Oliver A. Chadwick

• PhD
• Professor (Full) at University of California, Santa Barbara

Most studies of the food resource potential of early Polynesian populations focus exclusively on agricultural potential, and specifically starchy staples, despite the importance of marine resources to the Polynesians. To more accurately estimate total precontact food resource availability, we characterized the terrestrial and near-shore marine envi...

Most studies of the food resource potential of early Polynesian populations focus exclusively on agricultural potential, and specifically starchy staples, despite the importance of the marine world to the Polynesians. In an attempt to more accurately estimate total precontact food resource availability, we characterized the terrestrial and near-sho...

Plants absorb nutrients and water through their roots and modulate soil biogeochemical cycles. The mechanisms of water and nutrient uptake by plants depend on climatic and edaphic conditions, as well as the plant root system. Soil solution is the medium in which abiotic and biotic processes exchange nutrients, and nutrient concentrations vary with...

Plants absorb nutrients and water through their roots, and modulate soil biogeochemical cycles. The mechanisms of water and nutrient uptake by plants depend on climatic and edaphic conditions, as well as the plant root system. Soil solution is the medium in which abiotic and biotic processes exchange nutrients, and nutrient concentrations vary with...

Organic carbon (OC) association with soil minerals stabilizes OC on timescales reflecting the strength of mineral–C interactions. We applied ramped thermal oxidation to subsoil B horizons with different mineral–C associations to separate OC according to increasing temperature of oxidation, i.e. thermal activation energy. Generally, OC released at l...

Primary minerals that enter soils through bedrock weathering and atmospheric deposition can generate poorly crystalline minerals (PCM) that preferentially associate with soil organic carbon (SOC). These associations hinder microbial decomposition and the release of CO2 from soils to the atmosphere, making them a critical geochemical control on terr...

Characterizing the distribution and dynamics of organic carbon in soil is critical for quantifying changes in the global carbon cycle. In particular, weathering controls on near-surface and deep (>1 m) soil organic carbon (SOC) dynamics have been proposed but limited data prevents us from predicting SOC over topographically complex landscapes and q...

Manganese (Mn) exists as Mn(II), Mn(III), or Mn(IV) in soils, and the Mn oxidation state controls the roles of Mn in numerous environmental processes. However, the variations of Mn oxidation states with climate remain unknown. We determined the Mn oxidation states in highly weathered bulk volcanic soils (primary minerals free) across two rainfall g...

Dietary deficiency of selenium is a global health threat related to low selenium concentrations in crops. Despite the chemical similarity of selenium to the two more abundantly studied elements sulfur and arsenic, the understanding of its accumulation in soils and availability for plants is limited. The lack of understanding of soil selenium cyclin...

The availability of nutrient‐rich soils capable of supporting intensive cultivation was a key factor in the relative vulnerability and resilience of traditional Polynesian societies, whose economies were based on agricultural production. We tested the hypothesis that geological age was a key controlling factor in determining the nutrient status of...

The controls on potassium (K) isotope fractionation during chemical weathering are evaluated using two regolith profiles developed over ~ 350 kyr on the humid and arid sides of Kohala Mountain, Hawai‘i. The humid regolith shows 145% K enrichment relative to the basaltic parent in shallow (≤ 1 m) horizons, but losses of up to 90% in the deeper horiz...

We combine spectroscopic and geochemical approaches to interpret the fate of potassium (K) during forest soil development along a 4-million-year chronosequence sampled from relatively undisturbed rainforests in Hawai‘i. Potassium derived from weathering of lava is dominant in the youngest site (0.3 ky), but its contribution to the soil K budget dec...

Hawai‘i provides excellent constraints for quantifying and conceptualizing the role of climate in modulating soil development and biogeochemistry. It is a natural lab with clear orthogonal gradients of rainfall and substrate age, which afford state-factor based analysis of leaching power as a key driver of soil development with feedbacks to the ava...

The fate of soil carbon (C) is largely controlled by microbial oxidation of organic matter (OM), which is constrained by a variety of mechanisms. OM association with soil minerals provides pronounced protection against microbial decomposition. However, factors such as climate, occlusion, and resource limitations also contribute to OM preservation....

