Seasonal variation of eddy shedding from the Kuroshio intrusion in the Luzon Strait

Altimeter data and output from the HYbrid Coordinate Ocean Model global assimilation run are used to study the seasonal variation of eddy shedding from the Kuroshio intrusion in the Luzon Strait. The results suggest that most eddy shedding events occur from December through March, and no eddy shedding event occurs in June, September, or October. About a month before eddy shedding, the Kuroshio intrusion extends into the South China Sea and a closed anticyclonic eddy appears inside the Kuroshio loop which then detaches from the Kuroshio intrusion. Anticyclonic eddies detached from December through February move westward at a speed of about 0.1 m s⁻¹ after shedding, whereas eddies detached in other months either stay at the place of origin or move westward at a very slow speed (less than 0.06 m s⁻¹). The HYCOM outputs and QuikSCAT wind data clearly show that the seasonal variation of eddy shedding is influenced by the monsoon winds. A comparison between eddy volume and integrated Ekman transport indicates that, once the integrated Ekman transport exceeds 2 × 10¹² m³ (which roughly corresponds to the volume of an eddy), the Kuroshio intrusion expands and an eddy shedding event occurs within 1 month. We infer that the Ekman drift of the northeasterly monsoon pushes the Kuroshio intrusion into the SCS, creates a net westward transport into the Strait, and leads to an eddy detachment from the Kuroshio.     

The requirements for stable metallothionein clusters examined using synthetic lobster domains.

Metallothioneins (MTs) are small, cysteine-rich proteins which detoxify xenobiotic metals such as cadmium (Cd) and mercury (Hg). In crustaceans and mammals they consist of two independent domains which are folded around metal-thiolate clusters. MT clusters of different origins, exhibiting distinct, highly conserved cysteine positions on their sequences, show differences in metal-cysteine coordination and reactivity. Lobster-MT, containing two Cd3 beta domains, is an important model for structure-function relationships among the clusters. The influence of (1) the position of the cysteine residues and (2) steric and electrostatic effects of neighboring amino acids on the folding and stability of MT cluster were investigated. Thus, the native lobster beta C and beta N domains (each having nine cysteines and binding three M2+ ions) and a modified domain Cd3 beta C-->N, in which the cysteines of the C-terminal domain were relocated to match the positions of those in the N-terminal domain, were chemically prepared and characterized. The synthetic native domains (Cd3 beta C and Cd3 beta N) were found to exhibit spectroscopic properties, metal-binding affinities and kinetic reactivity similar to the holo-protein. However, the modified Cd3 beta C-->N domain was unusually reactive and in the presence of Chelex, metal chelation resin, aggregated to a Cd5(beta C-->N)2 dimer, which exhibited unusual structure as observed by its 113Cd-nuclear magnetic resonance. These differences in structure and reactivity demonstrated that the requirements for formation of a stable Cd3S9 beta-cluster are more stringent than simply the sequential positions of the cysteines along the peptide chain and must include interactions involving neighboring, noncysteine amino acids.     

Brittlestar Color-Change and Phototaxis (Echinodermata: Ophiuroidea: Ophiocomidae).

Abstract. In the first decisive study of color-change in brittlestars, four Caribbean species, Ophiocoma echinata, 0. paucigranulata, O. pumila, and O. wendti are reported to change color from day to night. Color-change is most striking in O. wendti, which is dark brown during the day, and is banded gray and black from dusk to dawn. The transformation occurs over a 3 to 4 hour period and is effected by chromatorphores which appear to respond to illumination, independently of the central nervous system. Color-change may also be mediated by an endogenous rhythm. Ophiocoma wendti is more responsive to light than the other 3 species tested. It reacts to lower levels of illumination at night than during the day, exhibiting negative phototaxis in moonlight as well as in sunlight. I suggest that color-change may expose (or shield) photosensitive tissues that control the brittlestar's detection of shaded fissures in the reef. Thereby, chromatophore activity may be connected with the brittlestar's chief defense from predators, the ability to detect shadow and escape into darkened crevices. Although experiments to date with predacious fish are equivocal. the color patterns of Ophiocoma species mav provide protective camouflage.     

Forecasting ocean wave energy: The ECMWF wave model and time series methods

Recently, the technology has been developed to make wave farms commercially viable. Since electricity is perishable, utilities will be interested in forecasting ocean wave energy. The horizons involved in short-term management of power grids range from as little as a few hours to as long as several days. In selecting a method, the forecaster has a choice between physics-based models and statistical techniques. A further idea is to combine both types of models. This paper analyzes the forecasting properties of a well-known physics-based model, the European Center for Medium-Range Weather Forecasts (ECMWF) Wave Model, and two statistical techniques, time-varying parameter regressions and neural networks. Thirteen data sets at locations in the Atlantic and Pacific Oceans and the Gulf of Mexico are tested. The quantities to be predicted are the significant wave height, the wave period, and the wave energy flux. In the initial tests, the ECMWF model and the statistical models are compared directly. The statistical models do better at short horizons, producing more accurate forecasts in the 1-5 h range. The ECMWF model is superior at longer horizons. The convergence point, at which the two methods achieve comparable degrees of accuracy, is in the area of 6 h. By implication, the physics-based model captures the underlying signals at lower frequencies, while the statistical models capture relationships over shorter intervals. Further tests are run in which the forecasts from the ECMWF model are used as inputs in regressions and neural networks. The combined models yield more accurate forecasts than either one individually.     

On the observed relationship between the Pacific Decadal Oscillation and the Atlantic Multi-decadal Oscillation

We studied the relationship between the dominant patterns of sea surface temperature (SST) variability in the North Pacific and the North Atlantic. The patterns are known as the Pacific Decadal Oscillation (PDO) and the Atlantic Multi-decadal Oscillation (AMO). In the analysis we used two different observational data sets for SST. Due to the high degree of serial correlation in the PDO and AMO time series, various tests were carried out to assess the significance of the correlations. The results demonstrated that the correlations are significant when the PDO leads the AMO by 1 year and when the AMO leads the PDO by 11–12 years. The possible physical processes involved are discussed, along with their potential implication for decadal prediction.