Organic biomarkers of carbon inputs and organic matter cycling in the south central Great Barrier Reef region

In April and September 2009, sediments were collected from 10 stations located across the continental shelf: inshore (IS9, IS10); mid-shelf (MS7, MS8, BR1, GR1); outer GBR lagoon (PRC4, PRC5); and the shelf break off the Pompey Complex (SB13, SB14). Sediments were collected to a maximum depth 25 cm using a modified 0.027 m² Bouma boxcorer (IS9, IS10, MS7, MS8, BR1, GR1, SB13, SB14) or a 0.25 m² Smith-McIntyre grab (PRC4, PRC5). Sub-samples were taken with methanol washed polycarbonate tubes. The core tubes were opened for deeper layers to be sampled. Surface sediments (0-1 cm) were taken with a clean stainless spoon. Sediments were stored frozen in glass jars and later freeze-dried in the laboratory to remove water.A moored sediment trap (made of stainless steel, 1 m tall and 10 cm diameter with 5 traps in an aluminium frame) was deployed for 10 days at 30 m in a 65 m deep water column, in September 2009 near reef station PRC4. The traps were filled with 2 x salinity brine containing 4 mg of HgCl2 to retard bacterial activity. However, the windy turbulent conditions caused the trap to drift approximately 8 nautical miles south toward station PRC5 during deployment. In February 2010 sediment traps (made of polycarbonate 0.8 m tall and 8 cm in diameter with 12 traps in a frame) were tethered to the anchored research vessel by a 100 m line at stations PRC4, PCR5, GR1. The tethered traps floated in mid water with a slight tilt in the direction of the currents. Offshore from station IS9, the trap array was free floating. The traps were only deployed during daylight hours (~10 h) and no bacterial retardant was added. Sediment trap samples were filtered though pre-weighed and pre-combusted glass fibre filters. After rinsing with SuperQ water to remove salt, the filters were folded in half and wrapped in pre-combusted aluminium foil and frozen. Prior to analysis, the trap filters were examined and visible crustacean zooplankton removed with tweezers. The following analyses were carries out on sediment and sediment trap samples: Trace elements; CHN; Organic carbon; Total extractable organic matter (EOM); Extraction of neutral lipids and separation by column chromatography into classes (F1-2 hydrocarbons, F3 esters and ketone, F4 sterols and n-alcohols); Extraction of F5 fatty acids from the polar fraction of the extracts; Full scan gas chromatography-mass spectroscopy (GC-MS) quantification of alkanes, Archaea biomarkers and unresolved complex mixtures (UCM); Selected ion monitoring (SIM) GC-MS quantification of a series of 298 PAHs and standards, plus the hopane and sterane series of petroleum biomarkers and the microbial biomarker, diploptene; and Crenarchaeol analysis using normal phase high performance chromatography (API-MS).
This research was undertaken to investigate the origin and cycling of organic matter in the south central Great Barrier Reef using a range of organic biomarkers.
Sediments were sub-sampled from the Boumer boxcorer and Smith-McIntyre grab samples described in:Alongi DM, Trott LA and Mohl M (2011) Strong tidal currents and labile organic matter stimulate benthic decomposition and carbonate fluxes on the southern Great Barrier Reef shelf. Continental Shelf Research 31: 1384-1395.

2009年4月与9月，研究人员在横跨大陆架的10个站位采集沉积物样品：近岸站位（IS9、IS10）、陆架中部站位（MS7、MS8、BR1、GR1）、大堡礁（Great Barrier Reef, GBR）外环泻湖站位（PRC4、PRC5）以及庞培复合体外侧陆架坡折站位（SB13、SB14）。对于IS9、IS10、MS7、MS8、BR1、GR1、SB13、SB14站位，采用改良型0.027 m²的Bouma箱式采泥器（Bouma boxcorer）采集沉积物，最大采样深度达25 cm；对于PRC4、PRC5站位，则使用0.25 m²的Smith-McIntyre采泥器（Smith-McIntyre grab）获取样品。研究人员使用经甲醇清洗的聚碳酸酯管（polycarbonate tubes）对沉积物样品进行分样：打开岩心管以采集深层沉积物样品，表层沉积物（0~1 cm）则采用洁净的不锈钢匙采集。所有沉积物样品均置于玻璃罐中冷冻保存，后续在实验室经冷冻干燥（freeze-dried）去除水分。

2009年9月，研究人员在PRC4站位附近水深65 m的水柱中30 m深度处，部署了一套由不锈钢制成的锚泊式沉积物捕获器（sediment trap）：该装置高1 m、直径10 cm，铝制框架内搭载5个捕集单元，部署时长为10天。捕集容器内预先注入2份盐度卤水，每份添加4 mg氯化汞（HgCl2）以抑制细菌活动。但受多风湍流环境影响，部署期间捕获器向南漂移了约8海里，接近PRC5站位。

2010年2月，研究人员在PRC4、PRC5、GR1站位部署了另一套沉积物捕获器：该装置由聚碳酸酯制成，高0.8 m、直径8 cm，框架内搭载12个捕集单元，通过100 m长缆绳系泊于锚定的科研船上，捕集器随流轻微倾斜于中层水体。在IS9站位外侧海域，捕获器阵列呈自由漂浮状态。本次捕获仅在日间（约10小时）开展，且未添加细菌抑制剂。

沉积物捕获器样品经预先称重并经高温灼烧的玻璃纤维滤膜过滤：用超纯水（SuperQ water）冲洗滤膜以去除盐分后，将滤膜对折并用高温灼烧过的铝箔包裹，随后冷冻保存。分析前，研究人员对滤膜进行检视，使用镊子移除可见的甲壳类浮游动物（crustacean zooplankton）。

针对沉积物及沉积物捕获器样品开展了以下分析测试：微量元素分析、CHN元素分析、有机碳含量测定、总可提取有机质（extractable organic matter, EOM）总量分析；通过柱层析法将中性脂质提取物分离为不同组分（F1~F2组分为烃类、F3组分为酯类与酮类、F4组分为甾醇与正构烷醇）；从提取物的极性组分中分离得到F5脂肪酸；采用全扫描模式气相色谱-质谱联用（gas chromatography-mass spectroscopy, GC-MS）技术对烷烃、古菌生物标志物及未分辨复杂混合物（unresolved complex mixtures, UCM）进行定量分析；采用选择离子监测（selected ion monitoring, SIM）模式的GC-MS技术，对298种多环芳烃（polycyclic aromatic hydrocarbons, PAHs）及其标准品、石油源生物标志物藿烷（hopane）与甾烷（sterane）系列，以及微生物生物标志物双萜烯（diploptene）进行定量分析；采用正相高效液相色谱-大气压电离质谱（normal phase high performance chromatography (API-MS)）开展泉古菌醇（Crenarchaeol）分析。

本研究旨在通过多类有机生物标志物，探究中南部大堡礁海域有机质的来源与生物地球化学循环过程。

本研究中使用的Bouma箱式采泥器与Smith-McIntyre采泥器沉积物分样方法，详见如下文献：Alongi DM、Trott LA与Mohl M（2011）《强潮流与活性有机质驱动大堡礁南部陆架底栖分解与碳酸盐通量》，《Continental Shelf Research》31卷：1384-1395。