Megathermal Climate Research Articles

Climatological water balance and climate classification of thornthwaite and mather for benin, west Africa, in 1970-2015 period

The climate is described by the predominant atmospheric conditions in a particular region and influences several human activities. In agriculture, water availability defines the growth and yield of crops and can be obtained by the water balance. The climate classification also aids to identify suitable areas for agricultural crops. Thus, the aim of this work was to elaborate the water balance and perform the climate classification through the method of Thornthwaite and Mather (1955) for six weather stations (Bohicon, Cotonou-Airport, Kandi-Airport, Natitingou, Parakou-Airport and Savè) located in Benin, Western Africa. For the execution of this work, monthly series of precipitation and potential evapotranspiration from 1970 to 2015 were used. Once the monthly water balance of the six seasons was elaborated, it was observed that the rainy (dry) period decreases (increases) from the coast (Cotonou-Airport) to the north of Benin (Kandi-Airport) and, coincides with Boreal summer and part of autumn (Boreal winter and part of spring). Regarding the climate classification, the Cotonou-Airport station was characterized as Subhumid Megathermal climate with moderate winter deficit (C2wA’a’); the stations of Bohicon and Savè presented similar climate classification with Subhumid Dry Megathermal climate with low or without water surplus (C1dA’a’); Natitingou with Subhumid Dry climate Megathermal with large summer surplus (C1s2A’a’); Parakou-Airport with Subhumid climate Dry Megathermic with moderate summer surplus (C1sA’a’) and, Kandi-Airport presented Semi-arid Megathermal climate with moderate summer surplus (DsA’a’). In Benin, subsistence and rainfed farming showed greater risk in the north of the country due to the decrease in the rainy season and the water surplus from the coast (south) to the north of the country, with the increase in aridity.

The second North American fossil horntail wood-wasp (Hymenoptera: Siricidae), from the early Eocene Green River Formation.

Eoteredon lacoi gen. et sp. nov., is described from the early Eocene Green River Formation in Wyoming, the second fossil siricid genus and species described from North America. We propose Eoteredon as sister to the genus Teredon, whose sole species is one of the rarest of extant Siricidae. The majority of siricids today inhabit temperate Northern Hemisphere forests; Teredon cubensis, however, is one of its few species that live in megathermal tropical lowlands. The Eocene forest that Eoteredon inhabited had a mesothermal to megathermal climate. We place Eoteredon in the context of broad Cenozoic climate change.

Climate change winners and losers: The effects of climate change on five palm species in the Southeastern United States.

Palms (Arecaceae) are a relatively speciose family and provide materials for food, construction, and handicraft, especially in the tropics. They are frequently used as paleo‐indicators for megathermal climates, and therefore, it is logical to predict that palms will benefit from predicted warmer temperatures under anthropogenic climate change. We created species distribution models to explore the projected ranges of five widespread southeastern North American palm species (Rhapidophyllum hystrix, Sabal etonia, Sabal minor, Sabal palmetto, and Serenoa repens) under four climate change scenarios through 2070. We project that the amount of habitat with >50% suitability for S. etonia will decline by a median of 50% by 2070, while the amount of habitat with >50% suitability S. minor will decline by a median of 97%. In contrast, the amount of suitable habitat for Rhapidophyllum hystrix will remain stable, while the amount of suitable habitat for Serenoa repens will slightly increase. The projected distribution for S. palmetto will increase substantially, by a median of approximately 21% across all scenarios. The centroid of the range of each species will shift generally north at a median rate of 23.5 km/decade. These five palm species have limited dispersal ability and require a relatively long time to mature and set fruit. Consequently, it is likely that the change in the distribution of these palms will lag behind the projected changes in climate. However, Arecaceae can modify physiological responses to heat and drought, which may permit these palms to persist as local conditions become increasingly inappropriate. Nonetheless, this plasticity is unlikely to indefinitely prevent local extinctions.

