Fred Mackenzie

... (On six continents, there is no difficulty in identifying the proper targets: They are Kilimanjaro in Africa, Denali [Mount McKinley] in North America, Elbrus in Europe, Aconcaqua in South America, Vinson in Antarctica and Everest in Asia; for Australasia, however, there is some ...

It has been speculated that the partial pressure of carbon dioxide (pCO) in shelf waters may lag the rise in atmospheric CO. Here, we show that this is the case across many shelf regions, implying a tendency for enhanced shelf uptake of atmospheric CO. This result is based on analysis of long-term trends in the air-sea pCOgradient (ΔpCO) using a global surface ocean pCOdatabase spanning a period of up to 35 years. Using wintertime data only, we find that ΔpCOincreased in 653 of the 825 0.5° cells for which a trend could be calculated, with 325 of these cells showing a significant increase in excess of +0.5 μatm yr(p < 0.05). Although noisier, the deseasonalized annual data suggest similar results. If this were a global trend, it would support the idea that shelves might have switched from a source to a sink of COduring the last century.

The tendency to represent natural processes as cycles—from Latin cyclus and Greek κυκλος—is undoubtedly rooted in the human observations of repeating or periodic phenomena. The oldest notions of the water cycle, as water cycling between the Earth, air, and back to earth, are mentioned in the Old Testament and by Greek philosophers, from the 900s to 300s bce. The life of plants, deriving their constituents from the soil and air, and returning them thereto, is a classic example of a cycling or recycling process. For chemical elements, the concept of their cycling developed gradually since 1875 to about 1950, as the knowledge of the parts of the Earth—its compartments or reservoirs—progressed and the flow of material between them became better understood.The main “bioessential” chemical elements are carbon (C), nitrogen (N), phosphorus (P), oxygen (O), and hydrogen (H). These are represented in the mean composition of aquatic photosynthesizing organisms as the atomic abundance ratio C:...

ABSTRACT In this chapter, a new Earth system model termed MAGic (Mackenzie, Arvidson, Guidry interactive cycles) model is used to examine how the weathering fluxes of calcium (Ca), magnesium (Mg), carbon (C), sulfur (S), and phosphorus (P) have influenced biogeochemical cycles in the ocean over the past 500 million years. In addition, the fluxes of these five components in relation to their sink reservoirs and the effect of the changes in these fluxes and those from basalt-seawater reactions on the chemistry of seawater are calculated. The chapter then goes on to show that the age distributions of inorganic and biogenic carbonate phases in the Phanerozoic carbonate rock record is related to the kinetics of the precipitation rates of these phases that in turn are controlled by changing atmosphere-seawater composition. Such an Earth system model is a global biogeochemical model, and in MAGic, each elemental cycle is explicITAy coupled to corresponding cycles of other elements via a reaction network. This network incorporates the basic reactions controlling atmospheric carbon dioxide and oxygen concentrations, continental and seafloor weathering of silicate and carbonate rocks, net ecosystem productivity, basalt-seawater exchange reactions, precipitation and diagenesis of chemical sediments and authigenic silicates, oxidation-reduction reactions involving C, S, and Fe, and subduction-decarbonation reactions. Geological and biological processes have acted in concert to alter atmospheric and seawater chemistry over the Phanerozoic. The evolution and rise of various planktonic siliceous and calcareous organisms over this period are direct evidence to this interplay of these processes.

This paper reports that prior to human activities, there was a net flux of COâ from the ocean through the atmosphere to the land. This flux fueled organic production in terrestrial ecosystems. Human interference in the COâ cycle has reversed the role of the ocean as a COâ source; it is now a net sink of anthropogenic COâ. The strength

The coastal zone, consisting of the continental shelves to −200 m, including bays, lagoons, estuaries, and near-shore banks, is an environment that is strongly affected by two much bigger environmental reservoirs adjacent to it: the land and open ocean. In the coastal zone, as ...

ABSTRACT The importance of silicon (Si) in global biogeochemical cycles is demonstrated by its abundance in the land and aquatic biomass, where Si/C is 0.02 in land plants and 0.15 in marine organisms. Estimates show that Si-bioproduction accounts for ~1.5% of terrestrial primary production, and ~4.5% in the coastal ocean. Human land-use activities have substantially changed regional patterns of vegetation distribution, soil conditions, and nutrient fluxes via runoff to the coastal ocean. Anthropogenic chemical fertilization of the land has caused a significant increase in fluvial nitrogen (N) and phosphorus (P) transport, whereas land-use and vegetation mass changes have caused variations in the riverine Si input, all eventually affecting the cycling of nutrients in the marine environment. We developed a global biogeochemical model of the Si cycle as coupled to the global C-N-P cycle model, TOTEM II (Terrestrial-Ocean-aTmosphere-Ecosystem-Model). In the model analysis from year 1700, taken as the start of the Anthropocene, to 2050, the bioproduction of Si on land and in the ocean is coupled to the bioproduction of C, perturbed by the atmospheric CO2 rise, land-use changes, and chemical fertilization. Also, temperature rise affects the Si cycling on land through bioproduction rates, terrestrial organic matter remineralization, and weathering, thereby affecting its delivery to the coastal zone. The results show that biouptake and subsequent release of Si on land strongly affect the Si river flux to the coastal ocean. During the 350-year period, Si river discharge has increased by ~10% until ~1940, decreasing since then to below its 1700 value and continuing to drop, under the current IPCC IS92 projections of CO2, temperature and other forcings. From 1700 to ~1950, land-use changes, associated with slash and burn of large areas of high-productivity land, caused a decrease of global land vegetation. Dissolution of Si in soil humus and weathering of silicate minerals are the main dissolved Si sources for rivers and groundwater. The decrease in Si uptake by land biomass made more Si available for river discharge, causing an increase in the Si river input until an increase in the land primary production reversed the process. Around 1950, the use of fertilizer on land, especially N and P, increased, driving the growth of coastal marine primary producers, including such Si organisms as diatoms, silicoflagellates, and sponge spicules, and thus causing a decrease of dissolved Si in the surface ocean. The percent decrease of coastal dissolved Si due to increased primary production is greater than that of surface open ocean due to the shorter residence time of Si in coastal water (~2.7 years) compared to that of surface open ocean (~10 years. The combination of the relatively small size and location of the coastal ocean at the junction of the land, atmosphere, and open ocean make it important to changes in water chemistry, in situ biological production, and sedimentary storage. Its buffer effect and fast response to perturbations are also shown in the results of this coupling study of the C-N-P-Si cycles.

Developments in Sedimentology 48 Geochemistry of Sedimentary Carbonates JW Morse and FT Mackenzie ... DEVELOPMENTS IN SEDIMENTOLOGY 48 Geochemistry of Sedimentary Carbonates ... FURTHER TITLES IN THIS SERIES VOLUMES 1 -11, 13-15 and 21 -24 ...

... Magnesian calcites; low-temperature occurrence, solubility and solid-solution behavior. Fred T. Mackenzie, William D. Bischoff, Finley C. Bishop, Michele Loijens, Jane Schoonmaker, and Roland Wollast Univ. Hawaii, Dep. Oceanogr., Honolulu, HI, United States. ...