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Arctic permafrost soils have recently been identified as the largest mercury (Hg) reservoir on Earth. Today, rapid warming in the high latitudes may be altering the Arctic Hg cycle by accelerating permafrost thaw, leading to changes including deepening of the active layer, increasing organic matter decay, and increasing seasonal groundwater flow. However, few studies have investigated how the Hg cycle has responded to past changes in climate, and there is a lack of Arctic records that span the late glacial to early Holocene when climate conditions changed abruptly. We propose that the geochemical and physical changes in the sediment record of Burial Lake (68.43ºN, 159.17ºW; 460 m ASL), which document climatic and environmental changes in northwestern Alaska after the Last Glacial Maximum (LGM), can be used as an analog to investigate how today’s rapid warming affects Hg mobilization from permafrost soils to surficial waters. Warming in the Northern Hemisphere between ~15.0 and 8.0 ka resulted in rapid changes in northwest Alaska, including the submergence of the Bering Land Bridge that reconnected the Pacific and Arctic Oceans (~11.0 ka), in addition to changes in the hydroclimate. Our results indicate that the Hg concentration was relatively low and stable in the Burial Lake record during the transition from the LGM to the late glacial (20.0 and 16.0 ka) with a mean concentration of 64±7 μg/kg. Mercury concentrations begin to increase after 16.0 ka. Then, coinciding with a rapid temperature increase at the beginning of the Bølling Allerød (14.7 to 12.9 ka), Hg concentrations increased by ~20% and showed higher variability as temperatures fluctuated until the end of the Younger Dryas (12.9 to 11.7 ka). At 11.0 ka, the Hg concentration increased rapidly. It peaked at 140 µg/kg, with a mean Hg concentration of 119 μg/kg between 11.0 to 8.8 ka, coinciding with evidence of a rapid increase in regional precipitation and flooding of the Bering Land Bridge. From 8.8 to 0.1 ka, the mean Hg concentration decreased to 107 μg/kg and then increased rapidly over the last 100 years to a maximum concentration of 196 μg/kg occurring during the 1990s. Throughout the majority of the Burial Lake sediment record, the Hg concentration is most strongly correlated with total organic carbon content and geochemical proxies sensitive to changes in redox conditions. We interpret this finding as an indication that a large fraction of Hg is mobilized from the lake catchment along with dissolved organic matter (DOM), iron (Fe), and manganese (Mn) that are mobilized as a result of saturation and deepening of the active layer during periods of warmer, but most importantly, wetter climate. The Hg record from Burial Lake suggests that as the climate warmed after the LGM, organic-rich permafrost soils and Hg accumulated in the catchment. The sudden increase in Hg mobilization from permafrost soils was then initiated at the onset of the Holocene due to the rapid increase in precipitation that coincided with the flooding of the Bering Land Bridge.

Early Pleistocene Marine Isotope Stage (MIS)-31 (1.081–1.062 Ma) is a unique interval of extreme global warming, including evidence of a West Antarctic Ice Sheet (WAIS) collapse. Here we present a new 1,000-year resolution, spanning 1.110–1.030 Ma, diatom-based reconstruction of primary productivity, relative sea surface temperature changes, sea-ice proximity/open ocean conditions and diatom species absolute abundances during MIS-31, from the Scotia Sea (59°S) using deep-sea sediments collected during International Ocean Discovery Program (IODP) Expedition 382. The lower Jaramillo magnetic reversal (base of C1r.1n, 1.071 Ma) provides a robust and independent time-stratigraphic marker to correlate records from other drill cores in the Antarctic Zone of the Southern Ocean (AZSO). An increase in open ocean species Fragilariopsis kerguelensis in early MIS-31 at 53°S (Ocean Drilling Program Site 1,094) correlates with increased obliquity forcing, whereas at 59°S (IODP Site U1537; this study) three progressively increasing, successive peaks in the relative abundance of F. kerguelensis correlate with Southern Hemisphere-phased precession pacing. These observations reveal a complex pattern of ocean temperature change and sustained sea surface temperature increase lasting longer than a precession cycle within the Atlantic sector of the AZSO. Timing of an inferred WAIS collapse is consistent with delayed warmth (possibly driven by sea-ice dynamics) in the southern AZSO, supporting models that indicate WAIS sensitivity to local sub-ice shelf melting. Anthropogenically enhanced impingement of relatively warm water beneath the ice shelves today highlights the importance of understanding dynamic responses of the WAIS during MIS-31, a warmer than Holocene interglacial., SI

International Ocean Drilling Program (IODP) Expedition 341 in the Gulf of Alaska recovered a 112-meter-long sedimentary record from the continental slope at Site U1419. At this site, an exceptionally expanded late Pleistocene sequence (sedimentation rates >100 cm/kyr) combined with a high-resolution radiocarbon chronology (Walczak et al., 2020), provide an opportunity to study Paleomagnetic Secular Variations (PSV) on centennial to millennial timescales over the past ~43,000 years.Natural and laboratory-induced magnetic remanence were measured on u-channels using the stepwise AF demagnetization procedure. In addition to continuous magnetic susceptibility measurements, hysteresis parameters were obtained on 95 discrete samples, and IRM acquisition curves on 9 discrete samples to obtain additional information on the magnetic mineralogy of the sediment. Due to the influence of lithology, magnetic mineralogy, depositional and post-depositional processes, Site U1419 is not suitable for paleointensity studies. However, with removal of intervals influenced by the environmental signal and/or coring deformation, the high sedimentation rates at this site have helped to preserve a reliable record of inclination. Because of signal to noise issues, inclination as measured after the 20 mT AF demagnetization step provides the most accurate estimate. This is demonstrated by comparing the U1419 inclination to a stack of the shipboard inclination at Site U1418 on a new age model developed from 19 radiocarbon dates on U1418 and 18 magnetic susceptibility-based tie-points to site survey core EW0408-87JC (Praetorius et al., 2015). This independently replicated inclination record verifies centennial to millennial scale variations in the Gulf of Alaska that can now be compared with other northeast Pacific and western North American records to begin deciphering geomagnetic variability and provide a new stratigraphic correlation tool for 15 and 30 cal kyr BP interval in this region.

This article elaborates on some of the heuristic dimensions of instructional development put forth by Haney, Lange, and Barson in the late sixties. In addition, several new heuristic guidelines are presented and more recent articles on heuristic guidelines are discussed. These new guidelines provide additional common sense approaches to instructional development (ID) which the authors discovered while working on a series of interinstitutional instructional development projects. The old and new heuristic approaches are based on first hand experience in the field. Some of the new guidelines are specific to multiple institution ID projects. Others have applicability for any type of ID project.