Evaluación de los índices de calidad del suelo de diversos cultivos en diferentes condiciones topográficas

Soil quality is a valuation tool that facilitates the application of management practices that promote sustainable agronomic systems. The objective is to characterize various land uses based on various physical-chemical properties of the soil and to estimate a soil quality index for various crops in different topographic. The study was carried out in three land uses that were Banana, Young and Ripe Cocoa located in the El Progreso belonging to the Canton of Pasaje-El Oro, with a tropical megathermal climate and an irregular topography. Fifteen soil samples were taken from the stratum (0 to 0.10 cm). An analysis of the physical and chemical variables of the soil was carried out. The variables that presented incompatibilities were put to a principal component analysis to select the minimum data set (MDS) of the components that explained the greatest variability and redundancy was verified from the correlation. The SQI was obtained from the average of the standardized indicators (0 to 1), the higher the SQI value the better the land quality of the land use.

Decomposition of green manure biomass in dystrophic Yellow Latosol in Piauí state, Brazil

Although most research demonstrates the importance of green manure, some aspects have yet to be elucidated. Thus, the present study aimed to determine the biomass decomposition pattern of plants used as green manure in dystrophic Yellow Latosol (coastal caatinga phase), under a dry megathermal climate, with a small water surplus. A completely randomized design was used, with nineteen treatments and four repetitions. The decomposition constant (k), remaining dry biomass and half-life (T1/2) of the residue after 120 days in the field were assessed. Cowpea, jack bean and sunflower (cv. Catissol and IAC Uruguai) are rapidly decomposing species with a half-life ranging from 98 to 112 days to decompose 50% of biomass. Dwarf pigeon pea, crotalária juncea, sorghum 1 and siratro are slow-decomposing species, with a 315 to 630-day half-life to decompose 50% of biomass. Both groups are recommended for intercropping because the decomposition rate of their plant residue is compatible with soil protection and nutrient supply, in addition to being sync with the nutrient requirements of cash crops.

Early Eocene (Ypresian) birds from the Okanagan Highlands, British Columbia (Canada) and Washington State (USA)

We survey the known avian fossils from Ypresian (early Eocene) fossil sites of the North American Okanagan Highlands, mainly in British Columbia (Canada). All specimens represent taxa that were previously unknown from the Eocene of far-western North America. Wings from the McAbee site are tentatively referred to the Gaviiformes and would constitute the earliest fossil record of this group of birds. A postcranial skeleton from Driftwood Canyon is tentatively assigned to the Songziidae, a taxon originally established for fossils from the Ypresian of China. Two skeletons from Driftwood Canyon and the McAbee site are tentatively referred to Coliiformes and Zygodactylidae, respectively, whereas three further fossils from McAbee, Blakeburn, and Republic (Washington, USA) are too poorly preserved for even a tentative assignment. The specimens from the Okanagan Highlands inhabited relatively high paleoaltitudes with microthermal climates (except Quilchena: lower mesothermal) and mild winters, whereas most other Ypresian fossil birds are from much warmer lowland paleoenvironments with upper mesothermal to megathermal climates. The putative occurrence of a gaviiform bird is particularly noteworthy because diving birds are unknown from other lacustrine Ypresian fossil sites of the Northern Hemisphere. The bones of the putative zygodactylid show a sulphurous colouration, and we hypothesize that this highly unusual preservation may be due to the metabolic activity of sulphide-oxidizing bacteria.

Fossil woods from the Cenozoic of Panama (Azuero Peninsula) reveal an ancient neotropical rainforest

Silicified woods from near the town of Ocú on the Azuero Peninsula, Panama were first reported by Stern and Eyde in 1963; however, the significance of these fossils has been largely overlooked. Well-characterized fossil floras from Central America can be used to test hypotheses related to the historical biogeography and paleoclimate of the Neotropics. We describe 10 new wood types and one palm based on 22 samples from Oligo-Miocene deposits. Affinities at the family/order level include Fabaceae, Lauraceae, Moraceae, Sapotaceae, Euphorbiaceae, Arecaceae, Sapindales, Ericales, and Humiriaceae. The fossil woods are fragmentary and have not been found in-place, but the size and angularity of the specimens suggests minimal transport from the site of growth. We compared these woods with calcareous woods from the Lower Miocene Cucaracha Formation and silicified woods from the upper Miocene Alajuela Formation using Rare Earth Element (REE) analysis to test the hypothesis that the Ocú woods were preserved under uniform conditions and not reworked. Although the results were ambiguous with respect to the original hypothesis, we note that the REE concentrations in silicified woods are much lower than in calcareous woods. We used comparative analysis of wood anatomical features to draw conclusions about the paleoclimate from the fossil flora. All the dicot woods are diffuse porous and none have distinct growth rings; some have very wide vessels at low frequencies. These features are typical of canopy trees in tropical lowland forests. Nonmetric multidimensional scaling of wood anatomical characters from a variety of communities and ecological categories showed that the anatomy of the Ocú woods is most similar to that found in tropical rainforests. Based on the combination of taxonomic identity and functional anatomy, we interpret these fossils as evidence for humid to perhumid megathermal climate in Panama during the late Paleogene-early Neogene.

