Problems, Questions & Thoughts

- Reconciliation of observations with model predictions. Original plan from last cruise entailed a crossing of the "salt wedge" between 0.5 and 4 psu, aiming for locating the 2 psu isosurface. On this cruise there was no such 2 psu line, as the water was vertically mixed until 3 psu; only later did a stratified salinity "wedge" appear. We hypothesized (as non-experts) that the 2-3 psu mixed water was left over from the previous high tide. Furthermore, there was a pronounced increase, maximum, and decrease in turbidity as bottom salinity increased, suggesting the presence of the ETM, with a maximum turbidity at 19 psu, not 2 psu as predicted.

- Agreement on terminology. As a result of this mixed water, unless these casts were anomalies, the 2 psu isosurface may not be the best definition of the "salt wedge." There was some confusion onboard as some called this the salt wedge, while others considered the "foot" on salinity/depth graphs (the sharpest salinity gradient) to be the salt wedge. This and other terms, such as "salt envelope" and "salt bore," need to be nailed down to ensure a common vocabulary.

- Extremely high turbidity at 12:34 PM. Is this an anomaly, or is it perhaps the real ETM? It is in front of the obvious salinity gradient, but it is in mixed water, not fresh. Instead of dismissing it, should we have chased it upstream to confirm the turbidity and watch its formation? Either way, if possible we should have taken another cast in between 12:34 and 1:03 PM for more detail.

- Acoustic backscatter problems. The measurements of the seabed depth were often as much as 60% too small, sometimes even vascillating between values such as 7 and 18 meters. Even when giving the larger value, the CTD instrument could be lowered a few meters beyond it. Since it can create turbidity and be dangerous in currents to touch bottom, a more accurate depth sensor would help in gathering data more representative of the bottom.

- Strange spikes in data. As the cruise went on, this noise became more frequent. Thus, at a given depth, only the minimum values nearby are correct.

- Possible applications of workflow/data management systems. A computer system with access to both forecasts and real-time cruise data could help make suggestions and recommendations on a cruise to facilitate the logistics of decisionmaking and so that some of these questions can be addressed immediately rather than surfacing later.