雷州半岛造礁珊瑚Porites lutea月分辨率的δ^(18)O温度计研究

A MONTHLY RESOLUTION δ^(18)O THERMOMETER OF A PORITES LUTEA CORAL FROM LEIZHOU PENINSULA

对雷州半岛西南部珊瑚岸礁区1995～1997年生长的造礁珊瑚Poriteslutea的骨骼密度、生长速度和δ18O分析表明：1）造礁珊瑚骨骼的密度、生长速度和δ18O与其生存环境的表层海水温度之间存在很好的相关性，高密度、低生长速率和高δ18O值对应于冬季；2）δ18O具有明显的年际和季节性变化。根据δ18O估计的表层海水温度变化范围与实测基本一致，进一步揭示了珊瑚骨骼δ18O可作为定量研究高分辨率表层海水温度变化的温度计。

Coral skeleton's δ18O is an important tracer for analyzing the recorded environmental information. Most study find that there is good correlation between coral skeleton's δ18O and sea surface temperature (SST) regardless of yearly, seasonally, monthly or weekly resolution, and SST is the dominated factor influencing coral's δ18O. This paper reports the skeleton's δ18O of a Porttes lutea coral from the southwest Leizhou Peninsula and its relationship to the SST with monthly resolution.Southwest Leizhou Peninsula is sitUated in the northern coast of the South ChinaSea, where periodically developed excellent coral fringing reefs during the Period of 6 500-4 000a B.P. The dominant species of the fringing reef were Porttes in tea and Goniopora. The coral reef ecosystem is recovery in this area.A living hemispherical specimen of Porttes in tea was chosen for our investigation,which grew in water at the depth of 0.5 m in the reef flat of Denglou corner (20° 13,N, 109°56, E), southwest Leizhou Peninsula. A core was drilled in the end of July of 1997. A high-speed band saw was used to cut 1-cm-thick skeletal slabs oriented parallel to the axis of growth. A 1 cm thick slab was cleaned and was taken for X-radiography Post bye printS was exandned visually tO determine annual growth. TWo years and seven months increment was used in aams study. Subannual samples forisotopic analysis were collected with tedious manually opefthed blades and needlesavoiding aragonite--calcite transformahon in the drilling process. The samplingfrequency varied from 0.4 mm to l.0 nun of linear growth. Samples of less than 5mg were dissolved in 100% ac PO. at 75t for an hour and resulhng COb gasanalyzed with MAT252. Of 38 coral samples analyzed, 11 samples were mn induplicate with an average standard deviahon of t 0.09%.The 6'O data shows clearly interannual cycles, and is very similar with themonthly SST pattern. The instrUment monthly SST was used tO compare with the 6'Odata and revealed a correlahon coefficient of ro.94. The correlated equahon correspondto a decrease in skeletal's 6 18O of 0.217hi Per loC seawater tomperature increase,which is idenhcal with the widely recognized 6'O temperatUre calibration of --0.2Iki/aC or -0.22‰/℃. The instrumental monthly SST ranges were I l.goC in 1995, I I.soCin 1996, and 10.3℃ from January to July 1997, respechvely, and the correspondingSST ranges revealed by 6 'SO were 13.7, I l.6, and 10.2oC respechvely. We explainthe wider 6'O temperatUre range in 1995 with the higher resoluhon of 6'8O revealingshoder Period tempefMire values than monthly SST. Our analyses shows that reefcoral's 6,'O is a reliable indicator of SST in Leizhou Pehinsula.The 6'O dam also indicated that the coral's incrementS were not well-distributed.gogh density incrementS, low growth, were formed during cold temperatllres in winterand were synchronous with the highest 6'O, low density incrementS, high growth,were formed during warm temperatures in summer and were synchronous with thelowest δ18O. With our sampling and analyhcal procedures, we can stUdy the coralskeleton's growing pattern and set up higher resoluhon, for example weekly resoluhon,δ18O thermometer.