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.

Analysis of pollen across the surface sediments of Lake Imbradas, Lithuania

In conventional pollen analysis, usually one sediment core per basin is analyzed to reconstruct past environmental conditions. This approach does not consider spatial heterogeneity of pollen assemblages, and assumes that one analyzed location is representative of the whole basin. To improve the spatial resolution of fossil pollen studies, further knowledge of the factors influencing variations in pollen assemblages throughout a basin is needed. We examined the spatial heterogeneity of pollen assemblages from 45 lacustrine surface samples from a lake with relatively simple hydrology and compared this dense network of surface pollen samples with the Lithuanian State Forest Service arboreal vegetation database. Calculations of pollen productivity at different locations across the lake revealed variations in the behavior of a pollen-vegetation relationship model in different parts of the basin. Our findings suggest that the model underestimated pollen contributions from the lakeshore vegetation. We demonstrate that detailed investigations of surface pollen as a step prior to fossil pollen investigations can provide useful insights, including understanding the influence of sedimentation rate on modelling results and spatial variations in pollen composition, thus providing guidance for site selection for fossil pollen studies.

Climate and human induced 2000-year vegetation diversity change in Yunnan, southwestern China

Understanding long-term vegetation diversity patterns and their potential responses to climate and/or human driven processes are important for ecosystem modeling and conservation. Late-Holocene fossil pollen assemblage and associated vegetation diversity estimates provide an opportunity to explore the interactions among vegetation, climate, and human activities. A continuous 2000-year palynological record was obtained from the Beihai Wetland, southwestern China, to represent regional vegetation history, particularly the vegetation diversity changes. The results indicate that regional vegetation was dominated by deciduous broadleaved forest components (e.g. Alnus, deciduous Quercus), which showed a gradual decrease accompanied by expansion of herbaceous taxa (mainly Poaceae) after AD 800. Such progressive decline of forest was attributed to regional deforestation driven by intensified human activities, which was further confirmed by the increasing non-pollen polymorph abundance, particularly an abrupt rise after AD 1350. Vegetation diversity based on the Hill numbers ( N0, N1, and N2) showed a dramatic decline between ca. AD 200–400, which was triggered by regional fire events as shown by increased charcoal abundance from a nearby lake. The vegetation diversity reduced gradually after AD 800, especially the vegetation richness reflected by N0, revealing the transitional process from climate-driven to human-dominated vegetation changes. Minor increases of vegetation diversity occurred during Chinese dynastical transitions, probably due to reduced human activities following war-induced population crises. On the multidecadal scale, variations in vegetation diversity correlated significantly with climate fluctuations (revealed by synthesized temperature of China and stable oxygen isotope record from Dongge Cave) before AD 800, indicating a climate dominant condition. Then, the correlation between vegetation diversity and climate declined after AD 800, representing a progressive transition to human-dominant condition. In addition, the compositional turnover based on DCCA of the fossil pollen assemblage revealed a stepwise decrease, indicating reduced vegetation turnovers under anthropogenic influences.

Evolution Of The Westerly Winds Belt In The Middle Latitudes Of The Southern Hemisphere Since The Last Glacial Maximum

