Mean Temperatures Of Warmest Month Research Articles

Latest Neogene monsoon of the Chotanagpur Plateau, eastern India, as revealed by fossil leaf architectural signatures

A fossil leaf assemblage from latest Neogene (Pliocene) sediments exposed in Jharkhand of Chotonagpur Plateau, eastern India, is subjected to a CLAMP (Climate Leaf Analysis Multivariate Program) analysis using a new high spatial resolution (~1 km2) WorldClim2 gridded climate data and PhysgAsia2 calibration. The CLAMP analysis of 80 different morphotypes of fossil leaves indicates a mean annual temperature (MAT) of 21.9 °C ± 2.3 °C; a cold month mean temperature (CMMT) of 16.7 °C ± 3.5 °C and a warm month mean temperature (WMMT) of 26.9 °C ± 2.9 °C. Precipitation estimates have high uncertainties but suggest a weak monsoon with a growing season (11.7 ± 1 months) precipitation (GSP) of 201.2 ± 64.3 cm. The new calibration also provides for the first time in India more detailed insights into the hydrological regime through the return of annual and seasonal vapour pressure deficit (VPD) and potential evapotranspiration (PET) estimates, as well as new thermal overviews through measures of thermicity and growing degree days. The new results confirm the overall warmth of the region. Although rainfall estimates have large uncertainties due to year-round wet soils, measures of VPD and PET show persistent high humidity, but with higher evaporative stress in the summer during late Neogene times than now.

The Cenozoic leaf morphotypes and palaeoclimate interpretation from the Doi Ton Formation, Mae Sot District, Tak Province, western Thailand

The Cenozoic palaeovegetation and palaeoclimate of Doi Ton, western Thailand, megaflora are reconstructed based on physiognomic climate analysis, including Leaf Margin Analysis (LMA), Leaf Area Analysis (LAA), Leaf Size Index (LSI), Climate Leaf Analysis Multivariate Program (CLAMP), and systematic descriptions of each leaf morphotype. The leaf fossils were divided into 23 dicotyledonous leaf morphotypes and two unknown leaf morphotypes. The mean annual temperature results from LMA indicate 32.3 ± 1.17 °C and CLAMP shows 21.2°C. CLAMP also provides temperature data of a warm month mean temperature (WMMT) of 27.4 °C and a CMMT of 14.2 °C, which is similar to the present climate. The mean annual precipitation is estimated by LAA to be ~ 125 cm. CLAMP suggests precipitation in the 11 months of growing period was 154.9 cm with the three wettest months having precipitation of 73 cm, widely contrasting with 15.5 cm for the three driest months. The precipitation shows the signal of the monsoon effect. The temperature, precipitation, and LSI mirrored the vegetation of the contemporary Doi Ton area which is a semi-evergreen forest in the tropical zone. The palaeoclimatic parameters of Doi Ton are in good agreement with those of south China and northwestIndia from the Eocene period and the present-day Mae Sot area. Moreover, the Doi Ton flora also closely matches the humid subtropical modern vegetation of south China. Palaeoclimate and vegetation analysis support an Eocene age estimate for the Doi Ton Formation however further independent age estimates are required to test this working hypothesis.

Palaeoclimatic estimates for a latest Miocene-Pliocene flora from the Siwalik Group of Bhutan: Evidence for the development of the South Asian Monsoon in the eastern Himalaya

