Decadal-centennial Scale Research Articles

Periodic paleo-environment oscillation on multi-timescales in the Triassic and their significant implications for algal blooms: A case study on the lacustrine shales in Ordos Basin

The Triassic climate has been a relatively neglected topic and conventionally considered a “hot-house” world. Using detailed petrographic characterization, in situ geochemical testing, and high-resolution cycle analysis, the Triassic lacustrine shale in the Ordos Basin was studied to confirm that periodic oscillations of the paleo-environment occurred at different timescales during the Triassic. On the millennial scale, increased obliquity induced enhanced transfer of heat and moisture to high latitudes, which then recharged continental aquifers, resulting in an increase in temperature, humidity, and levels of lakes in the mid-latitudes of the Northern Hemisphere. In contrast, decreased obliquity induced temperature and humidity reduction, followed by lake-level decline. Variations in eccentricity further regulated the magnitude of obliquity-forced paleo-environmental evolution. On the decadal–centennial scale, solar activity, including the 360–500 yr cycle I, 81–110 yr cycle II, and 30–57 yr cycle III, caused high-frequency oscillations of humidity and lake level. In the mid-latitudes of the Northern Hemisphere, intense (weak) solar activity promoted the decline (rise) in humidity and lake level. On the interannual scale, in the coastal area of western Panthalassa, El Niño-Southern Oscillation (ENSO)-like cycles also induced significant fluctuations in humidity and reducibility on a 2–8 yr scale. Whether complex paleo-environmental oscillations at different timescales occurred worldwide during the Triassic remains to be verified at other places. It is also noteworthy that high-frequency paleo-environmental oscillations in the Triassic stimulated algal blooms over a short period. The increase in rainfall caused by solar activity and ENSO-like cycles led to a frequent influx of nutrients into the Ordos Basin. The 30–57 yr cycle III induced red algae enrichment at intervals of decades. ENSO-like cycles also promoted algal bloom on 2–8 yr scale to form organic layers in lacustrine shale.

Response of Travertine Dam to Precipitation over the Past 800 Years in Zabuye Salt Lake, Southwestern Tibetan Plateau

The Tibetan Plateau is known as the core area of the third pole of the Earth and is a key area for global climate change research. This study uses the Zabuye Salt Lake travertine dam as the research object and U–Th dating as the chronological framework and proposes that the carbon and oxygen isotopes of travertine can be used as a precipitation index through the analysis of hydrogen and oxygen isotopes of spring water, and petrology, mineralogy, carbon and oxygen isotopes of travertine. The precipitation records of Zabuye Salt Lake over the last 800 years show a dry condition in 1191–1374 AD (Medieval Warm Period), a humid condition in 1374–1884 AD (Little Ice Age), and a dry condition in 1884–1982 AD (Current Warn Period), indicating a warm–dry/cold–moist climate pattern, which is consistent with precipitation records from many places on the Tibetan Plateau. We preliminarily point out that travertine can record the evolution of paleoprecipitation (paleomonsoon) at least on the decadal–centennial scale. The Indian summer monsoon has been the main factor influencing precipitation change in Zabuye Salt Lake over the past 800 years, and the change in evapotranspiration intensity caused by temperature change driven by solar radiation is also an important factor affecting dry–moist change.

Reconstruction of the Holocene hydro-ecological and environmental change of the Nile Delta: Insights from organic geochemical records in MZ-1 sediment core

The Holocene hydro-ecological and environmental change of the Nile Delta remains a knowledge gap. The study aimed to approach this objective by using multi-proxies of lipid biomarkers and bulk organic carbon (OC) in a well-dated MZ-1 core in Manzala lagoon off the Nile Delta. The data defined five distinctive stages at decadal-centennial scale. Stage I (ca. 8.2–7.7 ka) was characterized by remarkedly high reconstructed pH and low mean annual air temperature (the 8.2-ka cold event). The obviously low TOC and C/N, but higher short-chain n-alkanes indicated more marine OC deposition. This was followed by highly fluctuated organic geochemical proxies at Stage II (ca. 7.7–5.8 ka) indicating episodic but significant terrestrial OC input delivered by Nile floods during the African Humid Period (AHP, 11.0–5.4 BP). Subsequent increase in short- and medium-chain n-alkanes suggested macrophytes prevailing in the lagoon during Stage III (ca. 5.8–5.4 ka) with cooling-drying climate transitioned from the AHP. Stage IV (ca. 5.4–1.2 ka) witnessed decreased short-chain n-alkanes of marine origin and increased long-chain n-alkanes of terrestrial origin when the Nile climate entered into the mega-trend of aridification. Abnormal pulses of terrestrial OC with high TOC likely reflected the modified landscape due to early human occupation around the area. The highly fluctuated charcoal fluxes since ca. 6 ka implied such clearing-firing-aided land exploitation activity. The lagoon eco-setting was further affected by intensified anthropogenic-OC input after the latest millennium. Our study highlighted the land-ocean interactions on modulating the paleo-lagoonal ecology of the Nile Delta, which should be incorporated into healthy management in the Nile Delta.

