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Research about Dry Tortugas

Source-linked reports with geographic coverage including Dry Tortugas.

6 recordsLinked to original sources
USGS2017

Increased hurricane frequency near Florida during Younger Dryas Atlantic Meridional Overturning Circulation slowdown

The risk posed by intensification of North Atlantic hurricane activity remains controversial, in part due to a lack of available storm proxy records that extend beyond the relatively stable climates of the late Holocene. Here we present a record of storm-triggered turbidite deposition offshore the Dry Tortugas, south Florida, USA, that spans abrupt transitions in North Atlantic sea-surface temperature and Atlantic Meridional Overturning Circulation (AMOC) during the Younger Dryas (12.9–11.7 ka). Despite potentially hostile conditions for cyclogenesis in the tropical North Atlantic at that time, our record and numerical experiments suggest that strong hurricanes may have regularly affected Florida. Less severe surface cooling at mid-latitudes (∼20°–40°N) than across much of the tropical North Atlantic (∼10°–20°N) in response to AMOC reduction may best explain strong hurricane activity during the Younger Dryas near the Dry Tortugas and possibly along the entire southeastern coast of the United States.

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USGS2010

Holocene aggradation of the Dry Tortugas coral reef ecosystem

Radiometric age dating of reef cores acquired at the Dry Tortugas coral reef ecosystem (DTCRE) was merged with lidar topographic mapping to examine Holocene reef development linked to spatial variation in growth and erosion under the control of sea level. Analysis of variance of lidar topography confirmed the presence of three distinct terraces on all three major DTCRE banks (Loggerhead Bank, Garden Bank, and Pulaski Bank). Reef building on the middle terrace (T2) began atop Pleistocene edifices on Loggerhead Bank by 8.0 ka (thousands of years ago) and on Garden Bank by 7.2 ka at elevations of about −16.0 m and −11.9 m, respectively, relative to present mean sea level. Following this initiation at different elevations, T2 aggraded vertically on both banks at different rates during the early Holocene under foundering conditions until a highstand at 5.2 ka, resulting in a 2.21 m offset in present mean T2 elevation between these banks. Initiation of an upper terrace (T1) occurred on both Loggerhead Bank and Garden Bank in association with sea-level fall to a lowstand at near 4.8 ka. This upper terrace initiated on Garden Bank at about 5.0 ka and then grew upward at rate of 2.5 mm year −1 until approximately 3.8 ka . On Loggerhead Bank, the upper T1 terrace formed after 4.5 ka at a higher vertical aggradation rate of 4.1 mm year −1 , but at a lower elevation than on Garden Bank. Terrace T1 aggraded on Loggerhead Bank below the elevation of lowstands during late Holocene sea-level oscillation, and consequently erosion on Loggerhead Bank was minimal and likely limited to the crest of the upper terrace. In contrast, after 3.8 ka terrace T1 on Garden Bank likely tracked sea level and consequently underwent erosion when sea level fell to second, third and fourth lowstands at 3.3, 1.1, and 0.3 ka.

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USGS2008

Reef communities in the Dry Tortugas (Florida, USA): Baseline surveys for the new no-take area

To understand the current community structure on reefs in the Dry Tortugas, we conducted specieslevel surveys of macroalgae, coral diversity, herbivorous and game fishes, urchins, and substratum composition (e.g., rugosity) in shallow (3- to 5-m depth) low-relief reef and hardbottom habitats in October 2007. We had particular interest in the ecological process of herbivory inside and outside of the “no-take” Research Natural Area (RNA) designated by the U.S. National Park Service in 2007, and establishing a baseline to assess future changes to trophic functioning. Diadema antillarum and herbivorous fish abundance, percent cover of macroalgae, and species richness of corals and gorgonians at the 18 randomly selected survey sites were not significantly different inside vs. outside of the RNA. Mean densities of D. antillarum ranged from 0.01 to 0.54 individuals m -2 , with 11 of the 18 sites having densities above 0.10 individuals m -2 . Both D. antillarum density and coral species richness were positively correlated to rugosity of the substratum. Diadema antillarum density was also positively related to percentage of the substratum composed of Acropora cervicornis rubble. Improved trophic functioning and increases in D. antillarum can improve reef condition in the Dry Tortugas, and the RNA is an important management tool to achieve increases in reef resilience to global-scale stressors.

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USGS1977

Topographic control and accumulation rate of some Holocene coral reefs: south Florida and Dry Tortugas

Core drilling and examination of underwater excavation on 6 reef sites in south Florida and Dry Tortugas revealed that underlying topography is the major factor controlling reef morphology. Carbon-14 dating on coral recovered from cores enables calculation of accumulation rates. Accumulation rates were found to range from 0.38 m/1000 years in thin Holocene reefs to as much as 4.85 m/1000 years in thicker buildups. Cementation and alteration of corals were found to be more pronounced in areas of low buildup rates than in areas of rapid accumulation rates. Acropora palmata, generally considered the major reef builder in Florida, was found to be absent in most reefs drilled. At Dry Tortugas, the more than 13-meter thick Holocene reef did not contain A. palmata. The principal reef builders in this outer reef are the same as those which built the Pleistocene Key Largo formation, long considered to be fossilized patch reef complex.

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