Longshore drifts and longshore currents

After today, I will start posting on a weekly basis every Saturday. I will also include urls of the websites which I get my information from. I've been a little lazy recently, so this post would be on something I've learned in secondary school, hope it would be useful.


Waves and currents causes transportation of sediments in the coastline (the place where the land and sea meets and interacts) Longshore currents and longshore drifts are terms we need to know regarding this topic. They can be a little confusing.

Longshore currents are flows of water that move parallel to the coast. It is generated by winds, tides and waves that approaches the coast at an angle driving the flow of water along the length of the coastline. Very specifically, it is defined as such... ''the longshore current is the dominating current in the nearshore zone. It is running parallel to the shore. The longshore current is generated by the shore-parallel component of the stresses associated with the breaking process of obliquely incoming waves, the so-called radiation stresses, and by the surplus water which is carried across the breaker zone across the coastline.''


Longshore drift on the other hand refers to the movement of sediments along the coastline. How it occurs is simple. When waves approach the coast at an angle due to wind direction, it carries sediments to the coast at an angle. However gravity only causes the sediments to move downwards perpendicularly to the coastline thus the sediments would travel along the coastline in a zig-zag motion when it is repeatedly carried at an angle and returned vertically downwards. Note: Sediments are carried to the coast when a wave crashes onto the coast, know as a swash. The motion where the seawater retreats back into the sea is known as a backwash. The backwards motion that pulls the sediments back. Longshore currents may result in longshore drift. This is illustrated below: (due to the fact that my 2 mega pixel camera was horrible at taking good photographs and that I could not operate my new scanner I could not draw out the diagrams for use)  

I do not own this photograph check links below credits go to the website

The world's longest naturally occurring spit, the 'Dungeness Spit' is found in America. Spits are one type of coastal landform that we see, along with cliffs, beaches, bays just to name a few. It is a result when longshore currents that transport sediments in the sea encounters a place of shallow sheltered water, enabling the sediments to be deposited in those regions. The accumulation of these sediments along the direction of the long shore current creates a narrow ridge of sand we identify as a spit. 

I do not own this as well. Check links below credits go to the website

Stuff about longshore drift: From my textbook
Photo of spit: http://tidelineconsultingllc.com/
Longshore current definition: http://www.coastalwiki.org/coastalwiki/Longshore_current
More about longshore current: http://www.usoceansafety.com/safety/popup/lscurrent.asp
Photo on longshore drift:   http://cgz.e2bn.net/e2bn/leas/c99/schools/cgz/accounts/staff/rchambers/GeoBytes/GCSE%20Revision/Glossaries/Glossaries/Glossary%20Extra%20Page%20Links/LongshoreDrift1.gif

Ocean conveyor belt: Thermohaline circulation

I only know this much about the Thermohaline circulation. Its information would be useful to readers but there are two things I would like to discuss about at the end of my article. 
The Ocean conveyor belt or more accurately, the thermohaline circulation refers to the continuous cycle of water in the ocean due to its temperature and salinity. The working principle behind it is that water from different parts of the ocean has differing densities, whereby colder saltier water is denser than warmer less salty sea water. (expansion of liquids) Water which is less dense tends to float while denser water tends to sink, resulting in the movement of water in the oceans to achieve this balance.
How did this different density occur in the first place?
In the North Atlantic, winds blowing over the ocean remove latent heat of vapourisation as the water evaporates, becoming cooler. Less water in the ocean coupled with the same amount of salt causes the water to become denser. In addition, when ice is formed on the ocean in those regions, pure water tends to freeze rather than salt water. Again, less water in the ocean to dissolve the salt would cause the concentration to increase even further. This denser ocean water forms the North Atlantic Deep water (NADW) which flows southwards through deep abyssal plains found along the Atlantic.    
Down to the Antarctic this denser ocean water then flows along the Antarctic continent mixing with the Antarctic bottom water to give 'common water' where it splits up to the Indian Ocean and Pacific Ocean. Following this route.

The Pacific Ocean having a slightly higher water level than the Atlantic Ocean would flow its upper most water through Indonesia to replace the water from the Atlantic that had travelled along Antarctica. Thereafter it travels North back to Greenland where it all began, starting the cycle all over again. 

Ps: Any readers please enlighten me on the terms 'over turning' and 'Haline forcing' I did not use it in my text in fear of being inaccurate! Picture from politicalclimatewordpress.com

Permian mass extinction in a nutshell

Based on the knowledge acquired from discovery channel, do enlighten me if you happen to know some specific details which I left out. 


Trigger: Volcanic eruptions(Siberian Traps) lasting for up to a million years causing large amounts of sulfur dioxide and carbon dioxide to be released.
Direct consequence: Sulfur dioxide would have caused acid rain that damages the eco system, but the damage would not have been so extensive.
The carbon dioxide released in such enormous quantities would cause severe global warming that kills off 1/3 of land dwellers at that time.
Indirect consequence:The heated planet with its warmer oceans would devastate the 'conveyor belt' preventing proper circulation of oxygen in the ocean. With the absence of oxygen in the ocean marine aerobic life would die out. It also causes purple sulfur bacteria to thrive. Which is, bacteria that survives without oxygen. In addition, these bacteria produces highly toxic hydrogen sulfide which adds on to the devastation done on the marine life of the Permian period.  
The heated ocean would also cause highly temperature sensitive methane hydrate, combination of methane and water in its solid form frozen at the bottom of the ocean, to melt releasing methane which is a very potent green house gas. It further aggravates the problem of global warming increasing Earth's temperature even further and wiping out even more life on Earth in the Permian period.
Ps: I will be writing a few posts about the conveyor belt and methane hydrate really soon to further explain how it plays a role in the Permian mass extinction!