As rock-derived primary minerals weather to form soil, they create reactive, poorly crystalline minerals that bind and store organic carbon. By implication, the abundance of primary minerals in soil might influence the abundance of poorly crystalline minerals, and hence soil organic carbon storage. However, the link between primary mineral weatheri...

It has been postulated that the amount of soil organic carbon (SOC) associated with soil minerals exhibits a threshold relationship in response to effective soil moisture (estimated as precipitation less evapotranspiration). To better characterize the role of moisture in influencing mechanisms of SOC storage during pedogenesis, we compare soils fro...

Current understanding of phosphorus (P) dynamics is mostly based on experiments carried out under steady-state conditions. However, drying-rewetting is an inherent feature of soil behavior, and as such also impacts P cycling. While several studies have looked at net changes in P pool sizes with drying-rewetting, few studies have dynamically tracked...

Watershed degradation due to invasion threatens downstream water flows and associated ecosystem services. While this topic has been studied across landscapes that have undergone invasive-driven state changes (e.g., native forest to invaded grassland), it is less well understood in ecosystems experiencing within-system invasion (e.g. native forest t...

Phosphorus (P) availability in soils controls critical functions and properties of terrestrial ecosystems. Vertical distribution patterns of P concentration and speciation in soil profiles provide historical records of how pedogenic processes redistribute and transform P and thus change its availability in soils, which, however, remain poorly under...

We used a simple “toy” model to aid in the evaluation of the controls of biogeochemical patterns along a climate gradient. The model includes simplified treatments of water balance (precipitation minus Potential Evapotranspiration), leaching, weathering of cation- and P-bearing minerals, N cycling and loss, biomass production, and biological N fixa...

Plants play a critical role in the cycling of potassium (K) and the fractionation of its isotopes. However, little is known about K stable isotopic compositions in natural soil-plant systems and possible fractionation during intra-plant transport and root-soil uptake of K. This study focuses on K isotopic fractionation within a humid and an arid so...

Models suggest that rock-derived nitrogen (N) inputs are of global importance to ecosystem N budgets; however, field studies demonstrating the significance of rock N inputs are rare. We examined rock-derived N fluxes in soils derived from sedimentary rocks along a catena formed under a semi-arid climate. Our measurements demonstrate that there are...

Dust deposition is an important source of phosphorus (P) to many ecosystems. However, there is little evidence of dust-derived P-containing minerals in soils. Here we studied P forms along a well-described climatic gradient on Hawaii, which is also a dust deposition gradient. Soil mineralogy and soil P forms from six sites along the climatic gradie...

List of Supplementary Tables provided in a spreadsheet (548-07-SuppMat-Tables.xlsx) Table S1. 10Be data Table S2. 26Al data Table S3. Data for CRONUS-Earth online calculator version 2.3 (http://hess.ess.washington.edu) Table S4. Outlier evaluation by normalized deviation method (Batbaatar et al., 2018) Table S5. Outlier evaluation using Chauvenet'...

Text and figures for the following topics are included in this supplementary document: Selection of the study sites and literature data Sensitivity of apparent exposure ages to boulder erosion Quality assessment of the exposure ages Modern and MIS 2 ELA gradients along the latitude Photos of sampled boulders and surface features in the study sites...

Stephen C. Porter was an international leader in Quaternary science for several decades, having worked on most of the world’s continents and having led international organizations and a prominent interdisciplinary journal. His work influenced many individuals, and he played an essential role in linking Chinese Quaternary science with the broader in...

Magnesium (Mg) isotopes fractionate during rock/mineral weathering and leaching, secondary mineral neoformation, adsorption/desorption, and plant-related Mg recycling, but the mechanisms and extent of fractionation are not well understood. Here, we report the fate of Mg and its isotopes during basalt weathering and soil development in the Hawaiian...

Changes in the isotopic composition of oxygen associated with phosphate can provide information on the impact of phosphatase activity on soil P dynamics, whereas the use of radioactive P delivers information on P fluxes within soil systems. Although these two tracers may provide complementary data, they have rarely been used together to study soil...

Understanding the influence of terrestrial soil-atmosphere-biosphere exchanges on Li geochemical behaviors is vital before using Li isotopes as a weathering tracer. We investigated Li geochemistry of the humid and arid regolith profiles formed on the Pololu lavas, the Kohala Mountain, Hawaii. The shallow regolith (0-1 m depth) retains Li (τLi,Nb >...

