Spatial and Temporal Variability of Internal Wave Forcing on a Coral Reef

Abstract

The deployment of a dense spatial array of temperature sensors on a coral reef in the Florida Keys provided a unique view of the interaction of cool water incursions generated by internal waves with the three-dimensional reef bathymetry. Water temperature on the reef surface was sampled every 5 s at 100 points on a 100 m by 150 m grid with concomitant measurements of water column velocity and temperature from mid-May through mid-August 2003. Episodic incursions of cool, subsurface water were driven by periods of strong semidiurnal internal tide and higher-frequency internal wave activity. For every time step in the data record the mean profile of temperature as a function of depth is calculated with a 3-m vertical averaging length scale. Subtracting this mean profile from the raw record yields a within depth, horizontal temperature anomaly. Visualization through time of the anomaly mapped onto the measured reef bathymetry reveals episodic variability of thermal patchiness across the reef as well as persistent features associated with reef bathymetry. Variation in the nature of the cooling and resulting thermal heterogeneity among events and seasons suggests multiple modes of cool water incursion ranging from unbroken, tidal period internal waves to packets of higher-frequency, energetic, broken internal bores.

Large-amplitude internal waves sustain coral health during thermal stress

“…Internal waves can mix deep sub-pycnocline waters into shallow reef areas at tidal and higher frequencies (Leichter et al 2005;Schmidt et al 2012;Wall et al 2012). Although they are ubiquitous in stratified tropical regions with strong tidal flows (Jackson 2007), their role in shaping reef communities is largely unexplored.…”

The effects of a variable temperature regime on the physiology of the reef-building coralSeriatopora hystrix: results from a laboratory-based reciprocal transplant

“…DeSalvo et al, 2008;but see Dove, 2004;Putnam and Edmunds, 2009;Putnam et al, 2010;Oliver and Palumbi, 2011;Putnam and Edmunds, 2011). However, many coral reefs experience large variations in temperature (Craig et al, 2001; Leichter et al, 2005;Leichter et al, 2006;Sheppard, 2009), and some even undergo dramatic temperature changes over a time scale of minutes to hours. For instance, coral reefs of Nanwan Bay, the southernmost embayment of Taiwan, experience episodic upwelling (Lee et al, 1999) whereby the temperature may change up to 10°C over the course of a summer day during spring tides (Jan and Chen, 2008).…”

Nitrogen and oxygen isotopic signatures of subsurface nitrate seaward of the Florida Keys reef tract

“…The thermocline seaward of the Florida Keys is often relatively shallow (e.g., 50 m depth), especially in summer, and upward incursions of cool (22-26uC) water onto reef slopes occur frequently throughout the Keys (Leichter et al 2003). Previous water column sampling has shown relatively high concentrations of subsurface nitrate (5-20 mmol L 21 ) and soluble reactive phosphate (0.1-2.0 mmol L 21 ) below the thermocline (Lee et al 1992;Leichter et al 2003) and clearly points to the potential for the offshore subsurface nutrient pool to be an important source of nutrients reaching reef slopes, especially at depths of $10 m. In addition to being attenuated with depth, incident internal waves interact with reef topography, producing significant heterogeneity in cool water exposure and residence times within, as well as across depths (Leichter et al 2005).…”