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

本项目研究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通过模拟海底埋藏和再生率来量化，但质量（即，由于与海洋和陆地系统的老的难熔碳共同沉积，因此难以在大陆边评估其不稳定性。碳14（C14）是一种有用的海洋有机质示踪剂，但这种信号被大陆边缘颗粒所掩盖。通过从较浅的海洋沉积物中重新悬浮和再加工的较老和难熔的碳捕获样品和表层沉积物。大陆边系统中的表层存款摄食者由于其选择性的摄食和消化过程，已显示出可将到达海底的总有机通量中的不稳定部分隔离起来。因此，这些底栖动物的身体组织和消化道沉积物可以提供到达大陆边海底的不稳定物质的记录。最初的C14数据表明，相对于它们生活和进食的表层沉积物，表层沉积食虫动物的身体组织富含这种放射性同位素每密耳100至300。基于质量？根据碳14平衡计算，不稳定成分可能只占海底表层总有机物的百分之零点几，但表层存款饲养者的身体组织中显示出碳14的特征（每密耳+20至+80），主要是当地的炸弹？产生的信号。来自大陆边的钍数据表明，最近沉积在大陆边海底的有机物质中，多达50%可能在微生物降解或埋藏之前通过存款饲养者的内脏。因此，对底栖动物的C14测量可以提供一个独特的工具，用于评估有机物质到达海底的不稳定性，并追踪这种物质在底栖食物网中的归宿。许多现有的成岩模型将微生物和存款馈线的有机质再生处理为一个批量过程，具有单一的碳降解常数的散装有机质。C14数据清楚地表明，有机物的摄入和消化是非常有选择性的过程。来自加州边界和南极大陆边缘的C14分析表明，这种方法在记录表层沉积物有机碳不稳定性变化方面具有实用性。DeMaster和Smith博士将扩大初步研究，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？在前往加州边界的6次考察和前往南极大陆边缘的5次考察中收集了动物组织、肠道样品和表层沉积物，涵盖了有机碳供应的主要季节变化。请求提供资金，对这些样本进行150次C14分析（以及补充的C13、N15和C/N测量），以便确定到达海底的有机物的性质和流量的时间序列。他们将不仅评估有机物的颗粒选择和消化选择过程的性质的季节性变化，而且评估这些过程中由于摄食策略（底栖表面存款馈线，与地下存款馈线与头？向下的地下存款馈线）。

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.