Hydrological variation recorded in a subalpine peatland of Northeast Asia since the Little Ice Age and its possible driving mechanisms

Hydrological characteristics since the Little Ice Age (LIA) could provide a good reference for current climate analysis and future climate prediction. However, the hydrological variation since the LIA and its driving mechanisms in Northeast Asia remain unclear, which has severely restricted our understanding on the past, present and future hydroclimate changes in these regions. Here we reconstruct the hydrological dynamics over the past 700 years using samples from the Hani peatland a subalpine peatland of Changbai Mountains to reveal these issues. The analytical results from plant macrofossil and grain-size of the HN-1 core and the integrated moisture/precipitation records across the entire Northeast Asia indicate that the hydrological environments in Northeast Asia were wetter conditions during the period of 1300–1700 AD, dry conditions during the period of 1700–1850 AD, and wet conditions during the period of 1850–2018 AD, respectively. The possible driving mechanisms for the hydrological variations in Northeast Asia since the LIA can be divided into three models. La Niña-like conditions induced wetter conditions in Northeast Asia from 1300 to 1700 AD. From 1700 to 1850 AD, strong volcanic aerosol effects superimposed on weaker La Niña-like conditions, resulting in dry conditions in Northeast Asia. However, El Niño-like conditions induced wet conditions in Northeast Asia from 1850 to 2018 AD. These driving models suggest that the teleconnected influence of solar activity/sunspot could control the hydrological dynamics in Northeast Asia on a decadal-centennial scale through the ENSO activities and Walker Circulation changes since the LIA. Based on the periodicity relationship between hydrological conditions and sunspot, it can be predicted that the moisutre conditions in Northeast Asia would gradually decrease from 2030 to 2085 AD, and gradually increase from 2085 to 2140 AD.

Sedimentary rhythm of Mn-carbonate laminae induced by East Asian summer monsoon variability and human activity in Lake Ohnuma, southwest Hokkaido, northern Japan

Past and ongoing precipitations of Mn-carbonate (rhodochrosite) have occurred in the freshwater Lake Ohnuma, which is situated about 8 km south of the Hokkaido-Komagatake volcano, southwest Hokkaido (northern Japan). Lake sediments from a surface and a longer ∼4 m core contain the sedimentary rhythms of rhodochrosite laminae and volcanic deposits which were identified by nondestructive micro-XRF fluorescence analyses. The three tephra ash layers from the Hokkaido-Komagatake volcano, characterized by peaks of Al, Si, K, Ca, and Ti, correspond to regionally recognized tephras (1640, 1929 and 1996 CE) based on ashfall isopachs and 137Cs, 210Pb and 14C ages determined from the two cores. The sedimentation rate showed a drastic change around 1929 CE; ∼0.3 cm/yr for 1640–1929 CE and ∼2.7 cm/yr for 1929–2012 CE. The Mn content record of Lake Ohnuma sediments, composed of rhodochrosite laminae, showed a periodic variation with a decadal–centennial scale over the interval 1640–2012 CE. Sediment petrography and hydrochemical measurements suggest that the metastable phase of rhodochrosite was deposited during summer after being precipitated, followed by the crystal growth of rhodochrosite within the anoxic sediments. On the basis of these results, high Mn content is interpreted as an indicator of strengthened summer stratification associated with reduced rainfall runoff. The Ti/Si ratios are representative of the relative abundance of detrital inputs from the watershed. The combined signals of elevated Mn content and Ti/Si ratio for 1935–2012 CE indicate eutrophication and hypoxia in the lake and enhanced land erosion in the watershed, associated with the post-1970s intensive land use such as livestock farming. For 1640–1935 CE, the Lake Ohnuma record shows an antiphase relationship between the Mn content and Ti/Si ratio, which implies that the detrital inputs reflected the strength of the East Asian summer monsoon (EASM), and the reduced rainfall runoff resulted in weaker mixing, followed by depleted O2 in the water column. The antiphase variation in Mn content and Ti/Si ratio suggest weak EASM during the Little Ice Age (∼1850 CE), followed by strong EASM between 1860 and 1929 CE.

