Today (15 May), is another contrast in the late fall Antarctic weather. We arrived at Station #64 just after midnight and the station work began with a CTD. Over the course of the morning the winds have died down and the sea surface is now (1517 local) relatively calm, but there is still a large swell running - a remnant from yesterdays high winds. The skies are thickly clouded and there is fog - visibility is limited to a few hundred meters. We are currently working at Station #66 with winds out of the Northwest (340) at about 15 kts and the air temperature is -0.5°C. Our current position is -68 27.022°S; -73 39.608°W.
14 May began with BIOMAPER-II being towyoed to Station 57 and the sea conditions were again deteriorating. A Terrascan image of our region showed an intense low pressure system to our west and headed our way. By the time we reached the station about 0500, it was clear that the towed body should be brought on board because conditions were likely to get much worse. Unlike the missed recovery at Station 54, this time we were able to safely bring the towed body on board. The MOCNESS scheduled for this station was scrubbed, but a CTD profile to the bottom was made. Shortly after that as we started to steam out across the ACC, the weather window closed and seas were too rough along the route to permit us to do our planned work with the CTD or BIOMAPER-II. XBTs and XCTDs plus surface water samples were the only game in town for Stations 58, 59, 60, 61, 62, and 63. So we steamed on with BIOMAPER-II on deck while the offshore survey was being done in very rough seas. By late afternoon, we had reached the end point of offshore stations and turned onto a much more comfortable course for the steam to the next shelf station #64, some 37 miles away.
Eileen Hofman reports that the 14 May morning watch did a CTD cast at survey station 57. Following this station the weather rapidly got worse and by the time we arrived at station 58 conditions were such that we were unable to put the CTD in the water. As a result, survey stations 58 to 63 were done with XCTD casts. These are the closely spaced stations that cover a large bathymetric feature just off the shelf edge and were designed to see how the deep topography was steering the ACC in this area.
Preliminary analysis of the XCTD observations indicate that the bathymetric feature produced a large steep meander in the southern boundary of the Antarctic Circumpolar Current. The meander extends onto the continental shelf, with the 1.7°C isotherm being present at station 57 on survey transect eight.
After completion of survey station 63 we steamed towards the outer most station on survey transect nine. During this transit we did XBTs at intermediate points. These temperature data show the 2.3°C isotherm extending onto the flank of the continental shelf. This provides further support for the existence of a steep meander. Completion of survey transect nine will provide a better idea of the spatial extent of the meander.
Bob Beardsley has updated his analysis of the satellite drifter tracks from the drogues deployed on the mooring cruise and on this cruise. His report below makes reference to a figure which is not being transmitted with this report because of restrictions on what can be emailed:
Drifter Note 135 (7:30 AM, May 15)
The Figure shows the drifter tracks for the period starting yd 130 through 133.5. The red asterisk at the head of each track is the last position, indicating the direction of the drifter motion. Blue circles are plotted every 2 days along each track. Also shown are the mean wind stress in black to left and the wind stress scale (2 dynes/cm2) in green at 66.5°S. During this period, winds were gale force towards the south during 130.5 and 133.0.
1. Drifters 7, 8, 9, and 10 all move into or deeper in Marguerite Bay. Drifter speeds were ranged from 20 to 40 cm/s during the first half of day 133.
2. During this period, drifter 2 continued to move west and northwest at nearly right angles to the mean wind stress, in the opposite direction to the drifters entering Marguerite Bay.
3. Drifter 5 moved very little during this period (speeds <4 cm/s). Eileen's map of Tmax below 200 m suggests that this drifter may be in a bubble of cooler shelf water surrounded on three sides by warmer slope water.
4. Drifter 3 has moved downwind into the "iceberg graveyard" surrounding our CTD station 53 just off the tip of Alexander Island. It will be interesting to see if this drifter becomes trapped and frozen into the ice.
5. Next drifter deployment will be near station 66 today.
On 14 May, Chris Ribic and Erik Chapman observed for 4 hours, 37 minutes while transiting between stations 57 and 63 occurred. The saw very few birds overall and recorded species that are typically record in offshore transects. They recorded a single Broad-billed Prion, the first Prion that have observed since crossing the Drake Passage. Here are the summarized results for the day's survey effort.
|Species||Number (JD 134) 4hr 37min|
|Antarctic Petrel (Thalassoica antarctica)||7|
|Cape Petrel (Daption capense)||13|
|Southern Fulmar (Fulmarus glacialoides)||8|
|Blue Petrel (Halobaena caerulea)||18|
|Broad-billed Prion (Pachyptila vittata)||1|
Catherine Berchok reports that on May 14th she deployed the first sonobuoy of the day on route to station 59 and listened for over 2 hours. A couple of sounds were heard, probably either seals or wave noise. A second sonabuoy was tossed out before station 61. Results same as for the first buoy - some "blurp-like" sounds heard during a listening period of around 2 hours. The last buoy of the day was deployed during the dropping XBT's at station 63. Just a few audible blurbs and downsweeps were heard over a 2 hour period.
Regarding yesterday's possible finback or blue whale calls, Catherine
consulted with Mark MacDonald about them. This is what Mark had to say
about them: ".....The infrasonic upsweeps sound like the volcanic sound
which comes from a point about halfway between the southern tip of South
America and New Zealand. These used to be much stronger and I thought they
perhaps had gone away by now, but maybe not. It will be interesting to
see how the bearings on these plot."
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, S. Gallager and
As noted above, BIOMAPER-II was towyo'd between Stations 56 and 57. Upon arrival at the station around 0500, the decision was made to scrub the MOCNESS tow because it was already too rough to deploy the net system and to recover the fish before doing the CTD. Conditions for the recovery were marginal. The recovery team was quickly assembled: Scott Gallager, Carin Ashjian, MT David Green, Joe Warren, Andy Girard on the winch controls, Karen Fisher and me. The towed body was brought up from about 45 m to about 10 m and paused, but this time the drogue was not deployed in case at the last minute it was decided it was too rough to get it on board. Then Andy started hauling the wire in and as the towed body got close to the surface, it was clear that the seas were OK to bring it on up. The fish broke the surface straight and two poles with quick release lines when down to try and lock onto the SS railings at the front end. David got his on quickly and had some tension on the line when the fish started to do a horizontal 360 swing. As the tail came into the stern, David reached out and stopped it, and then gave it a push which sent it back out away from the stern. Andy kept the cable coming in and about the time the fish was lined up with the docking mechanism, the termination and boot slipped up and into it. Then Karen Fisher got the second tag line on and from then on it was easy to get it on board and it was landed on the deck by about 0600. BIOMAPER-II sat the rest of the day strapped down on the aft deck while the ship steamed into the wind and seas along the course for the offshore survey.