| environ. |
sea circulation Large-scale horizontal water motion within an ocean. The way energy from the sun, stored in the sea, is transported around the world. The currents explain, for example, why the UK has ice-free ports in winter, while St. Petersburg, at the same latitude as the Shetland Islands, needs ice breakers. Evidence is growing that the world's ocean circulation was very different during the last ice age and has changed several times in the distant past, with dramatic effects on climate. The oceans are vital as storehouses, as they absorb more than half the sun's heat reaching the earth. This heat, which is primarily absorbed near the equator is carried around the world and released elsewhere, creating currents which last up to 1.000 years. As the Earth rotates and the wind acts upon the surface, currents carry warm tropical water to the cooler parts of the world. The strength and direction of the currents are affected by landmasses, bottlenecks through narrow straits, and even the shape of the sea-bed. When the warm water reaches polar regions its heat evaporates into the atmosphere, reducing its temperature and increasing its density. When sea-water freezes it leaves salt behind in the unfrozen water and this cold water sinks into the ocean and begins to flow back to the tropics. Eventually it is heated and begins the cycle all over again (大洋中的大规模的水平的水的流动。通过这种方法可以将保存在海中的来自太阳的能量传到全世界。对水流的解释，例如，为什么英国有在冬天不结冰的港口，然而圣彼得斯堡和设得兰群岛有相同的纬度但需要破冰设备。证据说明世界的大洋环流在上次冰河时代非常不同，并且在很远的过去变化过几次，这对气候有很大影响。大洋像宝藏一样重要，因为它吸收了到达地球的太阳的热量的一大半。这些热量主要是在赤道附近被吸收的，被带到全世界并到处释放。它们产生了持续1000年的水流。当地球旋转和风吹过地面，水流带着热的热带的水到世界的寒冷地区。水流的强度和方向受到陆地、通过狭窄的海峡瓶颈、甚至海床的形状的影响。当热水到了地级附近，它的热量在大气中消失，它的温度降低，密度增加。当海水结冰了，它向未结冰的水中释放盐，冷水下沉到大海中并回流到热带。最后它变热并重新开始循环。) |
