Primary productivity, pulse amplitude modulated fluorometry and nutrient drawdown data from the marginal ice zone: BROKE-WEST survey 30o-80oE, 2006

This data set contains primary productivity, pulse amplitude modulated fluorometry, and nutrient drawdown numbers associated with the abstract presented below.14C Primary ProductivityGross column-integrated primary productivity determined through measurement of NaH14CO3 uptake by phytoplankton (1 hour incubations). Primary productivity was modelled from photosynthesis v irradiance curves, chlorophyll profiles, photosynthetically active radiation, and vertical light attenuation. Data for these parameters are also shown.Nutrient Draw-down DataSeasonal depletion of oxidised inorganic nitrogen and silicate in the mixed layer, and production of oxygen. Data was calculated by the subtraction of mixed layer concentrations (uM) from values below the mixed layer. Pulse Amplitude Modulated Fluorometry DataFv/Fm values determined using pulse amplitude modulated fluorometry (PAM). Samples were dark-adapted prior to measurement so that non-photochemical quenching was relaxed. Values provide an indication of cell health.AbstractPrimary productivity was measured in the Indian Sector of the Southern Ocean (30 degrees to 80 degrees E) as part of a multi-disciplinary study during austral summer; Baseline Research on Oceanography, Krill and the Environment, West (BROKE-West Survey, 2006). Gross integrated (0-150 m) productivity rates within the marginal ice zone (MIZ) were significantly higher than within the open ocean, with averages of 2110.2 plus or minus 1347.1 and 595.0 plus or minus 283.0 mg C m-2 d-1, respectively. In the MIZ, high productivity was associated with shallow mixed layer depths and increased Pmax up to 5.158 mg C (mg chl a)-1 h-1. High Si:N drawdown ratios in the open ocean (4.1 plus or minus 1.5) compared to the MIZ (2.2 plus or minus 0.79) also suggested that iron limitation was important for the control of productivity. This was supported by higher Fv/Fm ratios in the MIZ (0.50 plus or minus 0.11 above 40 m) compared to the open ocean (0.36 plus or minus 0.08). As well, in the open ocean there were regions of elevated productivity associated with the seasonal pycnocline where iron availability was possibly increased. High silicate drawdown in the north-eastern section of the BROKE-West survey area suggested significant diatom growth and was linked to the presence of the southern Antarctic Circumpolar Current front (sACCF). However, low assimilation numbers (12.8 to 23.2 mg C mg chl a-1 d-1) and Fv/Fm ratios indicated that cells were senescent with initial growth occurring earlier in the season. In the western section of the survey area within the MIZ, high NO3 drawdown but relatively low silicate drawdown were associated with a Phaeocystis bloom. NO3 concentrations were strongly negatively correlated with column-integrated productivity and chlorophyll biomass which was expected given the requirement for this nutrient by all phytoplankton groups. Regardless, concentrations of both NO3 and silicate were above limiting levels within the entire BROKE-West survey area (N greater than 15.7 micro M, Si greater than 18.3 micro M) supporting the high nutrient low chlorophyll status of the Southern Ocean.

本数据集包含与下述摘要相关的初级生产力、脉冲振幅调制荧光法（pulse amplitude modulated fluorometry, PAM）测定数据以及营养盐消耗数据。14C初级生产力：通过测定浮游植物对NaH¹⁴CO₃的摄取量（1小时培养实验）得到柱总初级生产力。初级生产力通过光合-辐照度曲线、叶绿素剖面、光合有效辐射以及垂直光衰减建模计算得出，上述各参数的测定数据亦一并收录。营养盐消耗数据：记录混合层内氧化态无机氮与硅酸盐的季节性消耗，以及氧气生成量。数据通过混合层下方水体浓度减去混合层浓度（单位：微摩尔每升）计算得到。脉冲振幅调制荧光法数据：使用脉冲振幅调制荧光仪测定的Fv/Fm值，测定前样品经暗适应以弛豫非光化学淬灭，该值可反映浮游植物细胞的健康状态。摘要：本研究作为2006年南极西部海洋学、磷虾与环境基线科考（BROKE-West Survey）多学科考察的一部分，于南大洋印度洋扇区（东经30°至80°）的南极夏季开展了初级生产力测定。海冰边缘带（Marginal Ice Zone, MIZ）的0-150米柱整合总初级生产力速率显著高于开阔大洋，平均速率分别为2110.2±1347.1 mg C m⁻² d⁻¹与595.0±283.0 mg C m⁻² d⁻¹。在海冰边缘带，高生产力水平与浅混合层深度以及最高达5.158 mg C (mg 叶绿素a)⁻¹ h⁻¹的最大光合速率（Pmax）相关。与海冰边缘带（2.2±0.79）相比，开阔大洋的硅氮消耗比更高（4.1±1.5），这表明铁限制对初级生产力的调控具有重要作用，该结论得到海冰边缘带（40米以深层位Fv/Fm为0.50±0.11）高于开阔大洋（0.36±0.08）的Fv/Fm比值的支持。此外，开阔大洋中存在与季节性密度跃层相关的高生产力区域，该区域的铁有效性可能有所提升。BROKE-West科考区域东北部的高硅酸盐消耗表明硅藻生长旺盛，这与南南极绕极流锋面（southern Antarctic Circumpolar Current front, sACCF）的存在密切相关。然而，较低的同化数（12.8至23.2 mg C mg 叶绿素a⁻¹ d⁻¹）与Fv/Fm比值表明细胞已进入衰老阶段，初始生长发生在该科考季节的早期。在科考区域西部的海冰边缘带内，高硝酸根（NO₃⁻）消耗但相对较低的硅酸盐消耗与棕囊藻（Phaeocystis）水华相关。硝酸根浓度与柱整合初级生产力及叶绿素生物量呈显著负相关，这符合所有浮游植物类群对该营养盐的需求规律。无论如何，整个BROKE-West科考区域内的硝酸根与硅酸盐浓度均高于限制水平（N>15.7 μM，Si>18.3 μM），印证了南大洋的高营养盐低叶绿素（HNLC）特征。