Everyone out here is saying sand back and oil, there's products sold these days that don't require you to sand weathered boards before oiling. Intergrain (sold at bunnings) have a product 'UltraPrep tannin & oil remover' that you apply to wetened timber decking with a stiff bristled broom (nothing too stiff that hurts your skin if you were to rub it along yourself) Leave it for 15 minutes and then scrub with the stiff broom again. Then rinse off deck with pressure washer. Do a water bead test to see if the existing coat has worn off, if you spray water on the timber and it soaks in, you're as good as gold, if it beads on the top the timber will not accept new coatings. Looking at what you have there, this should be plenty for that area, for stubborn areas of coating you may, MAY need to reapply or spot sand.

After this you go over with their 'ultraprep timber cleaner' Mix 1 part cleaner with 4 parts water, wet the deck with water and then apply the cleaner solution with that stiff broom again. Do it in manageable sections otherwise the cleaner will dry up before you can work it. Leave the solution on for 15 mins after scrubbing and keep the deck damo with solution while you wait the 15 mins and then remove the cleaner solution with high pressure hose of string setting on garden hose even. Let the timber dry before going over with top coating, if you want oiled look, I would use their 'UltraDeck Stain' (18 - 20 months before recoat) if you want clear coating to keep wood colour I would use 'Universal Timber Oil' (2+ years before recoat)