Impacts of mesoscale activity on the water masses and circulation in the Coral Sea

Abstract

The climatological vision of the circulation within the Coral Sea is today well established with the westward circulation of two main jets, the North Caledonian Jet (NCJ) and the North Vanuatu Jet (NVJ) as a consequence of the separation of the South Equatorial Current (SEC) on the islands of New Caledonia, Vanuatu, and Fiji. Each jet has its own dynamic and transports different water masses across the Coral Sea. The influence of mesoscale activity on mean flow and on water mass exchanges is not yet fully explored in this region of intense activity. Our study relies on the analysis of in situ, satellite, and numerical data. Indeed, we first use in situ data from the Bifurcation cruise and from an Argo float, jointly with satellite‐derived velocities, to study the eddy influence on the Coral Sea dynamics. We identify an anticyclonic eddy as participating in the transport of NVJ‐like water masses into the theoretical pathway of NCJ waters. This transfer from the NVJ to the NCJ is confirmed over the long term by a Lagrangian analysis. In particular, this numerical analysis shows that anticyclonic eddies can contribute up to 70–90% of the overall eddy transfer between those seemingly independent jets. Finally, transports calculated using S‐ADCP measurements (0–500 m) show an eddy‐induced sensitivity that can reach up to 15 Sv, i.e., the order of the transport of the jets.

Large to submesoscale surface circulation and its implications on biogeochemical/biological horizontal distributions during the OUTPACE cruise (SouthWest Pacific)

“…4 top) and the fate (Fig.4 bottom) that eddy-eddy interactions might be responsible for the emergence of complex paths between the NVJ and the NCJ. Indeed it matches the area described by Rousselet et al (2016) as the region of exchange between NCJ and NVJ waters through eddy trapping and transport. We identify a probable water mass mixing area, in the Coral Sea center, through complex mesoscale stirring.…”

Observed Characteristics and Vertical Structure of Mesoscale Eddies in the Southwest Tropical Pacific

“…They tend to have higher amplitudes than in the same latitude range east of Vanuatu, and have a signature in temperature and salinity higher than 0.3°C and 0.02, respectively, down to ∼500 m depth. Rousselet et al () suggested that AE participate in the transport and mixing of water masses from the NVJ to the NCJ in this Coral Sea Countercurrent region. In agreement with this study, we find that AE in the Coral Sea countercurrent region are indeed able to trap waters above 200 m, to transport salty SPTW waters from the NVJ to the NCJ above σ = 25 kg m −3 , and to contribute to the mixing of these two water masses.…”

“…Such a positive anomaly cannot result from diapycnal mixing with the over and underlying fresher water masses; it thus implies a trapping and an advection of saltier waters from the east and north (see trajectories in Figure ). This confirms previous assertions that AE in the Coral Sea Countercurrent region may contribute to the mixing of water masses from the saltier NVJ waters to the fresher NCJ waters (Rousselet et al, ). The trapping is however mainly restricted to the upper thermocline waters, and does not seem to affect the lower thermocline nor intermediate waters.…”

“…Previous studies in the Southwest Pacific have mostly focused on the EKE as inferred from altimetry (Qiu & Chen, ; Qiu et al, ). To our knowledge, the occurrence and properties of coherent mesoscale eddy structures (Chelton et al, ), have not been investigated specifically with observations, except in the EAC region, where large eddies impacting physics and ecosystems have attracted much attention (Brassington et al, ; Everett et al, ; Mata et al, ; Rykova & Oke, ; Suthers et al, ), and during synoptic cruises (Rousselet et al, ). Yet, investigating the generation, properties, and vertical structures of the mesoscale eddies in the whole region is important for several reasons.…”

“…The mean circulation in the upper 1,000 m of the SWTP can be summarized as follows (Ceccarelli et al, 2013;Ganachaud et al, 2014;Kessler & Cravatte, 2013b;Ridgway et al, 2002). Most surface and subsurface currents in the region flow westward and extend deep (blue arrows in Figure 1a), with the exception of some structures (Chelton et al, 2011), have not been investigated specifically with observations, except in the EAC region, where large eddies impacting physics and ecosystems have attracted much attention Everett et al, 2012;Mata et al, 2006;Suthers et al, 2011), and during synoptic cruises (Rousselet et al, 2016). Yet, investigating the generation, properties, and vertical structures of the mesoscale eddies in the whole region is important for several reasons.…”