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Hydrographic anomalies on the South Atlantic Bight Shelf during spring and summer of 2003

Hydrographic anomalies on the South Atlantic Bight Shelf during spring and summer of 2003. Aretxabaleta A., Nelson J. R., Werner F. E., Seim H. E., Blanton B. O., Blanton J. O., Li C., Moore T., Tzeng M. Outline. General aspects Anomalous atmospheric conditions

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Hydrographic anomalies on the South Atlantic Bight Shelf during spring and summer of 2003

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  1. Hydrographic anomalies on the South Atlantic Bight Shelf during spring and summer of 2003 Aretxabaleta A., Nelson J. R., Werner F. E., Seim H. E., Blanton B. O., Blanton J. O., Li C., Moore T., Tzeng M. ASLO 17-Jun-2004

  2. Outline • General aspects • Anomalous atmospheric conditions • Anomalous hydrographic conditions • River discharge • Salinity stratification • Temperature stratification • Origin of shelf water • Effect of Gulf Stream • Preliminary model results • Conclusions ASLO 17-Jun-2004

  3. Region • Main inputs of water : • river discharge • interaction with Gulf Stream through meanders and filaments • exchange with the Mid Atlantic Bight through the Cape Hatteras region. ASLO 17-Jun-2004 Bane et al., 2001

  4. Wind temporal variability Mean along-shelf wind statistical test comparison for Buoy 41008 (Gray’s Reef) 2003 Prev. years Signif. greater Apr -0.01 0.42 No May 1.42 0.66 Yes Jun 3.47 1.20 Yes Jul 3.83 2.51 Yes Aug 2.31 0.92 Yes Sep -3.29 -1.52 No ASLO 17-Jun-2004

  5. Wind persistence ASLO 17-Jun-2004

  6. Wind anomaly spatial variability ASLO 17-Jun-2004

  7. Rainfall ASLO 17-Jun-2004

  8. May Salinity ASLO 17-Jun-2004

  9. June Temperature ASLO 17-Jun-2004

  10. August Temperature ASLO 17-Jun-2004

  11. August Density ASLO 17-Jun-2004

  12. T-S characteristics ASLO 17-Jun-2004

  13. Origin of upwelled water where α is the thermal expansion, β is the saline contraction, TGS is the Gulf Stream temperature and Tj is the observed temperature ASLO 17-Jun-2004

  14. Sea Level ~15-20 cm lower than clim. values ASLO 17-Jun-2004 Weisberg & Liu, pers. comm.

  15. Gulf Stream transport Adapted from Baringer & Larsen, 2001 ASLO 17-Jun-2004

  16. Modeling results Barotropic + clim wind Vs Barotropic + 2003 wind ASLO 17-Jun-2004

  17. Modeling results Barotropic reduced mixing ASLO 17-Jun-2004

  18. Remaining questions Gulf Stream effects • Gulf Stream position • Meander activity anomalous Modeling activities • Relative importance of different forcings • Anomalous wind alone • Effect of river discharge and increased stratification in spring • Effect of Gulf Stream • Estimate volume of anomalous water on the shelf • Effects on circulation and biological implications ASLO 17-Jun-2004

  19. Conclusions • Anomalous upwelling favorable winds (strength and persistence) were a principal driver of the event • Increased river discharge could have preconditioned the shelf through late spring salinity stratification that by early summer became thermal stratification. • The cold water upwelled onto the shelf and the deep Gulf Stream water presented similar characteristics suggesting that the anomalous water came from the deep part of the Stream. • Further analysis of observations and model simulations are needed to quantify the effect of the different forcing mechanisms. ASLO 17-Jun-2004

  20. Acknowledgements Funding • SEACOOS (ONR) • SABLAM (NOPP) People: John Bane, Bob Weisberg, Chris Meinen, Ed Kearns … ASLO 17-Jun-2004

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