Fossil leaf floras, from the latest Miocene-Pliocene Siwalik Group exposed in Bhutan, sub-Himalaya, are subjected to a CLAMP (Climate Leaf Analysis Multivariate Program) analysis using a high-resolution gridded climate calibration. The CLAMP analysis of 27 different morphotypes of fossil leaves indicates a mean annual temperature (MAT) of 24.1 °C ± 2.8 °C; a cold month mean temperature (CMMT) of 18.9 °C ± 4 °C and a warm month mean temperature (WMMT) of 27.8 °C ± 3.3 °C. The analysis also suggests a weak monsoonal climate (the monsoon index, MSI 46.7; present MSI 52) with growing season precipitation (GSP) of 1819 ± 916 mm (present GSP 2490 mm). Here we also compare palaeoclimate estimates of the latest Miocene-Pliocene Siwalik Group flora from Bhutan (c. 6 to 3.8 Ma) with those of previously investigated Siwalik Group floras from the Miocene-Pleistocene of Arunachal, India and Miocene Siwalik floras of Darjeeling, India which characterise the monsoon signature at the time of deposition. Since all the Siwalik floras of the eastern Himalaya (Darjeeling and Arunachal Pradesh) spanning the mid-Miocene to Pleistocene yield almost the same values we suggest that overall the eastern Himalayan Siwalik climate appears to have been remarkably uniform over the past 15 million years. The MAT result of the Bhutan Siwalik flora differs by just 0.6 °C from Arunachal and 1.2 °C from Darjeeling Siwalik floras. For all Siwalik fossil assemblages, WMMTs, CMMTs and LGSs (length of the growing season) are similar and consistent (WMMTs around 28 °C, CMMTs around 18 °C and LGSs around 12 months). Similarly, the mean annual relative humidity (RH) and specific humidity (SH) appear to have been uniformly around 80% and 14 g/kg respectively throughout the Neogene of the eastern Himalayan Siwaliks. Changes in the monsoon index suggest that in both Bhutan and Arunachal sub-Himalaya, there has been little change in the intensity of the monsoon since mid-Miocene time, while further west in the Darjeeling area precipitation seasonality has increased since the mid-Miocene.

Environmental constraints on terrestrial vertebrate behaviour and reproduction in the high Arctic of the Late Cretaceous

Reconstructions of temperature and moisture regimes based on fossil leaves, combined with tree ring studies, detail the light regime, length of the growing season, and summer and winter temperatures of the Late Cretaceous Arctic. Such constraints have important implications for dinosaur feeding and reproductive behaviour, and the capacity to reside year-round in near-polar environments.At the highest palaeolatitudes where dinosaurs have been found (82–85 °N) winter darkness lasted for ~120days and the spring and autumn twilight periods for ~15days. A mostly cloud and mist-shrouded environment witnessed a mean annual temperature (MAT) of 6–7°C, a warm month mean temperature (WMMT) of 14.5±3.1°C and a cold month mean temperature (CMMT) of −2±3.9°C. Growth rings in wood suggest summer temperatures frequently fell below +10°C. Winter temperatures as low as −10°C were likely for short periods. Spring bud break in late February to early March and leaf fall in early October limited the time when fresh food was available in any quantity to not more than 6months.The diversity of Arctic dinosaur body sizes implies a range of overwintering strategies but year-round residency requires reproduction. Burrowing and enclosed nest building no doubt facilitated overwintering for small animals, but for larger dinosaurs shelter was problematical. No dinosaur egg remains have yet been found as far north as 82° palaeolatitude, but they occur 6° further south in the Early Maastrichtian Kakanaut Formation, Northeastern Russia. Here the winter darkness was shorter (45days), and the temperature regime warmer (MAT 10°C, WMMT 19°C, CMMT +3°C). The growing season (temperatures>10°C) was ~6.3months and fresh food was available in quantity for slightly longer. These summer temperatures constrain the thermal regime of nest environments and suggest sophisticated nest management and possibly brooding strategies for the necessary rapid incubation and hatching before the onset of winter.

Megaflora and palaeoclimate of a Late Oligocene tropical delta, Makum Coalfield, Assam: Evidence for the early development of the South Asia Monsoon

The fossil megaflora, from the late Oligocene deltaic sediments exposed in the Tirap coal mine, Assam, India (27° 17′ 20″ N, 95° 46′ 15″ E), laid down at a palaeolatitude of 10–15° N, records the composition and climate of tropical vegetation during the last episode of pronounced global warmth before the progressive overall cooling to present day conditions. Using a new calibration of the Climate Leaf Analysis Multivariate Program (CLAMP) that includes 18 sites from modern vegetation in India, the analysis of 80 fossil leaf morphotypes from the Tirap mine indicates a mean annual temperature (MAT) of 26.1±2.7°C, a warm month mean temperature (WMMT) of 27.9±3.3°C and a CMMT of 20.1±4.3°C. With adjustments for evapotranspirational cooling and underestimation of the WMMT at high temperatures these can be revised upwards to a minimum MAT of 28.3±3.7°C, a CMMT of 23±5.5°C and a WMMT of 33.6±5.2°C. Maximum estimates based on evaporative cooling seen in a modern analogue of the Tirap environment yield an MAT of 32.9±3.8°C, a CMMT of 26.8±6°C and a WMMT of 39±7.1°C. All uncertainties are 2 sigma. Precipitation estimates reveal a marked annual variation in rainfall showing a wet season with 20 times the rainfall of the dry season. This is a similar regime to that seen in the Sunderbans in the modern Ganges/Brahmaputra/Meghna delta. We interpret this to suggest that the South Asian Monsoon was already established by late Oligocene times at an intensity similar to that of today.

