Simulating transport pathways of pelagic Sargassum from the Equatorial Atlantic into the Caribbean Sea Progress in Oceanography

Since 2011, beach inundation of massive amounts of pelagic Sargassum algae has occurred around the Caribbean nations and islands. Previous studies have applied satellite ocean color to determine the origins of this phenomenon. These techniques, combined with complementary approaches, suggest that, rather than blooms originating in the Caribbean, they arrive from the Equatorial Atlantic. However, oceanographic context for these occurrences remains limited. Here, we present results from synthetic particle tracking experiments that characterize the interannual and seasonal dynamics of ocean currents and winds likely to influence the transport of Sargassum from the Equatorial Atlantic into the Caribbean Sea. Our findings suggest that Sargassum present in the western Equatorial Atlantic (west of longitude 50 degrees W) has a high probability of entering the Caribbean Sea within a year's time. Transport routes include the Guiana Current, North Brazil Current Rings, and the North Equatorial Current north of the North Brazil Current Retroflection. The amount of Sargassum following each route varies seasonally. This has important implications for the amount of time it takes Sargassum to reach the Caribbean Sea. By weighting particle transport predictions with Sargassum concentrations at release sites in the western Equatorial Atlantic, our simulations explain close to 90% of the annual variation in observed Sargassum abundance entering the Caribbean Sea. Additionally, results from our numerical experiments are in good agreement with observations of variability in the timing of Sargassum movement from the Equatorial Atlantic to the Caribbean, and observations of the spatial extent of Sargassum occurrence throughout the Caribbean. However, this work also highlights some areas of uncertainty that should be examined, in particular the effect of "windage" and other surface transport processes on the movement of Sargassum. Our results provide a useful launching point to predict Sargassum beaching events along the Caribbean islands well in advance of their occurrence and, more generally, to understand the movement ecology of a floating ecosystem that is essential habitat to numerous marine species.

自2011年以来，加勒比海沿岸国家及岛屿周边海域频繁发生大规模远洋马尾藻（pelagic Sargassum）海滩淤积事件。过往研究已借助卫星海洋色遥感技术，对该现象的成因展开溯源分析。结合互补性研究方法的相关技术分析表明，此类马尾藻藻华并非起源于加勒比海海域，而是来自赤道大西洋。然而，针对此类事件的海洋学背景研究仍较为匮乏。本研究通过合成粒子追踪实验，刻画了可能影响马尾藻从赤道大西洋向加勒比海输运的洋流与风场的年际及季节动态特征。研究结果显示，分布于西赤道大西洋（西经50°以西区域）的马尾藻，有极高概率在一年内抵达加勒比海海域。其输运路径涵盖圭亚那海流、北巴西流涡环，以及北巴西流折返点北侧的北赤道海流。各路径输送的马尾藻体量存在季节性差异，这对马尾藻抵达加勒比海所需的时长具有重要影响。本研究基于西赤道大西洋释放点位的马尾藻浓度，对粒子输运预测结果进行加权处理，模拟结果可解释约90%的观测到的输入加勒比海的马尾藻丰度年际变化。此外，本研究的数值实验结果，与马尾藻从赤道大西洋向加勒比海输运的时间变异观测结果，以及马尾藻在加勒比海全域的分布空间范围观测结果均吻合良好。不过本研究也指出了若干尚待厘清的不确定性领域，尤其是风力曳引效应（windage）及其他表层输运过程对马尾藻移动的影响。本研究结果可为提前预测加勒比海沿岸岛屿的马尾藻海滩淤积事件提供可靠的参考依据，同时也为理解这一作为众多海洋物种关键栖息地的漂浮生态系统的移动生态学特征提供了新的视角。