Comparison of the oxygen isotope signatures in speleothem records and iHadCM3 model simulations for the last millennium

• Verfasst von: Bühler, Janica C. [VerfasserIn]
• Verfasst von: Roesch, Carla [VerfasserIn]
• Verfasst von: Kirschner, Moritz [VerfasserIn]
• Verfasst von: Sime, Louise [VerfasserIn]
• Verfasst von: Holloway, Max D. [VerfasserIn]
• Verfasst von: Rehfeld, Kira [VerfasserIn]
• Titel: Comparison of the oxygen isotope signatures in speleothem records and iHadCM3 model simulations for the last millennium
• Verf.angabe: Janica C. Bühler, Carla Roesch, Moritz Kirschner, Louise Sime, Max D. Holloway, Kira Rehfeld
• E-Jahr: 2021
• Jahr: 5 May 2021
• Umfang: 20 S.
• Teil: volume:17
• Teil: year:2021
• Teil: number:3
• Teil: pages:985-1004
• Teil: extent:20
• Fussnoten: Gesehen am 07.07.2021
• Titel Quelle: Enthalten in: Climate of the past
• Ort Quelle: Katlenburg-Lindau : Copernicus Ges., 2005
• Jahr Quelle: 2021
• Band/Heft Quelle: 17(2021), 3, Seite 985-1004
• ISSN Quelle: 1814-9332
• DOI: doi:10.5194/cp-17-985-2021
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1762306387

Abstract

Abstract. Improving the understanding of changes in the mean and variability of climate variables as well as their interrelation is crucial for reliable climate change projections. Comparisons between general circulation models and paleoclimate archives using indirect proxies for temperature or precipitation have been used to test and validate the capability of climate models to represent climate changes. The oxygen isotopic ratio <span class="inline-formula"><i>δ</i>¹⁸O</span>, a proxy for many different climate variables, is routinely measured in speleothem samples at decadal or higher resolution, and single specimens can cover full glacial-interglacial cycles. The calcium carbonate cave deposits are precisely dateable and provide well preserved (semi-)continuous albeit multivariate climate signals in the lower and mid-latitudes, where the measured <span class="inline-formula"><i>δ</i>¹⁸O</span> in the mineral does not directly represent temperature or precipitation. Therefore, speleothems represent suitable archives to assess climate model abilities to simulate climate variability beyond the timescales covered by meteorological observations (<span class="inline-formula">10¹</span>-<span class="inline-formula">10²</span> years).</p> <p>Here, we present three transient isotope-enabled simulations from the Hadley Center Climate Model version 3 (iHadCM3) covering the last millennium (850-1850 CE) and compare them to a large global dataset of speleothem <span class="inline-formula"><i>δ</i>¹⁸O</span> records from the Speleothem Isotopes Synthesis and AnaLysis (SISAL) database version 2 <span class="cit" id="xref_paren.1">(<a href="#bib1.bibx14">Comas-Bru et al.</a>, <a href="#bib1.bibx14">2020</a><a href="#bib1.bibx14">b</a>)</span>. We systematically evaluate offsets in mean and variance of simulated <span class="inline-formula"><i>δ</i>¹⁸O</span> and test for the main climate drivers recorded in <span class="inline-formula"><i>δ</i>¹⁸O</span> for individual records or regions.</p> <p>The time-mean spatial offsets between the simulated <span class="inline-formula"><i>δ</i>¹⁸O</span> and the speleothem data are fairly small. However, using robust filters and spectral analysis, we show that the observed archive-based variability of <span class="inline-formula"><i>δ</i>¹⁸O</span> is lower than simulated by iHadCM3 on decadal and higher on centennial timescales. Most of this difference can likely be attributed to the records' lower temporal resolution and averaging or smoothing processes affecting the <span class="inline-formula"><i>δ</i>¹⁸O</span> signal, e.g., through soil water residence times. Using cross-correlation analyses at site level and modeled grid-box level, we find evidence for highly variable but generally low signal-to-noise ratios in the proxy data. This points to a high influence of cave-internal processes and regional climate particularities and could suggest low regional representativity of individual sites. Long-range strong positive correlations dominate the speleothem correlation network but are much weaker in the simulation. One reason for this could lie in a lack of long-term internal climate variability in these model simulations, which could be tested by repeating similar comparisons with other isotope-enabled climate models and paleoclimate databases.</p>