Raw CTD data from Port St Johns Conductivity Temperature Depth (CTD) and Bathymetry Survey on Algoa Voyage 198, May 2013

Raw Conductivity, Temperature, Depth (CTD) data from Port St Johns Conductivity, Temperature, Depth (CTD) and Bathymetry Survey on Algoa Voyage 198, 8 May - 13 May, 2013. This cruise has two scientific objectives: (1) to investigate the dynamics of the Port St. Johns eddy and biological implications and (2) to investigate the existence of mesoscale eddies in the Agulhas Current. In the case of the former, Oceans & Coasts was asked to provide input to the recent spate of shark attacks off Port St. Johns. Very little is known about the oceanography except that Roberts et al (2010) discovered during a cruise a lee-trapped cyclonic eddy off Port St. Johns that caused substantial slope upwelling. The cold upwelled water is nutrient-rich and appears to provide a biological pump to the local ecosystem. This cruise will deploy an ADCP in a depth of approximately 80 m to determine the frequency of appearance of this eddy coupled with Conductivity, Temperature, Depth (CTD) lines to measure the biological implications. In the case of the second objective - offshore mesoscale eddies interact strongly with the Agulhas Current, and have been shown to initiate the Natal Pulse, cause early retroreflections, and influence slope upwelling at Port Alfred. They also act as vectors carrying biological material to areas along their trajectory and therefore play a role in shaping biodiversity patterns. A recent study however using altimetry and VSP drifters indicates that mesoscale eddies from both Madagascar and the Mozambique Channel tend to move down the Agulhas Current on its offshore boundary, but that these eddies dissapate southwest of East London. On this cruise we investigated whether mesoscale eddies exist in the lower region of the Agulhas Current using in situ measurements. The results may have a profound impact on local altimetry processing and our understanding of the regional oceanography.

原始电导率、温度、深度（CTD）数据，来源于198次航次Algoa航行，时间范围为2013年5月8日至5月13日，在Port St Johns地区进行的CTD和水深测量。本次航次旨在探讨两个科学目标：（1）研究Port St. Johns涡旋的动力学及其生态学意义；（2）探究阿古拉斯海流中是否存在中尺度涡旋。针对第一个目标，Oceans & Coasts公司被要求为近期在Port St. Johns附近频繁发生的鲨鱼袭击事件提供数据支持。关于该地区的海洋学知识极为有限，仅知Roberts等（2010）在航次中发现，Port St. Johns附近存在一个受背风坡影响的气旋涡旋，导致显著的斜坡上升流。上升的冷水富含养分，似乎为当地生态系统提供了一个生物泵。本次航次将在约80米深的水层部署声学多普勒流速剖面仪（ADCP），以确定该涡旋出现的频率，并结合电导率、温度、深度（CTD）数据线来测量其生态学影响。对于第二个目标——离岸中尺度涡旋与阿古拉斯海流的相互作用强烈，已被证明是引发纳塔尔脉冲、导致早期反反射以及影响Port Alfred斜坡上升流的重要因素。它们还作为携带生物物质到其轨迹沿线区域的载体，因此在中尺度生物多样性格局的形成中扮演着角色。然而，近期利用卫星测高和VSP漂流器的研究表明，来自马达加斯加和莫桑比克海峡的中尺度涡旋倾向于沿着阿古拉斯海流的离岸边界向下移动，但这些涡旋在东伦敦西南方向消散。在本航次中，我们通过现场测量调查了阿古拉斯海流下部是否存在中尺度涡旋。研究结果可能对当地卫星测高数据处理以及我们对区域海洋学的理解产生深远影响。