From the moment that the Ottoman Empire entered the war the Russians were effectively fighting in isolation. 50% of Russia’s maritime trade, including 90% of her grain exports passed through the Bosporus. When the German commanding the forts of the Dardanelles, General Weber, ordered the Straights closed on the 26 September 1915 he did far more damage than anything Enver Pasha could have hoped to achieve by attacking the Caucasus. Not only was the shortest and safest rout to bring arms and equipment in from France, England and most importantly America cut off, but the only route for sending the grain to pay for it all out was likewise cut.
Had the Dardanelles been opened even as late as the start of 1916 it would have made an enormous difference. Arms and equipment could have flooded in, perhaps with would have been too late to save the Absolute Monarchy of the Romanovs but it would certainly have strengthened the Provisional Government of Alexander Karenski. People who think that the collapse in Russia was inevitable overlook the fact that the other major powers faced mutinies in their armies as well, particularly France, the difference being that the French could get aid from their allies while the Russians couldn’t.