The Practice of Green Cane Trash Blanketing in the Irrigated Zone of Mauritius: Effects on Soil Moisture and Water Use Efficiency of Sugarcane

Sugarcane growers in Mauritius are using mechanized harvesting to reduce costs. This practice results in a trash blanket which contributes to conserve soil moisture, but potential savings in irrigation water have yet to be quantified. An on-farm study was undertaken at three sites in the irrigated coastal zone of Mauritius under sub-humid to humid mega-thermal climate and soils that were oxisol or inceptisol. Trials were conducted in ratoon crops under centre pivot irrigation and treatments with or without trash blanket, as well as different irrigation regimes. Sensors were used to log soil moisture data at 20, 40 and 60 cm depths. Increased drainage was observed under trash blanket during rainfall events and cumulative drainage for a 4-month wet period amounted to 43 and 240 mm for no-trash and trash blanket treatments respectively. Daily crop water use was higher with trash blanket, consumption being 4.9 and 5.1 mm day−1 compared to 4.2 and 4.6 mm day−1 for no-trash during peak growth at Savannah and Medine. Sugarcane yield was higher by 7.2 and 6.6 t ha−1 year−1 with trash blanket compared to no-trash, whereas water use efficiency increased by 8 and 9 kg ha−1 mm−1. At Saint Antoine, trash blanket increased the yield difference between irrigated and rainfed crops by 8.6 t ha−1 and improved water use efficiency by 7 kg ha−1 mm−1 when irrigated. Seasonal water equivalence of the trash blanket amounted to 62, 54 and 72 mm water at Savannah, Medine and Saint Antoine, a potential saving of 10–15 % in irrigation water.

Why complex cognitive ability increases with absolute latitude

Evolutionary psychologists attribute the superior IQs of light-skinned populations to genetic imprints left by millenary processes promoted by cold. But a novel theory that explains IQ gains observed across recent generations ascribes them to a latitude→UVB radiation→vitamin D3→parents' sexual hormones→family size→child's intellectual environment→IQ chain of effects. Analyses of 506,347 Peruvian children's math and reading scores from a national census confirmed that complex cognitive ability increases with absolute latitude even under tropical megathermal climates and decreases with high altitude above sea level, birth rate and social development mediate most of the effects, and reading is more strongly influenced than math. The findings weaken the evolutionary cold hypothesis and strengthen the view that contraception has the potential to reduce latitudinal IQ gaps.

Regional-scale spatial heterogeneity in the late Paleocene paratropical forests of the U.S. Gulf Coast

The study of spatial patterns in biotic compositional variability in deep time is key to understanding the macroecological response of species assemblages to global change. Globally warm climatic phases are marked by the expansion of megathermal climates into currently extra-tropical areas. However, there is currently little information on whether vegetation in these “paratropical” regions resembled spatially modern tropical or extra-tropical biomes. In this paper we explore spatial heterogeneity in extra-tropical megathermal vegetation, using sporomorph (pollen and spore) data from the late Paleocene Calvert Bluff and Tuscahoma Formations of the formerly paratropical U.S. Gulf Coast (Texas, Mississippi, and Alabama). The data set comprises 139 sporomorph taxa recorded from 56 samples. Additive diversity partitioning, nonmetric multidimensional scaling, and cluster analysis show compositional heterogeneity both spatially and lithologically within the U.S. Gulf Coastal Plain (GCP) microflora. We then use sporomorph data from Holocene lake cores to compare spatial patterns in the late Paleocene GCP with modern tropical and extra-tropical biomes. Distance decay analysis of the Holocene data reveals a higher rate of spatial turnover in tropical versus extra-tropical vegetation types, consistent with a latitudinal gradient in floral compositional heterogeneity. The specific combination of rate and scale dependency of distance decay in the Holocene assemblages prevented us from associating the late Paleocene GCP with any particular modern biome. Our results demonstrate the importance of spatial scale, taphonomy, and lithology in determining patterns of spatial heterogeneity, and show the potential of the fossil sporomorph record for studying spatial patterns and processes in deep time.

