Bernhard Diekmann

The subarctic North Pacific receives and preserves substantial amounts of terrestrial organic matter, yet the limited taxonomic resolution of traditional isotope and biomarker proxies constrains our ability to identify its source taxa and source regions, leaving its provenance and transport dynamics poorly understood. Here we use land-plant sedimentary ancient DNA (sedaDNA) metabarcoding to trace terrestrial plant organic matter in marine sediment cores from off-Kamchatka and the Bering Sea. We achieved unprecedented taxonomic resolution for marine sedaDNA records, identifying 328 terrestrial plant taxa, including 173 resolved to species level, across the two marine cores. Comparison with Siberian and Alaskan lake sedaDNA records showed that terrestrial plant assemblages recovered from the marine cores broadly reflected regional vegetation patterns and their temporal changes, while contrasts in relative taxon abundances indicated taphonomic filtering in marine sedaDNA records. Compositional relationships between the marine and lacustrine records, together with Siberian- and Alaskan-associated indicator taxa (e.g., Spiraea salicifolia and Shepherdia canadensis), provided taxonomic evidence for regional source attribution. Across the glacial–interglacial transition, the two marine records preserved distinct regional vegetation histories. Diversity patterns differed between the sites, with the Bering Sea record more strongly influenced by deglacial terrigenous delivery and the off-Kamchatka record more closely associated with postglacial warming. Our results demonstrate the potential of targeted sedaDNA metabarcoding as a high-resolution tool for tracing terrestrial organic matter in high-latitude oceans and highlight the need for expanded DNA reference databases and improved understanding of marine sedaDNA taphonomy.

The subarctic North Pacific receives and preserves substantial amounts of terrestrial organic matter, yet the limited taxonomic resolution of traditional isotope and biomarker proxies constrains our ability to identify its source taxa and source regions, leaving its provenance and transport dynamics poorly understood. Here we use land-plant sedimentary ancient DNA (sedaDNA) metabarcoding to trace terrestrial plant organic matter in marine sediment cores from off-Kamchatka and the Bering Sea. We achieved unprecedented taxonomic resolution for marine sedaDNA records, identifying 328 terrestrial plant taxa, including 173 resolved to species level, across the two marine cores. Comparison with Siberian and Alaskan lake sedaDNA records showed that terrestrial plant assemblages recovered from the marine cores broadly reflected regional vegetation patterns and their temporal changes, while contrasts in relative taxon abundances indicated taphonomic filtering in marine sedaDNA records. Compositional relationships between the marine and lacustrine records, together with Siberian- and Alaskan-associated indicator taxa (e.g., Spiraea salicifolia and Shepherdia canadensis), provided taxonomic evidence for regional source attribution. Across the glacial–interglacial transition, the two marine records preserved distinct regional vegetation histories. Diversity patterns differed between the sites, with the Bering Sea record more strongly influenced by deglacial terrigenous delivery and the off-Kamchatka record more closely associated with postglacial warming. Our results demonstrate the potential of targeted sedaDNA metabarcoding as a high-resolution tool for tracing terrestrial organic matter in high-latitude oceans and highlight the need for expanded DNA reference databases and improved understanding of marine sedaDNA taphonomy.

