Neotropical Ostracodes as Indicator for Paleo-Hurricanes - High-temporal Calcification Periods traced by Oxygen Isotopes
Authors: Wrozyna Claudia , Brachert Thomas C. , Dietzel Martin , Geyer Stefan , Reuter Markus , Piller Werner E. 
Published: March 2021

&lt;p&gt;Overwash deposits in coastal lagoons are most commonly utilized for the identification of past hurricane landfalls. These deposits have a small spatial distribution and a limited preservation potential. Thus, geochemical approaches to indicate palaeo-hurricanes, such as &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O signatures of carbonate deposits, are rare besides most archives do not provide the requested high temporal resolution. Ostracodes are ideally suited for the application of paleo-hurricanes since they calcify new valves within hours to few days &amp;#8211; fast enough to document a rainstorm event. But, information on the ostracode life cycle and influences on modern oxygen isotope compositions are limited, especially in tropical regions.&amp;#160;&amp;#160; &amp;#160;&lt;/p&gt;&lt;p&gt;This study investigates the relationship between hydrochemistry, climate, and valve geochemistry (&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O, &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C) of living populations of the common Neotropical ostracode &lt;em&gt;Cytheridella &lt;/em&gt;on a large geographical range. Since most of the regions in the Neotropics are sparsely covered by hydrochemical data, especially with respect to stable isotopes (&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C), the present approach is based on estimation of &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;eq&lt;/sub&gt; values calcites at isotope equilibrium as references for the interpretation of oxygen isotope distribution of ostracodes.&lt;/p&gt;&lt;p&gt;As postulated in other studies &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;precipitation&lt;/sub&gt; and temperature are the most important controls on lake water and, consequently, ostracode &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O.&lt;/p&gt;&lt;p&gt;Oxygen isotope composition reveals inferences to be drawn on calcification periods of &lt;em&gt;Cytheridella &lt;/em&gt;within its geographical distribution. Offsets between &lt;em&gt;Cytheridella &lt;/em&gt;&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;eq&lt;/sub&gt; values vary throughout the year and coincide only during spring (April/May) and autumn (October) which indicates that &lt;em&gt;Cytheridella &lt;/em&gt;calcifies seasonally in all investigated regions. This implies a synchronous life cycle of &lt;em&gt;Cytheridella &lt;/em&gt;in all investigated regions. Since the regions differ in climatic conditions (i.e., precipitation seasonality and amounts, temperature gradients) an environmental control on Cytheridella&amp;#180;s life cycle can be excluded.&lt;/p&gt;&lt;p&gt;The above approach yields in an improved understanding of geochemical (i.e., &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O, &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C) signatures of ostracode valves on a seasonal basis especially in regions where few information on lake water hydrochemistry is available and points to &amp;#948;18O values of ostracode species to be used for the identification of hurricane-related precipitation extremes by their high-temporal resolution of seasonal calcification.&lt;/p&gt;