The conventional use of optically determined 1% of surface photosynthetically available radiation (PAR) depth (Z_1%^PAR, λ = 400–700 nm) as a metric for the euphotic zone depth (Z_eu) has been a matter of debate for several decades because of frequent inconsistencies with the base of euphotic zone determined biologically, that is, the compensation depth (Z_c). In this study, we attempt to reconcile between optical and biological determinants of the euphotic zone through the use of a large data set of coincidental profiles of downwelling irradiance and primary production. These measurements cover open ocean waters in the tropics, subtropics, temperate regions, and from two time‐series stations, the Hawaii Ocean Time‐series (HOT) and the Bermuda Atlantic Time‐series Study (BATS). We report that, at least for these measurements, Z_1%^PAR is too shallow (by 14.1%) compared to Z_c, while Z_0.1%^PAR is too deep (by 32.7%). Further, the irradiance at Z_c (i.e., the compensation irradiance, I_c) varies by a factor of more than five, but its ratio to surface irradiance is relatively stable. In general, I_c corresponds to 0.48 ± 0.23% of surface PAR, or 0.87 ± 0.40% of surface usable solar radiation (USR, for λ = 400–560 nm), or 1.50 ± 0.67% of surface downwelling irradiance at 490 nm. These results suggest that Z_0.5%^PAR, or Z_0.9%^USR, or Z_1.5%⁴⁹⁰ could be promising alternatives to bridge the optical and biological determinants of the euphotic zone depths for waters in the open ocean at low to middle latitudes.

中文翻译：

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调节富营养区深度的光学和生物决定因素之间的关系

对于光学确定的1％表面光合有效辐射（PAR）深度（Z _1％^PAR，λ= 400–700 nm）的常规使用，作为共光区深度（Z _eu）的度量标准已经引起了许多争论数十年来，由于频繁地与生物确定的富营养区基底不一致，即补偿深度（Z _c）。在这项研究中，我们试图通过使用大量的下沉辐照度和一次生产的重合数据集来协调常光区的光学和生物决定因素。这些测量涵盖了热带，亚热带，温带地区的开放海水，并且来自两个时间序列站，即夏威夷海洋时间序列（HOT）和百慕大大西洋时间序列研究（BATS）。我们报告，至少对于这些测量，与Z _c相比，Z _1％^PAR太浅（降低14.1％），而Z _0.1％^PAR则太深（降低32.7％）。此外，Z _c处的辐照度（即补偿辐照度I _c）相差五倍以上，但它与表面辐照度的比率相对稳定。通常，I _c相当于表面PAR的0.48±0.23％，或表面可用太阳辐射（USR，对于λ= 400-560 nm）的0.87±0.40％，或在490 nm处的表面下沉辐射度的1.50±0.67％。这些结果表明，Z _0.5％的^PAR或Z _0.9％的^USR或Z _1.5％⁴⁹⁰可能是有希望的替代方案，以桥接中低纬度公海水域富营养区深度的光学和生物决定因素。