The Arctic Ocean is the least known of all the ocean basins. To date oceanographic and geophysical work has been carried out from ice islands, icebreakers, aeroplanes, and satellites. Each of these approaches suffers from limitations that can be overcome with surveys utilizing a submarine. In the early 1990s a memorandum of agreement was signed by the Chief of Naval Research and the Chief of Naval Operations, the heads of National Science Foundation (NSF), National Oceanic and Atmospheric Administration (NOAA), U.S. Geological Survey (USGS) and submarine force type commanders to allow the use of US Navy nuclear powered submarines for scientific research in the Arctic Ocean, thus creating a platform for the Scientific Ice Experiment (SCICEX). A Sturgeon class submarine has been deployed to the Arctic Ocean six times since 1993. The two cruises in 1998 and 1999, using USS Hawkbill, have focussed on the acquisition of marine geophysical data. The programme after 1999, if any, is open.

The Office of Polar Programmes at NSF has funded the development, fabrication and testing of optimized geophysical instrumentation, known collectively as SCAMP, Seafloor Characterisation and Mapping Pod, for the SCICEX cruises. Three newly designed, tested and fabricated components form the backbone of the geophysical data acquisition system: two sonars, an optimized SeaMARCTM-type Sidescan Swath Bathymetric Sonar and a chirp type High-Resolution Sub-bottom Profiler, and an integrated Data Acquisition and Quality Control System, are the key components installed on the submarine. These systems were used during SCICEX 1998 and 1999.

The sidescan swath bathymetric sonar maps a strip of the seafloor as wide as 16 km across, revealing the detailed bathymetry and surface sediment texture of the Arctic sea bed. The chirp sub-bottom profiler penetrates as faras100m in to the seafloor to reveal the stratification of the Arctic sediments.

Our participation in the US SCICEX/SCAMP 1999 programme is based on three separate objectives:

1. to collect site survey data for scientific drilling on the Lomonosov Ridge,
2. to help develop a modern bathymetric database for the Arctic,
3. to further investigate the erosional surfaces indicated by chirp sonar data obtained during the Arctic Ocean 1996 expedition.

1. Seafloor sampling on the Lomonosov Ridge: the first objective for Arctic scientific drilling

Two seismic profiles were acquired across the Lomonosov Ridge in about 8/10 ice during the International Arctic Ocean Expedition 1991 (Jokat et al. 1993).

At 88°N in 1 km of water, the ridge is 80 km wide with a 450 to 500 m thick section of acoustically stratified sediments that cap the ridge above an unconformity. As the Lomonosov Ridge moved away from the Eurasian plate and subsided, sedimentation on top of this continental sliver began and continued to the present, providing what may be a continuous stratigraphic sequence. The elevation of the ridge above the surrounding abyssal plains, indicates that sediments on top of the ridge have been isolated from turbidites and are likely of purely pelagic origin. Assuming an average sedimentation rate of ~1 cm /1 000 years, the upper 450-500 m section of stratified sediments on the Lomonosov Ridge would represent a stratigraphic record spanning the last 50 million years. The 450-500 m thick hemipelagic sediment sequence draping the crest of the Lomonosov Ridge between 87°N and 88°N hence contains a unique archive of climatic and paleoceanographic information, which is the key to unravelling the Cenozoic environmental history of the central Arctic Ocean.

Together with colleagues from Canada, Denmark, Germany, Norway, Russia and USA, we have submitted a full proposal tothe international Ocean Drilling Programme (ODP), focusing on retrieving the complete ~500 m thick stratigraphic section on top of the ridge using an offset drilling strategy.

Swath mapping and chirp sub-bottom profiling from the USS Hawkbill during SCICEX 1999 is not yet fully processed. However, these data will be extremely valuable and assist the development of offset coring strategies that would exploit seafloor erosion to construct continuous, composite records from separate shorter drill holes. The SCICEX 1999 survey of the Lomonosov Ridge will provide the necessary detailed information for planning the drilling operations. By August 2000 we will presumably learn if our proposal will be scheduled for drilling. If it is successful, we are looking towards year 2003 for the field operation.

2. Developing a modern digital bathymetric data base for the Arctic

The data collected during SCICEX is the largest addition to the unclassified data base for the Arctic Ocean since the early seventies. Approximately 60,000 km of narrow beam bathymetry data, approximately 100,000 km of gravity anomaly data and 40,000 km of swath and sub-bottom profiler data have been collected. This data is being used to study some of the outstanding features in the basin, but it has a secondary use too. The aggregate data set also builds the scientific infrastructure of the basin. The data set is one of the primary contributions to the data base being used for the new International Bathymetric Chart of the Arctic Ocean (IBCAO; endorsed by IASC, IHO and IOC).

The goal of this initiative is to develop a digital data base containing all available bathymetric data north of 64 degrees North, for use by mapmakers, researchers, and others whose work requires a detailed and accurate knowledge of the depth and the shape of the Arctic seabed. The first version of the digital grid model representing the Arctic bathymetry was presented at the American Geophysical Union (AGU) in December 1999 (Jakobsson et al. 1999).

3. Ice-scouring at 1 km water depth in the central Arctic Ocean

Based on Arctic Ocean 1996 data, one of us (Jakobsson, 1999) inferred a prominent erosional event at 1 km water depth below present sea level on the Lomonosov Ridge crest at ca 87°N. It was not possible from the chirp data alone to make a conclusive interpretation of this event, although ice-scouring was suggested as one possible hypothesis. Side scan data obtained from SCICEX 1999 shed new light on this problem. The rough surface of the eroded area on the Lomonosov Ridge has a typical ice-scoured appearance, characterized by plough-marks several meters deep (Polyak et al. 1999). These results unambiguously indicate that a portion of the ridge crest at modern water depths down to 1 km has been scoured by extremely thick floating ice related to an extensive glacial event in the Arctic Ocean.

Studies of Arctic Ocean 1996 cores retrieved from the critical area on the Lomonosov Ridge indicate that the major ice-scouring event probably occurred during oxygen isotope 6, that is, about 150,000 years ago (Jakobsson et al., submitted).