Small water parcels across the Kuroshio Extension region in the main thermocline detected by Seaglider and BGC Argo floats

Abstract:

The exchange process across the Kuroshio Extension (KE) affects both water mass exchange and modification. Here we describe the detailed structures of small water parcels based on temporally and spatially frequent measurements by a Seaglider equipped with CTDO sensors and BGC O2 Argo floats, comparing with effectiveness of temporal sampling rate. In 2011-2012, over 30 BGC-Argo floats with dissolved oxygen sensors had been deployed around 30N,145E within a framework of S1-INBOX project in JAMSTEC, which aimed to clarify small scale physical and geochemical processes of a mesoscale eddy. Further, the Seaglider deployed in late Feb. 2014 at the south of Kuroshio Extension, continuously operating for 4 months through late winter to early summer. The Seaglider data showed the small water parcels with characteristics of low temperature, salinity and high dissolved oxygen in the lower thermocline (26.0- 27.0σθ), whose scales were ~ a few ten kilometers widths and ~ a few ten meters thickness. Based on apparent oxygen utility (AOU) analysis, the small water parcels had characteristics of less oxygen consumption, suggesting that the water mass took shorter time after contacting atmosphere than surrounded water. Also, the water parcels were subducted from subpolar northwestern North Pacific region to the north of the Kuroshio Extension. Similar small water parcels with the same characteristics had been observed by the BGC O2 Argo floats in the main thermocline from 500 to 1000 dbar. Based on the 1/30 degrees fine horizontal resolution numerical simulation (OFES), the small water parcels are possibly advected from the north of KE for about one month, indicating a possibility of the fast migration of the water parcels with meso- and submeso scale process. Such unknown process may play a key role to exchange and modify water mass characteristics in the North Pacific Ocean.