Modern pollen–climate relationships and their application for pollen-based quantitative climate reconstruction of the mid-Holocene on the southern Korean Peninsula

A modern pollen dataset is a prerequisite for reconstructing quantitative paleoclimate and paleovegetation cover using fossil pollen records. Although multiple modern pollen–climate datasets have been established covering a wide range of climate conditions, such datasets are exceedingly rare for the Korean Peninsula (KP). In this study, we acquired a modern pollen dataset from 198 surface soil samples collected on 37 mountains on the southern KP. Redundancy analysis (RDA) and variation partitioning results identified mean annual temperature (Tann) as the most important climate variable shaping pollen assemblages on the southern KP. Using the pollen–climate relationships inferred from the RDA, we applied the Huisman–Olff–Fresco model and determined that arboreal pollen taxa responded sensitively to the climatic gradient, whereas non-arboreal pollen taxa did not. We applied weighted averaging–partial least squares (WA-PLS) and the modern analog technique (MAT) to the pollen dataset, and a comparison of the results showed that MAT performed better than WA-PLS. A transfer function was applied to fossil pollen records from the areas covered by our dataset; the results confirmed that annual precipitation (Pann) and Tann were modulated by different mechanisms, with Pann strongly affected by El Niño–Southern Oscillation-driven typhoons during the Holocene, whereas Tann was mainly influenced by the Tsushima Warm Current from 7500 to 5100 cal yr BP depending on Kuroshio Current inflow intensity, and subsequently followed by the East Asian winter monsoon during 5100–3400 cal yr BP.

The German Landscape and Julio-Claudian Imperialism

Summary New scientific work on the ancient landscapes of Germany and Britain makes it very likely that the Roman decision to abandon attempts to conquer Germany as far as the Elbe, most clearly expressed by Tiberius in 16 AD, was strongly influenced by perceptions of the heavily wooded landscape of that region. There were other reasons too: the concern of emperors to hinder potential rivals; the sheer difficulty of advancing to the Elbe; and the increasing concern of the emperor and his advisers for the fiscal effects of this and other potential conquests. But what is new is that the evidence of arboreal and non-arboreal pollen shows that Germany was a less attractive target than agrarian England.

Changes in the prairie–forest ecotone in northwest Ontario (Canada) across the Holocene

Pollen and diatom assemblages from well-dated sediment cores from three lakes forming a west-to-east transect across the boreal forest in northwest Ontario (Canada) were used to evaluate the timing and nature of the movement of the prairie–forest ecotone (PFE) across the Holocene. Changes in vegetation, temperature, and effective moisture were inferred from pollen and pollen-based transfer functions. Analyses indicated site-specific vegetational and climate changes across short spatial distances, with prolonged prairie-like conditions during the middle Holocene at the westernmost site. Increased reconstructed temperatures at this westernmost site occurred from ~9000 to 3000 cal yr BP, alongside increases in diatom-inferred lake levels beginning at ~6000 cal yr BP. The abundance of Quercus peaked concurrently with rising lake levels before declining to trace levels by ~3000 cal yr BP. Increases in the abundance of non-arboreal pollen between ~8500 and ~4500 cal yr BP at the more eastern lakes suggest relatively delayed and truncated PFE influence, before the reestablishment of primarily boreal taxa by ~4500 cal yr BP, coincident with diatom-inferred increases in lake levels. This study shows that the PFE moved both farther east and north than previously determined, but generally agrees with established patterns in vegetation from other studied regions along the PFE.

