Assessing Coastal Wetland Carbon and Mineral Accumulation Response to Changing Climate, Cape Espenberg, Alaska

The high central Andes have experienced significant hydroclimatic changes in recent decades, impacting ecosystems through glacier retreat, temperature variations, and altered precipitation seasonality. Andean peatlands are crucial to water and biogeochemical cycles and are sensitive to climate change. To infer past climatic and environmental conditions, we analyzed X-ray fluorescence (XRF) core scanning data, principal component analysis (PCA) with clr-transformation, and total organic carbon (TOC) on the APA01 peat core (basal age ~2500 years). PCA-clr explained 88.8% of variance, revealing interactions between organic matter (OM) content, accumulation dynamics, and climatic influences. The correlation between Log [S/Ti] and PC1-clr highlighted the interplay of OM concentration and erosion intensity. Environmental proxies such as Ln [Si/S] and Ln [Zr/Ti] ratios provided insights into accumulation processes and climatic impacts. Analysis of carbon accumulation rates (CAR) and mineral accumulation rates (MAR) from 507 BCE to 1565 CE indicated distinct phases of organic and mineral accumulation, reflecting climatic changes.Comparative analysis with regional climate records (Quelccaya and Illimani ice cores, Pumacocha Lake sediments) during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) demonstrated broader climatic influences on peatland dynamics. Decreased OM accumulation during the MCA was linked to drier conditions, while increased accumulation during the LIA corresponded to wetter climates. Warming phases such as the MCA, post-LIA, and recent decades showed high clastic mineral input without necessarily wetter conditions, likely due to glacier and permafrost melting and increased snow-to-rain proportion. Our data indicate a decline in peatland growth and OM accumulation since 2010, emphasizing the need for careful monitoring and future restoration efforts.

Climatic and environmental changes in the Baidunzi wetland, Northwest China, over the last 800 years inferred from glycerol dialkyl glycerol tetraethers

In this study, simulations of 13 all‐forcing experiments from the Community Earth System Model Last Millennium Ensemble (CESM‐LME) archive were used to investigate the different spatiotemporal characteristics and corresponding mechanisms of the decadal megadroughts over the eastern China during two typical periods in the past millennium, that is, Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). The results show that there is no significant difference in either megadrought intensity or duration between the MCA and LIA, but there are significant differences in the megadrought frequencies. The frequency of megadroughts during the MCA is 1.44 times/hundred years, compared with 1.69 times/hundred years in LIA. Results from solar only sensitivity experiments and volcanic only sensitivity experiments show that this difference is mainly induced by the solar radiation. The mechanism analyses show that a spatial pattern of sea surface temperature anomalies (SSTA) resembling the positive Pacific Decadal Oscillation (PDO)‐like pattern have occurred simultaneously with the megadroughts during both the MCA and LIA. While, the megadroughts in MCA are strongly correlated with the strong PDO‐like SSTA patterns, and the megadroughts in LIA are strongly correlated with the weak PDO‐like SSTA patterns. In addition, the anomalous sea level pressure (SLP) field and wind field associate with the megadroughts during the MCA and LIA are consistent with the strengths of SSTA, with significant larger SLP and wind anomalies during the MCA than those during the LIA. Therefore, it can be concluded that the responses of the large‐scale atmospheric circulation patterns to SSTA are similar during these two typical periods, and the difference in the megadrought frequencies is due to the nonlinear response of the precipitation variability to the large‐scale atmospheric circulation patterns.

The Kangerlussuaq area of southwest Greenland is a lake-rich landscape that covers a climate gradient: a more maritime, cooler and wetter coastal zone contrasts with a dry, continental interior. Radiocarbon-dated sediment sequences (covering ~11,200–8,300 cal year) from paired lakes at the coast and the head of the fjord were analysed for lithostratigraphic variables (organic-matter content, bulk density, Ti, Ca). Minerogenic and carbon accumulation rates from the four lakes were compared to determine catchment and lake response to Holocene climatic variability. Catchment erosion at the coast was dominated by cryonival processes, with considerable sediment production due to the limited vegetation cover and exposed rock faces. Input of minerogenic sediment at one site (AT4) was high (>1 gDW cm−2 year−1) during the period 5,800–4,000 cal year BP, perhaps reflecting intensification of cryogenic processes on northeast-facing slopes and rapid delivery to the lake. This period of erosional activity was not observed at the nearby, higher elevation site (AT1) due to the lower catchment relief; instead, there was an abrupt decline in carbon and minerogenic accumulation rates at ~5,800 cal year BP. Sediment accumulation rates at the inland sites were much lower (<0.005 gDW cm−2 year−1) reflecting greater catchment stability (more extensive vegetation cover), lower relief and substantially lower precipitation, but synchronous increases in mineral accumulation rates from ~1,200 to 1,000 cal year BP may reflect wind erosion associated with regional cooling and local aridity. Carbon-accumulation-rate profiles were similar at the two inland sites, with higher-than-average accumulation (~6–8 g C m−2 year−1) during the early Holocene and a subsequent decline after ~6,000 cal year BP. At the inland lakes, both mineral and carbon accumulation rates exhibited a stronger link to climate, driven by trends in effective precipitation and regional aeolian activity. Catchment differences (relief, altitude) lead to more individualistic records in both erosion history and lake productivity at the coast.