Published marine sediment chronologies from the subarctic North Pacific differ in calibration curves, reservoir corrections, input selection, and modelling conventions, complicating comparisons among palaeoceanographic records. We present a chronology framework for 17 cores from the Bering Sea, Gulf of Alaska, Sea of Okhotsk, and open subarctic North Pacific. The main inventory contains 19 core or segment records: 16 Marine20–rbacon reconstructions, two separately identified legacy calendar-age models, and one segment without a chronology. The 18 canonical age-model tables provide posterior median ages and pointwise 95 % intervals on a standardized 201-depth grid. Users can assign these ages to depth-registered proxy measurements from the same cores after verifying depth-scale correspondence; the framework cannot date a new core without its own chronological constraints. The archive preserves 555 chronology-control rows with their provenance, material roles, and admission decisions. The 18 verified formal model-input files contain 285 rows representing 282 dated-depth clusters or legacy calendar-age nodes. Twenty-eight constraints misassigned to surface chronology during an earlier stage of this compilation are retained with their material-role and exclusion records, allowing users to inspect or revise the admission decisions. The primary precision descriptor is the median width of the pointwise 95 % posterior age interval within each dated interval. Among 14 inventory rows assigned a derived convenience bin, this statistic ranges from 677 to 2765 yr, with a median of approximately 1100 yr. Sampling diagnostics are reported at all evaluation depths. Independent reruns of four preselected records changed this continuous statistic by at most 6.64 yr, although one boundary-adjacent record crossed a derived-bin boundary. Posterior precision is conditional on calibration, the reservoir correction and its adopted date-level uncertainty, input representation, and the modelling protocol; it does not establish absolute chronological accuracy. The adopted reservoir corrections are based on modern observations, whereas deglacial reservoir histories remain incompletely constrained. The release combines age tables, audited inputs, cluster definitions, diagnostics, per-record JSON/CSV packages, source references, and implementation records to support reuse and alternative chronological modelling. Executed model inputs are preserved, but recovery of the full source-to-prepared transformation chain is incomplete. The data are deposited at PANGAEA under https://doi.pangaea.de/10.1594/PANGAEA.996868.

The subarctic North Pacific receives and preserves substantial amounts of terrestrial organic matter, yet the limited taxonomic resolution of traditional isotope and biomarker proxies constrains our ability to identify its source taxa and source regions, leaving its provenance and transport dynamics poorly understood. Here we use land-plant sedimentary ancient DNA (sedaDNA) metabarcoding to trace terrestrial plant organic matter in marine sediment cores from off-Kamchatka and the Bering Sea. We achieved unprecedented taxonomic resolution for marine sedaDNA records, identifying 328 terrestrial plant taxa, including 173 resolved to species level, across the two marine cores. Comparison with Siberian and Alaskan lake sedaDNA records showed that terrestrial plant assemblages recovered from the marine cores broadly reflected regional vegetation patterns and their temporal changes, while contrasts in relative taxon abundances indicated taphonomic filtering in marine sedaDNA records. Compositional relationships between the marine and lacustrine records, together with Siberian- and Alaskan-associated indicator taxa (e.g., Spiraea salicifolia and Shepherdia canadensis), provided taxonomic evidence for regional source attribution. Across the glacial–interglacial transition, the two marine records preserved distinct regional vegetation histories. Diversity patterns differed between the sites, with the Bering Sea record more strongly influenced by deglacial terrigenous delivery and the off-Kamchatka record more closely associated with postglacial warming. Our results demonstrate the potential of targeted sedaDNA metabarcoding as a high-resolution tool for tracing terrestrial organic matter in high-latitude oceans and highlight the need for expanded DNA reference databases and improved understanding of marine sedaDNA taphonomy.

Two joint Canadian-German expeditions at Lake Wiyâshâkimî (56.2°N, 74.4°W) were devoted to limnogeological research of the deglacial history of the Laurentide Ice Sheet in northeastern Canada. The lake is located on the Canadian Shield, roughly 150 km east of the southern Hudson Bay coast. It was formed by two meteorite impacts in the late Ordovician and early Permian. The intersected double crater structure of the 60 x 30 km large and up to 178 m deep lake is preserved until today. During the Quaternary, it was repeatedly covered by the Laurentide Ice Sheet. A hydrolological survey in summer 2023 confirmed the oligotrophic nature and well mixed water column of the freshwater lake. Geophysical subbottom profiling exhibited an ice-scoured bottom of the lake floor with only a thin veneer of postglacial mud. An 8 m-long sediment core was taken in spring 2024 at 110 m water depth within a depression including a pocket of preserved older sediments. Sediment analytics comprised radiocarbon dating, smear-slide studies, elemental x-ray scanning, determination of total organic carbon and nitrogen, pollen analysis as well as stable-isotope analysis of organic carbon (δ13C) and oxygen of diatom frustules (δ18O). The lower 6.5 m of the sediment core sequence comprises meltwater sands partly varve-like laminated. Radiocarbon ages of this interval scatter around 30 cal ka BP and are difficult to ascertain, because of reworked older organic matter. The sand is overlain by a 0.65 m thick grayish clay layer with a basal age of 22 cal ka BP. It provides evidence for stagnant glaciolacustrine conditions below or in front of the retreating Laurentide Ice Sheet. The deposition of brownish diatom-bearing organic muds started at 6.5 cal ka BP. Pollen data indicate Holocene reforestation in the catchment since that time. This timing is well consistent with geomorphological evidence of regional glacial decay. Based on geochemical indicators, there is no evidence for a marine incursion related to the 8.2-ka event.