The strong elevation gradient of the Himalaya allows investigation of altitude and orographic impacts on surface water δ¹⁸O and δD stable isotope values. This study differentiates the time- and altitude-variable contributions of source waters to the Arun River in eastern Nepal. It provides isotope data along a 5000-m gradient collected from tributa...

Wetting of dry soil triggers a pulse of microbial respiration that has been attributed to two broad mechanisms: (1) recycling of microbial cellular carbon (C), and (2) consumption of extracellular organic C made available to microbes by wetting. We evaluated these two mechanisms by measuring cumulative CO2 release, changes in the size and chemical...

Sequential chemical extraction has been widely used to study soil phosphorus (P) dynamics and inform nutrient management, but its efficacy for assigning P into biologically meaningful pools remains unknown. Here, we evaluated the accuracy of the modified Hedley extraction scheme using P K-edge XANES spectroscopy for nine carbonate-free soil samples...

Global‐scale models of rock‐derived nutrient availability often assume that physical erosion drives soils toward an approximate “steady state” over geologic timescales. By definition, steady‐state models do not represent landscape age—that is, the time elapsed since soil formation is initiated by major erosional or depositional events. We hypothesi...

Pedogenic thresholds describe where soil properties or processes change in an abrupt/nonlinear fashion in response to small changes in environmental forcing. Contrastingly, soil process domains refer to the space between thresholds where soil properties are either unchanged, or change gradually, across a broad range of environmental forcing. Here,...

Nitrogen (N) availability influences patterns of terrestrial productivity and global carbon cycling, imparting strong but poorly resolved feedbacks on Earth's climate system. Central questions concern the timescale of N cycle response to elevated CO2 concentration in the atmosphere and whether availability of this limiting nutrient increases or dec...

Radiocarbon ages and thermal stability measurements can be used to estimate the stability of soil organic carbon (OC). Soil OC is a complex reservoir that contains a range of compounds with different sources, reactivities, and residence times. This heterogeneity can shift bulk radiocarbon values and impact assessment of OC stability and turnover in...

The textbook concept of an equilibrium landscape, which posits that soil production and erosion are balanced and equal channel incision, is rarely quantified for natural systems. In contrast to mountainous, rapidly eroding terrain, low relief and slow‐eroding landscapes are poorly studied despite being widespread and densely inhabited. We use three...

Nitrogen (N) availability influences patterns of terrestrial productivity and global carbon cycling, imparting strong but poorly resolved feedbacks on Earth's climate system. Central questions concern the timescale of N cycle response to elevated CO2 concentration in the atmosphere, and whether availability of this limiting nutrient increases or de...

We evaluated N dynamics on a climate gradient on old (> 4 million year) basaltic substrate on the Island of Kaua’i, Hawai’i, to evaluate the utility of pedogenic thresholds and soil process domains for understanding N cycling in terrestrial ecosystems. Studies of nitrogen dynamics on the climate gradient on a younger basaltic substrate (~ 150,000 y...

Soil organic matter can release carbon dioxide to the atmosphere as the climate warms. Organic matter sorbed to reactive (iron and aluminum bearing) soil minerals is an important mechanism for long-term carbon storage. However, the global distribution of mineral-stored carbon across climate zones and consequently its overall contribution to the glo...

The strong elevation gradient of the Himalaya allows investigation of altitude and orographic impacts on precipitation isotope values as captured in river samples. This study provides new high-elevation data along a 5000 m gradient collected from rain, snow, and glacial-sourced surface waters and time-series data from April to October 2016 to diffe...

Meteoric ¹⁰Be (¹⁰Bem) is a widely used tracer of soil processes in terrestrial ecosystems, but complexity surrounding its delivery and retention in soils is frequently oversimplified. We measured ¹⁰Bem in ten soil profiles sampled on 150 ka lava flows of Kohala, Hawaii. The sampled soils receive annual rainfall of 160-3000 mm, and exhibit strong gr...

Current understanding of phosphorus (P) cycling in soils can be enhanced by integrating previously discrete findings concerning P speciation, exchange kinetics, and the underlying biological and geochemical processes. Here, we combine sequential extraction with P K-edge X-ray absorption spectroscopy and isotopic methods (33 P and 18 O in phosphate)...

