Expected Datasets from the Alpha Helix Bering Strait Cruise of 2004

Expected Datasets from the Alpha Helix Bering Strait Cruise of 2004

(HX-290)

Mooring work:

All three moorings (see Table 1) were successfully recovered and redeployed.

CTD and ADCP work:

A total of 121 CTD casts were taken along 8 different sections (see Figure 1 and sections in the appendices). The Bering Strait line (BSL) was CTDed twice, once at the start and once at the end of the cruise. At each major section (BSL, MBS, NBS, A3L, CHUK and EEXT), the CTD line was either preceded or followed immediately by an ADCP line run at 7 knots. The longer sections (PHL, CPL and CCL) could not be traversed twice and thus transit between CTD sections was undertaken at a compromise speed of ca. 8-10 knots, to acquire reasonable ADCP data whilst still maintaining quasi-synopticity of the line. In the shallow, changeable shelf system, the latter is important, as witnessed by the differences between various stations (especially A3 and the BSL line) taken days apart. The final ADCP lines (the western part of the repeat of the BSL line, and lines south of the Bering Strait) were also run at 10 knots.

The CTD package carried sensors for temperature, conductivity, fluorescence, PAR and

transmissivity.

Nutrient Analysis work (Lee, Thornton, Moreland):

A total of 745 nutrient samples were collected and analyzed on board for silicate, phosphate, nitrate, nitrite and ammonium by Lee, Thornton and Moreland. Nutrients were taken on all stations except for the 0.5 stations on the rerun of the BSL line. In addition, at every station (except BSL2.5, 3.5, and 4.5 on the second running of the BSL line) samples were taken at surface, mid-water column and bottom for chlorophyll. At 22 stations, including 8 productivity stations, samples were taken at surface, mid-water column and bottom for size-fractionated chlorophyll (>20mm, 20-5mm and 5-0.7 mm) to study the general distribution of phytoplankton sizes in the different water masses in the research area. At the 8 sites (A2, A3, EEXT3, PHL12.5, CCL20, CCL15, NBS12 and BSL3), primary productivity experiements were conducted using a 13C-15N dual tracer technique. To check the physiology status of phytoplankton, large volume productivity experiments were executed for the end products of photosynthesis at the 3 stations (A3, PHL12.5 and BSL3).

Oxygen isotope sampling (Morrow and deHart for Cooper, Tennessee):

A total of 368 water samples were taken for O18 sampling. Samples were taken at bottom, 5m and (where appropriate) midwater column at all stations except some of the productivity stations (see bottle list in the appendices). Higher vertical resolution was taken on the first BSL line. These samples were sealed with parafilm and shipped to Lee Cooper at the University of Tennessee for later analysis. To ensure the integrity of the bottle samples, when possible salinity samples (ca. 180) were taken from the bottles used for O18 samples.

Isotope and plankton sampling (deHart, UAF):

As part of the doctoral research of Pieter deHart, UAF, into the trophic fractionation effects of the environment throughout the migration route of the bowhead whale, net tows were taken for phytoplankton and zooplankton, and water samples were collected for O and H isotopic analysis. Water samples were collected along the initial BSL line (at 10m depths at stations BSL1 - BSL 5.5 inclusive and at the surface for BSL1, 2, 3, 4, 5) and at PHL13 (5m) and EEXT (5m). Both phytoplankton and zooplankton net tows and water samples were taken at the three mooring locations A2, A3 and A4. In addition, one water sample and two plankton tows were conducted at the westmost and eastmost point of the CHUK/EEXT line (i.e. CHUK1 and EEXT3), the eastern tip of the Point Hope Line (PHL13), and at the location between the Diomede Islands (LD1). A total of 18 water and 10 plankton samples were obtained to be processed at the University of Alaska Fairbanks for their Oxygen-18 and Deuterium composition. The O18 isotope analysis will coordinate with samples run by Cooper.

Underway ADCP data:

The Alpha Helix is now using a new 150 kHz hull-mounted ADCP. This collected data for the duration of the cruise. Particular lines (BSL, MBS, NBS, A3L and CHUK/EEXT) were run at ca. 7 knots to give better spatial resolution. Other lines (PHL, CPL, CCL and the western part of the repeat of the BSL line) were run at 8-10 knots due to cruise time limitations. At the end of the cruise, two further ADCP lines - one from BSL1 to Fairway Rock, just south of the Bering Strait and one from Fairway Rock to Wales on the Alaskan coast - were run at 10 knots.

Underway sampling:

Seachest data and standard underway meteorological sampling was conducted for the duration of the cruise.

Satellite (SEAWIFs and MODIS) imagery:

Satellite data of the region is extremely helpful in visualizing the horizontal structure of the flow. Mike Schmidt kindly watched over the SeaWifs and Modis imagery from land for the duration of the cruise, but cloud cover in the region obscured the satellite images during the trip. A precruise MODIS temperature image is given in the appendices, indicating the extent of the warm Alaskan Coastal Current and a manner in which it spreads over the southern Chukchi.