Spatial anomalies associated with seamounts and islands have been detected in the South West Indian Ocean using a new surface chlorophyll-a based enrichment index (EI). Calculated from daily L3 4-km MODIS chl-a data from 2003 to 2018, the EI was used to quantify recurrent (seasonal) surface enrichment associated with these features. Most notable were the shallow Walters Shoal (18 m) and nearby deeper WS-2 seamount (480 m), both located on the southern Madagascar Ridge, which showed high EI values of 40% and 15% local enhancement. Tromelin Island, east of Madagascar, exhibited more moderate values of 15% local increase. Other shallower seamounts including La Pérouse (60 m) and MAD-Ridge (240 m) exhibited sporadic or no measurable surface maxima. Regions of strong mesoscale activity such as south of Madagascar where the South East Madagascar Current detaches from the continent also revealed high EI values. A marked seasonality of the EI was observed over the Walters Shoal, with higher values during the oligotrophic season than in the austral winter. The seasonal variability of the MLD in combination with the seamount bathymetry appears to induce the thermal and biological anomalies observed there, possibly favoured by the presence of a Taylor cap at the summit. Ship-collected in situ measurements showed the satellite observed enrichment to be associated with shallowing of the deep chlorophyll maximum, as well as a shift of phytoplankton groups towards diatoms and small flagellates. No net increase of integrated chl-a was measured but a potential doubling in primary productivity is expected. The EI developed in this study, designed to reveal sporadic, small localised chl-a maxima, is likely applicable to other areas in the ocean where there is local enrichments.

使用新的基于叶绿素-a的表面富集指数（EI）在西南印度洋中发现了与海山和岛屿相关的空间异常。根据2003年至2018年每日L3 4公里MODIS chl-a数据计算得出的EI用于量化与这些特征相关的经常性（季节性）表面富集。最值得注意的是浅水的Walters浅滩（18 m）和附近的更深的WS-2海山（480 m），它们都位于马达加斯加山脊的南部，其EI值较高，分别为40％和15％局部增强。马达加斯加以东的Tromelin岛，当地价格上涨了15％，显示出较为温和的价值。其他浅海山包括LaPérouse（60 m）和MAD-Ridge（240 m），表现出零星的或没有可测量的表面最大值。中等强度活动活跃的地区，例如马达加斯加南部，马达加斯加东南流与大陆分离，也显示出较高的EI值。在Walters浅滩上观察到EI的明显季节性，在贫营养季节，EI值比南方冬季更高。MLD的季节性变化与海山测深法相结合，似乎会引起那里观测到的热异常和生物异常，这可能是由于在峰顶处存在泰勒帽所致。收货 MLD的季节性变化与海山测深法相结合，似乎会引起那里观测到的热异常和生物异常，这可能是由于在峰顶处存在泰勒帽所致。收货 MLD的季节性变化与海山测深法相结合，似乎会引起那里观测到的热异常和生物异常，这可能是由于在峰顶处存在泰勒帽所致。收货原位测量表明，卫星观测到的富集与深层叶绿素最大值的变浅以及浮游植物群向硅藻和小鞭毛的转移有关。没有测量出整合的chl-a的净增加，但预计初级生产力可能会翻倍。在这项研究中开发的EI旨在揭示零星的小局部chl-a最大值，很可能适用于海洋中其他具有局部富集的区域。