Mean Annual Precipitation Estimates Research Articles

PALEOCLIMATIC AND PALEOECOLOGICAL IMPLICATIONS OF A PALEOCENE-EOCENE FOSSIL LEAF ASSEMBLAGE, CHICKALOON FORMATION, ALASKA

Abstract New collections of a leaf compression-impression paleoflora preserved in fluvio-lacustrine sediments of the upper Chickaloon Formation, south-central Alaska, United States, provide leaf physiognomic climate estimates for the early Eocene in southern Alaska and rare data on plant-insect interactions from a subarctic setting. Thirty-nine broadleaf angiosperm morphotypes occur in a parautochthonous assemblage along with Metasequoia shoots and trunks, compressions of a diverse suite of seeds, monocotyledonous aquatic plants, freshwater gastropods, and inclusion-bearing dispersed amber. Leaf-character derived mean annual temperature estimates (11–14.6 °C) are significantly warmer than Alaska at present and indicate warm temperate conditions at the time of deposition. Leaf-derived mean annual precipitation estimates of ∼110–160 cm/annum are comparable to those from similar-age paleofloras in Arctic Canada and indicate wetter conditions than nearly coeval paleofloras further south in the North American ...

New weathering index improves paleorainfall estimates from Vertisols

Vertisols are clayey, shrink-swell soils that are widely recognized in the rock record, thus generating the need to better understand the dynamics of elemental concentrations on the development of weathering indexes for climate interpretations. We assessed the weathering performance of the four major base-forming oxides (CaO, MgO, Na 2 O, K 2 O) along a modern Vertisol climosequence spanning a strong precipitation gradient, and discovered that the concentration of bulk soil CaO and MgO yields the strongest correlation to mean annual precipitation (MAP). Based on this fi nding, we introduce the CALMAG weathering index, defi ned as Al 2 O 3 / (Al 2 O 3 + CaO + MgO) × 100, which improves rainfall estimates for Vertisols relative to the wellestablished CIA-K (chemical index of alteration minus potassium) weathering index. Rather than documenting the hydrolysis of weatherable minerals common in many other soil orders, in Vertisols CALMAG principally tracks the fl ux of calcium and magnesium sourced from calcium carbonate, detrital clay, and exchangeable Ca 2+ and Mg 2+ . Application to two Mesozoic paleosols reveals that in drier climates CIA-K yields higher MAP estimates than CALMAG, but that the reverse is true in wetter climates. This work improves paleorainfall estimates from Vertisols and suggests that a family of weathering indexes is needed for different paleosol types.

Factors of paleosol formation in a Late Cretaceous eolian sand sheet paleoenvironment, Marília Formation, Southeastern Brazil

The Marília Formation, which crops out in southeastern Brazil, is interpreted as a Late Cretaceous eolian sand sheet area. The sedimentary succession, ca 110 m thick, is characterized by alternating strata of eolian deposits and paleosols. The paleosols constitute more than 66% of the thickness, and are an important element in the interpretation of the paleoenvironmental controlling factors which affected the soil formation in this eolian sand sheet. In this paper six paleosol profiles are described and assigned to two pedotypes: Itaja and Apore. The Itaja pedotype is constituted of a sequence of five superimposed polygenetic profiles which show different phases of clay illuviation and carbonate precipitation, and it has been classified as Aridisol. The Apore pedotype overlies the Itaja pedotype. This pedotype shows an increase in leaching, CIA-K ratios, reddening, and illuvial clay features in respect to Itaja, and has been classified as Alfisol. The analysis of the factors which controlled the soil formation revealed that both pedotypes formed on a stable landscape probably covered by a community of low stature plants, in which the soils had sufficient time to develop very mature profiles. The changes in soil-forming processes were driven principally by variations in available soil moisture from precipitation. Using depth-to-carbonate functions from Bk and CIA-K proxy from Bt horizons of the Itaja pedotype, mean annual precipitation (MAP) estimates range from 240 to 1078 mm/yr, respectively. These contrasting climatic conditions resulted in the superimposition of arid or semi-arid with more humid climates and determined the considerable change in the pedogenic features, with many horizons showing the interlacing of calcite and clay features. In the Apore pedotype CIA-K proxy from Bt horizons estimates that averaged MAP was around 900 mm/yr, and the prevalent humid conditions can be attested by soil properties and abundance and depth of root traces. Our results show that the diversity in pedotypes is mainly attributed to differences in paleoclimatic conditions during Maastrichtian time, and that eolian sedimentation was restricted to periods of harsh arid conditions, as in semi-arid climates, with MAP estimates around 240 mm/yr, the formation of soils with well developed calcic horizons was possible.

