Subantarctic zone oceanography - SAZ Project 1997-1998 - Iron Related Data

Oceanographic processes in the subantarctic region contribute crucially to the physical and biogeochemical aspects of the global climate system. To explore and quantify these contributions, the Antarctic Cooperative Research Centre (CRC) organised the SAZ Project, a multidisciplinary, multiship investigation carried out south of Australia in the austral summer of 1997-1998.Taken from the abstracts of the referenced papers:In March 1998 we measured iron in the upper water column and conducted iron- and nutrient-enrichment bottle-incubation experiments in the open-ocean Subantarctic region southwest of Tasmania, Australia. In the Subtropical Convergence Zone (~42 degrees S, 142 degrees E), silicic acid concentrations were low (less than 1.5 micro-M) in the upper water column, whereas pronounced vertical gradients in dissolved iron concentration (0.12-0.84 nM) were observed, presumably reflecting the interleaving of Subtropical and Subantarctic waters, and mineral aerosol input. Results of a bottle-incubation experiment performed at this location indicate that phytoplankton growth rates were limited by iron deficiency within the iron-poor layer of the euphotic zone. In the Subantarctic water mass (-46.8 degrees S, 142 degrees E), low concentrations of dissolved iron (0.05-0.11 nM) and silicic acid (less than 1 micro-M) were measured throughout the upper water column, and our experimental results indicate that algal growth was limited by iron deficiency. These observations suggest that availability of dissolved iron is a primary factor limiting phytoplankton growth over much of the Subantarctic Southern Ocean in the late summer and autumn.The importance of resource limitation in controlling bacterial growth in the high-nutrient, low-chlorophyll (HNLC) region of the Southern Ocean was experimentally determined during February and March 1998. Organic- and inorganic-nutrient enrichment experiments were performed between 42 degrees S and 55 degrees S along 141 degrees E.Bacterial abundance, mean cell volume, and [3H]thymidine and [3H]leucine incorporation were measured during 4- to 5-day incubations. Bacterial biomass, production, and rates of growth all responded to organic enrichments in three of the four experiments. These results indicate that bacterial growth was constrained primarily by the availability of dissolved organic matter. Bacterial growth in the subtropical front, subantarctic zone, and subantarctic front responded most favourably to additions of dissolved free amino acids or glucose plus ammonium. Bacterial growth in these regions may be limited by input of both organic matter and reduced nitrogen. Unlike similar experimental results in other HNLC regions (subarctic and equatorial Pacific), growth stimulation of bacteria in the Southern Ocean resulted in significant biomass accumulation, apparently by stimulating bacterial growth in excess of removal processes. Bacterial growth was relatively unchanged by additions of iron alone; however, additions of glucose plus iron resulted in substantial increases in rates of bacterial growth and biomass accumulation. These results imply that bacterial growth efficiency and nitrogen utilisation may be partly constrained by iron availability in the HNLC Southern Ocean.The download file also contains three excel spreadsheets of iron data from the project. The file Sedwick_A9706_Fe_data contains water-column dissolved Fe and total-dissolvable Fe data from cruise A9706, which is presented in Sedwick et al. (1999) and Sedwick et al. (2008).The files Sedwick_A9706_ProcessStn1_Exp_data and Sedwick_A9706_ProcessStn2_Exp_data present data from shipboard experiments conducted during cruise A9706 at Process Stations 1 and 2, respectively, as reported in Sedwick et al. (1999).

南极亚极地海域的海洋过程对全球气候系统的物理与生物地球化学维度具有关键贡献。为探究并量化此类贡献，南极合作研究中心（Antarctic Cooperative Research Centre，CRC）牵头开展了SAZ项目，这是一项多学科、多船次的联合调查，于1997-1998年南半球夏季在澳大利亚以南海域实施。
本数据集内容源自相关论文摘要：1998年3月，研究团队在澳大利亚塔斯马尼亚岛西南侧的开阔洋面亚极地海域，测定了上层水柱中的铁元素含量，并开展了铁与营养盐添加的瓶式培养实验。在亚热带辐合带（约南纬42°，东经142°），上层水柱中的硅酸浓度较低（低于1.5微摩尔），而溶解铁浓度呈现显著的垂直梯度（0.12~0.84纳摩尔），推测该现象反映了亚热带与亚极地水团的交织作用，以及矿物气溶胶的输入。该站位的瓶式培养实验结果表明，真光层贫铁层内的浮游植物生长速率受铁限制。
在亚极地水团区域（南纬46.8°，东经142°），上层水柱中的溶解铁（0.05~0.11纳摩尔）与硅酸（低于1微摩尔）浓度均处于较低水平，实验结果显示藻类生长受铁限制。上述观测表明，在夏末与秋季的大部分亚极地南大洋海域，溶解铁的可获得性是限制浮游植物生长的核心因素。
1998年2月至3月期间，研究团队通过实验明确了资源限制对南大洋高营养低叶绿素（High-Nutrient, Low-Chlorophyll，HNLC）区域细菌生长的调控作用。研究沿东经141°，在南纬42°至55°区间开展了有机与无机营养盐添加实验。
在4~5天的培养周期内，研究人员测定了细菌丰度、平均细胞体积，以及[3H]胸腺嘧啶与[3H]亮氨酸的掺入量。四次实验中有三次的细菌生物量、生产力与生长速率均对有机添加物产生了响应。上述结果表明，细菌生长主要受溶解有机质的可获得性限制。在亚热带锋面、亚极地带与亚极地锋面区域，添加溶解游离氨基酸或葡萄糖加铵盐对细菌生长的促进效果最为显著。这些区域的细菌生长可能同时受有机质与还原态氮的输入限制。
与其他HNLC区域（亚北极与赤道太平洋）的类似实验结果不同，南大洋海域的细菌生长刺激可导致显著的生物量积累，这似乎是因为细菌生长速率超过了移除过程的速率。仅添加铁对细菌生长的影响相对有限；然而，添加葡萄糖加铁可显著提升细菌生长速率与生物量积累。上述结果暗示，HNLC南大洋海域的细菌生长效率与氮利用能力可能部分受铁的可获得性限制。
本次下载文件还包含本项目产生的三组铁元素数据Excel表格。其中Sedwick_A9706_Fe_data文件包含航次A9706的水柱溶解态铁与总可溶解铁数据，相关内容已发表于Sedwick等人1999年与2008年的研究论文。Sedwick_A9706_ProcessStn1_Exp_data与Sedwick_A9706_ProcessStn2_Exp_data文件分别呈现了航次A9706期间在作业站位1与2开展的船基实验数据，相关结果已发表于Sedwick等人1999年的研究论文。