Lateral advection of organic matter in cascading-dominated submarine canyons
Lateral advection of organic matter in cascading-dominated submarine canyons
复制标题
DOI：
10.1016/j.pocean.2009.10.004
复制
发表时间：
2010-03
影响因子：
4.1
通讯作者：
T. Tesi;P. Puig;A. Palanques;M. Goñi
中科院分区：
文献类型：
--
作者：
T. Tesi;P. Puig;A. Palanques;M. Goñi
在狮子湾(GOL)，密水从陆架外溢出来是季节性的，是影响颗粒有机物(OM)陆架-斜坡交换的主要机制。大部分稠水出口发生在戈尔湖西南部，特别是通过克雷斯角(CDC)海底峡谷。在这里，部署了海底仪器来收集峡谷下方的颗粒物通量，而表层沉积物是在层叠事件发生后沿着陆架、CDC峡谷和附近的Lacaze-Duthiers(LD)峡谷的沉积物扩散系统采集的。用有机和无机碳、总氮、生物硅、δ13C、Δ14C和碱性CuO氧化产物等指标研究了悬浮物和表层沉积物的化学组成。从2004年12月到2005年4月中旬，在CDC峡谷测量到了温盐异常和高流速事件，这表明峡谷中的稠水有明显的场外输出。在级联过程中，泥浆和相对较粗的陆架和峡谷上部沉积物是质量通量的主要组成部分。相反，在级联前后，细小物质通过云团层的平流主导着下坡通量。由此引起的颗粒大小的变化影响了矿物结合陆源有机碳的通量，表明峡谷下方陆源有机质的运移不是以散体的形式发生，而是其组成是由与不同运移机制相关的沉积物分选驱动的。表层沉积物和沉积物圈闭样品均表明，CDC峡谷与陆源扩散系统具有良好的连通性。相反，我们的结果表明陆源OM对LD峡谷的影响总体上是有限的。尽管河流营养物质供应减少，但在2005年4月，在级联期结束时观察到现代海洋有机质的显著脉冲输入。强烈的混合和缺乏强大的水柱层结可能起到了关键作用，使得营养丰富的水域扩散到真光带和海洋有机碳的有效垂直下沉。在前往海底的途中，这个新鲜的有机碳水池与从陆架溢出的密集羽流相互作用，成为横向平流到斜坡上的物质的一部分。
In the Gulf of Lions (GoL), dense water overflowing off the shelf occurs seasonally and represents the main mechanism affecting the shelf-slope exchange of particulate organic matter (OM). Most of the dense water export takes place in the south-western GoL and in particular through Cap de Creus (CdC) submarine canyon. Here, benthic instruments were deployed to collect down-canyon particulate fluxes whereas surface sediments were taken after the cascading event along the sediment dispersal system on the shelf, in CdC canyon and in the nearby Lacaze-Duthiers (LD) canyon. The chemical composition of the suspended material and surface sediments were investigated using several proxies including organic and inorganic carbon, total nitrogen, biogenic silica, δ13C, Δ14C, and alkaline CuO oxidation products. Thermohaline anomalies and high current speed events were measured in CdC canyon since December 2004 until mid-April 2005 indicating a marked off-shelf export of dense water trough the canyon. During the cascading, mud and relatively coarse shelf and upper canyon sediments were the major component of the mass flux. Conversely, advection of fine material via nepheloid layers dominated down-slope fluxes during pre- and post-cascading. The resulting change in grain-size affected the flux of mineral-bound terrigenous OC, indicating that the down-canyon transport of land-derived OM did not occur as bulk but rather its composition is driven by sediment sorting associated with different transport mechanisms. Both surface sediments and sediment trap samples indicated that CdC canyon is well connected to the GoL terrigenous dispersal system. Conversely, our results suggest an overall limited influence of land-derived OM in LD canyon. In spite of the reduced fluvial nutrient supply, a significant pulsed input of modern marine OM was observed in April 2005 at the end of the cascading period. Both intense mixing and lack of strong water column stratification likely played a key role allowing for both diffusion of nutrients-rich waters into the euphotic zone and efficient vertical sink of marine OC. On its way toward the seafloor, this fresh pool of OC interacted with the dense plume overflowing off the shelf, becoming part of the material laterally advected to the slope.