Science Update 01-april-2013

Three nights ago our SeaSoar CTD failed. It was probably a flooding, the second on this cruise. This is as unfortunate as it is unusual, and affected two units that had been recently calibrated . We were on our way towards the southeast corner of the initial SeaSoar survey to confirm the location of the low salinity feature we encountered there a couple of days ago. To our surprise the conditions at the surface had changed quite a bit. TSG and ADCP showed a very different picture than only 4 days ago. What seemed like a broad low salinity “blob” now was only a thin elongated filament.

We spent the night trying to figure out where this feature had gone. It was, after all close to 100 m deep, thus represents quite an amount of freshwater. The rapid changes are once again confirming the high variability in this ‘quiescent blob’ (as one might call it looking at mean climatologies), affirming the need to study it in detail and on various time and space scales.

The experience from that night led to the decision to deploy all our drifter assets now, to give time for a repair of the SeaSoar and furthermore to monitor the rapid changes within the SPURS box. As an additional bonus we are able to repeat most of the SeaSoar radiator survey with the TSG while we deploy the drifters and ASIP.

It turned out that a low salinity feature is now seen in the central eastern part of the SPURS box. Good drifter coverage by the end of today will enable us to plan where we should focus on a freshwater experiment, concentrating ASIP and additional drifters from the ENDEAVOR in a fresh patch to contrast the experiments within the saltiest patches. During that experiment in the last days of the cruise, the Spanish vessel will conduct another SeaSoar survey to provide the large scale context and might be able to examine the evolution of such an intrusion by following it from the ‘fresh’ frontal zone towards the origin, which might be to the south.

TSG surface salinity with SADCP vectors averaged over the upper 100m before (left) and after (right) march 28th 2013