Discuss how evidence from the world's oceans has been used to identify rapid environmental change at the end of the last glacial period?

Can someone also explain what it means when dextral N. pachyderma increases and sinistral N. pachyderma decreases? Is it oceans warming, or freezing of ice?

What do YOU think ?
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Take a look at [this]. Sinistral seem to prefer lower temperatures. The Dextral variant seems to prefer warmer temperatures. So when the Dextral levels increase and the Sinistral decrease, that will imply that the water is getting warmer.

So I've found a journal which shows the variation in the two over the past 15ka bp but sinistal seems to stay high and dextral remain low up until present day but I cant workout why? Surely sinistral should decrease and dextral increase?