Abstract. The ice bridge in Nares Strait is a well-known phenomenon
that affects the liquid and solid freshwater flux from the Arctic Ocean
through the strait and controls the downstream North Open Water polynya in
northern Baffin Bay. Recently, the ice bridge has been in a state of
decline, either breaking up earlier in the year or not forming at all and
thereby increasing the sea ice export out of the Arctic Ocean. The decline
in the ice bridge has been ascribed to thinner and therefore weaker ice from
the Arctic Ocean entering Nares Strait; however, local forcing also affects
the state of the ice bridge and thereby influences when it breaks up. Using
a variety of remotely sensed data we examine the spatial patterns of sea ice
thickness within the ice bridge, highlighting the presence of negative ice
thickness anomalies on both the eastern and western sides of the strait and
identifying a recurrent sensible heat polynya that forms within the ice
bridge near Cape Jackson in northwestern Greenland. Using the sea ice–ocean
model FESOM2, we then attribute these ice thickness anomalies to the heat
from warmer subsurface waters of Pacific and Atlantic origin that reduce
thermodynamic ice growth throughout winter on the western and eastern sides,
respectively. The consequently weaker and thinner areas within the ice
bridge are then suggested to promote instability and earlier breakup. This
work provides new insight into the structure of the Nares Strait ice bridge and highlights that warming of the modified Atlantic and/or Pacific waters
that enter the strait may contribute to its further decline.