SBI HLY-04-02 Final Cruise Report

Final Report: Western Arctic Shelf-Basin Interactions (SBI) Spring Cruise HLY-04-02 (15 May-23 June 2004) Edited by Jackie Grebmeier, Chief Scientist University of Tennessee, Knoxville, TN 37932 USA; email: jgrebmei@utk.edu

A. Introduction

The 2004 oceanographic field phase of the Western Arctic Shelf-Basin Interactions (SBI) project began on the USCGC Healy icebreaker on 15 May 2004. There are 18 research projects included in the ship-based program, ranging from hydrographic measurements to biochemical tracers and biological studies of various trophic levels. The goal of the SBI global change project is to investigate the production, transformation and fate of carbon at the shelf-slope interface in the Arctic as a prelude to understanding the impacts of a potential warming of the Arctic. We worked initially in ice-free stations on the southern Chukchi Sea shelf (Herald Valley [HV] transect), then moved into very heavy ice cover in the Chukchi outer shelf to Arctic Basin line (East Hanna Shoal [EHS] transect line). We terminated the EHS line at 2500m and proceeded SE past Barrow to occupy the East Barrow (EB) line. Extremely heavy ice precluded our occupation of the EB line and we moved over to the Barrow Canyon (BC) line via a shortened transect north of Smith Bay (SB) line in the nearshore Beaufort Sea.

The SBI project is an interdisciplinary program, where physical, biogeochemical and biological measurements are being made using a variety of sampling devices. CTD/rosette sampling collected physical and hydrochemical samples. Thirty-five stations were occupied during this cruise, with an additional 11 XCTD and 4 Video Plankton Recorder deployments. A total of 48 scientists from nineteen institutions in the United States, Bermuda, Canada, and Japan participated in this interdisciplinary scientific endeavor. In addition, a two-person BBC film crew joined us on June 11. Although an Alaskan community participant was scheduled to participate in the cruise, circumstances on land precluded that person joining the spring cruise.

In our sampling, we used a CTD/rosette system for collecting physical and hydrochemical samples. Subsamples from multiple CTD/rosette casts were used for primary production, chlorophyll content, nutrients, particulate carbon, inorganic carbon, biomarkers, microzooplankton, and radioisotopes. Various nets (vertical, bongo, multi-net) were used to collect size fractions of micro-macro- and meso-zooplankton for both population and experimental purposes. Benthic grabs and cores were used to collect benthic fauna and sediment samples for population, community structure, food web, chemistry and metabolism studies. In-situ pumps were also used to measure the activities of the particle-reactive radionuclide thorium-234. Off-ship sampling by lowering personnel to the ice occurred to undertake ice measurements and to collect ice cores. Floating sediment traps were deployed and moored to an ice flow for 12-24 hrs. Limited helicopter operations were used for ice reconnaissance, river sampling and port logistics.

Figure 1. Station location and cruise track for the spring SBI cruise on the USCGC Healy

(HLY-04-02). Due to heavy ice conditions sampling was limited to the Chukchi Sea shelf, East Hanna Shoal (EHS) west line and Barrow Canyon (BC) east line).

During the cruise, ice conditions were the main limiting factor for occupying only about half of the 5 transect lines outlined in the HLY-04-02 cruise plan. Heavy ice over the outer shelf of the Chukchi Sea made it slow going on the East Hanna Shoal (EHS) line, basically keeping the ship at a slow pace until the upper slope. We were in heavy ice past Icy Cape, only pulling into the northern limits of an open lead moving east past Barrow. The other factor to be resolved during the cruise was limitation on the availability of ambient seawater due to heavy ice conditions. The new USCG science seawater system (SSW) cl