The term "Gulf Stream" is sometimes used about the sum of what is described above and the North Atlantic drift.
As it travels north, some of the warm water transported by the Gulf Stream evaporates. This increases the salinity of the water in the stream, and in the North Atlantic Ocean the water is so cold and heavy with salt that it begins to sink. It then becomes a part of the North Atlantic Deep Water, a southgoing stream.
The effect of the Gulf Stream is sufficient to cause certain parts of the west of Britain and Ireland to be an average of several degrees warmer than most other parts of those countries. Indeed, in Cornwall, and particularly the Isles of Scilly, its effects are such that plants associated with much warmer climes, such as palm trees are able to survive the rigours of northern winters. Logan Botanic Garden in Scotland benefits strongly from the Gulf Stream, allowing their specimens of Gunnera Manicata to grow to over 3 metres tall.
With the recent phenomenon of global warming, some scientists have expressed concern about the sink mechanism outlined above. Specifically, fresh water resulting from the melting of the Arctic polar cap could dilute the Gulf Stream and make it light enough not to sink. The result would be a huge climate change in northern Europe, with unknown consequences. Some fossil remnants hint at the possibility that a similar event has already happened several times in the past, but fossil evidence is questioned. After an initial rejection, the scientific community is evaluating this theory more seriously, as data about historic climate show sudden changes between cold and warm periods.
