The purpose of the cruise is to conduct several types of studies in the Ross Sea Polynya region. The Neale (B203), Jeffrey (B200) and Gargett (B208) groups are investigating UV effects on phytoplankton and bacteria in the context of vertical mixing (collectively, the Mixing and Ultraviolet Radiation in the Ross Sea or MIXURS project). The Goes (B206) project has related goals of understanding UV effects on fatty acid, carbohydrate and amino acid metabolism in phytoplankton. The Kieber/ Kiene group (B002/266) is interested in both photochemical and biological processes affecting the fluxes of dimethylsulfide (DMS) and related sulfur compounds with an emphasis on UV effects for this years cruise. The Gast/Caron group (B207) will sample a variety of Ross Sea pelagic environments to study genetic diversity of protozoan groups. The cruise is also hosting an OPP postdoctoral fellow Brook Nunn studying iron acquisition by phytoplankton. The NBP departed Lyttleton, New Zealand late in the day on Wednesday, October 26, about a half-day delayed due to late arrival of cargo. We crossed open water on a SE course in favorable weather, only encountering seas too rough for over-the-side operations on the last day before the ice. This was appreciated by the science groups which concentrated on setting up and trial measurements. All groups have instrument and/or laboratory intensive programs, so set-up and trial measurements, as well as periodic underway samples, are continuing over the transit to the study area which is tentatively targeted around 77ºS 173ºE, north of the Ross Ice Shelf. CTDs, and water sampling were commenced on Day 3 (October 29), and occasioned stopping one hour each day. We entered the ice pack near 63ºS 178ºW on Day 5 (November 1) and Day 6 had a three hour stop in a open water area within the ice pack to wet-test several over-the-side instruments. Wet tests of the freefall Ocean Sensors CTD system revealed that the manufacturer has not improved sensor noise levels sufficiently to enable accurate calculation of Thorpe overturning scales in the weak density gradients typical of polar oceans. Instead, the Gargett group will use the ship’s Seabird CTD with processing routines developed for ship-lowered CTD profiles during the previous austral summer cruise in 2004/05. A test deployment was made of a dual-frequency HTI towed sonar package that will be used to image backscatter associated with Langmuir circulations near surface and internal wave displacements in the upper 150m of the water column, both processes with potential for producing large vertical displacement of immobile biological particles in surface-intensified UV light fields.
Since then, the NBP has been making steady progress through leads. Underway measurements are being taken by the standard suite of ship instrumentation, with solar radiation measurements supplemented by operation of two Smithsonian SR-19 UVB spectroradiometers (on the mast and at the helo deck level) and a multichannel GUV instrument (deployed by Jeffrey group at helo deck level). These instruments provide detailed information about UV exposure and support incubation experiments in UV transparent and opaque tanks postioned on the helo deck.
The ECO and Raytheon science staff have provided very solid and much appreciated support through the sometimes trying period of set-up and initial “shake-down”, especially considering the challenges of meeting the numerous and diverse requirements of the ship board science projects. Particular thanks go to Alice Doyle and the full team of RPSC staff for support during the hectic port call Also gratefully acknowledged is the efforts of MTs Greg Buikema, Rick Lichtenhan, and Emily Constantine construction of a temporary swinging door on the Helo Hangar to allow convenient passage of science personnel to the lab vans on the Helo Deck.