Holocene precipitation in the coastal temperate rainforest complex of southern British Columbia, Canada

Pollen data from 69 surface samples from Vancouver Island, Canada, were used to develop a ratio index of precipitation, Douglas fir-western hemlock index (DWHI). DWHI ratios were combined with interpolated estimates of mean annual precipitation to develop pollen-based precipitation transfer functions. The optimal regression model, with a predictive range of 960–2600 mm, was applied to 10 Holocene lake sediment records distributed across a ∼150 km long coastal–inland precipitation gradient. Predicted precipitation was spatially modelled in a geographic information system to examine the spatio–temporal history of precipitation from this representative portion of the coastal temperate rainforest (CTR) complex of western North America. The reconstructions show widespread early Holocene dry conditions coupled with a steep east–west precipitation gradient. Thereafter, the modern precipitation gradient established 7000 years ago, illustrating that the CTR complex has experienced marked short-distance east–west changes in precipitation in the past. Changes in the abundance of arboreal and non-arboreal vegetation, as well as fire disturbance, are often concomitant with changes in Holocene precipitation. Given the precipitation and vegetation history of the region, conservation initiatives should focus on the moist outer coastal zone since it appears to have the greatest amount of resilience to perturbations in precipitation, whereas monitoring programs for signs of climate change should be initiated in central and eastern areas as they appear sensitive to changes in the moisture regime.

Modern Tropical Forest Taphonomy: Does High Biodiversity Affect Paleoclimatic Interpretations?

Modern biodiversity hotspots are characterized by high species diversity and by biotas facing a substantial threat of extinction, largely due to a high proportion of endemic taxa living in these regions. Theoretically, hotspots of biodiversity are areas of particular interest in the fossil record because of the relatively high quality and quantity of data that they may contribute to a global understanding of vegetational response to changes in climate, tectonic uplift, and ecological disturbance. Current models for climatic reconstruction that depend on leaf physiognomy are based on data sets in which species-rich tropical floras are less well represented, relative to temperate floras. Eight modern Neotropical floras from a range of precipitation regimes were evaluated to determine the influence that high source floral diversity has on reconstruction of mean annual temperature (MAT) and mean annual precipitation (MAP). Floras are drawn from sites in Costa Rica to southern Peru, having species richness from 55 to >400 species per plot. MAT of the sites spans a range of 24 to 28°C, and MAP ranges from ∼1600 mm to 3000 mm. By subsampling the modern floras in rank order of dominance (basal area), the importance of collecting intensity and completeness on subsequent assessments of MAT and MAP is evaluated. Biodiverse floras are good at reconstructing MAT if at least 50% of the species are included. When only 25 species are used for temperature calculations, the accuracy of the parameter is compromised, but a ±3°C error encompasses the majority of the deviation. Application to the early Paleocene Castle Rock fossil flora of Colorado confirms the validity of subsampling in high-diversity fossil applications. However, reconstruction of MAP is fraught with problems that do not appear to be related to biodiversity of the floras. Errors on estimates of MAP currently are so large as to make the values too vague to be useful in most applications. This study has accepted a 20% error as necessary, but the applicability of data with errors > 20% is questionable in situations where rainfall is >1500 mm per year. MAP estimates using leaf area are almost universally underestimates of actual MAP, and frequently are >400 mm in error. Exploration of these data indicates that effort would be well placed in investigating the relative importance of precipitation parameters in altering leaf morphology before choosing one to reconstruct climates of the past.