Collaborations between biologists and geologists are key to understanding and projecting how landscapes function and change over time. Such collaborations are stimulated by on-going scientific developments, advances in instrumentation and technology, and the growing recognition that environmental problems necessitate interdisciplinary investigation...

Trees, the most successful biological power plants on earth, build and plumb the critical zone (CZ) in ways that we do not yet understand. To encourage exploration of the character and implications of interactions between trees and soil in the CZ, we propose nine hypotheses that can be tested at diverse settings. The hypotheses are roughly divided...

Studies in the leeward Kohala field system on Hawai‘i Island have considered the processes and timing of agricultural development associated with sociopolitical transformations and the production of agricultural surpluses. Using extensive soil sampling, we explore the use of relatively mobile and immobile soil parameters within the agricultural lan...

The incongruity between the small and apparently impoverished Rapa Nui population that early European travelers encountered and the magnificence of its numerous and massive stone statues has fed a deep fascination with the island. Ethnographic and archaeological evidence suggest that the indigenous population was previously greater than the estimat...

Changes in species richness along climatological gradients have been instrumental in developing theories about the general drivers of biodiversity. Previous studies on microbial communities along climate gradients on mountainsides have revealed positive, negative and neutral richness trends. We examined changes in richness and composition of Fungi,...

Trees, the most successful biological power plants on earth, build and plumb the critical zone (CZ) in ways that we do not yet understand. To encourage exploration of the character and implications of interactions between trees and soil in the CZ, we propose nine hypotheses that can be tested at diverse settings. Depending upon one's disciplinary b...

The supply of nitrogen (N) constrains primary productivity in many ecosystems, raising the question “what controls the availability and cycling of N”? As a step towards answering this question, we evaluated N cycling processes and aspects of their regulation on a climate gradient on Kohala Volcano, Hawaii. The gradient extends from sites receiving...

Organic matter–mineral associations stabilize much of the carbon (C) stored globally in soils. Metastable short-range-order (SRO) minerals such as allophane and ferrihydrite provide one mechanism for long-term stabilization of organic matter in young soil. However, in soils with few SRO minerals and a predominance of crystalline aluminosilicate or...

Erosion is a frequent result of human activity in natural environments. Heterogeneities within a landscape, (e.g. varying lithology) influence the spatial patterns of erosion. Commonly used cosmogenic radionuclides (CRN) measure erosion over timescales too long (105yr) for constraining newly triggered erosion. Spatially averaged CRN rates also obsc...

Soil pH regulates the capacity of soils to store and supply nutrients, and thus contributes substantially to controlling productivity in terrestrial ecosystems. However, soil pH is not an independent regulator of soil fertility-rather, it is ultimately controlled by environmental forcing. In particular, small changes in water balance cause a steep...

Pedogenic thresholds, where multiple soil properties vary substantially and coherently in a narrow portion of a broad environmental gradient, are well-described on basaltic soils in Hawaii. One such threshold occurs along climate gradients where primary minerals virtually disappear, base saturation decreases sharply, and aluminum is mobilized withi...

Chemical weathering in soils dissolves and alters minerals, mobilizes metals, liberates nutrients to terrestrial and aquatic ecosystems, and may modulate Earth's climate over geologic timescales. Climate-weathering relationships are often considered fundamental controls on the evolution of Earth's surface and biogeochemical cycles. However, surpris...

SUMMARY Andean grasslands ( páramos ) are highly valued for their role in regional water supply as well as for their biodiversity and large soil carbon stocks. Several Payment for Ecosystem Services (PES) programmes promote either afforestation or alteration of traditional burning regimes under the assumption that these land management strategies w...

Restoring degraded lands in rural environments that are heavily managed to meet subsistence needs is a challenge due to high rates of disturbance and resource extraction. This study investigates the efficacy of erosion control structures (ECSs) as restoration tools in the context of a watershed rehabilitation and wet meadow (bofedal) restoration pr...

Volcanic ash soils retain the largest and most persistent soil carbon pools of any ecosystem. However, the mechanisms governing soil carbon accumulation and weathering during initial phases of ecosystem development are not well understood. We examined soil organic matter dynamics and soil development across a high- Altitude (3,560-3,030 m) 20-kyr c...

