High resolution <sup>14</sup>C bomb-peak dating and climate response analyses of subseasonal stable isotope signals in wood of the African baobab – A case study from Oman

Abstract

<p><strong>Abstract.</strong> The African baobab, Adansonia digitata, has great paleoclimatological potential because of its wide distributional range and millennial lifespan. However, dendroclimatological approaches are hampered by dating uncertainties due to its parenchyma-dominated wood anatomy. Here, securely-dated time series of annual wood increment growth and intra-ring stable isotopes of carbon and oxygen of cellulose for a baobab tree from Oman covering 1941 to 2005 were established. Precise dating with the bomb peak by highly resolved <sup>14</sup>C measurements proved the annual character of the baobab's growth rings. But, F<sup>14</sup>C values of tree-ring cellulose were found up to 8.8 % lower than in the corresponding atmospheric CO<sub>2</sub> for the period around the bomb peak. In conjunction with a considerable autocorrelation of the δ<sup>13</sup>C series this points to the incorporation of previous years' carbon significantly affecting the average age of derived wood. Terminal parenchyma bands, marking the tree-ring boundaries, were found to be significantly younger than their corresponding tree ring indicating that parenchyma tissue is alive for many years undergoing cell division, reorganization and potential growth. No autocorrelation was found in the δ<sup>18</sup>O series of tree-ring cellulose despite the huge water-storage potential of this stem-succulent tree species. Tree-ring width and stable isotope ratios have revealed significant climate sensitivity. δ<sup>18</sup>O was found to be a good climate proxy followed by tree-ring width and δ<sup>13</sup>C. Tree-ring width and intra-ring δ18Omin correlated well with each other and with precipitation amount for the period from pre-monsoon May to the end of the monsoon season in September/October. Intra-annual stable isotope courses were found rather similar for both δ<sup>13</sup>C and δ<sup>18</sup>O. Years with particularly low monsoon rain were reflected by increased stable isotope values in the mid-section of intra-annual courses. Distinct patterns with low subseasonal isotope values seem indicative for years with heavy rainfall events from pre-monsoonal cyclones. Rain events from post-monsoonal cyclones may also be recorded, however, only two years of observation prevent from a conclusive evaluation.</p>

Exploring the Impact of Tropical Cyclones on Oman’s Maritime Cultural Heritage Through the Lens of Al-Baleed, Salalah (Dhofar Governorate)

“…The detection of evidence of tropical cyclones on tree rings (e.g. Slotta et al 2019; Collins-Key and Altman 2021) presents significant opportunities for creating a longterm precipitation record for Oman, should suitable tree species be identified and sampled. Suitable wood samples excavated in Al-Baleed have been used for dating and other analyses (e.g.…”

THE VERSATILE USES OF THE 14C BOMB PEAK

“…However, to verify reported anthropogenic CO 2 emissions with independent Earth system observations, a better understanding of both contributions from natural variations in the CO 2 cycle and of the uptake processes is needed (Peters et al 2017). These complex questions are being investigated from different angles for the oceans (Worden et al 2015;Gruber et al 2019), plants (Bastin et al 2019;Slotta et al 2021), and soil (Trumbore 2009;Shi et al 2020). Here, the 14 C bomb peak provides a convenient tracer to study decadal dynamics of CO 2 , whereas cosmogenic 14 C is useful at the millennium time scale.…”

Stable Isotope Composition of Cyclone Mekunu Rainfall, Southern Oman

“…Apart from groundwater, our findings might also be relevant for studies of high-resolution paleoclimate archives. The isotopic signature of cyclones may be recorded in freshwater mollusks (Lawrence, 1998) or tree rings (Slotta et al, 2019). Speleothems are particularly noteworthy archives on the Arabian Peninsula since much of the paleoclimatic framework is based on data from Omani caves (Burns et al, 1998(Burns et al, , 2001Fleitmann et al, 2003Fleitmann et al, , 2004.…”