Assessing decadal-scale variability and trends in Arctic Ocean surface topography with high latitude altimetry

PI: Sinead Farrell, University of Maryland, College Park
Start Year: 2025 | Duration: 4  years
Partners: NOAA, NASA

Project Abstract: 

Accelerated warming and increased storminess at high latitudes is driving rapid changes in the composition of the polar oceans and their sea ice cover. Ocean remote sensing has revealed a statistically significant decline in Arctic sea ice extent over the last four decades, and observations from dedicated polar altimeters, spanning the last twenty years, indicate a loss in mean sea ice thickness and volume. This includes the near disappearance of the oldest, thickest multi-year sea ice in the Arctic Ocean and the subsequent doubling of the seasonal sea ice zone, from ~35% in 1985 to ~70% in 2020. Multiple, positive feedbacks between the ocean, ice and atmosphere, most notably the ice-albedo feedback in the Arctic, have triggered this decline. Since sea ice regulates the exchange of heat, moisture, gases and momentum between the ocean and atmosphere, and its high albedo influences Earth’s energy budget, it plays a key role in the climate system. Declining sea ice is not only a leading indicator of a warming planet, but it is also an important driver of climate change. Improving knowledge of how and why the sea ice cover is evolving in both space and time is therefore essential for better prediction of Earth’s future climatic conditions. Our goal is to produce the highest-quality satellite altimeter observations of polar ocean surface topography and apply these data to address key questions in polar climate science. We address both sub-elements 2.2 “regional and coastal dynamics” and 2.3 “operations and applications” of the A.12 solicitation. First, we will evaluate and advance new geophysical algorithms to improve the quality of sea surface height (SSH) data in ice-covered water using merged altimetric data from ICESat, ICESat-2 and CryoSat-2. Using these data, we will conduct regional studies of the Arctic Ocean and Nordic Seas to investigate variability in SSH, dynamic ocean topography and geostrophic circulation. We will quantify changes in significant wave height (SWH) and sea state conditions in the Nordic Seas. We will also assess variability and trends in sea ice freeboard in the Arctic Ocean. We will generate new sea ice data products and publicly disseminate them for use in novel polar applications through the dedicated NOAA PolarWatch web portal. Through our proposed work we will contribute to the overarching goals of the NOAA / NASA Ocean Surface Topography Science Team (OSTST), i.e., “to demonstrate the value of the satellite altimetry records from the continued reference missions in Earth science and applications”. Our major objectives are: (1) To quantify seasonal and interannual variability and trends in SSH in the ice-covered Arctic Ocean using the suite of available radar/laser altimeter data for the period 2003-2028. (2) To quantify seasonal and decadal-scale variability and trends in SSH and SWH in the ice-free Nordic Seas and assess the impacts at the sea ice edge. (3) To generate a complete 25-year record of Arctic sea ice freeboard using all available radar/laser altimeter data. (4) To quantify changes in open water/lead fraction and sea ice distributions in the Arctic and subpolar seas. The investigators seek to renew their membership of the OSTST and to continue producing the best possible satellite-derived altimetry data products describing polar ocean surface topography. The team have extensive knowledge of the combined use of satellite laser and radar altimetry for monitoring the polar oceans and the relevant experience to successfully conduct the proposed studies. Our proposed work will advance knowledge of the role that polar sea ice plays in the climate system. We will contribute scientific analysis in preparation for the Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL) mission, the next dedicated polar altimeter due for launch in 2027/2028 and our work will also inform pre-launch algorithm development for Sentinel-3 Next Generation – Topography Mission (S3NG-TOPO).