Status of Caribbean coral reefs after bleaching and hurricanes in 2005

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Rain bandsRain bandsStatus of Caribbean Coral Reefs after Bleaching and Hurricanes in 2005Hurricane MotionEye wallWavesEyeEye wallWavesStorm surgeCool wakeLatentheatLatentheatWarm waterWell-mixed water columnTurbulentmixingUpwellingCoralsThis diagram illustrates how a hurricane forms over warm ocean waters and starts spinningin a counter-clockwise direction in the Northern Hemisphere. Large storm waves may result insignificant coral reef damage. However, a hurricane will also cool surface waters and can oftenmitigate coral bleaching.While there is a minimum ocean surface temperature for hurricanes to form, the energythat drives a hurricane is supplied by the upper section of the water column, not just thesurface. Hurricane intensity is more closely linked to the ocean heat content than to surfacetemperature alone (4.). Once the eye of a hurricane moves over land it experiences greaterfriction and loses its source of moisture and heat, causing it to weaken. Hurricanes canalso weaken at sea if their energy source is reduced by encountering cool waters (fronts,upwellings), or their vortex development is inhibited by entering a zone of high vertical windshear.Hurricanes help to regulate the earth’s temperature, extracting heat from the ocean andredistributing it into the atmosphere; thereby moving tropical heat poleward. In the absenceof regular hurricanes, tropical oceans retain more heat, which can then lead to larger, moreintense hurricanes. Recent increases in ocean temperatures, very likely due to human-inducedclimate change, have seen tropical storms becoming stronger but not necessarily increasingin number (7. and Executive Summary p. 14).Globally averaged land and ocean temperatures in 2005 were the highest on record accordingto NOAA and NASA analyses, with temperatures slightly warmer than in 1998. The 2005hurricane season in the Atlantic and Caribbean was unprecedented, experiencing morethan twice the annual average of named tropical storms over the past century and thegreatest number of hurricanes in recorded history. While some of this may be attributed toimprovements in hurricane observation skills through satellites and other instruments, therecan be no doubt that 2005 was an extreme year for storm activity.32
Hurricanes and their Effect on Coral ReefsHurricanes are classified by their wind speed in the well-known Saffir-Simpson scale. Category 1storms have sustained wind speeds greater than 64 knots (33 m/s) and generally cause only minordamage upon landfall; Category 5 hurricane winds exceed 135 knots (69 m/s) and can devastatestructures with both winds and storm surge.Hurricane Category12345ImpactsWind 64-82 knots, storm surge 1.0-1.6 m, no real damage tobuilding structures, damage to treesWind 83-95 knots, storm surge 1.7-2.5 m, some roofing and windowdamage, considerable damage to treesWind 96-113 knots, storm surge 2.6-3.8 m, some building damage,large trees blown downWind 114-135 knots, storm surge 3.9-5.5 m, complete removal ofsome roofs, extensive window damage, most trees blown downWind 136+ knots, buildings fall over, storm surge 5.6+ m,widespread loss of roofs, some buildings destroyed, all trees blowndown(a wind speed of 100 knots = 185.2 km per hour = 51.4 metres per second)So Wh y w a s 2005 so Ac t i v e?Several factors are involved. There was an extensive region across the equatorial Atlanticwhere the vertical wind shear (the change in wind speed with height) was unusually low.Vertical wind shear interferes with the vertical structure of a hurricane and inhibits hurricaneformation. The rate of latent heat exchange (the transfer of water vapour energy from oceanto atmosphere) was 20% greater than the largest value in the previous 25-year period and,therefore, strongly favoured hurricane activity. Record warm surface temperatures acrossthe Gulf of Mexico, Caribbean and tropical Atlantic provided the energy source to form andsustain hurricanes. Sea-level pressure was exceptionally low across the Caribbean, againaiding hurricane formation (5.).Many of these factors have been linked to climate-scale variabilities. Perhaps the most wellknownof these is the El Niño-Southern Oscillation (ENSO); however, during 2005 conditionswere ENSO neutral for most of the year. Other large-scale variabilities that have beenlinked to observed oceanic and atmospheric conditions include the Atlantic Multi-decadalOscillation, the North Atlantic Oscillation and the Madden-Julian (40-day) Oscillation. It wasthe juxtaposition and magnitude of these causal factors that likely induced the record activityduring the 2005 hurricane season. The effect of these was exacerbated by climate change, thelargest contributor to the warm temperatures in the tropical Atlantic. Of the 0.9°C tropicalAtlantic temperature anomaly (compared with a 1901-1970 baseline), 0.2°C was attributableto the weak 2004-05 El Niño; less than 0.1°C was attributable to the Atlantic Multi-decadalOscillation; and most of the anomaly (0.45°C) was attributable to climate change (6.).A side-note to the extreme nature of the 2005 season is that none of the named stormstraversed Puerto Rico and the Lesser Antilles (Windward and Leeward Islands). Despite the33
Page 1 and 2: Stat u s o fCa r i b b e a nCo r a
Page 3 and 4: Dedication: This book is dedicated
Page 5 and 6: Status of Caribbean Coral Reefs aft
Page 25 and 26: Status of Coral Reefs in the Caribb
Page 35: 3. Hu r r i ca n e s a n d t h e i
Page 39 and 40: Hurricanes and their Effect on Cora
Page 41 and 42: 4. Th e 2005 Bl e a c h i n g Ev e
Page 43 and 44: The 2005 Bleaching Event: Coral-Lis
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Page 67 and 68: Coral Reefs of the U.S. Caribbean19
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The Effects of Coral Bleaching in t
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Status of Caribbean Coral Reefs aft
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9. Th e Effects o f Co r a l Bl e a
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10. Ma n ag i n g f o r Ma s s Co r
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Managing for Mass Coral Bleaching:
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Status of Caribbean coral reefs after bleaching and hurricanes in 2005

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