Ecological connectivity shapes ecosystem responses to climate change and is thought to underpin stability, yet its millennial-scale dynamics remain poorly resolved. We asked how spatial and temporal connectivity of plant metacommunities changed over the last 40 ka and which processes drove it. We analysed and compiled plant sedimentary DNA from 20 lake cores across Beringia (Siberia, Alaska) to investigate community dynamics and, for a high-resolution subset, applied beta- and zeta-diversity to track connectivity. Vegetation changed coherently across the glacial–Holocene transition, with trait shifts mirroring functional composition. Connectivity peaked during the late MIS3 and Last Glacial Maximum—likely aided by the Bering Land Bridge, mass effects and facilitation—collapsed during the Deglacial with rapid turnover, and rebounded in the Holocene as shrub and boreal communities expanded. Temporal zeta within sites exceeded spatial zeta, indicating strong local persistence and resilience. Tundra sites uninvaded by forest maintained continuous species pools. Overall, these patterns underscore the value of a metacommunity perspective for assessing millennial-scale connectivity changes.

Amid accelerating defaunation, it remains unclear whether the loss of large mammals can trigger ecosystem collapse and through which functional pathways. Using sedimentary ancient metagenomics, we identify an overlooked role of large mammal defaunation in helping drive the collapse of the glacial mammoth-steppe. Network analyses identified rewiring of mammal interactions during the late glacial supporting cascading effects. Crucially, megafaunal-mediated long-distance seed dispersal buffered vegetation turnover during periods of rapid climate warming but weakened with progressive losses of vital dispersal interactions leading to the steppe–tundra’s transition to open woodland in the early Holocene. Trophic interactions did not offset turnover and became dominant afterwards with the more stable climate. We identified resilient interactions that may support recovery, suggesting the potential of rewilding to restore Arctic ecosystems. One-sentence Ancient metagenomics reveals disrupted long-distance seed dispersal helped drive mammoth-steppe collapse and informs Arctic rewilding efforts.

The Antarctic Zone has long been suspected to play a crucial role in the glacial-interglacial changes in atmospheric concentration of CO2. However, global climate has many possible influences on Antarctic Zone conditions, with the potential for interactions between ice, winds and circulation that, in turn, influence the biogeochemistry and carbon budget of the Antarctic Zone surface. In a sediment core from the polar Antarctic Zone, we analyzed diatom-bound nitrogen isotopes to reconstruct surface nitrate concentration, which reflects the balance between biological productivity and the flux of subsurface nitrate into the Antarctic surface. The record covers the last 150 kyr, which includes two peak glacial periods and the subsequent deglaciations and interglacials. During each glacial period, the data support prior interpretations of lower surface nitrate concentrations and reduced circulation-driven nitrate supply to the Antarctic surface, although the change appears to be weaker at this polar Antarctic Zone site than in records from further north in the open Antarctic Zone. Early in each deglaciation, there is a further decline in surface nitrate concentration, reflecting a rise in density stratification. This is followed by an increase in nutrient supply in each of the two interglacials, signaling more vigorous surface-subsurface exchange than during the glacials or the early deglaciations. Combining the data with other Antarctic records further from the continent, the deglacial changes echo model simulations of ongoing global warming, in which upwelling increases near the Polar Front, while subsurface influx to the surface closer to the Antarctic continent decreases in response to ice sheet melting. The findings have implications for the cause of the observed rise in atmospheric CO2 concentrations during deglaciations and also warrant consideration with regard to the future of the ocean’s uptake of global warming heat and fossil fuel-derived CO2.