Multi-scale temperature variations and their regional differences in China during the Medieval Climate Anomaly

The Medieval Climate Anomaly (MCA, AD950-1250) is the most recent warm period lasting for several hundred years and is regarded as a reference scenario when studying the impact of and adaptation to global and regional warming. In this study, we investigated the characteristics of temperature variations on decadal-centennial scales during the MCA for four regions (Northeast, Northwest, Central-east, and Tibetan Plateau) in China, based on high-resolution temperature reconstructions and related warm-cold records from historical documents. The ensemble empirical mode decomposition method is used to analyze the time series. The results showed that for China as a whole, the longest warm period during the last 2000 years occurred in the 10th–13th centuries, although there were multi-decadal cold intervals in the middle to late 12th century. However, in the beginning and ending decades, warm peaks and phases on the decadal scale of the MCA for different regions were not consistent with each other. On the inter-decadal scale, regional temperature variations were similar from 950 to 1130; moreover, their amplitudes became smaller, and the phases did not agree well from 1130 to 1250. On the multi-decadal to centennial scale, all four regions began to warm in the early 10th century and experienced two cold intervals during the MCA. However, the Northwest and Central-east China were in step with each other while the warm periods in the Northeast China and Tibetan Plateau ended about 40–50 years earlier. On the multi-centennial scale, the mean temperature difference between the MCA and Little Ice Age was significant in Northeast and Central-east China but not in the Northwest China and Tibetan Plateau. Compared to the mean temperature of the 20th century, a comparable warmth in the MCA was found in the Central-east China, but there was a little cooling in Northeast China; meanwhile, there were significantly lower temperatures in Northwest China and Tibetan Plateau.

Evidence for solar influence in a Holocene speleothem record (Père Noël cave, SE Belgium)

We present a decadal-centennial scale Holocene climate record based on trace elements contents from a 65 cm stalagmite from Belgian Père Noël cave. “Père Noël” (PN) stalagmite covers the last 12.7 ka according to U/Th dating. High spatial resolution measurements of trace elements (Sr, Ba and Mg) were done by Laser-Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Trace elements profiles were interpreted as environmental and climate changes in the Han-sur-Lesse region. Power spectrum estimators and continuous wavelet transform were applied on trace elements time series to detect any statistically significant periodicities in the PN stalagmite. Spectral analyses reveal decadal to millennial periodicities (i.e., 68–75, 133–136, 198–209, 291–358, 404–602, 912–1029 and 2365–2670 yr) in the speleothem record. Results were compared to reconstructed sunspot number data to determine whether solar signal is presents in PN speleothem. The occurrence of significant solar periodicities (i.e., cycles of Gleissberg, de Vries, unnamed 500 years, Eddy and Hallstatt) supports for an impact of solar forcing on PN speleothem trace element contents. Moreover, several intervals of significant rapid winter change were detected during the Holocene at 10.3, 9.3–9.5, around 8.2, 6.4–6.2, 4.7–4.5, and around 2.7 ka BP. Those intervals are similar to the cold winter events evidenced in different natural paleoclimate archives, suggesting common climate forcing mechanisms related to changes in solar irradiance.

Unmixing Progradational Sediments in a Southwestern Caribbean Gulf through Late Holocene: Backwash of Low-Level Atmospheric Jets

ABSTRACT Rua, A.; Liebezeit, G.; Molina, R., and Palacio, J., 2016. Unmixing progradational sediments in a southwestern Caribbean gulf through late Holocene: Backwash of low-level atmospheric jets. In the last few years there has been considerable interest in the assessment of the role of tropical seas in driving paleoclimate. Despite this interest, little is known about the evolution of progradational sediments near the Panama Isthmus during the late Holocene. This paper shows the dispersion assessment of fluvial sediments into a gulf from the southwestern Caribbean on a decadal-centennial scale as recorded in three sediment cores spanning between 300 and 960 ± 35 calibrated YBP. According to end-member modeling of size classes, sediments largely comprised clay, clayey fine silt, and silty mud that flocculated by differential settling. Coarsened facies were consistent with enhanced fluvial discharge owing to increased precipitation in the circum-Caribbean. Remarkably, decreased fluvial discharge into the...

Elemental signature of terrigenous sediment runoff as recorded in coastal salt ponds: US Virgin Islands

