1. at sea在海上航行，航行中，航海旅行中；比喻意义是：一片茫然，茫然，相当于be puzzled
After ten days at sea, we had our first sight of land.
我们在海上航行十天之后，首次看见陆地。
After twelve days at sea, they sighted land.
在海上航行十二天后他们看到了陆地。
After two days at sea, it was good to be back on terra firma again.
在海上度过两天之后，又回到使人觉得坚实的陆地，真是惬意。
After a week at sea, it was good to feel the earth beneath our feet again.
出海一周后，重新踏上陆地感到很愉快。
We sighted land after being at sea for ten days.
我们航行了10天，才看见陆地。
I love listening to his tales of life at sea.
我喜欢听他讲述他的海上生活。
They fought both at sea and on land.
他们在海上和陆上都打过仗。
When he woke up,the ship was at sea.
当他醒来时，船正在航行。
They had first met at sea.
他们是航海旅行中第一次相遇的。
He was all at sea when he began his new job.
当他刚开始干他的新工作时，他一片茫然。
If you had never seen a telly ad, you would be all at sea with popular culture.
如果你从没看过电视广告，你就搞不懂什么是大众文化。
另外，at sea向大海，在海里，在海上
Too much toxic waste is being dumped at sea.
太多的有毒废料在向大海里倾倒。
《牛津高阶英汉双解词典》
She wanted her ashes to be scattered at sea.
她希望自己的骨灰撒向大海。
《牛津高阶英汉双解词典》
The resulting salty water will be discharged at sea
所产生的盐水将被排入大海。《柯林斯高阶英汉双解学习词典》
The sewers discharge out at sea.
下水道的污水排入海里。
《汉英大词典》
He was drowned at sea.
他淹死在海里。
《牛津高阶英汉双解词典》
1,654 passengers were transferred at sea to a Norwegian cruise ship.
1,654名乘客在海上转搭了一艘挪威游轮。
《柯林斯高阶英汉双解学习词典》
His body was found at sea in waters off the Canary Islands.
他的尸体在离加那利群岛不远的海上被发现。
《柯林斯高阶英汉双解学习词典》
A third brigade is at sea, ready for an amphibious assault.
还有一个旅已在海上待命，准备两栖进攻。
Greenpeace managed to assemble enough boats to waylay the ship at sea
绿色和平组织设法聚集起足够数量的小船在海上拦截该船。
《柯林斯高阶英汉双解学习词典》
Sunrise at sea is particularly beautiful.
海上看日出，景色特别美丽。
2. at the sea在海边at the seaside
She spent the summer at the sea.
她在海滨度过了夏天。
Holidays at the sea are fun.
在海边度假真开心。
She had gotten a good tan after the holidays at the sea.
在海边度假之后，她的皮肤晒得黑黑的。
3. on the sea在海上，在海岸边
Brighton is on the sea.
布赖顿坐落在海岸边。
A later report said the oil fire on the sea was out.
随后的报道称，海上的石油大火已经熄灭。
The sun shone on the sea and the waves danced and sparkled.
太阳照在海面上，碧浪翻滚，波光粼粼。
The sunlight glared on the sea.
阳光照耀在海面上。
4. in the sea在海里
'Last one in the sea is a sissy,' proclaimed Idris.
伊德里斯大声地宣告说：“在海里，谁落在最后谁就不是爷儿们。”
Children were bathing in the sea.
孩子们在海里游泳。
They were detected at depths of more than a kilometre in the sea.
它们是在海面下超过一公里深的地方被检测出来的。
The waste was dumped in the sea.
废物倒入海中。
They disposed of the city's waste in the sea.
他们把城里的垃圾倒入海中。
Many organisms that die in the sea are soon buried by sediment.
海洋里死亡的许多生物会很快被沉淀物掩埋。
The wild weather did not deter some people from swimming in the sea.
尽管风雨交加，一些人还是会下海游泳。
I like to swim, especially in the sea.
我喜欢游泳，尤其喜欢在大海中游泳。
You will feel you are in the sea, but of course this is not true.
你会感觉身处海中，但这当然不是真的。
The weary walkers soothed their aching feet in the sea.
走累了的人们把脚伸进海水中浸泡以缓解疼痛。
Dolphins are smarter animals in the sea.
海豚是海洋中比较聪明的动物。