Late-Holocene climate variability of coastal East Asia reconstructed from the Yongneup fen in central Korea

<p>This study presents a reconstruction of climate change in central Korea during the last 3,000 years, using a core from a montane peatland of Yongneup. Multiple proxies of pollen, macrocharcoal, and geochemistry were analysed to provide three findings as follows: First, abrupt climate events at ca. 2.8 and 2.3 ka BP possibly accompanied dry summer as well as cold and arid winter seasons on the Korean peninsula. The first macrocharcoal analysis on the peninsula indicates increased wildfire activities during these dry periods. Next, a weakening of summer monsoon during El Niño-like phases was clearly found during the late Holocene. This confirms previous findings of a dominant oceanic influence on hydroclimate variability on the Korean peninsula. Finally, changes in temperature were likely synchronous with a global trend, indicated by the total organic content (TOC) and arboreal pollen percentages. Due to its location at a high-altitude, the environment of Yongneup has possibly sensitively responded to fluctuations in temperature. Altogether, these findings suggest that temperature and precipitation changes on the Korean peninsula have been separately influenced by insolation and oceanic circulations, respectively.</p>

Fire, humans and climate as drivers of environmental change on Broughton Island, New South Wales, Australia

In Australia, the drivers of precolonial fire regimes remain contentious, with some advocating an anthropogenic-dominated regime, and others highlighting the importance of climate, climatic variability or alternatively some nexus between climate and human activity. Here, we explore the inter-relationships between fire, humans and vegetation using macroscopic charcoal, archaeology and palynology over the last ~5430 cal. year BP from Broughton Island, a small, near-shore island located in eastern Australia. We find a clear link between fire and the reduction of arboreal pollen and rainforest indicators on the island, especially at ~4.0 ka and in the last ~1000 years. Similarities with comparable palaeoenvironmental records of fire in the region and a record of strong El Niño (dry, fire-prone) events supports the contention that climate was a significant influence on the fire regimes of Broughton Island. However, two periods of enhanced fire activity, at ~4000 years BP and ~<600 years BP have weaker links to climate, and perhaps reflect anthropogenic activity. Changes to the fire regime in the last ~600 years corresponds with the earliest evidence of Indigenous archaeology on the island, and coincides with implications that Polynesian people were present in the region. After the mid-Twentieth Century a human-dominated fire regime is also an obvious feature of the reconstructed fire record on Broughton Island.

Impacts of climatic extremes during MIS 3 on Alpine vegetation: evidence from Nesseltalgraben (SE Germany)

&lt;p&gt;The effects of extreme climatic changes on Alpine ecosystems during the last glacial are poorly understood. The recently discovered Nesseltalgraben site in the northern Alps provides a high-resolution sediment sequence covering the Marine Isotope Stage (MIS) 3 (59-28 ka BP), a period characterized by climatic extremes known as Dansgaard-Oeschger cycles or Greenland interstadials/stadials. The radiocarbon-dated composite profile of 21 m stratigraphic height provided a continuous pollen profile, bryophyte macrofossils, and wood remains. Additional to palaeobotanic studies, stable isotope analyses (&amp;#948;&lt;sup&gt;2&lt;/sup&gt;H, &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C, &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O) of bulk sedimentary cellulose and plant macrofossils (wood, monocots, and bryophytes) complemented the palaeoenvironmental and palaeoclimatic studies. Among the terrestrial pollen, Poaceae and arboreal pollen showed an antithetic behaviour and high variability reflecting interstadial-stadial climatic switches. Arboreal pollen are dominated by &lt;em&gt;Pinus sylvestris&lt;/em&gt;-type, with admixtures of &lt;em&gt;Picea&lt;/em&gt;, &lt;em&gt;Betula&lt;/em&gt;, &lt;em&gt;Alnus&lt;/em&gt;, and &lt;em&gt;Salix&lt;/em&gt;. The arboreal pollen record exhibits several maxima indicating milder climatic conditions, tentatively attributed to Greenland interstadials 5.1, 6, 8, 11/12 and 14-17. During Heinrich events 4 and 5, arboreal pollen show distinct minima underlining a severe impact of these events on regional climate and vegetation. Bryophyte assemblages show dominant wetland conditions at the site during the entire MIS 3. The sudden occurrence of &lt;em&gt;Drepanocladus turgescens&lt;/em&gt; after 31.6 ka cal BP indicates a change from a fen to a frequently drying wetland habitat linked to enhanced glacifluvial action caused by glaciers approaching towards the site. Stable isotope analyses of extracted bulk sedimentary cellulose revealed strongly fluctuating values best interpreted by variable mixtures between a terrestrial end member (lignified plants, monocots) with high &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H, &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C, and &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O values on the one hand, and wetland (bryophyte) cellulose sources with low isotope values on the other. Strong negative isotope excursions in the sedimentary and bryophyte cellulose records between 37.3 and 34.8 ka cal BP are best explained by a change to more humid conditions, possibly related to enhanced permafrost, and are contemporaneous with massive increases of Cyperaceae pollen. We conclude that the vegetation at Nesseltalgraben responded to several Greenland stadials/interstadials and Heinrich events. A straightforward correlation between vegetation oscillations and Greenland ice core records, as has been found in Alpine speleothem isotope records, is, however, not always obvious which could be the result of multiple additional abiotic and biotic factors influencing tree dissemination and growth.&lt;/p&gt;

