CoAuthors

John Kuhn (NOAA, USA); Sinead Farrell (University of Maryland, USA)

The surface waters of the Arctic Ocean and the marginal, subpolar seas freeze to form a seasonally-varying layer of sea ice, which can be centimeters to meters thick. The sea ice cover acts as a barrier between the ocean and atmosphere, attenuating ocean waves, particularly in the marginal ice zone. The mechanical impact of ocean waves on the sea ice cover remains poorly understood and is not well captured in climate and weather models. Satellite observations since the late 1970s reveal a diminishing ice pack in the Arctic Ocean, where ice extent is declining at a rate of approximately 4% per decade. The biggest changes are occurring in the sub-polar seas, and this is accompanied by an expanding marginal ice zone.

Since the 1990s satellite altimeters have provided daily measurements of sea surface height (SSH) and significant wave height (SWH) in the Arctic. In support of the NOAA/NASA Ocean Surface Topography Science Team (OSTST), our study assesses SWH just south of the ice edge, in the northern Atlantic and Pacific Oceans. We characterize the seasonal cycle, decadal trends, and inter-annual variability in SWH over two-decade period, spanning 1996 to present. As sea ice extent in the Arctic has diminished, we investigate if wave heights have increased, and if these regions have become stormier. Using daily radar altimeter measurements from ERS-2, Envisat, Jason-1 and -2, CryoSat-2, and SARAL/AltiKa, we track and trend instances of large SWH in the Bering and Chukchi Seas, and in the Greenland-Norwegian-Barents Seas region. Our results indicate a small increasing trend in median SWH in both regions during the study period. In the northern North Atlantic, the occurrence of “very high” or “phenomenal” seas has tripled over the 20-yr period, while in the Bering Sea it has doubled. These trends towards stormier seas have potential impacts on coastal inundation in low-lying regions of the Arctic coastline. Our results also have important consequences for operational activities in the subpolar seas, such as maritime transportation.

We discuss additional statistical analyses to investigate the decadal trends, and the impact that an increasing number of daily observations has had during the study period. We place our results in the context of recent and complementary modeling studies. Next steps include applying a daily sea ice concentration mask to investigate the occurrence of waves within the marginal ice zone to estimate SWH in these areas. We describe steps to disseminate our data products publicly through the NOAA CoastWatch/PolarWatch web portals. In anticipation of the launch of NASA’s ICESat-2 mission in 2018, which will carry a laser altimeter, we also briefly describe planned assessments of the absolute vertical accuracy of ICESat-2 SSH measurements in the Arctic and subpolar seas.