TY - JOUR
T1 - The influence of variable slope-water characteristics on dissolved oxygen levels in the northern California Current System
AU - Durski, Scott M.
AU - Barth, John A.
AU - McWilliams, James C.
AU - Frenzel, Hartmut
AU - Deutsch, Curtis
N1 - Funding Information:
This work was supported by funding from the Gordon and Betty Moore Foundation (GBMF#3775), the David and Lucile Packard Foundation, the National Science Foundation (OCE- 1419323), and the National Oceanic and Atmospheric Administration (NA15NOS4780186). Oregon NH-10 mooring data were made available thanks to the NANOOS project and efforts by M. Kosro, M. Levine, and C. Risien. Dissolved oxygen data for the Newport hydrographic line were kindly provided by S. Pierce. Argo and SODA data set are available from the Asia- Pacific Data-Research Center (APDRC) at the University of Hawaii (http:// apdrc.soest.hawaii.edu/data/data.php). The NARR data set is available from NOAA National Centers for Environmental Information (https:// www.ncdc.noaa.gov/data-access/ model-data/model-datasets/north- american-regional-reanalysis-narr).
Publisher Copyright:
© 2017. American Geophysical Union. All Rights Reserved.
PY - 2017/9
Y1 - 2017/9
N2 - Observations have suggested a trend of decreasing dissolved oxygen (DO) and increasing spiciness in summertime middepth slope waters and bottom shelf waters along the United States west coast over the past 50 years, but they have also demonstrated a large amount of interannual and decadal variability. Shelf bottom water and slope water properties can be influenced by both local and remote effects, including changes in circulation or changes in the characteristics of the source waters supplying the region. A regional-scale, coupled physical biogeochemical model has been developed to simulate seasonal-to-decadal scale variability along the US west coast to discern the physical dynamics behind these spatial and temporal patterns. A simulation run from 1981 to 2006 with forcing that incorporates the larger scale interannual trends reproduces the development of low DO late in the upwelling season, the considerable interannual variability and the reported tendency toward a shoaling, more spicy, and oxygen-depleted, northern California Undercurrent (CU). Whereas the trend in spiciness in the model results from increased influence of equatorial relative to subarctic source waters, the decreases in DO are found to additionally be a consequence of local biogeochemical processes. In order to better understand the interannual variability, years of the simulation were classified into four groups based on intensity of upwelling forcing and undercurrent strength. Slope water characteristics, shelf-slope exchange, and slope-basin exchange were compared across the four cases. Years with both strong upwelling and a strong undercurrent generated the most negative anomalies in slope-water DO late in the upwelling season.
AB - Observations have suggested a trend of decreasing dissolved oxygen (DO) and increasing spiciness in summertime middepth slope waters and bottom shelf waters along the United States west coast over the past 50 years, but they have also demonstrated a large amount of interannual and decadal variability. Shelf bottom water and slope water properties can be influenced by both local and remote effects, including changes in circulation or changes in the characteristics of the source waters supplying the region. A regional-scale, coupled physical biogeochemical model has been developed to simulate seasonal-to-decadal scale variability along the US west coast to discern the physical dynamics behind these spatial and temporal patterns. A simulation run from 1981 to 2006 with forcing that incorporates the larger scale interannual trends reproduces the development of low DO late in the upwelling season, the considerable interannual variability and the reported tendency toward a shoaling, more spicy, and oxygen-depleted, northern California Undercurrent (CU). Whereas the trend in spiciness in the model results from increased influence of equatorial relative to subarctic source waters, the decreases in DO are found to additionally be a consequence of local biogeochemical processes. In order to better understand the interannual variability, years of the simulation were classified into four groups based on intensity of upwelling forcing and undercurrent strength. Slope water characteristics, shelf-slope exchange, and slope-basin exchange were compared across the four cases. Years with both strong upwelling and a strong undercurrent generated the most negative anomalies in slope-water DO late in the upwelling season.
KW - California Undercurrent
KW - coastal hypoxia
KW - coastal upwelling
KW - northern California Current System
KW - slope-shelf exchange
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U2 - 10.1002/2017JC013089
DO - 10.1002/2017JC013089
M3 - Article
AN - SCOPUS:85030221387
SN - 2169-9291
VL - 122
SP - 7674
EP - 7697
JO - Journal of Geophysical Research: Oceans
JF - Journal of Geophysical Research: Oceans
IS - 9
ER -