Growth Interruptions in Arctic Rhodoliths Correspond to Water Depth and Rhodolith Morphology

Coralline algae that form rhodoliths are widespread globally and their skeletal growth patterns have been used as (paleo-) environmental proxies in a variety of studies. However, growth interruptions (hiati) within their calcareous skeletons are regarded as problematic in this context. Here we investigated how hiati in the growth of Arctic rhodoliths from the Svalbard archipelago correspond to their environment and morphology. Using X-ray micro-computed tomography and stepwise model selections, we found that rhodoliths from deeper waters are subject to more frequent hiatus formation. In addition, rhodoliths with a higher sphericity (i.e., roundness) are less often affected by such growth interruptions. We conclude that these correlations are mainly regulated by hydrodynamics, because, in deeper waters, rhodoliths are not turned frequently enough to prevent a dieback of coralline algal thalli forming on the underside of the rhodolith. In this coherence, spheroidal rhodoliths are turned more easily, therefore shortening the amount of time between turnover events. Moreover, the incidence of light is more advantageous in shallower waters where rhodoliths exhibit a greater share of their surface to diffused ambient light, thus enabling thallus growth also on the down-facing surface of the rhodoliths. In consequence, information on the frequency of hiatus formation combined with rhodolith morphology might serve as a valuable proxy for (paleo-)environmental reconstructions in respect to light availability and the hydrodynamic regime.

Holocene moisture variations in western arid central Asia inferred from loess records from NE Iran

<p>Holocene variations in precipitation in central and eastern arid central Asia (ACA) have been widely investigated, but the pattern in western ACA remains unclear. We present records of the stable carbon isotope composition of bulk organic matter (δ<sup>13</sup>C<sub>org</sub>), magnetic parameters, and sediment color, from five loess-paleosol sequences in NE Iran, in western ACA, with the aim of reconstructing Holocene precipitation. The Yellibadragh (YE) section (the thickest among the five sequences) was selected for OSL dating of the coarse-grained quartz (63-90 μm) fraction, and its δ<sup>13</sup>C<sub>org </sub>record was used to quantitatively reconstruct mean annual precipitation (MAP). The record indicates a dry early Holocene (~11.8-7.4 ka), with nearly constant MAP (~93 mm), followed by a wetting trend from the mid-Holocene (~7.4 ka) onwards, with the wettest period in the late Holocene (~4.0-0.0 ka, ~390 mm). The stratigraphic observations and environmental proxies support the reconstruction. The other loess profiles show stratigraphic features and trends of environmental proxies which are similar to those of the YE profile. A dry early Holocene and wetting trend since the mid-Holocene, with the wettest climate in the late Holocene in NE Iran, are both consistent with records from sand dunes and lake sediments from adjacent areas, and with loess records from central and eastern ACA. Comparison with loess records from monsoonal Asia supports the interpretation of a “westerlies-dominated climatic regime” (WDCR) which was proposed mainly on the basis of lake sediment records from the region. Changes in solar insolation may have been responsible for the persistent wetting trend during the Holocene in western ACA.</p>

Ancient Organic Residues as Cultural and Environmental Proxies: The Value of Legacy Objects

Often treated as an accessory science, organic residue analysis (ORA) has the capacity to illuminate otherwise hidden aspects of ancient technology, culture, and economy, and therein can play a central role in archaeological inquiry. Through ORA, both the intact vessel freshly excavated from a tomb and the sherd tucked away in a museum storage closet can offer insights into their contents, their histories, and the cultures that created them—provided the results can be carefully calibrated to account for their treatment during and after excavation. The case study below presents ORA data obtained from a range of artifacts from Late Bronze Age Crete, setting results from freshly-excavated and legacy objects alongside one another. Although legacy objects do tend to yield diminished results from both a quantitative and qualitative perspective, our comparative work has demonstrated both their value and untapped potential when their object biographies are carefully considered. It also sheds light on biomarker degradation processes, which have implications for methodologies of extraction and interpretation of legacy objects. Comparative studies such as these broaden the pool of viable ORA candidates, and therein amplify ORA’s ability to reveal patterns of consumption as well as ecological and environmental change. They also highlight the role and value of data-sharing in collaborative environments such as the OpenARCHEM archaeometric database.