Phytoliths as quantitative indicators for the reconstruction of past environmental conditions in China I: phytolith-based transfer functions

This study investigated the distribution of phytolith assemblages in China from surface soil samples at 243 sites along significant ecological and climatic gradients to develop transfer functions for quantitative reconstruction of palaeoenvironment. Canonical correspondence analysis (CCA) and detrended correspondence analysis (DCA) were used to determine the main environmental variables influencing phytolith distributions. The results reveal that mean annual precipitation (MAP) is the dominant variable controlling the spatial distribution of phytoliths, which accounts for 39% of the total variance. Mean annual temperature (MAT), relative humidity (Humi), and annual evaporation (VAP) are another three significant variables, accounting for 6%, 10%, and 5%, respectively, of the total variance in phytolith distributions. Transfer functions, based on weighted averaging plus partial least squares (WA-PLS), were developed for MAP ( R - boot 2 = 0.90 , root-mean-square-error of prediction (RMSEP)=148 mm), MAT ( R - boot 2 = 0.84 , RMSEP=2.52 °C), Humi ( R - boot 2 = 0.75 , RMSEP=6.36%) and VAP ( R - boot 2 = 0.59 , RMSEP=327 mm). Overall, our results confirm that phytoliths can provide reliable and robust estimates of MAP, MAT, Humi and VAP. Thus, WA-PLS is a robust calibration method for quantitative palaeoenvironmental reconstruction based on phytolith data.

Eocene dry climate and woodland vegetation in tropical Africa reconstructed from fossil leaves from northern Tanzania

Eocene vegetation and climate data from tropical latitudes are sparse despite special interest in the Eocene as the warmest epoch of the Cenozoic and an often-cited analogue for greenhouse Earth conditions. Tropical Africa is noteworthy for its shortage of Eocene fossils, which could serve as proxies for climate and reveal community structural evolution during the continent's geographic isolation. In this paper, we report paleobotanical remains from a middle Eocene crater lake at 12°S paleolatitude in north central Tanzania, which provide a plant community reconstruction indicating wooded, rather than forest, vegetation and precipitation estimates near modern (660 mm/year). The plant community was dominated by caesalpinioid legumes and was physiognomically comparable to modern miombo woodland. Paleoprecipitation estimates, the first for the Paleogene of Africa, are calculated from fossil leaf morphology using regression equations derived from modern low-latitude leaves and climate. Mean annual precipitation estimates are 643±32 and 776±39 mm/year, and wet months precipitation estimates (all months averaging≥50 mm) are 630±38 and 661±38 mm. A slightly larger proportion of annual precipitation occurred in the dry months compared with today, which may indicate greater equability of precipitation in the Eocene.

Eocene dry climate and woodland vegetation in tropical Africa reconstructed from fossil leaves from northern Tanzania

Eocene vegetation and climate data from tropical latitudes are sparse despite special interest in the Eocene as the warmest epoch of the Cenozoic and an often-cited analogue for greenhouse Earth conditions. Tropical Africa is noteworthy for its shortage of Eocene fossils, which could serve as proxies for climate and reveal community structural evolution during the continent's geographic isolation. In this paper, we report paleobotanical remains from a middle Eocene crater lake at 12°S paleolatitude in north central Tanzania, which provide a plant community reconstruction indicating wooded, rather than forest, vegetation and precipitation estimates near modern (660 mm/year). The plant community was dominated by caesalpinioid legumes and was physiognomically comparable to modern miombo woodland. Paleoprecipitation estimates, the first for the Paleogene of Africa, are calculated from fossil leaf morphology using regression equations derived from modern low-latitude leaves and climate. Mean annual precipitation estimates are 643±32 and 776±39 mm/year, and wet months precipitation estimates (all months averaging≥50 mm) are 630±38 and 661±38 mm. A slightly larger proportion of annual precipitation occurred in the dry months compared with today, which may indicate greater equability of precipitation in the Eocene.