<p><b>The Southern Westerly Winds (SWW) are a symmetric component of the global climate system that govern the modern climate of all Southern Hemisphere landmasses south of ~30°S. Changes in the strength and latitudinal position of the SWW influence the precipitation patterns in the southern mid-latitudes, and have been postulated as fundamental drivers of ocean-atmospheric CO2 exchange since the Last Glacial Maximum (LGM: ~34.0-18.0 ka). Despite their role in modern and past climatic dynamics, the evolution of the SWW at locations within their zone of influence is still uncertain; this is largely because of the paucity of paleoclimate records with well constrained chronology, adequate sampling resolution and an appropriate depositional setting. Resolving these issues will help understand the behaviour of the SWW in the past at different spatial (regional and hemisphere) and temporal (centennial to multi-millennial) scales. Here I present new paleoclimate data based on the examination of detailed chronologies of fossil pollen, charcoal and chironomids preserved in lake sediments from western Patagonia: Lago Emerenciana (43°S) and Lago Pintito (52°S) and New Zealand’s southwestern South Island: Lake Von (45°S). These data, spanning a broad range of the SWW zone of influence, provide insights into the role of shifting SWW in environmental and climate dynamics of the middle latitudes of the Southern Hemisphere spanning the last ~24,000 years.</b></p> <p>In the first study site, I performed detailed fossil pollen and charcoal analyses from sediment cores collected from Lago Emerenciana, a relatively small closed-basin lake located in northwestern Patagonian (43°S), to examine past vegetation, fire regime and climate change during the last ~24,000 years. I detect very low temperature and increased precipitation between ~24.0 and ~17.0 ka, followed by a warming trend and reduced precipitation between ~17.0 and ~14.3 ka. A cold reversal and increased precipitation regime occurred between ~14.3 and ~12.4 ka, followed by a return to warming and a slight decline in precipitation between ~12.4 and ~11.0 ka. I identify warmer temperatures and a major decline in precipitation at the beginning of the Holocene between ~11.0 and ~9.0 ka, conditions that persisted until ~6.2 ka. Centennial to millennial precipitation variability occurred during the last ~6200 years. </p> <p>In the second study site, I developed high resolution fossil pollen and charcoal records, along with an exploratory chironomid record from sediment cores obtained from Lake Von, a small closed-basin lake located in the southwestern sector of the South Island of New Zealand (45°S), to examine vegetation, fire and climate trends spanning the last ~18,000 years. I observe a trend toward warming and relatively dry conditions between ~18.0 and ~14.8 ka with relatively wet conditions between ~18.0 and ~16.7 ka, increased precipitation between ~16.7 and ~14.8 ka, and cooling conditions and enhanced precipitation between ~14.8 and ~12.8 ka, followed by a marked drop in precipitation between ~12.6 and ~11.2 ka. I detect warmer and diminished precipitation between ~10.8 and ~7.2 ka, followed by lower temperature and enhanced precipitation between ~7.2 and ~3.7 ka. The mid-late Holocene is also characterised by alternating dry and wet oscillations of millennial- and centennial-scale phases with low precipitation between ~6.0 and ~5.2, ~4.4 and ~4.1, ~3.7 and ~2.9, and ~1.9 and ~0.56 ka, and increased precipitation in the intervening intervals. In the third study site, I produced high resolution fossil pollen and charcoal records from sediment cores I collected from Lago Pintito, a small and shallow closed-basin lake located in southwestern Patagonia (52°S). This record allows the detection of past vegetation, fire and hydroclimatic shifts at millennial and centennial scales over the last ~17,000 years. From these data, I identify cold and dry conditions between ~17.0 and ~16.4 ka, increased precipitation between ~16.4 and ~14.2 ka and ~12.5 and ~11.4 ka, and intense precipitation but lower in magnitude than the neighbouring intervals between ~14.2 and~12.5 ka. I detect a major decline in precipitation at the beginning of the Holocene between ~11.4 and ~6.8 ka, followed by centennial-scale changes in precipitation until the present. </p> <p>The comparison between precipitation variability reconstructed from the records from western Patagonia (Lago Emerenciana and Lago Pintito) and New Zealand’s southwestern South Island (Lake Von) allows the inference of SWW changes at a hemispheric scale during and since the LGM, based on the premise that there is a strong and positive correlation between zonal wind speeds and local precipitation in these regions. The results of this thesis suggest: i) strong SWW influence at 43°S between ~24.0 and ~17.5 ka, ii) a southward shift of the SWW between ~17.5 and ~16.5 ka and reduced SWW influence north of 52°S, iii) strengthening and/or a northward shift of the SWW between ~16.5 and ~ 14.5 ka, with strong SWW influence between 52°S and 43°S, iv) a northward shift of the SWW between ~14.5 and ~12.6 ka which resulted in stronger SWW influence between 43°S and 46° S and weaker SWW influence at 52°S, v) a southward shift of the SWW between ~12.6 and ~11.2 ka leading to weaker SWW influence between 43°S and 46°S and stronger SWW influence at 52°S, vi) a generalized multi-millennial decline in the strength of the SWW between ~11.2 and ~7.2 ka, and vii) high variability in the SWW in Western Patagonian and New Zealand’s southwestern South Island during the last ~7200 years. Based on these findings, I postulate that hemisphere-wide changes in the position and/or strength of the SWW have modulated the atmospheric CO2 concentration through wind-driven upwelling of CO2-rich deep waters in the high southern latitudes during and since the LGM.</p>

