Incorporation of animal-based foods into early hominin diets has been hypothesized to be a major catalyst of many important evolutionary events, including brain expansion. However, direct evidence of the onset and evolution of animal resource consumption in hominins remains elusive. The nitrogen-15 to nitrogen-14 ratio of collagen provides…

The Younger Dryas cooling 12,700 years ago is one of the most abrupt climate changes observed in Northern Hemisphere palaeoclimate records. Annually laminated lake sediments are ideally suited to record the dynamics of such abrupt changes, as the seasonal deposition responds immediately to climate, and the varve counts provide an accurate…

The greater Agulhas Current region is an important component of the climate system, yet its influence on carbon and nutrient cycling is poorly understood. Here, we use nitrate isotopes (δ15N, δ18O, Δ(15–18) = δ15N–δ18O) to trace regional water mass circulation and investigate nitrogen cycling in the Agulhas Current and adjacent recirculating…

Biological dinitrogen fixation is the major source of new nitrogen to marine systems and thus essential to the ocean’s biological pump. Constraining the distribution and global rate of dinitrogen fixation has proven challenging owing largely to uncertainty surrounding the controls thereon. Existing South Atlantic dinitrogen fixation rate…

We have previously argued that the Antarctic and subarctic North Pacific are stratified during ice ages, causing to a large degree the observed low CO2 levels of ice age atmospheres by sequestering respired CO2 in the ocean abyss. Here, we suggest a mechanism for the major deglaciations of the late Pleistocene. The mechanism begins with…

North Atlantic (NA) deep-water formation and the resulting Atlantic meridional overturning cell is generally regarded as the primary feature of the global overturning circulation and is believed to be a result of the geometry of the continents. Here, instead, the overturning is viewed as a global energy-driven system and the robustness of NA…

Atmospheric deposition of nitrogen (N) and base cations was measured for 5-7 years on the island of Hawaii and for 1.5 years on Kauai. On Hawaii, mean annual fluxes of K+, Mg2+, and Ca2+ were 15, 17, and 13 kg ha-1 yr-1, respectively. Fog interception was the largest deposition pathway. Sea salt contributed the majority of cations, although…

We report a new method for measurement of the isotopic composition of nitrate (NO3-) at the natural-abundance level in both seawater and freshwater. The method is based on the isotopic analysis of nitrous oxide (N2O) generated from nitrate by denitrifying bacteria that lack N2O-reductase activity. The isotopic composition of both nitrogen and…

The cyclic growth and decay of continental ice sheets can be reconstructed from the history of global sea level. Sea level is relatively well constrained for the Last Glacial Maximum (LGM, 26,500 to 19,000 y ago, 26.5 to 19 ka) and the ensuing deglaciation. However, sea-level estimates for the period of ice-sheet growth before the LGM vary by …

It is easy to imagine that the terrestrial biosphere sequesters atmospheric carbon dioxide; the form and quantity of the sequestered carbon, living or dead organic matter, are striking. In the ocean, there are no aggregations of biomass comparable to the forests on land. Yet biological productivity in the ocean plays a central role in the…

We investigate the response of the calcite lysocline to changes in the export production of the low-latitude surface ocean (the combined equatorial, tropical, and subtroical regions). We employ different CaCO3 throughput schemes in a time-dependent ocean carbon cycle model to separate the CaCO3 production/iysocline balance from the other…

In a box model synthesis of Southern Ocean and North Atlantic mechanisms for lowering CO2 during ice ages, the CO2 changes are parsed into their component geochemical causes, including the soft-tissue pump, the carbonate pump, and whole ocean alkalinity. When the mechanisms are applied together, their interactions greatly modify the net CO2…

Atmospheric carbon dioxide concentrations were significantly lower during glacial periods than during intervening interglacial periods, but the mechanisms responsible for this difference remain uncertain. Many recent explanations call on greater carbon storage in a poorly ventilated deep ocean during glacial periods, but direct evidence…

In the anoxic Cariaco Basin of the southern Caribbean, the bulk titanium content of undisturbed sediment reflects variations in riverine input and the hydrological cycle over northern tropical South America. A seasonally resolved record of titanium shows that the collapse of Maya civilization in the Terminal Classic Period occurred during an…

The response of tropical forests to climate change will depend on individual plant species nutritional strategies, which have not been defined in the case of the nitrogen nutrition that is critical to sustaining plant growth and photosynthesis. We used isotope natural abundances to show that a group of tropical plant species with diverse growth…

Earth's history is marked by episodes of large-scale continental glaciation. Most recently, beginning 3 million years ago, northern hemispheric glaciation expanded and developed cyclic variations known as the ice age cycles. With the 19th-century discovery of these cycles in ice extent and climate, changes in atmospheric carbon dioxide…

The nitrogen-isotope record preserved in Southern Ocean sediments, along with several geochemical tracers for the settling fluxes of biogenic matter, reveals patterns of past nutrient supply to phytoplankton and surface-water stratification in this oceanic region. Areal averaging of these spatial patterns indicates that reduction of the CO2…

The nitrogen isotopes (δ15N) in the organic fraction of accretionary hard part structures, such as fish otoliths, may provide life histories of dietary change. We performed controlled experiments to validate the dynamics of the isotopic signal incorporation into biominerals following dietary shifts and also compared whole-otolith and serial…

For times prior to those represented by the air trapped in Antarctic ice core records, the concentration of CO2 in the atmosphere must be reconstructed using geochemical proxies. The δ13C of particulate organic carbon (POC) produced in ocean surface waters has previously been observed to covary with the concentration of CO2 in the water…

We report the first measurements of coupled nitrogen (N) and oxygen (O) isotopic variations of nitrate (NO3-) during its assimilation by laboratory cultures of marine phytoplankton and derive the N and O kinetic isotope effects for nitrate assimilation by three species of diatoms (Thalassiosira weissflogii, Thalassiosira oceanica, and…