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Citation: Nakamura, N., H. Kayanne, H. Iijima, T. R. McClanahan, S. K. Behera, and T. Yamagata (2010), Correction to ‘‘Mode shift in the Indian Ocean climate under global warming stress,’’ Geophys. Res. Lett., 37, L02603, doi:10.1029/ 2009GL042370. [1] In the paper ‘‘Mode shift in the Indian Ocean climate under global warming stress’’ by Nobuko Nakamura et al. (Geophysical Research Letters, 36, L23708, doi:10.1029/ 2009GL040590), ‘‘IOD-induced drought in 1998 [Abram et al., 2003],’’ in the second line from the bottom of paragraph [5], should be ‘‘IOD-induced drought in 1997 [Abram et al., 2003].’’ GEOPHYSICAL RESEARCH LETTERS, VOL. 37, L02603, doi:10.1029/2009GL042370, 2010 Click Here for Full Article

[1] Low-frequency variations in the seasonally phase-locked signal of the Indian Ocean Dipole (IOD) and the Pacific El Nino/Southern Oscillation (ENSO) recorded in 115-year coralδ18O variability from Kenyan coast, the tropical western Indian Ocean, were investigated. A comparison of the monthly coral δ18O corresponding to IOD and ENSO years shows that Kenyan coral distinctly records the East African Short Rain anomaly related to the IOD variability in January, a few months after the Short Rain peak due to oceanographic condition. On the other hand, the ENSO-induced signals do not appear clearly as the positive sea surface temperature (SST) and rainfall anomalies in the monthly coral record. Moreover, annual mean coralδ18O and ENSO show only a weak coherence at the periodicity of 4 to 5 years. These results support the suggestion that the IOD is the dominant climate mode rather than ENSO in the Kenyan coast. The coral records indicate that the negative IOD- like anomalously cold SST condition in the western Indian Ocean precedes the evolution of the Pacific El Nino by one year. The anomalously cold SST condition was prominent in the late 19th century, but weakened in the 20th century. This retreat of the cold SST condition due to warming of the western tropical Indian Ocean may influence the nature of the Pacific ENSO.

[1] Atoll islands are areas of low, flat land, and the sustainability of habitable land in such environments is sensitive to even slight changes in sea level. The projected rise in sea level during this century may lead to the submergence of atoll islands and the widespread loss of habitable land. However, the actual time sequence of past sea level change, island emergence events, and human settlement of newly emerged islands remain poorly constrained. The results of geomorphological and archaeological surveys, combined with calibrated radiocarbon age dates, at Majuro Atoll, Marshall Islands, central Pacific, reveal that the emergence of the island, triggered by a fall in sea level, was quickly followed by human settlement. The elevation of the central body of the island exceeded high water level at 2000 years CalBP, and the complete formation of the island occurred within an interval of 100 years. The island was colonized by people shortly after emergence, at 2000 years CalBP, prior to the establishment of dense vegetation, and has been continuously settled since that time.

[1] A 115-year coral record from Kenya has been found to preserve the history of rainfall anomalies in East Africa in relation to global warming-induced Indian Ocean Dipole (IOD) variability. The coral IOD index demonstrates a dominantly decadal periodicity in the early part of the 20th century. This low-frequency IOD occurred more frequently before 1924 with mostly quasi-biennial ranging from 18 months to 3 years events since 1960. The mode shift has also coincided with an intensified coupling with Indian summer monsoon rainfall. We suggest that a warming of the western Indian Ocean, which has attenuated and replaced the El Nino/Southern Oscillation effect over the Indian Ocean, has driven the observed shift.

[1] We measured the gas-transfer velocity (k) and analyzed factors regulating k at coral reefs and an estuary at Ishigaki Island, Japan, using the floating-chamber method and the measured energy-dissipation rate (ɛ) to represent turbulence in a small-eddy model. We confirmed the validity of the floating-chamber method quantitatively for the first time by the comparing ɛ values inside and outside the chamber device. We also compared k to ɛ and empirical parameters such as wind and current speeds. Measured k had a low correlation with the empirical parameters and a high correlation with ɛ, as indicated by the small-eddy model. The high ɛ values may have been regulated by topographic conditions, e.g., corals or seagrasses that generate wakes, and complex coastlines or large-scale (on the order of kilometers) topographic factors that generate horizontal current shear. Our measurements indicate that coastal k is regulated by ɛ and cannot be accurately determined using wind or current speeds. Topographic conditions in coastal regions are important factors that regulate ɛ; thus, a quantitative analysis of the effects of these conditions is necessary to accurately determine coastal air–water gas flux.

