Expression of the “4.2 ka event” in the southern Rocky Mountains, USA
<p>The use of the climatic anomaly known as the “4.2 ka event” as the stratigraphic division between the middle and late Holocene has prompted debate over its impact, geographic pattern, and significance. The anomaly has primarily been described as abrupt drying in the Northern Hemisphere at c...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-05-01
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| Series: | Climate of the Past |
| Online Access: | https://cp.copernicus.org/articles/18/1109/2022/cp-18-1109-2022.pdf |
| _version_ | 1811255604885323776 |
|---|---|
| author | D. T. Liefert B. N. Shuman |
| author_facet | D. T. Liefert B. N. Shuman |
| author_sort | D. T. Liefert |
| collection | DOAJ |
| description | <p>The use of the climatic anomaly known as the “4.2 ka event” as the
stratigraphic division between the middle and late Holocene has prompted
debate over its impact, geographic pattern, and significance. The anomaly
has primarily been described as abrupt drying in the Northern Hemisphere at
ca. 4 ka (ka, thousands of years before present), but evidence of the
hydroclimate change is inconsistent among sites both globally and within
North America. Climate records from the southern Rocky Mountains demonstrate
the challenge with diagnosing the extent and severity of the anomaly.
Dune-field chronologies and a pollen record in southeastern Wyoming reveal
several centuries of low moisture at around 4.2 ka, and prominent low stands
in lakes in Colorado suggest the drought was unique amid Holocene
variability, but detailed carbonate oxygen isotope (<span class="inline-formula"><i>δ</i><sup>18</sup></span>O<span class="inline-formula"><sub>carb</sub></span>) records from Colorado do not record drought at the same
time. We find new evidence from <span class="inline-formula"><i>δ</i><sup>18</sup></span>O<span class="inline-formula"><sub>carb</sub></span> in a small
mountain lake in southeastern Wyoming of an abrupt reduction in effective
moisture or snowpack from approximately 4.2–4 ka, which coincides in time
with the other evidence of regional drying from the southern Rocky Mountains
and the western Great Plains. We find that the <span class="inline-formula"><i>δ</i><sup>18</sup></span>O<span class="inline-formula"><sub>carb</sub></span> in
our record may reflect cool-season inputs into the lake, which do not appear
to track the strong enrichment of heavy oxygen by evaporation during summer
months today. The modern relationship differs from some widely applied
conceptual models of lake–isotope systems and may indicate reduced winter
precipitation rather than enhanced evaporation at ca. 4.2 ka.
Inconsistencies among the North American records, particularly in <span class="inline-formula"><i>δ</i><sup>18</sup></span>O<span class="inline-formula"><sub>carb</sub></span> trends, thus show that site-specific factors can prevent
identification of the patterns of multi-century drought. However, the
prominence of the drought at ca. 4 ka among a growing number of sites in the
North American interior suggests it was a regionally substantial climate
event amid other Holocene variability.</p> |
| first_indexed | 2024-04-12T17:27:39Z |
| format | Article |
| id | doaj.art-80d45e523d1e4b24bd556f0852bd77b6 |
| institution | Directory Open Access Journal |
| issn | 1814-9324 1814-9332 |
| language | English |
| last_indexed | 2024-04-12T17:27:39Z |
| publishDate | 2022-05-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Climate of the Past |
| spelling | doaj.art-80d45e523d1e4b24bd556f0852bd77b62022-12-22T03:23:16ZengCopernicus PublicationsClimate of the Past1814-93241814-93322022-05-01181109112410.5194/cp-18-1109-2022Expression of the “4.2 ka event” in the southern Rocky Mountains, USAD. T. LiefertB. N. Shuman<p>The use of the climatic anomaly known as the “4.2 ka event” as the stratigraphic division between the middle and late Holocene has prompted debate over its impact, geographic pattern, and significance. The anomaly has primarily been described as abrupt drying in the Northern Hemisphere at ca. 4 ka (ka, thousands of years before present), but evidence of the hydroclimate change is inconsistent among sites both globally and within North America. Climate records from the southern Rocky Mountains demonstrate the challenge with diagnosing the extent and severity of the anomaly. Dune-field chronologies and a pollen record in southeastern Wyoming reveal several centuries of low moisture at around 4.2 ka, and prominent low stands in lakes in Colorado suggest the drought was unique amid Holocene variability, but detailed carbonate oxygen isotope (<span class="inline-formula"><i>δ</i><sup>18</sup></span>O<span class="inline-formula"><sub>carb</sub></span>) records from Colorado do not record drought at the same time. We find new evidence from <span class="inline-formula"><i>δ</i><sup>18</sup></span>O<span class="inline-formula"><sub>carb</sub></span> in a small mountain lake in southeastern Wyoming of an abrupt reduction in effective moisture or snowpack from approximately 4.2–4 ka, which coincides in time with the other evidence of regional drying from the southern Rocky Mountains and the western Great Plains. We find that the <span class="inline-formula"><i>δ</i><sup>18</sup></span>O<span class="inline-formula"><sub>carb</sub></span> in our record may reflect cool-season inputs into the lake, which do not appear to track the strong enrichment of heavy oxygen by evaporation during summer months today. The modern relationship differs from some widely applied conceptual models of lake–isotope systems and may indicate reduced winter precipitation rather than enhanced evaporation at ca. 4.2 ka. Inconsistencies among the North American records, particularly in <span class="inline-formula"><i>δ</i><sup>18</sup></span>O<span class="inline-formula"><sub>carb</sub></span> trends, thus show that site-specific factors can prevent identification of the patterns of multi-century drought. However, the prominence of the drought at ca. 4 ka among a growing number of sites in the North American interior suggests it was a regionally substantial climate event amid other Holocene variability.</p>https://cp.copernicus.org/articles/18/1109/2022/cp-18-1109-2022.pdf |
| spellingShingle | D. T. Liefert B. N. Shuman Expression of the “4.2 ka event” in the southern Rocky Mountains, USA Climate of the Past |
| title | Expression of the “4.2 ka event” in the southern Rocky Mountains, USA |
| title_full | Expression of the “4.2 ka event” in the southern Rocky Mountains, USA |
| title_fullStr | Expression of the “4.2 ka event” in the southern Rocky Mountains, USA |
| title_full_unstemmed | Expression of the “4.2 ka event” in the southern Rocky Mountains, USA |
| title_short | Expression of the “4.2 ka event” in the southern Rocky Mountains, USA |
| title_sort | expression of the 4 2 thinsp ka event in the southern rocky mountains usa |
| url | https://cp.copernicus.org/articles/18/1109/2022/cp-18-1109-2022.pdf |
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