The relationship between climate and rock glacier distribution in the ben ohau range, new zealand

Landforms of ice and debris transport marginal to the glacierized zone of the Southern Alps, New Zealand, have been classified into debris‐covered glaciers, cirque floor lobes, and talus‐derived rock glaciers. Mapping of fossil and active landforms reveals a zonation within the Ben Ohau Range in terms of both landform type and activity status. The dominant distinction of active forms is between relatively ice‐rich forms (glacial origins) in the humid north and relatively debris‐rich forms (periglacial origins) in the more arid south. A secondary altitudinal zonation distinguishes currently or recently active forms at high elevations from fossil forms at lower elevations. Estimates of mean annual precipitation and of the altitude of the –2°C mean annual isotherm indicate that glaciers and active talus rock glaciers are located within the climatic boundaries identified for the European Alps. However, many fossil forms also occur within these boundaries where cirques are broader and shallower. These findings confirm earlier suggestions that permafrost occurs in the Southern Alps, but is restricted to a narrow zone above 2000 m. The study demonstrates the importance of relative ice‐to‐debris fluxes in determining the developmental pathways of landform genesis over both space and time.

The mutual climatic range method of palaeoclimate reconstruction based on insect fossils: New applications and interhemispheric comparisons

The Mutual Climatic Range (MCR) method of palaeoclimate reconstruction has been employed in Europe for the last decade. A quantitative, calibrated method, MCR has many advantages over qualitative methods. More recent applications deal with eastern and central North America, and the method is also being developed for desert and arctic faunas. The climate envelopes for North American beetles have been compiled using a 25-km gridded North American climate database that pairs climate parameters with modern collection sites. Modern tests of the reliability of the MCR method for North American species yielded similar results to prior European tests. Linear regressions of predicted on observed values yielded equations used to calibrate the MCR estimates. Work is under way to develop MCR estimates of mean annual precipitation for fossil assemblages from the desert southwest, where moisture conditions may play a more important role in determining beetle species' ranges. An examination of British and North American mean July temperature reconstructions during the Late Wisconsinan glacial interval compares and contrasts three sets of records. The North American records show no indication of the Younger Dryas cooling that is clearly marked in records from northwest Europe. The MCR method adds vigour to our reconstructions, and allows us to compare between regions and with other palaeoenvironmental methods.

Climate and vegetation dynamics in the tundra and forest zone during the late glacial and holocene

Analysis of palynological successions has enabled reconstruction of climate variations throughout the Late Glacial and Holocene in the tundra and forest zones of northern Eurasia. Statistical analysis allows estimation of mean annual precipitation, and mean annual and July temperatures, based on palynological assemblages. Thus, the dynamic relationships between climate and vegetation changes can be established. Throughout the Late Glacial and Holocene, climate fluctuations were more dramatic in eastern Europe than in Siberia, primarily as a result of the influence of westerly air masses. In contrast, the “autochthonous” climate of Siberia, dominated by local air masses, was less prone to influence from climate changes elsewhere in the Northern Hemisphere, and shows only an attenuated Younger Dryas signal. Mid-Holocene warming characterizes all of northern Eurasia, although the regions of Siberia most influenced by continental climates show less pronounced cooling during the later Holocene. Sharp changes between summer monsoonal and winter anti-cyclonic regimes characterize the Pacific Maritime region.

Estimation of mean annual precipitation as affected by elevation using multivariate geostatistics

This paper presents the results of the interpolation of annual precipitation over a regular grid performed in Aragon (Spain). The main objective was the quantification of the improvement in estimation uncertainty by including elevation in the interpolation and by using base 10 logarithms of both annual precipitation and elevation versus the original values.

