Response of the Arctic Freshwater Budget to Extreme NAO Forcing

A. Condron and P. Winsor (WHOI)

Freshwater release from the Arctic to the deepwater convective regions of the
Labrador and Nordic Seas is understood to play an important role in steering
decadal global climate variability. An observed freshening of the North
Atlantic since the mid-1960s appears to be related to changes in the export of
freshwater from the Arctic, and the persistence of a high North Atlantic
Oscillation (NAO) during this period. However, the specific response of the
Arctic freshwater budget to the NAO is unclear. To investigate this response
we use a high resolution (1/3 degree) regional version of the ocean-only
MITgcm forced for 12 years with daily NCEP reanalysis data from 1992-2001. At
this resolution the model resolves the major Arctic transport pathways,
including the Bering Strait and Canadian Archipelago. We ran the model twice,
keeping all reanalysis fields the same in both cases, but repeat the wind
field of two contrasting NAO years in each run for the extreme negative and
positive NAO phases of 1969 and 1989, respectively. Our results highlight a
clear response in the Arctic freshwater budget to NAO forcing. Repeat NAO
negative wind forcing results in virtually all freshwater being retained in
the Arctic. In contrast, repeat NAO positive forcing increases the freshwater
export out of the Arctic, primarily via the Fram Strait (54%) and Canadian
Archipelago (29%), and results in a total loss in freshwater storage of 14000
km3. We find that the freshwater export via these two pathways increases by
virtually the same amount (approx 700 km3 per yr) between the two forcing
scenarios, highlighting the important role that the Canadian Archipelago plays
in redistributing the freshwater of the Arctic.