Subsurface Temperature Anomalies Off Central Oregon During 2014–2021

We use moored observations in 80 m water depth at the NH‐10 site along the historic Newport Hydrographic Line from 1999 to 2021 to calculate water temperature anomalies at the surface, near surface, and bottom. Analysis is focused on the subsurface temporal and spatial characteristics of marine heatwaves (MHWs) during 2014–2016 and 2019–2020 on the continental shelf and slope. Warm anomalies extend throughout the water column in fall/winter 2014–2016 when winds are predominantly downwelling‐favorable, while the 2019–2020 period is characterized by shallower summer and fall anomalies on the shelf. Sustained temperature anomalies during the bottom MHW in late 2016 are the largest in the NH‐10 time series. Analysis of temporal patterns in wind stress during MHW and non‐MHW periods shows the onset of upwelling‐favorable winds interrupts warm events. Indices of cumulative upwelling and annual spring transition dates reveal the spring transition was unusually late in 2014, with only five years with later spring transitions since the upwelling index record began in 1967. In 2015 and 2019, in contrast, spring transition is close to the climatological mean of April 15. In 2016 and 2020, anomalous warming is observed when cumulative upwelling decreases after an early spring transition. Plain Language Summary In this study, we use water temperature observations from a stationary oceanographic platform located in 80 m water depth off Newport, Oregon to calculate variations from the long‐term mean temperature at the surface, near surface, and bottom from 1999 to 2021. The temperature observations are from several different programs that have not previously been combined into one long time series. Of particular interest are the details of the marine heatwave (MHW) periods of 2014–2016 and 2019–2020, which had widespread impacts on marine ecosystems. Strong deviations from the mean water temperature observed near the ocean bottom during late 2016 are the largest sustained warm anomalies in the time series. The 2019–2020 period shows warm anomalies in the summer and fall that are only observed near the surface. We also analyze the local winds during years with and without MHWs and find that spring/summer upwelling‐favorable, or northerly winds, which are important for bringing cold, nutrient rich water to the surface in coastal regions, interrupt MHW events and can lessen extreme heating during MHWs in coastal waters. Key Points Warm anomalies in 2014–2016 extend througho