P16S Chief Scientists' Weekly Report 3

26 September 2014

Weekly Report #3.  April 7, 2014.

Lynne Talley (SIO) and Brendan Carter (Princeton)

Our third week at sea of hydrography, float and surface drifter deployments, and bio-topical measurements began smoothly, with 10 stations, and 2 floats deployed in the relatively calm Ross Sea. By mid-week, we were sitting in a very wide tunnel of sustained westerly winds with gusts to more than 45 knots and very high seas centered at 60°S, right over our station plan. Most of the rest of the week was consumed with frequent consultations with Captain Souza, working with the Spawar and OTSR weather forecasters, who proved to be quite accurate. Because of the persistently bad conditions, we decided to sail northward out of the weather, from 62°S to 58°S. We then proceeded back to the south, making stations every 1 degree latitude, following the forecast of a developing lull between two low pressure systems, and were able to return to 61°S. Given the total cruise time, we then had to turn back northward, and began filling in our ½  degree stations. We had to abandon 2 stations and will be sampling for the next few days at station separations dictated by weather. Overall for the week we completed 15 stations, and deployed 3 floats and 4 surface drifters.

On the positive front, the data collection and quality are excellent, and the entire team from science to ASC to ECO dealt well with the protracted poor weather. The floats that we’ve deployed are returning their first profiles, and our first float has just reported its second profile. The two floats with the cutting edge pH sensors are reporting good pH profiles. Our first surface drifters for NOAA’s Global Velocity Program were deployed at 60°S. The NASA team been able to complete bio-optical profiling each day when we have been able to work, and their work was featured on the NASA outreach website, Image of the Day for April 5 (Cruising for Ocean Data) http://earthobservatory.nasa.gov/IOTD/ 

 An initial science result: The Ross Sea bottom waters continue to warm, with a monotonic increase over the 4 WOCE/CLIVAR surveys thus far: 1992, 2005, 2011, and now 2014. The bottom 1000 m thick layer is nearly adiabatic (well mixed with lower temperature variance than the abyssal thermocline above it), and can be easily compared from one survey to the next. Additionally, we note that the entire deep temperature structure has shifted from cooler to warmer, and hence it appears that the warming of the bottom layer is partly a function of warming of the abyssal layer, from 2500 to 4500 m.