Evolution Of The Westerly Winds Belt In The Middle Latitudes Of The Southern Hemisphere Since The Last Glacial Maximum

<p><b>The Southern Westerly Winds (SWW) are a symmetric component of the global climate system that govern the modern climate of all Southern Hemisphere landmasses south of ~30°S. Changes in the strength and latitudinal position of the SWW influence the precipitation patterns in the southern mid-latitudes, and have been postulated as fundamental drivers of ocean-atmospheric CO2 exchange since the Last Glacial Maximum (LGM: ~34.0-18.0 ka). Despite their role in modern and past climatic dynamics, the evolution of the SWW at locations within their zone of influence is still uncertain; this is largely because of the paucity of paleoclimate records with well constrained chronology, adequate sampling resolution and an appropriate depositional setting. Resolving these issues will help understand the behaviour of the SWW in the past at different spatial (regional and hemisphere) and temporal (centennial to multi-millennial) scales. Here I present new paleoclimate data based on the examination of detailed chronologies of fossil pollen, charcoal and chironomids preserved in lake sediments from western Patagonia: Lago Emerenciana (43°S) and Lago Pintito (52°S) and New Zealand’s southwestern South Island: Lake Von (45°S). These data, spanning a broad range of the SWW zone of influence, provide insights into the role of shifting SWW in environmental and climate dynamics of the middle latitudes of the Southern Hemisphere spanning the last ~24,000 years.</b></p> <p>In the first study site, I performed detailed fossil pollen and charcoal analyses from sediment cores collected from Lago Emerenciana, a relatively small closed-basin lake located in northwestern Patagonian (43°S), to examine past vegetation, fire regime and climate change during the last ~24,000 years. I detect very low temperature and increased precipitation between ~24.0 and ~17.0 ka, followed by a warming trend and reduced precipitation between ~17.0 and ~14.3 ka. A cold reversal and increased precipitation regime occurred between ~14.3 and ~12.4 ka, followed by a return to warming and a slight decline in precipitation between ~12.4 and ~11.0 ka. I identify warmer temperatures and a major decline in precipitation at the beginning of the Holocene between ~11.0 and ~9.0 ka, conditions that persisted until ~6.2 ka. Centennial to millennial precipitation variability occurred during the last ~6200 years. </p> <p>In the second study site, I developed high resolution fossil pollen and charcoal records, along with an exploratory chironomid record from sediment cores obtained from Lake Von, a small closed-basin lake located in the southwestern sector of the South Island of New Zealand (45°S), to examine vegetation, fire and climate trends spanning the last ~18,000 years. I observe a trend toward warming and relatively dry conditions between ~18.0 and ~14.8 ka with relatively wet conditions between ~18.0 and ~16.7 ka, increased precipitation between ~16.7 and ~14.8 ka, and cooling conditions and enhanced precipitation between ~14.8 and ~12.8 ka, followed by a marked drop in precipitation between ~12.6 and ~11.2 ka. I detect warmer and diminished precipitation between ~10.8 and ~7.2 ka, followed by lower temperature and enhanced precipitation between ~7.2 and ~3.7 ka. The mid-late Holocene is also characterised by alternating dry and wet oscillations of millennial- and centennial-scale phases with low precipitation between ~6.0 and ~5.2, ~4.4 and ~4.1, ~3.7 and ~2.9, and ~1.9 and ~0.56 ka, and increased precipitation in the intervening intervals. In the third study site, I produced high resolution fossil pollen and charcoal records from sediment cores I collected from Lago Pintito, a small and shallow closed-basin lake located in southwestern Patagonia (52°S). This record allows the detection of past vegetation, fire and hydroclimatic shifts at millennial and centennial scales over the last ~17,000 years. From these data, I identify cold and dry conditions between ~17.0 and ~16.4 ka, increased precipitation between ~16.4 and ~14.2 ka and ~12.5 and ~11.4 ka, and intense precipitation but lower in magnitude than the neighbouring intervals between ~14.2 and~12.5 ka. I detect a major decline in precipitation at the beginning of the Holocene between ~11.4 and ~6.8 ka, followed by centennial-scale changes in precipitation until the present. </p> <p>The comparison between precipitation variability reconstructed from the records from western Patagonia (Lago Emerenciana and Lago Pintito) and New Zealand’s southwestern South Island (Lake Von) allows the inference of SWW changes at a hemispheric scale during and since the LGM, based on the premise that there is a strong and positive correlation between zonal wind speeds and local precipitation in these regions. The results of this thesis suggest: i) strong SWW influence at 43°S between ~24.0 and ~17.5 ka, ii) a southward shift of the SWW between ~17.5 and ~16.5 ka and reduced SWW influence north of 52°S, iii) strengthening and/or a northward shift of the SWW between ~16.5 and ~ 14.5 ka, with strong SWW influence between 52°S and 43°S, iv) a northward shift of the SWW between ~14.5 and ~12.6 ka which resulted in stronger SWW influence between 43°S and 46° S and weaker SWW influence at 52°S, v) a southward shift of the SWW between ~12.6 and ~11.2 ka leading to weaker SWW influence between 43°S and 46°S and stronger SWW influence at 52°S, vi) a generalized multi-millennial decline in the strength of the SWW between ~11.2 and ~7.2 ka, and vii) high variability in the SWW in Western Patagonian and New Zealand’s southwestern South Island during the last ~7200 years. Based on these findings, I postulate that hemisphere-wide changes in the position and/or strength of the SWW have modulated the atmospheric CO2 concentration through wind-driven upwelling of CO2-rich deep waters in the high southern latitudes during and since the LGM.</p>

