Simulating sedimentation on the Great Bahama Bank – Sources, sinks and storms

Abstract

This study developed a high‐fidelity hydrodynamic simulation of sediment production, transport and deposition for the Great Bahama Bank. This model was run with a time‐step of 15 min for the entirety of 2016, forced by tides, off‐platform circulation and wind. Encompassed in this run are 364 days of fair‐weather conditions and two days when the passage of Category 4 Matthew brought hurricane‐force winds to the platform. This simulation therefore offers an excellent opportunity to contrast the sway of fair‐weather and storm‐weather conditions on sculpting the facies arrangement atop this 100 000 km2 shallow‐water carbonate platform. The work suggests that fair‐weather conditions are sufficient to deliver the platform's broad‐scale facies patterns. Even the lethargic currents of the platform interior can move mud (<63 μm) over 200 km from its source over the course of one year. Intense focusing of tidal currents between islands and close to the platform margin are ample to move coarse grains (>450 μm), at least locally, as is necessary to produce the vast ooid fairways for which the Great Bahama Bank is famed. Even at the height of Hurricane Matthew, average current speeds in these tidally‐dominated areas do not exceed the speeds simulated for fair‐weather conditions. Hence, the hurricane has negligible effect in these high‐energy areas. The hurricane does not have zero impact, though. For up to 110 km either side of the storm's track, winds exceeding 26 m/s induce currents that winnow mud over longer distances than delivered by fair‐weather conditions. Hence, the storm has a sedimentological signature which, albeit minor, might propagate into the depositional architecture of the platform when scaled over many storms through geological time. This work informs on the role of uniformitarianism versus catastrophism on carbonate sedimentation and casts doubt on geological interpretations of coarse‐grained storm deposits (tempestites) atop shallow‐water platforms.

Sedimentology of Modern Bahamian Carbonate Slopes: Summary and Update

“…The predominance of fine‐grained sediment export from platforms to slopes could be explained by the large amount of fine mud material covering the interior of the banks (Figure 1). Recent studies have discussed that wind‐induced currents and waves cause sediment suspension across the leeward margin of the GBB as tidal currents dominate this process along the wind‐dominated GBB margin (Lopez‐Gamundi et al., 2023). Hence, wind‐induced currents and waves move the mud easily toward the platform edges, forming peri‐platform ooze wedges present at the different margins (Chabaud, 2016; Chabaud et al., 2015; Droxler, 1984; Fauquembergue et al., 2018; Lantzsch et al., 2007; Roth & Reijmer, 2004, 2005; Wilber et al., 1990).…”

Sediment dynamics and geomorphology of a submarine carbonate platform canyon system situated in an arid climate setting

“…12). However, export of carbonate fines can be just as important during fair‐weather periods (Dierssen et al ., 2009; Lopez‐Garamundi et al ., 2022). The off‐platform transport may result in density cascading, as observed for the Great Bahama Bank (Wilson & Roberts, 1992, 1995; Hickey et al ., 2000; Roth & Reijmer, 2004, 2005; Dierssen et al ., 2009).…”

Spatial, seasonal and climatic drivers of suspended sediment atop Great Bahama Bank

“…, are agnostic to grain size. Atop GBB, however, fair‐weather currents are typically only swift enough to erode and suspend fine‐grained sediment (Lopez‐Gamundi et al ., 2022). Further, implicit to TSS Eq.…”

“…3B), which is the case for 52% of the GBB (Harris et al ., 2015; Purkis et al ., 2019). Of the remaining 48% of the platform where this correction is applied, <6% (2380 km 2 ) contains dense seagrass or algae meadows (Lopez‐Gamundi et al ., 2022). Hence, the authors contend for the corrected areas, R b (667) primarily represents the spectral signature of unvegetated carbonate sediment.…”

“…(B) True-colour MODIS satellite image of western margin of GBB acquired 14 February 2016 (left) and satellite retrieval of total suspended sediment (TSS) concentrations using method developed by Katlane et satellites have been used to map the end products of transportsuch as the size and geomorphology of shoals (Reeder & Rankey, 2008Harris et al, 2011;Purkis et al, 2012Purkis et al, , 2014)but, again, the focus of these studies is on coarse grains, and the distribution of suspended sediment in the water column is only inferred. Meanwhile, satellite-based studies on the suspension of fine-grained sediments atop GBB have focused on whitings (Robbins et al, 1997;Purkis et al, , 2023Yao et al, 2023) and storms (Acker et al, 2002;Rankey et al, 2004), rather than the sediment transport induced by fair-weather conditions across the entire platform (Lopez-Gamundi et al, 2022).…”