Seasonality And Biological Forcing Modify The Diel Frequency Of Nearshore Ph Extremes In A Subarctic Alaskan Estuary

Acidification in nearshore waters is influenced by a multitude of drivers that shape the dynamics of pH and carbonate chemistry variability on diurnal, seasonal, and yearly time scales. Monitoring efforts aimed at characterizing high temporal variability are lacking in many nearshore systems, particularly in high-latitude regions such as Alaska. To rectify this, a nearshore acidification sensor array was established in the Fall of 2017 within Kachemak Bay, Alaska. Presented here are the results from the first year of these deployments, and the first record of a year-long high-frequency pH time series for nearshore Alaska. SeaFET (TM) pH and O-2 sensors deployed in Jakolof Bay and Bear Cove reveal a seasonally dynamic system in which nearshore waters in these two enclosed bays transition to being predominantly net autotrophic systems for a period of 60-plus days. High rates and durations of primary production in late spring and early summer create high pH conditions and extreme variability. Observed pH values in Jakolof Bay and Bear Cove tracked hourly rates of change on the order of 0.18 and 0.10 units, respectively. In Jakolof Bay nondirectional variability within a 12-h period was > 1 pH unit, exposing organisms to unstable, nonstatic pH conditions on tidal and diurnal cycles. Consistent frequency patterns detailing the magnitude of pH variability was correlated to tidal and O-2 signatures, elucidating the dynamics and drivers of pH variability. This first year of observations is the first step in quantifying the anthropogenic contribution to acidification for Kachemak Bay in the forthcoming years.