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Sea Service Temperature Variability in the Northwestern Hawaiian Region

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Title:Sea Service Temperature Variability in the Northwestern Hawaiian Region
Authors:Veillerobe, Yves
Contributors:Becker, Janet (advisor)
Merrifield, Mark (advisor)
Oceanography (department)
Global Environmental Science (department)
Keywords:physical oceanography
Date Issued:2004
Publisher:University of Hawaiʻi at Mānoa
Place of Publication:Honolulu
Abstract:The first massive coral bleaching event reported in the Northwestern Hawaiian
Islands (NWHI), the world’s second largest coral reef reserve, occurred during summer
2002. Bleaching at these remote coral atolls is believed to be related to elevated surface
temperatures. The temporal and spatial variability of near-surface temperatures at the
NWHI are analyzed using Reynolds Sea Surface Temperature (SST) (1 week averages,
11/1981-11/2003), and in situ temperature measured within the coral atolls (15 minute
averages, 9/ 2002 – 8/2003) as part of the Northwestern Hawaiian Islands Reef
Assessment and Monitoring Program (NOWRAMP). The focus is on conditions leading
to high SST anomalies during the peak of the seasonal heating cycle (August-September).
Comparison of Reynolds and in situ data shows reasonable correlations (0.83-0.99),
regression coefficients (0.81-1.14), and residual errors (0.39-1.30°C). During summer
months, mean differences between in situ and Reynolds SST do not show a consistent
bias between the two instruments. These results suggest that Reynolds SST is a
reasonable indicator of temperature variability at the coral atolls. Lacking in situ data
before or during the 2002 bleaching event, Reynolds SST is used to characterize summer
surface temperature variability at the NWHI, and to identify possible bleaching periods.
Anomalously high SSTs occurred during summer 2002, but only at the three most
northern atolls: Kure, Midway, and Pearl & Hermes. SSTs at the other NOWRAMP
study sites were similar to long term conditions. The summer of 2002 was the only
period of sustained high temperatures during the 22 year record. The intensity and
duration of coral bleaching periods have been examined in terms of accumulated heat
stress based on estimated thermal thresholds for bleaching at every NOWRAMP station.
Again, only the 2002 event appears to have been significant, although the accumulated
heat stress values barely reached 20 Degree Heating Days. Comparison with NCEP
Reanalysis wind anomalies shows that the generation of high SSTs during summer 2002
is associated with a decrease in wind speeds, which occurs over short spatial scales. The
v
wind relaxation is caused by mid-latitude synoptic variations, which are essentially
weather related with low predictability. The conclusion is that the 2002 bleaching event
was caused by an unusual summer cessation of the Northeast Trades over the northern
most NWHI region, causing enhanced surface heat flux and warming of the surface layer.
Pages/Duration:88 pages
URI:http://hdl.handle.net/10125/69405
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Rights Holder:Veillerobe, Yves
Appears in Collections: Global Environmental Science (GES)


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