Matthew Winnick

University of Massachusetts Amherst | UMass Amherst · Department of Geosciences

Recent studies have suggested that thermodynamic limitations on chemical weathering rates exert a first-order control on riverine solute fluxes and by extension, global chemical weathering rates. As such, these limitations may play a prominent role in the regulation of carbon dioxide levels (pCO2) over geologic timescales by constraining the maximu...

Soil respiration is a primary component of the terrestrial carbon cycle. However, predicting the response of soil respiration to climate change remains a challenge due to the complex interactions between environmental drivers, especially plant phenology, temperature, and soil moisture. In this study, we use a 1-D diffusion-reaction model to calcula...

Rivers and streams act as globally significant sources of nitrous oxide (N2O) to the atmosphere, in part through denitrification reactions that will increase in response to ongoing anthropogenic nitrogen loading. While many factors that contribute to the release of N2O relative to inert dinitrogen (N2) are well described, the ability to predict N2O...

Inland waters are an important component of the global carbon budget. However, our ability to predict carbon fluxes from stream systems remains uncertain, as pCO2 varies within streams at scales of 1-100 m. This makes direct monitoring of large-scale CO2 fluxes impractical. We incorporate CO2 input and output fluxes into a stream network advection-...

Lithium isotopes have emerged as a powerful tool to probe the response of global weathering to changes in climate. Due to the preferential incorporation of 6 Li into clay minerals during chemical weathering, the isotope ratio d 7 Li may be used to interrogate the balance of primary mineral dissolution and clay precipitation. This balance has been l...

Speleothem oxygen isotope records (δ18O) of tropical South American rainfall in the late Quaternary show a zonal “South American Precipitation Dipole” (SAPD). The dipole is characterized by opposing east-west precipitation anomalies compared to the present—wetter in the east and drier in the west at the mid-Holocene (∼7 ka), and drier in the east a...

The deuterium excess (d-excess) of precipitation varies seasonally at sites across the globe, an observation that has often been linked to seasonal changes in oceanic evaporation conditions, continental moisture recycling, and sub-cloud raindrop re-evaporation. However, there have been very few studies to quantify and evaluate the relative importan...

Lithium isotopes have emerged as a powerful tool to probe the response of global weathering to changes in climate. Due to the preferential incorporation of 6Li into clay minerals during chemical weathering, the isotope ratio δ7Li may be used to interrogate the balance of primary mineral dissolution and clay precipitation. This balance has been link...

The shift from denser forests to open, grass‐dominated vegetation in west‐central North America between 26 and 15 million years ago is a major ecological transition with no clear driving force. This open habitat transition (OHT) is considered by some to be evidence for drier summers, more seasonal precipitation, or a cooler climate, but others have...

Oxidative weathering of sedimentary rocks plays an important role in the global carbon cycle. Rhenium (Re) has been proposed as a tracer of rock organic carbon (OCpetro) oxidation. However, the sources of Re and its mobilization by hydrological processes remain poorly constrained. Here, we examine dissolved Re as a function of water discharge, usin...

The deuterium excess (d-excess) of precipitation, which tracks kinetic fractionations during water phase changes, has been used to trace the regions and conditions of oceanic moisture sources, in particular from polar ice-core records. Still, many observations suggest that precipitation d-excess varies significantly across terrestrial environments,...

The Amazon forest is increasingly vulnerable to dieback and encroachment of grasslands and agricultural fields. Threats to these forested ecosystems include drying, deforestation, and fire, but feedbacks among these make it difficult to determine their relative importance. Here, we reconstruct the central and western Amazon tree cover response to a...

Most mineral-associated organic matter (MAOM) is protected against microbial attack, thereby contributing to long-term carbon storage in soils. However, the extent to which reactive compounds released by plants and microbes may destabilize MAOM and so enhance microbial access, as well as the underlying mechanisms, remain unclear. Here, we tested th...

Current understanding of the long-term carbon cycle posits that Earth's climate is stabilized by a negative feedback involving CO2 consumption by chemical weathering of silicate minerals. This theory holds that silicate weathering responds to climate: when atmospheric pCO2 and surface temperatures rise, chemical weathering accelerates, consuming mo...