High-resolution climatic (monsoonal) variability reconstructed from a continuous ~2700-year sediment record from Northwest Himalaya (Ladakh)

A chronologically well-constrained sedimentary archive from Upshi (Ladakh) was studied using a multi-proxy approach namely palynology, environmental magnetism, total organic carbon (TOC), total nitrogen (TN), stable isotopes of carbon and nitrogen providing a continuous vegetation, and paleoenvironmental history spanning the last ~2700 years with a temporal resolution of ~43 years. Pollen assemblage shows non-arboreal pollen (NAP) and non-pollen palynomorph (NPP) were dominant around the Upshi from ~2646 to 2431 cal. yr BP, indicating warmer conditions. Arboreal pollen (AP) and NAP gradually increased from 2431 to 1860 cal. yr BP in the study area, under warm and wet conditions, corresponding to the Roman Warm Period (RWP). This phase also witnessed enhanced sediment δ15N and χlf values. From ~1860 to ~1154 cal. yr BP increased Chenopodiaceae/Amaranthaceae and substantial spread of NPP suggest decreased temperature and prevalence of cold-dry climate. This period also records declining trends of χlf, δ15N, δ13Corg, TOC, and TN contents. From ~1154 to 293 cal. yr BP, the vegetation type reversed to mixed conifer and broad-leaved forest with significant increase in herbaceous taxa, rising δ15N, δ13Corg, TOC, and TN suggesting warm and wet conditions in the study area. This period broadly corresponds to the ‘Medieval Warm Period’ (MWP). Among all the proxies employed, depth profiles of TOC and TN (wt%) appear to respond best against external climate forcing showing remarkable correlation(s) with residual Δ14C in atmosphere, indicating dominance of intrinsic solar variability on regional climate/environment. The reconstructed recorded is well connected with established historical events and cultural activities of the Eurasian region.

Human and climate global-scale imprint on sediment transfer during the Holocene

Accelerated soil erosion has become a pervasive feature on landscapes around the world and is recognized to have substantial implications for land productivity, downstream water quality, and biogeochemical cycles. However, the scarcity of global syntheses that consider long-term processes has limited our understanding of the timing, the amplitude, and the extent of soil erosion over millennial time scales. As such, we lack the ability to make predictions about the responses of soil erosion to long-term climate and land cover changes. Here, we reconstruct sedimentation rates for 632 lakes based on chronologies constrained by 3,980 calibrated 14C ages to assess the relative changes in lake-watershed erosion rates over the last 12,000 y. Estimated soil erosion dynamics were then complemented with land cover reconstructions inferred from 43,669 pollen samples and with climate time series from the Max Planck Institute Earth System Model. Our results show that a significant portion of the Earth surface shifted to human-driven soil erosion rate already 4,000 y ago. In particular, inferred soil erosion rates increased in 35% of the watersheds, and most of these sites showed a decrease in the proportion of arboreal pollen, which would be expected with land clearance. Further analysis revealed that land cover change was the main driver of inferred soil erosion in 70% of all studied watersheds. This study suggests that soil erosion has been altering terrestrial and aquatic ecosystems for millennia, leading to carbon (C) losses that could have ultimately induced feedbacks on the climate system.