11  Dissolved Oxygen

Description Nearshore dissolved oxygen (DO) depends on many processes, including currents, upwelling, air–sea exchange, and community-level production and respiration in the water column and benthos. DO is required for organismal respiration; low DO can compress habitat and cause stress or die-offs for sensitive species. Waters with DO levels <1.4 mL/L (~ 2 mg/L, note unit change) are considered to be hypoxic; such conditions may occur on the shelf following the onset of spring upwelling, and continue into the summer and early fall months until the fall transition vertically mixes shelf waters. Upwelling-driven hypoxia occurs because upwelled water from deeper ocean sources tends to be low in DO, and microbial decomposition of organic matter in the summer and fall increases overall system respiration and oxygen consumption, particularly closer to the seafloor (Chan et al. 2008).

CalCOFI Indicators

• Locations:
  • 150m: Line 80, Station 80 (33.5 N, -122.5 E)
  • 150m: Line 90, Station 90 (31.4 N, -122 E)
  • 150m: Line 93, Station 30 (32.8 N, -117.5 E)
• Component Category: Climate and Ocean Drivers
• Time Range: 1950 - 2024
• CCIEA Data Contact: isaac.schroeder@noaa.gov
• Institution: NOAA SWFSC
• Source Data: Dissolved oxygen is measured by an automated oxygen titrator mounted to the CTD rosette and oxygen data is sampled at depths consistent with those of temperature and salinity. Additional information can be found at http://www.calcofi.org/new.data/index.php/reporteddata/hydrographic-data/introductions.
• Additional Calculations: Each unique depth profile of dissolved oxygen (DO) was linearly interpolated on 1 m intervals, without any extrapolation for intervals above/below sampled depths. Outliers a profile might contain were removed by applying a Hample filter. The filter had a window size of 5 m above and below an observation, and considers the observation an outlier if a sample differs from the median by more than four standard deviations (see https://www.mathworks.com/help/signal/ref/hampel.html). Outliers are filled by linear interpolation of the points above and below. Then the DO at 150 m (DO@150) was extracted from the linearly interpolated profile. A time series of DO@150 was created using each unique profile of DO data available. A monthly mean time series was calculated from this time series. A standard deviation value was calculated if more than one profile was made during a given month, otherwise the standard deviation value was NaN (not a number).

Newport Line Indicators

• Locations:
  • 150 m: NH25 (44.65 N, -124.65 E)
  • 50 m: NH05 (44.65 N, -124.18 E)
• Component Category: Climate and Ocean Drivers
• Time Range: 1998 - 2024
• CCIEA Data Contact: isaac.schroeder@noaa.gov
• Institution: NOAA SWFSC
• Source Data: Dr. Jennifer Fisher ( jennifer.fisher@noaa.gov) Dissolved oxygen is measured by an automated oxygen titrator mounted to the CTD rosette and oxygen data is sampled at depths conin Peterson, J.O, Morgan, C. A., Peterson, W.T., Di Lorenzo, E. 2013) Seasonal and interannual variation in the extent of hypoxia in the northern California Current from 1998-2012, Limnology and Oceanography, 58(6):2279-2292, DOI:10.4319/lo.2013.58.6.2279.
• Additional Calculations: Each unique depth profile of dissolved oxygen (DO) was linearly interpolated on 1 m intervals, without any extrapolation for intervals above/below sampled depths. Outliers a profile might contain were removed by applying a Hample filter. The filter had a window size of 5 m above and below an observation, and considers the observation an outlier if a sample differs from the median by more than four standard deviations (see https://www.mathworks.com/help/signal/ref/hampel.html). Outliers are filled by linear interpolation of the points above and below. Then the DO at 150 m (DO@150) was extracted from the linearly interpolated profile. A time series of DO@150 was created using each unique profile of DO data available. A monthly mean time series was calculated from this time series. A standard deviation value was calculated if more than one profile was made during a given month, otherwise the standard deviation value was NaN (not a number).

Indicator Download

ERDDAP™ link:

https://oceanview.pfeg.noaa.gov/erddap/tabledap/cciea_OC_DO.html

References

Chan, Francis, JA Barth, J Lubchenco, A Kirincich, H Weeks, William T Peterson, and BA Menge. 2008. “Emergence of anoxia in the California Current Large Marine Ecosystem.” Science 319 (5865): 920–20.