The selective use of seasonal precipitation by vegetation is critical to understanding the residence time and flow path of water in watersheds, yet there are limited datasets to test how climate alters these dynamics. Here, we use measurements of the seasonal cycle of tree ring δ18O for two widespread conifer species in the Rocky Mountains of North...

Soil microorganisms are known to survive periods of aridity and to recover rapidly after wetting events, with the ability to transition between a dormant state in dry conditions and an active state in wet conditions. Though this dynamic behavior has been previously incorporated into soil carbon respiration modeling frameworks, a direct comparison b...

Isotopes have a rich history as tracers of biogeochemical processes, but they are commonly interpreted using distillation models that lump multiple compounding effects, including advection, diffusion, and complex chemical transformations. Today, as our ability to measure small differences in relative mass continues to improve, a new generation of p...

Terrestrial gradients in the oxygen isotopic composition of meteoric water (δ¹⁸O), as reconstructed through proxies, reflect characteristics of ancient hydrologic conditions. These gradients are primarily influenced by the atmospheric transport of water vapor and the balance of precipitation and evapotranspiration, which are linked to climate and t...

Lake shoreline remnants found in basins of the western United States reflect wetter conditions during Pleistocene glacial periods. The size distribution of paleolakes, such as Lake Bonneville, provide a first-order constraint on the competition between regional precipitation delivery and evaporative demand. In this contribution we downscale previou...

Lithium isotopes have emerged as a powerful tool to probe the response of global weathering to changes in climate. Due to the preferential incorporation of 6Li into clay minerals during chemical weathering, δ7Li may be used to interrogate the balance of primary mineral dissolution and clay precipitation. This balance has in turn been linked to eros...

Poster board 224 in Session 08a, Thursday @ 17:15 - 19:15 Terrestrial gradients in the oxygen isotopic composition of meteoric water (δ18Ο), as reconstructed through proxies, reflect characteristics of ancient hydrologic conditions. These gradients are primarily influenced by the water balance, the transport of vapor, and topographic distillation....

The size distribution of lakes records the competition between precipitation delivery and evaporation. Lakes were abundant in the terminally draining basins of the western United States (USA) during both the colder-than-preindustrial latest Pleistocene glacial period (ca. 14-29 ka) and the warmer-than-preindustrial mid-Pliocene (ca. 2.9-3.3 Ma). To...

Observations show that soil microorganisms can survive periods of aridity and recover rapidly after wetting events. This behavior can be explained by a moisture-dependent adaptation (i.e. the ability to transition between a dormant state in dry conditions and an active state in wet conditions). Though this dynamic behavior has been previously incor...

Quantifying the functional relationships between river discharge and dissolved weathering products places key constraints on our understanding of the coupling between weathering processes and climate. In this study we analyze the concentration-discharge relationships of weathering products from geologically heterogenous global rivers as well as sma...

Although important for riverine solute and nutrient fluxes, the connections between biogeochemical processes and subsurface hydrology remain poorly characterized. We investigate these couplings in the East River, CO, a high-elevation shale-dominated catchment in the Rocky Mountains, using concentration-discharge (C-Q) relationships for major cation...

The timing of high surface topography and the corresponding climatic impacts of the many high ranges north of the Tibetan Plateau, such as the Altai and Tian Shan, remain poorly constrained. Most Neogene reconstructions of Central Asia climate come from interior China, where the influences of Altai and Tian Shan uplift are difficult to deconvolve f...

Although important for solute production and transport, the varied interactions between biogeochemical processes and subsurface hydrology remain poorly characterized. We investigate these couplings in the headwaters of the East River, CO, a high-elevation shale-dominated catchment system in the Rocky Mountains, using concentration-discharge (C-Q) r...

The persistence of large inland lakes in western North America during the Pliocene and Pleistocene provides first-order constraints on changes in the regional water balance. Furthermore, the spatial distribution of terminal lakes records changes in the regional moisture delivery dynamics. We investigate the climatological conditions driving termina...

Central Mongolia sits deep in the Asian continental interior between the Siberian craton to the north, the edge of the India-Asia collision to the south, and far-field subduction of the Pacific plate to the east. It has a complex geologic history comprising Archean to Early Proterozoic crystalline rocks modified by accretionary events in the Paleoz...