Successful land restoration in impoverished rural environments may require adoption of new resource management strategies; however, feedbacks between local knowledge and introduced restoration technologies have rarely been articulated. We used interview scenarios to analyze the role of local knowledge in land restoration at a large-scale, long-term...

Organic matter-mineral associations stabilize much of the carbon stored globally in soils. Metastable short-range-order (SRO) minerals such as allophane and ferrihydrite provide one mechanism for long-term stabilization of organic matter in soil. However, ancient and highly weathered soils that cover a large fraction of land area lack SRO minerals....

Topography strongly regulates soil formation at the hillslope scale through its effects on sediment redistribution and biological activities. Spatially explicit land surface parameters (LSPs) such as slope and curvature hold potential for modeling the resulting soil carbon (C) and nitrogen (N) distributions, but their representation of deep soil pr...

Significance We show for the first time, to our knowledge, that pedogenic (soil) carbonate mineral accumulations can preserve continuous paleoclimate records that rival the temporal resolution of widely used archives, such as speleothems or lake sediments. Using microanalysis of oxygen, carbon, and uranium isotopes coupled with uranium series datin...

Pedologists have traditionally constrained soil development processes by studying constructional features that can be aged and that have minimal soil erosion. Yet, these settings represent a subset of geomorphic features whose characteristics are not readily transferrable to eroding landscapes. In contrast, geomorphologists target hillslopes to und...

Plants are known to scavenge nutrients such as phosphorus (P) from rock subtrates and concentrate those nutrients at the surface in order to satisfy long-term nutritional requirements. Using the stable isotope systematics of calcium (Ca), strontium (Sr) and barium (Ba) as proxy tracers, here we test the hypothesis that soils along a Hawaiian climos...

Nutrient biolifting is an important pedogenic process in which plant roots obtain inorganic nutrients such as phosphorus (P) and calcium (Ca) from minerals at depth and concentrate those nutrients at the surface. Here we use soil chemistry and stable isotopes of the alkaline earth elements Ca, strontium (Sr) and barium (Ba) to test the hypothesis t...

Rain-fed, intensive field systems based on sweet potato and to a lesser extent dryland taro were essential to the political economies of emergent archaic states in late pre-contact Hawai'i. The productivity of these dryland field systems was dependent upon soil nutrient pools that are constrained primarily by geological substrate age and rainfall. We...

We used measurements from airborne imaging spectroscopy and LiDAR to quantify the bio-physical structure and composition of vegetation on a dryland substrate age gradient in Hawaii. Both vertical stature and species composition changed during primary succession, and reveal a progressive increase in vertical stature on younger substrates followed by...

Tree species interact with soil biota to impact soil organic carbon (C) pools, but it is unclear how this interaction is shaped by various ecological factors. We used multiple regression to describe how ~100 variables were related to soil organic C pools in a common garden experiment with 14 temperate tree species. Potential predictor variables inc...

Sulfur, a nutrient required by terrestrial ecosystems, is likely to be regulated by atmospheric processes in well-drained, upland settings because of its low concentration in most bedrock and generally poor retention by inorganic reactions within soils. Environmental controls on sulfur sources in unpolluted ecosystems have seldom been investigated...

Mass balance models have become standard tools for characterizing element gains and losses and volumetric change during weathering and soil development. However, they rely on the assumption of complete immobility for an index element such as Ti or Zr. Here we describe a dual-phase mass balance model that eliminates the need for an assumption of imm...

Significance Our paper evaluates a long-standing debate and examines whether the prehistoric population of Rapa Nui experienced a significant demographic collapse prior to European contact in AD 1722. We have used dates from hydrated obsidian artifacts recovered from habitation sites as a proxy for land use over time. The analysis suggests region-s...

We combines Mg isotopic analyses with soil characterization methods to determine Mg isotopic compositions of bulk soils, basalts, and carbonate fractions at an arid (∼30 cm MAP) soil chronosequence on the Island of Hawaii. This chronosequence is developed on Pololu (350 ka) and Hawi (170 ka) lava flows. Both profiles contain pedogenic carbonates an...

Lithium isotopes are a potential tracer of silicate weathering but the relationship between lithium isotope compositions and weathering state still need to be established with precision. Here, we report Li concentrations and Li isotope compositions of soils developed along a 4 million year humid-environment chronosequence in the Hawaiian Islands. L...