Wendi Ruef

Expansion of denitrification and anoxia in the eastern tropical North Pacific from 1972 to 2012

The eastern tropical North Pacific (ETNP) is a large region of anoxic water that hosts widespread water column N loss (denitrification). There is some disagreement about the long-term trends of denitrification and anoxia and long-term studies of water column denitrification within the anoxic zone are lacking. In this study, we compared ETNP water column nitrite, N*, and O2 data along the same transect for four studies ranging from 1972 to 2012. Anoxic water volume increased, and low-oxygen conditions expanded into shallower isopycnals from 1972 to 2012. A geochemical marker for cumulative N loss indicates that denitrification was highest in 2012 and the upper oxygen-deficient zone (ODZ) experienced the most change. Oxygen and N loss changes in the worlds largest ODZ for 2012 could not be explained by the Pacific Decadal Oscillation, and decreased O2 in supply currents and increased wind-driven upwelling are likely mechanisms contributing to increased N loss and anoxia.

In situ and remote monitoring of water quality in Puget Sound: The ORCA time-series

High frequency hydrological and meteorological measurements have been made in Puget Sound from 2001 to the present using remote profiling moorings. The moorings consists of a toroidal float upon which is mounted an electric winch that is powered by solar panels. Meteorological variables include, wind velocity and direction, air temperature, barometric pressure, and incident solar radiation while hydrographic variables include water temperature, salinity, dissolved oxygen, chlorophyll fluorescence and nitrate. Currently three moorings are operating in Puget Sound. All hydrographic variables displayed high frequency variability at all locations in Puget Sound, likely due to tidally advecting, patchy distributions. In the main basin of Puget Sound, the water column was well mixed during the winter months and water temperature was warmer than air temperature. With the onset of spring conditions plankton (fluorescence) bloomed and oxygen became supersaturated. However, there were numerous and frequent periods of destratification that could be correlated with wind events which mixed chlorophyll-containing surface waters downwards and nutrient-rich, oxygen-undersaturated water upwards. This process enhanced export production and injected oxygen into the deep waters. The chlorophyll maximum was found in the surface waters during the spring and fall bloom periods, but was located in the pycnocline during the summer months. By pooling all the oxygen data by hour of the day a diurnal oxygen curve was determined. The diurnal oxygen cycle was approximately sinusoidal with the minimum slightly before dawn and the maximum about at about 1800h and the amplitude was 17m moles of oxygen per liter. Primary production estimates derived from the oxygen cycle agreed with those determined from classical 14-C incubation methods. Statistical analysis of the data revealed that, at a minimum, daily sampling is necessary to assess the true values of the many measured variables. Without this sampling frequency resolving interannual differences or climate related changes would be difficult. However, given daily or greater sampling it should be possible to determine these types of changes as well as overall trends and cycles.

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

Fingerprinting ocean acidification (OA) in US 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 US 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 a largescale environmental context for ongoing research, adaptation, and management efforts throughout the US 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 ratios) 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, https://doi.pangaea.de/10.1594/PANGAEA. 866856 (Bakker et al., 2016a); – National Oceanic and Atmospheric Administration (NOAA) West Coast Ocean Acidification cruise data, https://doi.org/10.3334/CDIAC/otg.CLIVAR_NACP_West_Coast_Cruise_2007 (Feely and Sabine, 2013); https://doi.org/10.7289/V5JQ0XZ1 (Feely et al., 2015b); Published by Copernicus Publications. 1368 A. J. Fassbender et al.: Seasonal carbonate chemistry variability in marine surface waters https://data.nodc.noaa.gov/cgi-bin/iso?id=gov.noaa.nodc:0157445 (Feely et al., 2016a); https://doi.org/10.7289/V5C53HXP (Feely et al., 2015a); – University of Washington (UW) and Washington Ocean Acidification Center cruise data, https://doi.org/10. 5281/zenodo.1184657 (Fassbender et al., 2018); – Washington State Department of Ecology seaplane data, https://doi.org/10.5281/zenodo.1184657 (Fassbender et al., 2018); – NOAA Moored Autonomous pCO2 (MAPCO2) buoy data, https://doi.org/10.3334/CDIAC/OTG.TSM_ LAPUSH_125W_48N (Sutton et al., 2012); https://doi.org/10.3334/CDIAC/OTG.TSM_WA_125W_ 47N (Sutton et al., 2013); https://doi.org/10.3334/CDIAC/OTG.TSM_DABOB_122W_478N (Sutton et al., 2014a); https://doi.org/10.3334/CDIAC/OTG.TSM_TWANOH_123W_47N (Sutton et al., 2016a); – UW Oceanic Remote Chemical/Optical Analyzer buoy data, https://doi.org/10.5281/zenodo.1184657 (Fassbender et al., 2018); – NOAA Pacific Coast Ocean Observing System cruise data, https://doi.org/10.5281/zenodo.1184657 (Fassbender et al., 2018).