Posts Tagged ‘ocean’

What is the difference between a sea and a lake? (Environment Canada)

Friday, December 11th, 2009

[Editor's note: This Q&A from Environment Canada explains the rough difference between types of hydrological features. Names in the real world are often messier than this text book explanation. One way we've tried to help in Natural Earth is by indicating if a lake is freshwater, saline, natural, artificial, stable water level, seasonal water level, or simply ephemeral.]

Republished from Environment Canada. Feb. 2002.

What is the difference between a sea and a lake? Looking at the names of many sea and many lakes does not readily demonstrate an identifiable difference. There are salt water lakes and fresh water seas and some lakes that are bigger than other seas.
Bruce Schoenegge, Irvine, California, USA

Salt crust resulting from receding lake, Lake Frome, Australia.
Salt crust resulting from receding lake, Lake Frome, Australia.

In order to understand why some smaller salt water bodies are called lakes and others seas it is necessary to realize that lakes are, in geological time scales, transitory in nature–they form, mature and die.

Some water bodies that started out as saltwater seas over time became closed-off from the oceans. Depending on the quantity of fresh water flowing in from rivers, glacial melt water, or other sources, the salinity could have declined to the point where the water became relatively fresh. The Sea of Aral is probably an example of where this transition has occurred. Similarly the reverse can occur whereby freshwater lakes can become open to the sea so that the salinity increases, as in the Baltic Sea. The Black Sea is an example that has alternated between fresh and salt water conditions over geological time. Evidence for these changes can be found in ancient fossils of organisms some of which were known to be tolerant of saltwater while others were known to have been intolerant.

No doubt there was also some confusion in the naming of water bodies by the early explorers based on their first impressions and certainly one can understand why some may have been inappropriately named. In addition the subsequent translation of the names between different languages could also have added to the confusion.

Here are some definitions of water bodies:

Ocean
The whole body of salt water that covers nearly 3/4 of the surface area of the globe. In particular, each of the main areas into which the sea is divided geographically, e.g. Atlantic, Pacific. Oceans are tidal, living systems containing a multitude of biological organisms.

  • Average depth of the world’s oceans: 3,962 metres(13,000ft)
  • Maximum depth: 10,680 meters; (35,040ft)
  • Average salt content – 3.5% (mostly common salt, NaCl but with some magnesium and calcium salts)
  • Average density – 1.026
Sea
The expanse of salt water that covers most of the earth’s surface and surrounds the land masses. A body of salt water that is secondary in size to oceans.
Lake
A large area of water surrounded by land. Normally fresh water but in some cases can be appreciably saline depending on the geology of the underlying and surrounding terrain. Lakes are living systems containing various quantities of biological organisms. Lakes can be classified according to the level of bioproductivity as oligotrophic (low productivity), mesotrophic or eutrophic (high productivity). The productivity is usually controlled by the amount of nutrients (mostly phosphorus and nitrogen) present in the water and the amount of light that can penetrate the water column.
River
A large natural stream of water flowing in a channel to the sea, a lake or another such river. The flow can be permanent of seasonal.
Stream
A small, narrow river flowing on the surface of, or beneath, the ground.

RUMOR: Google Earth 5 on Monday (Google Earth Blog)

Friday, January 30th, 2009

[Editor's note: New features are coming to an application near you. Thanks Laris!]

Republished from Google Earth Blog.
Original publish date: January 26, 2009.

Big Google Earth Announcement with Al Gore and More

The tech world was abuzz this weekend with rumors about a big upcoming event concerning Google Earth. WebProNews and AppScout were the first to report on Friday. Google has sent out an invitation to the press, including Google Earth Blog, for a “Special announcement about Google Earth” on February 2nd in San Francisco. And this event looks like it could be the biggest announcement since Google Earth was released! Speakers include: former Vice President Al Gore, CEO of Google Eric Schmidt, VP of Google Marissa Mayer, and Director of Google Geo John Hanke. Wow!

There are no specifics on the announcement mentioned in the invitation. Just some comments about how Google Earth has reached hundreds of millions of people around the world. The last time Google had this many dignitaries to make an announcement for Google Earth was in June of 2006 when they announced the upcoming release of Google Earth 4. Eric Schmidt and the two co-founders of Google (Larry Page and Sergey Brin) were there for the announcement made by John Hanke at that event. Google Earth 4 introduced photorealistic textures to 3D models, GE for the Mac and Linux, multi-lingual support, and a huge global imagery update covering many countries for the first time.

Another clue for this announcement was some other speakers for the announcement: Sylvia Earle – Explorer-in-Residence for National Geographic Society; Terry Garcia – EVP for National Geographic Society, and Greg Farrington, Executive Director for California Academy of Sciences. The last one isn’t surprising because the invitation says the announcement will be held at the California Academy of Sciences.

The big clue is Sylvia Earle. As pointed out by everyone, Sylvia Earle is a world renowned oceanographer. So, of course, the immediate conclusion is that Google Ocean is finally about to be introduced. Rumors have been flying about Google Ocean for quite a while.

So, clearly Google Earth is going to get some new Ocean-related data. Google just added new detailed ocean floor imagery last week. And, it’s a known fact that several of the parties involved with that also have worked on 3D bathymetry. Google Earth to date has not had many layers which provide data about the ocean. And the ocean terrain has always been flat (2D) in Google Earth. More ocean data is an area I’ve been looking forward to with great anticipation. Especially since this year my wife and I are departing to spend the next five years circumnavigating the oceans by sailboat. Having Google Earth help us explore the oceans will be handy! Google Earth has needed more information about the 75% of the Earth most of us ignore.

I don’t think this announcement will be confined to just Google Ocean though. When Google makes an announcement like this, they always try to push the envelope on multiple fronts. And, with Al Gore headlining the event, I’m sure we’re going to get some data about the environment. I’m expecting lots of new features and data to write about in February. It’s going to be exciting! I just wish I could attend the event myself – but, unfortunately we’ve got plans for next week which keep me from going. But, have no fear, I’ll still be reporting on this major event!