Submesoscale tidal eddies in the wake of coral islands and reefs: satellite data and numerical modelling

Delandmeter, Philippe; Lambrechts, Jonathan; Marmorino, G. O.; Legat, Vincent; Wolanski, Eric; Remacle, Jean‐François; Chen, Wei; Deleersnijder, Éric

doi:10.1007/s10236-017-1066-z

Cited by 30 publications

(32 citation statements)

References 51 publications

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“…While some sources of processing and environment noise have been identified, further attention is needed for identifying and quantifying noise in the derived flow field. Despite these shortcomings, the approach examined here is generally applicable, as previous studies using WorldView imagery analyzed with the same optical-flow algorithm have shown it provides a new way to quantify spatially complex phenomena and to assess the fidelity of high-resolution coastal circulation models [8,9].…”

Section: Discussionmentioning

confidence: 99%

“…High spatial resolution imagery from satellites capable of along-track stereo, or from satellites that follow each other closely in time on similar orbits, can be exploited for target motion given appropriate time lags between the image acquisitions [1][2][3][4][5][6][7][8][9]. In the ocean, targets take the form of spatial gradients and other features in ocean color and surface temperature, suspended material, surface films, and (as in this work) algae.…”

Section: Introductionmentioning

confidence: 99%

“…In the ocean, targets take the form of spatial gradients and other features in ocean color and surface temperature, suspended material, surface films, and (as in this work) algae. Ocean currents can be deduced from time-lagged images by using various techniques such as maximum cross-correlation [2,4,8] and optical flow [4][5][6][7][8][9]. Particularly exciting is the possibility of using high-resolution time-lagged imagery to explore the realm of the ocean submesoscale, in which strong surface convergences and downwelling become associated with horizontal density fronts and cyclonic vortices e.g., References [10,11].…”

Section: Introductionmentioning

confidence: 99%

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Use of WorldView-2 Along-Track Stereo Imagery to Probe a Baltic Sea Algal Spiral

Marmorino

Chen

2019

Remote Sensing

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The general topic here is the application of very high-resolution satellite imagery to the study of ocean phenomena having horizontal spatial scales of the order of 1 kilometer, which is the realm of the ocean submesoscale. The focus of the present study is the use of WorldView-2 along-track stereo imagery to probe a submesoscale feature in the Baltic Sea that consists of an apparent inward spiraling of surface aggregations of algae. In this case, a single pair of images is analyzed using an optical-flow velocity algorithm. Because such image data generally have a much lower dynamic range than in land applications, the impact of residual instrument noise (e.g., data striping) is more severe and requires attention; we use a simple scheme to reduce the impact of such noise. The results show that the spiral feature has at its core a cyclonic vortex, about 1 km in radius and having a vertical vorticity of about three times the Coriolis frequency. Analysis also reveals that an individual algal aggregation corresponds to a velocity front having both horizontal shear and convergence, while wind-accelerated clumps of surface algae can introduce fine-scale signatures into the velocity field. Overall, the analysis supports the interpretation of algal spirals as evidence of a submesoscale eddy and of algal aggregations as indicating areas of surface convergence.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Use of WorldView-2 Along-Track Stereo Imagery to Probe a Baltic Sea Algal Spiral

Marmorino

Chen

2019

Remote Sensing

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“…Unstructured grids are particularly useful in coral reef systems (Lambrechts et al, 2008) as a high spatial resolution is required to avoid erasing small reefs and to accurately simulate the current shear distribution near reef edges (Wolanski et al, 1996). SLIM has been used to effectively model the hydrodynamics of the GBR system (e.g., Lambrechts et al, 2008;Delandmeter et al, 2017;Wildermann et al, 2017). The two-dimensional depth averaged version of SLIM was used in this study; this was valid because two-dimensional depth averaged models can realistically simulate observed currents in shallow, vertically well mixed water (Lambrechts et al, 2008).…”

Section: Biophysical Modelingmentioning

confidence: 99%

Wind Conditions on the Great Barrier Reef Influenced the Recruitment of Snapper (Lutjanus carponotatus)

