Collaborative Proposal: Using Radiocarbon Measurements of Benthic Megafauna as a Tool for Assessing Bentho-Pelagic Coupling in the Marine Organic Carbon Cycle

该项目考察了沉积在大陆边缘的有机碳性质的季节性变化。到达海底的有机碳通量可以通过使用颗粒捕集器或模拟海底埋藏和再生速率来量化，但由于与来自海洋和陆地系统的旧的难熔碳共沉积，在大陆边缘很难评估其质量（即不稳定性）。碳-14 （C14）是最近产生的海洋有机物的有用示踪剂，但这种信号在大陆边缘颗粒中被掩盖了。从浅海沉积物中再悬浮和再加工的较老的难熔碳捕获样品和表层沉积物。研究表明，大陆边缘系统中的表层沉积物捕食者通过其选择性的摄取和消化过程，将到达海底的总有机通量中的不稳定部分隔离掉。因此，这些底栖动物的身体组织和肠道沉积物可以提供到达大陆边缘海底的不稳定物质的记录。最初的C14数据表明，相对于它们生活和觅食的地表沉积物，地表沉积取食动物的身体组织每毫升富含100至300种放射性同位素。基于质量？根据C14的计算，不稳定成分可能只占海底表层有机物质总量的千分之几，然而，表层沉积物捕食者在它们的身体组织中表现出C14的特征（每毫升+20到+80），主要是局部炸弹。产生的信号。来自大陆边缘的钍（Th）数据表明，大陆边缘海底最近沉积的有机物中有多达50%可能在微生物降解或掩埋之前通过沉积物捕食者的肠道。因此，对底栖动物的C14测量可以提供一种独特的工具，用于评估到达海底的有机物质的不稳定性，并跟踪这些物质在底栖食物网中的命运。许多现有的成岩模型将微生物和沉积物饲料的有机质再生视为一个批处理过程，对大块有机质具有单一的碳降解常数。C14数据清楚地表明，有机物质的摄入和这种物质的消化是非常有选择性的过程。来自加利福尼亚边境地带和南极大陆边缘的C14分析显示了这种方法在记录地表沉积物有机碳不稳定性变化方面的实用性。DeMaster和Smith将扩展最初的研究，以便能够评估沉积在海底的有机碳质量的季节性变化。粒子?陷阱样本，底栖生物？在前往加州边境地区的6次巡航和前往南极大陆边缘的5次巡航中收集了动物组织、肠道样本和地表沉积物，涵盖了有机碳供应的主要季节性变化。要求提供资金对这些样品进行150次C14分析（以及补充C13、N15和C/N测量），以便确定一个量化到达海底的有机物的性质和通量的时间序列。他们不仅会评估有机物的颗粒选择和消化选择过程的季节性变化，还会评估这些过程中因摄食策略而产生的变化(底栖地表沉积物摄食者vs地下沉积物摄食者vs头部？向下（地下）沉积（喂食器）在海底。

This project examines the seasonal variation in the nature of the organic carbon deposited on continental margins. The flux of organic carbon reaching the seabed can be quantified by using particle traps or by modeling seabed burial and regeneration rates, but the quality (i.e., its lability) has been difficult to assess on continental margins because of co-deposition with old refractory carbon from marine and terrestrial systems. Bomb Carbon-14 (C14) is a useful tracer of recently produced marine organic matter, but this signal is masked in continental margin particle?trap samples and surface sediments by the older and refractory carbon that is re-suspended and reworked from shallower marine deposits. Surface deposit feeders in continental margin systems have been shown to sequester the labile fraction of the total organic flux reaching the seabed as a result of their selective ingestive and digestive processes. Therefore, the body tissues and the gut sediments of these benthic fauna can provide a record of the labile material reaching the continental margin seafloor. Initial C14 data indicate that the body tissues of surface depositing feeders are enriched in this radioisotope by 100 to 300 per mil relative to the surface sediments in which they live and feed. Based on mass?balance C14 calculations, the labile component may comprise only a few tenths of a percent of the total organic matter in the surface seabed, yet the surface deposit feeders exhibit C14 signatures in their body tissues (+20 to +80 per mil) dominated by the local bomb?produced signal . Thorium (Th) data from continental margins suggest that as much as 50% of the recently deposited organic matter on the continental margin sea floor may pass through the guts of deposit feeders prior to microbial degradation or burial. Therefore, C14 measurements on benthic fauna can provide a unique tool for assessing the lability of organic matter reaching the seafloor and for tracking the fate of this material in the benthic food web. Many existing diagenetic models treat organic matter regeneration by microbes and deposit feeders as a batch process with a single carbon degradation constant for the bulk organic matter. The C14 data clearly show that ingestion of organic matter and digestion of this material are very selective processes. The C14 analyses from the California Borderland and the Antarctic continental margin have shown the utility of this approach for documenting variations in the organic carbon lability of surface sediments.Drs. DeMaster and Smith will expand the initial studies to enable assessment of seasonal variations in the quality of organic carbon deposited on the seabed. Particle?trap samples, benthic?faunal tissues, gut samples and surface sediments have been collected during 6 cruises to the California Borderland and 5 cruises to the Antarctic continental margin covering the major seasonal variations in organic carbon supply. Funds are requested for making 150 C14 analyses (and complementary C13, N15, and C/N measurements) on these samples so that a time series quantifying the nature and flux of organic matter reaching the seabed can be determined. They will assess not only seasonal variations in the nature of particle selection and digestive selection processes for organic matter, but also the changes in these processes as a result of feeding strategy (epibenthic surface deposit feeders, vs. subsurface deposit feeders vs. head?down subsurface deposit feeders) on the seafloor.