Physicochemical sea ice and water characteristics near Point Barrow 2005-2006

Photosynthetic parameters of phytoplankton and sea ice algae from landfast sea ice of the Chukchi Sea off Point Barrow, Alaska, were assessed in spring 2005 and winter through spring 2006 using Pulse Amplitude Modulated (PAM) fluorometry including estimates of maximum quantum efficiency (Fv/Fm), maximum relative electron transport rate (rETRmax), photosynthetic efficiency (alpha), and the photoadaptive index (Ek). The use of centrifuged brine samples allowed to document vertical gradients in ice algal acclimation with 5 cm vertical resolution for the first time. Bottom ice algae (0-5 cm from ice-water interface) expressed low Fv/Fm (0.331-0.426) and low alpha (0.098-0.130 /(µmol photons/m**2/s)) in December. Fv/Fm and alpha increased in March and May (0.468-0.588 and 0.141-0.438 /(µmol photons/m**2/s), respectively) indicating increased photosynthetic activity. In addition, increases in rETRmax (3.3-16.4 a.u.) and Ek (20-88 µmol photons/m**2/s) from December to May illustrates a higher potential for primary productivity as communities become better acclimated to under-ice light conditions. In conclusion, photosynthetic performance by ice algae (as assessed by PAM fluorometry) was tightly linked to sea ice salinity, temperature, and inorganic nutrient concentrations (mainly nitrogen).2005年春季及2006年冬季至春季期间，研究人员针对阿拉斯加巴罗角外楚科奇海固定海冰中的浮游植物与海冰藻类的光合参数展开测定，采用脉冲振幅调制荧光法（Pulse Amplitude Modulated，PAM），测定指标包括最大量子效率（maximum quantum efficiency，Fv/Fm）、最大相对电子传递速率（maximum relative electron transport rate，rETRmax）、光合效率（photosynthetic efficiency，alpha）以及光适应指数（photoadaptive index，Ek）。借助离心处理的盐水样本，研究人员首次以5厘米的垂直分辨率记录了海冰藻类驯化的垂直梯度。12月时，底部海冰藻类（距冰-水界面0~5厘米）的Fv/Fm值（0.331~0.426）与alpha值（0.098~0.130 /(μmol 光子/(m²·s))）均处于较低水平。3月与5月期间，Fv/Fm与alpha值分别升高至0.468~0.588与0.141~0.438 /(μmol 光子/(m²·s))，表明光合活性有所提升。此外，从12月至5月，rETRmax（3.3~16.4 任意单位）与Ek（20~88 μmol 光子/(m²·s)）的升高表明，随着藻类群落更好地适应冰下光照环境，其初级生产潜力显著提升。综上，通过PAM荧光法测定的海冰藻类光合性能与海冰盐度、温度及无机营养盐浓度（主要为氮）密切相关。