The influence of differential production and dissolution on the stable isotope composition of planktonic foraminifera

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution November, 1978Planktonic foraminifera from plankton tows, sediment traps and sediments from the central North Atlantic were studied in order to understand how they acquire their oxygen and carbon isotope compositions. Shallow dwelling planktonic foraminifera (mostly spinose species), collected in plankton tows in the photic zone, show light isotopic compositions possibly in slight negative deviation from oxygen isotopic equilibrium. Radioactive tracer experiments using 14C and 45Ca were conducted on shallow dwelling benthonic foraminifera and hermatypic corals. They show that photosynthesis of symbiotic algae within these organisms increases the amount of metabolic C02 incorporated into the skeleton which consequently becomes isotopically lighter. Because shallow dwelling planktonic foraminifera contain symbiotic algae it is suggested that their light isotopic compositions are also caused by photosynthetically enhanced incorporation of metabolic C02 in the skeleton. Planktonic foraminifera collected in sediment traps and sediments show heavier oxygen isotope compositions that are in equilibrium for CaC03 deposited in the photic zone. At the same time the weight/individual for these foraminifera is almost doubled compared to those from plankton tows. I suggest that these apparent equilibrium compositions are achieved by a combination of light, perhaps non-equilibrium skeletons deposited in the photic zone and isotopically heavier calcite deposited below the photic zone. The latter being isotopically heavy because temperatures are lower, metabolic activity is reduced, and photosynthesis by the symbiotic algae stops. Dissolution of planktonic foraminifera on the ocean floor removes first the light-weight thin shelled individuals of a species population. Because these individuals are isotopically lighter, the isotopic composition of the surviving population is heavier. The scheme described above is applied to explain the effect of dissolution on the glacial-interglaical amplitude of the Pleistocene isotopic record in the Atlantic and the Pacific Oceans. The timing of dissolution cycles in the two oceans is out of phase. Dissolution during the glacial in the Atlantic and during the interglacial in the Pacific makes the isotopic composition heavier. Preservation in the Atlantic during interglacials and in the Pacific during the glacials makes the isotopic composition lighter. The net effect is amplification of glacial-interglacial amplitude in the Atlantic and reduction of the amplitude in the Pacific.This thesis was supported by the Ocean Sciences Division of the National Science Foundation under Grant #77-07732. Additional support came from the Geological Society of America, Grant #1995-75, and from the Woods Hole Oceanographic Institution Education Office

Fate of the one-dimensional Ising quantum critical point coupled to a gapless boson

The problem of a quantum Ising degree of freedom coupled to a gapless bosonic mode appears naturally in many one dimensional systems, yet surprisingly little is known how such a coupling affects the Ising quantum critical point. We investigate the fate of the critical point in a regime, where the weak coupling renormalization group (RG) indicates a flow toward strong coupling. Using a renormalization group analysis and numerical density matrix renormalization group (DMRG) calculations we show that, depending on the ratio of velocities of the gapless bosonic mode and the Ising critical fluctuations, the transition may remain continuous or become fluctuation-driven first order. The two regimes are separated by a tri-critical point of a novel type.Comment: 8 pages, 8 figures; published versio

Using Deep Learning and Google Street View to Estimate the Demographic Makeup of the US

The United States spends more than $1B each year on initiatives such as the American Community Survey (ACS), a labor-intensive door-to-door study that measures statistics relating to race, gender, education, occupation, unemployment, and other demographic factors. Although a comprehensive source of data, the lag between demographic changes and their appearance in the ACS can exceed half a decade. As digital imagery becomes ubiquitous and machine vision techniques improve, automated data analysis may provide a cheaper and faster alternative. Here, we present a method that determines socioeconomic trends from 50 million images of street scenes, gathered in 200 American cities by Google Street View cars. Using deep learning-based computer vision techniques, we determined the make, model, and year of all motor vehicles encountered in particular neighborhoods. Data from this census of motor vehicles, which enumerated 22M automobiles in total (8% of all automobiles in the US), was used to accurately estimate income, race, education, and voting patterns, with single-precinct resolution. (The average US precinct contains approximately 1000 people.) The resulting associations are surprisingly simple and powerful. For instance, if the number of sedans encountered during a 15-minute drive through a city is higher than the number of pickup trucks, the city is likely to vote for a Democrat during the next Presidential election (88% chance); otherwise, it is likely to vote Republican (82%). Our results suggest that automated systems for monitoring demographic trends may effectively complement labor-intensive approaches, with the potential to detect trends with fine spatial resolution, in close to real time.Comment: 41 pages including supplementary material. Under review at PNA

