Mixed layer depths from R/V Tangaroa cruise 61TG_3052 in the Southern Ocean in 1999 (SOIREE project)

SOIREE Mixed Layer Depth<br>
The mixed-layer depth is defined as the maximum depth at which the sea-water<br>
density is less than the density at 5m + 0.1 kg m-3. This picks up the top of<br>
the seasonal pycnocline, but is insensitive to the weaker stratification that<br>
occurred during the latter part of the experiment.<br><br>

There is considerable cast-to-cast variation, suggesting the presence of internal<br>
waves. Despite this it appears that the average mixed-layer depth decreased by 5-10m<br>
between the 9th and the 16th of February, and then shoaled by a similar amount during<br>
the remainder of the experiment. The apparent rapid decrease between the 8th and the<br>
9th of February is possibly due to the inclusion of CTD stations on the transect towards<br>
the experimental site, and may just reflect the general northward deepening of the surface<br>
layer.<br><br>

The development of thermal stratification within the surface layer is visible from Day 5.<br>
This stratification is an order of magnitude weaker than the stratification within the pycnocline<br><br>

<i><b>Comments preserved from the original file:</b><br>
Defined as the maximum depth at which the density is less than the density at 5m + 0.1 kg/m3.<br><br>
Casts where the mixed layer depth is undefined, either due to bad data or because the<br>
cast was too short, are assigned a value of -1.<br><br>
This depth is typically at the top of the seasonal pycnocline. During the latter part of the<br>
experiment there was persistent weak stratification at shallower depths.<br><br>
The upcast column is 0 for downcasts and 1 for upcasts.<br><br>
</i>