Temperatures, salinity, and stable oxygen isotope values of bottom water and of the mollusc shell Arctica islandica from Nantucket Shoals

The carbonate shell of the bivalve Arctica islandica has been recognized, for more than a decade, as a potentially important marine geochemical biorecorder owing to this species' great longevity (200+ years) and wide geographic distribution throughout the northern North Atlantic Ocean, a region vital to global climate and ocean circulation. However, until now this potential has not been realized owing to the difficulty of precisely sampling the shell of this slow growing species. Using newly available automated microsampling techniques combined with micromass stable isotope mass spectrometry, a stable oxygen isotope record (1956-1957 and 1961-1970) has been obtained from a live-captured, 38-year-old A. islandica specimen collected near the former position of the Nantucket Shoals Lightship (41°N. 69°W). The shell's delta18O signal is compared with an expected signal derived from ambient bottom temperature and salinity data recorded at the lightship for the same period. The results show that A islandica's delta18O record (1) is in phase with its growth banding, confirming the annual periodicity of this species' growth bands, (2) is in oxygen isotopic equilibrium with the ambient seawater, (3) shows a consistent shell growth shutdown temperature of ~6°C. which translates into an ~8-month (May–December) shell growth period at this location, and (4) records the ambient bottom temperature with a precision of ~ +/-1.2°C. These results add important information on the life history of this commercially important shellfish species and demonstrate that A. islandica shells can be used to reconstruct inter- and intra-annual records of the continental shelf bottom temperature.

十余年来，双壳类物种北极圆蛤（Arctica islandica）的碳酸盐壳体已被视作极具潜力的重要海洋地球化学生物记录器——这是因为该物种寿命长达200年以上，且广泛分布于对全球气候与海洋环流至关重要的北大西洋北部海域。然而，由于该物种生长缓慢，其壳体难以精准取样，迄今为止这一研究潜力尚未得到充分发掘。借助新兴的自动化微取样技术与微质量稳定同位素质谱法，研究人员从楠塔基特浅滩灯船旧址（41°N, 69°W）附近捕获的一只活体38岁北极圆蛤标本中，获取了1956-1957年及1961-1970年的稳定氧同位素（δ¹⁸O）记录。将该壳体的δ¹⁸O信号与同期灯船站点记录的底层水温及盐度数据推导得到的预期信号进行对比后，结果显示：北极圆蛤的δ¹⁸O记录（1）与其生长纹相位一致，证实了该物种生长纹的年周期性；（2）与周围海水处于氧同位素平衡状态；（3）呈现出稳定的壳体生长停止温度约6℃，对应该区域约8个月（5月至12月）的壳体生长周期；（4）以约±1.2℃的精度记录了周围底层水温。上述结果为这一具有商业价值的贝类的生活史补充了重要信息，并证实北极圆蛤壳体可用于重建大陆架底层水温的年际与年内变化记录。