Understanding long-term variability in storminess is essential for constraining future climate patterns in the eastern North Atlantic, a region shaped by complex ocean–atmosphere interactions. Here, we reconstruct storm, fire, and hydroclimate variability from grain size, inorganic geochemistry, plant macrofossil and molecular organic records since mid-Holocene at Glenties Bog, a coastal blanket bog in western Ireland. Comparing our results with existing palaeostorminess records, we provide new insights into a dynamic interplay between wind strength, fire incidence, and hydrological conditions throughout the Holocene.

Long-term temperature evolution influenced the background wind and hydroclimatic state, while volcanic activity became a key forcing mechanism during parts of the late Holocene. The warm mid-Holocene coincided with lower wind strength and enhanced fire activity, while no assoication between storm periods and volcanic activity was inferred, indicating that the climate state at the time of the volcanic forcing affects the climatic response.

These results indicate that future warming may lead to profound changes in wind strength, hydroclimate, and fire regimes. Notably, climate-change-induced lowering of peatland water tables may increase the susceptibility of blanket bogs to intense and deep peatland fires.

This study provides new insight into Holocene wind and hydroclimate dynamics in the eastern North Atlantic, improving understanding of the mechanisms driving North Atlantic climate variability across contrasting climate states.

After the last ice age, species migrated into a newly deglaciated Scandinavia. Brown bear recolonization is thought to have occurred from two directions—from the south and the northeast—resulting in a nonoverlapping distribution of two distinct mitochondrial clades. A contact zone in central Sweden separates populations with mitochondrial clade 1a in the south from those with clade 3a in the north. However, a paucity of brown bear subfossils in Scandinavia has limited testing of this prevailing model using ancient DNA. Here, we present a high-coverage brown bear mitogenome (231×) and nuclear genome-wide data (0.05×) extracted from lake sediment dated to 9.6 cal. ka BP from northern Sweden, representing the oldest known record of brown bear in the region. At this point in the Early Holocene, the Fennoscandian Ice Sheet was in its final stages of recession. Surprisingly, our analyses suggest that this environmental genome represents one male individual carrying clade 1a and with southern brown bear nuclear ancestry, despite being found far north of the contact zone. This suggests the individual was a migratory bear and had dispersed northward from its birthplace. Our finding adds to the scarce genomic record of Early Holocene brown bears and highlights the use of sedimentary ancient DNA as a powerful source of genomic information.

The Swedish Time Scale (STS), based on annual sediment sequences (varves), is a unique tool for detailing Scandinavian deglaciation and climate history. Over a century in development, the STS comprises ∼13,300 varve-years, yet its connections to calendar years are insecure, and it cannot yet be considered a true absolute time scale. Consequently, it has not been possible to reliably investigate leads and lags of paleoclimate and environmental changes recorded in the STS in relation to other climate archives in NW Europe and the North Atlantic region. Here, we radiocarbon dated a series of early Holocene ice-dammed lake drainage events that deposited recognizable varves downstream. In particular, we identified the lake drainage responsible for depositing the so-called “zero varve” of the STS and dated it to 10,008 ± 87 calibrated years before present, A.D. 1950 (cal. yr B.P.). Using a hydrological model, we demonstrate that drainage duration was subseasonal and that drainage marker beds are, in chronological terms, true annual varves. By doing so, we anchor the STS in absolute time, provide revised ages of key deglacial and climatic events of the last glacial-interglacial transition, and present a tightly chronologically constrained reconstruction of early Holocene ice-sheet retreat in central Scandinavia.

The condition of ancient marine ecosystems provides context for contemporary biodiversity changes in human-impacted oceans. Sequencing sedimentary ancient DNA (sedaDNA) is an emerging method for generating high-resolution biodiversity time-series data, offering insights into past ecosystems. However, few studies directly compare the two predominant sedaDNA sequencing approaches: metabarcoding and shotgun-metagenomics, and it remains unclear if these methodological differences affect diversity metrics. We compared these methods using sedaDNA from an archived marine sediment record sampled in the Skagerrak, North Sea, spanning almost 8000 years. We performed metabarcoding of a eukaryotic 18S rRNA region (V9) and sequenced 153–229 million metagenomic reads per sample. Our results show limited overlap between metabarcoding and metagenomics, with only three metazoan genera detected by both methods. For overlapping taxa, metabarcoding detections became inconsistent for samples older than 2000 years, while metagenomics detected taxa throughout the time series. We observed divergent patterns of alpha diversity, with metagenomics indicating decreased richness towards the present and metabarcoding showing an increase. However, beta diversity patterns were similar between methods, with discrepancies only in metazoan data comparisons. Our findings demonstrate that the choice of sequencing method significantly impacts detected biodiversity in an ancient marine sediment record. While we stress that studies with limited variation in DNA degradation among samples may not be strongly affected, researchers should exonerate methodological explanations for observed biodiversity changes in marine sediment cores, particularly when considering alpha diversity, before making ecological interpretations.

