Hydrocarbon fluxes in the Timor Sea with special reference to natural oil and gas seeps

In this study, aspects of the physical oceanography, groundwater and pore-water chemistry, and the geochemical and microbiological compositions of sediments have been investigated in the Bonaparte Basin. In particular, we have studied the outer shelf margins of the Timor Sea, in and around the Cartier Trough and Karmt Shoals, looking for evidence of hydrocarbon and groundwater vents associated with the giant Halimeda mounds. Previous work in this region had identified an apparently strong relationship between the location of hydrocarbon seeps and carbonate bank development. A few sites on the seaward margin of Pee and Karmt shoals were identified where surface sediment pore water was greatly enhanced in activities of 224Ra, 223Ra, 228Ra, and 226Ra, which should be an indicator of groundwater inputs. Some of these sediments also had above background concentrations of ultraviolet fluorescence (UVF) detected hydrocarbons. No convincing evidence of seeps from water column salinity, temperature, optical backscatter or oxygen profiles were found, but the radium isotope activity ratios were useful in suggesting that the water sources for this region were likely from the South China Sea via the Indonesian Throughflow (ITF).Geochemical analyses of bulk sediment grab samples of this region showed the expected aragonite (high Sr) dominance on the Halimeda mounds. We also found a zone of Al and Fe enhancement in the dominantly carbonate (Halimeda, foram, pteropod ooze) sediments seaward of the mounds. One radio-chemically dated core from these sediments indicated significant variations in marine and terrestrial (aeolian?) inputs over several centuries of deposition. A consortium of researchers is now being assembled to specifically locate the hydrocarbon and groundwater vents, and determine the influence of these energy and nutrient inputs on the unique biological diversity of these spectacular 400 m high mounds. The scientific objectives of this research was to:1. Search for hydrocarbon/groundwater seeps near Halimeda mounds in the Pee Shoals to Karmt Shoals region, shelf and slope using on-board chemical and radiochemical tracers and to test new methane and oxygen sensors on the CTD frame. 2. Devise methods to estimate carbon (organic and carbonate) burial rates, as a carbon sink or source, and obtain samples of Halimeda for biomass and identification by testing existing sediment sampling gear for use on and around the mounds.3. Preserve samples for nutrient, trace metal, hydrocarbon, radionuclide and microbiological studies to characterise potential study sites.4. Synthesize these preliminary results and develop plans for longer term, integrated and multi-institutional studies of these seep ecosystems.

本研究针对波拿巴盆地（Bonaparte Basin）开展了物理海洋学、地下水与孔隙水化学、沉积物地球化学及微生物群落组成等多维度调查。其中重点聚焦帝汶海（Timor Sea）外陆架边缘、卡地亚海槽（Cartier Trough）及卡姆特浅滩（Karmt Shoals）周边区域，旨在搜寻与巨型仙掌藻丘（Halimeda mounds）相关的烃类与地下水喷溢证据。
该区域既往研究已证实，烃类渗漏点位与碳酸盐岩滩发育之间存在显著关联。
在皮伊浅滩（Pee Shoals）与卡姆特浅滩（Karmt Shoals）向海一侧的边缘，我们识别出多个站位，其表层沉积物孔隙水中的²²⁴Ra、²²³Ra、²²⁸Ra及²²⁶Ra活度显著升高，该特征可作为地下水输入的指示标志。
部分此类沉积物的紫外荧光（UVF）检测烃类浓度亦高于背景水平。
尽管未通过水柱盐度、温度、光学后向散射及氧剖面观测到令人信服的渗漏证据，但镭同位素活度比分析表明，该区域水源大概率经由印度尼西亚贯穿流（Indonesian Throughflow, ITF）来自南海。
对该区域沉积物抓样（bulk sediment grab samples）的地球化学分析显示，仙掌藻丘以文石（高锶文石）为主，与预期结果一致。
我们还在仙掌藻丘向海一侧的碳酸盐主导沉积物（仙掌藻、有孔虫、翼足类软泥）中，发现了铝（Al）与铁（Fe）富集的区域。
对其中一件经放射化学定年的沉积物岩芯分析表明，在数百年的沉积过程中，海洋与陆源（风成？）输入物存在显著波动。
目前研究团队正集结多方科研人员，以期精准定位烃类与地下水喷溢口，并明确这些能源与营养物质输入对这座高达400米的壮观仙掌藻丘独特生物多样性的影响。
本研究的科学目标如下：
1. 借助船载化学与放射化学示踪剂，在皮伊浅滩至卡姆特浅滩区域的陆架与斜坡带仙掌藻丘周边搜寻烃类/地下水渗漏点位，并在温盐深仪（CTD）搭载框架上测试新型甲烷与氧气传感器；
2. 研发估算碳（有机碳与碳酸盐碳）埋藏速率的方法，以明确其作为碳汇或碳源的属性；同时针对仙掌藻丘及周边区域，通过测试现有沉积物采样设备，获取仙掌藻样品用于生物量测定与物种鉴定；
3. 留存样品用于营养盐、痕量金属、烃类、放射性核素及微生物学研究，以表征潜在研究站位的特征；
4. 整合上述初步研究结果，制定针对该渗漏生态系统的长期、综合性多机构研究计划。