Wednesday, October 26, 2011

Planning our cruise

Oceanographers plan cruises very carefully to meet the scientific goals of the project. In the Southern Ocean, those plans can be foiled by weather, as well as the usual difficulties of gear failures. For salps, there is the added challenge of their episodic and patchy patterns of distribution and abundance. Regardless, we have made careful and detailed plans for sampling during our “November Salp Survey” cruise (LMG11-10). Keep reading for (lots) more information and see the image of our station locations in the Western Antarctic Peninsula region.

Station plan
: At each station, a standard set of deployments will include one CTD cast with Niskin bottle water sampling to a depth of 750 m or the bottom (estimated time ~ 1 hr); one 1-m2 MOCNESS cast to 1000m (~ 4 hr); and one IKMT tow to 175 m (~ 1 hr). Net tows will be done at night (dark) when logistically possible, but we will not delay station operations to ensure this.

Small boat (Zodiac) operations: We will carry out small boat operations opportunistically and on a site-specific basis. These will include hand-net or bucket collection of salps and small-scale acoustic surveys. Estimated time for each small boat operation is 6 hrs. Eight operations are planned throughout the cruise.

Deep MOC-1 tows: MOCNESS tows will be carried out to near-bottom depth (2,500 m) at deep offshore stations. Estimated time for each tow is ~7 hrs. Deep MOC-1 tows will be conducted at four offshore stations.

Acoustic Towfish: The Biosonics towfish will be deployed for survey transects between stations for a 2 hour period at a speed of ~ 5 knots, depending on sea state, presence of animals in net tows, ice conditions, etc. The timing and duration of these tows may change due to shipboard operations and the station schedule.

Cruise plan: The cruise track will include 24 stations, each with a standard array of deployments; 8 sites for small boat operations; and 4 deep MOCNESS tows. Our cruise plan has been designed based on information available at this time and per RPSC estimation that time available for our use may total 17 days (408 hrs).

30 Oct Leave Punta Arenas

3 Nov Cape Shirreff

5-7 Nov Palmer Station

8-24 Nov Salp Survey [17 days total]

25-26 Nov Palmer Station

30 Nov Arrive Punta Arenas

The course under ideal weather conditions and ship operations will require 135 hrs steaming and 214 hrs station work, for a total of 355 hrs (Table 1). This leaves 53 hrs (2 days) for weather and other possible delays. We will drop deployments or stations as necessary to accommodate longer delays.

Station 1: A first station will be occupied near Cape Shirreff, Livingston Island after the ship is done offloading the field camp (estimated 03 Nov 2011). Deployments will include CTD, MOCNESS, and IKMT tows. Station time estimated ~ 6 hrs.

Stations 2 – 22: After departing Palmer Station, we will follow a cruise track offshore and sample at Stns. #2, 3, 4. We will steam northeast to sample at Stn. #5. The cruise track then takes us to the stations offshore of the South Shetland Islands (Stns. #6-12), turns back to sample the Bransfield Strait (Stns. #13-20) and coastal waters of the WAP (Stns. #21, 22).

Stations 23 – 24: Time and weather permitting, we will steam farther to the SW to sample shelf and slope waters at Stns. #23-24, before returning to Palmer Station by 25 Nov 2011.

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