Water exchange between the Gulf of Maine and open ocean induced by Gulf Stream warm core rings

Jiabi Du, Woods Hole Oceanographic Institution, United States, Weifeng Gordon Zhang, WHOI, Woods Hole, United States and Yizhen Li, CSS Inc., Under Contract to NCCOS, NOAA, Silver Spring, United States
Abstract:
Coastal Ocean-shelf exchange plays an important role in modulating the heat, salt, and nutrient transport in the shelf seas. Previous studies on the water exchange between Gulf of Maine and the open ocean mainly focused on processes on seasonal to interannual time scales, and few studied the dynamics of the episodic interaction between Gulf of Maine and the Gulf Stream warm-core rings (WCRs). Here we used satellite SST and SSH, long-term buoy data (vertical profile of velocity and CTD), and idealized numerical models to examine the influence of the WCRs on the water exchange processes at the Northeast Channel and the lower-frequency variabilities in the vicinity of the channel. Upon impinging at the shelf edge southeast of the Northeast channel, WCRs can contribute to intrusion of saltier and warmer ring water into the gulf. The intrusion process depends on factors such as the strength of the WCR and its approaching angle against the continental shelf. CTD and velocity data at several buoy stations in the Gulf of Maine show marked change in temperature and salinity signature and vertical structure of subtidal velocity in response to the WCR. We further discuss different underlying mechanisms with which the WCR influences the ocean-shelf exchange through idealized numerical models. The idealized model shows that large-amplitude wave crests on the ring periphery (also called ‘ring limbs’) can move onto the shelf break and directly influence the intrusion.