The CoralHydro2k database: a global, actively curated compilation of coral <i>δ</i>¹⁸O and Sr&thinsp;∕&thinsp;Ca proxy records of tropical ocean hydrology and temperature for the Common Era

<p>The response of the hydrological cycle to anthropogenic climate change, especially across the tropical oceans, remains poorly understood due to the scarcity of long instrumental temperature and hydrological records. Massive shallow-water corals are ideally suited to reconstructing past oceanic variability as they are widely distributed across the tropics, rapidly deposit calcium carbonate skeletons that continuously record ambient environmental conditions, and can be sampled at monthly to annual resolution. Climate reconstructions based on corals primarily use the stable oxygen isotope composition (<span class="inline-formula"><i>δ</i>¹⁸</span>O), which acts as a proxy for sea surface temperature (SST), and the oxygen isotope composition of seawater (<span class="inline-formula"><i>δ</i>¹⁸</span>O<span class="inline-formula">_sw</span>), a measure of hydrological variability. Increasingly, coral <span class="inline-formula"><i>δ</i>¹⁸</span>O time series are paired with time series of strontium-to-calcium ratios (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">Sr</mi><mo>/</mo><mi mathvariant="normal">Ca</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="33pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="05c54804891904b379974c95750768ee"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="essd-15-2081-2023-ie00003.svg" width="33pt" height="14pt" src="essd-15-2081-2023-ie00003.png"/></svg:svg></span></span>), a proxy for SST, from the same coral to quantify temperature and <span class="inline-formula"><i>δ</i>¹⁸</span>O<span class="inline-formula">_sw</span> variability through time. To increase the utility of such reconstructions, we present the CoralHydro2k database, a compilation of published, peer-reviewed coral <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">Sr</mi><mo>/</mo><mi mathvariant="normal">Ca</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="33pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="a8fcf3e6d62388e790f29de730d47925"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="essd-15-2081-2023-ie00004.svg" width="33pt" height="14pt" src="essd-15-2081-2023-ie00004.png"/></svg:svg></span></span> and <span class="inline-formula"><i>δ</i>¹⁸</span>O records from the Common Era (CE). The database contains 54 paired <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">Sr</mi><mo>/</mo><mi mathvariant="normal">Ca</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="33pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="24501397176f693c176ed06eccebf5db"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="essd-15-2081-2023-ie00005.svg" width="33pt" height="14pt" src="essd-15-2081-2023-ie00005.png"/></svg:svg></span></span>–<span class="inline-formula"><i>δ</i>¹⁸</span>O records and 125 unpaired <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">Sr</mi><mo>/</mo><mi mathvariant="normal">Ca</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="33pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="e4eb43ce70121447c45a804baadbd9dc"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="essd-15-2081-2023-ie00006.svg" width="33pt" height="14pt" src="essd-15-2081-2023-ie00006.png"/></svg:svg></span></span> or <span class="inline-formula"><i>δ</i>¹⁸</span>O records, with 88 % of these records providing data coverage from 1800 CE to the present. A quality-controlled set of metadata with standardized vocabulary and units accompanies each record, informing the use of the database. The CoralHydro2k database tracks large-scale temperature and hydrological variability. As such, it is well-suited for investigations of past climate variability, comparisons with climate model simulations including isotope-enabled models, and application in paleodata-assimilation projects. The CoralHydro2k database is available in Linked Paleo Data (LiPD) format with serializations in MATLAB, R, and Python and can be downloaded from the NOAA National Center for Environmental Information's Paleoclimate Data Archive at <a href="https://doi.org/10.25921/yp94-v135">https://doi.org/10.25921/yp94-v135</a> (Walter et al., 2022).</p>