Ma, L., Wu, J., Yu, H., Zeng, H. & Abuduwaili, J. 2011: The Medieval Warm Period and the Little Ice Age from a sediment record of Lake Ebinur, northwest China. Boreas, Vol. 40, pp. 518–524. 10.1111/j.1502-3885.2010.00200.x. ISSN 0300-9483. Lake Ebinur, Xinjiang, northwest China, is a closed-basin, shallow lake that responds rapidly to changes in the ratio of precipitation to evaporation (P/E). A sediment record spanning the last 1500 years was obtained from the lake. We used δ18O and δ13C in bulk carbonate, and δ13C of organic matter in the lake sediments to infer environmental changes in the Ebinur region during the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Decreased δ18O values of carbonate largely reflect an enhanced P/E ratio within the basin and a higher lake level. Bulk carbonates with higher δ13C values are deposited during periods when lake-water pH is high, while lower δ13C values reflect a lower pH in the water column. δ13C in organic matter is associated with the amount of precipitation. The results indicate that the Ebinur region experienced a dry MWP and a wet LIA, although the MWP and LIA were warm and cold periods, respectively, as expected. Furthermore, the MWP and LIA were hydrologically complex and cannot be characterized as uniformly wet or dry. Peak wet periods are recorded in the sediment core around AD 1000, 1400 and 1700, and a dry event also occurred in the period of temperature change within the LIA (cold to warm around AD 1500). A comparison of the Lake Ebinur data with proxy records for the strength of the Siberian High and climate proxy indicators suggests that precipitation in the Ebinur region was a consequence, in part, of an enhanced Siberian High during the LIA.

A 1000-year record of paleoclimate and paleoenvironment change inferred from sedimentary organic matter in Lake Azuei, Haiti

Climatic controls on peat swamp formation and evolution since 1300 year BP as recorded by phytoliths in the Xishan Mountains, Jiangxi Province, China

Few studies have assessed the relative importance of landscape, land use history, climate, and regional heterogeneity on lake ecosystem processes, despite the likelihood that interactions among these factors must be important for controlling lake dynamics. We used 14 sediment measures from 20 lake cores in a climatically sensitive region of the prairie-forest border in southern Minnesota to (1) assess relationships between modern lake productivity (Carlson’s Trophic State Index [TSI]), modern land-use, catchment, and lake morphometry, and (2) contrast regional responses to climatic transitions from the ‘Medieval Climatic Anomaly’(1000–1350) to the ‘Little Ice Age’ (1350–1800) to ‘Modern’(~1980–1996 AD). TSI was significantly positively correlated with modern sedimentation rate, and accumulation rates of organic matter (OM), biogenic silica (BSi), and total phosphorus (TP). TSI was not significantly correlated with “modern” land cover, catchment, or lake morphometry characteristics, but total organic N(N) was negatively correlated with percent cultivation in the catchment area and negatively correlated with δ15N of bulk organic matter in sediment. Regional, among-lake heterogeneity was high over the past 1,000 years, but Little Ice Age (LIA) cooling appeared to result in an approximately 20% decline in OM, BSi and TP accumulation, while warming and cultural eutrophication of the past 150 years corresponded to a 200–400% increase in accumulation rates as well as an 80% increase in carbonates and a small but significant 10% drop in C/N ratios consistent with greater in-lake productivity. Our results indicate that climate does have regional effects on lake ecosystems but that among-lake variability is high, reflecting the importance of local factors and suggesting a need for (1) more explicit definition of what ‘regional’ means, (2) a focus on degree as well as direction of change, and (3) estimating accumulation rates based on multiple lakes and multiple cores within lakes.