A comparison of geostatistical procedures for spatial analysis of precipitation in mountainous terrain

Spatially distributed measurements or estimates of precipitation over a region are required for modelling of hydrologic processes and soil moisture for agricultural and natural resource management. Simple interpolation methods fail to consider the effects of topography on precipitation and may be in considerable error in mountainous regions. The performance of three geostatistical methods for making mean annual precipitation estimates on a regular grid of points in mountainous terrain was evaluated. The methods were: (1) kriging; (2) kriging elevation-detrended data; and (3) cokriging with elevation as an auxiliary variable. The study area was the Willamette River basin, a 2.9 million hectare region spanning the area between the Coast Range and the Cascade Range in western Oregon. Compared with kriging, detrended kriging and cokriging both exhibited better precision (as indicated by estimation coefficients of variation of 16 and 17% vs. 21%; and average absolute errors of 19 and 20 cm vs. 26 cm) and accuracy (as indicated by average errors of −1.4 and −2.0 cm vs. −5.2 cm) in the estimation of mean annual precipitation. Contour diagrams for kriging and detrended kriging exhibited smooth zonation following general elevation trends, while cokriging showed a patchier pattern more closely corresponding to local topographic features. Detrended kriging and cokriging offer improved spatially distributed precipitation estimates in mountainous terrain on the scale of a few million hectares. Application of these methods for a larger region, the Columbia River drainage in the USA (57 million hectares), was unsuccessful due to the lack of a consistent precipitation-elevation relationship at this scale. Precipitation estimation incorporating the effects of topography at larger scales will require either piecewise estimation using the methods described here or development of a physically based orographic model.

APPLICATION OF KRIGING TO ESTIMATING MEAN ANNUAL PRECIPITATION IN A REGION OF OROGRAPHIC INFLUENCE1

ABSTRACT: Estimates of mean annual precipitation (MAP) over areas are the starting point for all computations of water and chemical balances for drainage basins and surface water bodies. Any errors in the estimates of MAP are propagated through the balance computations. These errors can be due to: (1) failures of individual gages to collect the amount of precpitation that actually falls; (2) operator errors; and (3) failure of the raingage network to adequately sample the region of interest. This paper attempts to evaluate the last of these types of error by applying kriging in two different approaches to estimating MAP in New Hampshire and Vermont, USA. The data base is the 1951–1980 normal precipitation at 120 raingages in the two states and in adjacent portions of bordering states and provinces. In the first approach, kriging is applied directly to the MAP values, while in the second, kriging is applied to a “precipitation delivery factor” that represents the MAP with the orographic effect removed. The first approach gives slightly better kriged estimates of MAP at seven validation stations that were not included in the original analysis, but results in an error surface that is highly contorted and in larger maximum errors over most of the region. The second approach had a considerably smoother error surface and, thus, is generally preferable as a basis for point and areal estimates of MAP. MAP estimates in the region have 95 percent confidence intervals of about 20 cm/yr at low and moderate elevations, and up to 35 cm/yr at high elevations. These uncertainties amount to about 20 percent of estimated MAP values.

A Climatological Estimate of Precipitation for the World Ocean

Abstract Climatological estimates of mean annual precipitation over the world ocean are presented and discussed. We obtained a value for mean annual oceanic precipitation (between 65°N and 60°S) of 93 cm, which is smaller than some other estimates. These results are supported by a recent analysis of tropical rainfall based on satellite techniques. Aspects of the need for and utility of climatological information are discussed.

Estimation of mean annual precipitation from snow‐survey data

A high degree of correlation is shown to exist between the mean water equivalent of the snow pack on March 1 at snow courses in the Snake River region and the mean annual precipitation at nearby precipitation stations. Attempts were made to improve the correlation by introducing various additional parameters, but the resulting changes were not significant. In attempting to introduce length of snow‐accumulation season as a parameter, a relation between elevation, latitude, and average beginning date of continuous winter snow cover with at least one inch of snow on the ground was developed.