Arctic sea ice affects Earth’s albedo, marine productivity and organic matter (OM) transport. Lipid biomarkers have been used to trace OM transport in the Arctic Ocean, but uncertainties remain regarding their spatio-temporal variations and sources over the last glacial cycle. Our study addresses these gaps by analyzing glycerol dialkyl glycerol tetraethers (GDGTs), n-alkanes, and total organic carbon (TOC) in nine central Arctic sediment cores spanning the Marine Isotope Stages (MISs) 3–1. Elevated IIIa/IIa values of branched GDGTs (brGDGTs) in the central Arctic throughout the studied interval suggest a marine origin, contrasting to the #rings_tetra ratios which indicate a terrigenous brGDGT source. We propose that the IIIa/IIa ratio may be a more sensitive indicator of in situ brGDGT production in the central Arctic marine sediments. TOC and biomarker concentrations in the Central Lomonosov Ridge (CLR) cores were higher compared to those from the Lomonosov Ridge off Greenland (LRG) and Morris Jesup Rise (MJR) cores. Low productivity in the central Arctic, along with similarity in the spatial patterns of marine-derived brGDGTs and isoprenoid GDGTs, as well as terrestrial long-chain n-alkanes, suggests that these biomarkers are primarily transported to the central Arctic from the Siberian shelves. This spatial pattern persisted throughout MISs 3–1, suggesting continued sea ice drift during glacial periods, albeit with weakened intensities. Meanwhile, the spatiotemporal variations of the Branched Isoprenoid Tetraether (BIT) index in the region plausibly reflect the relative changes in the crenarchaeol and brGDGT production on the shelf and/or selective degradation of crenarchaeol during its transport.

The Baltic Ice Stream, a large fast-flowing sector of the last Fennoscandian Ice Sheet that occupied the present-day Baltic Sea basin, was first conceptualized in the earliest days of glacial geological research in Scandinavia. Landform and sedimentological evidence from the terrestrial margins support the concept and numerical ice-sheet models demonstrate its existence and possible evolution. However, with evidence for the Baltic Ice Stream thus far limited to the terrestrial periphery, its true form, scale, function, and role in deglaciation have proven enigmatic. Here we present geomorphological evidence directly from the Baltic seabed that confirms the existence of and sheds light on the behaviour of the Baltic Ice Stream. Based on an extensive collection of high-, moderate- and low-resolution bathymetric terrain models covering a large proportion of the Baltic Sea floor, and complemented by LiDAR-data for the Baltic islands, we have identified and mapped >20 000 individual subglacial bedforms, meltwater landforms and grounding line landforms. We reconstruct a six-stage sequence of ice flow and retreat, finding that streaming was persistent in the Baltic but that pathways were variable in extent, timing and duration: different sectors of the Baltic exhibit asynchronous streaming and out-of-phase grounding line changes. During deglaciation, grounding line readvances occurred in both the southwestern and the northern Baltic Proper, and, while abundant iceberg ploughmarks attest to calving as a significant ice loss mechanism, lobate margins suggest supply to the Baltic catchment was consistently high. Our reconstruction is limited by a fragmentary geomorphic record. Here we put forward a first hypothesis for how the Baltic Ice Stream evolved, and hope it stimulates new geomorphic, stratigraphical and core data collection to extend the landform record, provide insights into subglacial and grounding line processes, and constrain the chronology for Baltic Ice Stream flow and retreat.

Substantial uncertainties exist regarding how future climate change will affect storminess (storm frequency and intensity) in Ireland and the United Kingdom (UK). Knowledge about spatiotemporal variations of past storminess gives us a better understanding of its mechanisms on centennial to millennial time scales, as well as the impact of external forcing on future storminess in climate models. Here, we present the oldest storm record to date from Ireland, covering the last 8000 years, reconstructed from the Roycarter Bog, a coastal blanket bog in north-western Ireland. The sequence was analysed for grain-size, chemical, mineral and organic molecular composition. The chronology was built on 11 AMS radiocarbon dates. The deposit characteristics, location and low inorganic content suggest aeolian transport of particles to the bog throughout the studied period. Cluster analysis of the grain-size frequency curves, along with the coarse to fine sand ratio, allowed the identification of eleven storm periods (cal yr BP): 6150–5500 (1); 4970–4130 (2); 4000 (3); 3490–3290 (4); 3230 (5); 2850–2590 (6); 2170–1920 (7); 1440 (8); 1225–890 (9); 620–470 (10); and 290–230 (11). During the mid-Holocene, the relative sea level was lower and the local beach sources located further away, giving a longer transport distance compared to the late Holocene. In the latter part of the mid-Holocene (6150–4130 cal yr BP), during the Holocene thermal maximum, increased storminess and wind strengths were inferred for north-western Ireland, manifested as two longer storm periods. During the late Holocene the storm frequency increased, and a greater number (9) of shorter storm periods were recorded. Comparison between our results and regional peat palaeostorm records from Scotland, north of our study site, showed an antiphase relationship between storminess in Ireland and Scotland during the latter part of the mid-Holocene, but mostly in-phase storminess over the last 3000 years. Taken together, enhanced wind strength and storminess were recorded during the warmer mid-Holocene, while an increased frequency of storm events occurred in the cooler late Holocene. Mid-Holocene storm periods occurred during locally wet periods, while most of the storm periods during late Holocene occurred during drier phases. Alternatively, the elevated mineral input during late Holocene promoted microbial activity and peat decomposition. The apparent variability in cyclicity and frequency between the mid- and late Holocene indicates that the processes governing storminess in the region shifted. This calls for further studies ahead, including climate modelling, to disentangle the complex processes governing storminess on millennial to centennial time scale.

