User:GEOG430Anon/sandbox

This is my sandbox page. I am using it to get a better understanding of how to create, edit and reference things for my project in GEOG 430. I am going to make a practice reference to the carbon isotopes carbon 16 and carbon 18 here.

I am assigning myself the same article that I edited and made comments on the talk page--Middle Miocene disruption. The talk page for this article has a more detailed summary of the changes I would like to make. In short, there is a lot more research that is relevant and has been published on this time period since the articles inception in '07 (I think). When I was looking for an article to write about several weeks back, I spent some time accumulating research studies via the journals we were shown in class. One example of an journal entry I plan to use would be "the middle miocene climatic transition: East Antarctic ice sheet development, deep ocean circulation and global carbon cycling" by Benjamin Flowers and James Kennett. This is one source of about 6 that I have accumulated and skimmed and plan on making reference to. I realize that some of these are specific hypotheses about the time period, and so there will be some struggle to fit them into the main body of the article. I think more than likely I can build the main section through consensus's in the articles and then go deeper into different ideologies in sub sections if necessary.

Week 6 - Improving an existing article
I am going to be improving an article titled Middle Miocene Disruption. In the current form of the article, the biggest thing that I found to be missing is a strong general explanation of what the Mid Miocene disruption is and its importance in a larger context. I think the current article is a bit too myopic in how it talks about this period of time. Further, I believe that the research cited in the article is largely irrelevant, or discussed in such a way that it cannot be clearly connected to the topic at hand. For example, a research study done by Madelaine Bohme is cited in the article that discusses survival of several species prior to the disruption in the mid Miocene climatic optimum...how this connects with the disruption itself is not explicitly stated or obvious. In general, while I think that there is some good bits of information in the article already, it is poorly organized and scattered in such a way that it is difficult to synthesize the important points or what the original author was trying to get across. One final point I would make is that based on my little bit of research using WebofScience.com, there has been a lot more research done on this time period. I was able to identify 5 or 6 papers that were applicable to this subject, even if some of them dive more specifically into the topic. I think it would be important to incorporate some of these insights into the article, even if at the very least they are talked about in subsections to the main article.

I am not sure whether or not I should actually writing my proposed changes as on the wiki.edu home page for this course it says:

"Improving an existing article?
 * Identify what's missing from the current form of the article. Think back to the skills you learned while critiquing an article. Make notes for improvement in your sandbox.

Peer review
Great topic for elaboration and good points about the original article! You'll be helping a lot by introducing connections between the environmental changes already noted and the biotic changes that the original author leaves unmentioned. You might consider introducing specific section divisions in the article (e.g., for Evidence, Suggested causes, and Theoretical implications). It could also help to tie this material in to broader discussions of extinction--for example, Professor Gavin mentioned the periodicity of mass extinctions, and the mid-Miocene event is one that was included in the original study from Raup and Sepkoski. Other texts that might be useful include Nitecki's anthology, Raup's book , and the survey by Ehrlich and Ehrlich. Dinosaurphilosophy (talk) 01:07, 13 May 2017 (UTC)

comments
This is a good choice but certainly a bit outside of my area of expertise. Try to find the broadest review articles on this topic and summarize the hypothesized causes and effects of the event. Cronin's book is obviously a good place to start. Include this figure perhaps? Answer.to.the.rock (talk) 13:24, 25 May 2017 (UTC)

Current Article
The term Middle Miocene disruption, alternatively the Middle Miocene extinction or Middle Miocene extinction peak, refers to a wave of extinctions of terrestrial and aquatic life forms that occurred around the middle of the Miocene, roughly 14.8 to 14.5 million years ago, during the Langhian stage of the Miocene. This period was preceded by the Miocene Climatic Optimum, a period of relative warmth from 18 to 14 Ma. Cooling that led to the Middle Miocene disruption has been attributed to CO2 being pulled out of the atmosphere by organic material before becoming caught in different locations like the Monterey Formation.

Madelaine Bohme observed the occurrence of Varanidae, Chameleon, Cordylidae, Tomistominae, Alligatoridae, and giant turtles which indicate survival through the Miocene Climatic Optimum (18 to 16 Ma) in Central Europe (45-42°N palaeolatitude). A major and permanent cooling step occurred between 14.8 and 14.1 Ma, associated with increased production of cold Antarctic deep waters and a major growth of the East Antarctic ice sheet. Two crocodilians of the genera Gavialosuchus and Diplocynodon were noted to have been extant in these northern latitudes prior to the permanent cooling step then became extinct 13.5 to 14 Ma.

