Colors were adjusted because of the smaller temperature range in the Nordic Seas. (b) Sea surface temperature map of the Nordic Seas. Red (blue) colors indicate warm (cold) temperatures.Figure 1 - (a) Sea surface temperature map of the North Atlantic.However, the warm water that continuously enters the Nordic Seas from the south seems to disappear ( Figure 1b). Some of the water from the Gulf Stream eventually makes it into the Nordic Seas, the region between Greenland, Iceland, and Norway ( Figure 1a). The Gulf Stream is one reason why winters are milder in western Europe compared to eastern Canada. The Gulf Stream is an ocean current that stretches from Florida to Europe ( Figure 1a). The surface ocean is much warmer where the ocean currents bring heat northward from tropical regions. In this article we focus on the North Atlantic Ocean, so we will talk about water flowing northward. But have you ever wondered why it is warm in western Europe, but cold in eastern Canada, even though both regions are the same distance from the equator? The reason is that air temperatures do not only depend on latitude-they are also influenced by ocean currents that carry heat toward the Earth’s poles. The air temperatures are warmest near the Earth’s equator and coldest near the poles. The water spills over the ridge as an underwater waterfall before it continues its journey, deep in the ocean, back toward the equator. The current brings the cold water to an underwater mountain ridge. But what happens to the cold water that disappears from the surface? While on a research ship, we discovered a new ocean current that solves this riddle. Cold seawater, which is heavier than warm seawater, sinks down to greater depths. What happens to the warm water that flows northward, since it cannot just pile up? It turns out that the characteristics of the water change: in winter, the ocean warms the cold air above it, and the water becomes colder. It is a main reason for northwestern Europe’s mild climate. The most famous ocean current, the Gulf Stream, is part of a large system of currents that brings warm water from Florida to Europe.
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