Last Interglacial sea-level proxies in the western Mediterranean

We describe a database of Last Interglacial (Marine Isotopic Stage 5) sea-level proxies for the western Mediterranean region. The database was compiled reviewing the information reported in 199 published studies and contains 396 sea-level data points (sea-level index points and marine- or terrestrial-limiting points) and 401 associated dated samples. The database follows the standardized WALIS template and is available as Cerrone et al. (2021b, https://doi.org/10.5281/zenodo.5341661).

Post-IR IRSL chronology of paleo-lacustrine sediments from yardangs in the Qaidam Basin, ne Tibetan Plateau

The Qaidam Basin preserves the largest Yardang field on Earth, and yardangs are intriguing landforms for studies of the paleo-environment and aeolian processes. Formation of yardangs involved both the initial lacustrine deposition and the subsequent wind-erosion processes. However, the timings of both processes in the Qaidam Basin are still controversial due to limited age data and unsuitable dating methodology. In this paper, we first compared two optical dating methods to determine the suitable one for the study area, then investigated the geomorphic processes based on the new ages. Two-step post-IR IRSL (pIRIR) and multi-elevated-temperature pIRIR (MET-pIRIR) methods of feldspar, were applied to date lacustrine sediments on the top parts of yardangs to decipher the transition time from depositional to an erosional environment. Comparisons of the two methods demonstrated that the influence from anomalous fading was very minimal thus negligible for MET-pIRIR method, as proved by the De plateau between MET-pIRIR250 and MET-pIRIR290; while the pIR50IR250 signals suffered from fading obviously, which was difficult to be corrected due to the high De close to saturation. Consequently, the chronology in this study was based on the MET-pIRIR250 method, potentially offering reliable ages of over 200 ka. Seven MET-pIRIR250 ages of 201–336 ka suggested that a mega-Qaidam Lake (>2714 m a.s.l. on Google Earth) maintained until Marine Isotopic Stage (MIS) 7. The absence of sediments since ca. 200 ka implied wind-erosion and yardang formation since MIS6. This transition from lacustrine to a wind-erosion environment was interpreted as a response to the glacial-interglacial scale climatic changes.

Last Interglacial sea-level proxies in the Western Mediterranean

We describe a database of Last Interglacial (Marine Isotopic Stage 5) sea-level proxies for the Western Mediterranean region. The database was compiled reviewing the information reported in 179 published studies and contains 371 sea-level datapoints (sea-level index points and marine or terrestrial limiting points) and 304 associated dated samples. The database follows the standardized WALIS template and is available as Cerrone et al, 2021b (https://doi.org/10.5281/zenodo.4497365).

Last Interglacial sea-level proxies in East Africa and the Western Indian Ocean

In this paper, we describe a sea-level database compiled using published Last Interglacial, Marine Isotopic Stage 5 (MIS 5), geological sea-level proxies within Eastern Africa and the Western Indian Ocean (EAWIO). Encompassing vast tropical coastlines and coralline islands, this region has many occurrences of well preserved last interglacial stratigraphies. Most notably, islands almost entirely composed by Pleistocene reefs (such as Aldabra, the Seychelles) have provided reliable paleo relative sea-level indicators and well-preserved samples for U-series chronology. Other sea-level proxies include uplifted marine terraces in the north of Somalia and tidal notches in luminescence limited aeolian deposits in Mozambique. Our database has been compiled using the World Atlas of Last Interglacial Shorelines (WALIS) interface and contains 57 sea-level indicators and 2 terrestrial limiting data points. The database is available open access at https://doi.org/10.5281/zenodo.4043366 (Version 1.02) (Boyden et al., 2020).