A Middle Miocene delta18O increase, that is a relative increase in the heavier isotope of oxygen, has been noted in the Pacific, the Southern Ocean and the South Atlantic.

Changes
The term Middle Miocene disruption, alternatively the Middle Miocene extinction or Middle Miocene extinction peak, refers to a wave of extinctions of terrestrial and aquatic life forms that occurred around the middle of the Miocene, roughly 14 million years ago, during the Langhian stage of the Miocene. This era of extinction is believed to be caused by a relatively steady period of cooling that resulted in the the growth of ice sheet volumes globally, and the reestablishment of the ice of the East Antarctic Ice Sheet (EAIS). Cooling that led to the Middle Miocene disruption has been attributed to CO2 being pulled out of the atmosphere by organic material before becoming caught in different locations like the Monterey Formation. Other ideas as to the cause for this cooling are connected to changes in oceanic and atmospheric circulation. This period was preceded by the Miocene Climatic Optimum, a period of relative warmth from 18 to 14 Ma.

Effects
One of the primary effects of the climatic cooling that took place during this time period was the growth of the East Antarctic Ice Sheet (EAIS). Significant sections of ice on the Antarctic continent are believed to have started growth at the beginning of the Middle Miocene disruption and continued to expand until about 10 Ma. This growth has been attributed primarily to changes in oceanic and atmospheric currents and is considered to have been amplified by the significant drop in atmospheric carbon dioxide (ppm). This drop in atmospheric CO 2 fell temporarily from about 300 to 140ppm as estimated by the relationship between atmospheric levels of CO 2 and pH levels in the ocean determined by boron isotopic levels in calcium carbonate. One of the primary indicators for this significant ice sheet growth globally is the higher concentration of 18O found in benthic foraminifera from oceanic sediment cores during this time period. During periods of ice sheet growth, the lighter 16O isotopes found in ocean water are drawn out as precipitation and consolidate in ice sheets while a higher concentration of 18O is left behind for foraminifera to utilize.

One of the other primary effects of the climatic cooling during the middle Miocene was the biotic impact on terrestrial and oceanic lifeforms. A primary example of these extinctions is indicated by the observed occurrence of Varanidae, Chameleon, Cordylidae, Tomistominae, Alligatoridae, and giant turtles through the Miocene Climatic Optimum (18 to 16 Ma) in Central Europe (45-42°N palaeolatitude). This was then followed was a major and permanent cooling step marked by the mid Miocene disruption between 14.8 and 14.1 Ma. Two crocodilians of the genera Gavialosuchus and Diplocynodon were noted to have been extant in these northern latitudes prior to the permanent cooling step, but then became extinct between 14 to 13.5 Ma. Another indicator that would lead to extinctions is the conservative estimate that temperatures in the Antarctic region may have cooled by at least 8o C in the summer months 14 Ma .This Antarctic cooling, along with significant changes in temperature gradients in Central Europe as indicated by Madelaine Bohme's study on ectothermic vertebrates provide evidence that plant and animal life needed to migrate or adapt in order to survive.

Suggested Causes
The primary causes for the cooling that came out of the middle Miocene Climatic Optimum are centered around significant changes in both oceanic circulation, as well as changing atmospheric CO2 levels. Oceanic circulation changes are defined by increases in Antarctic Bottom Water (AABW) production, the halting of saline water delivery to the southern ocean from the Indian Ocean and additional North Atlantic Deep Water (NADW) production. Falling CO2 concentrations in the atmosphere has been linked to drawdown of the gas into organic material deposited along continental margins like the Monterey Formation of coastal California. These sites of CO2 drawdown are to have been extensive enough to drop atmospheric concentrations in CO2 from about 300 to 140ppm and lead to processes of global cooling that helped in the expansion of the EAIS.

An additional suggested cause for the middle Miocene disruption has been attributed to a shift from a solar insolation cycle that is obliquity dominated to one that is dominated by eccentricity (see Milankovitch cycles). This change would have been significant enough for conditions near the Antarctic continent to allow for glaciation.

Extinction Event
The Middle Miocene disruption is considered a significant extinction event and has been analyzed in terms of it's importance in there being a possible periodicity between extinction events. A study from Raup and Sepkoski find that there is a statistically significant mean periodicity (where P is less than .01) of about 26 million years for 12 different extinction events. The debate about whether this potential periodicity is caused by some set of recurrent cycles or a biologic factor is unknown.