Ok... neither layer is set on soft light. They're both in normal mode.
I think you may have changed the blend mode of the paint tool instead of the layer blend mode. The layer mode is changed from the layer window, where the layers are, not from the toolbox. Same with layer opacity.
Here, I set the layers for you. I set the gradient layer on hard light because your colours are so bright, soft light doesn't show well on them... You might want to decrease the saturation of your colours somewhat. And make the ocean a bit darker maybe.
http://www.fileden.com/files/2010/2/7/2 ... export.xcf
Find the layer mode & layer opacity settings in the layer window, then you can play with the layer modes yourself... layer modes are one of the most powerful features of GIMP, you can do all kinds of neat stuff with them.
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I'll elaborate a bit on the difference of the paint tool blend mode (in the tool box, in the tool options of many tools, like paintbrush, fill, blend, etc. ) and the layer blend mode (or layer mode in short, which is in the layers window, in the layer options). The paint tool mode affects the blend mode of what you paint, interactively. So what you paint on the current layer is blended on it using the blend mode you select. Whereas, the layer mode affects the whole layer, regardless of what mode was used to paint on it, and it, unlike the paint mode, can always be changed later.