Mesoscale eddies are ubiquitous in the East Australian Current (EAC), a nutrient poor western boundary current, and exert considerable impact on the biogeochemical characteristics of the region. However, in-situ biogeochemical studies of these eddies are relatively rare. Here we combine ship-based and satellite measurements to characterize the physical and biogeochemical properties of three EAC eddies – one cyclone and two anticyclones – in the austral fall of 2018. Deep Chlorophyll Maxima (DCM) were observed in the two northernmost eddies, with Chlorophyll-a concentrations ranging from 0.4 to 1.3 mg m^-3 and generally decreasing with increasing depth of the DCM. The anticyclone farthest south, which was also the oldest observed eddy, was more productive and contained higher biomass than the northern eddies, including the cyclone. Deeper mixed layers in this anticyclone suggest that surface cooling resulting from poleward travel and seasonal cooling might have led to increased convection and an injection of nutrients. All eddies were nitrogen limited, and nitrogen fixation likely occurred in the surface waters of the two northernmost eddies. Where DCM were present, their depth was well explained as a consequence of an optimisation of light and nitrogen supply by phytoplankton. We observed prominent primary nitrite maxima (PNM) in the eddies. Their depths were highly correlated with, and consistently below, the depths of DCM, indicating that incomplete nitrate reduction by phytoplankton under low-light conditions was likely the main driver for their production. To our knowledge, this is the first description of PNM in eddies of the EAC.

中尺度涡旋在营养不良的西部边界流东澳大利亚洋流（EAC）中无处不在，并且对该地区的生物地球化学特征产生了很大影响。然而，这些旋涡的原位生物地球化学研究相对较少。在这里，我们结合了舰船和卫星测量，以表征三个EAC涡流的物理和生物地球化学性质（在2018年南半球秋季）。在最北端的两个涡流中都观察到了深叶绿素最大值（DCM），其中叶绿素-a浓度范围从0.4到1.3 mg m ^-3并且通常随着DCM深度的增加而减小。最南端的反气旋也是观察到的最古老的涡流，比包括旋风在内的北部涡流生产力更高，生物量更高。该反旋风器中较深的混合层表明，极地移动和季节性冷却导致的表面冷却可能导致对流增加和养分注入。所有涡流均受氮限制，并且最北端的两个涡流的地表水中可能发生固氮作用。在存在DCM的地方，由于浮游植物优化了光和氮的供应，因此很好地解释了其深度。我们在涡流中观察到了显着的主要亚硝酸盐最大值（PNM）。他们的深度与DCM的深度高度相关，并且始终低于DCM的深度，表明在弱光条件下浮游植物对硝酸盐的还原不完全可能是其生产的主要驱动力。据我们所知，这是EAC涡流中对PNM的首次描述。