SEARCH Projects

NOAA SEARCH Element 8: Monitoring Ice Thickness in the Western Arctic Ocean

J. Richter-Menge D. Perovich T. Tucker R. Lindsay H. Melling Institution: USACRREL

Abstract

Recent studies indicate that the sea ice cover is undergoing significant climate-induced changes, affecting both its extent and thickness. For instance, satellite-derived estimates of maximum ice extent suggest a net reduction between 1978 and 1996, at an average rate of –3% per decade (Parkinson et al, 1999). A recent report by Comiso (2002) indicates an even more rapid reduction in the perennial sea ice cover, of –9% per decade. Data on the ice thickness, derived from submarine-based upward looking sonar, also suggest a net thinning of the sea ice cover since 1958 (Rothrock et al., 1999; Wadhams and Davis, 2000; Tucker et al., 2001). It is important that we continue and expand efforts to monitor these changes to (a) improve the fundamental understanding of the role of the sea ice cover in the global climate system and (b) take advantage of the sensitivity of the sea ice cover as an early indicator of the magnitude and impact of climate change.

The extent of the sea ice cover is effectively monitored from satellite platforms using passive microwave imagery. Monitoring changes in the ice thickness is more problematic. As with ice extent, the ideal platform for monitoring ice thickness is a satellite because it provides a full-basin perspective. However, to date, no technique has been adequately developed to obtain satellite-base measurements of ice thickness. Until satellite imagery can be used to monitor ice thickness, we must reply on measurements made from submarines, aircraft, seafloor moorings, and drifting buoys. As determined at the recent SEARCH Workshop on Large-Scale Atmospheric/Cryospheric Observations (Overland et al, 2002), this is most effectively done through a coordinated effort to establish a large-scale sea ice observing system. It is also necessary to disseminate the data collected from the various components of this system to the scientific community in a timely and consistent fashion. Once available, the data can be used to gain insight on the relationship between the characteristics of the sea ice cover and climatic forcing. Specific emphasis should be placed on efforts to work in tandem with those developing satellite-based assets, designed to measure ice thickness. Data from the ice-based observing system can play a central role in assuring an optimal approach for obtaining accurate satellite-based measurements. Together, these platforms can provide an effective means of assessing the state of the sea ice cover over the entire Arctic basin.

The primary objective of this proposal and the related proposal “Monitoring the Eurasian Basin of the Arctic Ocean” (so-called Elements 8 and 9 of the NOAA SEARCH program) is to establish and maintain a large-scale sea ice thickness observing system. The establishment of two distinct elements recognizes the different logistical challenges in the western and eastern sectors of the Arctic region. This proposal focuses specifically on measurements within the western sector of the Arctic. This sector of the Arctic is currently more accessible and, therefore, makes it feasible to conduct a program involving instrumentation that must be maintained after deployment. Within the western sector of the Arctic, we propose to initiate an array of moored upward-looking sonar (ULS) and drifting buoys. In the eastern sector of the Arctic, the focus of the proposal “Monitoring the Eurasian Basin of the Arctic Ocean”, we have elected to limit instrumentation to the drifting buoy, which only need support during the deployment phase. Recently, it has been revealed that the Russians plan to establish a permanent, manned ice camp within the eastern sector of the Arctic, which will be available to the scientific community at large as an operational platform. If this resource becomes a reality, we will investigate the possibility of extending the deployment range of the moored ULS.

Instrumentation within the large-scale observing network will be located to complement existing measurement sites and activities and to take advantage of historical data records. Specifically, we look to augment the data currently being collected at the North Pole Environmental Observatory (NPEO, http://psc.apl.washington.edu/northpole/), by the International Arctic Buoy Program (IABP, http://iabp.apl.washington.edu/), and from SCICEX cruises. Specific site locations will be determined using models of ice motion, which incorporate recorded observations. Data from the observation sites will be combined with data from other sources to produce annual reports on the state of the sea ice cover, including both its extent and thickness. A contextual setting for current data will be established by summarizing earlier observations in the Western Arctic of sea ice mass balance over an annual cycle, which begins in 1957 (Untersteiner, 1961; Hanson, 1965; Maykut and McPhee, 1995; Perovich et al., 1997; Perovich et al., in press). We will also investigate the availability of data in the Russian literature, which is likely to cover the Eastern Arctic.