Author : Christopher Matthew Kovalik
Publisher :
ISBN 13 :
Total Pages : 128 pages
Book Rating : 4.:/5 (93 download)
Book Synopsis Tempo and Mode of Coral-reef Development in the Pacific Ocean by : Christopher Matthew Kovalik
Download or read book Tempo and Mode of Coral-reef Development in the Pacific Ocean written by Christopher Matthew Kovalik and published by . This book was released on 2015 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt: The full effects of climate change are still unknown, but the future of coral-reefs appears bleak. Recently, there have been major episodes of coral bleaching and coral disease around the world. The recent loss of coral has been extreme, but there is some precedent for coral-reef collapse in the geologic record; several millennial-scale hiatuses in reef growth have been found throughout the Pacific Ocean in the late Holocene. A ~2,500-year hiatus in reef growth was found at multiple sites in Pacific Panamá, Costa Rica, Australia and Hawaii, as well as several small-scale hiatuses in the northern Ryukyu Islands. I used push-coring to compare the Holocene histories of two sites on opposite sides of the Pacific Ocean to see if they experienced this same millennial-scale hiatus in reef growth. The first site was Coiba Island, Panamá. This site has some of the oldest and thickest reefs in the eastern Pacific, in part due to its relatively stable year-round sea-surface temperatures. Coiba is not affected by tropical cyclones, as they move westward across the Pacific. The second coring site was Kumejima, Japan. Kumejima is bathed by the warm waters of the Kuroshio Current. Kumejima is part of the Ryukyu Island Arc, which is highly exposed to storm activity, experiencing numerous tropical cyclones annually. The climatic conditions at each site were examined through wavelet analysis. Wavelet analysis of sea-surface temperature anomalies, using monthly data from 1870-2012, was undertaken for each site, highlighting the periodicity and timing of trends in anomalous temperatures. These records were then compared with each other using wavelet-coherence analysis. Wavelet-coherence analysis revealed correlations between the two wavelets, highlighting the periodicity and time period when these sites were experiencing similar anomalous temperatures. Using two different forms of wavelet coherence, it was shown that these sites experienced anomalous temperatures at the ENSO (El Niño/Southern Oscillation) timescale only periodically throughout the past century and a half. There was also visible correlation at the decadal timescale twice, likely reflecting the Pacific Decadal Oscillation. Wavelet analysis made shared climatic trends between these sites much easier to detect and also revealed that these two dissimilar sites are linked climatically. Using cores taken from coral-reef framework to assess coral growth of the past ~6000 cal BP (calibrated calendar years before 1950), a hiatus in reef growth was found from ~4290-2024 cal BP at Coiba. Even with some of the best conditions for coral growth in the eastern Pacific, Coiba Island also experienced this millennial-scale hiatus in reef growth. The hiatus found at Coiba occurred contemporaneously with the millennial-scale hiatuses in reef growth observed in other areas of Pacific Panamá. This hiatus in reef growth took place during a time of increased ENSO activity; a similar increase in ENSO activity is predicted under future climate-change conditions. Extreme El Niño and extreme La Niña events are predicted to increase with climate change, threatening the precious coral-reef ecosystem that is already sparse in the equatorial eastern Pacific. Nearly all corals in the cores analyzed from Kumejima were in very poor taphonomic condition and were comprised nearly entirely of Acropora spp. encrusted in coralline algae. Radiocarbon ages from the Kumejima cores revealed a mixed deposition. All dates collected from depths ranging from 30-235 cm below the surface were between the ages of 2966-3775 cal BP. All of these corals dated within the time frame of the hiatus observed in Panamá, showing that there was coral growth at Kumejima during this time. The dates obtained from coral from Kumejima were also during the short-term hiatus found at nearby Kodakarajima, in the Northern Ryukyus, meaning the hiatus at Kodakarajima was likely a localized event. Every coral dated from Kumejima was alive during the Pulleniatina Minimum Event (PME), which is believed to have resulted in the slowing of the Kuroshio Current. Any alteration in the flow of the Kuroshio could have altered reef growth at Kumejima: my record from this site may represent rubble deposits during this event. Both of these sites are largely controlled by oceanic-atmospheric processes taking place on a large scale. Reef dynamics at Coiba Island were likely controlled by ENSO activity, especially Eastern Pacific El Niño, and this site has low coral diversity. On the other hand, reef development at Kumejima is influenced by storm activity, mainly tropical cyclones, which, in both frequency and intensity, can be attributed to the same forces controlling ENSO activity in the eastern equatorial Pacific. With the current projections of climate change the oceanic waters will warm, storm intensity will increase, ENSO events will become more extreme, and patterns of precipitation will likely change. Similar changes have occurred in the past, driving corals beyond their threshold of survival. The prediction of a more El Niño-like conditions in the future could be disastrous for both Coiba and Kumejima. Coiba would face higher than normal temperatures whereas Kume would experience an increase in the intensity of typhoons. These reefs have been resilient to temperature changes in the past, with Panamanian reefs recovering from an over 2000 year hiatus; if we can slow or reverse the current rate of climate change in the immediate future, these reefs still may stand a chance to survive.