Two hundred twenty five rock samples and thirty seven oil samples from the Beibuwan Basin, South China Sea, were analyzed with geochemical and organic petrological techniques to evaluate the Eocene lacustrine source rocks, and investigate controls on their properties and the distribution of different oil families in the basin. Two types of organic facies are recognized in the Liushagang (LS) Formation. The first organic facies is algal-dominated, and mainly occurs in the organic-rich, laminated mudstones of the middle member of the LS (LS-2) that were deposited in an anoxic, stratified, medium–deep lake environment. It is geochemically identified by its high abundance of C30 4-methylsteranes and heavy δ13C values in the range of -22.4 to -27.5‰. The organic matter in this organic facies comprises type I and II1 kerogens, with its macerals dominated by fluorescent amorphous organic matter (AOM) and exinites, indicating a highly oil-prone character. The second organic facies is of terrestrial algal origin, and is mainly identified in the non-laminated mudstones of the upper (LS-1) and lower (LS-3) members of the Liushagang Formation that were deposited in shallow, dysoxic, weakly stratified, fresh-water environments. Source rocks of the second organic facies mainly contain type II1–II2 kerogens with mixed macerals of AOM, internites and vitrinites. It is geochemically differentiated from the algal-dominated organic facies by its relatively low abundance of C30 4-methylsteranes and lighter δ13C values in the range of -27.20 to -28.67‰. Three oil groups are identified by their biomarkers and stable carbon isotopes. The first two groups (A and B) are probably end-members of two major oil families (A and B) that correspond to the algal-dominated organic facies and algal-terrestrial organic facies, respectively. Most of the discovered oils belong to Group A oils that are characterized by a high abundance of C30 4-methylsteranes and heavy δ13C values, and show a good correlation with the algal-dominated organic facies in LS-2. Group B oils are found only within the LS-1 and LS-3 reservoirs, and they are recognized by their relatively low content of C30 4-methylsteranes and lighter δ13C values, showing a close relation to the algal-terrestrial source facies within the LS-1 and LS-3members, respectively. Group C oils display intermediate biomarker features and stable carbon isotope values, and are interpreted to be a mixture of Group A and B oils. The oil-source correlation reveals a strong control of organic facies on the geographic distribution of oil groups or oil fields in the basin.

Hydrology-mediated differential response of carbon accumulation to late Holocene climate change at two peatlands in Southcentral Alaska

Analysing three high resolution coupled model simulations for the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) regimes, available as the last millennium simulations of the PMIP3, we find that Northeastern Indian summer monsoon rainfall (NEISMR) did not change appreciably from the MCA to the LIA. This is in contrast to the signals in the rest of the Indian region. Our results from all the models suggest that, during the MCA, the simulated 100‐hPa tropical easterly jet (TEJ) becomes relatively more intense than that during LIA, due to a stronger Tibetan High. This strengthening of the TEJ results in an associated increase in relative vorticity at the 500 hPa over the Head Bay of Bengal and neighbouring east coast of the Bay of Bengal. This results in higher moisture availability and increased summer monsoon rainfall in the neighbourhood, including the central Indian region, during the MCA. However, the simulations do not show any such changes over northeastern India, indicating a relatively stable simulated NEISMR from MCA through LIA. Furthermore, just as the current day observations, the simulated correlations between the NEISMR with various concurrent ENSO indices are weak and statistically insignificant during the MCA and LIA regimes. Interestingly, an analysis of time‐slice simulations for the MCA and LIA from an atmospheric general circulation model broadly agree with the above conclusions, indicating that the tropical ocean and atmospheric coupling may not have played a major role in the northeast climate.

Widely distributed proxy records show that there were out-of-phase behaviors of moisture change between arid central Asia (ACA) and monsoonal northern China during the Little Ice Age (LIA) and Medieval Climate Anomaly (MCA). We examined spatial pattern differences between the MCA and LIA to identify contrasting patterns of summer precipitation variability, and to diagnose explanatory mechanisms through the analysis of a 1000-year global climate model simulation driven by natural and anthropogenic forcing. The results show that the model was able to roughly produce the general features of MCA-LIA hydroclimatic spatial differences between monsoonal northern China and ACA, with a relatively wet MCA found in monsoonal northern China and a relatively dry MCA found in ACA. A further analysis of associated circulations shows that increased summer precipitation in monsoonal northern China was caused by the strengthening of summer monsoon, while the decline in summer precipitation in ACA was caused by an anomalous northward displacement of the subtropical westerly jet stream. Our analyses suggest that both effective solar forcing and El-Nino Southern Oscillation (ENSO) may produce these contrasting patterns of precipitation between monsoonal northern China and ACA. Due to a change in the probability of ENSO phases at the centennial time scale found in our experiments may be attributed to solar irradiances, higher effective solar irradiances during the MCA relative to those of the LIA may have been the ultimate forcing mechanism for the simulated precipitation differences between the MCA and LIA.

