Seasonal Carbonate Chemistry Variability in Marine Surface Waters of the Pacific Northwest

Abstract

Abstract. Fingerprinting ocean acidification (OA) in U.S. West Coast waters is extremely challenging due to the large magnitude of natural carbonate chemistry variations common to these regions. Additionally, quantifying a change requires information about the initial conditions, which is not readily available in most coastal systems. In an effort to address this issue, we have collated high-quality, publicly-available data to characterize the modern seasonal carbonate chemistry variability in marine surface waters of the Pacific Northwest. Underway ship data from Version 4 of the Surface Ocean CO2 Atlas, discrete observations from various sampling platforms, and sustained measurements from regional moorings were incorporated to provide ~ 100,000 inorganic carbon observations from which modern seasonal cycles were estimated. Underway ship and discrete observations were merged and gridded to a 0.1° × 0.1° scale. Eight unique regions were identified and seasonal cycles from grid cells within each region were averaged. Data from nine surface moorings were also compiled and used to develop robust estimates of mean seasonal cycles for comparison with the eight regions. This manuscript describes our methodology and the resulting mean seasonal cycles for multiple OA metrics in an effort to provide large-scale, environmental context for ongoing research, adaptation, and management efforts throughout the Pacific Northwest. Major findings include the identification of unique chemical characteristics across the study domain. There is a clear increase in the ratio of dissolved inorganic carbon (DIC) to total alkalinity (TA) and in the seasonal cycle amplitude of carbonate system parameters when moving from the open ocean North Pacific into the Salish Sea. Due to the logarithmic nature of the pH scale (pH = −log10[H+], where [H+] is the hydrogen ion concentration), lower annual mean pH values (associated with elevated DIC : TA) coupled with larger magnitude seasonal pH cycles results in seasonal [H+] ranges that are ~ 27 times larger in Hood Canal than in the neighboring North Pacific open ocean. Organisms living in the Salish Sea are thus exposed to much larger seasonal acidity changes than those living in nearby open ocean waters. Additionally, our findings suggest that lower buffering capacities in the Salish Sea make these waters less efficient at absorbing anthropogenic carbon than open ocean waters at the same latitude. All data used in this analysis are publically available at the following websites: • Surface Ocean CO2 Atlas Version 4 coastal data, doi:10.1594/PANGAEA.866856; • National Oceanic and Atmospheric Administration (NOAA) West Coast Ocean Acidification cruise data, doi:10.3334/CDIAC/otg.CLIVAR_NACP_West_Coast_Cruise_2007; doi:10.3334/CDIAC/OTG.COAST_WCOA2011; doi:10.3334/CDIAC/OTG.COAST_WCOA2012; doi:10.7289/V5C53HXP; • University of Washington (UW) and Washington Ocean Acidification Center cruise data, doi:10.5281/zenodo.1184657; • Washington State Department of Ecology seaplane data, 10.5281/zenodo.1184657; • NOAA Moored Autonomous pCO2 (MAPCO2) Buoy data, doi:10.3334/CDIAC/OTG.TSM_LAPUSH_125W_48N; doi:10.3334/CDIAC/OTG.TSM_WA_125W_47N; doi:10.3334/CDIAC/OTG.TSM_DABOB_122W_478N; doi:10.3334/CDIAC/OTG.TSM_TWANOH_123W_47N; • UW Oceanic Remote Chemical/Optical Analyzer Buoy data, doi:10.5281/zenodo.1184657; • NOAA Pacific Coast Ocean Observing System cruise data, doi:10.5281/zenodo.1184657.

Autonomous seawater <i>p</i>CO<sub>2</sub> and pH time series from 40 surface buoys and the emergence of anthropogenic trends

“…Net calcification has been confirmed by independent assessments at some of these coral reef time series stations (Bates et al, 2010;Courtney et al, 2016;Drupp et al, 2011;Shamberger et al, 2011). which experiences greater water residence time and more persistent stratification, and therefore, increased influence of biological production and respiration on seawater xCO2 (Fassbender et al, 2018;Lindquist et al, 2017). These processes can cause subsurface hypoxia and low pH (<7.4) and aragonite saturation (<0.6) conditions in this region of Puget Sound (Feely et al, 2010) the offshore stations of WHOTS and BTM both exhibit climatological mean seawater pCO2 slightly below atmospheric values (Fig.…”

“…The coastal time series stations 25 suggest annual CO2 uptake with climatological means of seawater pCO2 less than atmospheric CO2 levels. Seasonal changes of SST and biological productivity drive the large seasonal amplitudes in pCO2 and pH at the U.S. coastal locations (Fassbender et al, 2018;Reimer et al, 2017;Sutton et al, 2016;Xue et al, 2016). The coastal stations Twanoh and Coastal MS exhibit the highest IAV of seawater pCO2 (reported as seawater xCO2 for Twanoh) due to large variability from year to year in circulation, freshwater input, and biological productivity (Fig.…”

Autonomous seawater &lt;i&gt;p&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt; and pH time series from 40 surface buoys and the emergence of anthropogenic trends

“…The coastal time series stations suggest annual CO2 uptake with climatological seawater pCO2 means less than atmospheric CO2 levels. Seasonal changes of SST and biological productivity drive the large seasonal amplitudes in pCO2 and pH at the U.S. coastal locations (Fassbender et al, 2018;Reimer et al, 2017;Sutton et al, 2016;Xue et al, 2016). The coastal stations Twanoh and Coastal MS exhibit the highest 10 IAV of seawater pCO2 (reported as seawater xCO2 for Twanoh) due to large variability from year to year in freshwater input and biological productivity ( Fig.…”

“…Seasonal variability and IAV are almost twice as large at the time series stations within the freshwater-influenced Puget Sound (Dabob and Twanoh) compared to the stations on the outer coast of Washington (Chá bă and Cape Elizabeth). Dabob is closer to the inlet of Puget Sound compared to Twanoh, which experiences greater water residence time and, therefore, greater influence of biological production and respiration on seawater xCO2(Fassbender et al, 2018; Lindquist et al, 2017). These processes can cause subsurface hypoxia and low pH (<7.4) and aragonite 20 saturation (<0.6) conditions in this region of Puget Sound(Feely et al, 2010), which likely contribute to the elevated surface seawater xCO2 levels observed at Dabob and Twanoh.…”