南海南部最近几十年珊瑚钙化趋势与大气CO2浓度升高和全球变暖的联系

摘要

本研究11个现代滨珊瑚年龄在16～ 49年之间,包括两个种属Porites lutea和P.labata,于2008年7～9月采自南海南部南沙群岛海域水深3～4m处.用数字图像技术和实测方法沿珊瑚骨骼主生长轴测量生长率、密度和钙化率.结果表明,自1993 ～ 2008年,11个珊瑚平均生长率为0.96±0.05cm/a,16年增加了10.77％,变化率0.67％/a;密度为1.17±0.03g/cm3,16年减小了6.92％,变化率为-0.43％/a;钙化率为1.13±0.05g/cm2·a,16年增加了2.69％,变化率为0.17％/a.标准差分析显示,密度是3个生长参数中最不易变化的参数,因此,钙化率变化主要取决于生长率.珊瑚3个生长参数的趋势变化为:多数珊瑚生长率和钙化率都增加而其密度减小,少数珊瑚3个生长参数都增加或都减小.线性相关分析显示,多数珊瑚生长率和钙化率与大气CO2浓度和温度正相关而其密度与之负相关,然而,少数珊瑚与之反相关或相关关系不明显.这些相关关系进一步揭示,过去50年,人类活动产生的温室气体增加引起南海表层温度升高使珊瑚呼吸作用增强,从而导致其生长率和钙化率增加而密度减小.而且,少数珊瑚对大气CO2浓度升高和全球增温显示的差异响应可能与珊瑚样品个体生长的差异和局地环境的影响有关.%The 11 modern Porites corals,including Porites lutea and P. lobata ,spanning last 15 to 48 years,were collected from 3 ~ 4m water depth at Nansha Islands of the southern South China Sea(SCS)in July ~ September 2008. The SCS is not only influenced by Asian monsoon but also adjusted by the north western Pacific Ocean. At Nansha Islands,the sun directly shines twice from March 27 to April 21 and August 21 to September 16, and both annual average air temperature and SST are more than 27℃. " wet seasons" are 7 months from June to December with highest rainfall and cloud cover in September; By contraries,"dry seasons" are 5 months from January to May with lowest rainfall and cloud cover in April. Natural geographical conditions are suitable for reef coral living.rnExtension rate represents coral upward linear extension growth per year ( cm/a) , density represents coral skeletal quality per cm (g/cm) reflecting comprehensive environment quality; Calcification rate represents quality of calcium carbonate per cm and year ( g/cm2· a) excreted by coral, and calculated from the product of extension rate and density. In this study,the 3 growth parameters of the 11 Porites colonies were obtained along their main growth axes using digital X-radiography image of which the reative density is transferred to density with measured true density. The results show that their average extension rate is 0. 96±0. 05cm/a, increasing 10. 77% in the last 16 years with a rate of 0. 67%/a; The average density is 1. 17±0. 03g/cm3, decreasing 6. 92% with a rate of -0. 43%/a; The average calcification rate is 1. 13±0. 05g/cm2·a,,increasing 2. 69% with a rate of 0. 17%/a. Two coral species of P. lutea and P. lobata show slightly different variations in their 3 growth parameters. Standard diviation analysis indicate that density is less variable than extension and calcification rate for Porites, which reveal that increase in calcification rate is mainly induced by increase in extension rate. Our analysis summarize three vriational forms for the three growth parameters in 11 Porites colonies:1 ) A lot of corals assume increase in extension and calcification rate and decrease in density; 2) A few of corals assume increase in all of the 3 growth parameters; 3)A few of P. lobata colonies show decrease in all of the 3 growth parameters. Linear regression analysis indicates that increase or decrease in the 3 growth parameters correlates significantly with increase in both CO2 concentration and temperature. However, positive responses of extension and calcification rate and negative response of density are much stronger than their opposite responses. Farther comprehensive analysis suggests that increase in SST induced by increase in anthropogenic greenhouse gas strengthens coral respiration so that a lot of corals increase their extension and calcification rates but decrease their densities. Moreover,due to effects of growth difference in sample individuals and local environmental factors, a few of corals may have different abilities to respond to rise in atmosperic CO2 concentration and global warming.