No abstract

Abstract. A new high-resolution paleointensity record for North America has been constructed using Holocene sediments from Lake Pepin, Minnesota. Lake Pepin sediments yield the same Holocene paleosecular variation curve as nearby Lake St. Croix and satisfy all of the criteria recommended for paleointensity studies. Absolute paleointensity data for North America recorded by Holocene volcanic and archeomagnetic samples provide an independent record of geomagnetic field paleointensity against which the relative intensity records from Lake Pepin and Lake St. Croix can be compared. Since the absolute field paleointensity is known a priori, the effects of the magnetic recording assemblage can be isolated. Anhysteretic remanent magnetization (ARM) is the best choice among normalization parameters for the Lake Pepin sediments as the natural remanent magnetization (NRM) normalized by ARM shows no coherence with magnetic grain size proxies and yields a record of relative paleointensity peaks and troughs whose amplitudes are very similar to those in the archeomagnetic (ARCMAG) and Lake St. Croix data sets. Features with a wavelength of 1000 years are correlative between the three paleointensity records. NRM normalized by saturation isothermal remanent magnetization (SIRM) and by susceptibility (Z) shows grain-size dependences that cause errors in the amplitudes of paleointensity features. NRM/SIRM and NRM/z are not coherent with their normalizers but are both strongly coherent with independent grain size proxies such as the median destructive field of the NRM and HcR. We successfully removed the grain size dependences from NRM/SIRM by applying a correction function based on the linear relationship between normalized intensity and the median destructive field of the NRM.

No abstract

Elevated concentrations of toxic elements in coal ash pose human and ecological health risks upon release to the environment. Despite wide public concerns about water quality and human health risks from catastrophic coal ash spills and chronic leaking of coal ash ponds, coal ash disposal has only been partially regulated, and its impacts on aquatic sediment quality and ecological health have been overlooked. Here, we present a multiproxy approach of morphologic, magnetic, geochemical, and Sr isotopic analyses, revealing unmonitored coal ash releases over the past 40 to 70 years preserved in the sediment records of five freshwater lakes adjacent to coal-fired power plants across North Carolina. We detected significant sediment contamination and potential chronic ecological risks posed by the occurrence of hundreds of thousands of tons of coal ash solids mainly resulting from high-magnitude stormwater runoff/flooding and direct effluent discharge from coal ash disposal sites. The proximity of hundreds of disposal sites to natural waterways across the U.S. implies that such contamination is likely prevalent nationwide and expected to worsen with climate change.

Antarctica is one of the most vulnerable regions to climate change on Earth and studying the past and present responses of this polar marine ecosystem to environmental change is a matter of urgency. Sedimentary ancient DNA (sedaDNA) analysis can provide such insights into past ecosystem-wide changes. Here we present authenticated (through extensive contamination control and sedaDNA damage analysis) metagenomic marine eukaryote sedaDNA from the Scotia Sea region acquired during IODP Expedition 382. We also provide a marine eukaryote sedaDNA record of ~1 Mio. years and diatom and chlorophyte sedaDNA dating back to ~540 ka (using taxonomic marker genes SSU, LSU, psbO). We find evidence of warm phases being associated with high relative diatom abundance, and a marked transition from diatoms comprising <10% of all eukaryotes prior to ~14.5 ka, to ~50% after this time, i.e., following Meltwater Pulse 1A, alongside a composition change from sea-ice to open-ocean species. Our study demonstrates that sedaDNA tools can be expanded to hundreds of thousands of years, opening the pathway to the study of ecosystem-wide marine shifts and paleo-productivity phases throughout multiple glacial-interglacial cycles.