Long-term increase in precipitation intermittency and intensity at Paleogene mid latitudes&#160;
Authors: Slawson Jacob , Plink-Bjorklund Piret 
Published: March 2022

&lt;p&gt;&lt;span xml:lang=&quot;EN-US&quot; data-contrast=&quot;auto&quot;&gt;&lt;span&gt;Unmitigated scenarios of greenhouse gas emissions produce climates like those of the &lt;/span&gt;&lt;span&gt;Early&amp;#160;&lt;/span&gt;&lt;span&gt;Eocene&lt;/span&gt;&lt;span&gt;&amp;#160;by 2150 CE&lt;/span&gt;&lt;span&gt;, suggest&lt;/span&gt;&lt;span&gt;ing&lt;/span&gt;&lt;span&gt;&amp;#160;that we are effectively&amp;#160;&lt;/span&gt;&lt;span&gt;reversing a&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;more than&lt;/span&gt;&lt;span&gt;&amp;#160;50-million-year cooling trend in less than two centuries.&lt;/span&gt;&lt;span&gt; Terrestrial records of rivers and floodplains from Paleogene sedimentary basins in the US Western interior and Europe indicate an increase in flash floods and droughts at &lt;/span&gt;&lt;span&gt;paleo-&lt;/span&gt;&lt;span&gt;mid latitudes, indicating increased precipitation intensity and intermittency. In t&lt;/span&gt;&lt;span&gt;he&amp;#160;&lt;/span&gt;&lt;span&gt;Uinta Basin, Utah&lt;/span&gt;&lt;span&gt;&amp;#160;magnetostratigraphic analyses&lt;/span&gt;&lt;span&gt;, a&lt;/span&gt;&lt;span&gt;bsolute age dates&lt;/span&gt;&lt;span&gt;,&lt;/span&gt;&lt;span&gt;&amp;#160;and biostratigraphy allow&amp;#160;&lt;/span&gt;&lt;span&gt;the re&lt;/span&gt;&lt;span&gt;construct&lt;/span&gt;&lt;span&gt;ion&lt;/span&gt;&lt;span&gt;&amp;#160;of changes in &lt;/span&gt;&lt;span&gt;hydroclimate&lt;/span&gt;&lt;span&gt;&amp;#160;from&lt;/span&gt;&lt;span&gt;&amp;#160;the&lt;/span&gt;&lt;span&gt; Early Paleocene, to the Paleocene-Eocene Thermal Maximum (PETM), and through the Early Eocene Climatic Optimum (EECO). Here we observe that the largest shifts in &lt;/span&gt;&lt;span&gt;hydroclimate&lt;/span&gt;&lt;span&gt;&amp;#160;are not linked to the PETM but rather occur during the warm&amp;#160;&lt;/span&gt;&lt;span&gt;L&lt;/span&gt;&lt;span&gt;ate Paleocene and&amp;#160;&lt;/span&gt;&lt;span&gt;then&amp;#160;&lt;/span&gt;&lt;span&gt;at the end of the EECO.&amp;#160;&lt;/span&gt;&lt;span&gt;This&amp;#160;&lt;/span&gt;&lt;span&gt;is indicated&lt;/span&gt;&lt;span&gt;&amp;#160;by&amp;#160;&lt;/span&gt;&lt;span&gt;the&amp;#160;&lt;/span&gt;&lt;span&gt;river sedimentary record&lt;/span&gt;&lt;span&gt;&amp;#160;that&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;shows a shift from normal rivers, such as are characteristic at mid-latitudes today,&amp;#160;&lt;/span&gt;&lt;span&gt;to&amp;#160;&lt;/span&gt;&lt;span&gt;flood-prone rivers in late Paleocene.&lt;/span&gt;&lt;span&gt; The rivers shifted back to normal at the end of the EECO. Coeval changes are&lt;/span&gt;&lt;span&gt;&amp;#160;observed&lt;/span&gt;&lt;span&gt;&amp;#160;in floodplain&amp;#160;&lt;/span&gt;&lt;span&gt;paleosols&lt;/span&gt;&lt;span&gt;&amp;#160;where the late Paleocene and early Eoce&lt;/span&gt;&lt;span&gt;ne&amp;#160;&lt;/span&gt;&lt;span&gt;pal&lt;/span&gt;&lt;span&gt;eosols&lt;/span&gt;&lt;span&gt;&amp;#160;indicate sustained droughts and intermittent seasonal rains. At&amp;#160;&lt;/span&gt;&lt;span&gt;the&amp;#160;&lt;/span&gt;&lt;span&gt;PETM&lt;/span&gt;&lt;span&gt;&amp;#160;there is no change in the stat&lt;/span&gt;&lt;span&gt;e of&amp;#160;&lt;/span&gt;&lt;span&gt;hydroclimate&lt;/span&gt;&lt;span&gt;, but rather a further&lt;/span&gt;&lt;span&gt;&amp;#160;intensification of floods and droughts. Comparison to other terrestrial basins at mid-latitudes show&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;&amp;#160;similar patterns. These results show that the most dramatic shifts in&amp;#160;&lt;/span&gt;&lt;span&gt;hydroclimate&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;were not linked&lt;/span&gt;&lt;span&gt;&amp;#160;to the largest amplitude of atmospheric drivers at the PETM&lt;/span&gt;&lt;span&gt;,&lt;/span&gt;&lt;span&gt;&amp;#160;but rather suggest a threshold-driven relationship between the atmos&lt;/span&gt;&lt;span&gt;pheric drivers and&amp;#160;&lt;/span&gt;&lt;span&gt;hydroclimate&lt;/span&gt;&lt;span&gt;. This may suggest that significant changes in&amp;#160;&lt;/span&gt;&lt;span&gt;hydroclimate&lt;/span&gt;&lt;span&gt;&amp;#160;are to&amp;#160;&lt;/span&gt;&lt;span&gt;be expected&lt;/span&gt;&lt;span&gt;&amp;#160;already&lt;/span&gt;&lt;span&gt;&amp;#160;before 2150 CE.&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;