Recent summer sea ice thickness surveys in Fram Strait and associated ice volume fluxes

Abstract

Abstract. Fram Strait is the main gateway for sea ice export out of the Arctic Ocean, and therefore observations there give insight into the composition and properties of Arctic sea ice in general and how it varies over time. A data set of ground-based and airborne electromagnetic ice thickness measurements collected during summer between 2001 and 2012 is presented here, including long transects well into the southern part of the Transpolar Drift obtained using fixedwing aircrafts. The primary source of the surveyed sea ice leaving Fram Strait is the Laptev Sea and its age has decreased from 3 to 2 years between 1990 and 2012. The thickness data consistently also show a general thinning of sea ice for the last decade, with a decrease in modal thickness of second year and multiyear ice, and a decrease in mean thickness and fraction of ice thicker than 3 m. Local melting in the strait was investigated in two surveys performed in the downstream direction, showing a decrease in sea ice thickness of 0.19 m degree −1 latitude south of 81 • N. Further north variability in ice thickness is more related to differences in age and deformation. The thickness observations were combined with ice area export estimates to calculate summer volume fluxes of sea ice. While satellite data show that monthly ice area export had positive trends since 1980 (10.9 × 10 3 km 2 decade −1 ), the summer (July and August) ice area export is low with high uncertainties. The average volume export amounts to 16.78 km 3 . Naturally, the volume flux estimates are limited to the period when airborne thickness surveys are available. Nevertheless, we could show that the combination of satellite data and airborne observations can be used to determine volume fluxes through Fram Strait and as such, can be used to bridge the lack of satellite-based sea ice thickness information in summer.

Relationships between Arctic sea ice drift and strength modelled by NEMO-LIM3.6

“…This period is chosen to match the satellite period. Sea ice thickness used in this study is the sea ice volume per grid cell area taking into account open water (named "sivol" according to SIMIP nomenclature) rather than the actual thickness Krumpen et al (2016) 1980-2012: significant positive trend Smedsrud et al (2016) Increase Wind 1979-2014:…”

“…However, a distinction needs to be made between area and volume exports: area export is the product of sea ice drift speed, concentration and transect length, while volume export is the product of area export and ice thickness. Several studies show an increase of ice area export at Fram Strait since the late 1970s (Langehaug et al, 2013;Krumpen et al, 2016;Smedsrud et al, 2016), while Kwok et al (2013) show a small decrease between 1982 and 2009. In terms of volume export, the amount of studies is limited by the relatively low ice thickness temporal coverage at Fram Strait.…”

Fram Strait sea ice export variability and September Arctic sea ice extent over the last 80 years

“…Positive trends were also found in the annual FS ice area export by Widell et al (2003) (4 % per decade from 1950 to 2000) and Smedsrud et al (2011Smedsrud et al ( ) (5 % per decade from 1957Smedsrud et al ( to 2010. Using the available NSIDC sea ice drift data, Krumpen et al (2016) recently found a much higher trend for 1980-2012 (37.6 % per decade) but noted that the large positive trend seemed "unrealistic". However, contrary to these studies, Kwok et al (2013) found a small negative trend in annual FS ice area export between 1982 and 2009, but with positive trends for [2001][2002][2003][2004][2005][2006][2007][2008][2009] for both annual (October-September) and summer (June-September).…”

Winter sea ice export from the Laptev Sea preconditions the local summer sea ice cover and fast ice decay

“…A comparison with ice drift information obtained from Environmental Satellite (ENVISAT) synthetic aperture radar (SAR) images and long-term moorings equipped with acoustic Doppler current profilers (ADCP) have shown that accuracy of the of IFREMER motion data is high and the uncertainty in the ice area export is around 81 × 10 3 km 2 for the NB and 57 × 10 3 km 2 for the EB over the entire winter (OctoberMay) (Rozman et al, 2011;Krumpen et al, 2013). For more detail about the applied ice drift and concentration products we refer to Ezraty et al (2007), Girard-Ardhuin and Ezraty (2012), Krumpen et al (2016).…”

“…Flaw polynyas are open water sites between pack ice and fast ice of high net ice production sustained by winds. For a detailed description of the HEM principle we refer to (Haas et al, 2009;Krumpen et al, 2016). In short, the instrument that is towed by a helicopter 15 m above the ice surface utilizes the contrast of electrical conductivity between sea water and sea ice to determine its distance to the ice-water interface.…”