Regional-scale spatial heterogeneity in the late Paleocene paratropical forests of the U.S. Gulf Coast

The study of spatial patterns in biotic compositional variability in deep time is key to understanding the macroecological response of species assemblages to global change. Globally warm climatic phases are marked by the expansion of megathermal climates into currently extra-tropical areas. However, there is currently little information on whether vegetation in these “paratropical” regions resembled spatially modern tropical or extra-tropical biomes. In this paper we explore spatial heterogeneity in extra-tropical megathermal vegetation, using sporomorph (pollen and spore) data from the late Paleocene Calvert Bluff and Tuscahoma Formations of the formerly paratropical U.S. Gulf Coast (Texas, Mississippi, and Alabama). The data set comprises 139 sporomorph taxa recorded from 56 samples. Additive diversity partitioning, nonmetric multidimensional scaling, and cluster analysis show compositional heterogeneity both spatially and lithologically within the U.S. Gulf Coastal Plain (GCP) microflora. We then use sporomorph data from Holocene lake cores to compare spatial patterns in the late Paleocene GCP with modern tropical and extra-tropical biomes. Distance decay analysis of the Holocene data reveals a higher rate of spatial turnover in tropical versus extra-tropical vegetation types, consistent with a latitudinal gradient in floral compositional heterogeneity. The specific combination of rate and scale dependency of distance decay in the Holocene assemblages prevented us from associating the late Paleocene GCP with any particular modern biome. Our results demonstrate the importance of spatial scale, taphonomy, and lithology in determining patterns of spatial heterogeneity, and show the potential of the fossil sporomorph record for studying spatial patterns and processes in deep time.

Testing the Water–Energy Theory on American Palms (Arecaceae) Using Geographically Weighted Regression

Water and energy have emerged as the best contemporary environmental correlates of broad-scale species richness patterns. A corollary hypothesis of water–energy dynamics theory is that the influence of water decreases and the influence of energy increases with absolute latitude. We report the first use of geographically weighted regression for testing this hypothesis on a continuous species richness gradient that is entirely located within the tropics and subtropics. The dataset was divided into northern and southern hemispheric portions to test whether predictor shifts are more pronounced in the less oceanic northern hemisphere. American palms (Arecaceae, n = 547 spp.), whose species richness and distributions are known to respond strongly to water and energy, were used as a model group. The ability of water and energy to explain palm species richness was quantified locally at different spatial scales and regressed on latitude. Clear latitudinal trends in agreement with water–energy dynamics theory were found, but the results did not differ qualitatively between hemispheres. Strong inherent spatial autocorrelation in local modeling results and collinearity of water and energy variables were identified as important methodological challenges. We overcame these problems by using simultaneous autoregressive models and variation partitioning. Our results show that the ability of water and energy to explain species richness changes not only across large climatic gradients spanning tropical to temperate or arctic zones but also within megathermal climates, at least for strictly tropical taxa such as palms. This finding suggests that the predictor shifts are related to gradual latitudinal changes in ambient energy (related to solar flux input) rather than to abrupt transitions at specific latitudes, such as the occurrence of frost.

Thermal Classification of Pakistan

This research work is designed to carry out the annual and seasonal thermal classification of Pakistan to provide better understanding to all the stake holders like farmers and scientists etc for obtaining maximum crop yield. The data of Climatic Normal’s (1971-2000) has been used to calculate Thornthwaites’s Thermal efficiency index for thermal classification of Pakistan. The results of annual thermal classification reveals that Pakistan’s northern half experiences Tundra to Microthermal climate type and southern half experiences all types of Mesothermal to Megathermal climate type. Seasonal analysis showed large variations like in winters the whole country ranges from Microthermal to Frost Type of climate except the extremely southern parts of the country which have Mild Mesothermal climate. In spring the northern half of the country lies between Tundra to Microthermal climate and southern half from Mesothermal to Megathermal climate. During summer and monsoon majority of the regions in the country experience Megathermal except Northern areas which show Moderate Mesothermal to Mesothermal climate. The autumn season mostly have Mild Mesothermal to Tundra climate excluding southern half which showed Moderate Mesothermal to Mesothermal climate.

