[1] Time series of sea ice thickness observed by moored sonars in the Transpolar Drift in Fram Strait are examined. Contrasting the post-2007 years against the 1990s, three remarkable changes in the monthly ice thickness distributions are highlighted:(1) The thickness of old level ice (modal thickness) is reduced by 32%, (2) the old ice modal peak width is reduced by 25%, and (3) the fraction of (ridged) ice thicker than 5 m is reduced by 50%. The combined effect on the mean ice thickness is a reduction from an annual average of 3.0 m during the 1990s to 2.2 m during 2008-2011. Most of the thinning took place after [2005][2006]. While the old ice modal thickness and peak width show signs of recovery after 2008, the decreasing trend in fraction of ridged ice and mean ice thickness persists until the end of the record in 2011. The ice observed in Fram Strait carries an integrated signal of Arctic change due to the advection of ice from many sites in the Arctic. Based on concurrence in timing, we conclude that much of the thinning quantified here is reflecting recent change in the age composition of the Arctic ice cover toward younger ice. The old level ice remains thin, and as such the ice cover remains preconditioned for new summers of very low sea ice extent.
[1] Seasonal fast ice thickness at the island of Hopen (Barents Sea) was monitored over 40 years. Sea ice thickness variability as a climate indicator provides more quantitative information on the state of the ice cover than solely sea ice extent. Usually, starting to form just before December Hopen fast ice reaches maximum thickness in May (on average 0.99 m), before the ice starts to decay. Swell, currents, and winds interrupt the fast ice development at Hopen during several of the winters observed, leading to ice removal and new ice formation. Since 2000, no ice thicker than 1.0 m was observed. We find a trend in the ice thickness anomalies of À0.11 m per decade, coinciding with decreasing seasonal maximum ice thickness, and an increase in local surface air and water temperatures. This is consistent with the decreasing sea ice extent in the Barents Sea and the entire Arctic.
The first convective chimney in the Greenland Sea to have its temperature and salinity structure fully mapped was discovered in March 2001 near 75°N 0°W [Wadhams et al., 2002]. Later cruises have shown that this remarkable feature has survived for a further 26 months, being remapped in summer 2001, winter 2002, summer 2002 and most recently in April–May 2003, making it the longest‐lived chimney yet seen in the world ocean. The chimney has an anticyclonically rotating core and experiences an annual cycle in which it is uniform in properties from the surface to 2500 m in winter, but is capped by lower‐density water in summer. The latest cruise also discovered a second chimney, 70 km NW of the first, during a thorough survey of 15,000 km2 of the gyre centre which left the existence of further chimneys unlikely. We conclude that the 75°/0° chimney is not unique, but that Greenland Sea chimneys are rare and are probably rarer than in 1997, when several such features were discovered by a float survey. This has implications for deep water renewal and for the role of Greenland Sea convection in the North Atlantic circulation.
CTD profiles from the north–western Barents August 1996, have been analysed and characteristics of have been compared with former analyses and investigations The barotropic and baroclinic modes of the Rossby radius of deformation have been estimated in order to give an estimate in order to give an estimate of the spatial scale of variations. The first baroclinic mode of the Rossby radius of deformation is estimated to be around 3 km. Cold halocline water (CHW) is found in the southern part of the investigation area, supporting a hypothesis that the production of CHW is located in the area around Storbanken, and not closer to the shelf break further north. Another hypothesis is proposed: tidal induced horizontal circulation and vertical currents may explain a northward transport of warmer water across sills and banks in the north–western Barents Sea.
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