A common approach to investigating species' niches is to examine relationships between spatial variation in environmental conditions and contemporary species occurrences, using species distribution models (SDM or niche models). The relationships between past species distributions and environmental variation over time are less commonly explored. One way to examine effects on species changes over time is to use paleo-datasets to parameterize niche models, where the use of temporal variation allows for making more direct links between past species and environmental conditions through records of past changes. We examined the impact of five environmental variables (temperature, incidence of external nutrient input, local [within bog] moisture, incidence of regionally dry periods, and fire activity) on temporal variation in peatland species composition, occurrences, and abundances (Sphagnum, Eriophorum, Carex, and Ericaceous dwarf shrubs) using a high-resolution peat macrofossil paleo-record spanning the last ~10,000 years from the Store Mosse bog (south-central Sweden). Our results showed that species composition was affected by external nutrient input, local moisture conditions and incidence of regionally dry conditions. The presence and abundance of different species groups were mainly affected by external nutrient input and the incidence of regionally dry periods. Moreover, hummock Sphagna benefited from external nutrient input and low moisture, and in one species, warmer temperatures. Intermediate Sphagna from cooler temperatures with no external nutrient input, and hollow Sphagna from cooler temperatures and external nutrient input. Lastly, our results showed that environmental effects differed between the successional stages of the peatland in one case. Overall, the observed species' responses imply that peatland carbon dynamics will shift with future changes in climate. By examining links between climate and species responses of the past, this study demonstrates that the paleo-data approach in SDMs can contribute to a better understanding of the environmental effects influencing species distributions on longer time scales, thereby providing a valuable tool to improve predictions of future climate change effects.

Geological reconstructions of relative sea level (RSL) from southern Norway show falling RSL during the last 7000 cal. a BP, but tide gauge measurements document a slow RSL rise since at least 1960 CE. With an age gap of c. 1400 years between the youngest geologically reconstructed sea-level index point (SLIP) and the installation of the Tregde tide gauge in southernmost Norway, the exact nature and timing of the onset of RSL rise in southern Norway remain unknown. To fill this gap, we collected peat cores from a salt marsh to reconstruct RSL trends over the past 1000 years using a multiproxy approach, including 210Pb and 14C dating, grain-size analysis, loss-on-ignition (LOI), geochemistry (stable carbon isotopes, carbon to nitrogen ratios and XRF) and diatoms. Our data suggest decreasing tidal current strength and salinity over most of the last millennium, suggesting falling RSL. Sediment geochemistry also appears to vary with wetter and drier climatic periods. An increase in marine-brackish diatoms in combination with an acceleration in sedimentation rates after 1930 CE (1899–1954 CE) suggest that the onset of RSL rise began around this time in southernmost Norway. While most of the proxy data appear to have delayed sensitivity to RSL changes and may be linked to other causal processes, they, nonetheless, provide valuable insight into the environmental response of high-latitude temperate salt marshes to slow rates of RSL change.

Assessing historical environmental conditions linked to habitat colonization is important for understanding long-term resilience and improving conservation and restoration efforts. Such information is lacking for the seagrass Zostera marina, an important foundation species across cold-temperate coastal areas of the Northern Hemisphere. Here, we reconstructed environmental conditions during the last 14,000 years from sediment cores in two eelgrass (Z. marina) meadows along the Swedish west coast, with the main aims to identify the time frame of seagrass colonization and describe subsequent biogeochemical changes following establishment. Based on vegetation proxies (lipid biomarkers), eelgrass colonization occurred about 2,000 years ago after geomorphological changes that resulted in a shallow, sheltered environment favoring seagrass growth. Seagrass establishment led to up to 20- and 24-fold increases in sedimentary carbon and nitrogen accumulation rates, respectively. This demonstrates the capacity of seagrasses as efficient ecosystem engineers and their role in global change mitigation and adaptation through CO₂ removal, and nutrient and sediment retention. By combining regional climate projections and landscape models, we assessed potential climate change effects on seagrass growth, productivity and distribution until 2100. These predictions showed that seagrass meadows are mostly at risk from increased sedimentation and hydrodynamic changes, while the impact from sea level rise alone might be of less importance in the studied area. This study showcases the positive feedback between seagrass colonization and environmental conditions, which holds promise for successful conservation and restoration efforts aimed at supporting climate change mitigation and adaptation, and the provision of several other crucial ecosystem services.