There remains substantial debate concerning the relative roles of tectonics and of global climate in pacing the evolution of aridity in Central Asia over the Cenozoic. Tibetan Plateau uplift, variable monsoonal strength, Paratethys retreat, and reduced moisture transport from the North Atlantic have all been hypothesized to drive aridity in Central...

The mid-Pliocene warm period (MPWP, 3.3–2.9 Ma), with reconstructed atmospheric pCO2 of 350–450 ppm, represents a potential analogue for climate change in the near future. Current highly cited estimates place MPWP maximum global mean sea level (GMSL) at 21 ± 10 m above modern, requiring total loss of the Greenland and marine West Antarctic Ice Shee...

We use a one-dimensional reactive transport model of isotopes in precipitation (δ18O) to investigate the physical mechanisms controlling global meridional isotope profiles under Early Eocene hothouse conditions. Simulations of Early Eocene precipitation isotopes display reduced meridional gradients relative to the modern climate with the largest in...

As anthropogenic emissions of greenhouse gasses continue to alter the Earth’s climate, it becomes increasingly vital to understand how the Earth system has responded to high temperatures and pCO2 in the past. The Cenozoic era in particular offers unique insights into climate systems equilibrated with modern to near-future radiative forcing and comp...

The hydroclimate history of North America includes the formation and desiccation of large inland lakes and the growth and ablation of glaciers throughout the Quaternary period. At the Last Glacial Maximum, expanded pluvial lakes in the south and aridity in the northwest suggest that the winter westerly storm track was displaced southwards and migra...

The Early Eocene Climatic Optimum (EECO), occurring roughly 52 million years ago, represents an Earth system response to elevated atmospheric CO2 levels and potentially serves as an analog for the Earth system response to anthropogenic CO2 emissions over the next several centuries. During EECO, global temperatures were 12-15 ºC warmer than modern,...

Central Asia has become increasingly arid during the Cenozoic, though the mechanisms behind this aridification remain unresolved. Much attention has focused on the influence and uplift history of the Tibetan Plateau. However, the role of ranges linked to India-Asia convergence but well north of the Plateau—including the Altai, Sayan, and Hangay—in...

The late Cenozoic was a time of global cooling, increased aridity, and expansion of grasslands. In the last two decades numerous records of oxygen isotopes have been collected to assess plant ecological changes, understand terrestrial paleoclimate, and to determine the surface history of mountain belts. The δ18O values of these records, in general,...

Understanding how the hydrologic cycle has responded to warmer global temperatures in the past is especially important today as concentrations of CO2 in the atmosphere continue to increase due to human activities. The Pliocene offers an ideal window into a climate system that has equilibrated with current atmospheric pCO2. During the Pliocene the w...

The origin of high topography in continental interiors is a first-order question in continental dynamics. Standing significantly above the median continental freeboard, higher-elevation surfaces having relatively low relief and wavelengths of hundreds to thousands of kilometers are common on the continents and are excellent sites to investigate the...

Understanding how the hydrologic cycle has responded to warmer global temperatures in the past is especially important today as concentrations of CO₂ in the atmosphere continue to increase due to human activities. The Pliocene offers an ideal window into a climate system that has equilibrated with current atmospheric p CO₂. Du...

As atmospheric concentrations of CO2 continue to increase due to human activities, it becomes increasingly vital to understand how the hydrologic cycle has responded to warmer global temperatures in the past. The Pliocene climate offers an ideal window into a climate system in equilibrium with current atmospheric pCO2. During the Pliocene, the Sout...

Pre-earthquake signals have been widely reported, including perturbations in the ionosphere. These precursory signals, though highly diverse, may be caused by just one underlying physical process: activation of highly mobile electronic charge carriers in rocks that are subjected to ever increasing levels of stress. The charge carriers are defect el...

Pre-earthquake signals have long been observed and documented, though they have not been adequately explained scientifically. These signals include air ionization, occasional flashes of light from the ground, radio frequency emissions, and effects on the ionosphere that occur hours or even days before large earthquakes. The theory that rocks functi...