Stable oxygen isotope record of corales from the Red Sea

In order to assess the ability of Porites corals to accurately record environmental variations, high-resolution (weekly/biweekly) coral delta18O records were obtained from four coral colonies from the northern Gulf of Aqaba, which grew at depths of 7, 19, 29, and 42 m along one transect. Adjacent to each colony, hourly temperatures, biweekly salinities, and monthly delta18O of seawater were continuously recorded over a period of 14 months (April 1999 to June 2000). Contrary to water temperature, which shows a regular and strong seasonal variation and change with depth, seawater delta18O exhibits a weak seasonality and little change with depth. Positive correlations between seawater delta18O and salinity were observed. The two parameters were related to each other by the equation delta18O Seawater (per mil, VSMOW) = 0.281 * Salinity - 9.14. The high-resolution coral delta18O records from this study show a regular pattern of seasonality and are able to capture fine details of the weekly average temperature records. They resolve more than 95% of the weekly average temperature range. On the other hand, attenuation and amplification of coral seasonal amplitudes were recorded in deep, slow-growing corals, which were not related to environmental effects (temperature and/or seawater delta18O) or sampling resolution. We propose that these result from a combined effect of subannual variations in extension rate and variable rates of spine thickening of skeletal structures within the tissue layer. However, no smoothing or distortion of the isotopic signals was observed due to calcification within the tissue layer in shallow-water, fast-growing corals. The calculations from coral delta18O calibrations against the in situ measurements show that temperature (T) is related to coral delta18O (delta c) and seawater delta18O (delta w) by the equation T (°C) = -5.38 (delta c - delta w) -1.08. Our results demonstrate that coral delta18O from the northern Gulf of Aqaba is a reliable recorder of temperature variations, and that there is a minor contribution of seawater delta18O to this proxy, which could be ignored.为评估多孔螅珊瑚（Porites corals）准确记录环境变化的能力，研究从亚喀巴湾北部的4个珊瑚群落获取了高分辨率（每周/每两周）的珊瑚δ¹⁸O（delta18O）记录，这些珊瑚沿一条断面分别生长于7、19、29和42米水深处。在每个珊瑚群落附近，研究人员于1999年4月至2000年6月的14个月期间，连续记录了每小时水温、每两周一次的盐度以及逐月的海水δ¹⁸O。与呈现出规律且显著的季节性变化并随水深改变的水温不同，海水δ¹⁸O的季节性较弱且随水深变化极小。研究观测到海水δ¹⁸O与盐度呈正相关关系，二者满足如下关系式：海水δ¹⁸O（‰，维也纳标准平均海洋水（VSMOW））= 0.281 × 盐度 - 9.14。本研究获取的高分辨率珊瑚δ¹⁸O记录呈现出规律的季节性模式，能够捕捉周平均水温记录的精细细节，可复现超过95%的周平均水温波动范围。另一方面，生长缓慢的深水珊瑚出现了珊瑚季节性振幅的衰减与放大现象，该现象与环境因素（水温及/或海水δ¹⁸O）或采样分辨率无关。研究认为该现象源于珊瑚延伸速率的年内变化与组织层内骨骼棘突增厚速率变化的共同作用。但在生长迅速的浅水珊瑚中，未观察到因组织层内钙化作用导致的同位素信号平滑或畸变现象。基于原位测量数据开展的珊瑚δ¹⁸O校准计算表明，水温（T）与珊瑚δ¹⁸O（Δ_c）及海水δ¹⁸O（Δ_w）满足如下关系式：T（℃）= -5.38×(Δ_c - Δ_w) - 1.08。本研究结果证实，亚喀巴湾北部的珊瑚δ¹⁸O是水温变化的可靠代用记录，且海水δ¹⁸O对该代用指标的贡献极小，可忽略不计。