日足P&Fの状況：（11月04日）～（11月08日）

Although biogenic carbonates, such as foraminifera and coccolithophorids, are valuable tools for reconstructing past environments, scleractinian corals also offer environmental data from tropical to subtropical regions with a higher time resolution. For example, oxygen isotopes (δ18O) and strontium-calcium (Sr/Ca) ratios have been utilized to reconstruct sea surface temperatures and salinity, primarily through the use of massive-type Porites sp. from the Pacific, as well as corals like Diploria and Montastrea from the Atlantic. While a few types of corals other than Porites have been utilized in paleoclimate studies, comprehensive evaluations of their geochemical tracers as temperature proxies have not been thoroughly conducted. Therefore, in this study, we focused on branching-type Acropora, which are found worldwide and are often present in fossil corals. We conducted a comparison of the chemical compositions (δ18O, δ13C, Sr/Ca, U/Ca, Mg/Ca, and Ba/Ca) of Acropora digitifera and Porites australiensis through temperature-controlled culture experiments. The validity of using the chemical components of A. digitifera as temperature proxies was then evaluated. Three colonies of A. digitifera and P. australiensis were collected for culture experiments on Sesoko Island, Okinawa, Japan. We reared coral samples in seawater with five different temperature settings (18, 21, 24, 27, 30°). The calcification rate and photosynthesis efficiency (Fv/Fm) of each nubbin were measured during the experimental period. After the culture experiment for 77 days, chemical components in skeletal parts grown during the experiment were then measured. Consequently, the mean growth rates and Fv/Fm throughout the experiment were higher for A. digitifera (0.22%/d and 0.63 for growth rate and Fv/Fm) compared to those for P. australiensis (0.11%/d and 0.38 for growth rate and Fv/Fm). This suggests that the higher efficiency of photosynthesis in A. digitifera would promote greater calcification compared to P. australiensis. Regarding the potential use as temperature proxies, A. digitifera exhibited a strong negative correlation, on average, between δ18O and the water temperature (r = 0.95, plt; 0.001). The temperature dependency was found to be comparable to that reported in Porites corals (-0.11 and -0.17 ‰/°C for P. australiensis and A. digitifera, respectively). Thus, the δ18O of A. digitifera appeared to be a useful temperature proxy, although it was also slightly influenced by skeletal growth rate at the same temperature. A strong negative correlation was also observed between the mean Sr/Ca ratio and temperature in A. digitifera (r = 0.61, plt; 0.001) as well as P. australiensis (r = 0.56, plt; 0.001), without a clear influence from the skeletal growth rate. Therefore, the skeletal Sr/Ca ratio in corals may have been primarily influenced by water temperature, although large deviations in Sr/Ca were observed in A. digitifera, even at the same temperature settings. This deviation can be reduced by subsampling an apical part of a polyp including the axis of skeletal growth. The U/Ca ratio of A. digitifera appeared to be affected by internal pH variation within the corals, especially at 30°C. Similar to U/Ca ratios, metabolic and kinetic effects on corals were observed in δ13C of A. digitifera at 18 and 30°C. In addition, considering the variation pattern of both U/Ca and δ13C of A. digitifera at 30°C, it has been suggested that respirations may overwhelm photosynthesis for coral samples at 30°C. Therefore, the U/Ca and δ13C of A. digitifera could potentially be used as proxies of biomineralization processes, whereas the δ18O and Sr/Ca displayed a high possibility of acting as temperature proxies.

11月上旬は様々な大学で文化祭が開催されます。その中でもファッションショーやワークショップなどクリエイティビティに特化した、文化服装学院ならではの企画は注目ポイントです。特に、期間限定セレクトショップや作品展示はファッションの世界の奥深さを感じることができると思います。年に1度のこの機会に、足を運んでみてはいかがでしょうか！

The impact of ocean acidification caused by the increasing atmospheric CO2 has been studied in marine calcifiers, including hermatypic corals. However, the effect of elevated pCO(2) on the early developmental life-cycle stage of corals has been little studied. In this study, we reared polyps of Acropora digitifera in seawater at pH(T) 6.55, 7.31, 7.64, 7.77, and 8.03, controlled by CO2 bubbling. We measured the dry weights of polyp skeletons after the 40-d experiment to investigate the relationship between the seawater aragonite saturation state and polyp growth. In addition, we measured skeletal U/Ca ratio to estimate their pH dependence. Skeletal weights of coral polyps increased with the aragonite saturation state and reached an apparent saturation plateau above pH 7.77. U/Ca ratios had a strong inverse relationship with pH and a negligible relationship with skeletal growth rate (polyp weight), suggesting that skeletal U/Ca could be useful for reconstructing paleo-pH. Citation: Inoue, M., R. Suwa, A. Suzuki, K. Sakai, and H. Kawahata (2011), Effects of seawater pH on growth and skeletal U/Ca ratios of Acropora digitifera coral polyps, Geophys. Res. Lett., 38, L12809, doi:10.1029/2011GL047786.

The Great Barrier Reef (GBR) is an internationally recognized and widely studied ecosystem, yet little is known about its sea surface temperature (SST) evolution since the Last Glacial Maximum (LGM) (similar to 20 kyr BP). Here, we present the first paleo-application of Isopora coral-derived SST calibrations to a suite of 25 previously published fossil Isopora from the central GBR spanning similar to 25-11 kyr BP. The resultant multicoral Sr/Ca- and delta O-18-derived SST anomaly (SSTA) histories are placed within the context of published relative sea level, reef sequence, and coralgal reef assemblage evolution. Our new calculations indicate SSTs were cooler on average by similar to 5-5.5 degrees C at Noggin Pass (similar to 17 degrees S) and similar to 7-8 degrees C at Hydrographer's Passage (similar to 20 degrees S) (Sr/Ca-derived) during the LGM, in line with previous estimates (Felis et al., 2014, ). We focus on contextualizing the Younger Dryas Chronozone (YDC, similar to 12.9-11.7 kyr BP), whose Southern Hemisphere expression, in particular in Australia, is elusive and poorly constrained. Our record does not indicate cooling during the YDC with near-modern temperatures reached during this interval on the GBR, supporting an asymmetric hemispheric presentation of this climate event. Building on a previous study (Felis et al., 2014, ), these fossil Isopora SSTA data from the GBR provide new insights into the deglacial reef response, with near-modern warming during the YDC, since the LGM.