Good question. Here is a global GRS map of Mars:

2001 Mars Odyssey - Status
March 01, 2002
http://mars.jpl.nasa.gov/odyssey/gallery/latestimages/latest2002/march/Fig2_NS_Global.html

There is a deep blue patch at middle-high latitudes in the northern hemisphere in this image, but you are right there isn't the deep concentration in the north pole as at the south pole.

This page on the observations of the northern hemisphere in December, suggests this is due to a deeper CO2 cover over the north pole during the northern summer:

New Signs of Water on Mars Create Hope of Great Discovery
By Leonard David
Senior Space Writer
and Robert Roy Britt
Senior Science Writer
posted: 09:07 am ET
14 December 2001
"The northern ice cap shrinks in summer to as little as 1,000 kilometers in diameter. In winter, it ranges as far south as 60 degrees latitude. Odyssey detected hydrogen farther south, at 55 degrees. The poles are at 90 degrees and zero represents the equator.
"This pass suggested that hydrogen was enriched in a high-latitude region extending from around 55 degrees North to near to the edge of the north polar cap, and that it was not enhanced over the north polar permanent cap,' Garvin said. 'This suggests, in a most preliminary sense, that if the hydrogen in the northern high latitudes is water, that there is ice in the upper meter or so of this region ... and that it is masked by a carbon dioxide frost cover on the permanent cap."
http://www.space.com/scienceastronomy/solarsystem/odyssey_hydrogen_011214.html

Anyone know what is the region represented by the deep hydrogen concentration in the northern hemisphere in the global map?

Bob Clark