Submarine groundwater discharge (SGD) is an important process responsible for transporting terrestrial dissolved chemical substances into the coastal ocean, thereby impacting the marine ecosystem. Despites its significance, there are few studies addressing SGD in the northern Baltic Sea. Here we investigate the potential occurrence of SGD in an area characterized by seafloor terraces formed in varved glacial clay located around Fifång Island, Southern Stockholm Archipelago. We analyzed 222Rn activity and porewater geochemistry in both marine and terrestrial sediment cores retrieved from Fifång Island and its surrounding offshore areas. Results from 222Rn mass-balance calculations, water isotopes, salinity, chloride concentration, and dating (including 14C and helium-tritium dating) indicate that modern groundwater flows through varved glacial clay layers and fractured rocks on Fifång Island and discharges into Fifång Bay. Additionally, the offshore cores reveal a saline groundwater source that, dating of the dissolved inorganic carbon, appears systematically younger than the hosting clay varves dated using the Swedish clay varve chronology. Acoustic blanking in our acquired sub-bottom profiles may be related to this fluid migration. The occurrence of this saline groundwater seems to be independent from the distance to the submarine terraces. Collectively, our study confirms the occurrence of submarine groundwater in the varved glacial clay close to Fifång Island and further offshore. Our findings help establish the significance of submarine groundwater discharge in influencing the past and present coastal environment in the Baltic Sea region.

The extent of the Scandinavian Ice Sheet in southwestern Norway is precisely located during the well-characterized Younger Dryas re-advance. However, the thickness of the ice sheet is less well constrained inland from the terminal position. Some exceptions include lateral moraines traced inland and up to 1000 m a.s.l. along Hardangerfjorden. Here, we apply ¹⁰Be dating in two areas: (1) bedrock and boulders in the high-relief landscapes near the Younger Dryas margin around the Bergen urban area, and (2) boulders from an upland 1600 m a.s.l. much farther (120 km) inland. We find that coastal summits ranging from ~400 to ~680 m a.s.l. and located only ~10–15 km up-flow from the ice margin, were covered by the Scandinavian Ice Sheet during the Younger Dryas. The scatter in the ¹⁰Be age population of 22 boulder samples is best explained by isotopic inheritance owing to inefficient subglacial erosion during the foregoing glaciation. Most of the 11 bedrock samples also exhibit inheritance, pointing to the source of inheritance in boulders and implying inefficient subglacial erosion during the last glaciation even in valley-bottoms near Bergen. Regional glacial striae compilations suggest that ice flow during maximum Younger Dryas ice-sheet configurations was for the most part cross-valley, with potentially low basal slip rates. Five new ¹⁰Be ages from the inland site help to constrain ice height far inland. We combine these new results with prior information to generate a cross profile of the Younger Dryas ice sheet in southern Norway.

Extensive glacial lakes dammed in the Scandinavian Mountains during the retreat of the last Scandinavian Ice Sheet were first hypothesised over a century ago. Here, using high-resolution LiDAR, we report >4500 relict shorelines, deltas and palaeo-channels related to ice-dammed lakes over a -30 000 km2 area of central Jämtland, west-central Sweden. Shorelines occur as flights on the valley sides, a consequence of sequential lowering of palaeo-lake levels during ice margin retreat and lower threshold outlets becoming ice-free. Based on the extent and elevation of shorelines, we identify requisite lake-damming ice-margin positions and lake drainage outlets, and we reconstruct the coupled evolution of ice-dammed lakes and the retreating ice margin. Beginning as a series of smaller ice-dammed lakes along the Swedish-Norwegian border, draining westward across the present-day water divide and into the Atlantic Ocean, the lakes successively coalesced during eastward ice margin retreat to form water bodies covering 1000s of km2 with 10s of km-long calving margins. Ultimately, the lake system coalesced into a single lake: the Central Jämtland Ice Lake, which exceeded 3500 km2 in area and 360 km3 in volume. Eventually, the damming ice-margin split in two, resulting in a large (-200 km2) catastrophic glacial lake outburst flood (GLOF) that reversed the drainage of the entire lake system from the west to an eastern outlet draining to the Baltic basin. We present new radiocarbon ages for one lake drainage event prior to the eastward outburst flood and, together with previously published deglacial ages and local varve records, we suggest that the region was possibly deglaciated within just 350 years, sometime between 10.5 and 9.2 cal ka BP. We tentatively correlate the penultimate drainage of the Central Jämtland Ice Lake to the zero-varve of the Swedish Time Scale, a drainage varve at Döviken, eastern Jämtland, raising the tantalising prospect of using the evolution of the ice-dammed lake system to tie the varve-based Swedish Time Scale to the radiocarbon timescale with a new programme of radiocarbon dating in central Jämtland.