Oxygen isotopes in biogenic silica (δ¹⁸O_BSi) from lake sediments allow for quantitative reconstruction of past hydroclimate and proxy-model comparison in terrestrial environments. The signals of individual records have been attributed to different factors, such as air temperature (T_air), atmospheric circulation patterns, hydrological changes, and lake evaporation. While every lake has its own local set of drivers of δ¹⁸O variability, here we explore the extent to which regional or even global signals emerge from a series of paleoenvironmental records. This study provides a comprehensive compilation and combined statistical evaluation of the existing lake sediment δ¹⁸O_BSi records, largely missing in other summary publications (i.e. PAGES network). For this purpose, we have identified and compiled 71 down-core records published to date and complemented these datasets with additional lake basin parameters (e.g. lake water residence time and catchment size) to best characterize the signal properties. Records feature widely different temporal coverage and resolution, ranging from decadal-scale records covering the past 150 years to records with multi-millennial-scale resolution spanning glacial–interglacial cycles. The best coverage in number of records (N = 37) and data points (N = 2112) is available for Northern Hemispheric (NH) extratropical regions throughout the Holocene (roughly corresponding to Marine Isotope Stage 1; MIS 1). To address the different variabilities and temporal offsets, records were brought to a common temporal resolution by binning and subsequently filtered for hydrologically open lakes with lake water residence times < 100 years. For mid- to high-latitude (> 45° N) lakes, we find common δ¹⁸O_BSi patterns among the lake records during both the Holocene and Common Era (CE). These include maxima and minima corresponding to known climate episodes, such as the Holocene Thermal Maximum (HTM), Neoglacial Cooling, Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). These patterns are in line with long-term air temperature changes supported by previously published climate reconstructions from other archives, as well as Holocene summer insolation changes. In conclusion, oxygen isotope records from NH extratropical lake sediments feature a common climate signal at centennial (for CE) and millennial (for Holocene) timescales despite stemming from different lakes in different geographic locations and hence constitute a valuable proxy for past climate reconstructions.

Grasslands on the northeastern Tibetan Plateau are particularly sensitive to changes in climate and herbivory. As two main compositions, Poaceae and Cyperaceae supply forage and support herbivory survival. However, to taxonomic resolution restriction of traditional plant proxies, the plant composition and richness change of vegetation in particular of Poaceae and Cyperaceae are still largely unknown. Here, we reconstruct the vegetation using Lake Donggi Cona sediment ancient DNA metabarcoding, targeting chloroplast trnL P6 loop (g h primer). To increase Poaceae and Cyperaceae taxonomic resolution we currently also investigate ITS1 of nuclear ribosomal DNA in Poaceae and Cyperaceae. A total of 257 terrestrial higher plant taxa, 14 Pteridophyta taxa and 9 aquatic taxa were detected. Before ca. 12.6 cal ka BP, Asteraceae dominate terrestrial plant communities, which are commonly associated with cold and arid conditions during the late glacial; after 12.6 cal ka BP, Asteraceae abundance decline, Poaceae, Rosaceae, and Salicaceae abundance increase likely related to an increase in precipitation and temperature. At 6.5 cal ka BP, the Asteraceae abundance increase, Poaceae and Salicaceae abundance decrease, which is possibly related to cold and dry environments. The plant richness increase sharply since 6.5 cal ka BP and continually maintain relatively high richness values, which may be related to herbivory. Our analyses combine different plant sedaDNA markers will help to elucidate vegetation shifts in the past with deeper taxonomic resolution and provide reference on grassland protection under future climate change scenarios.