Preheat the oven to 275 F and a line a baking sheet with parchment paper.
In a clean glass bowl, use an electric hand beater (or, alternatively, an electric mixer and the whisk attachment) to whip the egg whites to "soft peaks". (Take care to assure that all of the utensils and the bowl are very clean. Greasy residue on a bowl can greatly inhibit this process. The whites will start to gain volume but still seem somewhat yielding in texture.)
Beat in the cream of tartar and then start to add the 1 cup of sugar in small increments. When all of the sugar has been incorporated, whip until "stiff peaks" form. The texture of the whites should be firm and they should look glossy.
Use a spatula to transfer the whipped whites to the sheet tray in the form of a circle, roughly the size of the width of the trifle bowl. Put the sheet tray in the center of the oven and bake the meringue until firm and a very pale, light brown color. At this point, you can turn off the oven and leave the meringue sit in the oven until you are ready to serve the dessert.
In a medium glass bowl, combine the grapefruit juice, tangerine zest, 1/4 cup of sugar and gin. Whisk to blend, then stir in the orange and tangerine sections. Cover and refrigerate for 30 minutes and up to 2 hours.
Remove the meringue from the oven and set aside.
Put the citrus mixture into the bottom of the trifle bowl and stir in the pomegranate seeds. Cover with the meringue lid and serve immediately.