The influences of the AMO and NAO on the sedimentary infill in an Azores Archipelago lake since ca. 1350 CE

The climate of Siberia is primarily influenced by the Siberian High (SH), although other large-scale atmospheric circulation systems, in particular North Atlantic Oscillation (NAO) storm tracks, play an important role. How variability in the relative strength and trajectory of these climatic systems has affected local to regional palaeoclimatic conditions remains little known. Here, we employ multi-proxy peat core analysis (δ13C, δ15N in Sphagnum, plant macrofossil, pollen, charcoal) from Plotnikovo Mire, part of the Great Vasyugan Mire in western Siberia (Tomsk province, Russia). We provide a high-resolution record of variations in climatic conditions and the biogeochemical fluxes of carbon and nitrogen over the past 2000 years and then discus the link between local climatic conditions and larger scale atmospheric circulation patterns. Our record shows that generally warm and dry conditions prevailed from BC 500 to 500 CE. Warm and wet episodes occurred during the early (800–950 CE) and later (1150–1300 CE) part of the Mediaeval Climate Anomaly (MCA), and were interrupted by a warm and dry mid-MCA phase (1000–1200 CE). Progressively cooler and wetter conditions established from 1400 CE, which became most marked between 1600 and 1850 CE, coincident with the Little Ice Age (LIA). Finally, drying of the mire surface reflects the warming trend of recent decades. We found that C accumulation was greater (90 g C m−2 yr−1) at times of wetter conditions and when Sphagnum was dominant, and lowest (35 g C m−2 yr−1) during periods of mixed vascular plant growth and Sphagnum under drier/unstable hydrological conditions. This peatland has been an active C sink over the past 1500 years, however, its ability to sequester carbon has decreased with recent warming and may continue to decrease with ongoing climatic warming and drying. We hypothesise that generally warm and moist conditions at the study site and over wider Siberia during the MCA could have been linked to a weakening of the Siberian High, which in turn enhanced the ingress of Atlantic moisture-carrying air masses across Siberia. Conversely, a strengthened SH overlapping negative North Atlantic Oscillation (NAO) modes during the LIA, resulted in a longer cold season with a delayed snowmelt and diminished evapotranspiration. This study shows that the interplay of moisture bearing air masses from different origins led to complex local hydroclimate and biogeochemical patterns. However, to resolve the spatio-temporal coherency of such climate variability due to the interaction of different air masses, and therefore better predict future climate changes, a denser network of palaeo-records is needed.

The Little Ice Age (LIA) is a cold climatic event since Medieval Warm Period (MWP) and a previous period before global warming over the last 100 years. Recent years, the studies on LIA have achieved so many advances in the world by using the data such as ice core, tree-rings, stalagmite, lake sediment and historic documents, etc. The focuses of controversy about the LIA research are as follows: Is the LIA widespread climatic anomaly of last 1000 years? How long is the duration of the LIA? And does the duration have regional difference? The studies show there are three colder periods during the LIA, centered in the 15th century, the 17th century, and the 19th century on the average. The LIA is a climatic anomaly in worldwide. The time span of the LIA is about 500-600 years, but the length of the time span is not the same in different regions. The style of the dry/wet, warm/cold periods of the LIA exists regional discrepancy. Generally speaking, in the area of higher latitude and elevation, the beginning and end time of LIA is earlier than that in the area of lower latitude and elevation. And the vary argument of temperature is smaller for the latter. The formation of the LIA is impacted by the activities of volcanic and solar, the general circulation, the interaction between atmosphere and ocean, atmosphere and land surface. In this paper, integrated analysis is done by using the present research achievement about the LIA. The characteristics of the LIA of distribution in the world are given. The possible causes of the LIA are analyzed. Lastly, the main unresolved problems in the study of the LIA are proposed.