Seawater transport during coral biomineralization

Cation transport during skeletal growth is a key process controlling metal/calcium (Me/Ca) paleoproxy behavior in coral. To characterize this transport, cultured corals were transferred into seawater enriched in the rare earth element Tb^(3+) as well as stable isotopes of calcium, strontium, and barium. Subsequent NanoSIMS ion images of each coral skeleton were used to follow uptake dynamics. These images show a continuous region corresponding to new growth that is homogeneously enriched in each tracer. Isotope ratio profiles across the new growth boundary transition rapidly from natural abundance ratios to a ratio matching the enriched culture solution. The location of this transition is the same for each element, within analytical resolution. The synchronous incorporation of all these cations, including the dissimilar ion terbium, which has no known biological function in coral, suggests that: (1) there is cation exchange between seawater and the calcifying fluid, and (2) these elements are influenced by similar transport mechanisms consistent with direct and rapid seawater transport to the site of calcification. Measured using isotope ratio profiles, seawater transport rates differ from place to place on the growing coral skeleton, with calcifying fluid turnover times from 30 min to 5.7 h. Despite these differences, all the elements measured in this study show the same transport dynamics at each location. Using an analytical geochemical model of biomineralization that includes direct seawater transport we constrain the role of active calcium pumping during calcification and we show that the balance between seawater transport and precipitation can explain observed Me/Ca variability in deep-sea coral

Revisiting carbonate chemistry controls on planktic foraminifera Mg / Ca:implications for sea surface temperature and hydrology shifts over the Paleocene-Eocene Thermal Maximum and Eocene-Oligocene transition

Much of our knowledge of past ocean temperatures comes from the foraminifera Mg / Ca palaeothermometer. Several nonthermal controls on foraminifera Mg incorporation have been identified, of which vital effects, salinity, and secular variation in seawater Mg / Ca are the most commonly considered. Ocean carbonate chemistry is also known to influence Mg / Ca, yet this is rarely examined as a source of uncertainty, either because (1) precise pH and [CO32−] reconstructions are sparse or (2) it is not clear from existing culture studies how a correction should be applied. We present new culture data of the relationship between carbonate chemistry and Mg / Ca for the surface-dwelling planktic species Globigerinoides ruber and compare our results to data compiled from existing studies. We find a coherent relationship between Mg / Ca and the carbonate system and argue that pH rather than [CO32−] is likely to be the dominant control. Applying these new calibrations to data sets for the Paleocene–Eocene Thermal Maximum (PETM) and Eocene–Oligocene transition (EOT) enables us to produce a more accurate picture of surface hydrology change for the former and a reassessment of the amount of subtropical precursor cooling for the latter. We show that pH-adjusted Mg / Ca and δ18O data sets for the PETM are within error of no salinity change and that the amount of precursor cooling over the EOT has been previously underestimated by  ∼ 2 °C based on Mg / Ca. Finally, we present new laser-ablation data of EOT-age Turborotalia ampliapertura from St. Stephens Quarry (Alabama), for which a solution inductively coupled plasma mass spectrometry (ICPMS) Mg / Ca record is available (Wade et al., 2012). We show that the two data sets are in excellent agreement, demonstrating that fossil solution and laser-ablation data may be directly comparable. Together with an advancing understanding of the effect of Mg / Casw, the coherent picture of the relationship between Mg / Ca and pH that we outline here represents a step towards producing accurate and quantitative palaeotemperatures using this proxy

Basin-scale estimates of pelagic and coral reef calcification in the Red Sea and Western Indian Ocean.

Basin-scale calcification rates are highly important in assessments of the global oceanic carbon cycle. Traditionally, such estimates were based on rates of sedimentation measured with sediment traps or in deep sea cores. Here we estimated CaCO3 precipitation rates in the surface water of the Red Sea from total alkalinity depletion along their axial flow using the water flux in the straits of Bab el Mandeb. The relative contribution of coral reefs and open sea plankton were calculated by fitting a Rayleigh distillation model to the increase in the strontium to calcium ratio. We estimate the net amount of CaCO3 precipitated in the Red Sea to be 7.3 ± 0.4·10(10) kg·y(-1) of which 80 ± 5% is by pelagic calcareous plankton and 20 ± 5% is by the flourishing coastal coral reefs. This estimate for pelagic calcification rate is up to 40% higher than published sedimentary CaCO3 accumulation rates for the region. The calcification rate of the Gulf of Aden was estimated by the Rayleigh model to be ∼1/2 of the Red Sea, and in the northwestern Indian Ocean, it was smaller than our detection limit. The results of this study suggest that variations of major ions on a basin scale may potentially help in assessing long-term effects of ocean acidification on carbonate deposition by marine organisms