GMAT Sentence Correction (SC) | Re: Scientists have observed large concentrations of heavy-metal

Indeed not much difference in terms of meaning. From a Grammar perspective, in the phraseBaltic sea sediments , the wordBaltic sea is used as anadjective . In other words,Baltic sea (in the phraseBaltic sea sediments ) seems to depict atype of sediment.

This is what tilts the balance against it; we can havecoarse sediment,alluvial sediment etc. but notBaltic sea sediments ( Baltic
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