A high-resolution, multi-proxy approach is utilized on mm- to cm-scale laminated coastal salt pond sediments from St. John, U.S. Virgin Islands, to determine: (1) the sedimentological signature of depositional events/processes, (2) link this sedimentological signature with known depositional events/processes in the historical (past ∼100years) record; and, (3) project back into the recent geologic past (past ∼1400years) to investigate the natural variability of depositional events/processes. High-resolution, short-lived radioisotope geochronology (210Pb, 137Cs, 7Be) combined with high-resolution elemental scanning techniques (scanning XRF and scanning LA-ICP-MS) allows for the direct comparison of well-preserved salt pond deposits to historical records of depositional events (e.g., runoff/rainfall, tropical cyclones, tsunamis) to identify the sedimentary signature of each type of event. There is a robust sedimentary record of terrigenous sediment runoff linked to the frequency of rainfall events that exceed a threshold of ∼12mm/day (minimum to mobilize and transport sediment) for study sites. This is manifested in the sedimentary record as increases in terrigenous indicator elements (%Al, %Fe, %Ti, %Si), which agree well with rainfall records over the past ∼50years. Variability in the sedimentary record over the past ∼100years reflects decadal-scale fluctuations between periods of increased frequency of rainfall events, and decreased frequency of rainfall events. Dm-scale variability in terrigenous indicator elements over the past ∼1400years represents the natural system variability on a decadal–centennial scale, and provides a high-resolution, long-term baseline of natural variability of rainfall/runoff events. A period of increased terrigenous sediment delivery during the 1700s and 1800s likely indicates increased erosion in response to anthropogenic activities associated with the island’s plantation era, and perhaps increased frequency of rainfall events.

Ecological change in fragile floodplain wetland ecosystems, natural vs human influence: The Macquarie Marshes of eastern Australia

Arid and semi-arid floodplain wetlands play important ecological roles and are among the most vulnerable ecosystems worldwide. However, studies of environmental change from such systems are rare. Sediment cores from the northern Macquarie Marshes, Murray-Darling Basin, provide a high-resolution (decadal-centennial scale) multi-proxy record of the past diversity and ecological successions of a wetland system from semi-arid inland Australia. In Loudens Lagoon on the eastern Marshes, a hiatus separates the Late Pleistocene-age sediments (50–27ka BP) from late Holocene sediments (c. 2.3ka BP) which are barren of microfossils until the 13th century AD. Charophytes and emergent vegetation are recorded from c. 1200 AD and become richer in recent times, with a concomitant increase of dry-tolerant Chenopodiaceae, indicating variable water cover at the site. The approximately 500-year old record from adjacent ‘Bora Lagoon’ indicates that, by comparison, this site was more frequently inundated. The charophytes Sphaerochara (=Tolypella sect. Rothia) and Chara australis are only present between the 16th and 17th centuries, suggesting a relatively deep wetland which became shallower by the 1940s. Between the 1940s and 1960s, charophytes indicating shallow water are diverse and abundant, with diatoms appearing c. 1955 AD. The reduction in charophytes and change in the diatom assemblages indicates increasing turbidity and pH after 1965 AD. The increased sedimentation rate and turbidity between the 1940s and 1970s are related to land use change. Our results suggest that livestock grazing, the building of levees/channels in the Marshes, and river regulation (Burrendong Dam) have contributed to the deterioration of the Marshes.

Comparison of proxy records of climate change and solar forcing

The role of solar variability as a cause of decadal‐centennial scale climate change continues to be a topic of debate. Herein we compare two estimates of solar variability since 1600 with two estimates of northern hemispheric temperature change. Sun‐climate correlations vary between 0.57–0.74 and are significant at the 95% level. However, the small number of oscillations in the time series suggests to us that longer records are needed for a more convincing demonstration of a significant sun‐climate linkage. Forcing of an energy balance model with the solar time series indicates that modest amounts of solar variability and climate sensitivity yield temperature variations that represent a significant fraction of the inferred changes during the Little Ice Age. This latter result further supports the hypothesis that solar variability may be significantly contributing to climate change on decadal‐centennial time scales.

Towards development of a strategy for determining the origin of decadal-centennial scale climate variabiligy

Although virtually all climate records with annual resolution record decadal-centennial scale climate fluctuations, their origin is obscure. Three candidates have been proposed-solar variability, volcanism and internal variability in the ocean-atmosphere system. A brief review of available evidence suggests that there is some support for the influence of solar variability, that the importance of volcanism may have been overestimated and that there is at present only limited information on the thermohaline circulation that suggests perhaps at most a 10–20% variation around its mean Holocene value. It is suggested that each of the above mechanism has a different geographic signature of response in the surface temperature field. Some examples from energy balance model calculations indicate that: (1) solar variability has a near-global response, with the amplitude of response slightly larger over land; (2) volcanism has a proportionately larger amplitude of response over land than over ocean; and (3) the most oft-cited mode of internal variability, changes in the North Atlantic thermohaline circulation, has a hemispheric asymmetry in response. Preliminary comparison of solar results with observations indicates that, if the solar influence exists, it is not being manifested in terms of simple cooling; changes in the ocean-atmosphere system may be significantly modifying the response. Despite this disagreement it is proposed that climate model results can nevertheless be used to postulate key ‘centers of action’ that should be most sensitive to partitioning the effects of the above mechanisms. One example of a sampling strategy is presented. Although this strategy can be imporved by further analysis of data and model calculations, it is hoped that it will contribute to imposing a