想象一下，海滩上的海浪突然变成了亮粉色。2015年，科学家们在南加州海岸有意制造了这一景象。据斯克里普斯海洋研究所称，研究人员在帝国海滩附近进行了三次实验，释放无毒、亮粉色的荧光染料，以观察其沿海岸如何移动。染料被用来模拟污染物。斯克里普斯报告称，在强劲的南向涌浪作用下，染料以每天近8英里（约12.9公里）的速度向北穿过冲浪区。
Imagine a beach where the waves suddenly turn bright pink. In 2015, scientists made that happen on purpose off Southern California. According to Scripps Institution of Oceanography, researchers conducted three experiments near Imperial Beach, releasing non-toxic, bright pink fluorescent dye to see how it moved along the coast. The dye was used to simulate pollution. Scripps reports that the dye moved north through the surf zone at nearly eight miles per day during a strong south swell.
科学家为何让海洋变粉一旦污染物进入大海，就很难追踪，因为通常肉眼不可见。染料解决了这个问题。它会发光，因此研究人员可以利用水中的传感器和飞机上的成像设备对其进行追踪。这项工作是“冲浪区/内架染料交换”项目（CSIDE）的一部分，由美国国家科学基金会资助。
Why scientists turned the ocean pinkPollution is hard to track once it enters the sea, because you often cannot see it. Dye takes care of that problem. It glows, so researchers can track it with sensors in the water and imaging equipment on an airplane. The work was part of a project called Cross-Surfzone/Inner-shelf Dye Exchange, or CSIDE, funded by the National Science Foundation.A detailed scientific account comes from a 2021 study by Derek Grimes, Falk Feddersen, and Sarah Giddings published in the Journal of Geophysical Research: Oceans.
一份详细的科学记录来自德里克·格赖姆斯、法尔克·费德森和莎拉·吉丁斯于2021年发表在《地球物理研究杂志：海洋》上的研究。研究团队跟踪了一次于2015年10月8日进行的释放，地点在帝国海滩以北约0.6英里（约1公里）处。在约4小时内，他们泵入了约30加仑（约113.6升）染料溶液，并追踪了约30小时，仪器覆盖了约4英里（约6.4公里）的海岸线。染料的前沿在大约11小时内穿过了这段海岸。
The team followed a release made on October 8, 2015, about 0.6 miles north of Imperial Beach. Over about four hours, they pumped in about 30 gallons of dye solution and tracked it for about 30 hours, with instruments covering about 4 miles of coastline. The leading edge of the dye crossed that stretch in roughly 11 hours.
海浪如何携带染料海浪完成了大部分工作。当海浪以一定角度向海滩滚动时，会产生一股沿岸流。研究发现，染料按来浪预测的方向向北移动。这与斯克里普斯关于染料在强劲南向涌浪中向北移动的描述相符，这一路径通向圣地亚哥湾入口。
How the waves carried the dyeWaves did most of the work. When waves roll toward a beach at an angle, they create a current that runs along the shore. The study found that the dye moved north in the direction predicted by the incoming waves. That matches the Scripps account of dye moving north in a strong south swell, a route that leads toward the entrance of San Diego Bay.
但情况并不简单。在碎浪区之外，洋流缓慢向南流动，而冲浪区内的水流却向北流动。这意味着冲浪区内的染料和更远海面的染料被以不同的方式携带。这种染料还在海岸附近停留了很长时间。粉色为何消退在靠近释放点的碎浪区，最强的染料读数约为十亿分之九十。在顺着海岸约4英里外的地方，这一读数低于5。研究将这种大幅下降归因于离岸流——这是一种将水拉离海岸的狭窄、快速的水流，它们将染料从碎浪区输送到了更深的水域。作者估计，碎浪区的水大约每2.3小时与更深的水域置换一次。
But the picture wasn't simple. Beyond the breaking waves, currents moved slowly south, while water in the surf zone flowed north. This meant that dye in the surf zone and dye further out were carried differently. The dye also lingered near the coast for long periods of time. Why the pink fadedThe strongest dye reading in the surf, near the release point, was about 90 parts per billion. About 4 miles further up the coast, it was under 5. The study attributes much of that drop to rip currents, narrow, fast streams that pull water away from shore, which carried dye from the surf zone to deeper water. The authors estimate that surf-zone water was exchanged with deeper water about every 2.3 hours.
其中一些染料并没有永远被冲走。作者表明，储存在较深水域中的染料向南漂移的速度比碎浪区向北流动的速度要慢，在主羽状流过去之后，这些染料可能会重新进入碎浪区，他们将这一过程称为再循环。这拉长了羽状流的时间，并在沿海岸更远处的监测读数中产生了漫长而逐渐消退的尾流。这对海滩游客意味着什么碎浪区与较深水域之间的置换减少了人们最常接触的碎浪区中的染料，从而降低了污染事件对下游水质的影响。
Some of that dye did not rinse out forever. The authors show that dye stored in deeper water, which drifted south more slowly than the surf zone flowed north, could later re-enter the surf zone after the main plume had passed, a process they call recirculation. This lengthened the plume over time and produced long, fading tails in the readings at points farther along the coast. What this means for beachgoersExchange between the surf zone and deeper water reduces the dye in the surf zone, where most people are exposed, decreasing the downstream water quality impact of a pollution event.
斯克里普斯研究所还表示，需要更多的研究和模型工作，以便对圣迭戈、因佩里亚尔比奇和科罗纳多的海滩污染去向进行更好的实时预测。
Scripps also says more studies and model work are needed for better real-time forecasts of where pollution is going for beaches in San Diego, Imperial Beach and Coronado.
但这也存在局限性。该研究观察的是在一组特定条件下的单次释放，作者表示，需要进行类似的远程观测，以检验他们的模型在其他地方是否适用。即便如此，粉红色的水域让科学家们得以清晰地观察到通常隐藏的现象，并有助于解释海岸线污染是如何传播的。
But there are limits. The study looks at one release under one set of conditions, and the authors say similar long-range observations are needed to test whether their model holds up elsewhere. Even so, the pink water gave scientists a clear view of something normally hidden, and it helped explain how shoreline pollution may travel.