The chronological properties of otoliths are unparalleled in the animal world, allowing accurate estimates of age and growth at both the daily and the yearly scale. Based on the successes of calcified structures as environmental proxies in other taxa, it was logical that researchers should attempt to link otolith biochronologies with otolith chemistry. With the benefit of hindsight, this anticipation may have been naive. For instance, the concentrations of many elements are lower in the otolith than in corals, bivalves, seal teeth, or the other bony structures of fish, making them less than ideal for elemental analyses. Nevertheless, there is growing interest in the use of otolith chemistry as a natural tag of fish stocks. Such applications are directed at questions concerning fish populations rather than using the fish as a passive recorder of the ambient environment and do not rely upon any explicit relationship between environmental variables and otolith chemistry. The questions that can be addressed w...

Otoliths, increments, and elements: keys to a comprehensive understanding of fish populations?

The El Nino-Southern Oscillation (ENSO) is the most potent source of interannual climate variability. Uncertainty surrounding the impact of greenhouse warming on ENSO strength and frequency has stimulated efforts to develop a better understanding of the sensitivity of ENSO to climate change. Here we use annually banded corals from Papua New Guinea to show that ENSO has existed for the past 130,000 years, operating even during "glacial" times of substantially reduced regional and global temperature and changed solar forcing. However, we also find that during the 20th century ENSO has been strong compared with ENSO of previous cool (glacial) and warm (interglacial) times. The observed pattern of change in amplitude may be due to the combined effects of ENSO dampening during cool glacial conditions and ENSO forcing by precessional orbital variations.

https://science.sciencemag.org/content/sci/291/5508/1511.full.pdf

Variability in the El Niño-Southern Oscillation Through a Glacial-Interglacial Cycle

http://people.earth.yale.edu/sites/default/files/files/Affek/Ghosh%20et%20al%202006%20D47%20carbonate%20method.pdf

13 C- 18 O bonds in carbonate minerals: A new kind of paleothermometer

“Clumped-isotope” geochemistry—The study of naturally-occurring, multiply-substituted isotopologues

Coral reefs are degrading worldwide at an alarming rate. Nutrient over-enrichment is considered a major cause of this decline because degraded coral reefs generally exhibit a shift from high coral cover (low algal cover) to low coral cover with an accompanying high cover and biomass of fleshy algae. Support for such claims is equivocal at best. Critical examination of both experimental laboratory and field studies of nutrient effects on corals and coral reefs, including the Elevated Nutrient on Coral Reefs Experiment (ENCORE) enrichment experiment conducted on the Great Barrier Reef, does not support the idea that the levels of nutrient enrichment documented at anthropogenically-enriched sites can affect the physiology of corals in a harmful way, or for most cases, be the sole or major cause of shifts in coral- algal abundance. Factors other than nutrient enrichment can be significant causes of coral death and affect algal cover, and include decreased abundance of grazing fishes by fishing, and of grazing sea urchins to disease; grazing preferences of remaining grazers; temperature stress that kills coral (i.e., coral bleaching) and creates more open substrate for algal colonization; sedimentation stress that can weaken adult corals and prevent coral recruitment; coral diseases that may be secondary to coral bleaching; and outbreaks of coral predators and sea urchins that may be secondary effects of overfishing. Any factor that leads to coral death or reduces levels of herbivory will leave more substrate open for algal colonization or make the effects of even low-level enrichment more severe. Factors that contribute to an imbalance between production and consumption will result in community structure changes similar to those expected from over- enrichment. Over-enrichment can be and has been the cause of localized coral reef degradation, but the case for widespread effects is not substantiated.

/pdf/nutrient-enrichment-on-coral-reefs-is-it-a-major-cause-of-1eu0r3ex3s.pdf

Nutrient Enrichment on Coral Reefs: Is It a Major Cause of Coral Reef Decline?

The fractionation factor (α) between the 18O/16O ratio in calcite and CO2 gas produced as a result of reaction with phosphoric acid has been determined as a function of temperature for two of the most widely used variations of the dissolution technique, reaction in a sealed vessel and reaction in an acid bath. Although these methods show approximately the same relationship between temperature and α, they are offset from one another by between 0.2 and 0.4% over the temperature range 25–90°C. There appears to be no temperature- or technique-dependent fractionation on carbon over the range of temperatures examined in this study. The difference between these two methods arises from three main processes: (1) isotopic exchange between the CO2, the phosphate polymers in the acid and water produced in the reaction; (2) dissolution of CO2 in the acid; and (3) incomplete removal of CO2 during the extraction process. Of these two methods the “acid bath” method probably provides the most accurate isotopic composition of the calcite. As a result of the fact the original fractionation factors were determined using the “sealed vessel” method, we have calculated our temperature [T (K)] - dependent fractionation factor (αT) taking into account the difference between the two methods at 25°C. For the “sealed vessel” method: (a) αT= [5.60 (± 0.33) × 102] T−2 + 1.003943 (± 0.000067). For the “common acid bath” technique: (b) αT = [5.25 (± 0.08) × 102] T −2 + 1.003970 (± 0.000034).

Fractionation of the stable isotopes of oxygen and carbon in carbon dioxide during the reaction of calcite with phosphoric acid as a function of temperature and technique

The origin of variations in the isotopic record of scleractinian corals: II. Carbon

Density banding in coral skeletons can provide for reconstruction of the coral's growth en. vironment over long periods. The physical differences between low and high density portions of a skeletal band are not well understood. The skeletal architecture of M. annularis from Southeast Florida, the Florida Keys, St. Croix, the Bahamas, and Mexico was compared in X-ray revealed high density (HD), low density (LD), and stress HD bands. Density changes arose from differences in the size, but not spacing, of exothecal structural elements (horizontal dissepiments and vertical costae). Endothecal architecture size (e.g., columella, dissepiments, septa) was relatively constant between density band types. Results have implications for studies of coral growth, sclerochronology, and isotopic/trace element composition.

/pdf/skeletal-structural-basis-of-density-banding-in-the-reef-37ebsrqt4g.pdf

J. J. Leder

Papers

Fractionation of the stable isotopes of oxygen and carbon in carbon dioxide during the reaction of calcite with phosphoric acid as a function of temperature and technique

The origin of variations in the isotopic record of scleractinian corals: II. Carbon

Skeletal Structural Basis of Density Banding in the Reef Coral Montastrea Annularis

Corals, paleotemperature records, and the aragonite-calcite transformation: Comment and Reply