article is available in PDXScholar and can be found here: https://doi.org/10.15760/cee-data.03

Persistent Identifier

https://archives.pdx.edu/ds/psu/31015

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