17:15 〜 19:15
[MGI25-P04] Relationship between sea surface temperature reconstructed from coral skeletons and El Niño Modoki on Kure Island, Northwestern Hawaiian Islands
キーワード：サンゴ骨格、Sr/Ca比、表層海水温、中央太平洋、エルニーニョモドキ
Kure Island, located in the central Pacific Ocean, is an atoll approximately 10 km in diameter at the northwestern tip of the Hawaiian Islands. Paleoclimatic records from Kure Island, which has little anthropogenic influence and is in the open ocean, are essential for understanding the variability of atmospheric and oceanic environments in the Central Pacific. Using strontium/calcium ratios (Sr/Ca) of reef coral skeletons, we reconstruct the variability of seawater surface temperature over the past 63 years and discuss the factors contributing to this variability. This study used cores drilled at Kure Atoll (Siciliano et al., 2005). Soft X-ray images of the core samples, which were formed into plates, revealed 63 annual bands, indicating that records from 1939-2002 are preserved in this sample. Micro-powder samples were collected at 0.1 mm intervals (approximately 18 points/year) along the maximum growth axis of the annual bands. Sr/Ca ratio analysis was performed using an induction plasma atomic emission spectrometer, and the age model was determined by comparing the results of Sr/Ca crimping with the satellite-observed water temperature. During the period when the satellite-observed water temperature was not available, the time axis was extrapolated with the maximum value of Sr/Ca in February and the minimum value in August.
The Sr/Ca ratio varied from 8.93 to 10.2 mmol/mol and showed a distinct annual cycle. A comparison of the Sr/Ca with satellite-observed water temperatures showed a significant strong correlation (r=0.72, n=121, p<0.06). Correlation maps between the reconstructed SST from Sr/Ca of Kure Island and the satellite-observed water temperature were made for the summer (Aug-Oct) and winter (Dec-Feb) periods. The winter correlograms show a positive correlation from the western Pacific to the northeast and southeast and a significant negative correlation in the central Pacific. There is a similarity between the winter correlation and the spatial distribution of SST in the Pacific when El Niño Modoki occurs. When the water temperature in the central Pacific increases due to El Nino Modoki, the Hadley circulation becomes active, and the downdraft around Kure Island is enhanced, resulting in atmospheric cooling. This may weaken the North Pacific subarctic circulation, and the subarctic circulation may provide cooler seawater, which may be a mechanism that cools the central North Pacific.
The Sr/Ca ratio varied from 8.93 to 10.2 mmol/mol and showed a distinct annual cycle. A comparison of the Sr/Ca with satellite-observed water temperatures showed a significant strong correlation (r=0.72, n=121, p<0.06). Correlation maps between the reconstructed SST from Sr/Ca of Kure Island and the satellite-observed water temperature were made for the summer (Aug-Oct) and winter (Dec-Feb) periods. The winter correlograms show a positive correlation from the western Pacific to the northeast and southeast and a significant negative correlation in the central Pacific. There is a similarity between the winter correlation and the spatial distribution of SST in the Pacific when El Niño Modoki occurs. When the water temperature in the central Pacific increases due to El Nino Modoki, the Hadley circulation becomes active, and the downdraft around Kure Island is enhanced, resulting in atmospheric cooling. This may weaken the North Pacific subarctic circulation, and the subarctic circulation may provide cooler seawater, which may be a mechanism that cools the central North Pacific.