Abstract The rates of water exchange between coastal reef systems and the surrounding ocean are key physical drivers of water quality and reef ecosystems. It is generally assumed that water exiting a reef system through reef channels is predominantly replaced by ‘new’ water from offshore. However, exiting water may also recirculate back into the reef system reducing the rate of exchange between the reef and the ocean, which has implications for reef water temperatures, nutrient fluxes and population connectivity. To quantify flow re-entrainment at a rocky reef site in southwestern Australia, flow patterns were measured with GPS-tracked drifters during a two-week field experiment. The field observations were extended via a set of idealized numerical experiments to determine the effect of variable oceanic forcing and reef geometry on flow re-entrainment. The observations demonstrate that re-entrainment can vary significantly and the numerical results support the hypothesis that re-entrainment increases with increasing offshore wave height, increasing alongshore currents outside of the reef, and decreasing reef channel spacing but is largely not impacted by reef roughness. Re-entrainment was correlated with a predictor variable R, which is a measure of wave forcing versus the total offshore flow cross-section, and alongshore currents outside the reef. For large values of R and strong alongshore currents, flow re-entrainment increases the effective flushing time by a factor of three or more. The results suggest that flow re-entrainment may be particularly important in small-scale reef systems or reefs exposed to an energetic wave climate and/or strong alongshore currents.

中文翻译：

---

什么时候水流再夹带对沿海珊瑚礁系统的冲洗时间很重要？

摘要 沿海珊瑚礁系统与周围海洋之间的水交换率是水质和珊瑚礁生态系统的关键物理驱动因素。通常假设通过珊瑚礁通道离开珊瑚礁系统的水主要被来自近海的“新”水所取代。然而，离开的水也可能再循环回到珊瑚礁系统，降低了珊瑚礁与海洋之间的交换率，这对珊瑚礁水温、养分通量和人口连通性产生了影响。为了量化澳大利亚西南部岩礁地点的水流再夹带，在为期两周的现场实验中，使用 GPS 跟踪的漂流器测量了水流模式。通过一组理想化的数值实验扩展了实地观察，以确定可变海洋强迫和珊瑚礁几何形状对流动再夹带的影响。观察结果表明，再夹带可能会发生显着变化，数值结果支持这样的假设，即再夹带随着近海波高的增加、珊瑚礁外沿岸水流的增加和珊瑚礁通道间距的减小而增加，但在很大程度上不受珊瑚礁粗糙度的影响。再夹带与预测变量 R 相关，R 是波浪强迫与总离岸水流横截面和珊瑚礁外沿岸水流的量度。对于较大的 R 值和强大的沿岸水流，流动再夹带将有效冲洗时间增加了三倍或更多。