San Jacinto Peak
Dust is a key source of nutrients to soils, yet the impact of this source and its variability through time and space is not well known. We are currently conducting research at San Jacinto Peak, California (NSF award # 1946856) where 3 kilometers of topographic relief allows us to probe climate versus tectonic variations in dust flux and composition. Here we are using isotope measurements in bedrock, soil, dust, and vegetation to answer questions such as how does the dust cycle differ under spatially variable climates? What role does dust play in shaping ecosystem development? How does climate and land use change influence dust flux and composition?
Many glaciers in alpine and sub-Arctic regions are actively retreating at alarming rates due to climate change. Outwash plains of retreating glaciers are important sources of fine-grained sediment and dust, which can influence primary productivity both in the terrestrial and marine realm. Probing the geochemical behavior of key nutrients during transport—fluvial and aeolian—is a key goal of this research, to aid in understanding how biogeochemical cycling in polar regions will respond to future climate change.
Ice Core Dust
Variations in dust fluxes and sources to polar ice sheets during glacial-interglacial periods are related at first order to temperature and atmospheric dynamics. Geochemical compositions of dust preserved in ice core records can tell us about aridity, land surface conditions, and predominant wind directions. We use ‘horizontal ice core’ records from peripheral portions of the Antarctic ice sheet in an effort to probe nuances in regional climate during major climate transitions through the physical and geochemical analysis of ice core dust. Some questions we hope to address are: Can ice core records of dust deposition tell us information about regional environmental changes such as ice sheet extent? What role did dust play in marine productivity (and the carbon cycle) during Earth’s significant climate regime changes?
Stable titanium isotope systematics
The stable titanium (Ti) isotopic composition of igneous rocks fractionates with magmatic differentiation, with more evolved rocks such as granites having heavier Ti isotope compositions and more primitive rocks such as mid-ocean ridge basalts characterized by lighter Ti isotope compositions. Titanium isotopes fractionate distinctively for rocks formed in plume versus subduction settings, and we leveraged this observation to infer the magmatic settings of Earth’s oldest known rocks from the Acasta Gneiss Complex located in the Slave craton of northwest Canada. We found that rocks spanning the Hadean (4.6-4.0 Ga) to the Eoarchean (<3.75 Ga) fall on two distinct magmatic differentiation trends, with Hadean gneisses consistent with modern evolved tholeiitic magmas formed in plume environments and younger Eoarchean gneisses comparable to modern calc-alkaline magmas produced in convergent arcs (Aarons et al., 2020). We are actively working on exploring what fractionates Ti isotopes in a variety of samples from different environments.
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The climate of Earth’s surface is a driver of our planet’s habitability, and our interpretations of Earth’s climate history are rooted in our understanding of what is happening in the modern. The Earth’s surface is diverse, with different landscapes, ecosystems, and microclimates that all have unique chemical compositions, mechanisms of formation, and weathering histories. Isotopes in natural substances vary as a result of physical, chemical, and biologic processes, and they can be used as a tool for understanding and interpreting Earth’s history throughout time. We use isotope compositions of natural materials such as mineral dust, river sediment, water, and rocks to reconstruct the source, transport mechanism/distance, and conditions these materials were subjected to during the movement from source to sink.