I still have an unfinished manuscript on the 9...a5 variation of the Closed Ruy Lopez. It was intended to be a low-theory alternative to the Zaitsev in 'The Ruy Lopez: A Guide for Black'. But even before my GM co-author had had a look at it, we decided that 9...Qd7 was a better companion move - mainly because of the many possible transpositions. However, I recently had a new look at the line because of this game:
Ivanchuk - Carlsen
Corus (Wijk aan Zee) (5) 2009
1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.0–0 Be7 6.Re1 b5 7.Bb3 0–0 8.c3 d6 9.h3 a5 (D)
This somewhat exotic move seems to first have been played by the Swede Gösta Stoltz and has later been championed by the Dane Lars Bo Hansen and the Norwegian Simen Agdestein, so it doesn't seem unreasonable to name it 'The Scandinavian variation'.
If I ever complete the manuscript I will consider including a chapter on the even rarer 9...Bd7!? which can be treated as a 'sister variation' with the connecting line being 10.d4 a5!?.
10.a4 is White's other major option.
The oldest game in my database went 10...exd4 11.cxd4 a4 12.Bc2 Nb4 13.Nc3 Nxc2 14.Qxc2 c6 15.d5 cxd5 16.exd5 b4 17.Nxa4 Bd7 18.b3 Nxd5 =+ Thomas-Stoltz, Warsaw 1935.
11.Bc2 Bd7 12.Na3
This seems logical and after getting Ivanchuk's approval I assume it is the new main line. 12.Nbd2 has been played more frequently.
This looks more natural than 12...Qb8 which was Agdestein's preference: 13.Bd3 exd4 14.cxd4 Nb4 15.Bb1 Qb7 16.Bg5 Rad8 17.Nc2 Na6 18.Ne3 Rfe8 19.Qd3 g6 20.a3 c5 21.e5 dxe5 22.dxe5 Bc6 23.Qc3 Nd5 = Renet-Agdestein, Lyon 1988. However, it must be said that the rook returns quickly to a8 so who knows?
This must be more critical than 13.Bd3 when Yagupov-I.Zaitsev, Moscow 2000 continued 13...b4 14.Nc4 bxc3 15.dxe5 Nxe5 16.Nfxe5 dxe5 17.bxc3 Bd6 18.Bc2 Bc6 19.Bg5 a3 20.Qf3 h6 21.Bc1 Qe7 22.Ne3 Bd7 23.Bb3 Kh8 1/2–1/2.
One of Black's big challenges in most Closed Ruy Lopez systems is to activate his queenside knight. The alternative obviously was 13...Na5 which also seems satisfactory. One reasonable line suggested by Rybka goes 14.Qe2 Qc8 15.b4 axb3 16.axb3 c5 17.dxc6 Qxc6 18.b4 Nc4 19.Nxc4 Qxc4 20.Qxc4 bxc4 21.Be3 Ra8 22.Nd2 +=.
14.c4 Ra8 15.Be3 b4 16.Nb1 c5 17.a3 b3 18.Bd3 (D)
Typically Carlsen grabs the first opportunity to active play.
19.Bxe4 f5 20.Nfd2
Rybka initially prefers 20.Bd3 e4 21.Nc3 but after the further moves 21...Bf6 22.Rc1 Nc8 23.Bf4 exd3 24.Qxd3 Re8 25.Rxe8+ Qxe8 26.Re1 Qh5 27.Re3 h6 chances seems balanced.
20...fxe4 21.Qh5 Be8 22.Qe2 Bd7 23.Qh5 Be8 24.Qe2 Bd7 ½–½
If it wasn't for the repetition, the position still would have been fairly equal.