Hydrographic Changes in the Beaufort Sea in the 2005–2012 Period: Comparison of Models and CTD Surveys

The hydrographic output of two Arctic Ice-Ocean models, for the simulation years 2005-2012 and the region defined by 70N-80N /150W-130W, have been examined, with the principal focus being the detection of any warming or cooling trends and the depth of their variability. The model outputs were also compared with a comprehensive CTD data set from NODC/NOAA's world ocean data base WOD09 for the years 2005-2008, mostly along the longitude lines 150W,140W and 130W, at latitudes 71N and 75N. The models used were the Navy's HYCOM ACNFS (Ref 1) and NCOM (Ref 2), with resolutions varying from .083 deg (HYCOM) to .125 deg (Global NCOM).

Both the models and observations exhibited a significant warming trend in 2007, followed by a cooling trend in 2009 in the top 150m layer. The models further showed an even stronger warming, beginning in 2010 and peaking in 2012. In the central part of the region, in the HYCOM model the warming was particularly manifested by the development of a warm near-surface layer, peaking at 20m depth with an excess temperature of about 0.20 deg C in 2007 and 0.60 deg C in 2011; this layer has disappeared in 2009. In the NCOM model, this layer was attached to the surface, with a peak SST in 2007 of 0.90 deg C and a low of 0.40 deg C in 2009. At the region's center at 140W, 75N, the CTDs also showed the development of both near-surface and surface- attached warm layers similar to HYCOM and NCOM, respectively. The warmest CTD temperature observed was 0.0 deg C at 50m depth in 2007, followed by an SST of -0.10 in 2008. In 2004 and 2005 only the sub-surface warm layer is observed, with its temperature excess of about 0.4 - 0.5 deg C.

Ref 1: Validation of the 1/12 deg Arctic Cap Nowcast/Forecast System (ACNFS) Pamela G. Posey et al, Tech. Report NRL/MR/7320—10-9287, Nov 4, 2010, Naval Research Laboratory, Stennis Space Center, MS, 39529

Ref 2: User's Manual for the Global Ocean Forecast System (GOFS) Version 2.6 Lucy F. Smedstad et al, Tech. Report NRL/MR/7320—10-9210, March 31, 2010, Naval Research Laboratory, Stennis Space Center, MS, 39529