Coccolithophore productivity at the western Iberian Margin during the Middle Pleistocene (310–455 ka) – evidence from coccolith Sr∕Ca data

Coccolithophores contribute significantly to marine primary productivity and play a unique role in ocean biogeochemistry by using carbon for photosynthesis (soft-tissue pump) and for calcification (carbonate counter pump). Despite the importance of including coccolithophores in Earth system models to allow better predictions of the climate system's responses to planetary change, the reconstruction of coccolithophore productivity mostly relied on proxies dependent on accumulation and sedimentation rates and preservation conditions. In this study we used an independent proxy, based on the coccolith fraction (CF) Sr∕Ca ratio, to reconstruct coccolithophore productivity. We studied the marine sediment core MD03-2699 from the western Iberian margin (IbM), concentrating on glacial–interglacial cycles of Marine Isotopic Stage (MIS) 12 to MIS 9. We found that IbM coccolithophore productivity was controlled by changes in the oceanographic conditions, such as in sea surface temperature (SST) and nutrient availability, and by competition with other phytoplankton groups. Long-term coccolithophore productivity was primarily affected by variations in the dominant surface water mass. Polar and subpolar surface waters during glacial substages were associated with decreased coccolithophore productivity, with the strongest productivity minima concomitant with Heinrich-type events (HtEs). Subtropical, nutrient-poorer waters, increased terrigenous input, and moderate to strong upwelling during the deglaciation and early MIS11 are hypothesized to have attributed a competitive advantage to diatoms to the detriment of coccolithophores, resulting in intermediate coccolithophore productivity levels. During the progression towards full glacial conditions an increasing presence of nutrient-richer waters, related to the growing influence of transitional surface waters and/or intensified upwelling, probably stimulated coccolithophore productivity to maxima following the rapid depletion of silica by diatoms. We present conceptual models of the carbon and carbonate cycle components for the IbM in different time slices that might serve as a basis for further investigation and modelling experiments.

High frequency water isotopes records during glacial/interglacial cycles on EPICA Dome C ice core.

<p>The iconic curve of D in water showing the 8 glacial/interglacial cycles from the EPICA Dome C ice<br>core is now a reference in paleoclimate. It shows past temperature variability back to 800 ka over the<br>3200 m deep ice core with a 55 cm resolution. However, the millennial and centennial scale<br>variability gets more challenging to observe in the deepest part of the core. Indeed, the time<br>resolution worsens when going deeper in the ice because of the ice thinning: it is larger than 200<br>years at 2500 m depth. Furthermore, isotopic diffusion affects the signal at the bottom of the ice<br>core. Pol et al., (2010) have thus shown that the sub-millennial MIS (Marine Isotopic Stage) 19 signal<br>(3157-3181 m deep) is erased because of diffusion and high resolution doesn’t add any further<br>information at this depth. In this study we want to better characterize the increase of the isotopic<br>diffusion with depth by providing new high resolution water isotopes at several intervals over the<br>EPICA ice core (EDC).<br>We present here published high resolution (11 cm) d18O measurements over the EDC ice core as<br>well as new records of high resolution (11 cm) D over MIS 7;13 and 14). We use spectral analyses to<br>determine at which depth the isotopic diffusion erases the sub-millennial variability. We also show<br>that cold periods exhibit a larger variability of water isotopes than interglacial periods.<br>The information obtained here is crucial for the new project Beyond EPICA oldest ice core, which has<br>the goal of analyzing a 1.5 Ma old ice core. In the deepest part, 1 m of ice core could represent<br>10 000 years of climate archive.</p>

Tectonism and volcanism enhanced by deglaciation events in southern Iceland

Southern Iceland is one of the main outlets of the Icelandic ice sheet and is subject to seismicity of both tectonic and volcanic origins along the South Iceland Seismic Zone (SISZ). A sedimentary complex spanning Marine Isotopic Stage 6 (MIS 6) to the present includes evidence of both activities. It includes a continuous sedimentary record since the Eemian interglacial period, controlled by a rapid deglaciation, followed by two marine glacioisostasy-forced transgressions, separated by a regression phase connected to an intra-MIS 5e glacial advance. This record has been constrained by tephrostratigraphy and dating. Analysis of this record has provided better insights into the interconnectedness of hydrology and volcanic and tectonic activity during deglaciations and glaciations. Low-intensity earthquakes recurrently affected the water-laid sedimentation during the early stages of unloading, accompanying rifting events, dyke injection, and fault reactivations. During full interglacial periods, earthquakes were significantly less frequent but of higher magnitude along the SISZ, due to stress accumulation, favored by low groundwater levels and more limited magma production. Occurrence of volcanism and seismicity in Iceland is commonly related to rifting events. Subglacial volcanic events seem moreover to have been related to stress unlocking related to limited or full unloading/deglaciation events. Major eruptions were mostly located at the melting margin of the ice sheet.