First for charts.  You are looking at a stock that trades so lightly
with 1 hour bars and that gives the wrong picture.
Take a look at a 1 day chart with 1 minute for ATS
http://finance.yahoo.com/charts#chart1:symbol=ats;range=1d;indicator=...
You will see that trades do not happen at all times.

The rush at the end of the day (Dec 31, 2007 - if the link is followed
after today my comments will not apply) could be due to someone trying
to push up the closing price since that is the one reported in HK.
People not following closely will think that ATS is breaking out and
will push the price higher, which will push the price higher in US
until it slows down then boom - selling starts pushing the price
down.  Something like Pump and Dump.

Another reason is that someone places limit bids at rare prices like
$0.01 to buy and $5.00 to sell.  If someone comes along with a buy or
sell order without limit and there are no other BIDs and ASKs then
that person gets a bad deal.  If you have access to Level II quotes
you can see a number of  BIDs and ASKs with price limits.  For most
stocks the range of prices is close to the last bid but for ATS there
are often very few.  To get Level II quotes you have to pay more or be
a more active trader.

Think of selling a house in a hot or cool market.  Also realize that
the last sale does mean that all stock is worth that much.

I have learned from these Blogs, that is why I'm giving back a little.