Geologic and taphonomic context of El Bosque Petrificado Piedra Chamana (Cajamarca, Peru)

ABSTRACTVolcanic and volcaniclastic rocks in the northern Peruvian Andes (central Caja-marca, 79°10 ′ W, 6°35 ′ S) contain a diverse assemblage of permineralized woods known as El Bosque Petrifi cado Piedra Chamana. The fossil forest and associated paleosol are preserved in ash-fall and lahar deposits of the Huambos Formation. Dating of plagio-clase from the ash-fall deposit using 40 Ar/ 39 Ar methods yields a middle Eocene age of 39.35 ± 0.21 Ma. Accuracy of this age determination is supported by a more robust sanidine age of 39.52 ± 0.11 Ma from an underlying welded ignimbrite. Fossil wood and leaves associated with the ash-fall deposit include vertical trees rooted in the paleosol and buried in situ by the ash. Fossil wood is also present in high abun-dance and diversity in the overlying lahar. The fossils are signifi cant as a low-latitude assem-blage including a diversity of both monocots and dicots and in having fossil leaves occur-ring in close proximity to fossil woods. Pre-liminary analyses of wood and leaf characters suggest a megathermal climate with some limitations on plant growth associated with limited (seasonal) moisture availability. The assemblage represents lowland tropical forest that was probably growing near sea level and subsequently uplifted to the current elevation at the site (~2400–2600 m).INTRODUCTION

Growth interruptions in silicified conifer woods from the Upper Cretaceous Two Medicine Formation, Montana, USA: implications for palaeoclimate and dinosaur palaeoecology

Taphonomic studies suggest that most dinosaur bone assemblages in the Upper Cretaceous (Campanian) Two Medicine Formation of Montana originated from drought-induced mass mortalities on the floodplain. This hypothesis is tested further by studying intra-annual growth patterns in silicified woods of cupressaceous/taxodiaceous conifers found in association with dinosaur bone material at a palaeolatitude of 48°N. True growth rings are completely absent, but growth interruptions characterised by concentric, variably persistent zones, 1–8 latewood cells wide are common. Interruptions are irregularly spaced so that, for example, four interruptions may occur along a radius of only 25 cells in one specimen, whilst in another specimen a radius more than 650 cells wide may completely lack interruptions. Irregular growth patterns like this occur in Upper Cretaceous woods across a broad latitudinal belt in the US Western Interior demonstrating that they resulted from regional climatic forcing rather than localised phenomena. Growth interruptions record the occurrence of short-term, aperiodic disturbances to tree growth, under an equable, megathermal climate that was otherwise favourable for continuous, year-round cambial activity. The only probable cause of growth interruption formation were drought-induced fluctuations in the water table and resultant water stress. Growth patterns suggest that sufficient water for uninhibited growth was continuously available for years at a time, but when water stress did occur, it did so repeatedly over a very few months. Comparison with present-day East Africa, where trees show very similar growth patterns, implies that the equable, but erratically humid, environment of the Late Cretaceous Western Interior was exactly the kind of setting where mass mortalities amongst megafauna might be expected. Like East Africa, this environment would have had sufficient carrying capacity to permit large herds of megafauna to develop under normal conditions, but when repeated phases of droughts struck, such populations would have been highly vulnerable.

The seasonal climate and low frequency oscillation in the simulated mid—Holocene megathermal climate

The mid—Holocene climate about 6000 years ago was simulated by using the atmospheric general circulation model. The orbital parameters for 6 ka BP (before present) were prescribed and other forcing factors were set in the modern conditions. Results show that the large—scale climate change in the African—Asian monsoon areas during the summer—time is strongly compared to the present climate, while the changes in other seasons and regions are generally weak. The results also revealed the change of the low frequency oscillation in the atmosphere.

