Variability of cold‐water coral mounds in a high sediment input and tidal current regime, Straits of Florida

Abstract

Cold-water coral mound morphology and development are thought to be controlled primarily by current regime. This study, however, reveals a general lack of correlation between prevailing bottom current direction and mound morphology (i.e. footprint shape and orientation), as well as current strength and mound size (i.e. footprint area and height). These findings are based on quantitative analyses of a high-resolution geophysical dataset collected with an Autonomous Underwater Vehicle from three cold-water coral mound sites at the toe of slope of Great Bahama Bank. The three sites (80 km 2 total) have an average of 14 mounds km )2 , indicating that the Great Bahama Bank slope is a major coral mound region. At all three sites living coral colonies are observed on the surface of the mounds, documenting active mound growth. Morphometric analysis shows that mounds at these sites vary significantly in height (1 to 83 m), area (81 to 6 00 000 m 2 ), shape (mound aspect ratio 0AE1 to 1) and orientation (mound longest axis 0 to 180°). The Autonomous Underwater Vehicle measured bottom current data depict a north-south flowing current that reverses approximately every six hours. The tidal nature of this current and its intermittent deviations during reversals are interpreted to contribute to the observed mound complexity. An additional factor contributing to the variability in mound morphometrics is the sediment deposition rate that varies among and within sites. At most locations sedimentation rate lags slightly behind mound growth rate, causing mounds to develop into large structures. Where sedimentation rates are higher than mound growth rates, sediment partially or completely buries mounds. The spatial distribution and alignment of mounds can also be related to gravity mass deposits, as indicated by geomorphological features (for example, slope failure and linear topographic highs) in the three-dimensional bathymetry. In summary, variability in sedimentation rates, current regime and underlying topography produce extraordinarily high variability in the distribution, development and morphology of coral mounds on the Great Bahama Bank slope.

Morphometric patterns in Modern carbonate platforms can be applied to the ancient rock record: Similarities between Modern Alacranes Reef and Upper Palaeozoic platforms of the Barents Sea

“…10A), are infinite, a property that cannot occur in nature (Halley et al, 2004). Real-world carbonate depositional systems, though, can display both self-similarity and scale invariance within certain thresholds and therefore are akin to a mathematical fractal over a limited range of scales (Rankey, 2002;Purkis and Kohler, 2008;Correa et al, 2012;Schlager and Purkis, 2013).…”

Genesis and morphology of cold-water coral ridges in a unidirectional current regime

“…The recent IODP Expedition 307 (Challenger Mound) provided drilling evidence of modern mound constructors, documenting a 155 m column of cold-water corals that spanned the entire mound sequence (Ferdelman et al, 2006;Kano et al, 2007;Thierens et al, 2010). Elsewhere, cold-water corals are interpreted to drape over boulder deposits (Bahamas slope, Mullins et al, 1984;Correa et al, 2011), morainic ridges (Norwegian Shelf, Freiwald et al, 1999), pockmarks (Rockall Trough, Masson et al, 2003), or sediment waves (Belgica Mound province, Huvenne et al, 2005;Wheeler et al, 2005;Foubert et al, 2011). Early submersible dives at the base of Miami Terrace described corals forming muddy mounds (Neumann and Ball, 1970). These observations led to the popular coral mound formation concept, where coral frameworks baffle and trap fine sediments brought into suspension by the current (e.g.…”

Observation of sand waves in the Taiwan Banks using HJ-1A/1B sun glitter imagery

“…The ridgelength frequency distribution for each subregion is determined by plotting the exceedance probability versus length. This parameter represents the probability (y axis) that a given sand wave will be equal to or greater than a given length 23 [x axis; Fig. 15(b)].…”

“…23 The Taiwan Strait is located between mainland China and the Taiwan Island, and links the East China Sea in the north to the South China Sea in the south. The current regime in the Taiwan Strait is dominated by a semidiurnal tide and the M 2 tide which is the strongest and attracts a significant amount of research.…”

“…Correa et al studied the morphology and development of coral mounds based on quantitative analyses of a highresolution geophysical dataset collected with an autonomous underwater vehicle. 23 However, the existing MB data in the TB are too limited for complete regional distribution, density, and ridge length of the sand waves. Density and the ridge length of sand waves in the TB have not been reported or addressed in the literature so far.…”