R/V Roger Revelle Expedition KNOX03RR
CLIVAR/CO2 cruise I8S
Chief Scientist Weekly Report 3, 19 February 2007

1600 local; 61.4 °S, 82.0 °E; air temp 0 °C (32 °F), wind 5 knots from S

Captain Murline’s plan to work our way westward along 64 degrees south to 85 degrees east placed us south of the heavy seas and west-to-east winds and currents of the circumpolar zone. A further benefit was some westward currents and occasional following seas. Hence we arrived somewhat ahead of schedule in the region where we hoped to make our close approach to Antarctica. There, we faced a problem. Simply put, Antarctica is ringed by sea ice and R/V Roger Revelle, while a fine research ship, is not an icebreaker. To approach the continental shelf break - the oceanographically interesting region where the relatively flat bottom of the continental shelf begins to slope down steeply to the abyss - we required (1) working near the time of the local annual sea ice minimum (provided for us long ago thanks to the ship schedulers), (2) useful satellite ice edge imagery and analyses (kindly provided for us real time by the Navy/NOAA Joint Ice Center), (3) cool-headed navigational expertise (no problem with Captain Murline and his bridge staff in charge), and (4) a truly significant dose of good luck.

We were out of satellite communications (including email) for a few days, partly due to not being able to aim the ship's antenna low enough on the horizon to see geostationary satellites high over the equator (nearly blocked by the earth's curvature), and partly because SIO had to put together, ashore and at sea, the technical and business pieces to effect a transfer to an Indian Ocean satellite as we left behind the footprint of the Pacific one. But just when we needed the connection to receive ice images, the satellite connection was reestablished, and so we pored over fresh ice images together with our bathymetric charts. Such charts are only as reliable as is their underlying data from previous surveys, and in the Antarctic that’s not encouraging. But we were unusually lucky in that regard because one of the SIO grad students along, JJ Becker, works with SIO's Dave Sandwell, an expert in teasing out ocean bathymetry from satellite data. JJ had along on his computer the latest bottom depth information. Combined with the ice edge information, plus our operational limits (for example, having no spare time to hunt for the shelf farther to the west than planned), we came up with a plan to approach along 84 degrees, 35 minutes east longitude, in the western Davis Sea. It turned out to be a good choice, and in hindsight perhaps was the only one which would have worked: As we proceeded south early Thursday evening, the bottom beneath us rose, but meanwhile the ice was getting closer. Just when Captain Murline said "no further" the real-time bathymetry data showed that we'd reached our goal of the 500 meter isobath.

We lowered our instruments there for our first station, the late day sun illuminating the sea ice, with icebergs all about, in an embayment of open water, killer whales patrolling the ice edge for tasty seals and penguins, seals on the ice not inclined to join them, soon into sunset with an aurora above. Through the cold 25 °F night we completed our 500 meter station, then the 1200 meter station offshore of that, then the 2000 meter station, and so on, being chased north by encroaching ice, yet in the process completing a rare Antarctic shelf-slope-basin transect from a non-ice-strengthened ship. Success in such circumstances requires equipment that works well the first time and every time, and most of all, skilled staff to do the work. No problem there, not with this team.

We were not yet through our encounters with sea ice. The ice images showed a tongue of sea ice spreading eastward from an nearby ice shelf, nearly across our planned path out from the Davis Sea to the 1994 line. Sure enough, on the way to station 7 and 8, there it was. It provided an exciting moment, with parades of icebergs and myriad growlers about, but since "exciting", “sea ice”, and “R/V Roger Revelle” are not usually to be used in the same sentence, this encounter caused a bit of a detour. Meanwhile, as we passed one of the bergs, we saw four penguins (tiny specks by eye), and caught the photo attached to this email in reduced-resolution form.

Before we joined with the 1994 I8S stations (in 1994 they went as far south as they could at that time), we had the opportunity to sample oceanographic features farther south. For an example, we have attached a CTD temperature cross section up through this morning's station, on which the black vertical bar shows the farthest south reached in 1994. Oceanographers in the audience will see that we encountered waters with a determinably Antarctic character. Other research ships have sampled these waters, of course, but none previously in this region measuring our panoply of carbon-and-climate related parameters.

We are now leaving a cold but hospitable far south for our days-long crossing of the circumpolar ocean. Operations are mostly trouble free, though we have had to switch out the lowered-ADCP due to some yet-unexplained oddities in the data from the first instrument. Also, the large rosette is not sinking quite as well as we'd like. Since it weighs ca. 1100 lbs. in air, reluctance to sink is likely due to higher drag than desirable. Experience and small adjustments in lowering procedure are helping, but we're keeping an eye on this.

All is well.

Jim Swift and Annie Wong
chief and co-chief scientists, CLIVAR/I8S