Slow growth rate of a deep-sea clam determined by 228 Ra chronology ( growth bands / ages of deep-dwelling organisms with hard parts )
Slow growth rate of a deep-sea clam determined by 228 Ra chronology ( growth bands / ages of deep-dwelling organisms with hard parts )
复制标题
由 228 Ra 年代学确定的深海蛤的缓慢生长速度（具有坚硬部分的深海生物的生长带/年龄）
DOI：
--
复制
发表时间：
2003
期刊：
影响因子：
--
通讯作者：
John A. ALLENt
中科院分区：
文献类型：
--
作者：
K. Turekian;I. Cochran;D. Kharkar;R. Cerrato;J. Vaisnys;H. L. Sanders;J. F. GRASSLEt;John A. ALLENt
3800 m深处的深海蛤（Tindaria caifistiformis）的年龄是通过捕获种群的分离粒度组分的MRA（6.7年半衰期）年代学确定的。8.4毫米的长度在大约100年内达到。这种大小的贝壳显示出约100个规则间隔的条带，表明生长特征可能是一年一次的。有几份报告指出，深海海底的新陈代谢速度非常慢，通常比浅水系统中类似生物的新陈代谢速度慢一到两个数量级（1-4）。根据观察到的深海底栖生物的幼鱼数量少和成年鱼比例高的情况，Grassle和Sanders（5）假定生活史的繁殖率、生长率和死亡率都很低。深海是一个没有光的环境，在环境高压和低温下几乎不变，并且可能受到缓慢的食物供应率的影响。这些事实为深海代谢率缓慢的预期提供了基础，但它们也使得解释深海生物坚硬部分的生长特征变得困难。我们研究的目的是探讨是否可能用辐射测量法确定分泌坚硬矿物外壳的深海底栖生物的生长速度。我们最初的努力报告在这里是一个深海蛤，Tindaria callistiformis，一个专门的深海物种，定期生长带。我们的技术是使用228 Ra（半衰期= 6.7年）浓度在一些生长阶段，并从这些数据推断的生物体的生长速度。镭-228是由长寿命的钍-232衰变产生的，钍-232普遍存在于富含粘土的沉积物中，浓度约为百万分之十，但在海水中几乎不存在。α衰变产生的228 Ra通过扩散或物理迁移从沉积物中释放，通过沉积物的孔隙沃茨进入上覆水。在摩尔（6，7）的初步研究之后，228 Ra在海洋中的分布一直是几项深入研究的主题（8，9）。图1显示了特里尔等人（9）在本研究中使用的蛤蜊回收地点附近的北大西洋站的剖面图。深海表层沃茨中的镭-228来源于近岸浅水区沉积物-水的相互作用，特别是在物理混合和生物扰动速率高的地方。Dodge和他的同事们利用在不同珊瑚层中发现的228 Ra浓度（10，11）能够确定珊瑚的年代，并确定几个物种的生长带确实是一年一次的。此外，通过比较228 Ra/Ca比率与210 Pb测年，他们能够证明这个比率在至少30年的海洋表面中是明显不变的。深海底水-沉积物界面的228 Ra浓度也很高。其浓度预计也会稳定，甚至比地表沃茨中的浓度更稳定。因此，贝壳中28 Ra浓度的系统变化作为大小的函数将告诉我们该物种的生长特性，前提是贝壳属于单一物种的软体动物，它们来自捕获时活着的动物，并且所有贝壳都来自同一样品。
The age of a deep-sea clam, Tindaria caifistiformis, from 3800 m depth has been determined by MRa (6.7 year half-life) chronology of separated size fractions of a captured population. A length of 8.4 mm is attained in about 100 years. Shells of this size fraction show about 100 regularly spaced bands, indicating that the growth feature may be an annual one. There are several reports indicating that the rate of metabolism on the deep ocean floor is extremely slow-generally one to two orders of magnitude slower than the rate for comparable organisms in shallow water systems (1-4). From small brood size and the high proportion of adult size classes observed for deep ocean benthos Grassle and Sanders (5) have postulated life histories with low rates of reproduction, growth, and mortality. The deep sea is an environment devoid of light, virtually invariant in ambient high pressure and low temperature, and probably subject to a slow food supply rate. These facts provide the basis for expectation of slow metabolic rates at depth but they also make the interpretation of growth features in the hard parts of deep-sea organisms difficult. The aim of our study was to explore the possibility of radiometrically determining the rates of growth of deep-sea benthic organisms that secrete a hard mineral shell. Our initial effort reported here is on a deep-sea clam, Tindaria callistiformis, an exclusively deep-sea species with regular growth bands. Our technique is to use the 228Ra (half-life = 6.7 years) concentrations in a number of growth stages and to infer from these data the growth rate of the organism. Radium-228 is produced from the decay of long-lived 232Th, which is found ubiquitously in clay-rich sediments at a concentration of about 10 parts per million although virtually absent in sea water. The 228Ra produced by a-decay is subject to release from sediments by diffusion or physical transport via the pore waters of the sediment into the overlying water. The distribution of 228Ra in the ocean after the initial study by Moore (6, 7) has been the subject of several intensive investigations (8, 9). Fig. 1 shows a profile from Trier et al. (9) for a North Atlantic Ocean station in the general vicinity of the site from which the clams used in this study were recovered. Radium-228 in surface waters of the deep ocean is derived from the sediment-water interactions in shallow coastal regions, especially where physical mixing knd bioturbation rates are high. Using 228Ra concentrations found in different layers of coral, Dodge and coworkers (10, 11) were able to date corals and determine that for several species the growth bands were indeed annual. Furthermore, by comparing the 228Ra/Ca ratio with 210Pb dating, they were able to demonstrate that this ratio was sensibly invariant in the surface ocean over at least 30 years. The 228Ra concentration at the water-sediment interface of the deep ocean floor is also high. Its concentration there is expected to be stabilized as well or better than in the surface waters. Thus the systematic variation in 28Ra concentration in the shells as a function of size will tell us about the growth properties of that species, providing that the shells belong to a single species of molluscs, that they were derived from animals that were alive at the time of capture, and that all the shells came from the same sample.