Relationships between climate and phylogenetic community structure of fossil pollen assemblages are not constant during the last deglaciation

Disentangling the influence of environmental drivers on community assembly is important to understand how multiple processes influence biodiversity patterns and can inform understanding of ecological responses to climate change. Phylogenetic Community Structure (PCS) is increasingly used in community assembly studies to incorporate evolutionary perspectives and as a proxy for trait (dis)similarity within communities. Studies often assume a stationary relationship between PCS and climate, though few studies have tested this assumption over long time periods with concurrent community data. We estimated two PCS metrics—Nearest Taxon Index (NTI) and Net Relatedness index (NRI)—of fossil pollen assemblages of Angiosperms in eastern North America over the last 21 ka BP at 1 ka intervals. We analyzed spatiotemporal relationships between PCS and seven climate variables, evaluated the potential impact of deglaciation on PCS, and tested for the stability of climate-PCS relationships through time. The broad scale geographic patterns of PCS remained largely stable across time, with overdispersion tending to be most prominent in the central and southern portion of the study area and clustering dominating at the longitudinal extremes. Most importantly, we found that significant relationships between climate variables and PCS (slope) were not constant as climate changed during the last deglaciation and new ice-free regions were colonized. We also found weak, but significant relationships between both PCS metrics (i.e., NTI and NRI) and climate and time-since-deglaciation that also varied through time. Overall, our results suggest that (1) PCS of fossil Angiosperm assemblages during the last 21ka BP have had largely constant spatial patterns, but (2) temporal variability in the relationships between PCS and climate brings into question their usefulness in predictive modeling of community assembly.

Constraints on the paleoelevation history of the Eastern Cordillera of Colombia from its palynological record

We attempted to make an objective assessment of whether fossil pollen assemblages from the Sabana de Bogotá require surface uplift of ~2000 m since 6–3 Ma, as has been argued. We relied on recently published elevation ranges of plants for which fossil pollen has been found in sites 2000–2500 m high in the Sabana de Bogotá. The elevation ranges of fossil plants do not overlap, suggesting that those ranges may be too narrow. By weighting these elevation ranges by percentages of corresponding fossil pollen and summing them, we estimated probability density functions for past elevations. These probability distributions of past elevations overlap present-day elevations and therefore do not require surface uplift since deposition of the pollen. Fossil pollen assemblages include pollen from some plant taxa for which we do not know present-day elevation ranges, and therefore, with a more complete knowledge of elevation distributions, tighter constraints on elevations should be obtainable. The elevation of the oldest assemblage, from Tequendama, which lies at the southern edge of the Sabana de Bogotá and is thought to date from 16 to 6 Ma, is least well constrained. Although our analysis permits no change in elevation since the pollen was deposited, we consider 1000–2000 m of elevation gain since 15 Ma to be likely and consistent with an outward growth of the Eastern Cordillera.