et al. 2018

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Most coral reef fishes have a pelagic larval stage before recruiting to reefs. The survival of larvae and their subsequent recruitment can drive the dynamics of reef populations. Here we show that the recruitment of the snapper Lutjanus carponotatus to One Tree Island in the Capricorn Bunker Group, in the southern Great Barrier Reef, was highly variable over 23 years. We predicted that the currents in the Capricorn Bunker Group, including their wind driven components and the Capricorn Eddy (a nearby transient oceanic eddy), would affect patterns of recruitment. A biophysical model was used to investigate this prediction. L. carponotatus were collected from One Tree Island and the dates when they were in the plankton as larvae were determined from their otoliths. The winds present during the pelagic phases of the fish were examined; they were found to have survived either longshore (SSE) winds that induced little cross shelf movement in the larval plume or cross shelf (ENE) winds that induced little longshore movement. The unidirectional transportation of the larval plume in these conditions was favorable for recruitment as it kept the plume concentrated in the Capricorn Bunker Group. These winds were more prevalent in the periods of peak L. carponotatus production that preceded high recruitment. Dispersal under average winds (6.2 m s −1 from the prevailing ESE) and strong winds (velocity 1.5 times average), with and without the Capricorn Eddy, was also modeled. Each of these combinations were less favorable for recruitment than the longshore and cross shelf winds larval L. carponotatus survived before reaching OTI. The larval plume was comparatively less concentrated in the Capricorn Bunker Group under average winds. Strong winds transported the larval plume far longshore, to the NW, away from the Capricorn Bunker Group, while the Capricorn Eddy transported larvae seaward into oceanic waters. Larval swimming could counteract these dispersive forces; however, significant dispersion had occurred before larvae developed strong swimming and orientation abilities. This study provides a physical proxy for the recruitment of snapper. Further, we have demonstrated that great insights into recruitment variability can be gained through determining the specific conditions experienced by survivors.

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“…21 Though numerous studies have been performed on coral reefs, these analyses lack a 22detailed study of flow inside a single colony. Most of these studies were performed either 23 above the coral canopy or on a complete reef [22,23] without considering the arbitrary 24 shape of geometry. One of the reasons for the lack of such critical study might be the 25 complexity of measuring the flow parameters in close proximity to the coral's surface.…”

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confidence: 99%

Effects of coral colony morphology on turbulent flow dynamics

Hossain

Staples

2019

Preprint

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Local flow dynamics play a central role in physiological processes like respiration and nutrient uptake in coral reefs. Despite the importance of corals as hosts to a quarter of all marine life, and the pervasive threats currently facing corals, little is known about the detailed hydrodynamics of branching coral colonies. Here, in order to investigate the effects of the colony branch density and surface roughness on the local flow field, three-dimensional simulations were performed using immersed boundary, large-eddy simulations for four different colony geometries under low and high unidirectional oncoming flow conditions. The first two colonies were from the Pocillopora genus, one with a densely branched geometry, and one with a comparatively loosely branched geometry. The second pair of colony geometries were derived from a scan of a single Montipora capitata colony, one with the verrucae covering the surface intact, and one with the verrucae removed. We found that the mean velocity profiles in the densely branched colony changed substantially in the middle of the colony, becoming significantly reduced at middle heights where flow penetration was poor, while the mean velocity profiles in the loosely branched colony remained similar in character from the front to the back of the colony, with no middle-range velocity deficit appearing at the center of the colony. When comparing the turbulent flow statistics at the surface of the rough and smooth M. capitata colonies, we found higher Reynolds stress components for the smooth colony, indicating higher rates of mixing and transport compared to the rough colony, which must sacrifice mixing and transport efficiency in order to maintain its surface integrity in its natural high-flow environment. These results suggest that the densely branched, roughly patterned corals found in high flow areas may be more resistant not only to breakage, but also to flow penetration. motions transport planktonic food to the reef, while diffusion [3,4] takes place at a 6 much smaller scale at the coral surface. For the smaller scale processes, experimental 7 studies [5,6] show that growth direction, dimensions, and sparsity of branches depend 8 on the flow profile inside the coral [7][8][9]. Similarly, the velocity profile controls the 9 nutrient distribution [7,[10][11][12][13]. and physiological processes like photosynthesis and 10 respiration [14-17] near the coral surface. Flow motion also controls the thermal 11 micro-environment [18,19] at the coral surface, which is extremely important for 12 incidents like coral bleaching. Both the transfer of nutrients from the water column to 13 the coral and the transfer of byproducts from the coral to the water column depend on 14 the details of the flow through and around the coral [20, 21]. It is clear from the 15 discussion that all of these physical parameters are directly related to the flow 16 conditions in and around the coral geometry. To obtain a clear picture of this 17 interdependent relationship, the authors tried to find answers ...

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Submesoscale tidal eddies in the wake of coral islands and reefs: satellite data and numerical modelling

Abstract: z Important note To cite this publication, please use the final published version (if applicable). Please check the document version above.

Cited by 30 publications

References 51 publications

Use of WorldView-2 Along-Track Stereo Imagery to Probe a Baltic Sea Algal Spiral

Use of WorldView-2 Along-Track Stereo Imagery to Probe a Baltic Sea Algal Spiral

Wind Conditions on the Great Barrier Reef Influenced the Recruitment of Snapper (Lutjanus carponotatus)

Effects of coral colony morphology on turbulent flow dynamics

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