Using airflow-driven, evaporative gradients to improve sensitivity and fluid control in colorimetric paper-based assays

An airflow based, evaporative enrichment method for use in microfluidic paper-based assays. The method is used for fluid control in a multistep assay and as a technique to improve sensitivity in colorimetric detection assays.

Palaeotemperature estimation in the Holsteinian Interglacial (MIS 11) based on oxygen isotopes of aquatic gastropods from eastern Poland

For quantitative estimation of past water temperature of four Holsteinian (MIS 11) palaeolakes from eastern Poland, the oxygen isotope palaeothermometer was applied to shells of the aquatic gastropodsViviparus diluvianusandValvata piscinalis. The δ18O composition of their shells demonstrated the average growth-season water temperatures during the mesocratic stage of the interglacial (Ortel Królewski Lake), during its climatic optimum – theCarpinus–AbiesZone (Ossówka-Hrud, Roskosz and Szymanowo Lakes), and in the post-optimum (Szymanowo Lake). The calculation was based on δ18OShellvalues and the δ18OWaterassumed for the Holsteinian from the modern oxygen isotope composition of precipitation and the expected amount of evaporative enrichment. The mean oxygen isotope palaeotemperatures of Ortel Królewski lake waters were in the range of 18.1–21.9°C and were uniform for theTaxusandPinus–Larixzones. Ossówka-Hrud and Roskosz Lakes had mean temperatures of 17.4–21.0°C during the climatic optimum, whereas the temperature of Szymanowo lake waters was estimated at 20.6–21.7°C at that time. These values are concordant with the pollen-inferred July air temperatures noted during the Holsteinian in eastern Poland. Relatively high values of ~25°C in the post-optimum noted at Szymanowo were connected with the presence of a shallow and warm isolated bay indicated by pollen and mollusc records.

Geochemical characteristics of glacial Lake Agassiz sediments and new ages for the Moorhead Phase at Fargo, North Dakota, USA

The cause and age of the Moorhead low-water Phase of glacial Lake Agassiz remains uncertain. New geochemical (X-ray fluorescence (XRF) and elemental analysis) and chronological (optically stimulated luminescence (OSL)) data are used to test for evaporative enrichment within lacustrine sediment from Rabbit Lake, a small basin just above the highest Lake Agassiz strandline, and from two Lake Agassiz sediment cores at Fargo, North Dakota. Increases in quartz and gypsum interpreted to be of aeolian origin suggest increased aridity at Rabbit Lake sometime after 13 540–13 750 cal years BP. From the Fargo cores, lacustrine sediment of the Brenna and Sherack formations did not show convincing evidence for evaporative enrichment. However, this result is complicated by an erosional contact at the top of the Brenna Formation. A thin middle sand unit between the Brenna and Sherack formation clays is stratigraphically equivalent to the Poplar River Formation, West Fargo Member, but its properties differ from the fluvial sand of the West Fargo Member. Four OSL ages from the organic-poor, middle sand unit at Fargo range between 12.8 ± 0.2 and 13.5 ± 0.2 ka (with ±1.6 ka uncertainty) and suggest lake level fell at Fargo at, or before, 13.1 ± 0.2 ka, the average of the OSL ages. With different sedimentological properties, and a difference of ∼1750 years between the new OSL ages and previously published ages on the West Fargo Member sand, additional work is required to determine whether the middle sand unit is a new member of the Poplar River Formation, recording an earlier and different depositional environment than the West Fargo Member. From a plot of available ages for the Moorhead Phase, the regression remains poorly constrained in time.

Stable-isotope paleoclimate records for southern Ontario, Canada: comparison of results from marl and wood

Profiles of δ18O in two marl cores from southern Ontario, Canada, are compared in detail with the records of meteoric water isotopic composition and photosynthetic humidity obtained from previous isotopic studies using wood cellulose at Brampton, Ontario. By accounting for the inferred changes in meteoric water composition and temperature, the changes in the oxygen-isotope content of the marl arising from fluctuations in the evaporative enrichment of the lakewater can be estimated. The resulting synthetic profiles of relative evaporative enrichment from both marl cores exhibit strong correspondence to the photosynthetic humidity profile generated from the studies at Brampton, which substantiates the importance of evaporation in the water budgets of these two lakes. A striking analogy exists between the isotopic evaporative enrichment response of such lakewaters and that of the waters in terrestrial plants; both of the marl lakes approach close to isotopic steady state during the summer season, when carbonate precipitation occurs.The results of these studies strengthen the basis for paleoclimatic interpretations suggested in previous reports. Most notably, the marl data yield further evidence for relatively dry conditions in southern Ontario during the early part of the Hypsithermal interval, at a time that coincides with maximum eastward extension of prairie in the midwest United States.