Rainfall seasonality in the tropics has a substantial impact on both ecosystems and human livelihoods. Yet, reconstructions of past rainfall variability have so far generally been unable to differentiate between annual and seasonal precipitation changes. Past variations in seasonality are therefore largely unknown. Here, we disentangle hydrogen isotopic (δD) signals from terrestrial leaf waxes and algae in an 8000-year peat core from Sumatra, which reflect annual versus wet season rainfall signals, respectively. We validate these results using lipid biomarkers by reconstructing vegetation dynamics via n-alkane distributions and peatland hydrological conditions using glycerol dialkyl glycerol tetraethers (GDGTs), as well as biomass burning using levoglucosan concentrations in the core. Finally, we compare our proxy results to a transient climate model simulation (MPI-ESM1.2) to identify the mechanism for seasonality changes. We find that algal δD indicates stronger Indonesian-Australian Summer Monsoon (IASM) precipitation in the Mid-Holocene, between 8 and 4.2 cal ka BP. A period of alternating flooding, droughts and wildfires is reconstructed between 6 and 4.2 cal ka BP, implicating very strong monsoonal precipitation and drying out and burning during a longer and intensified dry season. We attribute this strong rainfall seasonality in the Mid-Holocene mainly to orbitally forced insolation seasonality and a strengthened IASM, consistent with the modeling results. In terms of annual rainfall, terrestrial plant δD, vegetation composition and GDGTs all indicate wetter conditions peaking between 3 and 4.5 cal ka BP, preceded by drier conditions, followed by drastic and rapid drying in the late Holocene from around 2.8 cal ka BP. Our multiproxy annual precipitation reconstruction thereby indicates the wettest overall conditions approximately 1500–2000 years later than a nearby speleothem δ¹⁸O record, which instead follows the seasonally biased algal δD in our record. We, therefore, hypothesize that speleothem reconstructions over the Holocene in parts of the tropics with low but significant seasonality may carry a stronger seasonal component than previously suggested. The data presented here contribute with new insights on how isotopic rainfall proxies in the tropics can be interpreted. Our findings resolve the seasonal versus annual components of Holocene rainfall variability in the Indo-Pacific Warm Pool region, highlighting the importance of considering seasonality in rainfall reconstructions.

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.

Inorganic geochemistry is a powerful tool in paleolimnology. It has become one of the most commonly used techniques to analyze lake sediments, particularly due to the development and increasing availability of XRF core scanners during the last two decades. It allows for the reconstruction of the continuous processes that occur in lakes and their watersheds, and it is ideally suited to identify event deposits. How earth surface processes and limnological conditions are recorded in the inorganic geochemical composition of lake sediments is, however, relatively complex. Here, we review the main techniques used for the inorganic geochemical analysis of lake sediments and we offer guidance on sample preparation and instrument selection. We then summarize the best practices to process and interpret bulk inorganic geochemical data. In particular, we emphasize that log-ratio transformation is critical for the rigorous statistical analysis of geochemical datasets, whether they are obtained by XRF core scanning or more traditional techniques. In addition, we show that accurately interpreting inorganic geochemical data requires a sound understanding of the main components of the sediment (organic matter, biogenic silica, carbonates, lithogenic particles) and mineral assemblages. Finally, we provide a series of examples illustrating the potential and limits of inorganic geochemistry in paleolimnology. Although the examples presented in this paper focus on lake and fjord sediments, the principles presented here also apply to other sedimentary environments.

Northern peatlands store globally-important amounts of carbon in the form of partly decomposed plant detritus. Drying associated with climate and land-use change may lead to increased fire frequency and severity in peatlands and the rapid loss of carbon to the atmosphere. However, our understanding of the patterns and drivers of peatland burning on an appropriate decadal to millennial timescale relies heavily on individual site-based reconstructions. For the first time, we synthesise peatland macrocharcoal records from across North America, Europe, and Patagonia to reveal regional variation in peatland burning during the Holocene. We used an existing database of proximal sedimentary charcoal to represent regional burning trends in the wider landscape for each region. Long-term trends in peatland burning appear to be largely climate driven, with human activities likely having an increasing influence in the late Holocene. Warmer conditions during the Holocene Thermal Maximum (∼9–6 cal. ka BP) were associated with greater peatland burning in North America's Atlantic coast, southern Scandinavia and the Baltics, and Patagonia. Since the Little Ice Age, peatland burning has declined across North America and in some areas of Europe. This decline is mirrored by a decrease in wider landscape burning in some, but not all sub-regions, linked to fire-suppression policies, and landscape fragmentation caused by agricultural expansion. Peatlands demonstrate lower susceptibility to burning than the wider landscape in several instances, probably because of autogenic processes that maintain high levels of near-surface wetness even during drought. Nonetheless, widespread drying and degradation of peatlands, particularly in Europe, has likely increased their vulnerability to burning in recent centuries. Consequently, peatland restoration efforts are important to mitigate the risk of peatland fire under a changing climate. Finally, we make recommendations for future research to improve our understanding of the controls on peatland fires.