Tertiary climatic changes at middle latitudes of western North America

A new multivariate analysis of leaf physiognomy provides the basis for estimating various climatic parameters for angiosperm leaf assemblages. Estimates from this Climate-Leaf Analysis Multivariate Program ( clamp) are both accurate (valid) and precise (repeatable). Application of clamp to fossil-leaf assemblages from western North America confirms that Eocene mean annual temperature ( mat) was generally high (early Eocene mat ≈ 19°C at paleolat. 70°N and >27°C at paleolat. 45°N). Significant fluctuations (≈5–8°) in mat occurred during the Eocene. Each successive warm period was cooler than the preceding warm period. Mean annual range of temperature ( mart) was generally low during the Eocene, especially at middle latitudes, but then markedly increased by ≈ 12–13°C at ≈33 Ma as mat decreased by ≈ 7–8°C. These changes at ≈ 33 Ma largely involved a decrease in cold-month mean temperature, which continued to decline into the early Miocene but then increased significantly into the mid-Miocene thermal optimum. Warm-month mean temperature changed little from the Eocene through the early Miocene; this parameter, however, markedly decreased at ≈ 13 Ma, which coincides with the growth of the east Antarctic ice sheet. clamp also indicates that the coastal region of western North America had significantly higher mat than interior regions such as the Great Basin and Rocky Mountains. These differences in mat appeared by, or during, the Eocene and indicate that much of the interior had high altitudes in the Paleogene. These inferences have a significant bearing on global circulation models proposed for Tertiary climates.

Palynology, paleoclimatology and correlation of middle Miocene beds from Porcupine River (locality 90-1), Alaska

Beds in the Upper Ramparts Canyon of the Porcupine River, Alaska (67° 20' N, 141° 20' W), yielded a flora rich in pollen of hardwood genera now found in the temperate climates of North America and Asia. The beds are overlain or enclosed by two basalt flows which were dated to 15.2 ± 0.1 Ma by the 40 Ar 39 Ar method, fixing the period of the greatest abundance of warm-loving genera to the early part of the middle Miocene. The assemblage is the most northern middle Miocene flora known in Alaska. Organic bed 1 underlies the basalt and is older than 15.2 Ma, but is of early to middle Miocene age. The pollen assemblage from organic bed 1 is dominated by conifer pollen from the pine and redwood-cypress-yew families with rare occurrences of temperate hardwoods. Organic bed 2 is a forest floor containing redwood trees in life position, engulfed by the lowest basalt flow. A pine log has growth rings up to 1 cm thick. Organic beds 3 and 4 comprise lacustrine sediment and peat between the two basalt flows. Their palynoflora contain conifers and hardwood genera, of which about 40% have modern temperate climatic affinities. Hickory, katsura, walnut, sweet gum, wingnut, basswood and elm pollen are consistently present, and beech and oak alone make up about 20% of the pollen assemblage. A warm high latitude climate is indicated for all of the organic beds, but organic bed 3 was deposited under a time of peak warmth. Climate data derived by comparison with modern east Asian vegetation suggest that, at the time of deposition of organic bed 3, the Mean Annual Temperature (MAT) was ca. 9°C, the Warm Month Mean Temperature (WMMT) was ≥ 20°C and the Cold Month Mean Temperature (CMMT) was ca. −2°C. In contrast, the modern MAT for the region is −8.6°C, WMMT is 12.6°C and CMMT is −28°C. Organic beds 3 and 4 correlate to rocks of the middle Miocene—late Seldovian Stage of Cook Inlet and also probably correlate to, and more precisely date, the lower third of the Suntrana Formation in the Alaska Range, beds at Unalaklect, part of the upper Mackenzie Bay sequence in the Beaufort-Mackenzie basin, and the Mary Sachs gravel of Banks Island. This suggests that forests with significant percentages of temperate deciduous angiosperms existed between latitudes 60° and 72°N during the early middle Miocene.