Paleoclimatic Data and the Ice Ages


 


The past 1.8 million years ago make up the Quaternary period. The Quaternary period is the most recent geologic age and the one in which Homo sapiens developed. The Quaternary is characterized by the presence of a large amount of land ice, which varied from the amount we have today to much larger amounts during periods of glacier advance. By looking at the jagged valleys in the map of reconstructed temperatures during the Pleisteocene, or glacial epoch, we can see repeated Ice Ages

In this map the warm peaks are interglacial periods which include the Eemian and at the far right, the present Holocene. From this map we can see how rare are times as warm as the present. In addition, we can also see that a large global interglacial-glacial-interglacial climate oscillation has been reoccurring on approximately a 100,000 year periodicity for about the last 900,000 years, though each individual cycle has had its own idiosyncrasies in terms of the timing and magnitude of changes

The temperatures in this representation of the last 800,000 years were not obtained directly, but based on the fluctuations of global ice volume, and scaled to what is known of conditions during the last glacial maximum. They are meant to represent estimates of the mean surface temperature of the Earth
Paleoclimatic Data

The temperatures represented in this graph are the outcome of paleoclimatic data. Analyses of geologic sediment and other layered materials extend what is known of surface temperature, precipitation, and other meteorological parameters many thousands and millions years ago. This information is categorized in several types of "natural" recording systems.
Tree Rings The width and structure of the tree rings give some information on the climatic conditions when the tree ring was formed . Annual growth rings allow precise dating of climatic events going back 5000 years. The amount of carbon-14 isotope in wood indicates the intensity of solar activity during the treeÕs growth and the amount of carbon dioxide in the atmosphere. Narrow growth rings in trees indicate periods of climatic stress, while the absence of growth rings indicates a warm tropical climate with no seasons 
> Pollen/Spores/Insects Found in lake sediments and bogs, may date back more than 20,000 years, can be used to reconstruct the presence of forests and other vegetation, which are indicators of climatic conditions
> Ocean Sediment Cores Ocean cores measure the history of the ocean ecology as it is laid down in the sediment. The sediment includes organic matter and the shells of various tiny sea creatures. Each of these sea creatures has its own particular niche in the ecology of the ocean. The relative abundance of some species is related to the sea surface temperature, so that relative abundance can be used to estimate sea surface temperature in the past.
Ice Cores Careful analyses of the air in the bubbles and trace elements in the ice give evidence of atmospheric and climatic changes like those caused by volcanic eruption. Like in trees, the ice is made up of annual layers. In the upper parts of the ice sheets, these annual layers can be observed. The farther you go down in the ice, the deeper you go back in time, therefor the ice is compacted and stretched out as the ice flows away from the accumulation regions toward the regions where the ice sheet either melt or break off into icebergs near a marine body

I used Paleoclimatic Data to look at the existence of the Eemian Period, Interstadials, Heirich Events, The Younger Dryas, the Holocene, and the Little Ice Ages
130,000 Y.A = Eemian Period

The last 130,000 have produced the most detailed paleoclimatic data from the land, the oceans and ice cores, and so this most recent climate oscillation has been the subject of most study.

The Interglacial period that began around 130,000 years ago is called the "Eemian." It appears to have begun with rapid global warming (of uncertain duration) that took the earth out of an extreme glacial phase, into conditions that are warmer than today. Regional temperatures were sometimes 1 to 2 degrees higher than that of the Holocene interglacial (the one we are still in). There are indications that there was climate instability during the Eemian, however they are controversial. In addition, there is less evidence that the temperature changes were globally synchronous, so in terms of global temperature change, conditions during the Eemian, may not have been much different from today.

Paleoclimatic data does show us that there is evidence of a single sudden cool event during the Eemian. Jonathan Adams states that "Evidence for a single sudden cool event during the Eemian is clearly present in a more solidly dated pollen record from a lake in central Europe studied by Field et al. (1994), from loess sedimentology in central china (Zhisheng & Porter 1997), and from certain ocean sediment records in the northern Atlantic (ODP site 658). These three sources of evidence each suggest a single cold and dry event (causing a several-degree decline in Atlantic surface temperature, and on land opening up the west European forests to give a mixture of steppe and trees) near the middle of the Eemian, about 121,000 y.a. It was followed by a return to warm conditions similar to the present." Paleoclimatic data also recorded from Ice cores, ocean sediment cores, and pollen records from across Eurasia show that the Eemian interglacial seems to have ended in a sudden cooling event around 110,000 years ago.
115,000 Y.A.

Following the Eemian there were numerous sudden changes and short lived warm and cold events. The extremes of these are the warm Interstadials and the cold Heinrich.

  • The Interstadials are short-lived warm events that occurred during the generally colder conditions between 110,000 and 10,000 years ago. Paleoclimatic data that gives evidence of these Interstadials show up strongly in Greenland Ice core records. From the time period between 115,000 and 14,000 years ago, 24 of these short-lived warm events have so far been recognized from the Greenland ice core data. The duration of an Interstadial can be counted from annual layers that have accumulated in the ice.
  • Heinrich events are extreme and short-lived cold events. Adams states that "These also occur against the general background of the glacial climate, and they represent the brief expression of them most extreme glacial conditions." Preliminary paleoclimatic data from marine sediments off California and Oregon, pollen records from Pacific Northwest lakes, and glacial records from western North America show that there might have been a global Heinrich event.
  • 12,900-11,500 Y.A. = The Younger Dryas

    The Younger Dryas were known as the return to cold conditions from 12,900-11,500 years ago. Paleoclimatic data shows this through pollen data that indicate that forests which had recently developed in Europe during the aborted warming following the ice ages were suddenly replaced again by artic shrubs, herbs and grasses, and Greenland ice cores indicate a local cooling of about 6 degrees C during this event.
    10,000 Y.A.= Holocene 

    Following the Younger Dryas is the present warm epoch, known geologically as the Holocene Interglacial.

    The Holocene started suddenly around 11,500 years ago. Greenland ice cores recorded a striking sudden cooling event about 8,200 years ago. This cooling event gave cool, dry conditions that lasted about 200 years, before there was a rapid return to conditions warmer and moister than today. In addition, this cooling shows up in records from North Africa across southern Asia as a phase of arid conditions due to failure of summer monsoon rains. Furthermore, the cold and aridity also looks like it hit northernmost South America, Eastern North America, and parts of North Western Europe.
    1250-1850 AD= The Little Ice Ages

    Following the Holocene there was a "Medieval Warm Period" which was followed by a longer span of considerably colder climates, often termed the "Little Ice Age" which was when the global mean temperature may have been 0.5 Ð1.0 degrees C colder than today.

    Paleoclimatic evidence shows that Alpine glaciers moved into lower elevations, rivers that rarely freeze today were often completely ice-covered in the winter time, and precipitation patterns also changed in many regions.
     


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