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Evidence
The Older Dryas is a period of cooling during the Bølling-Allerød warming, estimated to be from 13,900 to 13,600 years before present (BP), and the estimated ages can vary using different age dating methods. Numerous studies on chronology and palaeoclimate of last deglaciation show a cooling event within Bølling-Allerød warming that reflects the occurrence of Older Dryas. The determination of paleotemperatures varies from study to study depending on the sample collected. δ18O measurements are most common when analyzing Ice core samples whereas the changing abundance pattern of fauna and flora are most commonly used when examining lake sediments. Moraine belts are usually studied in places with palaeoglacier presented. As for ocean sediments, the variations of alkenone levels and faunal abundances were measured to model paleotemperatures in seperate studies showed in the following sections.

Ice core δ18O evidence
The North Greenland Ice Core Project (GRIP) members drilled an undisturbed ice core from North Greenland (75.1 8N, 42.3 8W). The ice core record showed a cold oscillation between 14,025 to13,904 years BP, which is reflected in the increased δ18O during this period. This cold oscillation was also observed in earlier ice core records (GRIP and GISP2  ) drilled in early 1990’s by GRIP members.

Lake sediment evidence
A multi-proxy study on late glacial lake sediments of Moervaart palaeolake shows multiple pieces of evidence in various aspects to support Older Dryas.

The lake sediment had an erosional surface prior to Older Dryas suggesting a change to colder climate. Microstructure observation of the sediments shows that fossil soil wedges or frost cracks were observed in the top of Older Dryas deposits, which indicates mean annual air temperatures below -1 to 0 ℃ and cold winters. This conclusion is also supported by the presence of Juniperus, which indicates a protecting snow cover in winter. This change is also shown on the records at the Rieme sites on the Great SandRidge of Maldegem-Stekene at Snellegem in NW Belgium, and many other sites in north-western Europe.

δ18O measurements show a decreasing trend in δ18O at the transition to the Older Dryas, which corresponds to the ice core record of precipitation in the northern hemisphere.

Pollen analysis shows a temporary decrease in the pollen levels of trees and shrubs with a short-term increase of herbaceous pollen. The changed pollen pattern suggests an increased abundance of grass as well as a retreat of tree and shrubs. The change of vegetation distribution further indicates a colder and drier climate during this period. As for aquatic plant evidence, both aquatic and semi-aquatic botanical taxa show a sharp decrease, suggesting lower lake levels caused by drier climate. The drier climate is also reflected by increased salinity indicated by diatom analysis.

The change of Chironomids population also indicates a colder climate. Microtendipes is an indicator of intermediate temperature in Late glacial deposits in northern Europe (Brooks and Birks, 2001). The abundance of Microtendipes peaked in the early part of Older Dryas suggesting a cold oscillation. The mollusc data (Valvata piscinalis as a cold-water indicator) suggests a lower summer temperature comparing to previous Bølling period.

Ocean sediment evidence
Recent research on sea surface temperature (SST) for the past 15,000 years in southern Okinawa modelled the Paleoclimate of ocean sediment core (ODP 1202B) using an alkenone analysis. The results show a cooing stage at 14,300 to 13,700 years BP between Bølling and Allerød warm phases, corresponding to the Older Dryas event.

Another study on an ocean sediment core from Norwegian Trench also suggests a cooling between Bølling and Allerød warm phases. The glacial polar faunal study on ocean sediment core Troll 3.1 based on Neogloboquadrina pachyderma abundances suggests that there were two cooling events before Younger Dryas in which one of the events occurred within Bølling-Allerød interstadial and can be associated with Older Dryas.

Moraine evidence
The study on late-glacial climate change in White Mountains (New Hampshire, USA) refined the deglaciation history of White Mountain Moraine System (WMMS) by mapping moraine belts and related lake sequences. The result suggests that the Littleton-Bethlehem (L-B) readvance of ice sheet occurred between 14,000 to 13,800 years BP. The L-B readvance coincided with the Older Dryas events and provides the first well-documented and dated evidence of Older Dryas.

Another Glacial chronology and palaeoclimate study on moraine suggests a cold oscillation in the second late-glacial (LG2) following the first late-glacial readvance (LG1) at around 14,000±700 to 13,700±1200 years BP. The LG2 cold oscillation around 14,000 years BP can correspond to the cooling of Greenland Interstadial 1 (GI-1d-Older Dryas) that happened around the same time period, which is the first chronological evidence that supports the presence of Older Dryas in the Tatra Mountains.

Evaluating Wikipedia -- Sphagnum
Evaluating the wikipedia page on Sphagnum.

The parts that can be improved:


 * The lead section is not refined, containing too many functional details of sphagnum rather than introducing the species. The water storage function of sphagnum was described before the morphology and physiology of sphagnum, which is a not favoured structure for introducing a species to readers.


 * All points are summed up into one paragraph, makes it tedious to read. In this way, readers are unable to extract key points easily from their first overview.


 * The whole article is composed of pure text and photos. Informative tables and diagrams can help readers to understand this article better.


 * The content regarding “life cycle” is too obscure for the average readers of the field and it’s also not clearly structured. (too obscure for the average readers, and is barely informative)


 * Some links of the references are invalid for access. (outdated source - minor issue)


 * Lack of subtitle in the content of “uses”. The types of “uses” are mixed and disorderly distributed throughout the part. In this case, use of subtitles regarding different “uses” should be considered in order to separate and frame out the key terms.


 * Use of the value statement like “the most” indicates non properly referenced information. The use of “most” without statistical evidences.


 * Lack of information. The sentence “Peat can accumulate to a depth of many meters” did not clarify the exact depth of the accumulation.

The good parts of this page:


 * The various topics are balanced well and equally important. The article mentioned the biological component (life cycle, taxonomy), ecological component (usage, conservation) and their distributions, which provided enough information for viewers to understand this special vegetation type.


 * This article used 38 references consisted of databases, primary articles, and review articles with proper citations, which provides reliable information to the readers. However, some of the links are invalid.

Add to an article
The ram pressure is a function of wind speed and density. The formula is

P = mp * n * V2= 1.6726 * n * V2 where mp is the proton mass, pressure P is in nPa (nanopascals), n is the density in particles/cm3 and V is the speed in km/s of the solar wind.