A regional aridity phase and its possible cultural impact during the Holocene Megathermal in the Guanzhong Basin, China

Evidence of climatic variations and the impact of past farming was identified in a Holocene loess profile near Xi'an in the Guanzhong Basin, China. Detailed studies of the profile indicate that crop cultivation began at 7000 yr BP in the Neolithic and carried on to present in the area. Disturbance of the profile by cultivation has not masked evidence of changes in aeolian dust deposition and bio-pedogenic processes caused by climatic variations. Increased dust deposition indicates that a remarkable aridity phase occurred from 6000 to 5000 yr BP during the Holocene Megathermal (8500–3000 yr BP). The aridity and intensified aeolian dust deposition interrupted the formation of the brown soil developing under a warm-humid subtropical climate during the Megathermal. The palaeosol S0, normally associated with the Megathermal period, is thus separated into two distinct soils, namely S01 and S02. This variability in Megathermal climate may have been widespread across northwestern China. It is also possible that the marked decline in Neolithic culture in the periods of the middle and late Yangshao Culture (6000–5000 yr BP) in the Guanzhong Basin can be attributed to the climatic aridity at the time.

Role of vegetation and soil in the Holocene megathermal climate over China

There was significant difference between vegetation cover in mid‐Holocene and that at present over China based on various evidences as concluded by Shi et al [1992]. These changes were introduced to the climate model to study the role of the changing vegetation and associated soil to the simulated climate of mid‐Holocene at 6000 years before present (BP) with bigger seasonal cycle of insolation than present (caused by the change of orbital parameters). Results show that the changes in vegetation and soil could further strengthen the monsoon rainfall over China. We found that replacing the today's seasonal cycle of insolation by that of mid‐Holocene increases the summer (June‐August) precipitation by 20% in eastern China (100°–120°E, 18°–42°N); while considering both the effect of changing orbital forcing and the vegetation and soil, the total summer precipitation increase is 29% in the same region. Compared with the reconstructed precipitation over China, the result of that including changing vegetation and soil is quantitatively better.

North American nonmarine climates and vegetation during the Late Cretaceous

Analyses of physiognomy of Late Cretaceous leaf assemblages and of structural adaptations of Late Cretaceous dicotyledonous woods indicate that megathermal vegetation was an open-canopy, broad-leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year, with a moderate increase at about 40–45°N. Many dicotyledons were probably large, massive trees, but the tallest trees were evergreen conifers. Megathermal climate extended up to paleolatitude 45–50°N. Mesothermal vegetation was at least partially an open, broad-leaved evergreen woodland (perhaps a mosaic of woodland and forest), but the evapotranspirational stress was less than in megathermal climate. Some dicotyledons were large trees, but most were shrubs or small trees; evergreen conifers were the major tree element. Some mild seasonality is evidenced in mesothermal woods; precipitational levels probably varied markedly from year to year. Northward of approximately paleolatitude 65°N, evergreen vegetation was replaced by predominantly deciduous vegetation. This replacement is presumably related primarily to seasonality of light. The southern part of the deciduous vegetation probably existed under mesothermal climate. Comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational-climatic patterns suggested from North American data. Limited data from equatorial regions suggest low rainfall. Late Cretaceous climates, except probably those of the Cenomanian, had only moderate change through time. Temperatures generally appear to have warmed into the Santonian, cooled slightly into the Campanian and more markedly into the Maastrichtian, and then returned to Santonian values by the late Maastrichtian. The early Eocene was probably warmer than any period of the Late Cretaceous. Latitudinal temperature gradients were lower than at present. For the Campanian and Maastrichtian, a gradient of about 0.3°C/1° latitude is inferred. Equability was high: a mean annual range of temperature of about 8°C is inferred for paleolatitude 51–56°N during the Campanian. Most Late Cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation. A brief, low-temperature excursion and a major, long-lasting increase in precipitation occurred at the Cretaceous-Tertiary boundary. In megathermal climates, these events selected for plants that could exist in rainforest environments. In mesothermal climates, deciduousness and contamitant structural adaptations were selected. The events at the Cretaceous-Tertiary boundary had a major and long-lasting impact on the evolution of land plants and their ecosystems. Low precipitation at low to middle Late Cretaceous latitudes is suggested to be the result of high levels of atmospheric CO 2, which, in turn, are probably related to inability of warm, saline oceans to store large amounts of carbon. Conditions appear to have rapidly changed at the Cretaceous-Tertiary boundary, when oceanic circulation and stratification may have been fundamentally altered. After the boundary, the oceans were apparently able to store much greater amounts of carbon, and the oceans withdrew large amounts of CO 2 from the atmosphere. In turn, more precipitation fell at low to middle latitudes; the resulting high-biomass vegetation formed a second major carbon reservoir to keep atmospheric CO 2 low relative to the Late Cretaceous. Changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean-atmosphere system.