[1] Two field campaigns (March 2005 and March 2006) for measurements of biological indicators and eyewitness accounts confirm that large coseismic and postseismic surface deformation occurred over the Andaman Islands in association with the 2004 Sumatra-Andaman earthquake. Amount of uplift was as large as 1.3 m in the islands off NW coast, and decreased to ESE with a zone of subsidence in the SE Andaman. The coseismic deformation did not generate large seismic waves or tsunamis, indicating that slip was much slower than that off Sumatra. The coseismic uplift was followed by postseismic subsidence, which was evidenced by local residents to have occurred within two months after the earthquake. A simple dislocation model explains the deformation pattern by a coseismic rupture (50 km wide with its down-dip limit 130 km east of the trench axis) followed by an up-dip propagation of the rupture front for about 10 km.

[1] The Indian Ocean Dipole (IOD), which governs climate variability not only over the Indian Ocean but also globally, produces precipitation anomalies in the East African short rain period from October to November. These precipitation anomalies were recorded in annual bands from a coral core obtained in the Malindi Marine Park, Kenya. A signature of the IOD in precipitation was detected in the coral core by luminescence intensity under UV light and by oxygen isotope values dated to January, a few months after the short rain period. Anomalies of the oxygen isotope values correlated well with high and low precipitation, which were related to positive and negative IOD indices, respectively. This study suggests that the coral annual band record is effective for reconstructing IOD events and should be able to reconstruct the IOD record prior to instrumental observations.

[1] Monitoring seawater CO2 for a full year with seasonal observations of community metabolism in Ishigaki Island, Japan, revealed seasonal variation and anomalous values owing to the bleaching event in 1998. The daily average pCO2 showed a seasonal pattern on an annual scale, 280 to 320 μatm in winter and 360 to 400 μatm in summer, which was determined primarily by the seasonal change in seawater temperature. By contrast, the range in the diel variation in pCO2, 400 to 500 μatm in summer 200 to 300 μatm in winter, was attributed to the seasonal variation in community metabolism: Gross primary production (Pg) and respiration (R) were high in summer and low in winter. During the 1998 bleaching event, although Pg and R increased, community excess organic production (E) decreased by three quarters compared with the same month in 1999, when the coral community showed high recovery. This change in metabolism led to large diel range and increased average value of pCO2 levels in the seawater on the reef flat. The decrease in the range and increase in the average value of pCO2 were observed by monitoring the Palau barrier reef flat, where overall mortality of corals occurred after the bleaching. All the metabolic parameters, Pg, R, E and calcification (G) were reduced by half after the bleaching, which increased the average pCO2 value by 10 μatm and decreased its diel range from 200–400 μatm to 100–200 μatm. Bleaching and resultant mortality of coral reefs led to degradation of their metabolic performance, and thus resulted in the loss of their active interaction with the carbon cycle.

[i] Changes in sea surface salinity (SSS) in the western Pacific warm pool (WPWP) provide information on the variability of the El Nino Southern Oscillation (ENSO) because SSS reflects the balance between evaporation and precipitation. We reconstructed the long-term variability of SSS at the northwestern edge of the WPWP from oxygen isotope analysis of annual coral bands. The estimated SSS corresponded well with in situ observations, demonstrating that isotopic records from coral can be used as a paleosalinometer. Estimated SSS between 1954 and 2000 peaked during the El Ninos of 1972-73, 1982-83, and 1997-98. These SSS peaks were caused by anomalously low precipitation accompanying the eastward shift in the WPWP. Citation: Iijima, H., H. Kayanne, M. Morimoto, and O. Abe (2005), Interannual sea surface salinity changes in the western Pacific from 1954 to 2000 based on coral isotope analysis.

[1] Seasonal sea surface salinity (SSS) records can be of great value in reconstructing El Nino/Southern Oscillation (ENSO) variability in the equatorial Western and Central Pacific, a region where ENSO-related evaporation and precipitation (E-P) changes are dramatic. The δ18O values of coral skeleton (δ18Ocoral) reflect seawater δ18O (δ18Oseawater) changes, which in tropical oceans are also generally influenced by E-P changes. Therefore, δ18Ocoral is a good indicator of rainfall and ENSO variability. We present biweekly data from Palau, in the northern part of the Western Pacific Warm Pool, for the period 1998–2000, which indicate a strong quantitative relationship between δ18Ocoral, sea surface temperature, δ18Oseawater and SSS. The coral skeletal δ18O values documented the SSS changes after the 1997–98 El Nino; therefore, δ18Ocoral can be used to estimate paleosalinity changes. However, the slope of the δ18Oseawater - SSS relationship cannot be assumed to be constant throughout the tropics, making site-specific calibrations is essential.