IV. Conclusion III. Discussion Currents: • Geostrophic balance existed between FC and sea levels at weekly intervals, in an inverse relation by the 180°phase (Fig 2). • Currents were consistent at all locations, with along-shelf currents dominating (Fig 3). • Stronger semidiurnal and weaker diurnal signals in currents and sea level (Fig 4). Subtidal Hydrodynamics at Cape-Associated Shoals Sabrina Marie Parra 1* , Arnoldo Valle-Levinson 2 , Peter N. Adams 3 , Juan Felipe Paniagua-Arroyave 3 1 American Society of Engineering Education Research Associate at Naval Research Laboratory, Stennis Space Center, MS; 2 Department of Civil and Coastal Engineering, University of Florida, Gainesville, FL; 3 Department of Geological Sciences, University of Florida, Gainesville, FL. Inner-shelf subtidal currents at Cape Canaveral were dominated by the along-shelf component, which was controlled by the geostrophic balance between FC and sea levels, with secondary effects from weekly north winds. The inner-shelf is mainly affected by wind and surface gravity waves with secondary forcing from offshelf currents [1]. The influence of winds, waves and the Florida Current (FC) on subtidal currents were investigated at the Cape Canaveral inner-shelf in Florida. The study focused on two cape-associated shoals: Chester Shoal at False Cape and Canaveral II Shoal at Cape Canaveral (Fig 1). I. Introduction II. Data Acoustic Doppler current profilers (ADCPs) were moored on either side (seaward and landward) of Canaveral (Can.) and Chester (Che.) shoals for 52 days in 2013 (Fig 1). The following variables were filtered to remove tides and the inertial period: • ADCP depth, and depth-averaged currents and backscatter • NOAA buoy wind velocity and wave parameters • Florida Current transport • Sea level at Trident Pier south of Cape Canaveral Fig. 1: Bathymetric map of Cape Canaveral with the four moorings (circles), National Oceanographic and Atmospheric Administration (NOAA) buoy #41009 (diamond), the NOAA Trident Pier tidal gauge location (black square) and FC transport obtained from cable measurements over the green line in the inset Florida map. Fig 3: Cape Canaveral subtidal parameters. All vectors are in oceanographic convention. Currents and echo anomaly were depth-averaged. Fig. 4: Spectra of depth-averaged currents, sea levels and depth-averaged echo intensity anomaly from each mooring. Black lines represent the 95% confidence interval. Fig. 5: CEOF of currents. A) CEOF mode 1 time series for the cross-shelf (blue) and along-shelf (green) velocity components. Mode 1 vertical profiles for the B) cross and C) along shelf velocities for each mooring. Fig. 6: Wavelet coherences between CEOF mode 1 of the cross-shelf (first column) and along-shelf (second column) currents and forcing parameters. Fig. 2: Geostrophic balance. A) Subtidal sea level at Trident Pier (blue) and FC transport (black). B) Wavelet coherence between blue and black lines. Contours show high (red) and low (blue) coherences. Areas enclosed by black contours represent coherence >95% confidence limit. Shaded areas are the cone of influence where values are less reliable. Coherence phase angles are represented by the vectors [2, 3]. VI. References [1] Lentz & Fewings (2012) Annu. Rev. Marine. Sci. 4. [2] Torrence & Compo (1998) Bull. Am. Meteorol. Soc. 79. [3] Grinsted et al. (2004) Nonlinear. Proc. Geoph. 11. [4] Bjornsson & Venegas (1997) CCGCR Report 97. Fig. 2: Geostrophic Balance: Florida Current Complex Empirical Orthogonal Function (CEOF): • CEOF shows dominant spatial and temporal structures [4]. • Mode 1 accounted for 92% of the variance, with unidirectional vertical profiles throughout (Fig 5B,C). • Along-shelf current vertical structures had same direction and magnitude, while cross-shelf currents varied with Chester weaker than Canaveral. • Cross-shelf vertical structure at Chester east was opposite the rest, showing convergence/divergence at Chester Shoal. Wavelet Coherence: EOF 1 vs Forcings • Fortnightly and weekly north winds played a role in shelf currents, suggesting passage of weather systems (Fig 6). • Sea levels dominated the along-shelf currents at almost all periods (Fig 6). • Weekly FC oscillations dominated both current components during the first half when FC variability was high. V. Acknowledgements This work was supported by a Bureau of Ocean Energy Management grant. Special thanks to Viktor Adams, Michael Dickson, Lauren Ross, Jackie Branyon and others that helped with fieldwork. The FC transport is freely available from the Atlantic Oceanographic and Meteorological Laboratory (www.aoml.noaa.gov/phod/floridacurrent/). Thanks to Aslak Grinsted, John Moore and Svetlana Jevrejeva for their MATLAB wavelet package (noc.ac.uk/using-science/crosswavelet-wavelet-coherence). *[email protected] Fig. 3: Parameters Fig. 5: Complex Empirical Orthogonal Function - Mode 1 Fig. 4: Spectral Analysis Fig. 6: Wavelet Coherence Analysis Fig. 1: Study Area B A A B C Cross-Shelf Along-Shelf Along-Shelf Cross-Shelf Chester East Chester West Canaveral East Canaveral West Trident Pier FC Florida Latitude, °N Longitude, °E Along-Shelf Currents Cross-Shelf Currents Sea Level Chester East Chester West Canaveral East Canaveral West Cross-Shelf EOF vs … Along-Shelf EOF vs …