Severe extratropical winter storms are a recurrent feature of the European climate and cause widespread socioeconomic losses. Due to insufficient long-term data, it remains unclear whether storminess has shown a notable response to changes in external forcing over the past millennia, which impacts our ability to project future storminess in a changing climate. Reconstructing past storm variability is essential to improving our understanding of storms on these longer, missing timescales. Peat sequences from coastal ombrotrophic bogs are increasingly used for this purpose, where greater quantities of coarser grained beach sand are deposited by strong winds during storm events. Moving inland however, storm intensity decreases, as does sand availability, muting potential paleostorm signals in bogs. We circumvent these issues by taking the innovative approach of using mid-infrared (MIR) spectral data, supported by elemental information, from the inorganic fraction of Store Mosse Dune South (SMDS), a 5000-year-old sequence from a large peatland located in southern Sweden. We infer past changes in mineral composition and thereby, the grain size of the deposited material. The record is dominated by quartz, whose coarse nature was confirmed through analyses of potential local source sediments. This was supported by further mineralogical and elemental proxies of atmospheric input. Comparison of SMDS with within-bog and regionally relevant records showed that there is a difference in proxy and site response to what should be similar timing in shifts in storminess over the ∼100 km transect considered. We suggest the construction of regional storm stacks, built here by applying changepoint modelling to four transect sites jointly. This modelling approach has the effect of reinforcing signals in common while reducing the influence of random noise. The resulting Southern Sweden-Storm Stack dates stormier periods to 4495–4290, 3880–3790, 2885–2855, 2300–2005, 1175–1065 and 715-425 cal yr BP. By comparing with a newly constructed Western Scotland-Storm Stack and proximal dune records, we argue that regional storm stacks allow us to better compare past storminess over wider areas, gauge storm track movements and by extension, increase our understanding of the drivers of storminess on centennial to millennial timescales.

Atmospheric mineral dust not only interacts with the climate system by scattering incoming solar radiation and affecting atmospheric photochemistry, but also contributes critical nutrients to marine and terrestrial ecosystems. In a high-resolution analysis of paleodust deposition, peat development and soil dust sources, we assess the interplay between dust deposition and bog development of the Davidsmosse bog in south-western Sweden. Analyses of the 5400-year record (458 cm) included radiocarbon dating, bulk density, ash content, chemical and mineralogical composition and carbon stable isotopes, subsequently explored using principal component analysis. Fourteen dust events (DEs) were recorded (cal BP) in the peat sequence: 3580–3490; 3280; 3140; 3010–2840; 2740; 2610; 2480; 2340; 2240–2130; 1690; 1240; 960, 890–760, and 620–360. The majority of the DEs were coupled to increases in peat accumulation rates and increased nutrient content (N, P and K) suggesting that the DEs contributed with nutrients to the bog ecosystem, promoting increased accumulation. We also analyzed the chemical and mineral composition of potential mineral source deposits (separated into 6 grain-size fractions) from sites within a 4 km radius as well as aeolian dunes closer to the coast (25 km). The composition deposited on the present-day bog surface indicates that the bulk of the contemporary minerals have a local origin (<1.5 km), but the DEs may be of a more distant origin. The results also indicate that quartz and plagioclase feldspar content consistently increase with increasing grain-size, both in the source samples as well as in the peat sequence, and that the Si/Al ratio can be used to infer grain size changes in the peat. Two longer phases saw numerous DEs, between 2800 and 2130 cal BP and a stepwise increase from 960 towards 360 cal BP. The episodic character of the events, together with the inferred coarse grain size, suggest that the particles were deposited by (winter) storms. Future studies should include grain size analysis as well as a more in-depth comparison with regional paleo dust and storm records to increase knowledge on both transport processes (creep, saltation, suspension) and the climate processes driving late Holocene dust and storm events in Scandinavia.

Sediments from the only permanent lake on the island of Jan Mayen (71°N, 08°30′W), Lake Nordlaguna (NL), were investigated. The lake, with an area of ∼1 km2, is situated at the foot of the world's northernmost active subaerial volcano and is separated from the sea by a 150–240 m wide beach barrier, which reaches 4–5 m above sea level. Most of the lake is deeper than 25 m, with the deepest part being 36 m. Altogether five coring sites, evenly spread out, were chosen and the sediment cores were retrieved from the lake ice with Uwitec and Nesje corers. After detailed descriptions of the very organic-poor and silt dominated sediments (of supposedly tephra-dominated origin), three sites were chosen for further analyses: macrofossils for 14C dating, tephra chemistry, C, S, grain-size, and XRF analyses. Based on 14C dates and the occurrence of the so-called Eggøya tephra (AD 1732), age models show variable bottom ages for the three sites: ∼3000, 600 and 400 cal yr BP. Due to the position of the core sites, with different sediment source areas, the elemental signals vary considerably between sites. An interesting feature of the lake is an isolated stock of Arctic char, which shows that the now land-locked lake has once been in contact with the sea. The almost total lack of organic material excluded any advanced paleo-ecologic investigations of the lake, and the study therefore focused on its marine-limnic history by different examinations of the XRF data with focus on the oldest and longest record. This development is based on elemental ratios (Br/Zn), PCA analyses of a center log ratio (clr) transformation of the original XRF data and magnetic susceptibility. It shows that the lake was isolated just before the time of the Eggøya tephra fall-out (∼220 cal yr BP), when the stock of Arctic char was most likely isolated from the sea. This was preceded by a ∼2200 yr long period of marine bay with a more or less open connection with the sea, and thus varying fresh-water impact. Between ∼2400 and 2600 cal yr BP the basin was more or less isolated, preceded by almost full marine conditions for at least the 300–400 preceding years we have data from, a period when relative sea level might have been higher.