Title | Intraseasonal Cross-Shelf Variability of Hypoxia along the Newport, Oregon, Hydrographic Line |
Publication Type | Journal Article |
Year of Publication | 2016 |
Authors | Adams, KA, Barth, JA, Shearman, RK |
Journal | Journal of Physical Oceanography |
Volume | 46 |
Pagination | 2219-2238 |
Type of Article | Journal Article |
Keywords | Circulation/Dynamics, Coastal flows, Upwelling/downwelling |
Abstract | Observations of hypoxia, dissolved oxygen (DO) concentrations < 1.4 ml L−1, off the central Oregon coast vary in duration and spatial extent throughout each upwelling season. Underwater glider measurements along the Newport hydrographic line (NH-Line) reveal cross-shelf DO gradients at a horizontal resolution nearly 30 times greater than previous ship-based station sampling. Two prevalent hypoxic locations are identified along the NH-Line, as is a midshelf region with less severe hypoxia north of Stonewall Bank. Intraseasonal cross-shelf variability is investigated with 10 sequential glider lines and a midshelf mooring time series during the 2011 upwelling season. The cross-sectional area of hypoxia observed in the glider lines ranges from 0 to 1.41 km2. The vertical extent of hypoxia in the water column agrees well with the bottom mixed layer height. Midshelf mooring water velocities show that cross-shelf advection cannot account for the increase in outer-shelf hypoxia observed in the glider sequence. This change is attributed to an along-shelf DO gradient of −0.72 ml L−1 over 2.58 km or 0.28 ml L−1 km−1. In early July of the 2011 upwelling season, near-bottom cross-shelf currents reverse direction as an onshore flow at 30-m depth is observed. This shoaling of the return flow depth throughout the season, as the equatorward coastal jet moves offshore, results in a more retentive near-bottom environment more vulnerable to hypoxia. Slope Burger numbers calculated across the season do not reconcile this return flow depth change, providing evidence that simplified two-dimensional upwelling model assumptions do not hold in this location. |
DOI | 10.1175/Jpo-D-15-0119.1 |
Array | Coastal Endurance |
Bibliometrics |
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